United States Department of Agriculture

Climate Change Vulnerability and Adaptation 

in the Northern Rocky Mountains

Part 1

Jessica E. Halofsky, David L. Peterson, S. Karen Dante-Wood, Linh Hoang, Joanne J. Ho, 

Linda A. Joyce, Editors

Forest Rocky Mountain General Technical Report

Service Research Station RMRS-GTR-374 March 2018
Halofsky, Jessica E.; Peterson, David L.; Dante-Wood, S. Karen; Hoang, Linh; Ho, Joanne J.; Joyce, Linda A., eds. 

2018. Climate change vulnerability and adaptation in the Northern Rocky Mountains. Gen. Tech. Rep. RMRSGTR-374. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 

Part 1. pp. 1–273.

Abstract

The Northern Rockies Adaptation Partnership (NRAP) identified climate change issues relevant to resource 

management in the Northern Rockies (USA) region, and developed solutions intended to minimize negative effects 

of climate change and facilitate transition of diverse ecosystems to a warmer climate. The NRAP region covers 183 

million acres, spanning northern Idaho, Montana, northwestern Wyoming, North Dakota, and northern South Dakota, 

and includes 15 national forests and 3 national parks across the U.S. Forest Service Northern Region and adjacent 

Greater Yellowstone Area. U.S. Forest Service scientists, resource managers, and stakeholders worked together over 

2 years to conduct a state-of-science climate change vulnerability assessment and develop adaptation options for 

national forests and national parks in the Northern Rockies region. The vulnerability assessment emphasized water, 

fisheries, wildlife, forest and rangeland vegetation and disturbance, recreation, cultural heritage, and ecosystem 

services which are regarded as key resource areas for local ecosystems and communities. Resource managers used 

the assessment to develop a detailed list of ways to address climate change vulnerabilities through management 

actions. The large number of adaptation strategies and tactics, many of which are a component of current 

management practice, provide a pathway for slowing the rate of deleterious change in resource conditions.

Keywords: adaptation, climate change, ecological disturbance, climate-smart resource management, Northern 

Rocky Mountains, vulnerability assessment

Front cover: Top left, Twin Lakes Campground, Beaverhead-Deerlodge National Forest; top right, Holland Lake, Flathead National 

Forest; bottom left, Horse Prairie Guard Station, Beaverhead-Deerlodge National Forest; bottom right, Rock Creek, Lolo National 

Forest (photos, Eric Henderson, used with permission).

All Rocky Mountain Research Station publications are published by U.S. Forest Service employees and are in the 

public domain and available at no cost. Even though U.S. Forest Service publications are not copyrighted, they 

are formatted according to U.S. Department of Agriculture standards and research findings and formatting cannot 

be altered in reprints. Altering content or formatting, including the cover and title page, is strictly prohibited.
Editors

Jessica E. Halofsky is a Research Ecologist with the University of Washington, School of Environmental and Forest 

Sciences in Seattle, Washington.

David L. Peterson was a Senior Research Biological Scientist with the U.S. Department of Agriculture, Forest 

Service, Pacific Northwest Research Station in Seattle, Washington. He is currently a Professor with the University of 

Washington, School of Enviromental and Forest Sciences, Seattle, Washington.

S. Karen Dante-Wood is a Natural Resource Specialist, U.S. Department of Agriculture, Forest Service, Office of 

Sustainability and Climate in Washington, DC.

Linh Hoang is the Regional Inventory, Monitoring, Assessment and Climate Change Coordinator, U.S. Department of 

Agriculture, Forest Service, Northern Region in Missoula, Montana.

Joanne J. Ho is a Research Environmental Economist with the University of Washington, School of Environmental 

and Forest Sciences in Seattle, Washington.

Linda A. Joyce is a Research Ecologist with the U.S. Department of Agriculture, Forest Service, Rocky Mountain 

Research Station, Human Dimensions Research Program in Fort Collins, Colorado.

Summary

The Northern Rockies Adaptation Partnership (NRAP) is a science-management partnership consisting of 15 national 

forests in the Northern Region of the Forest Service, U.S. Department of Agriculture (USFS); 3 national parks; the 

USFS Pacific Northwest and Rocky Mountain Research Stations; the University of Washington; and numerous other 

organizations and stakeholders. These organizations worked together over a period of 2 years to identify climate 

change issues relevant to resource management in the Northern Rocky Mountains (USA) and to find solutions that 

can minimize negative effects of climate change and facilitate transition of diverse ecosystems to a warmer climate. 

The NRAP provided education, conducted a climate change vulnerability assessment, and developed adaptation 

options for national forests and national parks that manage more than 28 million acres in northern Idaho, Montana, 

northwestern Wyoming, North Dakota, and northern South Dakota.

Global climate models project that the Earth’s current warming trend will continue throughout the 21st century in the 

Northern Rockies. Compared to observed historical temperature, average warming across the five NRAP subregions 

is projected to be about 4 to 5 °F by 2050, depending on greenhouse gas emissions. Precipitation may increase 

slightly in the winter, although the magnitude is uncertain.

Climatic extremes are difficult to project, but they will probably be more common, driving biophysical changes in 

terrestrial and aquatic ecosystems. Droughts of increasing frequency and magnitude are expected in the future, 

promoting an increase in wildfires, insect outbreaks, and nonnative species. These periodic disturbances, will rapidly 

alter productivity and structure of vegetation, potentially altering the distribution and abundance of dominant plant 

species and animal habitat.

Highlights of the vulnerability assessment and adaptation options for the Northern Rockies include the following:

Water resources and infrastructure

• Effects: Decreasing snowpack and declining summer flows will alter timing and availability of water supply, 

affecting agricultural, municipal, and public uses in and downstream from national forests, and affecting other 

forest uses such as livestock, wildlife, recreation, firefighting, road maintenance, and instream fishery flows. 

Declining summer low flows will affect water availability during late summer, the period of peak demand (e.g., 

for irrigation and power supply). Increased magnitude of peak streamflows will damage roads near perennial 

streams, ranging from minor erosion to extensive damage, thus affecting public safety, access for resource 

management, water quality, and aquatic habitat. Bridges, campgrounds, and national forest facilities near 

streams and floodplains will be especially vulnerable, reducing access by the public.

• Adaptation options: Primary adaptation strategies to address changing hydrology in the Northern Rockies include 

restoring the function of watersheds, connecting floodplains, reducing drainage efficiency, maximizing valley 

storage, and reducing hazardous fuels. Tactics include adding wood to streams, restoring beaver populations, 

modifying livestock management, and reducing surface fuels and forest stand densities. Primary strategies for 
infrastructure include increasing the resilience of stream crossings, culverts, and bridges to higher peakflows and 

facilitating response to higher peakflows by reducing the road system and disconnecting roads from streams. 

Tactics include completing geospatial databases of infrastructure (and drainage) components, installing higher 

capacity culverts, and decommissioning roads or converting them to alternative uses. It will be important to 

map aquifers and alluvial deposits, improve monitoring to provide feedback on water dynamics, and understand 

the physical and legal availability of water for aquifer recharge. Erosion potential to protect water quality can 

be addressed by reducing hazardous fuels in dry forests, reducing nonfire disturbances, and using road 

management practices that prevent erosion.

Fisheries

• Effects: Decreased snowpack will shift the timing of peakflows, decrease summer low flows, and in combination 

with higher air temperature, increase stream temperatures, all of which will reduce the vigor of cold-water fish 

species. Abundance and distribution of cutthroat trout and especially bull trout will be greatly reduced, although 

effects will differ by location as a function of both stream temperature and competition from nonnative fish 

species. Increased wildfire will add sediment to streams, increase peakflows and channel scouring, and raise 

stream temperature by removing vegetation.

• Adaptation options: Primary strategies to address climate change threats to cold-water fish species include 

maintaining or restoring functionality of channels and floodplains to retain (hence, to cool) water and buffer 

against future changes, decreasing fragmentation of stream networks so aquatic organisms can reach similar 

habitats, and developing wildfire use plans that address sediment inputs and road failures. Adaptation tactics 

include using watershed analysis to develop integrated actions for vegetation and hydrology, protecting 

groundwater and springs, restoring riparian areas and beaver populations to maintain summer baseflows, 

reconnecting and increasing off-channel habitat and refugia, identifying and improving stream crossings that 

impede fish movement, decreasing road connectivity, and revegetating burned areas to store sediment and 

maintain channel geomorphology. Removing nonnative fish species and reducing their access to cold-water 

habitat reduces competition with native fish species.

Forest vegetation

• Effects: Increasing air temperature, through its influence on soil moisture, is expected to cause gradual changes 

in the abundance and distribution of tree, shrub, and grass species throughout the Northern Rockies, with 

more drought-tolerant species becoming more competitive. The earliest changes will be at ecotones between 

lifeforms (e.g., upper and lower treelines). Ecological disturbance, including wildfire and insect outbreaks, will 

be the primary facilitator of vegetation change, and future forest landscapes may be dominated by younger age 

classes and smaller trees. High-elevation forests will be especially vulnerable if disturbance frequency increases 

significantly. Increased abundance and distribution of nonnative plant species, as well as the legacy of past land 

uses, create additional stress for regeneration of native forest species.

• Adaptation options: Most strategies for conserving native tree, shrub, and grassland systems focus on increasing 

resilience to chronic low soil moisture (especially extreme drought and low snowpack), and to more frequent 

and extensive ecological disturbance (wildfire, insects, nonnative species). These strategies generally include 

managing landscapes to reduce the severity and patch size of disturbances, encouraging fire to play a more 

natural role, and protecting refugia where fire-sensitive species can persist. Increasing species, genetic, and 

landscape diversity (spatial pattern, structure) is an important “hedge your bets” strategy that will reduce the risk 

of major loss of forest cover. Adaptation tactics include using silvicultural prescriptions (especially stand density 

management) and fuel treatments to reduce fuel continuity, reducing populations of nonnative species, potentially 

using multiple genotypes in reforestation, and revising grazing policies and practices. Rare and disjunct species 

and communities (e.g., whitebark pine, quaking aspen) require adaptation strategies and tactics focused on 

encouraging regeneration, preventing damage from disturbance, and establishing refugia.

Rangeland vegetation

• Effects: A longer growing season is expected to increase net primary productivity of many rangeland types, 

especially those dominated by grasses, although responses will depend on local climate and soil conditions. 

Elevated atmospheric carbon dioxide may increase water use efficiency and productivity of some species. In 

many cases, increasing wildfire frequency and extent will be particularly damaging for big sagebrush and other 

shrub species that are readily killed by fire. The widespread occurrence of cheatgrass and other nonnative 

species facilitates frequent fire through annual fuel accumulation. In montane grasslands, wildfire may kill 

Douglas-fir and other species that have recently established in rangelands through fire exclusion. Shrub species 

that sprout following fire may be very resilient to increased disturbance, but may be outcompeted by more 

drought-tolerant species over time.

ii
• Adaptation options: Adaptation strategies for rangeland vegetation focus on increasing resilience of rangeland 

ecosystems, primarily through control and prevention of invasion by nonnative species. Ecologically based 

management of nonnative plants focuses on strategies to repair damaged ecological processes that facilitate 

invasion, and seeding of desired native species can be done where seed availability and dispersal of these 

species are low. Proactive management to prevent establishment of nonnative species is also critical (early 

detection-rapid response), including tactics such as weed-free policies, education of employees and the public, 

and collaboration among multiple agencies to control weeds. Livestock grazing can also be managed through 

the development of site-specific indicators that inform livestock movement guides and allow for maintenance and 

enhancement of plant health.

Wildlife

• Effects: Few data exist on the direct effects of climatic variability and change on most animal species. Therefore, 

projected climate change effects must be inferred from what is known about habitat characteristics and the 

autecology of each species. Habitat for mammals that depend on high-elevation, snowy environments, whether 

predators (Canada lynx, fisher, wolverine) or prey (snowshoe hare), is expected to deteriorate relatively soon if 

snowpack continues to decrease. Species that are highly dependent on a narrow range of habitat (pygmy rabbit, 

Brewer’s sparrow, greater sage-grouse) will be especially vulnerable if that habitat decreases from increased 

disturbance (e.g., sagebrush mortality from wildfire). Species that are mobile or respond well to increased 

disturbance and habitat patchiness (deer, elk) will probably be resilient to a warmer climate in most locations. 

Some amphibian species (Columbia spotted frog, western toad) may be affected by pathogens (e.g., amphibian 

chytrid fungus) that are favored by a warmer climate.

• Adaptation options: Adaptation strategies for wildlife are focused on maintaining adequate habitat and healthy 

wildlife populations, and increasing knowledge of the needs and climate sensitivities of species. Connectivity 

is an important conservation strategy for most species in the Northern Rockies. Maintaining healthy American 

beaver populations will provide riparian habitat structure and foraging opportunities for multiple species. Quaking 

aspen habitat, which is also important for several species, can be enhanced by allowing wildfire, protecting 

aspen from grazing, and reducing conifer encroachment. Restoration of open stands of ponderosa pine and 

mixed-conifer forest through reduction of stand densities will benefit species such as fisher and flammulated owl. 

Excluding fire and reducing nonnative species will maintain sagebrush habitats that are required by several bird 

and mammal species.

Recreation

• Effects: Recreation has a significant economic impact throughout the Northern Rockies. A warmer climate will 

generally improve opportunities for warm weather activities (hiking, camping, sightseeing) because it will create 

a longer time during which these activities are possible, especially in the spring and fall “shoulder seasons.” 

However, it will reduce opportunities for snow-based, winter activities (downhill skiing, cross-country skiing, 

snowmobiling) because snowpack is expected to decline significantly in the future. Recreationists will probably 

seek more water-based activities in lakes and rivers as refuge from hotter summer weather. Higher temperatures 

may have both positive and negative effects on wildlife-based activities (hunting, fishing, birding) and gathering of 

forest products (e.g., berries, mushrooms), depending on how target habitats and species are affected.

• Adaptation options: Recreationists are expected to be highly adaptable to a warmer climate by shifting to different 

activities and different locations, behavior that is already observed from year to year. For example, downhill 

skiers may switch to ski areas that have more reliable snow, cross-country skiers will travel to higher elevations, 

and larger ski areas on Federal lands may expand to multi-season operation. Water-based recreationists may 

adapt to climate change by choosing different sites that are less susceptible to changes in water levels. Hunters 

may need to adapt by altering the timing and location of hunts. Federal management of recreation is currently 

not very flexible with respect to altered temporal and spatial patterns of recreation. This can be at least partially 

resolved by assessing expected use patterns in a warmer climate, modifying opening times of facilities, and 

deploying seasonal employees responsible for recreational facilities earlier in the year.

Ecosystem services

Ecosystem services are increasingly valued on Federal lands, beyond just their economic value. Climate change 

effects will vary greatly within different subregions of the Northern Rockies, with some ecosystem services being 

affected in the short term and others in the long term. Of the many ecosystem services provided in the Northern 

Rockies, eight are considered here, most of which are relevant to other resource categories included in the 

assessment.

iii
• Although annual water quantity (or water yield or water supply) is not expected to change significantly, timing 

of water availability is likely to shift, and summer flows may decline. These changes may result in some 

communities experiencing summer water shortages, although reservoir storage can provide some capacity. Rural 

agricultural communities will be disproportionately affected by climate change if water does become limiting.

•	 Water quality will decrease in some locations if wildfires and floods increase, adding sediment to rivers and 

reservoirs. Agriculture is currently the major source of impairment, affecting riparian systems, aquatic habitat, 

water temperatures, and fecal coliform. Climate change is expected to amplify these effects. Hazardous fuels 

treatments, riparian restoration, and upgrading of hydrologic infrastructure can build resilience to disturbances 

that damage water quality.

•	 Wood products are a relatively small component of the Northern Rockies economy, and economic forces will 

probably have the biggest impacts in the future. As wildfires and insect outbreaks become more common, wood 

supply could become less reliable, but overall effects will generally be small except in small towns that depend 

on a steady timber supply.

•	 Minerals and mineral extraction are important economic drivers in eastern Montana and western North Dakota. 

The biggest effects on this industry will be economic factors and factors related to how it connects to other 

ecosystem services, particularly water quality. Wildfires and floods can put mineral extraction infrastructure at risk 

in some watersheds.

•	 Forage for livestock is expected to increase in productive grasslands as a result of a longer growing season 

and in some cases elevated carbon dioxide. Therefore, ranching and grazing may benefit from climate change. 

Primary effects on grazing include loss of rural population, spread of nonnative grasses, and fragmentation of 

rangelands.

•	 Viewsheds and air quality will be negatively affected by increasing wildfires and longer pollen seasons. A growing 

percentage of the Northern Rockies population will be in demographic groups at risk for respiratory and other 

medical problems on days with poor air quality. Treatments of hazardous fuels can help build resilience to 

disturbances that degrade air quality.

•	 Regulation of soil erosion will be decreased by agricultural expansion, spread of nonnative plants, and increased 

frequency of wildfire and floods. Increased capital investments may be needed for water treatment plants if water 

quality declines significantly. Climate-smart practices in agriculture and road construction can reduce some 

negative effects.

•	 Carbon sequestration will be increasingly difficult if wildfires, insect outbreaks, and perhaps plant disease 

increase as expected, especially in the western part of the Northern Rockies. At the same time, managing forests 

for carbon sequestration is likely to become more important in response to national policies on carbon emissions. 

Hazardous fuel treatments can help build resilience to disturbances that rapidly oxidize carbon and emit it to the 

atmosphere.

Cultural resources

Disturbances such as wildfires, floods, and soil erosion place cultural and heritage values at risk. Damage to cultural 

and historic sites is irreversible, making protection a key management focus. Climate-induced changes in terrestrial 

and aquatic habitats affect abundance of culturally valued plants and animals (especially fish), affecting the ability 

of Native American tribes to exercise their treaty rights. Effects on cultural resources are amplified by external social 

forces that include a growing regional population, vandalism, and loss of traditional practices in a globalizing culture.

Conclusions

The NRAP facilitated the largest climate change adaptation effort on public lands to date. This collaboration included 

participants from Federal agencies and stakeholder organizations interested in a broad range of resource issues. It 

achieved specific goals of national climate change strategies for the USFS and National Park Service, providing a 

scientific foundation for resource management and planning in the Northern Rockies. The large number of adaptation 

strategies and tactics, many of which are a component of current management practice, provide a pathway 

for slowing the rate of deleterious change in resource conditions. Rapid implementation of adaptation—in land 

management plans, National Environmental Policy Act documents, project plans, and restoration—will help maintain 

functionality of terrestrial and aquatic ecosystems in the Northern Rockies, as well as build the organizational capacity 

of Federal agencies to incorporate climate change in their mission of sustainable resource management. Long-term 

monitoring will help detect potential climate change effects on natural resources, and evaluate the effectiveness of 

adaptation options that have been implemented.

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Contents—Part 1

Chapter 1: Introduction............................................................................................................1

S. Karen Dante-Wood

Climate Change Response in the Forest Service and National Park Service..................................................... 1

Science-Management Partnerships................................................................................................................. 3

The Northern Rockies Adaptation Partnership Process.................................................................................... 4

All-Lands Approach to Climate Change Adaptation........................................................................................ 6

Acknowledgments.......................................................................................................................................... 6

References..................................................................................................................................................... 6

Appendix 1A—Northern Rockies Adaptation Partnership Workshop Participants............................................ 9

Appendix 1B—Author Affiliations................................................................................................................ 14

Chapter 2: Biogeographic, Cultural, and Historical Setting of the 

Northern Rocky Mountains................................................................................................16

S. Karen Dante-Wood

Western Rockies Subregion.......................................................................................................................... 16

Central Rockies Subregion ........................................................................................................................... 18

Eastern Rockies Subregion ........................................................................................................................... 20

Greater Yellowstone Area Subregion............................................................................................................. 22

Grassland Subregion .................................................................................................................................... 24

References................................................................................................................................................... 26

Chapter 3: Historical and Projected Climate in the Northern Rockies Region.................28

Linda A. Joyce, Marian Talbert, Darrin Sharp, Jeffrey Morisette, and John Stevenson

Introduction................................................................................................................................................. 28

Climate Model Projections: CMIP3 and CMIP5............................................................................................ 28

Climate of the Northern Rockies Region ...................................................................................................... 28

Historical Climate.............................................................................................................................................28

Projected Climate .............................................................................................................................................30

Comparisons of CMIP5 Projections With the CMIP3 Projections Used in the Resource Chapters ................. 32

Climatic Variability and Change in Northern Rockies Adaptation Partnership Subregions............................. 33

Western Rockies Subregion...............................................................................................................................34

Central Rockies Subregion ................................................................................................................................36

Eastern Subregion .............................................................................................................................................39

Greater Yellowstone Area Subregion .................................................................................................................41

Grassland Subregion.........................................................................................................................................44

Acknowledgments........................................................................................................................................ 46

References................................................................................................................................................... 46

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and 

Water Resources in the Northern Rockies Region..........................................................48

Charles H. Luce

Introduction................................................................................................................................................. 48

Snowpack and Glaciers................................................................................................................................ 51

Snowpack .........................................................................................................................................................51

Glaciers............................................................................................................................................................52

Streamflow................................................................................................................................................... 53

Streamflow Projections .....................................................................................................................................54

Adapting Water Resources to Climatic Variability and Change in the Northern Rockies................................ 57

Conclusions................................................................................................................................................. 62

Acknowledgments........................................................................................................................................ 62

References................................................................................................................................................... 62

Appendix 4A—Adaptation Options for Water Resources in the Northern Rockies........................................ 65

v
Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the 

Northern Rockies Region ..................................................................................................87

Michael K. Young, Daniel J. Isaak, Scott Spaulding, Cameron A. Thomas, Scott A. Barndt, 

Matthew C. Groce, Dona Horan, and David E. Nagel

Introduction................................................................................................................................................. 87

Analysis Area and Methodology................................................................................................................... 88

Climate Scenarios.............................................................................................................................................88

Focal Species....................................................................................................................................................89

Trout Distribution Models.................................................................................................................................90

Native Trout Vulnerability to Climate Change............................................................................................... 91

Stream Temperature Status and Projected Trends...............................................................................................91

Cutthroat Trout Status and Projected Trends.......................................................................................................94

Bull Trout Status and Projected Trends...............................................................................................................94

Additional Fish Species.....................................................................................................................................95

Interpreting and Applying the Assessment .................................................................................................... 95

Adapting Fisheries to Climatic Variability and Change.................................................................................. 99

Adaptation Strategies and Tactics ......................................................................................................................99

Toward Climate-Smart Management ...............................................................................................................104

Acknowledgments...................................................................................................................................... 105

References................................................................................................................................................. 105

Appendix 5A—Adaptation Options for Fisheries in the Northern Rockies Adaptation 

Partnership Subregions .......................................................................................................................... 110

Chapter 6: Effects of Climate Change on Forest Vegetation in the 

Northern Rockies Region ................................................................................................128

Robert E. Keane, Mary Frances Mahalovich, Barry L. Bollenbacher, Mary E. Manning, 

Rachel A. Loehman, Terrie B. Jain, Lisa M. Holsinger, Andrew J. Larson, and Meredith M. Webster

Introduction............................................................................................................................................... 128

Terminology....................................................................................................................................................129

Assessment Levels...........................................................................................................................................130

Geographic Stratification ................................................................................................................................131

Uncertainty.....................................................................................................................................................132

Climate Change Assessment Techniques..........................................................................................................133

MC2 Model ....................................................................................................................................................135

Forest Vegetation Responses to Climate...................................................................................................... 136

Individual Plant...............................................................................................................................................136

Climate Change Assessments ..................................................................................................................... 147

Tree Species....................................................................................................................................................147

Vegetation Types.............................................................................................................................................176

Resources of Concern .....................................................................................................................................179

Vulnerability Assessment............................................................................................................................ 184

Adaptation Strategies and Tactics ............................................................................................................... 185

Discussion ................................................................................................................................................. 195

Conclusions............................................................................................................................................... 196

Acknowledgments...................................................................................................................................... 196

References................................................................................................................................................. 196

Appendix 6—Vegetation Model Output, Vulnerability Assessment Descriptions, and Adaptation 

Options for Forest Vegetation in the Northern Rockies. .......................................................................... 213

vi
USDA Forest Service RMRS-GTR-374. 2018 1

The Northern Rockies Adaptation Partnership (NRAP) 

is a science-management partnership among the Forest 

Service, U.S. Department of Agriculture (USFS) regional 

offices and national forests (mostly in the Northern Region, 

and small portions of the Intermountain and Rocky 

Mountain Regions); USFS Pacific Northwest and Rocky 

Mountain Research Stations; Glacier, Yellowstone, and 

Grand Teton National Parks; Great Northern and Plains and 

Prairie Potholes Landscape Conservation Cooperatives; 

Department of the Interior North Central Climate Science 

Center; Greater Yellowstone Coordinating Committee; 

Oregon State University; and EcoAdapt.

Initiated in 2013, the NRAP is a collaborative project 

with the goals of increasing climate change awareness, 

assessing vulnerability, and developing science-based adaptation strategies to reduce adverse effects of climate change 

and ease the transition to new climate states and conditions 

(see http://adaptationpartners.org/nrap). Developed in 

response to proactive climate change strategies of the USFS 

(USDA FS 2008, 2010b,c), and building on previous efforts 

in national forests (Halofsky et al. 2011; Littell et al. 2012; 

Raymond et al. 2013, 2014; Rice et al. 2012; Swanston 

and Janowiak 2012; Swanston et al. 2011), the partnership 

brings together resource managers and research scientists to 

plan for climate change in the Northern Rockies.

Climate Change Response 

in the Forest Service and 

National Park Service

Climate change is an agency-wide priority for the USFS, 

which has issued direction to administrative units for responding to climate change (USDA FS 2008) (table 1.1). In 

2010, the USFS provided specific direction to the National 

Forest System in the form of the National Roadmap for 

Responding to Climate Change (USDA FS 2010c) and the 

Performance Scorecard for Implementing the Forest Service 

Climate Change Strategy (USDA FS 2010c). The goal of the 

USFS climate change strategy is to “ensure our national forests and private working lands are conserved, restored, and 

made more resilient to climate change, while enhancing our 

water resources” (USDA FS 2010c). To achieve this goal, 

starting in 2011, each national forest and national grassland 

began using a 10-point scorecard system to report accomplishments on 10 elements in 4 dimensions: (1) increasing 

organizational capacity; (2) partnerships, engagement, and 

education; (3) adaptation; and (4) mitigation and sustainable 

consumption. Progress toward accomplishing elements of 

the scorecard must be reported annually by each national 

forest and grassland; all units are expected to accomplish 

7 of 10 criteria by 2015, with at least one “yes” in each 

dimension.

Similarly, the National Park Service (NPS) Climate 

Change Response Strategy provides direction for addressing the effects of climate change on NPS lands (NPS 2010) 

(table 1.2). The strategy has four components to guide NPS 

actions: science, adaptation, mitigation, and communication. The science component involves conducting and 

synthesizing research at various scales, monitoring trends 

and conditions, and delivering information to resource 

managers and partners. It also provides the scientific basis 

for adaptation, mitigation, and communication. Adaptation 

involves developing capacity within the agency to assess 

climate change scenarios and risks and implementing actions to better manage natural and cultural resources aswnd 

infrastructure for a changing climate. Mitigation efforts 

focus on reducing the agency’s carbon footprint and enhancing carbon sequestration. Finally, the strategy requires the 

NPS to take advantage of agency capacity for education and 

interpretation to communicate the effects of climate change 

to NPS employees and to the public. Park rangers and other 

employees are encouraged to engage visitors about climate 

change, because national parks are visible examples of how 

climate change can affect natural and cultural resources. 

The similarity of USFS and NPS climate response strategies 

facilitated coordination between the two agencies.

The NRAP is built on existing efforts in ecosystem-based 

management and ecological restoration to address climate 

change and put these efforts in a broader regional context 

in the Northern Rockies. Restoration is a priority in most national forests in this region, particularly related to hazardous 

fuels reduction in dry forests (stand density reduction plus 

surface fuel removal, often with prescribed burning), and 

restoration of riparian areas to improve hydrologic and biological function. The NRAP works in conjunction with these 

management priorities to access the best available science 

on climate change effects and implement climate change 

adaptation plans.

In 2010, a climate change report was developed for the 

Kootenai and Idaho Panhandle National Forests planning 

effort (USDA FS 2010a). At the time, this was the most 

comprehensive climate change vulnerability assessment and 

adaptation document compiled for the Northern Region. 

Although this report addressed many issues, it did not 

include nonforest vegetation, cultural resources, recreation 

resources, or ecosystem services. The Northern Region 

Chapter 1: Introduction

S. Karen Dante-Wood
2 USDA Forest Service RMRS-GTR-374. 2018

also funded the University of Washington, Climate Impacts 

Group to provide datasets of historical (1916–2006) and future (2040s, 2080s) downscaled climate and hydrologic data 

for the Upper Missouri River and Columbia River basins 

(Littell et al. 2011).

Building on these downscaled data, the Northern Region 

developed climate change “primers” to help assess and 

evaluate regionally specific climate-related trends. Primers 

for wildland fire, watershed ecology, forest regeneration, 

and forest landscapes were in progress when the NRAP was 

begun and have been incorporated into this publication. In 

addition to these primers, the Northern Region is currently 

developing a watershed-based climate change vulnerability 

assessment using downscaled regional water and stream 

temperature data for the Lolo National Forest; the assessment focuses on bull trout (Salvelinus confluentus) and 

includes a preliminary discussion of the western pearlshell 

mussel (Margaritifera falcata), water supply, and forest 

infrastructure (USDA FS 2015).

The NRAP also incorporates existing Northern Region 

efforts to consider and address climate change effects in 

management operations. In 2011, the Northern Region 

developed an Integrated Restoration & Protection Strategy 

that provided a framework for climate change adaptation 

Table 1.1—U.S. Forest Service policies related to climate change. 

Policy Description

Forest Service Strategic 

Framework for 

Responding to Climate 

Change

(USDA FS 2008)

Developed in 2008, the Strategic Framework is based on seven strategic goals in three broad 

categories: foundational, structural, and action. The seven goals are science, education, policy, 

alliances, adaptation, mitigation, and sustainable operations. Like the challenges themselves, the 

goals are interconnected; actions that achieve one goal tend to help meet other goals. The key is 

to coordinate approaches to each goal as complementary parts of a coherent response to climate 

change. All seven goals are ultimately designed to achieve the same end (the USFS mission): 

to ensure that Americans continue to benefit from ecosystem services from national forests and 

grasslands. 

USDA 2010–2015 

Strategic Plan

(USDA FS 2010d)

In June 2010, the U.S. Department of Agriculture released the Strategic Plan that guides its 

agencies toward achieving several goals including Strategic Goal 2—Ensure our national forests 

and private working lands are conserved, restored, and made more resilient to climate change, 

while enhancing our water resources. This goal has several objectives. Objective 2.2 is to lead 

efforts to mitigate and adapt to climate change. The performance measures under this objective 

seek to reduce greenhouse gas emissions by the U.S. agricultural sector, increase the amount of 

carbon sequestered on U.S. lands, and bring all national forests into compliance with a climate 

change adaptation and mitigation strategy. The USFS response to this goal includes the National 

Roadmap for Responding to Climate Change and Performance Scorecard.

National Roadmap for 

Responding to Climate 

Change

(USDA FS 2010c)

Developed in 2011, the Roadmap integrates land management, outreach, and sustainable 

operations accounting. It focuses on three kinds of activities: assessing current risks, vulnerabilities, 

policies, and gaps in knowledge; engaging partners in seeking solutions and learning from as well 

as educating the public and employees on climate change issues; and managing for resilience in 

ecosystems and human communities through adaptation, mitigation, and sustainable consumption 

strategies.

Climate Change 

Performance Scorecard

(USDA FS 2010a)

To implement the Roadmap, starting in 2011, each national forest and grassland began using a 

10-point scorecard to report accomplishments and plans for improvement on 10 questions in 

four dimensions: organizational capacity, engagement, adaptation, and mitigation. By 2015, each 

was expected to answer “yes” to at least seven of the scorecard questions, with at least one “yes” 

in each dimension. The goal was to create a balanced approach to climate change that includes 

managing forests and grasslands to adapt to changing conditions, mitigating climate change, 

building partnerships across boundaries, and preparing employees to understand and apply 

emerging science.

2012 Planning Rule

(USDA FS 2012)

The 2012 Planning Rule is based on a planning framework that will facilitate adaptation to 

changing conditions and improvement in management based on new information and monitoring. 

There are specific requirements for addressing climate change in each phase of the planning 

framework, including in the assessment and monitoring phases, and in developing, revising, 

or amending plans. The 2012 Planning Rule emphasizes restoring the function, structure, 

composition, and connectivity of ecosystems and watersheds to adapt to the effects of a changing 

climate and other ecosystem drivers and stressors, such as wildfire and insect outbreaks. A 

baseline assessment of carbon stocks required in assessment and monitoring will check for 

measureable changes in the plan area related to climate change and other stressors. Requirements 

of the Roadmap and Scorecard and requirements of the 2012 Planning Rule are mutually 

supportive and provide a framework for responding to changing conditions over time.

Chapter 1: Introduction
USDA Forest Service RMRS-GTR-374. 2018 3

Table 1.2—National Park Service policies related to climate change. 

Policy Description

National Park Service 

Climate Change 

Response Strategy

(NPS 2010)

Developed in 2010, the Climate Change Response Strategy is designed to guide management 

actions and collaboration, from the national to park levels, to address the effects of climate 

change. The Response Strategy is based on four components: science, mitigation, adaptation, and 

communication. These components provide a framework for consistent, legal, and appropriate 

management decisions. The Response Strategy calls for a scientific approach to updating 

interpretations of previous policy and mandates in order to uphold the mission of the NPS in the 

face of new conditions created by climate change.

A Call to Action: 

Preparing for a Second 

Century of Stewardship 

and Engagement

(NPS 2011)

A Call to Action outlines themes and goals for the second century of stewardship and engagement 

of the NPS. The plan provides actions for the achievement of each goal before the NPS centennial 

in 2016. Under the theme of preserving America’s special places, the plan sets the goal for 

management of resources to increase resilience to climate change stressors. Specific actions 

include revised management objectives, increases in sustainability, and changes in investments.

Green Parks Plan

(NPS 2012b)

The Green Parks Plan (GPP) outlines how the NPS will achieve the commitment set in A Call 

to Action, to “Go Green.” An overarching vision and strategy for sustainable management in 

the future, the GPP is based on nine strategic goals that focus on the effects of park operations 

on the environment and human welfare. The goals are to continually improve environmental 

performance; be climate friendly and climate ready; be energy smart; be water wise; develop a 

green NPS transportation system, buy green and reduce, reuse, and recycle; preserve outdoor 

values; adopt best practices; and foster sustainability beyond NPS boundaries.

Revisiting Leopold: 

Resource Stewardship in 

the National Parks

(NPS 2012c)

In August 2012, the NPS released Revisiting Leopold, intended as an updated interpretation of the 

guiding document The Leopold Report (Leopold et al. 1963). Members of the current NPS Science 

Committee were tasked with revisiting three questions: (1) What should be the goals of resource 

management in the national parks? (2) Which policies for resource management are necessary to 

achieve these goals? (3) Which actions are required to implement these policies? The interpretation 

presents general principles and guidance for the enlarged scope of all natural and cultural 

resources of the NPS. The committee stresses that the NPS needs to act quickly on structural 

changes and long-term investments in management in order to preserve resources through the 

uncertainties of environmental change. 

Climate Change Action 

Plan 2012—2014

(NPS 2012a)

The 2012 Climate Change Action Plan builds on the 2010 NPS Climate Change Response Strategy 

to communicate how the NPS can respond to climate change at different geographic scales. The 

plan outlines parameters for introducing science, adaptation, mitigation, and communication 

actions to address climate change. The plan also identifies high-priority actions for addressing 

climate change in NPS operations, and describes how to anticipate and prepare for future changes.

(Bollenbacher et al. 2014; USDA FS 2011). In addition, 

periodic Northern Region restoration and resilience reports 

provide baseline information on vegetative characteristics 

to better understand the effects of adaptive management 

(USDA FS 2014).

Most previous efforts to consider climate change effects 

and adaptation strategies in the Northern Rockies have 

focused on vegetation and aquatic resources. The NRAP 

broadens these efforts to develop a synthesis for a more 

comprehensive list of resource values, and to develop adaptation strategies for resources that have not been emphasized 

in management operations.

Science-Management 

Partnerships

Previous efforts in the Pacific Northwest and beyond 

have demonstrated the success of science-management 

partnerships for increasing climate change awareness among 

resource managers and adaptation planning on Federal 

lands. Olympic National Forest and Tahoe National Forest 

initiated the first science-management partnerships for 

developing adaptation options for individual national forests 

(Littell et al. 2012). The Olympic climate change study 

assessed resource vulnerabilities and developed adaptation 

options for Olympic National Forest and Olympic National 

Park on the Olympic Peninsula in Washington (Halofsky et 

al. 2011). Similar to efforts on the Olympic Peninsula, the 

North Cascadia Adaptation Partnership assessed vulnerabilities and formulated adaptation options for two national 

forests and two national parks in Washington (Raymond et 

al. 2014).

In collaboration with three management units in 

California—Tahoe National Forest, Inyo National Forest, 

and Devils Postpile National Monument—the USFS Pacific 

Southwest Research Station held climate change education 

workshops and developed the Climate Project Screening 

Chapter 1: Introduction
4 USDA Forest Service RMRS-GTR-374. 2018

Tool in order to incorporate adaptation into project planning 

(Morelli et al. 2012). In response to requests from Shoshone 

National Forest in northern Wyoming, the USFS Rocky 

Mountain Research Station synthesized information on past 

climate, future climate projections, and potential effects of 

climate change on the multiple ecosystems within the forest 

(Rice et al. 2012).

In the largest effort to date in the eastern United States, 

the USFS Northern Research Station, in collaboration with 

the Chequamegon-Nicolet National Forest in northern 

Wisconsin and numerous other partners, conducted a 

vulnerability assessment for natural resources (Swanston et 

al. 2011) and developed adaptation options (Swanston and 

Janowiak 2012). Another joint national forest and USFS 

research vulnerability assessment effort focused on the 

vulnerability of watersheds to climate change (Furniss et 

al. 2013). Watershed vulnerability assessments, conducted 

on 11 national forests throughout the United States, were 

locally focused (at a national forest scale) and included 

water resource values, hydrologic reaction to climate 

change, watershed condition, and landscape sensitivity. The 

assessments were intended to help national forest managers 

identify where limited resources could be best invested to 

increase watershed resilience to climate change.

The processes, products, and techniques used for several 

studies and other climate change efforts on national forests 

have been compiled in a guidebook for developing adaptation options for national forests (Peterson et al. 2011). The 

guidebook outlines four key steps to facilitate adaptation in 

national forests: (1) become aware of basic climate change 

science and integrate that understanding with knowledge of 

local conditions and issues (review), (2) evaluate sensitivity 

of natural resources to climate change (rank), (3) develop 

and implement options for adapting resources to climate 

change (resolve), and (4) monitor the effectiveness of onthe-ground management (observe) and adjust as needed. The 

NRAP is focused on implementation of the principles and 

practices in the guidebook.

The Northern Rockies 

Adaptation Partnership Process

The NRAP region includes 15 national forests, 7.8 

million acres of wilderness, and 3 national parks across 

the USFS Northern Region and the adjacent Greater 

Yellowstone Area. The region covers 183 million acres 

(fig.1.1), spanning northern Idaho, Montana, northwestern 

Wyoming, North Dakota, and northern South Dakota. To 

facilitate analyses and interpretations, the NRAP assessment 

is divided into the following five subregions:

•	 Western Rockies: Idaho Panhandle National Forest, 

Kootenai National Forest, Nez Perce-Clearwater 

National Forest, Glacier National Park

•	 Central Rockies: Bitterroot National Forest, Flathead 

National Forest, Lolo National Forest

•	 Eastern Rockies: Beaverhead-Deerlodge National 

Forest (eastern portion), Custer National Forest 

(eastern portion), Gallatin National Forest (northern 

portion), Helena National Forest, Lewis and Clark 

National Forest

•	 Greater Yellowstone Area: Bridger-Teton National 

Forest, Caribou-Targhee National Forest, Shoshone 

National Forest, Gallatin National Forest (southern 

portion), Custer National Forest (western portion), 

Beaverhead-Deerlodge National Forest (western 

portion), Grand Teton National Park, Yellowstone 

National Park

•	 Grassland: Custer National Forest (part), Dakota 

Prairie National Grassland

The NRAP process includes: (1) a vulnerability assessment of the effects of climate change on hydrology and 

roads, fisheries, wildlife, forest and nonforest vegetation 

and disturbance, recreation, cultural resources, and ecosystem services; (2) development of adaptation options that 

will help reduce negative effects of climate change and assist the transition of biological systems and management to 

a warmer and otherwise changing climate; and (3) development of an enduring science-management partnership to 

facilitate ongoing dialogue and activities related to climate 

change in the Northern Rockies region. These resource 

sectors were selected based on their importance in the 

region and current management concerns and challenges.

Vulnerability assessments typically consider exposure, 

sensitivity, and adaptive capacity (Parry et al. 2007), where 

exposure is the degree to which the system is exposed to 

changes in climate, sensitivity is an inherent quality of 

the system that indicates the degree to which it could be 

affected by climate change, and adaptive capacity is the 

ability of a system to respond and adjust to the exogenous 

influence of climate. Vulnerability assessments can be both 

qualitative and quantitative and focus on whole systems or 

individual species or resources (Glick et al. 2011). Several 

tools and databases are available for systematically assessing sensitivity (e.g., Lawler and Case 2010; Luce et al. 

2014) and vulnerability (e.g., Potter and Crane 2010) of 

species.

For the NRAP, we used scientific literature and expert 

knowledge to assess exposure, sensitivity, and adaptive 

capacity to identify key vulnerabilities for the identified 

resource areas. The assessment process took place over 16 

months, and involved monthly phone meetings for each of 

the resource-specific assessment teams. Each assessment 

team refined key questions that the assessment needed to 

address, selected values to assess, and determined which 

climate change impact models best informed the assessment. In some cases, assessment teams conducted spatial 

analyses or ran and interpreted models, selected criteria 

with which to evaluate model outputs, and developed maps 

of model output and resource sensitivities. To the greatest 

extent possible, teams focused on effects and projections 

Chapter 1: Introduction
USDA Forest Service RMRS-GTR-374. 2018 5

specific to the NRAP region and used the finest scale projections that are scientifically valid (Littell et al. 2011).

By working collaboratively with scientists and resource 

managers and focusing on a specific region, the goal 

of NRAP was to provide the scientific foundation for 

operationalizing climate change in planning, ecological 

restoration, and project management (Peterson et al. 2011; 

Raymond et al. 2013, 2014; Swanston and Janowiak 

2012). After key vulnerabilities were identified for each 

resource sector, five workshops were convened in October 

and November 2014 in Bismarck, North Dakota; Bozeman, 

Montana; Coeur d’Alene, Idaho; Helena, Montana; and 

Missoula, Montana, to present and discuss the vulnerability assessment, and to elicit adaptation options from 

resource managers (see Appendix 1A for workshop 

participants).

During these workshops, scientists and resource 

specialists presented information on climate change effects and current management practices for each of the 

resources. Facilitated dialogue was used to identify key 

sensitivities and adaptation options. Participants identified 

strategies (general approaches) and tactics (on-the-ground 

actions) for adapting resources and management practices 

to climate change, as well as opportunities and barriers 

Figure 1.1—Project 

area for the Northern 

Rockies Adaptation 

Partnership (NRAP) 

(map by Robert 

Norheim, University 

of Washington).

Chapter 1: Introduction
6 USDA Forest Service RMRS-GTR-374. 2018

for incorporating these adaptation actions into projects, 

management plans, partnerships, and policies. Participants 

generally focused on adaptation options that can be 

implemented given our current scientific understanding of climate change effects, but they also identified 

research and monitoring that would benefit future efforts 

to assess vulnerability and guide management practices. 

Information from the regionwide assessment was also 

downscaled to identify the most significant vulnerabilities 

to climate change for priority resources in each subregion. Facilitators captured information generated during 

the workshops with a set of spreadsheets adapted from 

Swanston and Janowiak (2012). Initial results from the 

workshops were augmented with continued dialogue with 

Federal agency resource specialists.

This publication contains a chapter on expected climatic 

changes in the Northern Rockies, and one chapter for each 

of the resource sectors covered in the vulnerability assessment (water resources, fisheries, forested and rangeland 

vegetation and disturbance, wildlife, recreation, ecosystem 

services, and cultural heritage) (see Appendix 1B for 

author affiliations). Each of the resource chapters includes 

a review of climate change effects, sensitivities, current 

management practices, and results of the discussions on 

adaptation strategies and tactics.

Resource managers and other decisionmakers can use 

this publication in several ways. First, the vulnerability 

assessment will provide information on climate change 

effects needed for national forest and national park plans, 

project plans, conservation strategies, restoration, and 

analysis of environmental effects. Second, climate change 

sensitivities and adaptation options developed at the 

regional scale will provide the scientific foundation for 

subregional and national forest and national park vulnerability assessments, adaptation planning, and resource 

monitoring. We expect that over time, and as needs and 

funding align, appropriate adaptation options will be incorporated into plans and programs of Federal management 

units. Third, we anticipate that resource specialists will 

apply this assessment to implement climate-smart resource 

planning and management on lands throughout the region.

Adaptation planning is an ongoing and iterative process. 

Implementation may occur at critical times in the planning 

process, such as when managers revise USFS land management plans and other planning documents, or after the 

occurrence of extreme events and ecological disturbances 

(e.g., wildfire). We focus on adaptation options for the 

USFS and NPS, but this publication provides information 

that can be used by other land management agencies as 

well. Furthermore, the NRAP process can be emulated by 

national forests, national parks, and other organizations 

outside the Northern Rockies, thus propagating climatesmart management across larger landscapes (e.g., the 

Intermountain Adaptation Partnership in Utah, Nevada, 

and southern Idaho; http://adaptationpartners.org/iap).

All-Lands Approach to 

Climate Change Adaptation

The USFS and NPS climate change strategies identify 

the need to build partnerships and work across jurisdictional 

boundaries when planning for adaptation. This concept of 

responding to the challenge of climate change with an “alllands” approach is frequently mentioned, but a process for 

doing so is rarely defined. Unique in its effort to implement 

an all-lands approach to adaptation for a specific region, 

NRAP is an inclusive partnership of multiple agencies and 

organizations with an interest in managing natural resources 

in a changing climate. In addition to representatives from 

the national forests, grasslands, and parks, several other 

agencies and organizations participated in the resource 

sector workshops (Appendix 1A). This type of partnership 

enables a coordinated and complementary approach to adaptation that crosses jurisdictional boundaries. The NRAP also 

provides a venue for agencies to learn from the practices of 

others so that the most effective adaptation strategies can be 

identified.

Risks and vulnerabilities resulting from climate change 

and gaps in scientific knowledge and policy need to be 

assessed. Adaptation is a prominent focus of the NRAP, 

with emphasis on creating resilience in human and natural 

systems. Communicating climate change information and 

engaging employees, partners, and the public in productive 

discussions are also integral parts of successfully responding 

to climate change. The need for partnerships and collaborations on climate change issues was also identified in the 

NRAP. Sharing climate change information, vulnerability 

assessments, and adaptation strategies across administrative 

boundaries will contribute to the success of climate change 

responses in the Northern Rockies.

Acknowledgments

We thank the many individuals who contributed to this 

report, including assessment team members, workshop 

participants, chapter reviewers, and other supporters. We 

are especially grateful to the U.S. Geological Survey, 

North Central Climate Science Center for providing stateof-science climate projections. Funding was provided by 

the USFS Office of Sustainability and Climate, Northern 

Region, Pacific Northwest Research Station, and Rocky 

Mountain Research Station, and by the National Oceanic 

and Atmospheric Administration.

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Chapter 1: Introduction
USDA Forest Service RMRS-GTR-374. 2018 9

Bozeman, Montana, 

October 9–10, 2014

Vegetation

Cavan Fitzsimmons – Custer-Gallatin National Forest

Andrew Hansen – Montana State University

Bob Keane – USFS, Rocky Mountain Research Station

Keith Konen – Gallatin National Forest

Mary Mahalovich – USFS, Rocky Mountain Research 

Station

Kelly McCloskey – Grand Teton National Park

Jill McMurray – USFS, Region 1/Region 4, Air Quality

Traute Parrie – Custer-Gallatin National Forest

Ben Poulter – Montana State University

Ann Rodman – Yellowstone National Park

Julie Shea – Custer-Gallatin National Forest

Nonforest Vegetation

Diane Abendroth – Grand Teton National Park

Walt Allen – Custer-Gallatin National Forest

Jeff DiBenedetto – Custer National Forest

Susan Lamont – Gallatin National Forest

Rose Lehman – Caribou-Targhee National Forest

Mary Manning – USFS, Region 1 Regional Office

Matt Reeves – USFS, Rocky Mountain Research Station

Jessi Salix – Beaverhead-Deerlodge National Forest

Kevin Suzuki – Beaverhead-Deerlodge National Forest

Denice Swanke – Little Bighorn Battlefield National 

Monument

Travis Ziehl – Teton County

Wildlife

Polly Buotte – University of Idaho

Jeff Burrell – Wildlife Conservation Society, Northern 

Rockies and Yellowstone Program

Jodie Canfield – Gallatin National Forest

Sue Consolo Murphy – Grand Teton National Park

Mary Erickson – Custer-Gallatin National Forest

Rachel Feigley – Custer-Gallatin National Forest

Kristin Legg – Greater Yellowstone Network

Kevin McKelvey – USFS, Rocky Mountain Research 

Station

Rob Mickelson – Caribou-Targhee National Forest

Amie Shovlain – Beaverhead-Deerlodge National Forest

Hydrology

Karri Cary – Shoshone National Forest

Pam Fletcher – Beaverhead-Deerlodge National Forest

Gretchen Hurley – BLM

Appendix 1A—Northern Rockies Adaptation Partnership 

Workshop Participants

Richard Raione – Bridger-Teton National Forest

Andy Ray – NPS Inventory and Monitoring

Alex Sienkiewicz – Custer-Gallatin National Forest

Ed Snook – USFS, Region 1 Regional Office

Mike Tercek – Yellowstone National Park

Dave Thoma – NPS Inventory and Monitoring

Eric Winthers – Bridger-Teton National Forest

Fisheries

Robert Al-Chokhachy – USGS, Northern Rocky Mountain 

Science Center

Shawn Anderson – Shoshone National Forest

Scott Barndt – Custer-Gallatin National Forest

Yvette Converse – Great Northern Landscape Conservation 

Cooperative/NPS

Molly Cross – Wildlife Conservation Society

Dave Hallac – Yellowstone National Park

Dan Isaak – USFS, Rocky Mountain Research Station

Jessi Kershner – EcoAdapt

Brad Shepard – Wildlife Conservation Society 

Lisa Stoeffler – Custer-Gallatin National Forest

Gary Tabor – Center for Large Landscape Conservation

Michael Young – USFS, Rocky Mountain Research Station

Recreation

Krista Gebert – USFS, Region 1 Regional Office

Virginia Kelly – Greater Yellowstone Coordinating 

Committee

Megan Lawson – Headwaters Economics

Natalie Little – USFS, Region 4

Jane Ruchman – Custer-Gallatin National Forest

Trey Schillie – USFS, Region 2

Jamie Schoen – Bridger-Teton National Forest

Travis Warziniack – USFS, Rocky Mountain Research 

Station

Bismarck, North Dakota, 

October 15–16, 2014

Nonforest Vegetation

Adnan Akyuz – North Dakota State University

Bernadette Braun – Dakota Prairie Grassland

Chad Prosser – Dakota Prairie Grassland

Karen Dunlap – Dakota Prairie Grassland

Kurt Hansen – Custer National Forest – Sioux Ranger 

District

Libby Knotts – Dakota Prairie Grassland

Mary Manning – USFS, Region 1 Regional Office

Meghan Dinkins – Dakota Prairie Grassland

Chapter 1: Introduction
10 USDA Forest Service RMRS-GTR-374. 2018

Hydrology

Babete Anderson – Dakota Prairie Grassland

Scott Barndt – Custer-Gallatin National Forest

Andy Efta – Custer National Forest

Pam Fletcher – Beaverhead-Deerlodge National Forest

Steven Krentz – USFWS, Mountain Prairie Region

Rick Nelson – Plains and Prairie Pothole Landscape 

Conservation Cooperative

Mike Philbin – BLM

Karen Ryberg – USGS, North Dakota Water Science Center

Alison Schlag – Dakota Prairie Grassland

Kevin Shelley – USFWS

Robert Swithers – Dakota Prairie Grassland

Meredith Webster – USFS, Region 1 Regional Office

Missoula, Montana, 

October 20–21, 2014

Vegetation

Jeremy Amberson – Bitterroot Restoration Committee

Barry Bollenbacher – USFS, Region 1 Regional Office

C. Alina Cansler – University of Washington

Rob Carlin – Flathead National Forest

Gregg DeNitto – USFS, Region 1 Regional Office

Linda Donner – Flathead National Forest

Bruce Erikson – Lolo National Forest

Shelagh Fox – USFS, Region 1 Regional Office

Sheryl Gunn – Lolo National Forest 

Cheri Hartless – Bitterroot National Forest

Melissa Hayes – Montana Forest Restoration Committee

LaWen Hollingsworth – Fire Modeling Institute

Melissa Jenkins – Flathead National Forest

Bob Keane – USFS, Rocky Mountain Research Station

Elaine Kennedy Sutherland – USFS, Rocky Mountain 

Research Station

Jerry Kruger – Bitterroot National Forest

Heidi Trechsel – Flathead National Forest

Nonforest Vegetation

Tara Carolin – Glacier National Park

Chantelle Delay – Flathead National Forest

Gil Gale – Bitterroot National Forest

Holger Jensen – USFS, Region 1 Regional Office

Mary Manning – USFS, Region 1 Regional Office

Matt Reeves – USFS, Rocky Mountain Research Station 

Susan Rinehart – USFS, Region 1 Regional Office

Karen Stockmann – Lolo National Forest

Wildlife

Len Broberg – University of Montana 

Polly Buotte – University of Idaho

Renate Bush – USFS, Region 1 Regional Office

Alan Dohmen – USFS, Region 1 Regional Office

Kari Eneas – Confederate Salish and Kootenai Tribes

Greg Gustina – Lolo National Forest

Whisper Means – Confederate Salish and Kootenai Tribes

Peter Nelson – Defenders of Wildlife

Kuennen Reed – Flathead National Forest

Tom Reed – Lee Metcalf National Wildlife Refuge 

Melly Reuling – Center for Large Landscape Conservation

Hydrology

Chris Brick – Clark Fork Coalition

Nate Dieterich – Flathead National Forest

Craig Kendall – Flathead National Forest

Charlie Luce – USFS, Rocky Mountain Research Station

Caryn Miske – Flathead Basin Commission

Regan Nelson – Crown of the Continent Conservation 

Initiative

Amber Richardson – Bitterroot National Forest

Ed Snook – USFS, Region 1 Regional Office

Fisheries

Aubree Benson – Lolo National Forest

Dan Brewer – USFWS

Anne Carlson – Wilderness Society

Robert Davies – Flathead National Forest

Bruce Farling – Trout Unlimited

Wade Fredenberg – Montana Ecological Services Suboffice

Dan Isaak – USFS, Rocky Mountain Research Station

Ryan Kovach – USGS

Clint Muhlfeld – USGS, Northern Rocky Mountain Science 

Center

David Schmetterling – Montana Fish, Wildlife and Parks 

Erin Sexton – University of Montana

Scott Spaulding –– USFS, Region 1 Regional Office 

Cameron Thomas – USFS, Region 1 Regional Office

Pat Van Eimeren – Flathead National Forest

Sims Wade – Idaho Panhandle National Forest

Michael Young – USFS, Rocky Mountain Research Station 

Recreation

Carl Davis – USFS, Region 1 Regional Office 

Krista Gebert – USFS, Region 1 Regional Office

Michael Hand – USFS, Rocky Mountain Research Station

Cynthia Manning – USFS, Region 1 Regional Office 

Marsha Moore – Flathead National Forest

Rosa Nygaard – USFS, Region 1 Regional Office

Keith Stockmann – USFS, Region 1 Regional Office

Byron Stringham – Lolo National Forest

Jeff Ward – USFS, Region 1 Regional Office

Rusty Wilder – Lola National Forest

Coeur d’Alene, Idaho, 

October 23–24, 2014

Vegetation 

Pat Behrens – Idaho Panhandle National Forest

Bob Boeh – Idaho Forest Group

Barry Bollenbacher – USFS, Region 1 Regional Office

Chapter 1: Introduction
USDA Forest Service RMRS-GTR-374. 2018 11

Malcolm Edwards – Kootenai National Forest

Mike Giesey – Kootenai National Forest

Kevin Greenleaf – Kootenai Tribe of Idaho

Jessie Grossman – Yaak Valley Forest Council

Jason Jerman – Idaho Panhandle National Forest

Carol McKenzie – Idaho Panhandle National Forest

Lee Pederson – USFS, Region 1 Regional Office

Christopher Schnepf – University of Idaho Extension

Megan Strom – Kootenai National Forest 

Art Zack – Idaho Panhandle National Forest 

Paul Zambino – USFS Region 1 Regional Office

Nonforest Vegetation

LeAnn Abell – BLM

Derek Antonelli – Idaho Native Plant Society

Jennifer Costich-Thompson – Idaho Panhandle National 

Forest

Valerie Goodnow – Idaho Panhandle National Forest

Mike Hays – Nez Perce-Clearwater National Forest

Megan Lucas – Nez Perce-Clearwater National Forest

Mary Manning – USFS, Region 1 Regional Office

Wildlife

Polly Buotte – University of Idaho

Jason Flory – USFWS, Northern Idaho Field Office

Lynn Johnson – Kootenai National Forest

Kevin McKelvey – USFS, Rocky Mountain Research 

Station 

Rema Sadak – Nez Perce-Clearwater National Forest

Leona Svancara – Idaho Department of Fish and Game

JJ Teare – Idaho Department of Fish and Game

Guy Wagner – Nez Perce-Clearwater National Forest

Hydrology

Shandra Dekome – Idaho Panhandle National Forest

Cara Farr – Nez Perce-Clearwater National Forest

Laura Jungst – Kootenai National Forest

Ed Snook – USFS, Region 1 Regional Office

Fisheries

Jim Fredericks – Idaho Fish and Game

Greg Hoffman – U.S. Army Corps of Engineers

Dan Isaak – USFS, Rocky Mountain Research Station

Dan Kenny – Nez Perce-Clearwater National Forest

Jessi Kershner – EcoAdapt

Katherine Thompson – Nez Perce-Clearwater National 

Forest

Michael Young – USFS, Rocky Mountain Research Station 

William Young – Idaho Panhandle National Forest 

Recreation 

Pam Fletcher – Beaverhead-Deerlodge National Forest 

Krista Gebert – USFS, Region 1 Regional Office

Morai Helfen – Idaho Panhandle National Forest

Diane Jones – Nez Perce-Clearwater National Forest

Timory Peel – Kootenai National Forest

Loretta Stevens – Kootenai National Forest/Confederated 

Salish and Kootenai Tribes

Helena, Montana, 

November 4–5, 2014

Vegetation

Elisa Stamm – Beaverhead-Deerlodge National Forest

Rob Gump – Beaverhead-Deerlodge National Forest

Amanda Milburn – Helena National Forest

Tanya Murphy – Helena National Forest

Alicia Torregrosa – USGS

Andrea Woodward – USGS

Nonforest Vegetation

Beth Anderson – Lewis and Clark National Forest

Steve Black – Bighole Battlefield

Tammy Cherullo – Beaverhead-Deerlodge National Forest 

Amanda Hendrix – Helena-Lewis and Clark National Forest

Casey Johnson – Lewis and Clark National Forest

Mary Manning – USFS, Region 1 Regional Office

Matt Reeves – USFS, Rocky Mountain Research Station 

Steve Shelly – USFS, Region 1 Regional Office

Rowdy Wood – Helena-Lewis and Clark National Forest

Wildlife

Bray Beltron – Heart of the Rockies Initiative

Polly Buotte – University of Idaho

Gregg DeNitto – USFS, Region 1 Regional Office

Justin Gude – Montana Fish, Wildlife and Parks

Kevin McKelvey – USFS, Rocky Mountain Research 

Station

Denise Pengeroth – Helena National Forest 

Ryan Quire – Helena National Forest

Anne Roberts – Beaverhead-Deerlodge National Forest

Hydrology

David Callery – Helena-Lewis and Clark National Forest

Larry Dolan – Montana Department of Natural Resources 

and Conservation

Deb Entwistle – Helena National Forest

Pam Fletcher – Beaverhead-Deerlodge National Forest

Wayne Green – Lewis and Clark National Forest

Sue Higgins – Roundtable on the Crown of the Continent 

Robert Ray – Montana Department of Environmental 

Quality

Sara Rouse – Beaverhead-Deerlodge National Forest

Ed Snook – USFS, Region 1 Regional Office

Brian Sugden – Plum Creek

Chapter 1: Introduction
12 USDA Forest Service RMRS-GTR-374. 2018

Fisheries

Jim Brammer – Beaverhead-Deerlodge National Forest

Anne Carlson – Wilderness Society

Kendall Cikanek – Lewis and Clark National Forest

Jessi Kershner – EcoAdapt

David Moser – Montana Fish, Wildlife and Parks

Lee Nelson – Montana Fish, Wildlife and Parks

Scott Spaulding – USFS, Region 1 Regional Office 

Peru Suernam – Beaverhead-Deerlodge National Forest

Recreation

Patty Bates – Beaverhead-Deerlodge National Forest

Charlene Bucha – Beaverhead-Deerlodge National Forest

Elizabeth Casselli – Helena-Lewis and Clark National 

Forest

Jocelyn Dodge – Beaverhead-Deerlodge National Forest

David Fothergill – Helena National Forest

Michael Hand – USFS, Rocky Mountain Research Station

Mike Munoz – Lewis and Clark National Forest

Lis Novack – USFS, Region 1 Regional Office

Acronyms 

BLM: Bureau of Land Management

NPS: National Park Service

USFS: U.S. Forest Service

USFWS: U.S. Fish and Wildlife Service

USGS: U.S. Geological Survey

Chapter 1: Introduction
USDA Forest Service RMRS-GTR-374. 2018 13

• Bitterroot Restoration Committee

• Bureau of Land Management 

• Center for Large Landscape Conservation

• Clark Fork Coalition

• Climate Impacts Research Consortium 

• Confederated Salish and Kootenai Tribes

• Crown of the Continent Conservation Initiative

• Defenders of Wildlife

• Department of the Interior, North Central Climate Science Center

• EcoAdapt

• Fire Modeling Institute

• Flathead Basin Commission

• Great Northern Landscape Conservation Cooperative

• Greater Yellowstone Coordinating Committee

• Headwaters Economics

• Heart of the Rockies Initiative

• Idaho Fish and Game

• Idaho Forest Group

• Idaho Native Plant Society

• Kootenai Tribe of Idaho

• Lee Metcalf National Wildlife Refuge

• Montana Department of Environmental Quality

• Montana Department of Natural Resources and Conservation

• Montana Fish, Wildlife and Parks

• Montana State University

• National Park Service

• North Dakota State University

• Oregon State University 

• Plains and Prairie Pothole Landscape Conservation Cooperative

• Plum Creek

• Roundtable on the Crown of the Continent 

• Trout Unlimited

• University of Idaho

• University of Montana

• University of Washington

• U.S. Army Corps of Engineers

• U.S. Fish and Wildlife Service

• U.S. Forest Service

• U.S. Geological Survey

• Walking Shadow Ecology

• Wilderness Society

• Wildlife Conservation Society

• Yaak Valley Forest Council

Organizations Represented in the Northern Rockies Adaptation Partnership

Chapter 1: Introduction
14 USDA Forest Service RMRS-GTR-374. 2018

Chapter 1

S. Karen Dante-Wood is a Natural Resource Specialist, U.S. 

Department of Agriculture, Forest Service, Office of 

Sustainability and Climate in Washington, DC.

Chapter 2

S. Karen Dante-Wood is a Natural Resource Specialist, U.S. 

Department of Agriculture, Forest Service, Office of 

Sustainability and Climate in Washington, DC.

Chapter 3

Linda A. Joyce is a Research Ecologist with the U.S. 

Department of Agriculture, Forest Service, Rocky 

Mountain Research Station, Human Dimensions 

Research Program in Fort Collins, Colorado.

Marian Talbert is a Biostatistician with the U.S. Department 

of the Interior, North Central Climate Science Center in 

Fort Collins, Colorado.

Darrin Sharp is a Faculty Research Assistant with Oregon 

State University, Oregon Climate Change Research 

Institute, College of Earth, Ocean, and Atmospheric 

Sciences in Corvallis, Oregon.

Jeffrey Morisette is the Director of the U.S. Department of 

the Interior, North Central Climate Science Center in Fort 

Collins, Colorado.

John Stevenson is a Regional Climate Extension Specialist 

with Oregon State University, Climate Impacts Research 

Consortium in Corvallis, Oregon.

Chapter 4

Charles H. Luce is a Research Hydrologist with the U.S. 

Department of Agriculture, Forest Service, Rocky 

Mountain Research Station in Boise, Idaho.

Chapter 5

Michael K. Young is a Research Fisheries Biologist with the 

U.S. Department of Agriculture, Forest Service, Rocky 

Mountain Research Station in Missoula, Montana.

Daniel J. Isaak is a Research Fish Biologist with the U.S. 

Department of Agriculture, Forest Service, Rocky 

Mountain Research Station in Boise, Idaho.

Scott Spaulding is the Fisheries Program Leader with the 

U.S. Department of Agriculture, Forest Service, Northern 

Region in Missoula, Montana.

Cameron A. Thomas is an Aquatic Ecologist with the U.S. 

Department of Agriculture, Forest Service, Northern 

Region in Missoula, Montana.

Scott A. Barndt is a Fisheries Program Leader with the 

U.S. Department of Agriculture, Forest Service, Gallatin 

National Forest in Bozeman, Montana.

Appendix 1B—Author Affiliations

Matthew C. Groce is an ORISE Technology Transfer 

Specialist with the U.S. Department of Agriculture, 

Forest Service, Rocky Mountain Research Station in 

Boise, Idaho.

Dona Horan is a Fish Biologist with the U.S. Department of 

Agriculture, Forest Service, Rocky Mountain Research 

Station in Boise, Idaho.

David E. Nagel is a Physical Scientist with the U.S. 

Department of Agriculture, Forest Service, Rocky 

Mountain Research Station in Boise, Idaho.

Chapter 6

Robert E. Keane is a Research Ecologist with the U.S. 

Department of Agriculture, Forest Service, Rocky 

Mountain Research Station, Missoula Fire Sciences 

Laboratory in Missoula, Montana. 

Mary Frances Mahalovich is the Regional Geneticist with 

the U.S. Department of Agriculture, Forest Service, 

Northern, Rocky Mountain, Southwestern, and 

Intermountain Regions, Forestry Sciences Laboratory in 

Moscow, Idaho. 

Barry L. Bollenbacher (retired), was the Regional 

Silviculturist with the U.S. Department of Agriculture, 

Forest Service, Northern Region in Missoula, Montana. 

Mary E. Manning is the Regional Vegetation Ecologist 

with the U.S. Department of Agriculture, Forest Service, 

Northern Region in Missoula, Montana. 

Rachel A. Loehman is a Research Landscape Ecologist, U.S. 

Geological Survey, Alaska Science Center in Anchorage, 

Alaska. 

Terrie B. Jain is a Research Forester with the U.S. 

Department of Agriculture, Forest Service, Rocky 

Mountain Research Station in Moscow, Idaho. 

Lisa M. Holsinger is an Ecologist with the U.S. Department 

of Agriculture, Forest Service, Rocky Mountain Research 

Station, Missoula Fire Sciences Laboratory in Missoula, 

Montana. 

Andrew J. Larson is an Associate Professor of Forest 

Ecology with the University of Montana, College 

of Forestry and Conservation, Department of Forest 

Management in Missoula, Montana.

Meredith M. Webster (retired), was the Regional Soil 

Scientist with the U.S. Department of Agriculture, Forest 

Service, Northern Region in Missoula, Montana.

Chapter 7

Matt C. Reeves is a Research Ecologist with the U.S. 

Department of Agriculture, Forest Service, Rocky 

Mountain Research Station in Missoula, Montana.

Mary E. Manning is the Regional Vegetation Ecologist 

with the U.S. Department of Agriculture, Forest Service, 

Northern Region in Missoula, Montana. 

Chapter 1: Introduction
USDA Forest Service RMRS-GTR-374. 2018 15

Jeff P. DiBenedetto is a Landscape and Vegetation Ecologist 

with the U.S. Department of Agriculture, Forest Service, 

Custer National Forest in Billings, Montana.

Kyle A. Palmquist is a Postdoctoral Research Associate with 

the University of Wyoming, Department of Botany in 

Laramie, Wyoming.

William K. Lauenroth is a Professor with the University of 

Wyoming, Department of Botany in Laramie, Wyoming.

John B. Bradford is a Research Ecologist with the U.S. 

Geological Survey, Southwest Biological Science Center 

in Flagstaff, Arizona.

Daniel R. Schlaepfer is a Junior Group Leader with the 

University of Basel, Department of Environmental 

Sciences in Basel, Switzerland.

Chapter 8

Rachel A. Loehman is a Research Landscape Ecologist, U.S. 

Geological Survey, Alaska Science Center in Anchorage, 

Alaska. 

Barbara J. Bentz is a Research Entomologist, U.S. 

Department of Agriculture, Forest Service, Rocky 

Mountain Research Station in Logan, Utah.

Gregg A. DeNitto is the Forest Health Protection Missoula 

Field Office Leader with the U.S. Department of 

Agriculture, Forest Service, Northern Region in 

Missoula, Montana.

Robert E. Keane is a Research Ecologist with the U.S. 

Department of Agriculture, Forest Service, Rocky 

Mountain Research Station, Missoula Fire Sciences 

Laboratory in Missoula, Montana. 

Mary E. Manning is the Regional Vegetation Ecologist 

with the U.S. Department of Agriculture, Forest Service, 

Northern Region in Missoula, Montana. 

Jacob P. Duncan is a Doctoral Student with Utah State 

University, Department of Mathematics and Statistics in 

Logan, Utah.

Joel M. Egan is an Entomologist with the U.S. Department 

of Agriculture, Forest Service, Northern Region in 

Missoula, Montana. 

Marcus B. Jackson is a Plant Pathologist with the U.S. 

Department of Agriculture, Forest Service, Northern 

Region in Missoula, Montana. 

Sandra Kegley is an Entomologist with the U.S. Department 

of Agriculture, Forest Service, Northern Region in 

Missoula, Montana.

I. Blakey Lockman is a Regional Forest Pathologist with the 

U.S. Department of Agriculture, Forest Service, Pacific 

Northwest Region in Portland, Oregon.

Dean E. Pearson is a Research Ecologist with the U.S. 

Department of Agriculture, Forest Service, Rocky 

Mountain Research Station in Missoula, Montana.

James A. Powell is a Professor with Utah State University, 

Department of Mathematics and Statistics in Logan, 

Utah.

Steve Shelly is the Regional Botanist with the U.S. 

Department of Agriculture, Forest Service, Northern 

Region in Missoula, Montana. 

Brytten E. Steed is an Entomologist with the U.S. 

Department of Agriculture, Forest Service, Northern 

Region in Missoula, Montana. 

Paul J. Zambino is a Plant Pathologist with the U.S. 

Department of Agriculture, Forest Service, Northern 

Region in Coeur d’Alene, Idaho. 

Chapter 9

Kevin S. McKelvey is a Research Ecologist with the U.S. 

Department of Agriculture, Forest Service, Rocky 

Mountain Research Station in Missoula, Montana.

Polly C. Buotte is a Postdoctoral Research Associate with 

the Oregon State University, Department of Forest 

Ecoystems and Society in Corvallis, Oregon.

Chapter 10

Michael S. Hand is a Research Economist with the U.S. 

Department of Agriculture, Forest Service, Rocky 

Mountain Research Station in Missoula, Montana.

Megan Lawson is an Economist with Headwaters 

Economics in Bozeman, Montana.

Chapter 11

Travis Warziniack is a Research Economist with the U.S. 

Department of Agriculture, Forest Service, Rocky 

Mountain Research Station, Human Dimensions Program 

in Fort Collins, Colorado.

Megan Lawson is an Economist with Headwaters 

Economics in Bozeman, Montana.

S. Karen Dante-Wood is a Natural Resource Specialist, U.S. 

Department of Agriculture, Forest Service, Office of 

Sustainability and Climate in Washington, DC.

Chapter 12

Carl M. Davis (retired), was the Regional Archaeologist 

with the U.S. Department of Agriculture, Forest Service, 

Northern Region in Missoula, Montana.

Chapter 13

S. Karen Dante-Wood is a Natural Resource Specialist, U.S. 

Department of Agriculture, Forest Service, Office of 

Sustainability and Climate in Washington, DC.

Linh Hoang is the Regional Inventory, Monitoring, 

Assessment and Climate Change Coordinator, U.S. 

Department of Agriculture, Forest Service, Northern 

Region in Missoula, Montana.

Chapter 1: Introduction
16 USDA Forest Service RMRS-GTR-374. 2018

The Northern Rockies Adaptation Partnership (NRAP) 

includes diverse landscapes, ranging from high mountains 

to grasslands, from alpine glaciers to broad rivers (fig. 1.1). 

This region, once inhabited solely by Native Americans, 

has been altered by two centuries of settlement by EuroAmericans through extractive practices such as timber 

harvest, grazing, and mining, water diversions, and other 

activities. Although relatively little urbanization is present in this region, paved and unpaved roads and electrical 

transmission wires permeate much of the landscape. 

Federal agencies own and manage a significant portion of 

the Northern Rockies, including 15 national forests and 3 

national parks.

Resource conditions, resource management issues, effects of climatic variability and change, and climate change 

adaptation options differ greatly from Idaho to North Dakota 

and from the Canadian border to Wyoming. To capture these 

differences, the NRAP climate change vulnerability assessment and adaptation strategy were conducted for each of 

five subregions: Western Rockies, Central Rockies, Eastern 

Rockies, Greater Yellowstone Area, and Grassland. These 

subregions are briefly described next.

Western Rockies Subregion

The Western Rockies subregion occupies about 17 million acres across portions of Idaho and Montana, including 

the Idaho Panhandle, Kootenai, and Nez Perce-Clearwater 

National Forests and several Native American reservations 

(e.g., Nez Perce Indian Reservation, Coeur d’Alene Indian 

Reservation). Most of this subregion is extremely mountainous and heavily forested; the mountains are broken by river 

and stream valleys and two large grassland ecosystems, 

Big Camas Prairie and Palouse country. The subregion also 

includes 1.7 million acres of wilderness lands.

The Rocky Mountains encompass a large area of Idaho 

and extend from the Idaho panhandle along the Wyoming 

border. To the west of the Rockies lie the prairie lands of 

Washington and Oregon, and the east is home to mountainous western Montana. A distinguishing feature of this region 

is the rugged mountains that extend lengthwise along the 

panhandle. The Bitterroot Mountains occupy the Idaho panhandle along the Montana/Idaho border, the Coeur d’Alene 

Mountains lie in the northern portion of the panhandle from 

Lake Pend Oreille in the north to Lake Coeur d’Alene in the 

south, and the Clearwater and Salmon River Mountains are 

located south of the Coeur d’Alene Mountains.

Continental glaciers shaped the topography of this 

panhandle region by excavating lake basins and depositing glacial till and outwash. The bedrock found here is 

composed of sedimentary rocks of the Belt Supergroup, 

deposited 1,470 to 1,400 million years B.P. Deposition took 

place in a large basin where space was not a limiting factor 

and the sediment was able to build up vertically (Idaho State 

University 2014a). This process created large deposits of 

silver, lead, and zinc in the Coeur d’Alene area.

The Western Rockies subregion contains many large 

rivers. Commonly referred to as the “River of No Return,” 

the Salmon River winds 425 miles through central Idaho 

and divides the northern and southern part of the State. 

The canyon gorge is deeper than the Grand Canyon of 

Arizona. It is one of the longest rivers in the State and 

renowned for its spawning beds for Pacific salmon species. 

The Clearwater River, also in Idaho, is fed by the Bitterroot 

Mountains and was preferred by explorers, trappers, miners, 

and loggers because it was easier to navigate than the turbulent Salmon River (Idaho State University 2014b). Other 

rivers include the Kootenai and Pend Oreille, which flow 

into the Columbia River. The Clark Fork of the Columbia 

River feeds into Lake Pend Oreille; and the Saint Maries, 

Saint Joe, and Coeur d’Alene Rivers flow into Lake Coeur 

d’Alene. Priest Lake and Hayden Lake near Pend Oreille are 

heavily used for recreation because of their scenic setting 

among forested mountains (Idaho State University 2014b).

Idaho is only 300 miles from the Pacific Ocean, so its 

climate is affected by a maritime atmospheric pattern that 

brings more precipitation to northern Idaho than to southern 

Idaho. Summers are typically hot and dry, and winters are 

relatively cold due to the high amount of moisture carried 

through the Columbia River Gorge.

The most actively managed forests in the Western 

Rockies are found in northern Idaho, which is characterized as a steppe-coniferous forest alpine meadow province 

(Schnepf and Davis 2013). A 2012 Forest Service, U.S. 

Department of Agriculture (USFS) report used Forest 

Inventory and Analysis data to describe various forest 

cover types in the subregion. The six most common forest 

Chapter 2: Biogeographic, Cultural, and 

Historical Setting of the Northern Rocky 

Mountains

S. Karen Dante-Wood
USDA Forest Service RMRS-GTR-374. 2018 17

groups are Douglas-fir (Pseudotsuga menziesii), subalpine 

fir (Abies lasiocarpa)/Engelmann spruce (Picea engelmannii)/mountain hemlock (Tsuga mertensiana), lodgepole 

pine (Pinus contorta var. latifolia), ponderosa pine (Pinus 

ponderosa), western hemlock (Tsuga heterophylla)/Sitka 

spruce (Picea sitchensis), and quaking aspen (Populus 

tremuloides)/paper birch (Betula papyrifera) (Sullivan et al. 

1986). Commercially harvested coniferous species in this 

area include Douglas-fir, Engelmann spruce, grand fir (Abies 

grandis), lodgepole pine, ponderosa pine, subalpine fir, 

western hemlock, western larch (Larix occidentalis), western redcedar (Thuja plicata), and western white pine (Pinus 

monticola). Other species not used for wood products include whitebark pine (Pinus albicaulis), limber pine (Pinus 

flexilis), alpine larch (Larix lyallii), mountain hemlock, and 

western juniper (Juniperus occidentalis). Quaking aspen, 

black cottonwood (Populus nigra), and paper birch are also 

commonly found.

Western white pine is an important tree species to this 

region. It grows on a variety of soil types and slopes and can 

regenerate across a broad range of environments. Western 

white pine forests usually originate from wildfires and when 

the species matures, it can survive fire better than nearly all 

of its shade-tolerant competitors. Although the species can 

survive to an age of 300 to 400 years, it is declining due to 

white pine blister rust (causal agent: Cronartium ribicola).

Common shrub species in the subregion include western 

serviceberry (Amelanchier alnifolia), red osier dogwood 

(Cornus sericea), oceanspray (Holodiscus discolor), Lewis 

mockorange (Philadelphus lewisii), huckleberry (Vaccinium 

membranaceum), and smooth sumac (Rhus glabra). 

Evergreen shrubs include Oregon-grape (Berberis aquifolium), snowbrush ceanothus (Ceanothus velutinus), and 

mountain lover (Paxistima myrsinites); evergreen groundcovers include kinnikinnick (Arctostaphylos uva-ursi), and 

twinflower (Linnaea borealis) (Sullivan et al. 1986).

Ecologically diverse habitats in the Western Rockies 

subregion also support a large number of rare plant species. 

The warm, dry grassland areas in the western part of the 

subregion harbor populations of Spalding’s catchfly (Silene 

spaldingii), a Federally threatened species, and Palouse 

goldenweed (Pyrrocoma liatriformis). In contrast, the much 

wetter forests in the Clearwater River drainage contain several narrowly endemic plants such as Constance’s bittercress 

(Cardamine constancei), as well as a number of disjunct 

species that are geographically isolated from their main 

ranges in the Cascade Mountains, such as Pacific dogwood 

(Cornus nuttallii). In the northern part of the subregion, 

fens (groundwater-dependent wetlands where peat has accumulated) are uncommon habitats that support peripheral 

populations of more-northern plant species such as spoonleaved sundew (Drosera intermedia) and small cranberry 

(Vaccinium oxycoccos).

The Western Rockies provide habitat for more than 300 

animal species. Large mammal species include woodland 

caribou (Rangifer tarandus caribou), black bear (Ursus 

americanus), grizzly bear (U. arctos), white-tailed deer 

(Odocoileus virginianus), mule deer (O. hemionus hemionus), elk (Cervus elaphus), moose (Alces alces), coyote 

(Canis latrans), gray wolf (Canis lupus), bobcat (Lynx 

rufus), cougar (Puma concolor), and wolverine (Gulo gulo). 

Smaller vertebrates include Coeur d’Alene salamander 

(Plethodon idahoensis) and pygmy shrew (Sorex hoyi).

Among the broad range of avian taxa are bald eagle 

(Haliaeetus leucocephalus), golden eagle (Aquila chrysaetos), osprey (Pandion haliaetus), many species of 

owls, wild turkey (Meleagris gallopavo), California quail 

(Callipepla californica), greater sage-grouse (Centrocercus 

urophasianus), blue jay (Cyanocitta cristata), and calliope 

hummingbird (Stellula calliope).

Both native and nonnative fish are found in many 

Western Rockies rivers and lakes, making it a popular 

area for angling and spawning. Fish species include native 

cutthroat trout (Oncorhynchus clarkii), rainbow trout (O. 

mykiss), the Federally threatened bull trout (Salvelinus 

confluentus), and nonnative brook trout (Salvelinus fontinalis). The Kootenai River is home to the endangered white 

sturgeon (Acipenser transmontanus) and threatened burbot 

(Lota lota).

Wildfire is a dominant influence on the structure, function, and productivity of forest ecosystems in the Western 

Rockies. Fire frequency varies greatly depending on biogeographic conditions, with stand replacement fires occurring 

at 50- to 500-year intervals, and surface fires occurring in 

dry forests at 2- to 50-year intervals. Frequent fires keep 

many forests in the early stages of succession, as indicated 

by high numbers of western larch and pine (Schnepf and 

Davis 2013). In contrast, fire exclusion during the past 80 

years or so has reduced fire frequency in lower-elevation dry 

forests, resulting in dense stands and elevated accumulation 

of surface fuels.

Mountain pine beetle (Dendroctonus ponderosae) kills 

large numbers of lodgepole pine, often in outbreaks of 

thousands of acres, and it increasingly kills whitebark pine 

and limber pine at high elevations as the climate continues 

to warm. Western spruce budworm (Choristoneura occidentalis) causes sporadic outbreaks in Douglas-fir and 

true firs (Abies spp.), and Douglas-fir tussock moth (Orgyia 

pseudotsugata) is a prominent defoliator of Douglas-fir.

White pine blister rust, a nonnative fungus, causes mortality in five-needle pines (western white pine, whitebark 

pine, limber pine), and has greatly reduced the dominance 

of western white pine (Schwandt et al. 2013). Forests 

dominated by Douglas-fir and grand fir have increased as a 

result, accelerating forest succession toward shade-tolerant, 

late-successional true firs, western hemlock, and western 

redcedar (Bollenbacher et al. 2014). Attempts to control the 

spread of blister rust through removal of currant (Ribes), its 

alternate host, were mostly unsuccessful (Russell and Jain 

2007).

Various root diseases kill and reduce the vigor of 

Douglas-fir and grand fir, especially north of the Salmon 

River. Parasitic dwarf mistletoes (Arceuthobium spp.) reduce 

the vigor of and sometimes kill several species of conifers, 

Chapter 2: Biogeographic, Cultural, and Historical setting of the northern rocky mountains
18 USDA Forest Service RMRS-GTR-374. 2018

including western larch, Douglas-fir, ponderosa pine, and 

lodgepole pine (Idaho Forest Products Commission 2011).

Several silvicultural treatments are used to reduce the effects of these disturbances and stressors, including thinning, 

mechanically mixing the soil, and prescribed burning to favor the regeneration of different species and reduce surface 

fuels (Graham and Jain 2005). Treatments can be targeted 

to modify different portions of forest stands, from the soil to 

the upper canopy. Harvesting larger trees can create canopy 

openings, and encourage regeneration. Thinning to remove 

the mid-story of forests can result in various species combinations. Ground-level vegetation treatments can increase the 

density of small trees, creating a continuous distribution of 

low-stature fuels.

The economic structure of the Western Rockies integrates 

northern Idaho, northeastern Washington, and western 

Montana as “the inland empire.” In the early 1950s, the 

timber industry was the second largest industry after agriculture. Large-scale lumbering operations did not occur 

until after Weyerhauser Corporation opened plants near 

Sandpoint and Moscow in northern Idaho. Before 1900, 

timber was used locally for lumber, fuelwood for homes, 

railroad ties, and fence posts. After outside markets developed, operating sawmills produced various products such as 

2 x 4 studs, plywood, oriented strand board, particleboard, 

house logs, posts, poles, pulp and paper, wood beams, 

mobile homes, roof supports, and much more. Although 

the forest industry maintains a significant presence in the 

Western Rockies, it has declined in the past 20 years because of changing economic conditions, competition with 

other markets, and greatly reduced harvest on Federal lands.

Agriculture is a dominant industry on private lands, and 

cultivation and livestock grazing have occurred continuously on fertile prairie lands since the 1860s. Mining, which 

began in the 1880s, is another important industry in some 

areas, especially the Coeur d’Alene region, which leads the 

Nation in silver production and produces other nonferrous 

metals such as lead and zinc. Water that originates in high 

mountains of the Western Rockies is an extremely important 

resource because of its value for agriculture, hydroelectric 

power, industry, and municipal consumption. Forests are 

increasingly recognized and managed for their capacity to 

produce large amounts of clean water and to reduce erosion 

that would degrade water quality.

As extractive industries have declined in the past 30 

years and affluence of human populations has increased, 

recreation and aesthetically based activities have increased 

in popularity and economic importance. Rugged topography, 

forests, lakes, and streams are a major attraction for primary 

residences, seasonal residences, and recreational travel 

(fig. 2.1). Hunting, fishing, hiking, mountain biking, offroad vehicle use, and snow skiing are popular activities for 

local residents and visitors from throughout North America. 

Federal management increasingly focuses on providing opportunities for a broad range of recreational activities.

The Western Rockies have large populations of the Nez 

Perce, Kalispel, Kootenai, and Coeur d’Alene Tribes, who 

have lived for thousands of years in the terrestrial ecosystems, and more recently urban areas, of this subregion. 

Most tribes in this area had many villages and camps. They 

lived in teepees during the warmer months, and in large 

camps with primarily underground houses during the winter. 

Hunting, fishing (especially for salmon), and gathering 

of wild foods occurred year round, and men and women 

typically had separate duties. Men hunted and fished, and 

women gathered vegetables and fruits such as chokecherry 

(Prunus virginiana), huckleberry, wild strawberry (Fragaria 

virginiana), and common camas (Camassia quamash). 

Native people in this subregion excelled at making baskets, 

which were used for collecting nuts, storing fruits and roots, 

and cooking food. Federal agencies increasingly collaborate 

with tribal partners to ensure that tribal values (including 

cultural values) and access to resources are considered in 

land management planning.

Central Rockies Subregion

The Central Rockies subregion occupies about 12 million 

acres across portions of western Montana and Idaho and 

includes the Bitterroot, Flathead, and Lolo National Forests; 

Glacier National Park; and Flathead Indian Reservation 

(fig. 1.1). The subregion contains steep mountains, rolling meadows, large rivers and lakes (fig. 2.2), and alpine 

ecosystems that span the Sapphire Mountains, Bitterroot 

Mountains, Mission Mountains, and many other ranges. It 

also contains the largest contiguous area of designated wilderness in the United States outside of Alaska. The northern 

portion of the Central Rockies is referred to as “the Crown 

of the Continent,” and includes Glacier National Park and 

the Flathead National Forest.

Figure 2.1—Highly dissected watersheds with mixed conifer 

forest adjacent to streams are common in the Western 

Rockies subregion (photo: USDA Forest Service). 

Chapter 2: Biogeographic, Cultural, and Historical Setting of the Northern Rocky Mountains
USDA Forest Service RMRS-GTR-374. 2018 19

The Bitterroot and Missoula Valleys located in westcentral Montana have an inland mountain climate. Air 

masses that develop over the Pacific Ocean release moisture 

in the Cascade Range and over the mountains of northern 

Idaho. West-central Montana occupies the rain-shadow area, 

which receives dried-out Pacific air and little moisture in the 

valley bottoms—about 13 inches annually (Lackschewitz 

1991). Humidity is high in this region, except during the 

summer months, and winters are cold and moist. Similarly, 

the climate in the Flathead and Glacier region is influenced 

by the Pacific Maritime atmospheric pattern, with warm, dry 

summers and wet, cold winters.

Alluvial sediments filled the Bitterroot River Valley during the Tertiary period, and glacial Lake Missoula drained 

and refilled several times as a section of a continental 

glacier repeatedly washed out and redeveloped. Glacial lake 

sediments of various depths and qualities cover the slopes, 

bottomlands, and terraces in west-central Montana today 

(Lackschewitz 1991). During the Pleistocene era, low elevation valleys were scoured by continental glaciers, while the 

mountains were shaped by alpine glaciers in the Flathead 

and Glacier region (Newlon and Burns 2009).

In the Central Rockies, microclimate has a big effect on 

the distribution, abundance, and productivity of vegetation. 

For example, steep south-facing slopes with low retention 

of snow and soil moisture in summer are generally less 

productive and have different species composition than 

north-facing slopes. The bottoms of mountain canyons 

support lush vegetation due to the high level of moisture, 

whereas ridgetops support vegetation that requires little 

moisture for growth and survival.

Due to the Pacific-influenced climate, forests found in 

the west-central region (Bitterroot and Missoula Valleys) 

are drier than those in Idaho and northwestern Montana. 

Only a few species typical of the Pacific Coast are found 

here, such as western redcedar, western white pine, Pacific 

yew (Taxus brevifolia), bride’s bonnet (Clintonia uniflora), 

American trail plant (Adenocaulon bicolor), and threeleaf 

foamflower (Tiarella trifoliata). Intermountain forest species 

dominate the west-central Montana landscape, including 

western larch, subalpine larch (Larix lyallii), ponderosa 

pine, mock azalea (Menziesia ferruginea), Hitchcock’s 

smooth woodrush (Luzula hitchcockii), and common 

beargrass (Xerophyllum tenax). Bottomland ponderosa pine 

and hardwood species are commonly found in moist sites, 

whereas different types of bunchgrass species (Agropyron 

spp. and Festuca spp.) and a mixture of ponderosa pine and 

bunchgrasses is found in dry sites. Douglas-fir, grand fir, and 

subalpine fir dominate at higher elevations (Lackschewitz 

1991). Extensive stands of lodgepole pine are present at 

mid-to-upper elevations. Much of the native vegetation in 

the lower Bitterroot and Missoula Valleys has been lost to 

pasture or urban development.

In the Flathead Valley and Glacier National Park, 

lower elevations are dominated by Douglas-fir, ponderosa 

pine, grand fir, Engelmann spruce, and western redcedar. 

Douglas-fir, western larch, and subalpine fir are common at 

midelevations, and whitebark pine is found at high elevations (Newlon and Burns 2009). Black cottonwood (Populus 

trichocarpa) and quaking aspen are common deciduous 

trees found at lower elevations near Glacier National Park, 

often along lakes.

Wildfire is a major disturbance in the Central Rockies. 

Fires were fairly regular at lower and middle elevations 

in the Bitterroot and Missoula Valleys before 1900. Seral 

western larch and lodgepole pine previously dominated 

north-facing slopes, but fire exclusion has led to increased 

dominance of shade-tolerant species. As a result, silvicultural and prescribed burning treatments are being used to 

increase the distribution and abundance of seral tree and 

shrub species (Lackschewitz 1991).

The Central Rockies contain more than 60 species of 

mammals, with wilderness locations having relatively 

intact populations. Species include gray wolf, Canada lynx 

(Lynx canadensis), cougar, elk, mountain goat (Oreamnos 

americanus), bighorn sheep (Ovis canadensis), northern 

bog lemming (Synaptomys borealis), grizzly bear, goldenmantled ground squirrel (Callospermophilus lateralis), 

and pygmy shrew. Canada lynx and grizzly bear are on 

the threatened species list, and gray wolf, bald eagle, and 

Figure 2.2—Glacially carved 

landscapes, dense coniferous forest, 

and deep lakes are common in the 

Central Rockies subregion (photo: 

National Park Service). 

Chapter 2: Biogeographic, Cultural, and Historical Setting of the Northern Rocky Mountains
20 USDA Forest Service RMRS-GTR-374. 2018

peregrine falcon (Falco peregrinus) have been removed 

from the Federal threatened and endangered species list.

Hundreds of bird species are found in the Central 

Rockies, including killdeer (Charadrius vociferus) and spotted sandpiper (Actitis macularius) in riparian areas, song 

sparrow (Melospiza melodia) in grassland, willow flycatcher 

(Empidonax traillii) and MacGillivray’s warbler (Geothlypis 

tolmiei) in shrubby habitat, and bald eagle and Bullock’s 

oriole (Icterus bullockii) in mature forest canopy.

Diverse native cold-water fish and nonnative fish are 

abundant in Central Rockies rivers. For example, Flathead 

National Forest is well known for its populations of native 

bull trout and westslope cutthroat trout (Oncorhynchus 

clarki lewisi), which are found in Flathead Lake and the 

Flathead River. The Bitterroot River is home to many native 

fish species including bull trout, westslope cutthroat trout, 

northern pike minnow (Ptychocheilus oregonensis), and 

largescale sucker (Catostomus macrocheilus). As a result 

of the diversity and abundance of fish species, angling is a 

popular recreational activity in this area.

Wildfires and insect outbreaks are disrupting ecosystems 

in the Central Rockies. Although wildfires play an important 

ecological role, recently there have been more occurrences 

of larger wildfires and longer wildfire seasons because of 

warmer spring and summer temperatures. These fires are becoming increasingly expensive to control as they make their 

way across the forested landscape but also as they enter the 

wildland-urban interface, the zone where housing borders 

forests and woodlands. Insect invasions in this subregion 

have also damaged and killed trees.

Mountain pine beetle is one of the most destructive bark 

beetles in North America and has caused severe damage and 

mortality to whitebark pine in this subregion. Lodgepole 

pine in the forests of Idaho and Montana were affected 

by the beetle between 1911 and 1942. These outbreaks 

originally occurred at lower elevations and moved upward 

into whitebark pine habitat. This occurred in the Flathead 

National Forest in the 1970s, where the mountain pine 

beetle invaded lodgepole pine forests first and then moved 

upward into whitebark pine (Bartos and Gibson 1990). 

White pine blister rust has caused extensive mortality in 

whitebark pine in the Central Rockies, especially in Glacier 

National Park and adjacent areas, where more than 70 percent of the trees are infected and 30 percent have died.

Many of the aforementioned flora and fauna were documented by Meriwether Lewis and William Clark during 

their expedition in the early 1800s. The explorers traveled 

across the Bitterroot River and Lolo Creek Valley twice 

and never passed through the Flathead Valley. Other early 

explorers to the region included fur companies and independent trappers. Fur companies obtained fur by trading goods 

for furs with Native Americans, employing hunters and trappers, and trading furs with hunters and trappers at trading 

posts (McKay 1994). Hudson’s Bay Company had a good 

rapport with the Flathead, Pend d’Oreille, and Kootenai 

Tribes, trading products for bison (Bison bison) provided by 

Native Americans.

In 1855, the Hellgate Treaty established the Flathead 

Indian Reservation for the Flathead, Pend d’Oreille, and 

Kootenai Tribes. As the tribes began to live on the reservation, Euro-American settlement accelerated. Initially 

inhabited by quartz miners, fur trappers, and French 

Canadians, the Upper Flathead Valley was settled more 

heavily after the Northern Pacific Railroad connected with 

Missoula in 1883.

Timber harvest was a primary extractive activity in the 

Central Rockies in the late 1800s. With the passage of the 

1891 Forest Reserve Act, the President had authority to create forest reserves to revise public land laws (McKay 1994), 

and various protections gradually spread across Federal 

lands. Yellowstone was the first forest reserve established by 

President Harrison. In 1897, the Flathead, Bitterroot, Lewis 

and Clark, and Priest River became the first four reserves 

in the Northern Region established by President Cleveland. 

Much of the lower elevation land in the Central Rockies 

today has been converted to agriculture and urban and 

suburban development. The major industries are agriculture, 

ranching, forestry, and recreation/tourism.

Eastern Rockies Subregion

The Eastern Rockies subregion occupies about 12 million 

acres in central, west-central, north-central, and southwestern Montana (fig. 1.1). Included in this area are the 

Beaverhead-Deerlodge (eastern portion), Helena, and Lewis 

and Clark National Forests. These forests are mostly found 

on the eastern side of the Continental Divide. The subregion 

extends from high mountains (often exceeding 11,000 feet) 

in the west to broad plains in the east, including several 

large wilderness areas. It contains numerous mountain 

ranges—the Beaverhead, Bitterroot, Pioneer, Centennial, 

Bridger, Madison, Absaroka, Beartooth, Crazy, Gallatin, 

Elkhorn, and Big Belt Mountains—most of which have 

reasonably intact ecosystems at higher elevations.

Climate in the Eastern Rockies varies considerably, 

depending on location relative to the Continental Divide. 

The western side receives more precipitation as air masses 

from the west cool and release moisture over the mountain 

ranges; on the eastern side, the air becomes warmer and 

drier, often accompanied by downslope air movement 

known as “Chinook winds,” which create a more moderate 

climate than that of the Great Plains (Phillips 1999). In general, the eastern portion of the subregion experiences a drier 

continental climate.

The Rocky Mountains were developed from intense 

plate tectonic movement during the Jurassic, Cenozoic, and 

Laramide orogeny periods. The Laramide orogeny, which 

took place approximately 70 to 40 million years B.P., is 

responsible for elevating the Rocky Mountains. California, 

Oregon, and Washington were added to North America during the Mesozoic Era, whereas the Rockies were added to 

the continent much later (70 million years B.P.). Although 

mountain building usually occurs 200 to 400 miles inland 

Chapter 2: Biogeographic, Cultural, and Historical Setting of the Northern Rocky Mountains
USDA Forest Service RMRS-GTR-374. 2018 21

from the boundary of a tectonic plate (the subduction zone), 

the Rocky Mountains are several hundred miles inland. In 

the Rockies, the oceanic plate sank beneath the continental 

plate at a flat angle that led to mountain building farther inland than might be expected (U.S. Geological Survey 2014).

Numerous rivers flow through the Eastern Rockies, 

including the Missouri, Blackfoot, and Smith Rivers. The 

longest river in North America, the Missouri begins at the 

confluence of the Jefferson and Madison Rivers near Three 

Forks, Montana and includes three reservoirs (Canyon 

Ferry, Hauser, and Upper Holter). The Smith River is a 

tributary of the Missouri River and flows between the 

Little Belt and Big Belt Mountains. The Blackfoot River, 

a snow- and spring-fed river, begins at the Continental 

Divide in Lewis and Clark County, and is the river featured 

in the book A River Runs Through It by Norman Maclean. 

These rivers are known for their blue ribbon trout fishery 

status, scenic floats, and other water-based recreational 

activities.

Vegetation in the Eastern Rockies varies primarily as 

a function of elevation and aspect. Lower elevations are 

dominated by grassland and sagebrush steppe that include 

needle-and-thread grass (Hesperostipa comata), Idaho 

fescue (Festuca idahoensis), sagebrush (Artemisia spp.), 

rabbitbrush (Chrysothamnus spp.), milkvetch (Astragalus 

spp.), and wildflowers such as lupine (Lupinus) and 

balsamroot (Balsamorhiza spp.). Fremont’s cottonwood 

(Populus fremontii), yellow willow (Salix lutea), coyote 

willow (S. exigua), woods rose (Rosa woodsii), and golden 

currant (Ribes aureum) are commonly found along rivers 

and streams. Dominant species in foothills and woodlands 

include limber pine, Rocky Mountain juniper (Juniperus 

scopulorum), Douglas-fir, and ponderosa pine. Understory 

species include antelope bitterbrush (Purshia tridentata), 

curl-leaf mountain mahogany (Cercocarpus ledifolius), 

and skunkbrush sumac (Rhus aromatica var. simplicifolia). 

Douglas-fir and ponderosa pine dominate upper montane 

slopes, and lodgepole pine and Engelmann spruce are common at high elevations (Phillips 1999).

Common wildlife species in the Eastern Rockies include 

mountain goat, bighorn sheep, elk, cougar, Canada lynx, 

wolverine, and black bear. Hunters from around the world 

purchase tags to hunt in this subregion for many of these 

big-game species. Also common are bald eagle, greater 

sage-grouse, peregrine falcon, and red-tailed hawk (Buteo 

jamaicensis). Fly fishing opportunities are plentiful due to 

abundant populations of westslope cutthroat trout, rainbow 

trout, brook trout, and northern pike (Esox lucius). There 

are a few populations of grizzly bear and gray wolf in the 

region, but these species are concentrated in the western section of the Eastern Rockies, particularly in wilderness areas.

Forests in the Eastern Rockies have been subject to widespread drought, wildfire, and insect outbreaks over the past 

20 years (Montana Department of Environmental Quality 

2013). Several large wildfires have burned with uncharacteristic intensity because the absence of fire for several decades 

has resulted in elevated accumulation of fuels. Mountain 

pine beetle has led to extensive mortality of lodgepole pine 

and some ponderosa pine as older, non-vigorous stands 

succumb to attacks by elevated beetle populations caused by 

warmer temperatures. Western spruce budworm has caused 

mortality and stunted growth in Engelmann spruce and 

Douglas-fir in some areas.

The travels of Meriwether Lewis and William Clark 

through the Eastern Rockies have created a prominent 

historical legacy (fig. 2.3). Their expedition began in 1804 

near St. Louis, Missouri and in the spring of 1805, they traveled to Three Forks, Montana, via the Jefferson River. On 

this route, the explorers interacted with Shoshone Indians, 

and after passing over the Bitterroot Mountains, they made 

their way down to Fort Clatsop on the Oregon side of the 

Columbia River. The Lewis and Clark National Forest and 

other place names commemorate the expedition.

Figure 2.3—Populations of the grizzly bear, an iconic species in the Greater Yellowstone Area subregion, have increased over 

the past several decades as a result of successful conservation efforts (photo: U.S. Fish and Wildlife Service). 

Chapter 2: Biogeographic, Cultural, and Historical Setting of the Northern Rocky Mountains
22 USDA Forest Service RMRS-GTR-374. 2018

Thousands of years before Euro-Americans arrived, the 

Blackfoot, Sioux, Cheyenne, Flathead, and Crow Indians 

used the area as hunting grounds and a place to winter. 

Prior to 1806, the Blackfoot had exchanged wolf and beaver pelts with Canadian and English settlers for guns and 

ammunition. The livelihoods and cultures of these tribes 

were highly dependent on hunting the American bison, 

which provided food, shelter, and clothing. After horses 

were introduced to the region in the mid-1700s, hunters 

had much greater mobility to pursue bison, and horses 

themselves became part of the livelihood, commerce, and 

culture. The decimation of bison herds by Euro-Americans 

in the mid-1800s contributed to a rapid decline in Native 

American populations.

In the mid-1800s, mining for gold and other precious 

minerals was a common activity along the Continental 

Divide, particularly near the town of Helena, which was 

founded in 1864 and had the second largest placer gold 

deposit in Montana. Within 4 years, Last Chance Gulch (the 

original name for Helena) produced $19 million of gold. 

Because of its location adjacent to major transportation 

routes, the mining town was able to persist through the gold 

rush (A&E Television Networks 2009).

Agriculture is the largest industry in Montana, and 

Beaverhead County is the leading producer of cattle in the 

State, followed by Gallatin County, Jefferson County, and 

Madison County (Ranch and Recreational Group 2011). In 

the past several years, ranchland has been increasingly at 

risk to subdivision development. The wave of development 

in this region has transformed the landscape of forests and 

grasslands into one of towns, farms, and increasingly fragmented forested areas. Several organizations such as The 

Nature Conservancy are working with private landowners 

to add conservation easements on their lands to restrict 

subdivision, thereby limiting the fragmentation of wildlife 

landscapes and deleterious effects on ranching operations. 

The USFS often coordinates with the U.S. Department of 

the Interior (DOI), Bureau of Land Management (BLM) 

and Montana Department of Fish, Wildlife and Parks on 

natural resource issues related to landscape connectivity 

and restoration.

Greater Yellowstone 

Area Subregion

The Greater Yellowstone Area (GYA) subregion occupies about 23 million acres, extending across portions of 

Wyoming, Montana, and Idaho (fig. 1.1). It includes both 

the United States’ first national park (Yellowstone) and 

first national forest (Shoshone), in addition to Grand Teton 

National Park and portions of Bridger-Teton, CaribouTarghee, Gallatin, Custer, and Beaverhead-Deerlodge 

National Forests. One of the defining features of the subregion is a group of 24 conterminous mountain ranges that 

wrap around the Yellowstone Plateau (Morgan 2007).

The Yellowstone “hotspot” and associated geological activity have shaped the geography, topography, climate, soils, 

and biota of the GYA. The hotspot is a thermal disturbance 

fixed in the Earth’s mantle below the North American continental plate, moving to the northeast at the rate of 1 inch per 

year (Morgan 2007). This volcanic hotspot is responsible 

for eruptions that have left calderas in Oregon, Nevada, 

and Idaho and for creating the eastern Snake River plain. 

Volcanism formed the Yellowstone rhyolite plateau, and 

faulting formed sediment-filled basins and steep mountains 

such as the Teton Range/Jackson Hole and Madison Range/

Madison Valley. Uplift contributed to the high altitude of the 

GYA and associated deep valleys (Morgan 2007). The heat 

of eruptions that created calderas is also the source of heat 

for hot springs and geysers. These features are a primary 

reason that Yellowstone National Park was established; 

more geysers are found here than anywhere else in the world 

(National Park Service [NPS] 2015a).

The GYA is the source of three major river systems—

the Missouri/Mississippi, Snake/Columbia, and Green/

Colorado. The Missouri River begins in the northwest corner of the GYA and merges into the Mississippi River, the 

Snake River begins in the southeast corner of the GYA and 

merges into the Columbia River, and the Green River is the 

main tributary of the Colorado River. Anglers are drawn to 

these river systems for their blue ribbon fishing streams.

The GYA is one of the largest relatively intact and functional natural ecosystems in the temperate zone (Keiter and 

Boyce 1991). Abiotic factors such as topography and soils 

strongly influence vegetation composition and structure 

of the area. Differences in elevation greatly affect local 

climate, with valley bottoms having substantially higher 

annual temperatures than higher elevations. Soils are deeper 

in valley bottoms than on the Yellowstone Plateau, which 

is more affected by nutrient-poor soils derived from the 

Yellowstone Caldera (Hansen et al. 1999). Valley bottoms 

are generally occupied by lodgepole pine (NPS 2013). 

Lower slopes and richer soils (on basaltic or andesitic 

volcanic rocks, sedimentary rocks, and Precambrian crystalline rocks) support Engelmann spruce, subalpine fir, and 

Douglas-fir (Morgan 2007).The highest elevations are 

dominated by whitebark pine (NPS 2012). Quaking aspen, 

willows, and cottonwoods are also found on richer soils, 

such as valley toe slopes and bottoms.

In lodgepole pine forests, elk sedge (Carex geyeri) and 

grouse whortleberry (Vaccinium scoparium) are dominant 

understory plants, whereas understories of Douglas-fir 

forests are dominated by pinegrass (Calamagrostis rubescens). Utah honeysuckle (Lonicera utahensis), snowberry 

(Symphoricarpos albus), and buffaloberry (Shepherdia canadensis) are dominant understory species around the edge 

of the northern range of the GYA. Mountain big sagebrush 

(Artemisia tridentata var. vaseyana) and Idaho fescue dominate lower elevation grassland and meadows (NPS 2012).

The GYA appears to have retained most of its historical 

complement of vertebrate wildlife species (NPS 2013). The 

largest elk and bison herds in North America and the United 

Chapter 2: Biogeographic, Cultural, and Historical Setting of the Northern Rocky Mountains
USDA Forest Service RMRS-GTR-374. 2018 23

States, respectively, are found in the area. The northern 

range—the grassland in the northern part of Yellowstone 

National Park—sustains large populations of these animals. 

This ecosystem supports other charismatic megafauna such 

as grizzly bear (fig. 2.4), moose, white-tailed deer, gray 

wolf, and coyote; distinctive avifauna such as trumpeter 

swan (Cygnus columbianus) and bald eagle; several hundred 

species of other small mammals and birds; and thousands of 

species of insects and other invertebrates (Keiter and Boyce 

1991). This rich diversity of fauna allows for intact predator-prey interactions and other aspects of trophic dynamics.

Of the many fish species found in the GYA, westslope cutthroat trout and Yellowstone cutthroat trout 

(Oncorhynchus clarkii bouvieri) are keystone species 

preyed upon by many wildlife species, including grizzly 

bears. Cutthroat trout are currently at risk from hybridization and competition with nonnative lake trout (Salvelinus 

namaycush) (NPS 2012). Apart from fishing pressure, water 

resources will become increasingly important if the population of the 21 counties in the GYA continues to increase.

Climate, soil, and plant productivity are some of the 

many factors that influence where organisms are found. 

For example, many bird species are predominantly found 

at lower elevations, because primary productivity is highest there and climate is moderate (Hansen et al. 1999). In 

the GYA, plant assemblages dominated by lodgepole pine, 

cottonwood, quaking aspen, and willow have high bird 

abundance and diversity.

The topography of the GYA has influenced human use 

of the region for more than 10,000 years. Native Americans 

entered the Greater Yellowstone region soon after they 

entered North America 13,500 to 12,800 years B.P. For their 

survival, hunter-gatherer groups would forage for seeds, 

fruit, and animals at lower elevations and follow the maturation of plants and migration of animals into mountainous 

areas. Around 1872, Native Americans were moved to a 

reservation in central Wyoming. Soon after, roads were 

developed for gold camps in Montana. During the development of roads, Native Americans tried to protect their 

hunting grounds. Pioneering ranchers eventually settled 

in the lower valleys of the region. It was the construction 

of the railroad from Livingston, Montana, to Yellowstone 

National Park that brought increasing numbers of tourists to 

the area (Morgan 2007).

Current land allocations and land use in the GYA indicate 

that human activities are more prevalent at low elevations 

than at higher elevations. From the Yellowstone Plateau to 

the Gallatin Valley, land use changes from timber management, grazing, and agriculture to rural and urban residences. 

Development in urban areas such as Bozeman has increased 

in the past several years, with most of the population 

concentrated along the foothills, near streams, or along 

transportation routes (Hansen et al. 1999).

The GYA has faced many land use changes and disturbances, both natural and human caused. Wildfire has had an 

enormous impact, especially the fires of 1988, which burned 

more than 1.2 million acres. These fires helped change how 

scientists, resource managers, and the public think about 

the role of large fires in the fire ecology of Western forests. 

Mountain pine beetle has killed thousands of acres of lodgepole pine in the GYA, although the outbreaks have not been 

as extensive as in other areas of North America.

One of the most controversial issues in the region to date 

involves the restoration of wolves to the area. Many scientists consider the reintroduction of wolves to be successful 

in restoring ecological completeness in the GYA (NPS 

2013). However, others consider it to be a disruption to 

existing conditions and local resources, including big-game 

species such as elk, and livestock on adjacent private and 

public lands. As of September 2014, the western gray wolf 

has been removed from the endangered species list and listed as a nonessential experimental population in Wyoming.

Figure 2.4—A rich diversity of grasses and forbs, often mixed with ponds and lakes provide excellent habitat for waterfowl in the 

Grassland subregion (photo: Jim Ringelman, Ducks Unlimited).

Chapter 2: Biogeographic, Cultural, and Historical Setting of the Northern Rocky Mountains
24 USDA Forest Service RMRS-GTR-374. 2018

The Yellowstone grizzly bear population is also 

important to this subregion (fig. 2.4). The U.S. Fish and 

Wildlife Service listed grizzly bears as a threatened species 

in 1975 as the species range was reduced to 2 percent of 

its former range. To help the population recover, Federal 

and State agencies implemented many actions such as 

placing a stop on grizzly hunting seasons, establishing a 

Yellowstone grizzly bear recovery area, and forming two 

interagency teams—Interagency Grizzly Bear Study Team 

and Interagency Grizzly Bear Committee—to coordinate 

management and increase communication. Although the 

population has recovered to some extent, the species is back 

on the threatened species list today. Managers and scientists 

continue to monitor the population and strive to maintain a 

viable population (NPS 2015c).

The GYA attracts visitors from all over the world to tour 

the national parks and participate in recreational activities 

such as fishing, hunting, skiing, and hiking. The economy of 

the area is therefore driven by the character and quality of 

the natural and social environment, which draws permanent 

residents as well as visitors to the area. Communities such 

as Gardiner and West Yellowstone depend on Yellowstone 

National Park for economic activity, whereas communities 

such as Bozeman, Livingston, and Cody are less dependent 

on the park and have more diverse economies (Graff 2005).

Grassland Subregion

The Grassland subregion occupies 119 million acres, 

extending across portions of Montana, Wyoming, North 

Dakota, and South Dakota (fig. 1.1). The area includes 

portions of Custer National Forest, all of the Dakota Prairie 

National Grassland and several Indian reservations including the Crown Indian, Fort Peck, Standing Rock, Blackfoot, 

Cheyenne River, and Spirit Lake Reservations.

The Wisconsinan glacier shaped the rolling and flat 

plains of North Dakota at the end of the last glacial period, 

about 12,000 years B.P. The southwestern corner of North 

Dakota was untouched by the glacier, which in turn led to 

the formation of the Little Missouri Badlands. Although this 

ice age glacier did not help shape the badlands, a previous 

glacier did. The Little Missouri River flowed northward 

until 600,000 years B.P., when a glacier blocked its path 

and diverted its flow east (Herman and Johnson 2008a). The 

resulting cycle of erosion and downcutting led to the development of badlands.

Sedimentary layers found here are primarily continental 

sediments deposited by rivers and streams. Siltstone, claystone, sandstone, and lignite coal are common sediments 

in this environment (Bluemle 1996). Clinkers (or scoria), 

rocks produced by burning coal beds, are also commonly 

found in the Badlands. They are mostly reddish but also 

include shades of pink to black. The landforms found in 

the Badlands—hills, valleys, cliffs, buttes—are a result of 

the differential hardness of minerals and their resistance to 

erosion (Bluemle 1996). As Theodore Roosevelt remarked, 

“The Badlands grade all the way from those that are almost 

rolling in character to those that are so fantastically broken 

in form and so bizarre in color as to seem hardly properly to 

belong to this earth.”

The rugged badlands were carved from rocks from the 

Late Cretaceous through the Eocene period. Cretaceous and 

Tertiary sedimentary formations mark the period when dinosaurs became extinct. The Hell Creek formation, located 

in the southern portion of the Little Missouri Badlands, has 

remnants of the last species of dinosaurs that existed on 

Earth, the most common of which were Triceratops species 

(Bluemle 1996). Along with dinosaur remains, other common fossils found in the area include those of fish, turtles, 

alligators, birds, and small mammals. Fossils of broadleaf 

trees, cycads, palms, and ground ferns are also present, 

indicating the presence of a subtropical coastal plain environment during the Cretaceous period. Petrified wood is 

commonly found in the Badlands and is thought to be the 

remains mostly of dawn redwood (Metasequoia glyptostroboides) (Bluemle 1996).

The Missouri, Red, and Souris (or Mouse) Rivers are the 

three major river systems in the Dakota Prairie portion of 

the Grassland subregion. The Missouri River is the largest 

and longest in North Dakota. The Red River borders North 

Dakota and Minnesota, and the Souris River begins in eastern Saskatchewan and flows into North Dakota, after which 

it loops back into Canada. The Tongue and Powder Rivers 

are the major river systems that flow into the Yellowstone 

River in the southern portion of the Grassland subregion.

The subregion is characterized by three very different 

ecosystem types: badlands, prairie, and ponderosa pine 

forest. The badlands are located mostly along the Little 

Missouri River. Sioux Indians, who lived in the region 

before Euro-American settlement, called the badlands 

“makosika” (land bad), and the French explorers called it 

“les mauvais terrers a traverser” (bad lands to travel across) 

(Bluemle 1996). The pine forests are found in “islands of 

green in a sea or rolling prairie” (Herman and Johnson 

2008a). Most of the ponderosa pine forest in the Custer 

National Forest burned in the last decade.

Most of the vegetation found in the badlands is native and consists of grasses, forbs, trees, and shrubs. 

Shortgrasses are dominant because average precipitation 

is only 10 to 12 inches annually. Common bunchgrasses 

include little bluestem (Schizachyrium scoparium), blue 

grama (Bouteloua gracilis), and needle-and-thread grass. 

In areas where precipitation reaches close to 15 inches, 

western wheatgrass (Pascopyrum smithii) is fairly common. 

Open areas that can retain moisture throughout the year can 

support trees and shrubs. Deciduous trees include eastern 

cottonwood (Populus deltoides), green ash (Fraxinus 

pennsylvanica), boxelder (Acer negundo), and American 

elm (Ulmus americana). Ponderosa pine and Rocky 

Mountain juniper (Juniperus scopulorum) are common in 

some locations. Drainages dominated by trees also provide 

habitat for shrubs such as western serviceberry, chokecherry 

(Prunus virginiana), currant species, and American plum (P. 

Chapter 2: Biogeographic, Cultural, and Historical Setting of the Northern Rocky Mountains
USDA Forest Service RMRS-GTR-374. 2018 25

americana). Shrubs found in drier locations include sagebrush, winterfat (Krascheninnikovia lanata), rabbitbrush, 

and buckbrush (Ceanothus cuneatus). Prairie wildflowers 

include gumbo lily (Mentzelia decapetala), scarlet globemallow (Sphaeralcea coccinea), soapweed yucca (Yucca 

glauca), and brittle pricklypear cactus (Opuntia fragilis) 

(Herman and Johnson 2008a).

The badlands landscape provides wildlife habitat in 

native prairie, sagebrush, woody draws, shrubby areas, and 

buttes. Large animals include bighorn sheep, pronghorn 

(Antilocapra americana), elk, white-tailed deer, and mule 

deer. When Lewis and Clark passed through North Dakota 

in 1804, the most abundant animal they encountered was 

bison, followed by pronghorn. Populations of wildlife 

considered food and game species were greatly reduced 

after Euro-American settlement. Other mammals found in 

the Grassland include black-tailed prairie dog (Cynomys 

ludovicianus), cougar, porcupine (Erethizon dorsatum), 

cottontail rabbit (Lepus sylvaticus), and bobcat. Common 

reptiles include prairie rattlesnake (Crotalus viridis), 

bullsnake (Pituophis catenifer), and sagebrush lizard 

(Sceloporus graciosus). Common amphibians include 

Woodhouse’s toad (Anaxyrus woodhousii), Great Plains 

toad (A. cognatus), and plains spadefoot toad (Spea bombifrons) (Herman and Johnson 2008a).

The badlands support a diversity of bird species such 

as long-billed curlew (Numenius americanus), yellowbreasted chat (Icteria virens), mountain bluebird (Sialia 

currucoides), rock wren (Salpinctes cabanis), western 

kingbird (Tyrannus verticalis), eastern kingbird (T. tyrannus), black-billed magpie (Pica hudsonia), prairie falcon 

(Falco mexicanus), and burrowing owl (Athene cunicularia). Greater sage-grouse is found in southwestern North 

Dakota and depends on sagebrush habitat, which is in 

decline; sharp-tailed grouse (Tympanuchus phasianellus) is 

found in similar sagebrush and prairie habitat (Herman and 

Johnson 2008a).

The native prairie component of the Grassland subregion is dominated by grasses and forbs (fig. 2.5) that 

tolerate low precipitation, strong winds, cold winters and 

hot summers, frequent fire, and herbivory. Native grasses 

have deep and extensive connected root systems that allow 

them to persist under stressful conditions (Herman and 

Johnson 2008b). Native prairie is divided into tallgrass, 

mixed grass, and shortgrass. Tallgrass prairie, which dominates eastern North Dakota, requires the most moisture, 

and shortgrass prairie requires the least.

The largest remaining tallgrass prairie is in the Red 

River Valley, dominated by big bluestem (Andropogon 

gerardii), switchgrass (Panicum virgatum), Indian grass 

(Sorghastrum spp.), and prairie dropseed (Sporobolus heterolepis) (North Dakota Game and Fish Department 2012). 

Humus, which develops as grasses and forbs decompose, 

helps retain soil moisture. This fertile soil led to the near 

extinction of the tallgrass prairie as farmers cultivated the 

land for wheat and other crops. The Sheyenne National 

Grassland contains most of the remaining tallgrass prairie 

in North Dakota today. Cedar River National Grassland, 

which connects with Grand River National Grassland in 

South Dakota, contains both tallgrass and shortgrass species. Warm- and cool-season grasses dominate this area, 

such as prairie junegrass (Koeleria macrantha), crested 

wheatgrass (Agropyron cristatum), green needlegrass 

(Nassella viridula), needle-and-thread grass, blue grama, 

little bluestem, and needleleaf sedge (Carex duriuscula). 

Dominant forbs include eastern pasque flower (Anemone 

patens), western wall-flower (Erysimum asperum), prairie smoke (Geum triflorum), blacksamson (Echinacea 

angustifolia), and common yarrow (Achillea millefolium) 

(Herman and Johnson 2008b).

Shortgrass prairie, found in the higher elevation region 

of the Missouri Slope of North Dakota, is dominated by 

warm-season species that require little rainfall, including 

spikemoss (Selaginella spp.), blue grama, needleleaf sedge, threadleaf sedge (Carex filifolia), buffalo 

grass (Urochloa mutica), and needle and thread. These 

grasses are 3 to 7 inches tall. The Little Missouri National 

Grassland contains both mixed and shortgrass prairie. 

Common prairie forbs include wild prairie rose (Rosa 

arkansana), blacksamson, showy milkweed (Asclepias 

speciosa), soapweed yucca, gumbo lily, and tenpetal 

blazingstar (Mentzelia decapetala) (Herman and Johnson 

2008b).

American bison was formerly the iconic “ruler of the 

prairies,” and Native Americans depended on bison for 

their livelihood. However, Euro-American settlement and 

hunting nearly drove the bison to extinction. Other mammals found in prairie habitat of the Grassland subregion 

include elk, red fox (Vulpes vulpes), coyote, American 

badger (Taxidea taxus), several species of ground squirrel 

(Spermophilus spp.) and pocket gopher (Thomomys spp.), 

white-tailed jackrabbit (Lepus townsendii), eastern cottontail (Sylvilagus floridanus), and meadow vole (Microtus 

pennsylvanicus) (Herman and Johnson 2008b).

Reptiles found in the prairie include garter snakes 

(Thamnophis spp.), smooth green snake (Opheodrys vernalis), and western hognose snake (Heterodon nasicus). 

Bird species include greater prairie chicken (Tympanuchus 

cupido), sharp-tailed grouse, greater sage-grouse, upland 

sandpiper (Bartramia longicauda), nonnative ring-necked 

pheasant (Phasianus colchicus), and many songbird species (Herman and Johnson 2008b).

The Grassland subregion is home to more than 100 

species of fish, including northern pike, walleye (Sander 

vitreus), and sauger (Sander canadensis). Walleye inhabit 

large reservoirs such as Lake Sakakawea and Lake Oahe, 

whereas sauger are found mostly in the Missouri River 

(Herman and Johnson 2008c). In addition, this subregion 

contains a variety of endemic prairie fish assemblages, 

including sensitive species such as northern redbelly dace 

(Phoxinus eos) and associated native macroinvertebrates 

such as fatmucket mussels (Lampsilis siliquoidea).

The Sioux, Assiniboine, Cheyenne, Mandan, Hidatsa, 

and Arikara were the first inhabitants of the land. In 1910, 

Chapter 2: Biogeographic, Cultural, and Historical Setting of the Northern Rocky Mountains
26 USDA Forest Service RMRS-GTR-374. 2018

approximately 6,000 Native Americans lived in North 

Dakota. That number increased to more than 25,000 in 

1970 and more than 30,000 today. Today, Federally recognized tribes live in five reservations in North Dakota: 

Fort Berthold, Lake Traverse Indian Reservation, Standing 

Rock Indian Reservation, Spirit Lake Reservation, and 

Turtle Mountain Reservation.

With the majority of the Grassland subregion located 

on fertile soil, agriculture drives the economy. Wheat, flaxseed, canola, peas, lentils, and oats are some of the many 

products grown here, especially in the Red River Valley 

(also known as “the Breadbasket of the World”). Livestock 

production occurs on the less suitable lands and includes 

beef, dairy cattle, and hogs. North Dakota is currently in a 

boom phase of oil production, focused on the Bakken and 

Three Forks formations, making it the second largest oilproducing State. Petroleum refining and food processing 

are also major industries.

The declining sage-grouse population is of extreme concern to western States. Over half of the greater sage-grouse 

habitat has been lost, resulting in sage-grouse population 

numbers of 200,000 to 500,000. The BLM, USFS, U.S. 

Fish and Wildlife Service, and the Natural Resources 

Conservation Service are working together to conserve the 

western sagebrush habitat. These agencies have developed 

several environmental impact statements to incorporate 

sage-grouse conservation measures into land use plans 

(USDOI BLM 2015). Although agencies continue to monitor and evaluate the western landscape, the U.S. Fish and 

Wildlife Service determined in 2015 that protection of the 

species under the Endangered Species Act was not warranted (USFWS 2015).

Many organizations such as the USFS, U.S. Fish and 

Wildlife Service, The Nature Conservancy, North Dakota 

Game and Fish Department, and Ducks Unlimited are 

working to protect existing grassland and aquatic habitat. 

Although most of the land is under private ownership, 

many landowners have converted cropland to grassland 

under the Conservation Reserve Program, in which the 

Federal government pays farmers to plant grass on less 

fertile lands. In many cases, reserve lands produce higher 

populations of white-tailed deer, ducks, ring-necked pheasant, and many nongame species. Unfortunately, West Nile 

virus (Flavivirus spp.), oil and gas development, and conversion of sagebrush land to cropland have reduced greater 

sage-grouse range habitat and populations (U.S. Fish and 

Wildlife Service 2014).

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Chapter 2: Biogeographic, Cultural, and Historical Setting of the Northern Rocky Mountains
28 USDA Forest Service RMRS-GTR-374. 2018

Introduction

Climate influences the ecosystem services we obtain 

from forest and rangelands. Climate is described by the 

long-term characteristics of precipitation, temperature, wind, 

snowfall, and other measures of weather that occur over a 

long period in a particular place, and is typically expressed 

as long-term average conditions. Resource management 

practices are implemented day-to-day in response to weather 

conditions; resource management strategies and plans are 

developed using our understanding of climate. With the 

need to consider climate change in planning and management, an understanding of how climate may change in the 

future in a resource management planning area is valuable. 

In this chapter, we present the current understanding of 

potential changes in climate for the Forest Service, U.S. 

Department of Agriculture (USFS) Northern Region and 

the Greater Yellowstone Area (GYA), hereafter called the 

Northern Rockies region.

Climate Model Projections: 

CMIP3 and CMIP5

Global climate models have been used to understand the 

nature of global climate by modeling how the atmosphere 

interacts with the ocean and the land surface. Scientists can 

use these models to pose questions about how changes in the 

atmospheric chemistry would affect global temperature and 

precipitation patterns. Given a set of plausible greenhouse 

gas scenarios, these models can be used to project potential 

future climate. These projections can be helpful in understanding how the environmental conditions of plants and 

animals might change in the future; how runoff and seasonal 

flows might vary with precipitation and timing of snowmelt; 

how wildfire and outbreaks of insects and disease might 

be affected by changes in climate; and how humans might 

respond in their use of the outdoors and natural resources.

The Coupled Model Intercomparison Project (CMIP) 

began in 1995 to coordinate a common set of experiments 

for evaluating changes in past and future global climate 

(Meehl et al. 2007). This approach allows comparison of 

results from different global climate models around the 

world and improves our understanding of the “range” of 

possible climate change. The third CMIP modeling experiments, or CMIP3, were used in the Intergovernmental Panel 

on Climate Change (IPCC) Fourth Assessment Report 

(Solomon et al. 2007); the latest experiments, or CMIP5, 

were used in the IPCC Fifth Assessment Report (Stocker et 

al. 2013).

A key difference between CMIP3 and CMIP5 is the set 

of emissions scenarios that drive, or force, the simulations 

of future climate (fig. 3.1, taken from Walsh et al. 2014). 

The CMIP3 simulations of the 21st century were forced with 

emissions scenarios from the Special Report on Emissions 

Scenarios (SRES) (Nakićenović et al. 2000). The CMIP3 

scenarios represent futures with different combinations of 

global population growth and policies related to alternative 

energy and conventional fossil fuel sources (Solomon et 

al. 2007). The CMIP5 simulations of the 21st century are 

driven by scenarios describing representative concentration 

pathways (RCPs) (van Vuuren et al. 2011). The RCPs do 

not define emissions, but instead define concentrations of 

greenhouse gases and other agents influencing the climate 

system. RCPs present the range of current estimates for the 

evolution of radiative forcing, which is the total amount of 

extra energy entering the climate system throughout the 21st

century and beyond. Projections made with RCP 2.6 show a 

total radiative forcing increase of 2.6 Watts per square meter 

(2.2 Watts per square yard) by 2100; projected increased 

radiative forcing through the scenarios of RCP 4.5, RCP 6.0, 

and RCP 8.5 indicate increases of 4.5, 6.0, and 8.5 Watts 

per square meter, respectively (3.75, 5.0, and 7.1 Watts 

per square yard, respectively). Unlike the SRES scenarios 

used in CMIP3, the RCPs in CMIP5 do not assume any 

particular climate policy actions. Rather, policy analysts 

and social scientists are free to develop mitigation scenarios 

that lead to one of the RCPs. Comparisons between CMIP3 

and CMIP5 model results for Oregon and Washington are 

described in box 3.1.

Climate of the Northern 

Rockies Region

Historical Climate

For historical data, we drew from and contrasted three 

common gridded historical datasets; Parameter-elevation 

Chapter 3: Historical and Projected Climate 

in the Northern Rockies Region

Linda A. Joyce, Marian Talbert, Darrin Sharp, Jeffrey Morisette, 

and John Stevenson
USDA Forest Service RMRS-GTR-374. 2018 29

Regressions on Independent Slopes Model (PRISM) 

(PRISM Climate Group 2014), Maurer (Maurer et al. 2002), 

and TopoWx (Oyler et al. 2015b). These three gridded 

historical products are knowledge-based systems that use 

point measurements of precipitation, temperature, and other 

climatic factors to produce continuous, digital grid estimates 

of monthly, yearly, and event-based climatic parameters. 

Due to differences in the weather-station data used by these 

gridded products as well as the models and assumptions 

used to interpolate to a grid, these climate models do not 

always agree on the historical climate or trend for a region. 

This is especially true in the western mountains, where 

PRISM has been shown to have an artificial amplification 

of a warming trend (Oyler et al. 2015a). For this reason we 

chose to compare all models rather than the trend and values 

produced by a single model.

Figure 3.1—Comparison of global temperatures projected with emission levels from CMIP3 (left panel) and 

with emission levels from CMIP5 (right panel) (figure 2.4 from Walsh et al. 2014). Different amounts of 

heat-trapping gases released into the atmosphere by human activities produce different projected increases 

in Earth’s temperature. In the figure, the red and blue lines represent a central estimate of global average 

temperature rise (relative to the 1901–1960 average) for a specific emissions pathway. The shaded areas 

for a given color indicate the range (5th to 95th percentile) of results from a suite of climate models. 

The bars to the right of each panel indicate projections in 2099 for additional emissions pathways. In all 

cases, temperatures are expected to rise, although the difference between lower and higher emissions 

pathways is substantial. (Left) The panel shows the two main scenarios (SRES – Special Report on Emissions 

Scenarios): A2 assumes continued increases in emissions throughout this century, and B1 assumes much 

slower increases in emissions beginning now and significant emissions reductions beginning around 2050, 

though not due explicitly to climate change policies. (Right) The panel shows results from the most recent 

generation of climate models (CMIP5) using the most recent emissions pathways (RCPs – Representative 

Concentration Pathways). The newest set includes both lower and higher pathways than did the previous set. 

The lowest emissions pathway shown here, RCP 2.6, assumes immediate and rapid reductions in emissions 

and would result in about 2.5 °F of warming in this century. The highest pathway, RCP 8.5, roughly similar 

to a continuation of the current path of global emissions increases, is projected to lead to more than 8 °F 

warming by 2100, with a high-end possibility of more than 11 °F (data from CMIP3, CMIP5, and NOAA 

NCDC). These results draw on raw GCM data summarized for the entire Earth rather than bias corrected to 

spatially downscaled GCM models for our regions depicted in all other graphics. 

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
30 USDA Forest Service RMRS-GTR-374. 2018

Projected Climate

For an overview of projected climate in the Northern 

Rockies region, we use downscaled CMIP5 projections 

based on RCP 4.5 and RCP 8.5 scenarios (fig. 3.2). Output 

from global climate models is at a scale too coarse to 

represent climate dynamics in subregions and management 

areas relevant for the region. Many methods have been 

developed to bring climate projection information down to 

a scale that can be helpful to resource managers. We drew 

on climate projections that had been downscaled using the 

bias-correction and spatial disaggregation (BCSD) method 

(Maurer et al. 2007). We obtained the downscaled projection data from the Downscaled CMIP3 and CMIP5 Climate 

and Hydrology Projections archive (U.S. Department of the 

Interior, Bureau of Reclamation 2013). We use projections 

from 36 climate models for RCP 4.5 and 34 climate models 

for RCP 8.5 (table 3.1). The variables available for each 

BCSD climate projection include monthly precipitation and 

monthly surface air temperature for the 1950–2099 period. 

Spatial resolution of the data is 1/8-degree latitude-longitude 

(~7.5 miles by 7.5 miles) and covers the entire region. We 

use a base period of 1970–2009 for the historical climate, 

and compare projections for two periods (2030–2059, 

2070–2099) with this historical climate. These time periods 

were selected in an attempt to summarize climate that has 

influenced the current conditions (base period) and two future periods that will be relevant to long-term management 

action (such as road construction, hydrologic infrastructure, 

or vegetation planting).

The currently cooler climates associated with the Rocky 

Mountains are evident as are the warmer parts of eastern 

Montana and South Dakota (fig. 3.2). All areas warmed 

under both projections, with a greater warming in RCP 8.5. 

Box 3.1—Comparing CMIP3 and CMIP5 for Temperature and Precipitation Projections for Oregon and 

Washington

Model Evaluation

One way to evaluate a model’s “skill” is to have it simulate (recreate) past climate and compare those results to 

observed climate. Both CMIP3 and CMIP5 models reproduce important characteristics of climate in the NRAP region 

fairly well, including wet winters, dry summers, annual temperature, and a 20th-century warming trend (~1.4 °F per 

century). However, both CMIP3 and CMIP5 models predict annual precipitation that is higher than observations 

(Mote and Salathé 2010; Rupp et al. 2013). 

Future Temperature

• CMIP5 climate experiments based on RCP 4.5 and RCP 8.5 are warmer for the NRAP region, on average, than 

the CMIP3 scenarios based on SRES-B1 and SRES-A2.

• Most of the difference in temperature projections can be explained through increased forcing between the two 

sets of emissions-concentration scenarios, rather than modifications to the models between CMIP3 and CMIP5.

Future Precipitation

• CMIP3 and CMIP5 both project a slightly wetter future on average by the mid-21st century. 

• CMIP3 and CMIP5 both project slightly drier summers and slightly wetter conditions the rest of the year.

• High natural variability in precipitation masks differences between CMIP3 and CMIP5.

Figure 3.2—Historical (1970–2009) and projected (2030–2059 

and 2070–2099) mean annual monthly temperature (°F) for 

Northern Rockies Adaptation Partnership Region (NRAP) 

under RCP 4.5 and RCP 8.5 scenarios. Projected climate 

results are the mean of 36 models for RCP 4.5 and 34 

models for RCP 8.5 (see table 3.1). Spatial resolution of the 

data is 1/8-degree latitude-longitude.

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 31

Table 3.1—CMIP5 climate projections for RCP 4.5 and RCP 8.5 scenarios were obtained for these models using the Downscaled CMIP3 and 

CMIP5 Climate and Hydrology Projections” archive at: http://gdo-dcp.ucllnl.org/downscaled_cmip_projections. The first model run was 

selected for this analysis.

Institution Climate model RCP 4.5 RCP 8.5

Commonwealth Scientific and Industrial Research Organization and Bureau of 

Meteorology, Australia

ACCESS1-0 X X

ACCESS1-3 X X

Beijing Climate Center, China Meteorological Administration bcc-csm1-1 X X

Beijing Climate Center, China Meteorological Administration bcc-csm1-1-m X X

Canadian Centre for Climate Modelling and Analysis CanESM2 X X

National Center for Atmospheric Research CCSM4 X X

Community Earth System Model Contributors CESM1-BGC X X

CESM1-CAM5 X X

Centro Euro-Mediterraneo per I Cambiamenti Climatici CMCC-CM X X

Centre National de Recherches Météorologiques/ Centre Européen de Recherche et 

Formation Avancée en Calcul Scientifique CNRM-CM5 X X

Commonwealth Scientific and Industrial Research Organization, Queensland Climate 

Change Centre of Excellence CSIRO-Mk3-6-0 X X

EC-EARTH consortium EC-EARTH X X

Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid 

Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, and Center for 

Earth System Science, Tsinghua University

FGOALS-g2 X X

Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid 

Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences, and Center for 

Earth System Science, Tsinghua University

FGOALS-s2 X X

The First Institute of Oceanography, State Oceanic Administration, China FIO-ESM X X

NOAA Geophysical Fluid Dynamics Laboratory GFDL-CM3 X X

GFDL-ESM2G X X

GFDL-ESM2M X X

NASA Goddard Institute for Space Studies GISS-E2-H-CC X

GISS-E2-R X X

GISS-E2-R-CC X

Met Office Hadley Centre (additional HadGEM2-ES realizations contributed by Instituto 

Nacional de Pesquisas Espaciais) HADGEM2-AO X X

Met Office Hadley Centre (additional HadGEM2-ES realizations contributed by Instituto 

Nacional de Pesquisas Espaciais) HADGEM2-CC X X

Met Office Hadley Centre (additional HadGEM2-ES realizations contributed by Instituto 

Nacional de Pesquisas Espaciais) HADGEM2-ES X X

Institute for Numerical Mathematics INM-CM4 X X

Institut Pierre-Simon Laplace IPSL-CM5A-LR X X

IPSL-CM5A-MR X X

IPSL-CM5B-LR X X

Japan Agency for Marine-Earth Science and Technology, Atmosphere and Ocean Research 

Institute (The University of Tokyo), and National Institute for Environmental Studies

MIROC-ESM X X

MIROC-ESM-CHEM X X

Atmosphere and Ocean Research Institute (The University of Tokyo), National Institute for 

Environmental Studies, and Japan Agency for Marine-Earth Science and Technology MIROC5 X X

Max Planck Institute for Meteorology (MPI-M) MPI-ESM-LR X X

Max Planck Institute for Meteorology (MPI-M) MPI-ESM-MR X X

Meteorological Research Institute MRI-CGCM3 X X

Norwegian Climate Centre NorESM1-M X X

Norwegian Climate Centre MorESM1-ME X X

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
32 USDA Forest Service RMRS-GTR-374. 2018

Average annual precipitation ranges from less than 6 inches 

to just over 85 inches with the wetter areas occurring in the 

northern parts of the mountains in Montana (fig. 3.3). See 

box 3.2 for key messages associated with the maps for the 

region.

Comparisons of CMIP5

Projections With the CMIP3

Projections Used in the 

Resource Chapters

The CMIP3 projections have been widely used in assessments such as the National Climate Assessment (Walsh 

et al. 2014) and the Forest Service, U.S. Department of 

Agriculture (USFS) Resource Planning Act Assessment 

(USDA FS 2012). Many of the resource chapters in this 

report are based on published literature using the CMIP3 

projections developed by Littell et al. (2011); figure 3.4 

compares the CMIP5 results used in this overview with 

CMIP3 projections of Littell et al. (2011) for use in natural 

resource assessments. There are many ways to compare 

projections, for example, by comparing the change in 

temperature with the change in precipitation over a common period. The downscaled projections from Littell et al. 

(2011) did not cover the entire Northern Rockies region 

(they cover the western area but stop at the Continental 

Divide). However, because we are interested in comparing 

Figure 3.3—Historical (1970–2009) and projected (2030–

2059 and 2070–2099) total annual precipitation (inches) 

under RCP 4.5 and RCP 8.5. Projected climate results are 

the mean of 36 models for RCP 4.5 and 34 models for 

RCP 8.5 (see table 3.1). Spatial resolution of the data is 1/8 

degree latitude-longitude.

Box 3.2—Summary: Climatic Variability and Change for the Northern Rockies Region

• The mountainous Western Rockies, Central Rockies, Eastern Rockies, and Greater Yellowstone Area (GYA) 

subregions sit at the boundary between the warm, wet, maritime airflows from the Pacific Ocean, and the cooler, 

drier airflows from Canada. The Grassland subregion is influenced primarily by the cooler, drier airflows from 

Canada.

• Climatic variability in the mountainous areas of Idaho, Montana, and the GYA is strongly influenced by 

interactions with topography, elevation, and aspect. 

• Historically, the coolest areas are found in the GYA, and the warmest areas are associated with grasslands in 

central Montana and into South Dakota and North Dakota.

• By the 2040s, mean annual monthly temperatures are projected to increase in the Northern Rockies region. The 

warmest areas continue to be associated with central Montana. For the Grassland subregion, projections show 

a pattern of a drier west and wetter east, with the mean of climate models showing a slight increase in the extent 

of the wetter eastern area.

• Projections for precipitation suggest a very slight increase in the future. Precipitation projections, in general, 

have much higher uncertainty than those for temperature.

• Seasonally, projected winter maximum temperature begins to rise above freezing (32 oF) in the mid-21st century 

in several of the subregions. 

• Projected climate was derived from climate models in the Coupled Model Intercomparison Project version 5 

(CMIP5) database, which was used in the most recent IPCC reports.

• Some chapters in this publication draw from existing scientific literature that used climate projections from the 

2007 IPCC reports (CMIP3 database). In the mid-21st century (2040–2060), CMIP3 and CMIP5 temperature 

projections are similar, whereas CMIP5 precipitation projections are slightly wetter than those in CMIP3.

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 33

the differences in temperature and precipitation between 

the CMIP3 and CMIP5 models for the entire region, we 

estimated the change in temperature and precipitation using global results for the models that Littell et al. (2011) 

used: 10 CMIP3 model projections using the A1B scenario. 

We obtained these 1-degree global model projections for 

the entire Northern Rockies region (Jeremy Littell, U.S. 

Geological Survey, Alaska Science Center, Anchorage, AK, 

written communication, August 2014). Using these data, 

we estimate the change in temperature and percent change 

in precipitation between a future period (2040–2060) and 

a historical period (1979–2009) for the models that Littell 

et al. (2011) used and the CMIP5 models that used in this 

study. In figure 3.4, the projected change in mean annual 

temperature is shown on the horizontal axis, and the percent change in precipitation is shown on the vertical axis. 

Change is described as the difference in temperature (future 

mean annual value minus historical mean annual value) and 

percent change in precipitation (100 × [future mean annual 

value minus historical mean annual value]/historical mean 

annual value).

Across all models, projected change in temperature by 

the 2040–2060 period ranges from just under 2 oF to nearly 

8 oF (fig. 3.4). Generally, the projected change for models 

using the RCP 8.5 scenario (shown in red) is greater than 

the change projected for the RCP 4.5 scenario (shown in 

yellow). Change in precipitation ranges across these CMIP5 

models from a decrease of about 5 percent to an increase of 

25 percent with a mean projected change of approximately 

6 and 8 percent for RCP 4.5 and RCP 8.5, respectively. 

Change in the CMIP3 projections developed by Littell et al. 

(2011) is shown on this graph as pcm1, Ensemble (average 

of 10 model projections), and miroc_3.2 (where pcm1 and 

miroc_3.2 are individual climate models). We conclude that 

when this set of CMIP3 results (Littell et al. 2011) is compared with CMIP5 results for the Northern Rockies region, 

the CMIP3 results are in the same temperature range for 

2040–2060, although CMIP5 precipitation projections are 

slightly wetter in the future (fig. 3.4).

Climatic Variability and Change 

in Northern Rockies Adaptation 

Partnership Subregions

The following five sections summarize historical and 

projected climate for the five Northern Rockies Adaptation 

Partnership subregions: Western Rockies, Central Rockies, 

Eastern Rockies, Greater Yellowstone Area, and Grassland 

(see figure 1.1 for location of subregions). Each section 

contains a set of figures based on a common template that 

we describe here. Key messages for each region are given in 

a series of boxes.

The first figure in each section shows the annual mean 

daily maximum temperature (oF), the annual mean daily 

minimum temperature (oF), and the total annual precipitation (inches) for 1949 through 2010. For these historical 

data, we drew from and contrasted three common gridded 

historical datasets; PRISM, Maurer, and TopoWx. In both 

temperature and precipitation there is variability, so we 

show the 10-year rolling average to highlight any short-term 

trends (bold lines).

The second figure in each section shows the historical 

modeled and projected annual mean of the daily maximum 

and minimum temperatures (oF), and total annual precipitation (inches) for the RCP 4.5 and the RCP 8.5 scenarios 

based on the CMIP5 1/8th degree BCSD data available 

on the Green Data Oasis (Lawrence Livermore National 

Laboratory n.d.). Typically, the scenario with the higher 

greenhouse gas concentrations (RCP 8.5) will show a 

higher temperature by 2100. In these figures, each model 

was backcast and we display the modeled historical data, 

which include all CMIP5 models that are bias corrected 

and downscaled in the same manner as the model projections. We overlay the 1/8-degree spatial resolution (about 

7.5 miles) gridded historical observation dataset (blue line) 

(Maurer et al. 2002), which was used in the bias correction 

Figure 3.4—For the entire NRAP region, percent change in 

total annual precipitation (%) and change in mean annual 

temperature (°F) from the simulated historical climate 

(1979–2009) and the projected climate (2040–2060) 

using the CMIP5 RCP 4.5 and RCP 8.5 scenarios and the 

CMIP3 A1B scenario. Each CMIP5 model result is labeled 

by a number with a key in the legend (e.g., 29 is MIROCESM) in colors to indicate RCP 4.5 (yellow) and RCP 8.5 

(red) (see table 3.1). The crosses in the middle represent 

the median and 25–75% of the RCP 4.5 and the RCP 

8.5 projections used in this study. The mean values for 

the CMIP5 changes are shown on the figure as colored 

diamonds. The CMIP3 results are labeled in black triangles 

(Littell et al. 2011).

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
34 USDA Forest Service RMRS-GTR-374. 2018

of the modeled data. The projections are shown in the colors 

used in figure 3.6: yellow for RCP 4.5 and red for RCP 8.5. 

The ensemble median from all models for each scenario is 

shown in the heavy line; the 5th and 95th percent quantiles 

for all models are shown by the shaded area. The precipitation projections have a greater variability than either 

temperature projection, and there is less confidence in any 

one particular model’s projection for precipitation.

The third figure in each section shows the seasonal 

means of the daily maximum temperature (oF) for the historical and projected period. We use box plots here, where 

each box is an aggregation of 20 years of modeled historical 

or projected seasonal data. For example, the box labeled 

as 1960 represents the seasonal average of 1950 through 

1969. The modeled historical boxes are gray, and boxes for 

projections use the same colors as in other figures: yellow 

for RCP 4.5 and red for RCP 8.5. The central line in each 

box is the median: the same number of modeled historical 

or projections lies above and below this line. The hinges or 

edges of the boxes are the first and third quartiles. Whiskers 

extend past the first and third quartile by 1.5 times the interquartile range.

The fourth figure in each section shows the seasonal 

means of the daily minimum temperature (oF) for the historical and projected period 1950–2100. The figure is set up 

in the same way as the third figure just described. We do not 

show the seasonal mean precipitation values as there is large 

variability and no discernible trend and hence, less confidence overall in the finer-scale precipitation projections.

Western Rockies Subregion

The primary results of analysis of historical and projected 

climate in the Western Rockies subregion are summarized in 

box 3.3, with specific detail in figs. 3.5, 3.6, 3.7, and 3.8.

Box. 3.3—Summary: Historical and Projected Climate for the Western Rockies Subregion

• This mountainous region sits at the boundary between warm, wet, maritime airflows from the Pacific Ocean, and 

cooler, drier airflows from Canada.

• Changes in climate affecting mountain snowpack will have important hydrologic implications.

• Over the historical period of record (1895–2012), the annual mean monthly minimum temperature increased by 

about 3.0 °F, while the annual mean monthly maximum temperature increased by about 0.6 °F. During the same 

period, annual mean monthly precipitation increased slightly, by an average of about 0.1 inch per month.

• Temperature is projected to increase 5 to 10 °F by 2100, including increases in both the annual mean monthly 

minimum and annual mean monthly maximum. 

• Mean monthly maximum and minimum temperatures are projected to increase for all seasons. The mean 

monthly minimum temperature (spring and fall) and the mean monthly maximum temperature (winter) may rise 

above freezing. 

• Seasonal precipitation is projected to be slightly higher in winter and spring, and slightly lower in summer than 

during the historical period of record.

Figure 3.5—Annual historical mean monthly maximum 

temperature, annual mean monthly minimum temperature, 

and total annual precipitation from monthly gridded 

PRISM, Maurer and TopoWx for 1949 to 2010 for the 

NRAP Western subregion. The heavy lines are the 10-year 

rolling average to show short-term trends. 

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 35

Figure 3.6—Historical modeled and projected annual mean 

monthly maximum temperature, annual mean monthly 

minimum temperature, and total annual precipitation for 

the RCP 4.5 and RCP 8.5 emission scenarios based on 

CMIP5 data for the NRAP Western subregion. Historic 

modeled results are indicated in gray, projections in 

colors. The shaded area shows the 5th and 95th percent 

quantiles for all models. The grey, red, or yellow heavy 

line illustrate ensemble median; the heavy blue line is 

the gridded historical observed data from Maurer et al. 

(2002). 

Figure 3.7—Seasonal mean 

monthly maximum 

temperature for 1950–2100 for 

the NRAP Western subregion. 

Each box is an aggregation of 

20 years of modeled historical 

or projected seasonal data 

centered on the year listed 

(historical, grey boxes; RCP 

4.5, yellow boxes; RCP 8.5, 

red boxes). For example, 

1960 represents the seasonal 

average of 1950 to 1969. The 

central line in each box is the 

median. Hinges or edges of 

the boxes are the first and third 

quartiles; whiskers extend 

past the first and third quartile 

by 1.5 times the interquartile 

range (middle 50); points 

outside of the whiskers are 

extreme values.

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
36 USDA Forest Service RMRS-GTR-374. 2018

Central Rockies Subregion

The primary results of analysis of historical and projected 

climate in the Central Rockies subregion are summarized in 

box 3.4, with specific detail in figures 3.9, 3.10, 3.11, and 

3.12.

Figure 3.8—Seasonal mean monthly 

minimum temperature for 

1950–2100 for the NRAP Western 

region. Each box is an aggregation 

of 20 years of modeled historical 

or projected seasonal data 

(historical, grey boxes; RCP 

4.5, yellow boxes; RCP 8.5, 

red boxes). For example, 1960 

represents the seasonal average 

of 1950 to 1969. The central 

line in each box is the median. 

Hinges or edges of the boxes 

are the first and third quartiles; 

whiskers extend past the first and 

third quartile by 1.5 times the 

interquartile range (middle 50); 

points outside of the whiskers are 

extreme values.

Box. 3.4—Summary: Historical and Projected Climate for the Central Rockies Subregion

• This mountainous region sits at the boundary between warm, wet, maritime airflows from the Pacific Ocean, and 

cooler, drier airflows from Canada.

• Changes in climate affecting mountain snowpack will have important hydrologic implications.

• Over the historical period of record (1895–2012), the annual mean monthly minimum temperature increased by 

about 2.6 °F, while the annual mean monthly maximum temperature increased by about 1.3 °F. 

• By 2100, temperature is projected to increase 6 to 12 °F for the annual mean monthly minimum, and 5 to 11 °F 

for the annual mean monthly maximum. 

• Mean monthly minimum and maximum temperatures are projected to increase for all seasons. The mean 

monthly minimum temperature (spring and autumn) and the mean monthly maximum temperature (winter) may 

rise above freezing. 

• Seasonal precipitation is projected to be slightly higher in winter and spring and slightly lower in summer than 

during the historical period of record.

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 37

Figure 3.10—Historical modeled and projected annual 

mean monthly maximum temperature, annual mean 

monthly minimum temperature, and total annual 

precipitation for the RCP 4.5 and RCP 8.5 emission 

scenarios based on CMIP5 data for the NRAP Central 

subregion. Historic modeled results are indicated in 

gray, projections in colors. The shaded area shows the 

5th and 95th percent quantiles for all models. The grey, 

red, or yellow heavy line illustrate ensemble median; 

the heavy blue line is the gridded historical observed 

data from Maurer et al. (2002).

Figure 3.9—Annual historical mean monthly 

maximum temperature, annual mean monthly 

minimum temperature, and total annual 

precipitation from monthly gridded PRISM, 

Maurer and TopoWx for 1949 to 2010 for the 

NRAP Central subregion. The heavy lines are 

the 10-year rolling average that show shortterm trends. 

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
38 USDA Forest Service RMRS-GTR-374. 2018

Figure 3.11—Seasonal 

mean monthly maximum 

temperature for 1950–2100 for 

the NRAP Central subregion. 

Each box is an aggregation of 

20 years of modeled historical 

or projected seasonal data 

(historical, grey boxes; RCP 

4.5, yellow boxes; RCP 8.5, 

red boxes). For example, 

1960 represents the seasonal 

average of 1950 to 1969. The 

central line in each box is the 

median. Hinges or edges of 

the boxes are the first and third 

quartiles; whiskers extend 

past the first and third quartile 

by 1.5 times the interquartile 

range (middle 50); points 

outside of the whiskers are 

extreme values. 

Figure 3.12—Seasonal mean 

monthly minimum temperature 

for 1950–2100. Each box is 

an aggregation of 20 years of 

modeled historical or projected 

seasonal data for the NRAP 

Central subregion (historical, 

grey boxes; RCP 4.5, yellow 

boxes; RCP 8.5, red boxes). For 

example, 1960 represents the 

seasonal average of 1950 to 

1969. The central line in each 

box is the median. Hinges or 

edges of the boxes are the first 

and third quartiles; whiskers 

extend past the first and third 

quartile by 1.5 times the 

interquartile range (middle 50); 

points outside of the whiskers 

are extreme values.

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 39

Eastern Subregion

The primary results of analysis of historical and projected 

climate in the Eastern Rockies subregion are summarized in 

box 3.5, with specific detail in figures 3.13, 3.14, 3.15, and 

3.16.

Box. 3.5—Summary: Historical and Projected Climate for the Eastern Rockies Subregion

• This mountainous region sits at the boundary between warm, wet, maritime airflows from the Pacific Ocean, and 

cooler, drier airflows from Canada.

• Changes in climate affecting mountain snowpack will have important hydrologic implications.

• Over the historical period of record (1895–2012), the annual mean monthly minimum temperature increased by 

about 2.2 °F, while the annual mean monthly maximum temperature increased by about 1.8 °F. During the same 

period, annual mean monthly precipitation was unchanged.

• By 2100, temperature is projected to increase 6 to 11 °F for the annual mean monthly minimum, and 5 to 11 °F 

for the annual mean monthly maximum. 

• Mean monthly minimum and maximum temperatures are projected to increase for all seasons. The mean 

monthly minimum temperature (spring and fall) and the mean monthly maximum temperature (winter) may rise 

above freezing. 

• Seasonal precipitation is projected to be slightly higher in winter and spring and slightly lower in summer than 

during the historical period of record.

Figure 3.13—Annual historical mean monthly 

maximum temperature, annual mean 

monthly minimum temperature, and total 

annual precipitation from monthly gridded 

PRISM, Maurer and TopoWx for 1949 to 

2010 for the NRAP Eastern subregion. The 

heavy lines are the 10-year rolling average 

that show short-term trends.

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
40 USDA Forest Service RMRS-GTR-374. 2018

Figure 3.14—Historical modeled and projected annual mean 

monthly maximum temperature, annual mean monthly 

minimum temperature, and total annual precipitation 

for the RCP 4.5 and RCP 8.5 emission scenarios based 

on CMIP5 data for the NRAP Eastern subregion. Historic 

modeled results are indicated in gray, projections in 

colors. The 5th and 95th percent quantiles for all models 

are shown by the shaded area. The ensemble median is 

illustrated by the grey, red, or yellow heavy line; the heavy 

blue line is the gridded historical observed data from 

Maurer et al. (2002).

Figure 3.15—Seasonal 

mean monthly maximum 

temperature for 1950–2100 

for the NRAP Eastern 

subregion. Each box is an 

aggregation of 20 years 

of modeled historical or 

projected seasonal data 

(historical, grey boxes; RCP 

4.5, yellow boxes; RCP 8.5, 

red boxes). For example, 

1960 represents the seasonal 

average of 1950 to 1969. The 

central line in each box is 

the median. Hinges or edges 

of the boxes are the first 

and third quartiles; whiskers 

extend past the first and third 

quartile by 1.5 times the 

interquartile range (middle 

50); points outside of the 

whiskers are extreme values.

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 41

Greater Yellowstone Area Subregion

The primary results of analysis of historical and projected 

climate in the Greater Yellowstone Area subregion are summarized in box 3.6, with specific detail in figures 3.17, 3.18, 

3.19, and 3.20.

Figure 3.16—Seasonal mean 

monthly minimum temperature 

for 1950–2100 for the NRAP 

Eastern subregion. Each box is 

an aggregation of 20 years of 

modeled historical or projected 

seasonal data (historical, grey 

boxes; RCP 4.5, yellow boxes; 

RCP 8.5, red boxes). For 

example, 1960 represents the 

seasonal average of 1950 to 

1969. The central line in each 

box is the median. Hinges or 

edges of the boxes are the first 

and third quartiles; whiskers 

extend past the first and third 

quartile by 1.5 times the 

interquartile range (middle 50); 

points outside of the whiskers 

are extreme values.

Box. 3.6—Summary: Historical and Projected Climate for the Greater Yellowstone Area Subregion

• In the Greater Yellowstone Area subregion, climatic variability is strongly influenced by interactions with 

topography, elevation, and aspect. 

• Over the historical period of record (1895–2012), the annual mean monthly minimum temperature increased by 

about 2.9 °F, while the annual mean monthly maximum temperature increased by about 1.2 °F. 

• By 2100, temperature is projected to increase 5 to 10 °F for the annual mean monthly minimum, and 7 to 12 °F 

for the annual mean monthly maximum. 

• Annual mean monthly precipitation is projected to increase slightly by 2100, although projections for precipitation 

have high uncertainty compared to temperature projections.

• Winter maximum temperature is projected to increase above freezing in the mid-21st century. Summer 

temperatures are projected to increase 5 °F by 2060 and 10 °F by 2100

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
42 USDA Forest Service RMRS-GTR-374. 2018

Figure 3.17—Annual historical mean 

monthly maximum temperature, annual 

mean monthly minimum temperature, and 

total annual precipitation from monthly 

gridded PRISM, Maurer and TopoWx 

for 1949 to 2010 for the NRAP Greater 

Yellowstone subregion. The heavy lines 

are the 10-year rolling average that show 

short-term trends. 

Figure 3.18—Historical modeled and projected annual 

mean monthly maximum temperature, annual mean 

monthly minimum temperature, and total annual 

precipitation for the RCP 4.5 and RCP 8.5 emission 

scenarios based on CMIP5 data for the NRAP Greater 

Yellowstone subregion. Historic modeled results are 

indicated in gray, projections in colors. The shaded 

area shows the 5th and 95th percent quantiles for all 

models. The grey, red, or yellow heavy line illustrate 

ensemble median; the heavy blue line is the gridded 

historical observed data from Maurer et al. (2002).

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 43

Figure 3.19—Seasonal 

mean monthly maximum 

temperature for 1950–2100 

for the NRAP Greater 

Yellowstone subregion. Each 

box is an aggregation of 20 

years of modeled historical 

or projected seasonal data 

(historical, grey boxes; RCP 

4.5, yellow boxes; RCP 8.5, 

red boxes). For example, 

1960 represents the seasonal 

average of 1950 to 1969. 

The central line in each 

box is the median. Hinges 

or edges of the boxes are 

the first and third quartiles; 

whiskers extend past the 

first and third quartile by 1.5 

times the interquartile range 

(middle 50); points outside 

of the whiskers are extreme 

values.

Figure 3.20—Seasonal mean 

monthly minimum temperature 

for 1950–2100 for the NRAP 

Greater Yellowstone subregion. 

Each box is an aggregation of 

20 years of modeled historical 

or projected seasonal data 

(historical, grey boxes; RCP 

4.5, yellow boxes; RCP 8.5, 

red boxes). For example, 1960 

represents the seasonal average 

of 1950 to 1969. The central 

line in each box is the median. 

Hinges or edges of the boxes 

are the first and third quartiles; 

whiskers extend past the first 

and third quartile by 1.5 times 

the interquartile range (middle 

50); points outside of the 

whiskers are extreme values.

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
44 USDA Forest Service RMRS-GTR-374. 2018

Grassland Subregion

The primary results of analysis of historical and projected 

climate in the Grassland subregion are summarized in box 

3.7, with specific detail in figures 3.21, 3.22, 3.23, and 3.24.

Box. 3.7—Summary: Historical and Projected Climate for the Grassland Subregion

• Warming trends indicate that future climate will be similar to the area south of this subregion.

• Even with little or no change in precipitation, there is the potential for summer drying or drought due to the 

increased heat and increased evapotranspiration.

• Early snowmelt from the west will imply changes in streamflow, with implications for streamflow and temperature 

and therefore reservoir management and stream ecology.

• There is a pattern of a drier west and wetter east, with the average of climate models showing a shift toward a 

slightly larger area of the wetter east.

Figure 3.21—Annual historical mean monthly 

maximum temperature, annual mean 

monthly minimum temperature, and total 

annual precipitation from monthly gridded 

PRISM, Maurer and TopoWx for 1949 to 

2010 for the NRAP Grassland subregion. The 

heavy lines are the 10-year rolling average 

that show short-term trends.

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 45

Figure 3.22—Historical modeled and projected annual mean 

monthly maximum temperature, annual mean monthly 

minimum temperature, and total annual precipitation for 

the RCP 4.5 and RCP 8.5 emission scenarios based on 

CMIP5 data for the NRAP Grassland subregion. Historic 

modeled results are indicated in gray, projections in colors. 

The shaded area shows the 5th and 95th percent quantiles 

for all models. The grey, red, or yellow heavy line illustrate 

ensemble median; the heavy blue line is the gridded 

historical observed data from Maurer et al. (2002).

Figure 3.23—Seasonal mean 

monthly maximum temperature 

for 1950–2100 for the NRAP 

Grassland subregion. Each box 

is an aggregation of 20 years of 

modeled historical or projected 

seasonal data (historical, grey 

boxes; RCP 4.5, yellow boxes; 

RCP 8.5, red boxes). For 

example, 1960 represents the 

seasonal average of 1950 to 

1969. The central line in each 

box is the median. Hinges or 

edges of the boxes are the first 

and third quartiles; whiskers 

extend past the first and third 

quartile by 1.5 times the 

interquartile range (middle 50); 

points outside of the whiskers 

are extreme values.

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
46 USDA Forest Service RMRS-GTR-374. 2018

Acknowledgments

We acknowledge the World Climate Research 

Programme’s Working Group on Coupled Modelling, which 

is responsible for CMIP, and we thank the climate modeling groups (listed in table 3.1) for producing and making 

available their model output. For CMIP the U.S. Department 

of Energy’s Program for Climate Model Diagnosis and 

Intercomparison provides coordinating support and led development of software infrastructure in partnership with the 

Global Organization for Earth System Science Portals.

References

Lawrence Livermore National Laboratory. [n.d.]. Green data oasis. 

https://computing.llnl.gov/resources/gdo/ [Accessed May 1, 

2017].

Littell, J.S.; Elsner, M.M.; Mauger, G.S.; [et al.]. 2011. Regional 

climate and hydrologic change in the northern US Rockies and 

Pacific Northwest: Internally consistent projections of future 

climate for resource management. Unpublished project report. 

http://cses.washington.edu/picea/USFS/pub/Littell_etal_2010 

[Accessed March 31, 2016].

Maurer, E.P.; Wood, A.W.; Adam, J.C.; [et al.]. 2002. A long-term 

hydrologically based dataset of land surface fluxes and states 

for the conterminous United States. Journal of Climate. 15: 

3237–3251.

Maurer, E.P.; Brekke, L.; Pruitt, T.; [et al.]. 2007. Fine-resolution 

climate projections enhance regional climate change impact 

studies. Eos Transactions of the American Geophysical Union. 

88: 504.

Meehl, G.A.; Covey, C.; Delworth, T.; [et al.]. 2007. The WCRP 

CMIP3 multimodel data set. Bulletin of the American 

Meteorological Society. 88: 1383–1394.

Mote, P.W.; Salathé, E.P. 2010. Future climate in the Pacific 

Northwest. Climatic Change. 102: 29–50.

Nakićenović, N.; Davidson, O.; Davis, G.; [et al.]. 2000. Special 

report on emissions scenarios: A special report of Working 

Group III of the Intergovernmental Panel on Climate Change. 

Cambridge, UK: Cambridge University Press. 599 p.

Oyler, J.W.; Ballantyne, A.; Jencso, K.; [et al.]. 2015b. Creating a 

topoclimatic daily air temperature dataset for the conterminous 

United States using homogenized station data and remotely 

sensed land skin temperature. International Journal of 

Climatology. 35: 2258–2279.

Oyler, J.W.; Dobrowski, S.Z.; Ballantyne, A.P.; [et al.]. 2015a. 

Artificial amplification of warming trends across the mountains 

of the western United States. Geophysical Research Letters. 

42: 153–161.

PRISM Climate Group. 2014. Oregon State University. PRISM 

4km climate data, 2014. http://prism.oregonstate.edu/ 

[Accessed March 31, 2016].

Rupp, D.E.; Abatzoglou, J.T.; Hegewisch, K.C.; [et al.]. 2013. 

Evaluation of CMIP5 20th century climate simulations for the 

Pacific Northwest USA. Journal of Geophysical ResearchAtmospheres. 118: 10,884–10,906.

Figure 3.24—Seasonal mean 

monthly minimum temperature 

for 1950–2100 for the NRAP 

Grassland subregion (historical, 

grey boxes; RCP 4.5, yellow 

boxes; RCP 8.5, red boxes). 

Each box is an aggregation of 

20 years of modeled historical 

or projected seasonal data. For 

example, 1960 represents the 

seasonal average of 1950 to 

1969. The central line in each 

box is the median. Hinges or 

edges of the boxes are the first 

and third quartiles; whiskers 

extend past the first and third 

quartile by 1.5 times the 

interquartile range (middle 50); 

points outside of the whiskers 

are extreme values.

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 47

Solomon, S.; Qin, D.; Manning, M.; [et al.], eds. 2007. Climate 

change 2007: The physical science basis. Contribution 

of Working Group I to the fourth assessment report of the 

Intergovernmental Panel on Climate Change. Cambridge, UK 

and New York, NY: Cambridge University Press. 996 p.

Stocker, T.F.; Qin, D.; Plattner, G.-K.; [et al.], eds. 2013. Climate 

change 2013: The physical science basis. Contribution 

of Working Group I to the fifth assessment report of the 

Intergovernmental Panel on Climate Change. Cambridge, UK 

and New York, NY: Cambridge University Press. 1535 p.

USDA Forest Service. 2012. Future of America’s forests and 

rangelands: Forest Service 2010 Resources Planning Act 

Assessment. Gen. Tech. Rep. WO-87. Washington, DC: U.S. 

Department of Agriculture, Forest Service. 198 p.

U.S. Department of the Interior, Bureau of Reclamation. 2013. 

Downscaled CMIP3 and CMIP5 climate and hydrology 

projections: Release of downscaled CMIP5 climate projections, 

comparison with preceding information, and summary of user 

needs. Denver, CO: U.S. Department of the Interior, Bureau 

of Reclamation, Technical Services Center. 47 p. Available 

at http://gdo-dcp.ucllnl.org/downscaled_cmip_projections

[Accessed May 1, 2017].

van Vuuren, D.P.; Edmonds, J.; Kainuma, M.; [et al.]. 2011. The 

representative concentration pathways: An overview. Climatic 

Change. 109: 5–31.

Walsh, J.; Wuebbles, D.; Hayhoe, K.; [et al.]. 2014. Our changing 

climate. In: Melillo, J.M.; Richmond, T.C.; Yohe, G.W., eds. 

Climate change impacts in the United States: The third National 

Climate Assessment. Washington, DC: U.S. Global Change 

Research Program: 19–67.

Chapter 3: Historical and Projected Climate in the Northern Rockies Region
48 USDA Forest Service RMRS-GTR-374. 2018

Introduction

Water is critical to life, and the effects of climate change 

on ecosystems are mediated through changes in hydrology. 

Changes in how snow accumulates and melts are one of the 

more consistently noted climate-induced changes to water 

in the western United States (Barnett et al. 2005; Service 

2004), and these changes affect when water will be available 

for forests and fish alike. Changes in summer atmospheric 

circulation patterns may alter the ability of summer precipitation to allow midsummer respite from seasonal drought 

and dampening of wildfire spread (Intergovernmental Panel 

on Climate Change [IPCC] 2013; see chapter 8). Fish will 

be affected by both lower low flows with earlier snowmelt 

and higher midwinter floods caused by rain-on-snow events. 

Declining summer water supplies will likewise challenge 

municipal and agricultural water supplies. All of these 

meaningful effects can be traced to interactions between 

temperature and precipitation changes projected for the future and described in chapter 3. In this chapter, we describe 

mechanisms of hydrologic change, and provide maps illustrating variations in effects across the Forest Service, U.S. 

Department of Agriculture Northern Region and the Greater 

Yellowstone Area, hereafter called the Northern Rockies 

region. We also discuss some uncertainties relevant to these 

effects. Climate change effects on stream temperature in the 

region are discussed in chapter 5.

Warming temperatures are the most certain consequence 

of increased CO2 in the atmosphere. The hydrologic consequences of warmer temperatures include less snowpack and 

greater evaporative demand from the atmosphere. Snowpack 

depth, extent, and duration are expected to decrease due to 

a combination of less precipitation falling as snow (Pierce 

et al. 2008), and slightly earlier melt (Luce et al. 2014). The 

degree of change expected as a result of warming varies 

dramatically over the landscape as a function of temperature 

(Luce et al. 2014). Places that are warm (near the melting 

point of snow) are expected to be more sensitive than places 

where temperatures remain subfreezing throughout much 

of the winter despite warming (Woods 2009). In the coldest 

locations, snowpack may increase with increasing winter 

precipitation under a changing climate (Hamlet et al. 2013).

The relationship of evapotranspiration to a warming 

climate is more complicated (Roderick et al. 2014). Warmer 

air can hold more water, which means that even if the relative humidity stays constant, the vapor pressure deficit, the 

difference between the actual water content of the air and 

the water content at saturation, increases. That difference 

drives a water vapor gradient between leaves and the atmosphere that can draw more moisture out of the leaves. This 

has led many to expect greater evaporation during climate 

change (e.g., Cook et al. 2014; Dai 2013) using potential 

evapotranspiration formulations dependent on temperature, 

reflecting the increased “demand.”

Evaporation, however, is an energy-intensive process, 

and there is only so much additional energy that will be 

available for evaporation. In addition, both the water balance and the energy balance need to be considered under 

future warming (Roderick et al. 2015). The observation that 

temperatures are warmer during drought is more generally 

related to the lack of water to evaporate leading to warmer 

temperatures than to warmer temperatures causing faster 

evaporation (Yin et al. 2014). Unfortunately, when potential 

evapotranspiration models based on air temperature (including Penman-Monteith) are applied as post-processing to 

general circulation model (GCM) calculations, an overestimate of increased evapotranspiration is likely because the 

energy balance is no longer tracked (Milly 1992; Milly and 

Dunne 2011). The reality is that most of the increased energy from increased longwave radiation will result in warming 

rather than increased evaporation (Roderick et al. 2015).

Changing precipitation is less often discussed in climate 

change projections because it is more uncertain (Blöschl and 

Montanari 2010; IPCC 2013). Nevertheless, it has a much 

more direct impact on hydrologic process than temperature 

and cannot be ignored. On average, across many GCMs, 

precipitation is expected to increase very slightly in the 

Northern Rockies. The bounds are quite large, however, 

ranging from on the order of +30 percent to –20 percent (see 

chapter 3). Unfortunately, because many hydrologic processes are sensitive to precipitation (e.g., floods, hydrologic 

drought, snow accumulation), this represents a profoundly 

large uncertainty. As a consequence, the general approach in 

this and other analyses is to use an ensemble average (i.e., 

average across many GCMs) precipitation outcome. In this 

report, we discuss some of the uncertainty surrounding that 

mean estimate to illustrate which processes or hydrologic 

outcomes are most uncertain and where. Not all processes 

Chapter 4: Effects of Climate Change on 

Snowpack, Glaciers, and Water Resources in 

the Northern Rockies Region

Charles H. Luce
USDA Forest Service RMRS-GTR-374. 2018 49

are sensitive to precipitation, and uncertainty in outcomes 

caused by uncertainty in precipitation is not the same everywhere for a given process. Acknowledging the substantial 

quantitative disagreement among models in projected precipitation behavior, we now turn to discussion of the general 

physical mechanisms behind precipitation change, on which 

there is some agreement.

Two primary concepts are applied for precipitation 

change: dynamic and thermodynamic (Seager et al. 2010). 

Dynamic drivers of precipitation change include changes in 

global circulation patterns (e.g., the Hadley cell extent) and 

changes in mid-latitude eddies. Changes in teleconnection 

patterns, for example the North American Monsoon System 

(NAMS), would also fall into this category. Thermodynamic 

changes refer to the fact that the atmosphere can hold more 

water (Held and Soden 2006) according to a nonlinear 

Clausius-Clapeyron relationship (saturation vapor pressure 

vs. temperature), leading to an expectation of roughly a 

7-percent increase in precipitation per 1.8 oF of temperature 

change. There are, however, other physical limits on the 

disposition of energy driving the cycling of water in the 

atmosphere, leading to lesser estimates on the order of 1.6 

percent per 1.8 oF at the global scale, with individual grid 

cells being less or potentially negative, particularly over 

land (Roderick et al. 2014). Different approaches to scaling 

the thermodynamic contribution is one of the reasons for 

differences among models, although the dynamic process 

modeling differences can be great as well.

When considering the impacts of precipitation change 

on streamflow, the seasonality of precipitation is important. 

One key outcome of the thermodynamically driven changes 

is that when precipitation happens, it is expected to fall with 

greater intensity. In turn, this is expected to result in longer 

dry spells between events. This process can be important in 

determining drought duration (and consequently severity) in 

locations where summer precipitation is an important component of the summer water budget (Luce et al. 2016), such 

as much of eastern Montana, and low elevation stations in 

western Montana (fig. 4.1). Locations with more exposure to 

Figure 4.1—Bar graphs of annual precipitation amounts and distribution from several representative locations. More western 

and higher elevation sites tend to have stronger winter precipitation, with a pronounced lull in July and August. May and June 

precipitation is generally more pronounced than July and August precipitation and so is likely an important water source for 

vegetation during the summer drought.

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
50 USDA Forest Service RMRS-GTR-374. 2018

westerly windflows (e.g., Idaho stations and the Yellowstone 

area), and high elevations in northern Montana, show a 

more pronounced winter-wet pattern, which is broadly more 

representative of high elevation stations than low elevation 

stations (figs. 4.1 and 4.2). Note that much of the region has 

a substantially wetter May and June than July and August, 

and in some cases, the May through June precipitation is 

on a par with or exceeds the winter snowpack contribution 

to the annual water budget (fig. 4.2). In these locations, the 

snowpack changes may have less consequence than any 

circulation changes driving summer precipitation, such as 

expected shifts in NAMS (IPCC 2013). The May through 

June precipitation contributions, for example, can be an 

important determination of the severity of summer drought 

and the fire season (Abatzoglou and Kolden 2013). Longer 

periods of precipitation deficit in summer paired with 

decreasing snowpack may be particularly challenging for 

vegetation and fishes.

Changes in orographic enhancement of precipitation 

over mountain areas in the Pacific Northwest is another effect within the class of dynamic effects. Historical changes 

in westerly windflows have led to a decrease in the 

enhancement of winter precipitation by orographic lifting 

over mountain ranges (Luce et al. 2013), raising the important question of whether such a pattern may continue into 

the future. Westerly winds across the Pacific Northwest are 

strongly correlated with precipitation in mountainous areas 

(fig. 4.3), but valley precipitation is not, nor is precipitation in much of eastern Montana. The historical trend in 

westerlies was driven by pressure and temperature changes 

spatially consistent with those expected under a changing 

climate, but were a consequence in part (~50 percent) of 

normal climate variability. Dynamic downscaling using a 

regional climate model (RCM) with small (~12.5 miles) 

cells provides a means to estimate orographically induced 

precipitation (fig. 4.4b), which cannot be simulated with 

the large cell size of GCMs (fig. 4.4a). Although the GCM 

shows general moistening over most of the area, the RCM 

shows a pattern of drying or no change on the upwind 

side of major mountain ranges, with moistening limited 

to valleys in the lee. Because precipitation falls mostly 

in mountain areas where streamflows originate, this is a 

potentially important aspect of future changes to consider. 

The variable infiltration capacity (VIC) model simulations 

detailed later in this chapter do not include this effect, so 

for purposes of general discussion, it can be lumped as an 

additional source of uncertainty for precipitation.

The range of potential changes in climate looks complex, 

particularly for such a varied landscape as the Northern 

Figure 4.2—An index of precipitation seasonality in the 

Northern Rockies, a ratio of early summer (May–June) to 

winter (December–January) precipitation. Greener colors 

are wetter in May and June. July and August precipitation is 

low for most locations. Of note is the relative contribution 

of May through June precipitation in western Montana 

and central Idaho compared to mountains (SNOTEL sites) 

further south. There is also a notable difference in mountain 

versus local valley (COOP sites) seasonality.

Figure 4.3—Correlation of winter 

precipitation to winter westerly 

wind speed across the Pacific 

Northwest (from Luce et al. 

2013).

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 51

Rockies. Perhaps the most important point to summarize 

from the previous discussion is that the current climatic 

settings vary over the landscape at both macroscales and 

fine scales. There are broad east-west changes in precipitation seasonality and amount, and local differences between 

nearby mountain and valley weather stations echo that 

pattern. Trends and drivers for climate variations will differ 

greatly from east to west. Fundamentally, topography is an 

important factor affecting seasonality, precipitation amount, 

and potential trends. Given that forests and much of the 

water supply generation are generally in mountain areas, it 

is important to recognize the role of topography in affecting the climate. Specific hydrologic outcomes of interest 

are changes to snowpacks and glaciers, streamflow, and 

drought.

Snowpack and Glaciers

Snowpack

Snowpack declines are among the most widely cited 

changes occurring with climate change, as warmer temperatures will reduce the fraction of precipitation falling as 

snow (Klos et al. 2014; Pierce et al. 2008). About 70 percent 

of the water supply in the western United States is tied to 

mountain snowpacks (Service 2004); thus, changes in snowpack are particularly relevant to municipal and agricultural 

water timing (Stewart et al. 2005).

Historical trends in snowpack accumulation have been 

negative across much of the Northern Rockies region (Mote 

et al. 2005; Regonda et al. 2005). Although earlier work has 

ascribed the changes primarily to warming temperatures, 

the interior parts of the Northern Rockies are cold enough to 

be relatively insensitive to warming and strongly sensitive 

to precipitation variation (Luce et al. 2014; Mote 2006). 

Consequently, decreased interior snowpacks are likely to 

be primarily a response to reduced precipitation (Luce et al. 

2013). In contrast, the low elevation mountains of northern 

Idaho, the westernmost mountains in the region, are heavily 

influenced by a maritime snow climate (Armstrong and 

Armstrong 1987; Mock and Birkeland 2000; Roch 1949), 

and are still sensitive to temperature variability, particularly 

with respect to snow durability (Luce et al. 2014) (fig. 4.5).

Precipitation uncertainty can be substantial, but it does 

not translate into uncertainty in snowpack changes everywhere (fig. 4.6). An index of uncertainty can be calculated 

as a ratio of the effects of the likely range of precipitation 

values (about ±7.5 percent for one standard deviation across 

models) to the relatively certain temperature change (the 

timing is uncertain, but a change in temperature is certain as 

long as CO2 concentrations continue to increase):

Ru = ∆ (+7.5%)

 ∆

Figure 4.6 shows strong certainty of large changes in 

April 1 snow water equivalent for the Cascades, but substantial uncertainty in outcomes for the Greater Yellowstone 

Figure 4.4—October through March precipitation change for 2041–2070 versus 1971–2000 as represented by (a) a global 

circulation model (CanESM2) and (b) a regional climate model with finer topographic detail.

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
52 USDA Forest Service RMRS-GTR-374. 2018

Figure 4.5—Estimated loss of (a) April 1 snow water equivalent and (b) mean snow residence time as related to warming of 

5.4 °F (from Luce et al. 2014).

Figure 4.6—Uncertainty ratio for April 1 snow water equivalent. Orange to dark red sites are strongly influenced by precipitation 

in contrast to temperature. Thus, temperature-based projections in those sites may be inaccurate if precipitation changes are 

large. At dark green (and white) sites, temperature effects will predominate, and precipitation changes in either direction are 

inconsequential.

Area, where cold temperatures leave the snowpack more 

sensitive to precipitation than to temperature changes. The 

uncertainty ratio in these areas suggests that relatively large 

increases in precipitation could counter the effects of warming on snowpack loss.

Glaciers

Glaciers are well-known features in the Northern 

Rockies, with a large number located in and near Glacier 

National Park, on the northern edge of the region, and in 

the Wind River, Absaroka, and Beartooth Ranges in and 

near Yellowstone National Park, at the southern edge. 

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 53

They are also found in several other mountain ranges in 

Montana and Wyoming (see Portland State University 

[2009] for maps). Significant changes have been noted in 

the glaciers of Glacier National Park over the course of the 

20th century (Fagre 2005), with the Grinnell Glacier having around 10 percent of the ice that it had at its peak in 

1850 (fig. 4.7). Declines have also been seen in the Wind 

River Range over the 20th century (Marston et al. 1991).

Estimating future changes in glaciers is complex (Hall 

and Fagre 2003), but empirical relationships derived for 

the glaciers indicate a brief future for them, with many 

glaciers becoming fragmented or disappearing by the 

2030s. Increasing temperatures yield a rising equilibrium 

line altitude, decreasing the effective contributing area 

for each glacier as warming progresses. A warming of 

5.4 °F can translate into between 1,000 and 1,600 feet of 

elevation rise in snow-rain partitioning and summer temperatures. Unfortunately, for the sake of simplicity, those 

changes do not directly equate to shift in equilibrium line 

altitude, which depends on the geometry and topography 

of the contributing cirque. Temperate alpine glaciers are 

well known for being as, or more, sensitive to precipitation 

variations as they are to temperature changes (McCabe and 

Fountain 1995), which has probably contributed to changes in glaciers across the Pacific Northwest. Westerlies and 

their contribution to winter precipitation have changed 

over the Glacier National Park region since the 1940s (fig. 

4.3) and April 1 snow water equivalent at these elevations and latitudes is relatively insensitive to temperature. 

However, this area receives significant spring and summer 

precipitation (fig. 4.1), and changing summer temperatures 

affect both the melt rate and additional summertime mass 

contributions (new snow) in these glaciers. Thus, summer 

temperature is a strong predictor of their behavior, and 

regardless of changes in precipitation, significant reduction in area of glaciers is expected by the end of the 21st

century (Hall and Fagre 2003).

Streamflow

Streamflow changes of significance for aquatic species, 

water supply, and infrastructure include:

• Annual yield

• Summer low flows—average and extreme

• Peakflows—scouring floods

• Peakflow seasonality

• Center of runoff timing

Annual yield, summer low flows, and center of runoff 

timing are all important metrics with respect to water 

supply. Irrigation water for crops and urban landscapes is 

typically needed in summer months, and these metrics are 

most relevant to surface water supplies rather than groundwater supplies, although changes in long-term annual 

means could be informative for the latter. For summer low 

flows, two metrics are used, the mean summer yield (June 

through September), and the minimum weekly flow with 

a 10-year recurrence probability (7Q10). Center of runoff 

timing refers to the timing of water supply, and shifts in 

runoff earlier in the winter or spring disconnect streamflow 

timing from water supply needs. Center of timing can be 

redundant with other metrics that measure impact more 

directly, but with care in interpretation, it can help clarify 

different potential causal mechanisms: changing precipitation versus changing temperature.

Peakflows are important to fishes and infrastructure. 

Scouring flows can damage eggs in fish redds if they occur 

while the eggs are in the gravel or alevin are emerging 

(DeVries 1997; Goode et al. 2013; Montgomery et al. 

1996; Tonina et al. 2008). Winter peakflows can affect 

fall-spawning fish: Chinook salmon (Oncorhynchus 

tschawytscha), bull trout (Salvelinus confluentes), and 

brook trout (S. fontinalis). Spring peakflows affect 

spring-spawning cutthroat trout (O. clarkia), steelhead (O. 

mykiss), and resident rainbow trout (O. mykiss) (Wenger 

Figure 4.7—Oblique view of Grinnell Glacier taken from the summit of Mount Gould, Glacier National Park (after Fagre 2005).

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
54 USDA Forest Service RMRS-GTR-374. 2018

et al. 2011a,b). Spring peakflows associated with the annual snowmelt pulse are typically muted in magnitude in 

comparison to winter rain-on-snow events. Scouring is less 

of a risk to spring-spawning fishes, whereas rain-on-snow 

events tend to affect much larger portions of a basin at a 

time. A shift to more midwinter events can yield greater 

peakflow magnitudes, which can threaten infrastructure 

such as roads, recreation sites, or water management facilities (diversions, dams).

Historical changes in some of these streamflow metrics 

have been examined in some of the western and southern 

basins in the Northern Rockies. For instance, earlier runoff 

timing was noted by Cayan et al. (2001) and Stewart et al. 

(2005), and declining annual streamflows were noted by 

Luce and Holden (2009) and Clark (2010). Declining low 

flows (7Q10) have also been seen in the western half of the 

Northern Rockies (Kormos et al. 2016) associated more 

with declining precipitation than warming temperature 

effects for the historical period. Projected changes in low 

flow and timing are generally associated with the expected 

changes in snowpack related to temperature (e.g., more 

melt or precipitation as rain in winter, yielding a longer 

summer dry period).

Streamflow Projections

Streamflow projections were produced from the VIC 

model (Liang et al. 1994) for the western United States 

(University of Washington, Climate Impacts Group 

n.d.). Climate projections are based on Coupled Model 

Intercomparison Project Phase 3 (CMIP3) GCM runs, the 

full details of which are discussed in Littell et al. (2011). 

Differences between the climate described by CMIP3 

and CMIP5 are provided in Chapter 3. The gridded data 

were used to estimate streamflow by using area-weighted 

averages of runoff from each VIC grid cell within a given 

basin, following the methods of Wenger et al. (2010), to 

accumulate flow and validate. Streamflow metrics were 

calculated for stream segments in the NHD+ V2 stream 

segments (USDA FS n.d.).

Uncertainty in climate model inputs can be a significant 

factor in uncertainty for outcomes for natural resources 

(e.g., Wenger et al. 2013). Besides showing the projected 

change from the ensemble average, metrics were calculated for two additional climate scenarios; MIROC 3.2 and 

PCM GCMs were chosen to show warmer-drier and cooler-wetter summers than the ensemble mean, respectively 

(Littell et al. 2011). The difference between these two runs 

is shown in the second panel of the figures for each metric 

to give a sense of the certainty with which the change is 

projected in a given basin. Downscaling for these runs was 

done statistically, so GCM expectations for precipitation 

are implicit. No effects of change in orographic enhancement (e.g., fig. 4.4) are inherent in these images, so readers 

may wish to consider an additional degree of uncertainty 

(in a drier direction) on the windward side of mountain 

ranges.

Although calculations were made for all 6th-level 

hydrologic units in the Northern Rockies, only the western 

half of the region is shown in figures 4.8 through 4.13. 

Trimming the domain allows easier comparison of the 

uncertainty map to the ensemble mean projection, at the 

loss of display for eastern Montana and western North 

Dakota. Fortunately, the easternmost part of the maps that 

are shown indicate little change going east.

Mean annual flow (fig. 4.8) shows minor increases in 

the western and southern portions of the domain, with 

lesser changes across eastern Montana, whereas mean 

summer flow shows consistent decreases throughout the 

region (fig. 4.9). Higher mountains in northern Idaho and 

northwestern Montana show substantial uncertainty in 

the annual-scale water yield compared to the size of the 

change. Over much of the rest of the domain, the range of 

uncertainty is on par with the magnitude of the expected 

change in runoff. Changes in the ensemble mean are comparable to ensemble changes in precipitation.

Despite projections of increased annual flow, low 

flows are expected to decline (fig. 4.10). Uncertainty is 

low compared to the magnitude of changes, particularly 

in mountain areas. Patterns are nominally similar, with 

relatively uniform changes, though with somewhat more 

pronounced changes in mountain areas, particularly in wetter ranges. Those areas showing more pronounced change 

in low flows generally show a large shift in timing (on the 

order of 2 months; fig. 4.11), again with uncertainty mostly 

lower than magnitudes of change in mountain areas, and 

more substantial changes in mountains with greater precipitation. The primary mechanism expected to drive lower 

low flows is reduced snowpack in winter, leading to less 

stored water.

Summer wet portions of the region are more likely to 

have low flows affected by summer precipitation patterns. 

Shifts in circulation that affect how moisture flows from 

the Gulf of Mexico during summer months are expected 

to have a net negative effect on precipitation, and spacing 

between precipitation events is likely to increase (IPCC 

2013; Luce et al. 2016). These summer wet areas are also 

more likely to see greater losses in precipitation with 

increased evaporation, but it is important to recognize the 

energy balance constraints when estimating the degree of 

loss (Roderick et al. 2014). This is not done in the VIC 

modeling, which uses only the temperature outputs from 

GCMs without reevaluating the change in energy balance 

from a different hydrologic formulation, which is known to 

potentially lead to overestimation of loss (Milly and Dunne 

2011).

Changes to flood magnitude across the region are much 

more uncertain and spatially heterogeneous at fine scales 

(fig. 4.12). The second metric on flood timing shows 

changes in the number of days in winter that are in the top 

5 percent of flows for the year (a maximum of 18.25 days 

on average; fig. 4.13). Bull trout are sensitive to this metric 

and tend to be rare when values exceed 5 percent (Wenger 

et al. 2011a,b). The shift to more midwinter rain and more 

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 55

Figure 4.8—Projections for fractional change in mean annual flow for the 2080s compared to 1977–2006. The ensemble mean 

is on the left, and the range between two disagreeing projections is shown on the right.

Figure 4.9—Projections for fractional change in mean summer flow (June–September) for the 2080s compared to 1977–2006. 

The ensemble mean is on the left, and the range between two disagreeing projections is shown on the right.

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
56 USDA Forest Service RMRS-GTR-374. 2018

Figure 4.10—Projections for fractional change in minimum weekly flow with a 10-year return probability (7Q10) for the 2080s 

compared to 1977–2006. The ensemble mean is on the left, and the range between two disagreeing projections is shown on 

the right.

Figure 4.11—Projections for number of days of change in center of streamflow timing for the 2080s compared to 1977–2006. 

The ensemble mean is on the left, and the range between two disagreeing projections is shown on the right.

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 57

rain-on-snow flooding depends strongly on the elevation 

range of each given basin. Generally, the maps reflect large 

declines in flood magnitude in higher elevation basins near 

the crest of major mountain ranges, with large increases at 

mid-elevations and little change below that. This matches 

well with the information on number of midwinter events, 

which shows the greatest increases at mid-elevations and 

less pronounced changes at both higher and lower elevations. Although there is less snow and more rain at higher 

elevations, it is probably more a process of shifting shoulder 

seasons (Woods 2009) than more midwinter flood events, 

thus producing more rain or rain-on-spring snowmelt floods, 

which tend to be less severe (MacDonald and Hoffman 

1995). With less snow accumulating, the annual snowmelt 

and rain events during snowmelt are likely to be smaller 

because less area will be snow-covered. At mid-elevations, 

temperatures will increase enough that rain is likely on 

snowpacks, even in midwinter. Uncertainty in peakflow 

magnitudes are generally as large as or larger than the expected magnitude of the change. There is less uncertainty in 

the amount of flooding occurring in midwinter.

Adapting Water Resources to 

Climatic Variability and Change 

in the Northern Rockies

With many potential changes in water resources, questions naturally arise about what we might be able to do to 

shift water and land management practices to reduce the 

impacts or consequences of a changing climate on water 

resources. Because the NRAP region includes diverse 

topography, geology, watershed configurations, and ecosystems, adaptation responses to climatic variability and 

change vary considerably across the region. However, 

several themes prevail across most of the region in response 

to dominant sensitivities to climate change (table 4.1). Many 

of these strategies and tactics may do little to alleviate some 

of the more direct consequences of shifting precipitation, 

snowpack timing, and temperature changes to forests during 

drought conditions (e.g.,Vose et al. 2016); they are largely 

directed toward affecting downstream water availability and 

consequences of drought.

Of greatest concern is reducing the vulnerability of 

roads and infrastructure to flooding, a phenomenon that is 

expected to increase considerably as snowpack declines 

and snow:rain ratios decrease. National forests in particular 

Figure 4.12—Projections for fractional change in 1.5-year flood magnitude (approximate “bankfull” flow) for the 2080s 

compared to 1977–2006. The ensemble mean is on the left, and the range between two disagreeing projections is shown on 

the right.

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
58 USDA Forest Service RMRS-GTR-374. 2018

contain thousands of miles of roads, mostly unpaved. 

Damage to those roads and associated drainage systems reduces access by users and is extremely expensive to repair. 

Road damage often has direct and deleterious effects on 

aquatic habitats as well, particularly when roads are adjacent 

to streams. Resilience to higher peakflows and frequency of 

flooding can be increased by maintaining the capability of 

floodplains and riparian areas to retain water, conducting a 

risk assessment of vulnerable roads and infrastructure, and 

modifying infrastructure where possible (e.g., increasing 

culvert size, improving road drainage, relocating vulnerable 

campgrounds or road segments).

Climate-induced occurrence of disturbances such as 

drought and flooding are expected to increase, thus reducing 

water quality. Building an information base on potential 

locations of and responses to disturbances will help ensure 

informed and timely decisionmaking when disturbances 

occur. Within this overall strategy, tactics include prioritizing data collection based on projections of future drought, 

collecting pre-disturbance data on water resources, and 

developing a clearinghouse for programs related to fire and 

other disturbance. All tactics are focused on Federal lands 

(table 4.1).

In contrast to the effects of winter peakflows, reduced 

overall base flows (especially in summer) are expected to 

reduce riparian habitat, water storage, and shallow aquifers. 

The primary adaptation strategies in this case are to increase 

natural storage and build storage where appropriate, as well 

as increase knowledge about groundwater. Specific tactics 

focus on (1) increasing storage with constructed wetlands, 

American beavers (Castor canadensis), and obliterated 

roads; and (2) considering small-scale storage in dams, 

retention ponds, and swales, where appropriate. In addition, 

it will be important to map aquifers and alluvial deposits, 

improve monitoring to provide feedback on water dynamics, 

and understand the physical and legal availability of water 

for aquifer recharge.

Public lands are a critical source of municipal water supplies, for which both quantity and quality are expected to 

decrease as snowpack declines. A critical adaptation strategy 

is to reduce erosion potential to protect water quality, as 

well as prioritize municipal water supplies. Water quality 

can be addressed by: (1) reducing hazardous fuels in dry 

forests to reduce the risk of crown fires, (2) reducing other 

types of disturbances (e.g., off-road vehicles, unregulated 

livestock grazing), and (3) using road management practices 

that reduce erosion. These tactics should be implemented 

primarily in high-value locations (near communities and 

reservoirs) on public and private lands.

Figure 4.13—Projections for number of days in winter that exceed the 95th percentile flow in each year, an indicator of when 

floods are likely to happen, for the 2080s compared to 1977–2006. The value of this metric can take on values between 0 

and 18.25, and the difference can take on the same range. The ensemble mean is on the, and while the range between two 

disagreeing projections is shown on the right.

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 59 Table 4.1—Adaptation options that address climate change effects on water resources in the Northern Rockies. Sensitivity to climatic variability and change: Increased flooding will increase damage to roads and infrastructure. Adaptation strategy/approach: Identify and proactively decrease vulnerability of infrastructure to flooding. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Increase resilience of stream resources by identifying and restoring degraded riparian areas to reduce flooding and increase natural storage; add large woody debris, improve floodplain connectivity, increase riparian roughness, restore beavers. Conduct a basin-wide risk assessment of hydrologic interactions with roads and other infrastructure where vulnerability of infrastructure is highest. Increase resilience of infrastructure: culvert sizing, hardened fords, road drainage, etc.; remove or relocate infrastructure (e.g., roads, campgrounds). Where can tactics be applied? All lands Federal and private lands Mostly Federal lands Sensitivity to climatic variability and change: Increased occurrence of disturbances such as drought and flooding will reduce water quality. Adaptation strategy/approach: Build an information base for a timely response to disturbance, thus ensuring that data are available to inform decisionmaking. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Prioritize data collection based on projections of future drought. Collect pre-disturbance data on stream and riparian conditions, including high- quality values and habitat in need of protection. Develop a clearinghouse for available funding and programs related to fire and other disturbances. Where can tactics be applied? Mostly Federal lands Mostly Federal lands Mostly Federal lands Sensitivity to climatic variability and change: Reduced base flows will cause smaller riparian habitats and morphological changes, affecting groundwater, storage, and shallow alluvial aquifers. Adaptation strategy/approach: Increase knowledge about the groundwater resource. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Map aquifers and alluvial deposits Determine legal availability and better understanding of physical availability of water for aquifer recharge. Improve monitoring of streamflow and groundwater to improve understanding of surface water-groundwater interactions; obtain real-time data. Where can tactics be applied? All lands All lands All lands

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
60 USDA Forest Service RMRS-GTR-374. 2018 Table 4.1 (cont.)—Adaptation options that address climate change effects on water resources in the Northern Rockies. Sensitivity to climatic variability and change: Reduced base flows will cause smaller riparian habitats and morphological changes, affecting groundwater, storage, and shallow alluvial aquifers. Adaptation strategy Approach: Increase natural storage and build storage. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Increase natural water storage (mirroring natural processes) with constructed wetlands, beavers, and road obliteration. Promote distributed small-scale water storage in small dams, retention ponds, and swales in stream channels and uplands. Improve streamflow and groundwater monitoring to improve understanding of surface water-groundwater interactions and obtain real-time data. Where can tactics be applied? Multiple land ownerships Agricultural lands, headwaters without native fish species All lands Sensitivity to climatic variability and change: Reduced snowpack will reduce the quantity and quality of municipal water supplies. Adaptation strategy/approach: Reduce erosion potential to protect municipal water supplies; prioritize municipal systems for protection. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Reduce hazardous fuels. Reduce disturbances (off-road vehicles, grazing, etc.). Use road management practices that reduce erosion. Where can tactics be applied? High-value locations High value-locations on public and private lands High value locations on public lands Sensitivity to climatic variability and change: Higher temperatures and decreased snowpack will reduce water availability. Adaptation strategy/approach: Reduce water use and increase efficiency, demonstrate leadership in water efficiency, and create outreach opportunities. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Communicate water saving tactics and benefits. Research successful water saving tactics and apply tactics where appropriate. Install low-f﻿low appliances at administrative sites; replace landscaping with drought tolerant plants. Where can tactics be applied? All lands, where appropriate All lands, including administrative locations (campgrounds, visitor centers, etc.) All lands, including administrative locations (campgrounds, visitor centers, etc.); use Internet, press releases, interpretive sign, etc. 

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 61

Harvesting trees to increase water yield has been a practice of interest for some time (e.g., Bates and Henry 1928). 

Trees use water, so it is not surprising that water yields 

generally increase after canopy loss (Brown et al. 2005; 

Jones and Post 2004; Troendle and King 1987; Troendle et 

al. 2010). There are, however, certain caveats to be considered. For example, increases in water yield are generally 

greater in moister environments or years, with less increase 

in drier locations or years (e.g., Brown et al. 2005), and 

in some circumstances in drier climates, decreased yields 

may be seen (Adams et al. 2011; Guardiola-Claramonte et 

al. 2011). In broad terms, the general places and times one 

would want to see increases in water yield are the places 

and times when forest harvest is least effective (Troendle 

et al. 2010; Vose et al. 2012). Furthermore, thinning has 

proven to be ineffective in increasing water yield (Lesch 

and Scott 1997; Wilm and Dunford 1948). But it can 

be useful in augmenting snow accumulation depths, for 

example for wildlife or recreation benefit (Sankey et al. 

2015; Wilm 1944).

Consequences of canopy removal for streamflow augmentation are likewise not all positive. A negative effect of 

canopy reduction treatments is that they advance the timing of runoff (Luce et al. 2012). An example of large-scale 

canopy loss in an area with similar vegetation and climate 

is the Boise River Basin, where about 45 percent of one 

basin burned while the other was left relatively unchanged 

after 46 years of calibration. Water yield from the 494,211-

acre basin increased 5 percent, providing an average of 

an additional 50,000 acre-feet each year. However, the 

average timing of release advanced by 2 weeks because 

the exposed snowpack melted faster, and most of the additional runoff was available before April, when it would 

be of little use in bolstering low flows. In warmer regions 

of the Northern Rockies, such large-scale canopy removal 

could increase the magnitude of midwinter rain-on-snow 

floods (Marks et al. 1998; Tonina et al. 2008). There are 

also water quality consequences to large-scale canopy 

treatments, such as warming stream temperatures (Isaak et 

al. 2010) or sediment from increased road construction and 

use (Black et al. 2012; Luce and Black 1999).

Conceptually, replacing snowpack storage with storage in constructed reservoirs to carry over water from the 

winter wet season into the summer could be beneficial to 

irrigators in regions with significant irrigated agriculture. 

But the degree of potential benefit varies substantially 

with context of existing water right regulations, reservoir 

operating rules, snowpack sensitivity to temperature and 

precipitation, expectations for future precipitation, and 

the role and future of summer precipitation. The benefits 

of replacing snowpack storage with reservoir storage are 

somewhat built around the notion that the only factor 

changing is timing and that total volumes are unchanged. 

If, for instance, precipitation rises, temperature-induced 

changes could be compensated for in relatively cold 

regions (Luce et al. 2014), such as those found across 

most of the Northern Rockies. If, on the other hand, 

precipitation declines, total flow volume will be reduced, 

and it will be harder to fill reservoir storage because of 

other rights for water farther downstream that might not 

be fulfilled. Ironically, this would be most difficult in dry 

years when the timing would be most strongly shifted 

because of the effect of snow water equivalence on duration of the melt period (Luce and Holden 2009). Given 

the large expenses, both financial and ecological, of dam 

construction, and the considerable uncertainties about 

precipitation, it would be worthwhile to perform a detailed 

economic and ecological analysis before dam construction 

is seriously considered.

Shifting dam operation is another possibility, which 

would cost significantly less, but still requires some 

infrastructure investment in monitoring upstream snowpack, soil, and weather. Streamflow forecasting allows 

more informed management of the tension between water 

storage for irrigation and maintaining empty reservoirs 

to buffer potential flooding (e.g., Wood and Lettenmaier 

2006). Information on current state of the snowpack is a 

great boon to runoff forecasting in basins with substantial 

snowmelt contributions (Wood et al. 2015), even more 

so than climate and weather forecasting. Under such 

circumstances, it is reasonable to taper reservoir filling in 

such a way as to bring the reservoir to operational levels 

without undue flood risks; later in the season, snowpack 

area is substantially reduced and rain-on-snow during 

the spring is generally less severe (or variable) than midwinter events, when snowpack coverage over the basin is 

greater (MacDonald and Hoffman 1995). Predictability is 

declining in some regions as we lose snowpack, but the 

Northern Rockies region will still retain significant snowpack, making improved forecasting through investment 

in instrumentation a viable alternative. Note that besides 

informing reservoir operation, improved forecasting can be 

used to better determine downstream financial investments 

in crops and community choices in how to invest water 

(Broad et al. 2007).

A final strategy for addressing water availability is to 

reduce water use by increasing efficiency, an important 

connection between the source of water on public lands 

and use of water downstream on public and private lands. 

First, it will be helpful to identify effective water-saving 

tactics and where they can be successfully implemented. 

Second, low water-use appliances can be installed at 

administrative sites (e.g., restrooms), and drought-tolerant 

plants can be used for landscaping (e.g., adjacent to 

management unit buildings). Third, the benefit of water 

conservation can be communicated to users of public 

lands (e.g., in campgrounds). These tactics demonstrate 

leadership in water conservation as an agency, providing outreach and public relations that extend to local 

communities.

More-specific details on adaptation strategies and tactics that address climate change effects on water resources 

in each NRAP subregion are in Appendix 4A.

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
62 USDA Forest Service RMRS-GTR-374. 2018

Conclusions

Changes in climate over the Northern Rockies are likely 

to have substantial impacts on hydrology. A primary change 

will be shifts in snowpack storage, although other changes 

in precipitation and atmospheric circulation could have 

significant consequences for forests, grasslands, streams, 

fishes, and agriculture in the region. Information is still 

the best tool for adaptation to a changing climate, and 

summaries provided here give a sense of both the general 

expectation for change as well as uncertainties that need to 

be considered in adaptation planning.

A range of adaptation options exists for the future of 

water resources, and although there is a bias in human 

nature toward taking action, information may yet be one 

of our better choices for future adaptation to an uncertain 

and varying climate. If we continue to invest in monitoring 

to track changing climate and outcomes, we can be better 

prepared, as what are now challenges of the future become 

current challenges. Armed with better knowledge of how 

shifting temperatures and circulation have played out on our 

landscapes, snowpacks, and streams, we can make better 

decisions.

This effort illustrated that adapting to climate change 

does not necessarily entail management actions drastically different from those that are currently implemented. 

Many of the current Federal agency management actions to 

improve and restore watersheds and riparian areas are consistent with the adaptation strategies and tactics identified 

here, as fully functional watersheds and riparian areas are 

more resilient to change. Thus, in many cases, adaptation 

to climate change involves increasing restoration activities 

and reprioritizing actions, and agencies are well prepared for 

these types of shifts in management.

Acknowledgments

We thank Patrick Kormos and Abigail Lute for generating many of the figures in this report.

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Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 65

Appendix 4A—Adaptation Options for Water Resources in 

the Northern Rockies.

The following tables describe climate change sensitivities and adaptation strategies and tactics for water resources, 

developed in a series of workshops as a part of the Northern Rockies Adaptation Partnership. Tables are organized by 

subregion within the Northern Rockies. See Chapter 4 for summary tables and discussion of adaptation options for water 

resources.

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
66 USDA Forest Service RMRS-GTR-374. 2018 Table 4A.1—Adaptation options that address climate change effects on water resources in the Central Rockies subregion. Sensitivity to climatic variability and change: Increased flooding will increase damage to roads and infrastructure. Adaptation strategy/approach: Identify and proactively decrease vulnerability of infrastructure to flooding. Strategy objective: Increase resilience. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Identify and restore degraded riparian areas in order to reduce flooding and increase natural storage. Reduce the amount of infrastructure in the floodplain. Conduct a basin-wide risk assessment of hydrologic interactions with roads and other infrastructure where vulnerability of infrastructure is highest. Educate private landowners, county managers, and recreational users to increase knowledge on benefits of riparian vegetation, water storage, and effects of floodplain development. Tactic effectiveness (risks) High High Moderate Implementation urgency Near term and ongoing Near term Near term and ongoing Where can tactics be applied? (geographic) All lands Federal and private lands Partnerships with State agencies, county and municipal governments, and private property owners Opportunities for implementation Partnerships with other Federal and State agencies, and county and municipal governments Partnerships with other Federal and State agencies, and county and municipal governments Partnerships with other Federal and State agencies, and county and municipal governments Cost Moderate Inexpensive, mostly employee time required Low Barriers to implementation Property rights issues Social resistance to change (e.g., property rights) Social resistance to change (e.g., property rights)

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 67 Table 4A.2—Adaptation options that address climate change effects on water resources in the Central Rockies subregion. Sensitivity to climatic variability and change: Reduced base flows will shrink riparian habitats and alter morphology, affecting groundwater, storage, and shallow alluvial aquifers. Adaptation strategy/approach: Increase natural storage and built storage. Strategy objective: Increase resilience. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Increase natural water storage (mirroring natural processes) with constructed wetlands, beavers, and road obliteration. Promote distributed small-scale water storage, using small dams, retention ponds, and swales in stream channels and uplands. Use groundwater injection wells and sills to retain water upstream in alluvial deposits (and retain higher water table). Tactic effectiveness (risks) Highly effective at small scales Dams – high Swales – low to unknown Variable Implementation urgency Near term Mid term to long term Near term to long term Where can tactics be applied? (geographic) Multiple land ownerships Agricultural lands, headwaters without native fish species Injection wells, large aquifers, sills Opportunities for implementation Collaboration with other land management activities (timber sales, road decommissioning) Collaboration with Bureau of Reclamation and NGOs, combined with hydropower projects Areas near high-value water supplies Cost Moderate to high High High Barriers to implementation Lack of available sites, plans for future land use, social acceptance For dams—significant environmental effects, safety risks, cost, access Lack of available sites

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
68 USDA Forest Service RMRS-GTR-374. 2018 Table 4A.3—Adaptation options that address climate change effects on water resources in the Central Rockies subregion. Sensitivity to climatic variability and change: Reduced base flows will shrink riparian habitats and alter morphology, affecting groundwater, storage, and shallow alluvial aquifers. Adaptation strategy/approach: Increase knowledge about the groundwater resource. Strategy objective: Increase knowledge. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Map aquifers and alluvial deposits. Determine legal availability and better understanding of physical availability of water for aquifer recharge. Improve monitoring of streamflow and groundwater to improve understanding of surface water-groundwater interactions; obtain real-time data. Tactic effectiveness (risks) Moderate Moderate Moderate Implementation urgency Near term—information needed for both water and fisheries Near term—information needed for both water and fisheries Near term—information needed for both water and fisheries Where can tactics be applied? (geographic) All lands and locations All lands and locations All lands and locations Opportunities for implementation Collaboration with USFS Rocky Mountain Research Station Collaboration with state of Montana Water Court and Dept. of Natural Resources and Conservation Collaboration with USGS; state and research partnerships Cost Low to moderate Moderate High Barriers to implementation Availability of staff and funding Availability of staff and funding Availability of staff and funding

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 69 Table 4A.4—Adaptation options that address climate change effects on water resources in the Central Rockies subregion. Sensitivity to climatic variability and change: Reduced base flows will shrink riparian habitats and alter morphology, affecting groundwater, storage, and shallow alluvial aquifers. Adaptation strategy/approach: Reduce evaporation and transpiration losses. Strategy objective: Increase resilience. Specific tactic – A Specific tactic – B Tactic Evaluate how increasing western larch cover would decrease evapotranspiration. Selectively use forest harvest (patch clearcuts) to increase water yield. Tactic effectiveness (risks) Unknown Low Implementation urgency Near term Long term Where can tactics be applied? (geographic Areas where western larch is currently present Areas with moderate to high precipitation Opportunities for implementation Projects where western larch is planted Minimal opportunities Cost Moderate for study Moderate for treatment, high for maintenance Barriers to implementation Cost Environmental consequences (loss of forested habitat, more edge, less interior species, more roads); political and social acceptance

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
70 USDA Forest Service RMRS-GTR-374. 2018 Table 4A.5—Adaptation options that address climate change effects on water resources in the Central Rockies subregion. Sensitivity to climatic variability and change: Reduced snowpack will reduce the quantity and quality of municipal water supplies. Adaptation strategy/approach: Reduce erosion potential to protect municipal water supplies; prioritize municipal systems for protection. Strategy objective: Increase resilience. Specific tactic – A Specific tactic – B Tactic Evaluate how increasing western larch cover would decrease evapotranspiration. Selectively use forest harvest (patch clearcuts) to increase water yield. Tactic effectiveness (risks) Unknown Low Implementation urgency Near term Long term Where can tactics be applied? (geographic) Areas where western larch is currently present Areas with moderate to high precipitation Opportunities for implementation Projects where western larch is planted Minimal opportunities Cost Moderate for study Moderate for treatment, high for maintenance Barriers to implementation Cost Environmental consequences (loss of forested habitat, more edge, less interior species, more roads); political and social acceptance

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 71 Table 4A.6—Adaptation options that address climate change effects on water resources in the Central Rockies subregion. Sensitivity to climatic variability and change: Increased occurrence of disturbances such as drought and flooding will reduce water quality. Adaptation strategy/approach: Build an information base for a timely response to disturbance, thus ensuring that data are available to inform decision making. Strategy objective: Increase knowledge. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Prioritize data collection based on projections of future drought. Collect pre-disturbance data on stream and riparian conditions, including high- quality values and habitat in need of protection. Develop a clearinghouse for available funding and programs related to fire and other disturbances. Tactic effectiveness (risks) Moderate High Moderate Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) Mostly Federal lands Mostly Federal lands Mostly Federal lands Opportunities for implementation NEPA, USFWS NEPA, ESA, USFWS Emergency Relief for Federally Owned Roads; BAER implementation; NRCS, Federal Highway Administration Cost Low Low Low Barriers to implementation Agency culture, staffing, budget Agency culture, staffing, budget Agency requirements and time to manage clearinghouse

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
72 USDA Forest Service RMRS-GTR-374. 2018 Table 4A.7—Adaptation options that address climate change effects on water resources in the Eastern Rockies subregion. Sensitivity to climatic variability and change: Large riverine systems are susceptible to a change in timing and quantity of peak flows as well as lower low flows associated with warming temperatures. Lower low flows and flashier flow regimes could lead to bank instability due to loss of vegetation. Changes in precipitation and/or temperature may reduce base flows. Adaptation strategy/approach: Determine how climate change will alter lakes and reservoirs. Strategy objective: Increase resilience; reduce stressors. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Optimize grazing management practices to enhance riparian health and stream channel stability, soil water holding capacity, and shallow groundwater storage. Promote beaver recolonization and maintenance of beavers where appropriate. Promote cottonwood, willow, and aspen to improve riparian health and support beaver recolonization. Tactic effectiveness (risks) High for riparian health and baseflows High Moderate Implementation urgency Near term—information needed for water, fisheries, and amphibians Near term—information needed for water, fisheries, and amphibians Near term—information needed for water, fisheries, and amphibians Where can tactics be applied? (geographic) Forest wide, especially priority watersheds and allotments Where appropriate, based on local knowledge and inventory and monitoring data Where appropriate, based on local knowledge and inventory and monitoring data Opportunities for implementation Collaboration with private partners, local ranchers, permittees, non-governmental organizations (NGOs), and Montana Fish, Wildlife and Parks; Clean Water Act, Endangered Species Act, grass banking Collaboration with private partners, local ranchers, permittees, NGOs, and Montana Fish, Wildlife and Parks; Clean Water Act, Endangered Species Act, grass banking Collaboration with USFS wildlife program, NGOs, and Montana Fish, Wildlife and Parks Cost Inexpensive Inexpensive Moderate Barriers to implementation Political and social opposition, concern about offsite water use; education and perhaps incentives needed Social opposition; need education and identification of appropriate locations Funding, staff availability, competing priorities

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 73 Table 4A.8—Adaptation options that address climate change effects on water resources in the Grassland subregion. Sensitivity to climatic variability and change: Decreased snowpack will lead to increased frequency of high peak flows. Adaptation strategy/approach: Maintain hydrological and ecological function of watersheds. Strategy objective: Promote resilience, reduce stressors, engage coordination Specific tactic – A Specific tactic – B Specific tactic – C Tactic Implement 17 Indicators of rangeland health, and maintain or restore forest vegetation resilience. Promote/maintain proper functioning condition of riparian areas and wetlands, including: ensure adequate grazing regimes, adequate riparian buffers, beaver colonization, and restoration of riparian vegetation. Maintain/improve streamflow continuity by optimizing hydrologic connectivity, including: reduce sediment loading, properly design in-channel infrastructure, ensure adequate culvert size, promote beaver colonization, and procure in-stream flow water rights. Tactic effectiveness (risks) High High High Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) All Federal lands All Federal lands Where watersheds have been heavily fragmented, prioritizing intact habitat where native guilds exist Opportunities for implementation State wildlife action plans, grassland/forest plan direction, interdisciplinary approach to management Coordination with tribes. Watershed Condition Framework documents where this is an issue at the 6th code scale Opportunities exist, but need work to be identified; coordination with federal and state agencies, tribes, counties, and watershed restoration plans Cost Inexpensive to moderately expensive Inexpensive to expensive, depending on treatments Inexpensive to expensive, depending on treatments Barriers to implementation Personnel availability, litigation barriers with vegetation management projects, common understanding of purpose Social barriers—lack of understanding, not valued by some. Funding, coordination, data gaps

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
74 USDA Forest Service RMRS-GTR-374. 2018 able 4A.8 (cont.)—Adaptation options that address climate change effects on water resources in the Grassland Subregion Sensitivity to climatic variability and change: Decreased snowpack will lead to increased frequency of high peak flows. Adaptation Strategy / Approach: Maintain hydrological and ecological function of watersheds. Strategy Objective: Promote resilience, reduce stressors, engage coordination Specific Tactic – D Specific Tactic – E Specific Tactic – F Tactic Minimize expansion of drainage network by disconnecting road system from stream system, including improved road drainage and road decommissioning. Develop off-channel watering strategies; minimize in-stream dewatering (e.g., horizontal wells), for both livestock and other water uses. Move infrastructure out of floodplains, and encourage use of best management practices throughout watershed to protect and restore water quality. Tactic effectiveness (risks) High Low High Implementation urgency Near term Near term Near to mid term Where can tactics be applied? (geographic) Prioritize by value of downstream water and associated biota Priority watersheds Where assets exist on floodplains Opportunities for implementation Prioritize by value of downstream water and associated biota Coordination with tribes, federal and state agencies, and counties Prioritize by values at risk associated with assets; public education opportunity Cost Inexpensive to expensive Inexpensive to moderate Moderate to expensive Barriers to implementation Funding, legal authority (including NEPA), social opposition (road access, changing traditional land-use practices) Water rights, social opposition Social opposition (effects on recreation sites, public perception), cultural resource concerns

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 75 Table 4A.9—Adaptation options that address climate change effects on water resources in the Grassland subregion. Sensitivity to climatic variability and change: Higher temperatures will lead to lower low stream flows in the summer. Adaptation strategy/approach: Maintain hydrological and ecological function of watersheds. Strategy objective: Promote resilience, reduce stressors, engage coordination Specific tactic – A Specific tactic – B Specific tactic – C Tactic Implement 17 Indicators of rangeland health, and maintain or restore forest vegetation resilience. Promote/maintain proper functioning condition of riparian areas and wetlands, including: ensure adequate grazing regimes, adequate riparian buffers, beaver colonization, and restoration of riparian vegetation. Maintain/improve streamflow continuity by optimizing hydrologic connectivity, including: reduce sediment loading, properly design in-channel infrastructure, ensure adequate culvert size, promote beaver colonization, and procure in-stream flow water rights. Tactic effectiveness (risks) High High High Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) All Federal lands All Federal lands Where watersheds have been heavily fragmented, prioritizing intact habitat where native guilds exist Opportunities for implementation State wildlife action plans, grassland/forest plan direction, interdisciplinary approach to management Coordination with tribes. Watershed Condition Framework documents where this is an issue at the 6th code scale Opportunities exist, but need work to be identified; coordination with federal and state agencies, tribes, counties, and watershed restoration plans Cost Inexpensive to moderate Inexpensive to expensive, depending on treatments Inexpensive to expensive, depending on treatments Barriers to implementation Personnel availability, litigation barriers with vegetation management projects, common understanding of purpose Social barriers – lack of understanding, not valued by some. Funding, coordination, data gaps

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
76 USDA Forest Service RMRS-GTR-374. 2018 Table 4A.10—Adaptation options that address climate change effects on water resources in the Grassland subregion. Sensitivity to climatic variability and change: Increasing air temperature will lead to increased stream temperature, changes in the hydrograph, and changes in land use, affecting water quality. Adaptation strategy/approach: Ensure riparian function and resilience, including groundwater-surface water interactions Strategy objective: Promote resilience, reduce stressors, engage coordination Specific tactic – A Specific tactic – B Specific tactic – C Tactic Promote/maintain proper functioning condition of riparian areas and wetlands: ensure adequate grazing regimes and adequate riparian buffers, promote beaver colonization, and restore riparian vegetation. Develop adequate inventory and promote protection of spring sources and shallow aquifers. Promote and educate regarding best management practices for agricultural runoff; form/participate in task forces and working groups. Tactic effectiveness (risks) Moderate to high, depending on degree of implementation Moderate to high Low to moderate, depending on social factors Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) All lands Priority watersheds Mostly non-Federal lands Opportunities for implementation Coordination with tribes; Watershed Condition Framework documents where this is an issue at the 6th HUC scale Work with botanists, soil scientists, hydrologists to compile existing information Partnerships with NRCS, Prairie Potholes Landscape Conservation Cooperative Cost Inexpensive to expensive, depending on treatments Inexpensive to moderate, depending on scale Inexpensive to moderate Barriers to implementation Social opposition—lack of understanding and not valued by some Lack of funding and staff time Social opposition, lack of staff time, crop values 

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 77 Table 4A.11—Adaptation options that address climate change effects on water resources in the Greater Yellowstone Area subregion. Sensitivity to climatic variability and change: Higher temperatures and decreased snowpack will reduce water availability. Adaptation strategy/approach: Reduce water use and increase efficiency, demonstrate leadership in water efficiency, and create outreach opportunities. Strategy Objective: Reduce stressors, facilitate transition, increase knowledge. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Research successful water saving tactics and apply tactics where appropriate. Install low-flow appliances at administrative sites; replace landscaping with drought tolerant plants. Communicate water saving tactics and benefits. Tactic effectiveness (risks) High High Variable—difficult to measure effects Implementation urgency Near term Mid term Near term Where can tactics be applied? (geographic) All lands, where appropriate All lands, including administrative locations (campgrounds, visitor centers, etc.) All lands, including administrative locations (campgrounds, visitor centers, etc.); use Internet, press releases, interpretive signing, etc. Opportunities for implementation Collaboration with GYCC Collaboration with GYCC Collaboration with GYCC Cost Inexpensive Inexpensive Inexpensive Barriers to implementation None Resistance to xeriscaping, low-flow toilets None

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
78 USDA Forest Service RMRS-GTR-374. 2018 Table 4A.12—Adaptation options that address climate change effects on water resources in the Greater Yellowstone Area subregion. Sensitivity to climatic variability and change: Discharge from natural springs and seeps may be reduced, affecting water quantity and quality, wetland plant species, wildlife habitat, and water for livestock. Adaptation strategy/approach: Protect natural springs and seeps from potential degradation and development. Strategy objective: Reduce stressors. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Develop map/inventory of springs and seeps locations (6th code level). Instrument (piezometer) prioritized representative springs to get detailed flow information. Develop local protection strategies such as fencing, stock fencing; develop alternative water sources; moratoriums on wells where appropriate. Tactic effectiveness (risks) High High Variable depending on strategy and stakeholder support Implementation urgency Near term Near to mid term Near to mid term Where can tactics be applied? (geographic) All lands Priority areas with springs and seeps Priority areas with springs and seeps Opportunities for implementation Collaborations with USGS, State agencies that manage water, NOAA, USFS remote sensing center Collaborations with USGS, State agencies that manage water, NOAA Collaborations with Federal and State agencies, private landowners, range permittees Cost Moderate Inexpensive to moderate Inexpensive to moderate Barriers to implementation Information may be sensitive None Social and legal opposition, especially based on water rights

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 79 Table 4A.13—Adaptation options that address climate change effects on water resources in the Greater Yellowstone Area subregion. Sensitivity to climatic variability and change: Higher flows may lead to flooding of valuable infrastructure (roads, buildings, campgrounds, etc.). Adaptation strategy/approach: Reduce risk of damage to infrastructure. Strategy objective: Promote resilience. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Map and prioritize areas with higher peak flows to determine high-risk locations. Implement tactic A—replace, remove, adjust, and resize as necessary; implement early warning systems. Communicate risk with all stakeholders, including affected public and private entities. Tactic effectiveness (risks) High Variable, depending on tactic/location. Low—replacing culverts, due to variable nature of stream types and unknown changes in climate affecting flows High—removal of campgrounds from floodplains, installation of bridges, removal of culverts Variable, depending on reception of information, severity of risk, and ability to implement changes Implementation urgency Near term – need this information to take further steps toward adaptation Near to long term, depending on model predictions and expected flows Near term, especially where human safety is a concern Where can tactics be applied? (geographic) All lands Priority areas All locations where stakeholders are at risk Opportunities for implementation Collaboration with USGS, FEMA, county emergency management, NOAA Collaboration with State and local, USGS, FEMA, county emergency management, NOAA Collaboration with State and local, USGS, FEMA, county emergency management, NOAA Cost Inexpensive Inexpensive to moderate Inexpensive Barriers to implementation None Legal—NEPA, Social—removal of favorite recreation spots None

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
80 USDA Forest Service RMRS-GTR-374. 2018 Table 4A.14—Adaptation options that address climate change effects on water resources in the Greater Yellowstone Area subregion. Sensitivity to climatic variability and change: Higher temperatures, higher evapotranspiration rates, and earlier runoff may reduce recharge to shallow aquifers, reducing downstream domestic water yields. Adaptation strategy/approach: Identify and protect shallow aquifer recharge zones by communicating and partnering with stakeholders. Strategy objective: Reduce stressors, facilitate transition, engage coordination. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Map/inventory recharge zones, especially in areas where water is heavily utilized (municipal watersheds). Form watershed user groups— coordinated resource management groups (CRM—Federal, State, stakeholders) to identify concerns and solutions. Improve diversion efficiencies (install headgatess, convert from ditch to pipeline, install weirs as needed, etc.). Tactic effectiveness (risks) High High to moderate High Implementation urgency Near term Near to mid term Near to mid term Where can tactics be applied? (geographic) Recharge zones and identified CRMs Identified CRMs, identified watersheds with stakeholders Site specific within affected watersheds Opportunities for implementation GYA partners. USGS, university, GYCC Conservation districts, NRCS, state agencies that regulate water, advisory groups, landscape conservation cooperatives, Trout Unlimited Conservation districts, NRCS, state agencies that regulate water, advisory groups, landscape conservation cooperatives, Trout Unlimited Cost Moderate Inexpensive Inexpensive to moderate Barriers to implementation None Social opposition; need communication to work through barrier Variable legal and social opposition; concerns about listed fish species and downstream users. 

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 81 Table 4A.15—Adaptation options that address climate change effects on water resources in the Greater Yellowstone Area subregion. Sensitivity to climatic variability and change: Higher temperatures and evapotranspiration rates may lead to increased loss of lower elevation, isolated wetlands. Adaptation strategy/approach: Increase understanding of location and risk for all wetland types and apply appropriate management actions to reduce loss. Strategy objective: Reduce stressors, promote resilience. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Update National Wetland Inventory maps for all wetlands, including hydrologic regime and type. Assess vulnerability of all wetlands. Increase connectivity of wetlands (e.g., prevent road bisections); avoid degradation of wetlands by new structures; protect beaver dams; consider artificial wetland construction/augmentation of natural wetlands in vulnerable watersheds. Tactic effectiveness (risks) High High Variable, depending on action Implementation urgency Near term Near term Mid to long term Where can tactics be applied? (geographic) All lands All lands Mostly Federal lands Opportunities for implementation Collaborations with GYCC, Ducks Unlimited, National Academy of Sciences, National Science Foundation, USFWS, National Wildlife Federation Collaborations with GYCC, Ducks Unlimited, National Academy of Sciences, National Science Foundation, USFWS, National Wildlife Federation Collaborations with State and Federal agencies, private land owners Cost Inexpensive Inexpensive Moderate Barriers to implementation None None Social and legal opposition (road removal, augmenting wetlands)

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
82 USDA Forest Service RMRS-GTR-374. 2018 Table 4A.16—Adaptation options that address climate change effects on water resources in the Western Rockies subregion. Sensitivity to climatic variability and change: Decreased snowpack will increase flooding and damage to roads and infrastructure. Adaptation strategy/approach: Identify and proactively decrease vulnerability of roads and infrastructure to flooding. Strategy objective: Increase resilience. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Identify and restore degraded riparian areas in order to reduce flooding and increase natural storage; reduce the amount of infrastructure in the floodplain. Increase resilience of infrastructure: culvert sizing, hardened fords, road drainage; remove and relocate infrastructure (e.g., roads, campgrounds). Increase resilience of stream resources by identifying and restoring degraded riparian areas to reduce flooding and increase natural storage; add large woody debris, improve floodplain connectivity, increase riparian roughness, restore beavers. Tactic effectiveness (risks) Moderate Moderate Moderate Implementation urgency Near term and ongoing Near term and ongoing Near term and ongoing Where can tactics be applied? (geographic) Across the Western Rockies subregion Across the Western Rockies subregion Across the Western Rockies subregion Opportunities for implementation Partnerships with Federal and State agencies, county and municipal governments, NGOs, private landowners Partnerships with Federal and State agencies, NGOs, Avista, U.S. Army Corps of Engineers, Idaho Power Partnerships with Federal and State agencies, NGOs, Avista, U.S. Army Corps of Engineers, Idaho Power Cost Moderate to expensive Expensive Inexpensive to expensive Barriers to implementation Property rights advocates Public acceptance; depends on location, scale of project, and partnerships. Public acceptance; depends on location, scale of project, and partnerships. 

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 83 Table 4A.17—Adaptation options that address climate change effects on water resources in the Western Rockies subregion. Sensitivity to climatic variability and change: Decreased snowpack will reduce base flows and shrink riparian habitats, altering groundwater, storage, and shallow alluvial aquifers. Adaptation strategy/approach: Increase knowledge of the groundwater resource. Strategy objective: Increase knowledge. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Map aquifers and alluvial deposits; identify groundwater influenced streams. Determine legal availability and better understanding of physical availability of water for aquifer recharge. Improve streamflow and groundwater monitoring information to improve understanding of surface water-groundwater interactions; obtain real-time data. Tactic effectiveness (risks) Moderate Moderate Moderate Implementation urgency Near term—Information is needed for both water and fisheries Near term—Information is needed for both water and fisheries Near term—Information is needed for both water and fisheries Where can tactics be applied? (geographic) All lands All lands All lands Opportunities for implementation USFS Rocky Mountain Research Station, universities, Montana Bureau of Mines State agencies USGS, State and research partnerships Cost Moderate Moderate High Barriers to implementation Availability of staff and funding Availability of staff and funding Availability of staff and funding

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
84 USDA Forest Service RMRS-GTR-374. 2018 Table 4A.18—Adaptation options that address climate change effects on water resources in the Western Rockies subregion. Sensitivity to climatic variability and change: Decreased snowpack and increased disturbance will reduce municipal water supply and quality. Adaptation strategy/approach: Reduce erosion potential to protect municipal water supplies; prioritize municipal systems for protection. Strategy objective: Increase resilience. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Reduce hazardous fuels. Reduce disturbance (e.g., off-road vehicles, grazing, riparian roads). Manage roads to reduce erosion. Tactic effectiveness (risks) Moderate High High, although detecting improvements can be difficult and site dependent Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) High-value locations High-value locations on public and private lands High value locations on public lands Opportunities for implementation Partnerships with municipalities, counties, NGOs, tribes, private landowners. Partnerships with municipalities, counties, NGOs, tribes, private landowners. Partnerships with municipalities, counties, NGOs, tribes, private landowners. Cost Expensive Inexpensive to moderate Moderate to high Barriers to implementation Public acceptance, cost Public acceptance, cost Public acceptance, cost, some user groups

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 85 Table 4A.19—Adaptation options that address climate change effects on water resources in the Western Rockies subregion. Sensitivity to climatic variability and change: Increased droughts and flooding will reduce water quality. Adaptation strategy/approach: Build an information base for a timely response to disturbance, thus ensuring data are available to inform decision making. Strategy objective: Increase knowledge. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Prioritize data collection based on forecasted drought. Collect pre-disturbance data on stream and riparian conditions (high-quality values, habitat most in need of protection). Develop a directory/checklist for sites where disturbance has a direct effect on water quality (metals). Tactic effectiveness (risks) Moderate High Moderate Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) Mostly Federal lands Mostly Federal lands All lands Opportunities for implementation Collaboration with other agencies, universities Collaboration with other agencies, universities Collaborate with USEPA (TMDL, CERCLA, Natural Resource Damage Assessment) Cost Moderate Moderate Expensive Barriers to implementation Staffing, budget Staffing, budget Agency requirements, time to staff and manage the clearinghouse

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
86 USDA Forest Service RMRS-GTR-374. 2018 Table 4A.20—Adaptation options that address climate change effects on water resources in the Western Rockies subregion. Sensitivity to climatic variability and change: Decreased snowpack and increased disturbance will alter water quantity and quality of lakes and reservoirs (including dam operations). Adaptation strategy/approach: Determine how climate change will alter lakes and reservoirs. Strategy objective: Increase knowledge. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Develop a clearinghouse of information on the effects of climate change from all available sources. Increase coordination between all partners (Federal, State, tribal, private). Improve understanding about connectivity and interaction of streams and lakes (temperature, nutrient sinks, sources, etc.). Tactic effectiveness (risks) High High Moderate Implementation urgency Near term—Information needed for water, fisheries, and amphibians Near term—Information needed for water, fisheries, and amphibians Near term—Information needed for water and fisheries Where can tactics be applied? (geographic) All lands All lands All lands Opportunities for implementation Forest or regional level for identified sources of data Forest or regional level for identified sources of data Collaborations with USGS, State, and research institutions Cost Moderate Moderate Expensive Barriers to implementation Availability of staff and funding Availability of staff and funding Availability of staff and funding

Chapter 4: Effects of Climate Change on Snowpack, Glaciers, and Water Resources in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 87

Introduction

During the 21st century, climate change is expected 

to alter aquatic habitats throughout the Northern Rocky 

Mountains, intermountain basins, and western Great Plains. 

Particularly in montane watersheds, direct changes are likely 

to include warmer water temperatures, earlier snowmeltdriven runoff, earlier declines to summer baseflow, downhill 

movement of perennial channel initiation, and more-intermittent flows (see Chapter 4), as well as indirect changes 

attributable to altered and perhaps novel disturbance 

regimes. For animals restricted to freshwater aquatic environments for most or all of their lives—fishes, amphibians, 

crayfish, mussels, and aquatic macroinvertebrates—changes 

in habitat and in hydrologic regimes are likely to lead to 

marked shifts in their abundance and distribution. This is 

primarily because many of these species are ectothermic 

(cold blooded); thus, environmental conditions dictate their 

metabolic rates and nearly every aspect of their life stages, 

including growth rate, migration patterns, reproduction, and 

mortality (Magnuson et al. 1979).

A vast and growing literature describes the myriad interactions among climate change, aquatic environments, and 

biotic communities. Rather than revisit this topic, we refer 

the reader to syntheses of the nexus between climate change 

and aquatic species in the northwestern United States (especially Rieman and Isaak 2010, but also Independent Science 

Advisory Board 2007; Isaak et al. 2012a,b; Mantua and 

Raymond 2014; Mantua et al. 2010; Mote et al. 2003) and 

beyond (Ficke et al. 2007; Furniss et al. 2010, 2013; Luce et 

al. 2012; Poff et al. 2002; Schindler et al. 2008). However, 

assessments rarely provide empirically based, spatially 

explicit, and precise climate change projections for species 

across broad geographic regions.

To address this gap, we developed high-resolution stream 

temperature and flow scenarios that translate outputs from 

global climate models (GCMs) into reach-scale habitat 

factors relevant to aquatic biota (Isaak et al. 2015). Those 

scenarios were coupled with species distribution datasets 

crowdsourced from the peer-reviewed literature and State 

and Federal agency reports to develop accurate species 

distribution models for contemporary relationships between 

climate and biology. These models were used to project the 

probability of species habitat occupancy in streams throughout the inland northwestern United States, facilitating the 

identification of streams that are most likely to be occupied 

in the future and serve as invasion-resistant climate refugia.

We focused on climate vulnerabilities and current and 

projected distribution of two native salmonid fishes—

bull trout (Salvelinus confluentus) and cutthroat trout 

(Oncorhynchus clarkii)—because of their importance to 

society, the large amount of data on their distribution and 

abundance, and their sensitivity to warm stream temperature 

(Eby et al. 2014; USDA FS 2013). We confined our inferences to suitable habitat for juveniles of each native species 

because they are more thermally constrained than adults. 

We directly addressed how the presence of nonnative species, such as brook trout (S. fontinalis), brown trout (Salmo 

trutta), and rainbow trout (O. mykiss) (the latter native to a 

portion of the analysis area) further restricts climate-suitable 

habitats for native species now and in the future. A full explanation of our rationale, approach, and results are in Isaak 

et al. (2015). The associated Climate Shield website (USDA 

FS n.d.a) provides access to a comprehensive archive of 

user-friendly digital maps and ArcGIS (ESRI, Redlands, 

CA) databases showing stream-specific model projections 

for multiple climate and brook trout invasion scenarios 

across most of the northwestern and interior western United 

States.

In this assessment, we summarize information for stream 

populations of bull trout and cutthroat trout in the Northern 

Rockies and discuss adaptation measures and future research directions (see Rieman and Isaak 2010 for a more 

comprehensive discussion). We regard our inferences as 

robust, but foresee the arrival of improved models fostered 

by ongoing improvements in measuring and modeling the 

attributes of populations and streams. Databases describing the distributions of many aquatic species via rapid, 

cost-effective environmental DNA surveys (McKelvey et 

al. 2016a; Wilcox et al. 2016) are rapidly proliferating and 

can be used with new geostatistical stream models (Isaak 

et al. 2014; Ver Hoef et al. 2006) to develop more precise 

information for many aquatic taxa. This combination of 

advanced survey methods and sophisticated stream network 

models has already been adopted for assessing the validity 

Chapter 5: Climate Vulnerability of Native 

Cold-Water Salmonids in the Northern 

Rockies Region

Michael K. Young, Daniel J. Isaak, Scott Spaulding, Cameron A. Thomas, 

Scott A. Barndt, Matthew C. Groce, Dona Horan, and David E. Nagel
88 USDA Forest Service RMRS-GTR-374. 2018

and refining the predictions of the Climate Shield model for 

bull trout (M. Young, K. McKelvey, and D. Isaak, unpublished data).

Analysis Area and Methodology

This assessment encompasses all streams in national 

forests and national parks encompassed by the Northern 

Region of the Forest Service, U.S. Department of 

Agriculture (USFS) (fig. 5.1). To delineate a stream network for this area, geospatial data for the 1:100,000-scale 

National Hydrography Dataset (NHD)-Plus were downloaded from the Horizons Systems website (Cooter et al. 

2010; Horizon Systems Corp. n.d.) and filtered by minimum 

flow and maximum stream slope criteria. Summer flow 

values predicted by the Variable Infiltration Capacity (VIC) 

hydrologic model (USDA FS n.d.; Wenger et al. 2010) were 

obtained from the Western United States Flow Metrics website (USDA FS n.d.c) and were linked to individual stream 

reaches.

Stream reaches with summer flows less than 0.2 cubic 

feet per second, approximating a wetted width of 3.3 feet 

(based on an empirical relationship developed in Peterson 

et al. [2013b]), or with slopes greater than 15 percent were 

trimmed from the network because they tend to be unoccupied or support very low numbers of fish (Isaak et al. 2015). 

In the case of the stream slope criterion, reaches steeper 

than 15 percent occur at the top of drainage networks where 

slopes become progressively steeper, and populations are 

more vulnerable to disturbances (e.g., post-wildfire debris 

torrents) that result in periodic extirpations (Bozek and 

Young 1994; Miller et al. 2003). The slope and flow criteria 

were set liberally to minimize the exclusion of fish-bearing 

reaches from the analysis, but doing so results in the inclusion of many reaches with intermittent flows or migration 

barriers that prevent fish access. Thus, the network extent 

of 113,733 miles used as baseline habitat in this assessment 

probably overestimates potential habitat, but the current 

resolution of the NHD-Plus hydrology layer and VIC flow 

model prevents further refinement.

Climate Scenarios

Average summer flow values for three 30-year climate 

periods were available from the flow metrics website: a 

baseline period (1970–1999, hereafter 1980s) and two future 

periods (2030–2059, hereafter 2040s; 2070–2099, hereafter 

2080s) associated with the A1B (moderate) emissions 

scenario. An ensemble of 10 GCMs that best represented 

historical trends in air temperatures and precipitation for 

the northwestern United States during the 20th century was 

used for future projections (table 5.1). Due to the significant 

uncertainties about the timing of change in the future, we 

deemphasize the dates associated with scenarios and refer to 

them instead as baseline (1980s), moderate change (2040s), 

and extreme change scenarios (2080s). With respect to 

scenarios used in other chapters of this publication, the A1B 

scenario is similar to the RCP 6.0 scenario associated with 

Coupled Model Intercomparison Project 5 (CMIP5) simulations (see chapter 3).

To complement the streamflow information, geospatial 

data for August mean stream temperatures were downloaded 

for the same A1B trajectory and climate periods from the 

NorWeST website and linked to the stream hydrology layer 

(USDA FS n.d.b). Within the study area, the NorWeST 

scenarios were developed using spatial statistical network 

models (Isaak et al. 2010; Ver Hoef et al. 2006) applied to 

Figure 5.1—Northern Rockies Adaptation Partnership analysis area for cutthroat trout and bull trout, including 

the U.S. Forest Service Northern Region (white border). Bull trout range encompasses basins west of the 

Continental Divide and the St. Mary River basin (yellow dashed line), whereas historical cutthroat trout range 

includes most of the analysis area.

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 89

data at 5,461 unique stream sites monitored with digital 

sensors during the summer from 1993 through 2011. 

The density and spatial extent of the temperature dataset, 

combined with the predictive accuracy (r2 = 0.91; RMSE = 

1.8 °F) and resolution (~0.62 mile) of the NorWeST model 

across those sites, were deemed sufficient for this assessment. Details about the rationales associated with climate 

scenarios and the stream temperature model are discussed in 

Isaak et al. (2015).

Focal Species

Bull trout in the Northern Rockies are largely from 

an inland lineage (Ardren et al. 2011) primarily west of 

the Continental Divide (U.S. Fish and Wildlife Service 

[USFWS] 2014). Bull trout may exhibit migratory or 

resident life histories. Migratory fish travel long distances 

as subadults to more-productive habitats and achieve 

larger sizes and greater fecundity as adults before returning 

to natal habitats to spawn. Resident fish remain in natal 

habitats and mature at smaller sizes, although often at the 

same age as migratory adults. Adults spawn and juveniles 

rear almost exclusively in streams with average summer 

water temperatures less than 54 °F and flows greater than 

1.2 cubic feet per second (Isaak et al. 2010; Rieman et al. 

2007). Relative to its historical distribution, this species 

has undergone substantial declines because of water development and habitat degradation (particularly activities 

leading to water temperature increases, but also cumulative 

losses of in-channel habitat complexity), elimination of 

migratory life histories by human-created barriers, harvest 

by anglers, and interactions with introduced nonnative 

fishes (Rieman et al. 1997). Nonnative species such 

as brook trout, brown trout, and lake trout (Salvelinus 

namaycush) may compete with or prey on bull trout (AlChokhachy et al. 2016; Martinez et al. 2009), or lead to 

wasted reproductive opportunities (Kanda et al. 2002). As 

a consequence, bull trout was listed as threatened under 

the U.S. Endangered Species Act (ESA) by the USFWS in 

1998 (USFWS 2015).

Cutthroat trout are represented by two subspecies. 

Westslope cutthroat trout (O. clarki lewisi) has a complicated lineage structure that can be roughly broken into 

a single lineage in the north and east that occupied and 

colonized river basins directly influenced by glaciation 

or glacial dams, and a southern and western group of 

several presumably older lineages in basins never directly 

influenced by glaciation (M. Young, unpublished data). 

These fish also exhibit resident and migratory life history 

strategies. Spawning and juvenile rearing can occur in 

streams smaller (<2 feet wide) and warmer (up to 57 °F) 

than those used by bull trout (Isaak et al. 2015; Peterson 

et al. 2013a,b; M. Young, unpublished data). Yellowstone 

cutthroat trout (O. c. bouvieri) has an unresolved distribution because certain lineages are found in portions of 

the Bonneville basin (Campbell et al. 2011; Loxterman 

and Keeley 2012), probably because of periodic hydrologic connectivity between the Bonneville and Upper 

Snake River basins associated with passage of the North 

American plate across the Yellowstone mantle plume, 

Basin and Range faulting, and stream drainage reversals 

(Smith et al. 2002). Undisputed members of this taxon are 

Table 5.1—Projected changes in mean August air temperature, stream temperature, and streamflow for major river 

basins in the Northern Rockies.

2040s (2030–2059) 2080s (2070–2099)

NorWeST unita

Air 

temperatureb

change

Streamflowb,c

 change

Stream 

temperatured

change

Air 

temperature 

change

Streamflow 

change

Stream 

temperature 

change

°F Percent °F °F Percent °F

Yellowstone 5.06 - 4.1 1.82 9.14 - 5.4 3.26

Clearwater 5.71 -23.9 2.92 9.81 -34.2 5.00

Spokane-Kootenai 5.49 -20.1 2.29 9.59 -31.5 3.94

Upper Missouri 5.85 -14.9 2.11 9.85 -21.3 3.49

Marias-Missouri 5.24 -10.0 1.35 9.54 -18.7 2.47

a For boundaries of NorWeST production units, see the NorWeST Web site (USDA FS n,d,b).

b Changes in air temperature and streamflow are expressed relative to the 1980s (1970–1999) baseline climate period. Projections 

are based on the A1B emissions scenario represented by an ensemble of 10 global climate models that best projected 

historical climate conditions during the 20th century in the northwestern United States (Hamlet et al. 2013; Mote and Salathé 

2010). Additional details about the scenarios are provided elsewhere (Hamlet et al. 2013; Wenger et al. 2010).

c For more information on streamflow, see the western United States flow metrics website (USDA FS n,d,c) and the Pacific 

Northwest Hydroclimate Scenarios Project website (University of Washington, Climate Impacts Group 2010).

d Changes in stream temperatures account for differential sensitivity to climate forcing within and among river basins as described 

in Luce et al. (2014) and at the NorWeST website (USDA FS n,d,b). For more information on stream temperatures, see Isaak et 

al. (2010), Luce et al. (2014), and the NorWeST website (USDA FS n,d,b).

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
90 USDA Forest Service RMRS-GTR-374. 2018

represented by a single mtDNA clade found throughout the 

analysis area in the Yellowstone River basin (Campbell et 

al. 2011). For this analysis, we assume that life histories 

and presumably spawning and juvenile habitats are the 

same as for westslope cutthroat trout.

The distributions of both subspecies have declined 

substantially (>50 percent) in response to the same stressors affecting bull trout (Gresswell 2011; Shepard et al. 

2005), although each subspecies appears to occupy a larger 

proportion of its historical habitat and is often found in 

larger populations at higher densities than are bull trout. 

Both subspecies of cutthroat trout have been petitioned 

under the ESA, but found not warranted for listing. Brook 

trout have replaced cutthroat trout in many waters in the 

region, disproportionately so in the Upper Missouri River 

basin (Shepard et al. 1997). These invasions in part seem 

influenced by the distribution of low-gradient alluvial valleys that may serve as nurseries for brook trout (Benjamin 

et al. 2007; Wenger et al. 2011a). Where rainbow trout 

have been introduced outside their native range, introgressive hybridization occurs with both taxa of cutthroat trout 

at lower elevations and in warmer waters (Rasmussen et 

al. 2012), similar to patterns where westslope cutthroat 

trout occurred historically with native rainbow trout 

(the Clearwater River basin in Idaho and the Kootenai 

River basin in Idaho-Montana) (McKelvey et al. 2016b). 

Yellowstone cutthroat trout have also been widely stocked 

throughout the historical range of westslope cutthroat trout 

(Gresswell and Varley 1988) and these two taxa readily 

hybridize to form hybrid swarms (Forbes and Allendorf 

1991; McKelvey et al. 2016b). Lake trout predation decimated adfluvial populations of Yellowstone cutthroat trout 

in Yellowstone Lake at the beginning of the 21st century, 

but predator control efforts are enabling cutthroat trout 

populations to rebound (Syslo et al. 2011).

Trout Distribution Models

Species distribution models were developed that predicted the occurrence probabilities of juvenile bull trout 

and cutthroat trout. We focused on juveniles as indicators 

of important natal habitats and the presence of locally 

reproducing populations (Dunham et al. 2002; Rieman and 

McIntyre 1995). This approach provides more precision 

than also considering distributions of subadults and adults, 

which migrate widely, occupy an array of habitats, and occur with many other fish species (Behnke 2010). Juvenile 

distributions, by contrast, are restricted in ecological scope 

and geographic extent, especially with respect to temperature (Elliott 1994). For example, juvenile bull trout are 

rarely found where mean summer temperatures exceed 54 

°F (Dunham et al. 2003; Isaak et al. 2010), whereas adult 

bull trout sometimes occupy habitats as much as 9 to 18 °F 

warmer (Howell et al. 2010). Similar patterns are evident 

with cutthroat trout (Peterson et al. 2013a; Schrank et al. 

2003). Therefore, we used a thermal criterion to delimit 

potentially suitable habitats for juvenile native trout.

Temperature Criterion for Juvenile 

Trout Habitat

A mean August stream temperature of 52 °F was selected 

as the temperature criterion from a set of standardized 

thermal niches that were developed by cross-referencing 

thousands of species occurrence locations in Montana, 

Idaho, and Wyoming with the NorWeST baseline scenario 

(fig. 5.2). Fish data were contributed by national forest 

monitoring programs; Idaho Department of Fish and Game; 

Montana Fish, Wildlife and Parks; and Wyoming Game 

and Fish Department (Isaak et al. 2015). These niches 

revealed that most juvenile native trout (90 percent of 

bull trout observations and 75 percent of cutthroat trout 

observations) occurred at sites with temperatures less than 

52 °F, whereas nonnative species such as brown trout and 

rainbow trout were rare at those sites. The thermal niche 

of brook trout overlapped that of the native species, but its 

occurrence peaked at a slightly warmer temperature and declined thereafter. Just as especially cold temperatures limit 

rainbow trout incursions, colder temperatures also restrict 

introgression with rainbow trout, such that stream reaches 

with temperatures less than 48 °F usually support only 

genetically pure cutthroat trout (McKelvey et al. 2016b; 

Rasmussen et al. 2012; Yau and Taylor 2013; M. Young, 

unpublished data).

Habitat Attributes and Logistic 

Regression Models

Spatially contiguous 0.6-mile reaches of stream with 

temperatures less than 52 °F were aggregated into discrete 

cold-water habitats (CWHs), and occupancy status (present 

or absent) of native trout juveniles and brook trout within a 

subset of those CWHs (bull trout, n = 512; cutthroat trout, 

n = 566) was determined using the fish survey database 

Figure 5.2—Presence of juvenile bull trout and cutthroat trout 

and all age classes of other trout species at sampling sites 

relative to temperature projections from the NorWeST 

baseline scenario of mean August temperature (figure 

reproduced from Isaak et al. (2015).

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 91

described earlier. Logistic regressions were used to model 

the probability of native trout occupancy as a function of 

CWH size, stream slope, brook trout prevalence, and stream 

temperature. Habitat size was represented as the channel 

length of each CWH, stream slope as the average value 

across all the reaches within a CWH, and brook trout prevalence as the percentage of sample sites within a CWH where 

they occurred. Temperature was represented as mean August 

temperature averaged across all 0.6-mile sections constituting a CWH or the lowest mean temperature of any 0.6-mile 

section within a CWH.

The four variables were good predictors of juvenile 

trout occurrence within the training dataset; classification 

accuracy of the models at a 50 percent occupancy threshold 

was 78.1 percent for bull trout and 84.6 percent for cutthroat 

trout. The final logistic regression models included the four 

main predictor variables and some interactions among those 

variables. Plots of species response curves from the final 

models matched expectations based on the ecology of bull 

trout and cutthroat trout, but also revealed important differences between the species (fig. 5.3). Habitat occupancy for 

both native trout was positively related to CWH size, but 

bull trout required habitats five times larger than cutthroat 

trout to achieve comparable probabilities of occupancy. Bull 

trout occupancy declined as minimum temperature warmed, 

whereas cutthroat trout occupancy was positively related to 

mean temperature. Stream slope negatively affected both 

species, as did their co-occurrence with brook trout, especially in small streams. The presence of brook trout masked 

the apparent preference of cutthroat trout for habitats with 

low slopes. Additional details on modeling procedures and 

variable selection are summarized in Isaak et al. (2015).

Application of Models for Status and 

Vulnerability Assessment

The logistic regression models were applied to the full 

set of CWHs within the historical range of each native 

species across the Northern Rockies to project probabilities 

of native trout occupancy. Projections were made for the 

baseline and future climate periods. To account for uncertainties in brook trout distributions, occupancy probabilities 

were calculated and mapped for a pristine scenario (no 

brook trout) and a broad invasion scenario that assumed 

brook trout would be present at half the sites within each 

CWH (50 percent brook trout). For this exercise, we did 

not map a scenario in which brook trout were present at all 

sites for two reasons. First, their prevalence rarely exceeded 

50 percent in the large CWHs (i.e., >25 miles) that were 

most likely to serve as strongholds for native trout (Isaak 

et al. 2015) show brook trout prevalence in more than 500 

streams; further, not all locations appear suitable for brook 

trout (Wenger et al. 2011a). In some small streams with 

native trout, brook trout prevalence occasionally reaches 

100 percent, so probabilities for a full range of invasion 

scenarios were integrated into the ArcGIS databases at the 

Climate Shield website (USDA FS n.d.a) and can be used 

for stream-specific assessments of brook trout invasions.

After species probability maps were developed for all 

streams, the information was cross-referenced with land 

administrative status using geospatial data from the U.S. 

Geological Survey Gap Analysis Program (Gergely and 

McKerrow 2013). The total length and percentage of CWHs 

and stream temperatures were summarized by jurisdiction 

for different climate periods. Also noted were the proportions of CWHs that were administratively protected within 

national parks and wilderness areas. Finally, we denoted 

those CWHs with probabilities of occupancy exceeding 90 

percent as climate refugia.

Native Trout Vulnerability 

to Climate Change

Stream Temperature Status and Projected 

Trends

Considerable thermal heterogeneity exists across 

Northern Rockies streams because of the complex topography and range of elevations in this region (fig. 5.4). Of the 

114,000 miles of stream habitat within the analysis area, 

43,000 miles (38 percent) had mean temperatures less than 

52 °F (table 5.2). Most of those CWHs (86 percent) were 

in publicly administered lands, primarily (69 percent) in 

national forests. Areas with concentrations of cold streams 

were generally associated with high-elevation, high-relief 

Figure 5.3—Relations between environmental covariates and 

probability of occupancy of juvenile native trout developed 

from 512 bull trout (a, b, c) and 566 cutthroat trout (d, 

e, f) cold-water habitats. Relations are conditioned on 

mean values of two independent variables not shown in a 

panel. An exception occurs for cutthroat trout with regard 

to stream slope (f) where brook trout values of 0% and 

100% were used to highlight the interaction between these 

covariates (figure reproduced from Isaak et al. (2015).

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
92 USDA Forest Service RMRS-GTR-374. 2018

mountain ranges in Montana (e.g., Whitefish Range, 

Mission Mountains, Swan Range, Flathead Range, Lewis 

and Clark Range, Sawtooth Range, Anaconda Range, 

Flint Creek Range, Big and Little Belt Mountains, Crazy 

Mountains, and ranges associated with the topographic rise 

produced by the Yellowstone mantle plume). In contrast, 

comparable mountain ranges and clusters of CWHs are 

absent in most of northern Idaho.

Mean August stream temperatures were projected to 

increase across the Northern Rockies by an average of 2.2 

°F in the 2040s and 3.6 °F in the 2080s (table 5.1, fig. 5.4). 

Larger than average increases are expected in the warmest streams at low elevations, and smaller than average 

increases are expected for the coldest streams. Differential 

warming occurs because cold streams tend to be buffered 

by local influxes of groundwater (Luce et al. 2014), a trend 

represented in the NorWeST scenarios we used. Averaged 

across all streams, future projections imply faster rates of 

warming (0.4–0.5 °F per decade) than were observed in 

recent decades (0.2–0.3 °F per decade) (Isaak et al. 2012a). 

If future projections are accurate, the length of streams with 

temperature less than 52 °F will decrease to 27,000 miles in 

the 2040s and 17,000 miles in the 2080s (table 5.3). In both 

scenarios, more than 75 percent of these cold streams are in 

national forests. Groups of exceptionally cold streams still 

likely to support bull trout or cutthroat trout would originate 

from the Sawtooth and Lewis and Clark Ranges along the 

Continental Divide in northern Montana, several smaller 

mountain ranges scattered throughout central Montana, 

and along the northern flank of the Yellowstone topographic high (fig. 5.4). Persistent CWHs are more isolated 

elsewhere.

Figure 5.4—NorWeST August mean 

stream temperature maps interpolated 

from 11,703 summers of monitoring 

data at 5,461 unique stream sites 

across the 114,000 mi of streams in 

the analysis area. Map panels show 

conditions during baseline (a, 1980s), 

moderate (b, 2040s), and extreme 

change scenarios (c, 2080s). Networks 

were trimmed to represent potential 

fish-bearing streams by excluding 

reaches with slopes greater than 

15 percent and Variable Infiltration 

Capacity model summer flows less 

than 0.20 ft3 s-1. High-resolution digital 

images of these maps and ArcGIS 

databases with reach-scale predictions 

are available at the NorWeST website 

(http://www.fs.fed.us/rm/boise/AWAE/

projects/NorWeST.html).

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 93 Table 5.2—Length of streams in the Northern Rockies, categorized by mean August stream temperature during the baseline climate period and by land administrative status. Values in parentheses are percentages of the total in the last row. Land status a, b <46 °F 46–52 °F 52–57 °F 57–63 °F 63–68 °F >68 °F Total Miles (percent of total) Private 274 (3.2) 5,494 (15.8) 16,524 (47.2) 14,465 (64.4) 8,178 (73) 1,067 (66.1) 46,002 (40.4) The Nature Conservancy 1 (0) 191 (0.5) 99 (0.3) 9 (0) 1 (0) 0 (0) 301 (0.3) Tribal 170 (2.0) 769 (2.2) 3,371 (9.6) 4,181 (18.6) 1,593 (14.2) 380 (23.5) 10,464 (9.2) State/City 137 (1.6) 1,578 (4.5) 2,529 (7.2) 1,156 (5.1) 723 (6.5) 62 (3.8) 6,185 (5.4) Bureau of Land Management 49 (0.6) 826 (2.4) 838 (2.5) 268 (1.2) 207 (1.8) 55 (3.4) 2,243 (2.0) National Park Service 537 (6.2) 1,689 (4.9) 654 (1.9) 296 (1.3) 70 (0.6) 1 (0.1) 3,247 (2.9) Forest Service Wilderness 2,269 (26.2) 3,516 (10.1) 1,174 (3.4) 175 (0.8) 39 (0.3) 1 (0) 7,174 (6.3) Forest Service Non-Wilderness 4,825 (55.8) 19,299 (55.5) 8,168 (23.3) 1,041 (4.6) 206 (1.8) 16 (1) 33,555 (29.5) Other 386 (4.5) 1,438 (4.1) 1,596 (4.6) 876 (3.9) 193 (1.7) 33 (2.1) 4,522 (4.0) Total 8,648 34,800 34,953 22,467 11,210 1,615 113,693 a Stream reaches with slope less than 15 percent and summer flows greater than 0.20 ft3 s-1, based on the Variable Infiltration Capacity model (see text). b Other category includes U.S. Army Corps of Engineers, U.S. Fish and Wildlife Service, U.S. Bureau of Reclamation, and lands with undesignated status. Table 5.3—Length of streams in the Northern Rockies, categorized by mean August stream temperature during the baseline and two future climate periods and by land administrative status (Forest Service [FS] and non-Forest Service [Non-FS]). Values in parentheses are percentages of the total in the last column. Land status a <46 °F 46–52 °F 52–57 °F 57–63 °F 63–68 °F >68 °F Total Miles (percent of total) b FS lands 1980s 7,094 (17.4) 22,815 (56.0) 9,342 (22.9) 1,216 (3.0) 244 (0.6) 17 (0) 40,728 2040s 2,504 (6.3) 17,858 (44.7) 15,911 (39.8) 3,092 (7.7) 445 (1.1) 121 (0.3) 39,931 2080s 961 (2.4) 12,701 (32.3) 19,051 (48.5) 5,525 (14.1) 836 (2.1) 237 (0.6) 39,311 Non-FS lands 1980s 1,554 (2.1) 11,986 (16.4) 25,645 (35.1) 21,260 (29.1) 10,963 (15.0) 1,597 (2.2) 73,005 2040s 569 (0.8) 5,960 (8.4) 20,980 (29.5) 24,422 (34.3) 15,434 (21.7) 3,820 (5.4) 71,185 2080s 253 (0.4) 3,448 (4.9) 16,401 (23.3) 25,128 (35.7) 18,410 (26.1) 6,798 (9.7) 70,438 a Stream reaches with slope less than 15 percent and summer flows greater than 0.20 ft3 s-1, based on the Variable Infiltration Capacity model (see text). b Reductions in network extent result from projected decreases in summer flows as described in table 5.1.

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
94 USDA Forest Service RMRS-GTR-374. 2018

Cutthroat Trout Status and Projected 

Trends

The historical range of cutthroat trout extends through 

most of the Northern Rockies. The number of discrete 

CWHs for cutthroat trout during the baseline climate period 

was estimated to exceed 5,000 and encompass over 28,000 

miles of streams (table 5.4, fig. 5.5). More than 90 percent 

of the CWHs were predicted to have probabilities of occupancy exceeding 50 percent (table 5.4), largely because 

of the relatively small stream networks that cutthroat trout 

populations require for persistence (6 miles is associated 

with a 90-percent probability of occupancy) (Peterson et al. 

2013a) (fig. 5.3). Nonetheless, the largest CWHs accounted 

for a disproportionate amount of the habitat most likely to 

be occupied; 32.6 percent of CWHs were climate refugia, 

but these accounted for 70.7 percent of the length of CWHs. 

As expected, the number and extent of CWHs decreased by 

20 to 60 percent in future periods, but nearly 3,500 potential 

habitats encompassing over 12,000 miles were projected to 

remain under the extreme scenario.

Some streams are currently too cold for cutthroat trout, 

so future warming will increase the probability of occupancy in some basins (e.g., the Teton River basin along the 

Rocky Mountain Front and streams in the northern portion 

of Yellowstone National Park). Assuming that brook trout 

were present within half of each CWH did not affect the 

number or amount of CWHs, because the habitats remained 

potentially suitable for cutthroat trout, but occupancy probabilities declined (table 5.4). Reductions were particularly 

severe in categories with the highest probabilities of occupancy (>75 percent). The sensitivity of streams to brook 

trout invasions varied with local conditions, but reductions 

were most pronounced in small streams with relatively low 

slopes.

Bull Trout Status and Projected Trends

The historical range of bull trout covers a smaller portion 

of the Northern Rockies than cutthroat trout, but the number 

of discrete CWHs for bull trout during the baseline climate 

period was still estimated to exceed 1,800 and encompass 

over 14,000 miles (table 5.5, fig. 5.6). Probabilities of occupancy for most bull trout CWHs were less than 50 percent 

because of the relatively large stream networks that bull 

trout require for persistence (30 miles is associated with 

a 90 percent probability of occupancy; fig 5.3). Although 

fewer than 6 percent of CWHs constituted climate refugia, 

they provided 30 percent of the total length of CWHs, 

emphasizing the contribution of large CWHs to the amount 

of habitat projected to be occupied. The requirement for 

larger CWHs caused projected decreases in the number and 

network extent of bull trout CWHs to be more substantial 

(38–71 percent) than those for cutthroat trout, particularly 

Table 5.4—Number and length of cold-water habitats for juvenile cutthroat trout by probability of occurrence 

for three climate periods and two brook trout invasion scenarios across the Northern Rockies.

Probability of occurrence (percent)

<25 25–50 50–75 75–90 >90 Total

Cold-water habitat number

0% brook trout prevalence 1980s 71 392 1,140 1,817 1,739 5,159

2040s 41 328 1,405 1,505 1,148 4,427

2080s 86 659 949 977 770 3,441

50% brook trout prevalence 1980s 73 501 2,790 1,384 581 5,329

2040s 41 382 2,571 1,065 367 4,426

2080s 86 684 1,837 673 161 3,441

Cold-water habitat length Miles

0% brook trout prevalence 1980s 268 794 4,068 7,730 32,646 45,506

2040s 78 558 3,832 6,034 17,964 28,466

2080s 142 1,031 2,938 4,151 10,459 18,721

50% brook trout prevalence 1980s 387 1,456 6,413 8,203 12,023 28,482

2040s 126 855 5,079 5,451 6,404 17,915

2080s 228 1,238 3,931 3,908 2,857 12,162

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 95

for the CWHs with the highest probabilities of occupancy. 

More than 800 CWHs representing over 4,200 miles were 

projected to remain, even in the extreme scenario.

Brook trout invasions reduced bull trout occupancy rates. 

These declines were more pronounced for bull trout than 

cutthroat trout, especially in the CWHs most likely to be 

occupied (those with greater than 50-percent probability of 

occupancy); fewer than 10 climate refugia for juvenile bull 

trout are projected to remain under any warming scenario if 

brook trout occupy half of each CWH. However, many of 

the large habitats that bull trout require appear less susceptible to broad-scale brook trout invasions (Isaak et al. 2015). 

As expected, CWHs with the highest bull trout occupancy 

probabilities during all climate periods and brook trout invasion scenarios coincided with river networks with the largest 

number of cold streams: headwater portions of the North 

and Middle Forks of the Flathead River, the Whitefish River, 

and the North Fork Blackfoot River (figs. 5.4, 5.6). Due to 

the lower elevations and warmer streams in northern Idaho, 

few or no climate refugia were projected to remain under 

either warming scenario.

Additional Fish Species

See boxes 5.1 and 5.2 for narratives on other fish species 

in the Northern Rockies that are at risk from climate change 

and are candidates for the habitat occupancy-climate vulnerability approach described here.

Interpreting and Applying 

the Assessment

The assessment just described provides accurate, spatially explicit projections of habitat occupancy in the Northern 

Rockies by combining (1) ecological understanding of cutthroat trout and bull trout, (2) distribution data from public 

data sources, and (3) broad-scale, high-resolution stream 

temperature and flow projections. Assuming that species 

responses are related to the effects of climate on stream 

ecosystems—and the accuracy of the models supports this 

contention—the models also provide reasonably robust projections of habitat occupancy in light of anticipated climate 

Figure 5.5—Distribution of cold-water habitats with probabilities of occupancy greater than 0.1 for juvenile cutthroat 

trout during baseline (a and d, 1980s), moderate change (b and e, 2040s), and extreme change scenarios (c and f, 

2080s). Panels a–c illustrate occupancy when brook trout are absent. Panels d–f illustrate occupancy when brook 

trout prevalence is 50 percent. High-resolution digital images and ArcGIS databases of these maps with streamspecific projections are available at the Climate Shield website (http://www.fs.fed.us/rm/boise/AWAE/projects/

ClimateShield/maps.html).

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
96 USDA Forest Service RMRS-GTR-374. 2018

Table 5.5—Number and length of cold-water habitats for juvenile bull trout by probability of occurrence 

during three climate periods and two brook trout invasion scenarios in the Northern Rockies.

Probability of occurrence (percent)

<25 25–50 50–75 75–90 >90 Total

Cold-water habitat number

0% brook trout prevalence 1980s 875 534 248 92 106 1,855

2040s 664 314 98 41 32 1,149

2080s 474 274 81 24 13 866

50% brook trout prevalence 1980s 995 484 181 65 28 1,753

2040s 697 270 63 17 5 1,052

2080s 535 260 49 5 3 852

Cold-water habitat length Miles

0% brook trout prevalence 1980s 2,906 3,168 2,565 1,616 4,657 14,912

2040s 2,222 1,934 1,129 769 1,340 7,394

2080s 1,310 1,324 773 386 579 4,372

50% brook trout prevalence 1980s 3,920 3,762 2,712 1,891 2,351 14,636

2040s 2,728 2,208 1,191 589 408 7,124

2080s 1,569 1,645 704 153 266 4,337

Figure 5.6—Distribution of cold-water habitats 

with probabilities of occupancy greater than 

0.1 for juvenile bull trout during baseline (a and 

d, 1980s), moderate change (b and e, 2040s), 

and extreme change scenarios (c and f, 2080s). 

Panels a–c illustrate occupancy when brook 

trout are absent. Panels d–f illustrate occupancy 

when brook trout prevalence is 50 percent. 

High-resolution digital images and ArcGIS 

databases of these maps with stream-specific 

predictions are available at the Climate Shield 

website (http://www.fs.fed.us/rm/boise/AWAE/

projects/ClimateShield/maps.html). 

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 97

Box 5.1—Effects of Climate Change on Arctic Grayling

Arctic grayling (Thymallus arcticus) is a salmonid species native to Arctic Ocean drainages in North America 

and northern Eurasia, and Pacific Ocean basins in Alaska and British Columbia, with two disjunct inland groups 

in Michigan (now extinct) and the Upper Missouri River basin in Montana and Wyoming (Kaya 1992; Scott and 

Crossman 1998). Within its range in Montana and Wyoming, grayling was represented by four adfluvial (lake-living, 

stream-spawning) populations in the Red Rock and Big Hole River basins, and by fluvial populations widely but 

irregularly distributed in the Missouri River basin above the Great Falls (USFWS 2014). Relative to this historical 

distribution, the current range and abundance of Arctic grayling have decreased greatly. Lacustrine populations are 

more common recently because of introductions inside and outside its historical range (Kaya 1992). Declines of 

riverine populations were caused by habitat degradation and fragmentation, inundation by reservoirs, overharvest, 

and interactions with nonnative fish, particularly rainbow trout, brook trout, and brown trout (Kaya 1992). The distinct 

population segment in the Upper Missouri River basin was petitioned for listing under the Endangered Species Act, 

but has not been listed (USFWS 2014). Evidence indicates that recent activities focused on increasing instream 

flows, improving habitat connectivity, supplementing existing populations, and founding new populations (some in 

historically fishless lakes) have arrested declines in most grayling populations in this basin (USFWS 2014).

Arctic grayling is regarded as a cold-water species (Elliott and Elliott 2010). Grayling life histories are often 

characterized by extensive movements to habitats for growth, reproduction, and overwintering, especially in riverine 

systems (Northcote 1995). Access to thermal refugia may be important to population persistence at the southern 

extreme of its range; many of the fluvial systems that retain grayling in the Upper Missouri River basin are heavily 

influenced by groundwater inputs (USFWS 2014). Although the thermal preferences of this species are uncertain, the 

upper thermal limits of grayling in the Big Hole River basin are comparable to those of cutthroat trout (Johnstone and 

Rahel 2003; Lohr et al. 1996; Wagner et al. 2001).

The influence of climate change on Arctic grayling is uncertain because of insufficient data, but its reliance on 

mobility emphasizes the need for connectivity among complementary habitats. Ameliorating the effects of low 

summer discharge has been a target of management (USFWS 2014), but this problem may become more severe 

and difficult to overcome if projected climate-related changes in discharge (Chapter 4) are realized. Many of the 

extant populations are in high-elevation lakes that are presumed to be less vulnerable to the effects of warming or 

reduced streamflow (USFWS 2014). 

Responses to warmer stream temperatures may be complex. With warming summer water temperatures, initiation 

of the spawning season advanced by more than 3 weeks during four decades in a population of adfluvial European 

grayling (T. thymallus) in Switzerland (Wedekind and Küng 2010). Paradoxically, earlier spawning meant a longer 

exposure of incubating eggs and fry to colder spring water temperatures, patterns that coincide with substantial 

declines in the number of female spawners. This pattern may reflect declining survival of juvenile fish (Wedekind 

and Küng 2010) or sex-specific vulnerability to changes in thermal regimes (Pompini et al. 2013). Whether this is 

symptomatic of a broader trend or case study is unknown, but warming stream temperatures, population declines, 

and sex ratio shifts in salmonids have been observed elsewhere in Europe (Hari et al. 2006). Regardless, the few 

Arctic grayling populations extant in their historical range are likely to remain the focus of management efforts 

(USFWS 2014), and the continuation of these efforts may play a significant role in the near-term persistence of 

grayling in the Upper Missouri River basin. At longer time scales, the “climate velocity” associated with warming of 

low-gradient stream habitats (Isaak and Rieman 2013) may challenge our ability to maintain recent improvements in 

the conservation status of this species.

change. These projections have several implications for the 

future viability of native fish populations in the Northern 

Rockies and for developing management strategies targeted 

at conservation of these species.

Although both native trout species require cold-water 

habitat, their response to a changing climate is expected 

to differ. Bull trout, and most members of the genus 

Salvelinus, are adapted to some of the coldest freshwater 

environments in the Northern Hemisphere (Klemetsen 

et al. 2003). These species also tend to inhabit variable 

environments, often with strong gradients in productivity that appear to favor migration as a life history tactic 

(Klemetsen 2010). It is unsurprising that a species near 

the southern end of its distribution that relies on large 

areas of CWHs and is often found at low density (High 

et al. 2008) would be susceptible to range contraction as 

temperatures warm. In the Northern Rockies, we anticipate 

large declines in their distribution because relatively 

few areas have the capability to serve as climate refugia. 

Nevertheless, retention of at least some climate refugia implies that bull trout will not be extirpated from the region. 

However, the conditions favoring migratory or resident life 

histories may change, although how to accommodate or 

exploit this is uncertain. As we learn more about the extent 

and prevalence of populations occupying CWHs with 

varying probabilities of occupancy, a better understanding 

of environmental drivers of bull trout life history may 

emerge.

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
98 USDA Forest Service RMRS-GTR-374. 2018

By contrast, cutthroat trout can accommodate a wider 

range of thermal environments, commensurate with its 

broad latitudinal distribution and an evolutionary history 

(since the late Miocene or early Pliocene) that exposed them 

to fluctuation in warm/arid and cold/moist periods in western North America (McPhail and Lindsey 1986; Minckley 

et al. 1986). They are relatively flexible with respect to life 

history strategies, ranging from highly migratory populations dependent on large rivers or lakes for growth and 

fecundity, to resident populations that move little and have 

been isolated for many decades (Northcote 1992; Peterson 

et al. 2013a). Although we anticipate net losses in their 

distribution within the Northern Rockies, losses are not 

expected to be as severe as for bull trout, and some basins 

that are currently too cold to support cutthroat trout will 

become high-quality climate refugia (Coleman and Fausch 

2007; Cooney et al. 2005). Of greater importance may be 

how nonnative salmonids, which often displace or replace 

cutthroat trout, respond to warming conditions (Wenger et 

al. 2011a).

The presence of brook trout is problematic for both 

native species. The tolerance of brook trout to cold temperature is nearly equivalent to that of cutthroat trout, and 

brook trout favor the low-gradient environments preferred 

by cutthroat trout and bull trout (Wenger et al. 2011a). 

Nonetheless, larger habitats (e.g., those >40 miles long) 

Box 5.2—Effects of Climate Change on Fish Species in the Grassland Subregion

Several native fish species are found in the Grassland subregion of the NRAP. Located in the eastern portions of 

the Custer-Gallatin National Forest and the Dakota Prairies National Grassland, these species have received little 

scientific study and monitoring compared to cold-water salmonids and warm-water sportfish. Many prairie streams 

have never been sampled or are sampled sporadically at best. As a result, fish distribution and aquatic habitat are 

poorly understood at all spatial scales. However, as in most dendritic stream networks, small streams constitute 

the majority of fish habitat, and species favoring those habitats are likely to be the most common. Small streams 

may also provide seasonal habitats for spawning and rearing of species favoring larger streams, rivers, and lakes 

(Thornbrugh and Gido 2009). 

Prairie streams are dynamic, tending to vary between periods of floods and flow intermittency, among and sometimes 

within years (Dodds et al. 2004). Extirpation and recolonization of local habitats by fish species is typical (Falke et al. 

2012), and patterns of occupancy by fish species can be considered in the context of metapopulation theory, in which 

the presence of subpopulations of each species depends on habitat connectivity and duration (Falke and Fausch 

2010). Although it is typical for prairie streams to be reduced to sets of disconnected pools in some years, this 

pattern is more prevalent in agricultural landscapes where surface and groundwater withdrawals are common (Falke 

et al. 2011; Gido et al. 2010). Climate change is expected to exacerbate these patterns (Jaeger et al. 2014) and 

lead to greater extremes, including severe droughts and more-intense storms and wet intervals in plains and dryland 

systems (Michels et al. 2007; Starks et al. 2014). 

Projecting the responses of prairie fishes to climate change is complicated by difficulty in identifying habitat 

preferences, partly because many fish species are habitat generalists (Wuellner et al. 2013) and because the 

dynamics of prairie streams lead to difficulties in predicting interannual habitat occupancy (Falke et al. 2012). Prairie 

fish assemblages in the analysis area are represented by four species guilds—northern headwaters, darter, madtom, 

and turbid river guilds (Clingerman et al. 2013)—that are likely to differ in their vulnerability to climate change. Annual 

air temperature and various indicators of streamflow are strong predictors of presence for the northern headwaters, 

madtom, and darter guilds.

Observed and modeled patterns allow some inferences to be made about climate vulnerability and adaptation for 

prairie fishes. First, the northern headwaters guild may be most vulnerable to increasing temperature, as well as 

to climate-related decreases in groundwater recharge (Clingerman et al. 2013). This guild includes the northern 

redbelly dace (Chrosomus eos), a sensitive species in the USFS Northern Region, that occupies small, stable, and 

relatively cool headwater streams (Stasiak 2006). Accurate mapping of habitat types and species assemblages 

present in them, and monitoring of habitat conditions will help refine possible climate change effects on both habitat 

and species, as well as define appropriate management responses. Buffering variations in flow extremes (e.g., 

securing instream flows) and encouraging the presence of riparian vegetation are practical responses to climate 

change where the northern headwaters guild is present. Although the other prairie fish guilds seem less vulnerable 

to changes to temperature, all are influenced by amount and timing of flow. Therefore, climate change adaptation 

strategies for the northern headwater guild should also be appropriate for the other guilds. Finally, all guilds are 

currently at risk, and may become more so if flow regimes become more variable, especially if migration barriers 

prevent fish from moving along stream courses. Many of these species may be ill-adapted to surmounting either 

height or velocity barriers (Perkin and Gido 2012; Rosenthal 2007). Therefore, removing barriers to fish passage 

between habitats is a prudent adaptation strategy. This strategy carries the risk of allowing nonnative species to 

invade, so it should be implemented within the larger context of conservation of a site (Fausch et al. 2009). 

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 99

appear less susceptible to invasion by this species, which 

may be attributed to their preference for small streams but 

also to the likelihood that large systems will contain other 

salmonid species, such as rainbow trout or brown trout, 

that constrain brook trout distributions in their native range 

in eastern North America (Fausch et al. 2009). Rainbow 

trout and brown trout are expected to shift their distribution 

upstream as temperature isotherms optimal for these species 

move in that direction (Isaak and Rieman 2013; Wenger et 

al. 2011b). Both species appear to have negative effects on 

cutthroat trout, but cold headwaters that thwart their invasions are expected to remain widespread.

Most CWHs in the Northern Rockies are in national 

forests (tables 5.2, 5.3). This emphasizes the critical role 

that the USFS will play in the conservation of populations 

of native fish. Active management that conserves native 

fish will be possible, because most of the CWHs are outside 

designated wilderness areas and national parks that limit 

many management activities. Conservation options will vary 

by location. For example, even under extreme warming, 

some CWHs are expected to persist in some river basins in 

Montana. Maintaining those conditions may be all that is 

necessary to ensure the persistence of native fish populations. By contrast, very few habitats regarded as climate 

refugia are anticipated to remain in the Clearwater, Spokane, 

and Kootenai River basins in Idaho. Those circumstances 

favor more active yet strategic management to promote 

population persistence through manipulation of habitat, fish 

populations, or both. Many CWHs in Montana and Idaho 

are situated in landscapes where multiple resource values 

and ecosystem services are important (see chapter 11), so 

fish conservation strategies that are compatible with other 

resource objectives will be an important issue in public 

land management (Rieman et al. 2010). Retaining native 

trout populations in some areas may require conservation 

investments that are unacceptably high or that could prove 

ineffective as climate warms. In these circumstances, reallocating those investments to areas where native populations 

are more likely to persist may be preferable.

The model projections described earlier contain 

uncertainties associated with emissions scenarios and 

unanticipated characteristics of future climate (Hallegatte 

et al. 2012). The future scenarios we considered reflect 

trends qualitatively similar to those that have been occurring 

in the Northern Rockies during the last 50 years: summer 

streamflow decreases, air temperature increases, and stream 

temperature increases (Isaak et al. 2010, 2012a,b; Leppi 

et al. 2012; Luce and Holden 2009). Consequently, these 

estimates of occupancy probabilities should be a biologically robust and spatially explicit ranking of habitats critical 

to the persistence of native trout. The Climate Shield fish 

distribution maps (fig. 5.7) and databases developed in 

association with this project were designed for ease of 

use, allowing users to gauge the amount, distribution, and 

persistence of native trout habitats. In addition, this information can be summarized for multiple spatial scales and 

biogeographic entities (e.g., stream, river network, national 

forest, species or subspecies, State, region).

As with all models, current predictions and future projections of occupancy by juvenile native trout are estimates. 

These projections could be improved by including more local information on habitat conditions (Peterson et al. 2013a), 

the presence of barriers that influence habitat size and 

connectivity among populations (Erős et al. 2012), and the 

application of spatial statistical network models (Isaak et al. 

2014). The potential for improvement notwithstanding, the 

accuracy of these simple models suggests that environmental gradients are the primary drivers of habitat occupancy by 

juvenile native trout.

The next step in an ongoing assessment process is to 

continue to reduce uncertainties associated with the distribution of aquatic species and their responses to a changing 

climate. Although we used data from thousands of sites to 

develop occupancy models, data on thousands of other sites 

would improve existing models and help build new ones 

for additional species. Compiling a comprehensive aquatic 

species database from all national forests has the potential 

to provide information on the recent presence of species in 

locations from which they may have disappeared, or from 

which they may have been absent but now exist. These data, 

and outputs from occupancy models, form the basis for 

projecting and detecting trends in aquatic species distributions, especially if coupled with new surveys, such as those 

based on rapid and reliable environmental DNA surveys 

(McKelvey et al. 2016a). Although DNA surveys are often 

conducted with one or a few species in mind, the samples 

constitute a snapshot of the entire aquatic community and 

can be archived to support future analyses of multiple species. Finally, better distribution data, an understanding of 

changes in occupancy, and geospatial analysis will improve 

the accuracy of existing species occupancy models and 

facilitate the development of new ones, ranging from an 

individual reach to an entire species range.

Adapting Fisheries to Climatic 

Variability and Change

Adaptation Strategies and Tactics

Many options are available to facilitate climate change 

adaptation and improve the resilience of fish populations, 

perhaps more options than for any other resource assessed 

in the Northern Rockies Adaptation Partnership (NRAP). 

Adaptation for fish conservation has been the subject of 

comprehensive reviews, including for the Northern Rockies 

(Rieman and Isaak 2010, especially table 2) and other parts 

of the Northwest (Beechie et al. 2013; Independent Science 

Advisory Board 2007; Isaak et al. 2012a; Luce et al. 2013; 

Williams et al. 2015). Having a relatively well-known set 

of climate sensitivities and adaptation options (Isaak et al. 

2015; Mantua and Raymond 2014; Rieman et al. 2007) 

provides for credibility and consistency in sustainable 

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
100 USDA Forest Service RMRS-GTR-374. 2018

management of fisheries in the Northern Rockies and 

beyond.

The Western Rockies, Central Rockies, Eastern Rockies, 

and Greater Yellowstone Area subregions within NRAP all 

have steep mountain topography, complex stream systems, 

and cold-water fish populations. Therefore, climate change 

sensitivities and adaptation options across this broad area 

tend to be similar (table 5.6), although the effects of livestock grazing as a stressor are more important in the Eastern 

Rockies subregion. The Grassland subregion has no coldwater fish species and is dominated by warm-water species, 

many of which are nonnatives. Although some concern 

exists about aquatic systems in this subregion, no adaptation 

options were developed for fisheries at the Grassland workshop (but see box 5.2).

Reduced snowpack is one of the best-documented effects 

of warmer temperatures in mountainous regions (see chapter 

4), resulting in lower summer streamflows and warmer 

stream temperatures. Adaptation strategies can attempt to 

either maintain higher summer flows or mitigate the effects 

of lower flows (table 5.6). Specific adaptation tactics include 

pulsing flows from regulated streams when temperature is 

high, reducing water withdrawals for various human uses, 

and securing water rights for instream flows to maintain 

more control of overall water supply.

Another strategy is to increase CWH resilience by maintaining and restoring the structure and function of streams. 

Specific tactics include restoring the functionality of 

channels and floodplains to retain (cool) water and riparian 

vegetation, and ensuring that passages for aquatic organisms 

are effective. These tactics could be particularly appropriate 

in areas where restoration activities are already underway 

and where habitat is limiting or declining, especially near 

roads and where high peakflows are frequent. In addition, 

accelerating riparian restoration may be a particularly effective and long-lasting way to improve hydrologic function 

and water retention. Maintaining or restoring American 

beaver (Castor canadensis) populations provides a “natural” 

engineering alternative for retention of cool water. In conjunction with restoration, road removal and relocation from 

sensitive locations near stream channels and floodplains can 

significantly improve local hydrologic function.

Interactions with nonnative fish species and other aquatic 

organisms are a significant stress for native cold-water fish 

species in the Northern Rockies. One adaptation strategy 

is to facilitate movement of native fish to locations with 

Figure 5.7—Example of a detailed Climate Shield map available at the project website that shows 

probabilities of juvenile bull trout occupancy in cold-water habitats during the 1980s baseline period in 

the North Fork Flathead River basin. Maps with identical formats for three climate periods and five brook 

trout invasion scenarios are available as .pdf and ArcGIS files for all bull trout and cutthroat trout streams 

across the northwestern United States.

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 101 Table 5.6—Adaptation options that address climate change effects on fisheries in the Northern Rockies. Sensitivity to climatic variability and change: Reduced snowpack will decrease summer streamflows. Adaptation Strategy / Approach: Increase streamflows and moderate changes in instream flows. Specific Tactic – A Specific Tactic – B Specific Tactic – C Tactic Pulse flows from regulated streams during critical times (high temperatures) Reduce water withdrawals and improve efficiency for agriculture (especially irrigation), municipal, and industrial uses Secure water rights for instream flows Where can tactics be applied? All regulated streams Where water demands overlap with current and future suitable habitat Where fish and suitable habitat overlap Sensitivity to climatic variability and change: Reduced snowpack will increase stream temperatures and alter flow regimes. Adaptation Strategy / Approach: Increase habitat resilience for cold-water aquatic organisms by restoring structure and function of streams. Specific Tactic – A Specific Tactic – B Specific Tactic – C Tactic Restore natural channel and floodplain form and function (e.g., restore areas with human-caused bank and bed instability) Restore aquatic organism passage structures through design and placement of appropriate structures. Maintain functional stream channel morphology with adequate width:depth ratios, pool frequency, and healthy riparian vegetation Where can tactics be applied? Areas with ongoing restoration activities and where habitat is a primary limiting factor (especially where roads are present) Drainages with frequent high peakflows, areas with sensitive geology, areas with important rearing streams Areas with ongoing restoration activities and where habitat is a primary limiting factor (especially where roads are present) Sensitivity to climatic variability and change: Reduced snowpack will increase stream temperatures and alter flow regimes. Adaptation Strategy / Approach: Increase habitat resilience for cold-water aquatic organisms by restoring structure and function of streams. Specific Tactic – A Specific Tactic – B Specific Tactic – C Tactic Restore riparian areas to increase hydrologic function and retain cold water Reintroduce beaver where beaver and management of westslope cutthroat trout are compatible Remove or relocate roads adjacent to riparian areas, channels, and floodplains where they inhibit complexity; minimize cumulative effect of road network on surface and subsurface flow Where can tactics be applied? Where riparian areas limit the availability of cold-water habitat Where beaver will not affect barriers; in stream reaches >1 mile; in larger population conservation networks; where brook trout are absent Where roads currently cause problems or may do so in the future, especially where roads occupy lengthy portions of the riparian zone

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
102 USDA Forest Service RMRS-GTR-374. 2018 Table 5.6 (cont.)—Adaptation options that address climate change effects on fisheries in the Northern Rockies. Sensitivity to climatic variability and change: Reduced snowpack will increase stream temperatures, affecting native species and interactions between natives and nonnatives. Adaptation Strategy / Approach: Provide opportunities for native fish to move and find suitable stream temperatures. Specific Tactic – A Specific Tactic – B Specific Tactic – C Tactic Increase the patch size of favorable habitat to enhance viable populations and allow migratory life histories Modify or remove barriers to increase connectivity between areas of cold-water habitat Identify and map where groundwater inputs provide cold water Where can tactics be applied? Where native fish currently exist; where suitable habitat is nearby; where nonnatives are not present or can be effectively managed; where populations are fragmented and need greater connectivity Where barriers prevent movement to suitable habitat, and where removal will not increase invasion of nonnatives All locations Sensitivity to climatic variability and change: Warmer temperatures will increase stream temperature and risk of invasion by nonnative fish species. Adaptation Strategy / Approach: Manage nonnative fish populations to eliminate or reduce their impact on native fish. Specific Tactic – A Specific Tactic – B Specific Tactic – C Tactic Encourage increased take/harvest of nonnatives, especially near long-term strongholds for natives Remove nonnatives with manual or chemical techniques Exclude nonnatives with physical or electrical barriers Where can tactics be applied? Areas with heavy recreation and sport fishing; most effective at the front of invasions Where long-term suitable habitat for natives is available and nonnatives are present Where long-term suitable habitat for natives is available and nonnatives are present Sensitivity to climatic variability and change: Continued livestock grazing will compound stress caused by increased stream temperatures. Adaptation Strategy / Approach: Manage livestock grazing to restore ecological function of riparian vegetation and channels. Specific Tactic – A Specific Tactic – B Specific Tactic – C Tactic Comply with all existing standards and guidelines for maintaining water quality in streams and riparian areas; facilitate compliance through monitoring Use innovative techniques to fund, maintain, and implement improvements (e.g., riparian fencing, rest-rotation systems, off-channel water, exclosures) Identify and prioritize vacant allotments for retirement Where can tactics be applied? All locations, with emphasis on areas that are important in terms of ecological value and large financial investment All locations, with emphasis on areas that are important in terms of ecological value and prior financial investment; prioritize areas with core conservation fish populations that are under imminent threat All locations where vacant allotments exist and opportunities allow 

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 103 Table 5.6 (cont.) —Adaptation options that address climate change effects on fisheries in the Northern Rockies. Sensitivity to climatic variability and change: Higher temperatures will increase wildfire occurrence that can lead to erosion and mass wasting. Adaptation Strategy / Approach: Increase resilience to fire-related disturbance. Specific Tactic – A Specific Tactic – B Specific Tactic – C Tactic Implement fuel treatments (thinning, prescribed burning) to reduce wildfire severity and size Disconnect roads from stream networks to reduce erosion and sediment delivery to streams Install erosion control structures following wildfires Where can tactics be applied? Areas where canopy and surface fuels are high, adjacent to known native fish populations and habitat Areas adjacent to known native fish populations and habitat Where wildfire has occurred and erosion would affect known native fish populations and habitat

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
104 USDA Forest Service RMRS-GTR-374. 2018

suitable stream temperatures. Adaptation tactics include 

increasing the patch size of suitable habitat, modifying or 

removing barriers to fish passage, and documenting where 

groundwater inputs provide cold water. All of these tactics 

will be more effective if native fish populations are healthy 

and nonnative species are not already dominant. Another 

adaptation strategy is to focus management on reduction of 

nonnative fish species. Adaptation tactics include increased 

harvest of nonnative fish (e.g., sport fishing), manual or 

chemical removal of nonnative species, and excluding nonnatives with physical or electrical barriers where feasible. 

These tactics will generally be more effective if nonnative 

species are not already well established.

In stream systems adjacent to grasslands and shrublands, 

livestock grazing can damage aquatic habitat, causing stress 

that may be compounded by warmer stream temperatures. 

An important adaptation strategy is to manage grazing to 

restore as much ecological and hydrologic function of riparian systems as possible. Specific adaptation tactics include 

ensuring that standards and guidelines for water quality are 

adhered to and monitored, making improvements that benefit water quality (e.g., fencing), and reducing the presence 

of cattle through the retirement of vacant grazing allotments. 

It will make sense to prioritize these actions for locations 

that have high ecological value.

In a warmer climate, it is almost certain that increased 

wildfire occurrence will contribute to erosion and sediment delivery to streams, thus reducing water quality for 

fisheries. Increasing resilience of vegetation to wildfire may 

reduce the frequency and severity of fires when they occur. 

Hazardous fuels treatments that reduce forest stand densities and surface fuels are an adaptation tactic that is already 

widely used in dry forest ecosystems. Disconnecting roads 

from stream networks, another tactic already in practice, 

is especially important, because most sediment delivery 

following wildfire is derived from roads. Finally, erosion 

control structures can reduce postfire sediment delivery 

and are often a component of Burned Area Emergency 

Rehabilitation on Federal lands.

More-specific details on adaptation strategies and tactics 

that address climate change effects on fisheries in NRAP 

subregions are in Appendix 5A. The process used to elicit 

adaptation options differed among subregions; some information was general and some was geographically specific.

Toward Climate-Smart Management

The broad range of adaptation options summarized in 

table 5.6 and Appendix 5A provides a diverse toolkit for 

fisheries managers. In addition to specific strategies and 

tactics, several overarching issues help guide applications in 

Federal lands.

Be Strategic

Prioritizing watershed restoration such that the most 

important work is done in the most important places is critical because funds, labor, and time for management of native 

fish populations are limited (Peterson et al. 2013b). For 

example, climate refugia for native trout in wilderness areas 

may not require or be amenable to habitat modification to 

ensure the persistence of those populations. Similar refugia 

outside wilderness might be targeted to improve habitat 

conditions or reduce nonnative species, particularly if doing 

so increases the probability of occupancy of such habitats. 

Regardless of such efforts, some basins are unlikely to 

provide suitable habitat for native trout in the future, so 

directing conservation investments elsewhere, or for other 

species, may be prudent.

Implement Monitoring Programs

Being strategic means reducing current and future uncertainties for decisionmaking. In the case of fisheries, more 

data are needed for streamflow (more sites), stream temperature (annual data from sensors maintained over many years), 

and fish distributions. These data can be used for better 

status-and-trend descriptions, and to develop robust (more 

accurate and precise) models for species to understand the 

interaction of climate change, natural variation, and land 

management. The feasibility of monitoring at small to broad 

scales is increasing with the advent of rapid, reliable eDNA 

inventories of aquatic organisms (Thomsen et al. 2012) and 

the availability of inexpensive, reliable temperature and 

flow sensors (U.S. Environmental Protection Agency 2014).

Restore and Maintain Cold Stream 

Temperatures in Summer

Persistence of native trout species will depend on a 

variety of management techniques to restore and maintain 

stream shade and narrow unnaturally widened channels. 

Actions may include relocating roads away from streams, 

limiting seasonal grazing in some areas, and managing 

streamside riparian forest buffer zones to maintain effective 

shade and cool, moist riparian microclimates. The tactics described in this chapter have implications and consequences 

far beyond enhancing the persistence of native fish populations, but being open to opportunities to do so is part of 

strategic thinking.

Manage Connectivity

Beyond climate change concerns, obstacles to fish migration are often removed in hopes of enhancing the success of 

migratory life history forms, or permitting native species to 

reoccupy former habitat or supplement existing populations. 

However, this presents a dilemma: Accessible waters can 

be invaded by nonnative fish species that can replace native 

species (Fausch et al. 2009). In some cases, barriers can 

be installed to prevent these invasions. Native populations 

above barriers may be secure if they can adopt resident life 

histories, but could be susceptible to loss from extreme 

disturbance events in small habitats, requiring human intervention to reestablish or supplement populations. Barriers 

are usually temporary, and may require reconstruction if 

nonnative species remain downstream.

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 105

Remove Nonnative Species

Removal of nonnative fish species, although challenging 

in some locations, may be the best option for maintaining or 

restoring some native fish populations. These efforts typically consist of chemical treatments or electrofishing, and both 

tend to be feasible only in smaller, simpler habitats. Both 

are also costly, in part because they need to be conducted 

on multiple occasions to be effective. Chemical treatment 

can be controversial because of its perceived effects on 

water quality. Furthermore, any method of removal is successful only if the source of nonnative species is removed, 

often by installation of a migration barrier (see “Manage 

Connectivity”). Public resistance to removal of nonnative 

fishes may also be an obstacle, particularly if sport fish are 

involved. Unauthorized introductions are also common, 

and can undermine conservation efforts. Finally, using 

control measures to manage the abundance of nonnative 

species rather than removing all of them has been helpful 

in some areas (e.g., removal of lake trout to promote bull 

trout persistence, electrofishing to depress brook trout and 

favor cutthroat trout). Such activities will be successful only 

if conducted at regular intervals for the foreseeable future, 

which assumes social acceptance and indefinite availability 

of project funding.

Implement Assisted Migration?

Moving native fish species from one location to another, 

a historically common activity in fish management, has typically been used to found populations in previously fishless 

waters. This practice, alternately termed “assisted migration” or “managed relocation,” has become controversial for 

some taxa in recent years. However, assisted migration may 

be useful in the Northern Rockies where basins are currently 

fishless (or contain nonnative species only in limited numbers) because of natural barriers such as waterfalls, and may 

constitute high-quality climate refugia in the future. Moving 

native fish to such areas is feasible, but potential effects on 

other native taxa (e.g., amphibians or invertebrates) must be 

considered. Reintroductions of native species may also be 

warranted when natural refounding is not an option, such as 

when populations in a specific location are isolated and periodically fail or suffer population bottlenecks (Dunham et 

al. 2011). This degree of management intervention requires 

a thorough understanding of genetic principles and broodstock establishment.

In conclusion, fisheries managers responding to the 

environmental trends associated with climate change will 

require a diverse portfolio comprising many of the actions 

described in this chapter. Equally important is adapting our 

mindsets—and our administrative processes—to a new paradigm of dynamic disequilibrium for the 21st century. Under 

this paradigm, stream habitats will become more variable, 

undergo gradual shifts through time, and sometimes decline. 

Many populations will retain enough flexibility to adapt and 

track their habitats, but others could be overwhelmed by 

future changes. It is unlikely that we will be able to preserve 

all populations of all fish species as they currently exist. 

However, as better information continues to be developed 

in the future, managers will have increasingly precise tools 

at their disposal to know when and where resource commitments are best made to enhance the resilience of existing 

fish populations or to benefit other species for which management was previously not a priority. There is much to do 

as climate change adaptation continues in future years, and 

Federal lands will play a critical role in providing important 

refuge habitats for aquatic resources.

Acknowledgments

We thank the many biologists who contributed ideas, 

refinements, and data to the assessment described in this 

chapter.

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110 USDA Forest Service RMRS-GTR-374. 2018

Geographically specific adaptation options for fisheries were compiled for four subregions of the Northern 

Rockies Adaptation Partnership. 

Western Rockies Subregion

Adaptation options for fisheries in the Western Rockies subregion are summarized by climate change stressor.

Temperature

Adaptation tactics

• Identify and protect groundwater areas and side channels

○ Increase density of temperature sensor network

○ Develop GIS layer and incorporate into stream temperature maps

§ Action application: where groundwater has not yet been captured; everywhere native cold-water fish species 

occur

○ Remote sensing at microscale (longitudinal profile of larger rivers), which provides more fine-scale temperature 

mapping to help identify areas of groundwater inputs

§ Action application: Clearwater, St. Joe; anywhere there is private land or proposed development (feeds into 

floodplain or road development issues); rivers large enough to support this kind of sampling

• Restrict floodplain development and channelization

○ Action application: 3rd-order streams

• Remove/relocate roads from creeks/streams

○ Action application: prioritize areas based on proximity to and presence of fish doing well. For example, the Clearwater has one HUC 6 with no human effects that is prioritized for restoration. In contrast, the Selway is connected 

to large areas of good habitat so less important to prioritize for road removal/relocation.

§ At a site-specific scale, prioritize similarly to watershed but on smaller scale; look at the potential of that habitat 

to support native fish both now and in the future

• Limit exploitation of groundwater/water withdrawals

○ Action application: anywhere tied to groundwater upwelling

• Hypolimnitic withdrawal 

○ Action application: where possible (e.g., Priest Lake, Libby Dam, Albany Falls, Dworshak and Clark Fork dams)

In some cases (e.g., Kootenai) the water has been too cold for fish species, but this may change in the future

• Use beaver or large woody debris, or both, to increase groundwater storage

○ Action application: headwaters/headwater storage in high elevation areas

• Maintain current shade and microclimate characteristics

○ Action application: everywhere

• Identify, prioritize, and protect high-quality watersheds (HUC 6/7) and generate specific standards and guidelines for 

the area

○ Implement in national forest land management plans. Use this as an overarching strategy to identify high, moderate, and low priority watersheds with specific actions in each

• Reduce grazing effects

○ Identify thresholds that, once exceeded, trigger movement of the cattle to another pasture

○ Generate and implement adaptive management scenarios (similar to those just described)

○ Reevaluate timing of grazing and the amount of time between grazing activities

○ Riparian fencing (not as feasible in forested environments)

○ Retire allotments

§ Action application: target areas most susceptible to grazing (low elevation meadows) (especially on Nez PerceClearwater NF)

• Remove barriers to fish passage

○ Action application: remove if barrier prevents bull trout migration (not necessarily westslope cutthroat trout)

○ Other: westslope cutthroat trout database can be compared with stream temperature maps

Appendix 5A—Adaptation Options for Fisheries in the 

Northern Rockies Adaptation Partnership Subregions

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 111

• Water temperature management through dams. For example, Dworshak dam has contributed to resilience of downstream fish because of temperature mitigations (i.e., by creating thermal refugia downstream of these facilities). 

○ Need to match fish migration with thermal window (i.e., when fish migrate and when temperatures occur that are 

necessary to sustain that migration) and consider the possibility of longer periods of warmer stream temperatures in 

the future and how they may affect fish migration ability

○ Reexamine water temperature release in light of climate change (e.g., Kootenai)

○ Develop temperature models to better inform this action

• Install snowpack sensors to better anticipate changes in stream temperature and flow regimes

Runoff Regime

• Address site-specific activities that make narrower and deeper channels and affect runoff characteristics and peak flow 

(e.g., clearcutting) by reducing ratio of surface area to depth

○ Action application: anywhere with narrow and deep channels, clearcut areas

• Limit actions (e.g., vegetation removal) that contribute to peak yield

○ Action application: primarily in rain-on-snow areas; north end of Clearwater has private/State/Federal lands interspersed; need an analysis to determine effects from management activities (e.g., vegetation removal) on all lands to 

understand potential impacts on runoff characteristics and sedimentation

• Reconnect floodplains to improve the ability of system to deal with large flow events

○ Consider using beavers and large woody debris to facilitate this process

○ Action application: prioritize areas of past dredge mining, where possible/feasible given social/financial constraints

• Restore water holding capacity using beaver or mechanical storage methods

○ Action application: degraded headwater streams

• Reexamine flow release (variable Q) from dams with projected climate changes (currently use from 1999 and earlier)

○ Action application: dams

• Increase connectivity, where possible, to allow fish to move to cope with changing conditions

○ Action application: remove mainstem dam passages/impoundments (although these may also be selectors favoring 

nonnative species, so this needs to be considered at site level)

• Increase capacity of infrastructure to handle flows (e.g., upsizing culverts/structures to 100-year flood)

○ Action application: take advantage of Burned Area Emergency Rehabilitation and other vegetation projects to 

replace culverts; relocate roads and trails outside of 100-year floodplain

• Conduct roads analysis within proposed timber harvest areas, considering riparian/aquatic habitat and fish impacts 

(e.g., road density is a concern for fish)

• Hydrologically disconnect roads from streams (e.g., by adding cross-drains or culverts or outsloping roads)

• Examine current and proposed future campgrounds/dispersed campgrounds on creeks and potential future changes in 

flow regimes (permanent disturbance regimes for fish habitat)

Invasive Species

• Remove brook trout in higher elevations that are likely to be cold-water refugia for bull trout

○ Action application: headwater lakes in wilderness (rotenone can be used for brook trout suppression in wilderness); 

when removing fish, we need to provide an alternative for recreational fisheries

• Create an integrated strategy across the subregion that supports multiple species. For example, leave some lakes fishless for amphibians, incorporate brook trout strategy (following) at basin scale (HUC 5) to balance public need (i.e., 

recreational fishery) with ecological need (i.e., bull trout)

• Identify brook trout locations and prioritize where to eradicate

○ Need: strong partnership with State and other wildlife agencies to do a cross-agency effort (see preceding action as 

well); also support from leadership and funding

○ Eradication and preventing re-invasion by:

§ Installing barriers

§ Avoiding rotenone by using a combination of electrofishing and tiger muskie (Esox masquinongy × Esox lucius) 

(although may be difficult to eliminate source entirely)

§ Expanding options for brook trout management (e.g., gill netting)

§ Manipulating gametes and “swamping” current population so species essentially eradicates itself

○ Action application: meadow creeks in upper North Fork Clearwater

• Public education and outreach

• Brown trout and pike are newer invasive species, although management options are limited

○ Take limit off the fisheries (already done)

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
112 USDA Forest Service RMRS-GTR-374. 2018

○ Where feasible and biology of species lends itself to it (e.g., Pend d’Oreille), can do some suppression

• Manage reservoirs and lakes (e.g., suppression efforts) to protect adult bull trout breeders from smallmouth bass and 

lake trout

• Utilize changing flow regimes and temperatures to keep invasives out

○ This has been used in Pend d’Oreille to keep pike out

○ Action application: dams/reservoirs

• Reservoir manipulation

○ Fertilization of species (kokanee; Oncorhynchus nerka); application: putting kokanee in headwater areas

• Establish barriers to invasive species movement

○ Have to make conscious decision to write off fluvial form of bull trout

○ Many factors have to coincide to make this work

○ Small-scale application for cutthroat (e.g., above barriers and more opportunistic)

In areas projected to be cold-water refugia until 2040:

• Suppress nonnative fish

• Conduct a status assessment of current species and management actions

• Manage fire and fire effects

• Note: many of these areas in Nez Perce-Clearwater NF are in wilderness, so fewer management options

• Aggressive fish management (e.g., hatcheries)

○ Action application: Lake Coeur d’Alene drainage is historical drainage and critical habitat for bull trout, but none 

there now

§ Questions: where to get fish and how many

§ This is a viable future habitat but there may be social barriers (cattlemen’s association, political/social will) to 

implementation

§ Use this as template for future

○ Action application: in areas with nonnative species, use hatcheries to bring fish in, apply rotenone to habitat, and 

aggressively restock

In areas with fish currently, but projected to be gone by 2040:

• Suppress nonnative fish

• Improve connectivity

• Address higher river mainstem temperatures that act as barrier

• Monitor areas (fish present now, historical records, eDNA, presence/absence of juveniles, physical characteristics)

During warm phases of the Pacific Decadal Oscillation

• Warmer, drier conditions may affect year-class strength; potential barometer of how populations may respond in the 

future

High-severity wildfire areas

• With connectivity, fire effects and debris torrents may not be an issue

• Nez Perce-Clearwater National Forest probably would not move fish unless they were spawning populations with 

limited connectivity

○ Strategy: monitor over time to understand distributions of spawning populations and how they respond to disturbances

○ Action application: translocate brood stocks only in certain situations (no connectivity)

Valued Species Other Than Cold-Water Fish

• Sturgeon and burbot

○ Opportunities: management of dam (temperature and flow), specifically temperature for these species (dependent 

on season and species)

○ Potential conflict: want to reduce flow in winter for water to cool off, but Bonneville Power Administration wants 

to release more flow during this time to generate power

• Western pearlshell mussel: increased peak flows may wipe out colonies

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 113

Central Rockies Subregion

Following are adaptation tactics and other issues summarized for locations in the Central Rockies subregion as a 

complement to table 5A.1. Table 5A.1—Adaptation options that address climate change effects on fisheries in the Central Rockies subregion.

Sensitivity to climatic variability and change: Reduced snowpack will alter the thermal regime of streams in space and time.Adaptation strategy/approach: Improve riparian function and increase functional riparian areas. Strategy objective: Promote resilience, reduce stressors.

Specific tactic – A Specific tactic – B Specific tactic – C

Tactic Re-vegetate denuded sections of 

riparian areas (leading to additional refined tactics for grazing effects, fire effects, etc.).

Strategically relocate, eliminate, and minimize the effects of riparian and upland road segments.

Restore groundwater and hyporheic exchange through beaver reintroduction/protection, channel restoration, and reestablishment of fire regimes.

Tactic effectiveness (risks) High High HighImplementation urgency Near term Near term Near term Where can tactics be applied?

All locations where riparian areas have been damaged, especially if native fish populations are present or nearby

All locations where streams have been or could be damaged, especially if native fish populations are present or nearby

All locations where each specific tactic is appropriate and likely to be effective

Opportunities for implementationCostBarriers to implementation

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
114 USDA Forest Service RMRS-GTR-374. 2018

Flathead National Forest

• Need aggressive suppression and eradication of nonnative fish

• More brook trout are in the Middle Fork Flathead than in the North Fork; bull trout populations dropped sharply on the 

west side of Glacier National Park (Bowman, Logging, Kintla) because of brook trout; Quartz Lake has very active 

suppression of nonnative fish species

• Some effects from logging (lack of wood in streams, some roads) in Coal Creek, Big Creek, Whale, Red Meadow; 

active logging in Canada in same drainage has effects (nonnative fish going upstream, logging effects coming downstream)

• To protect westslope cutthroat trout, Montana Fish, Wildlife and Parks (FWP) is focused on eradicating rainbow trout 

through rotenone application and other techniques

• Efforts to slow spread of hybrids; targeting rainbow trout sources in lower Flathead

• Barriers being installed or removed in North Fork Flathead; removing barriers in Rose Creek; removing culverts in 

Langford tributary to Big Creek

• Ongoing habitat work by Montana FWP in South Fork of Cold Creek

• Suppression of brook trout in Flathead Lake is a high priority

• Translocated bull trout this year; can use stocks to move them above barriers

• Genetic rescue of westslope cutthroat trout (tributary to Swan Lake)

• Land acquisition presents huge opportunities for protection of habitat

South Fork of the Flathead River

• Try to maintain the status quo in Hungry Horse Reservoir, a genetic refuge for bull trout

• Try to manage more natural burns in South Fork of the Flathead; could apply this tactic to land around Hungry Horse 

Reservoir

• Need a check station at the dam and ranger station to prevent introduction of nonnative fish, in combination with public 

outreach on this issue

• Montana FWP restored connectivity around Hungry Horse reservoir (also around Emery Creek) that was severed when 

road was constructed, but additional opportunities exist

Swan River

• Nonnative issues are similar to Flathead River

• Westslope cutthroat trout are more hybridized with more brook trout characteristics

• Need small barriers to protect bull trout headwater populations

• Need to explore passage barrier issues

• Consider pulling road segments back from streams in critical locations

• Major road management issues exist on former Plum Creek lands, which have a large amount of spawning and rearing 

habitat relative to size 

• Need thermographs throughout floodplains because of the importance of groundwater upwelling for bull trout; this will 

help improve models of these cold-water systems 

Clearwater River, Blackfoot River

• Long-term effects of timber harvest and roads, including the effects of roads on connectivity of the hydrologic system

• Unmanaged roads deliver low amounts of sediment

• Continuing work with The Blackfoot Challenge to expand voluntary drought response plans; irrigation efficiency programs are addressing dewatering issues (particularly in drought years)

• Livestock grazing issues in Monture Creek

• Need to address contaminants issues near Mike Horse Mine

• Conservation easements need to be added more strategically (rather than only opportunistically)

• Restorative work is needed to narrow and deepen creeks to significantly reduce stream temperatures (Nevada Creek); 

could be applied strategically in other areas (Shanley Creek), as suggested by bull trout recovery plan 

• Restoration of the main stem of the Blackfoot River is needed to reduce channel simplification and restore functionality and complexity

• One option is to identify reaches on private land and work to connect landscape and habitat up to higher elevation 

habitat on public lands

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 115

• Ongoing efforts to connect cold-water tributaries in the Upper Blackfoot; also need to restore streambanks in locations 

with land conversion

• This area has high use for recreation and fishing; this level of use may not be sustainable if habitat quality declines in 

the future

Upper Clark Fork River, Bitterroot River

• Heavy fishing pressure (catch and release) in this location

• East side of Bitterroot is a stronghold for native fish, but west side has no apparent occupancy (need to confirm)

• Dewatering events in tributaries are important, including issues for mitigation of water quality and quantity

• West Fork of Bitterroot above Painted Rocks Dam has been affected by forest management; road mitigation and removal are helping

• Sleeping Child/Darby timber land restoration is removing roads 

• Habitat in Daily Creek (strong producer of bull trout out of Skalkaho) is being improved by placing woody debris in 

streams 

• South Fork Lolo Creek is probably a native fish stronghold, although Highway 12 and private land management limit 

potential restoration options 

Middle and Lower Clark Fork River

• Fish passage at the reservoir dams has a huge effect on downstream rearing of westslope cutthroat trout and bull trout

• Legacy effects of management (e.g., placer mining) on cold-water patches (Cedar Creek, Trout Creek) have degraded 

habitat, requiring structural channel remediation and road relocation and mitigation

• Thompson River native fish strongholds (Fish Trap, West Fork Thompson) provide options for improving channel 

complexity and habitat

• Little Joe River is a very cold water patch but with seasonal disconnection; unclear if this hinders access by bull trout

• Moore Lake is a source of brook trout to the South Fork Little Joe River

Rock Creek

• Bull trout populations are decreasing faster here than anywhere else; brown trout numbers are correspondingly increasing; East Fork above the reservoir has agricultural issues including effects of dewatering events caused by irrigation 

withdrawals

• Easy restoration options have already been implemented to improve connectivity 

• Options on east side for road relocation (Burnt Fork)

• Lower Rock Creek has heavy angling pressure

• Water and land restoration options on Ranch Creek

Rattlesnake Creek

Current bull trout producer, but warming with few options for improving management

Large wood and channel complexity, especially in the urban interface.

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
116 USDA Forest Service RMRS-GTR-374. 2018

Eastern Rockies Subregion

Adaptation options for fisheries in the Eastern Rockies subregion are summarized in tables 5A-2 through 5A-7 Table 5A.2—Adaptation options that address climate change effects on fisheries in the Eastern Rockies subregion. Sensitivity to climatic variability and change: Reduced snowpack will increase stream temperatures and alter flow regimes. Adaptation strategy/approach: Increase habitat resilience for cold-water aquatic organisms by restoring structure and function of streams. Strategy objective: Promote resilience Specific tactic – A Specific tactic – B Specific tactic – C Tactic Restore natural channel and floodplain form and function (e.g., restore areas with human-caused bank and bed instability). Restore aquatic organism passage structures through design and placement of appropriate structures. Maintain functional stream channel morphology with adequate width:depth ratios, pool frequency, and healthy riparian vegetation. Tactic effectiveness (risks) Moderate–high High High Implementation urgency Near term (gradual process, but need to get started) Near term Near term Where can tactics be applied? (geographic) Areas with ongoing restoration activities and where habitat is a primary limiting factor (especially where roads are present) Drainages with frequent high peak flows, areas with sensitive geology, areas with important rearing streams Areas with ongoing restoration activities and where habitat is a primary limiting factor (especially where roads are present) Opportunities for implementation Mining restoration projects Talk to insurance companies to see if they will fund replacements (e.g., in locations where flows can affect downstream communities) Cost Barriers to implementation

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 117 Table 5A.3—Adaptation options that address climate change effects on fisheries in the Eastern Rockies subregion. Sensitivity to climatic variability and change: Reduced snowpack will increase stream temperatures and alter flow regimes. Adaptation strategy/approach: Increase habitat resilience for cold-water aquatic organisms by restoring structure and function of streams. Strategy objective: Promote resilience Specific tactic – A Specific tactic – B Specific tactic – C Tactic Restore riparian areas to increase hydrologic function and retain cold water. Reintroduce beaver where beaver and management of westslope cutthroat trout are compatible. Remove or relocate roads adjacent to riparian areas, channels, and floodplains where they inhibit complexity; minimize cumulative effect of road network on surface and subsurface flow. Tactic effectiveness (risks) High Moderate High, but spatially limited Implementation urgency Near term Long term Near-medium term Where can tactics be applied? (geographic) Where riparian areas limit the availability of cold-water habitat Where beaver will not affect barriers; in stream reaches >1 mile; in larger population conservation networks; where brook trout are absent Where roads currently cause problems or may in the future, especially where roads have substantial linear effects Opportunities for implementation Mining restoration projects Talk to insurance companies to see if they will fund replacements (e.g., in locations where flows can affect downstream communities) Cost Very high cost Barriers to implementation Beaver habitat can enhance brook trout populations

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
118 USDA Forest Service RMRS-GTR-374. 2018 Table 5A.4—Adaptation options that address climate change effects on fisheries in the Eastern Rockies subregion. Sensitivity to climatic variability and change: Reduced snowpack will increase stream temperatures and alter flow regimes. Adaptation strategy/approach: Increase habitat resilience for cold-water aquatic organisms by restoring structure and function of streams. Strategy objective: Promote resilience. Specific tactic – A Specific Tactic – B Tactic Acquire Montana water compact/rights in a strategic way. Increase efficiency of irrigation techniques. Tactic effectiveness (risks) Low–moderate (for instream flows) Low–moderate Implementation urgency Long term Long term Where can tactics be applied? (geographic) Where future plans for water development may overlap with areas where native fish populations may be declining Where future plans for water development may overlap with areas where native fish populations may be declining Opportunities for implementation Cost Barriers to implementation

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 119 Table 5A.5—Adaptation options that address climate change effects on fisheries in the Eastern Rockies subregion. Sensitivity to climatic variability and change: Continued livestock grazing will compound stress caused by increased stream temperatures. Adaptation strategy/approach: Manage livestock grazing to restore ecological function of riparian vegetation and channels. Strategy objective: Promote resilience, reduce stressors Specific tactic – A Specific tactic – B Specific tactic – C Tactic Comply with all existing standards and guidelines for maintaining water quality in streams and riparian areas; facilitate compliance through monitoring. Use innovative techniques to fund and maintain and implement improvements (e.g., riparian fencing, rest-rotation systems, off-channel water, exclosures). Identify and prioritize vacant allotments for retirement. Tactic effectiveness (risks) Moderate Moderate–high (high for techniques that physically prevent access) High, but spatially limited and opportunistic Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) All locations, with emphasis on areas that are important in terms of ecological value and large financial investment All locations, with emphasis on areas that are important in terms of ecological value and prior financial investment; prioritize areas with pure native fish populations that are under imminent threat All locations where vacant allotments exist and opportunities allow Opportunities for implementation Cost Barriers to implementation Lack of public support Beetle-killed trees damage fences

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
120 USDA Forest Service RMRS-GTR-374. 2018 Table 5A.6—Adaptation options that address climate change effects on fisheries in the Eastern Rockies subregion. Sensitivity to climatic variability and change: Continued livestock grazing will compound stress caused by increased stream temperatures. Adaptation strategy/approach: Manage livestock grazing to restore ecological function of riparian vegetation and channels. Strategy objective: Promote resilience, reduce stressors. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Incorporate aquatic resource values in prioritization and implementation of land management plans. Convene regional meeting to identify and prioritize key fisheries areas; develop implementation plan that describes line officer actions. Continue and formalize agency coordination for fish habitat conservation (where projects are planned). Tactic effectiveness (risks) Moderate–high, depending on how well values are incorporated High, but depends on spatial extent and number of stakeholders involved High, but spatially dependent Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) All locations, as management plan revisions occur All areas of Montana Where projects are planned and where existing conservation issues related to grazing exist Opportunities for implementation East-side range meetings; efforts to avoid listing of westside cutthroat trout populations; monitoring plans Cost Barriers to implementation

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 121 Table 5A.7—Adaptation options that address climate change effects on fisheries in the Eastern Rockies subregion. Sensitivity to climatic variability and change: Warmer temperatures will increase stream temperature and risk of invasion by nonnative fish species. Adaptation strategy/approach: Manage nonnative fish populations to eliminate or reduce their impact on native fish. Strategy objective: Promote resilience, reduce stressors. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Construct barriers to restrict nonnative fish. Remove nonnative fish and re-establish or restore western cutthroat trout populations. Secure, maintain, and improve riparian stream function and flows, including temperature. Tactic effectiveness (risks) High High Moderate Implementation urgency Near term (Big Hole and other locations with urgent issues); Long term (everywhere else) Near term (Big Hole and other locations with urgent issues); Long term (everywhere else) Near term Where can tactics be applied? (geographic) Where feasible and necessary (Big Hole, Selway Meadows-Red Rock, all drainages on Rocky Mountains front) Where feasible and necessary (Big Hole, Selway Meadows-Red Rock, all drainages on Rocky Mountains front) Where native fish populations and impaired riparian function exist, as identified in annual coordination meetings Opportunities for implementation East-side range meetings; efforts to avoid listing of westside cutthroat trout populations; monitoring plans Cost Potentially high Barriers to implementation Not socially feasible Not socially feasible (e.g., high value recreational fishery) or may be unacceptable to kill all nonnatives

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
122 USDA Forest Service RMRS-GTR-374. 2018

Greater Yellowstone Area Subregion

Adaptation options for fisheries in the Greater Yellowstone Area are summarized in tables 5A-8 through 5A-5A-13. Table 5A.8—Adaptation options that address climate change effects on fisheries in the Greater Yellowstone Area subregion. Sensitivity to climatic variability and change: Reduced snowpack will reduce summer streamflows. Adaptation strategy/approach: Increase streamflows and moderate changes in instream flows. Strategy objective: Promote resilience. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Pulse flows during critical times (high temperatures) from regulated streams. Reduce water withdrawals and improve efficiency for agriculture (especially irrigation), municipal, and industrial uses. Secure water rights for instream flows. Tactic effectiveness (risks) Moderate–high High High Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) All regulated streams Where water demands overlap with current and future suitable habitat Where fish and suitable habitat overlap Opportunities for implementation Cost Barriers to implementation

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 123 Table 5A.9—Adaptation options that address climate change effects on fisheries in the Greater Yellowstone Area subregion. Sensitivity to climatic variability and change: Reduced snowpack will reduce summer streamflows. Adaptation strategy/approach: Provide opportunities for native fish to move and find suitable stream temperatures. Strategy objective: Promote resilience. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Increase the patch size of favorable habitat to enhance viable populations and allow adfluvial life histories. Modify or remove barriers to increase connectivity between areas of cold- water habitat. Identify and map where groundwater inputs provide cold water. Tactic effectiveness (risks) High High High Implementation urgency Near term Near term Mid term Where can tactics be applied? (geographic) Where native fish currently exist; where suitable habitat is nearby; where non-natives are not present or can be effectively managed; where populations are fragmented and need greater connectivity Where barriers prevent movement to suitable habitat, and where removal will not increase invasion of non-natives All locations Opportunities for implementation Locations that are economically advantageous Cost Barriers to implementation

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
124 USDA Forest Service RMRS-GTR-374. 2018 Table 5A.10—Adaptation options that address climate change effects on fisheries in the Greater Yellowstone Area subregion. Sensitivity to climatic variability and change: Water temperature will increase, and the hydrograph will change in terms of magnitude and seasonality. Adaptation strategy/approach: Protect and enhance fish habitat. Strategy objective: Promote resilience. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Restore degraded riparian vegetation, reconnect floodplains to rivers. Reintroduce beaver, encourage beaver recolonization. Disconnect roads from stream networks to reduce sedimentation. Tactic effectiveness (risks) Moderate–high Moderate High Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) Smaller streams will be most effective, especially in lower-elevation valleys; prioritize areas with native fish or potentially suitable habitat Where brook trout do not occur (beaver dams tend to facilitate brook trout) and where suitable beaver habitat exists Where roads adjacent to streams have the potential to erode and deliver sediment Opportunities for implementation Smaller streams Locations that are economically advantageous Cost Barriers to implementation

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 125 Table 5A.11—Adaptation options that address climate change effects on fisheries in the Greater Yellowstone Area subregion. Sensitivity to climatic variability and change: Water temperature will increase, and cold-water fish habitat will decline. Adaptation strategy/approach: Reduce stress on native fish species to enhance their ability to tolerate climate-induced stress. Strategy objective: Reduce stressors Specific tactic – A Specific tactic – B Specific tactic – C Tactic Limit angling pressures on native fish. Reduce effects of recreation and grazing disturbance in streams. Reduce nonnative (non-fish) aquatic species and diseases. Tactic effectiveness (risks) Moderate Moderate Moderate Implementation urgency Mid term Mid term Near term Where can tactics be applied? (geographic) Locations that are at or near temperature thresholds for native fish Where recreation and grazing activities are high, coincident with occupied or projected suitable fish habitat Where nonnative aquatic species and diseases occur, coincident with occupied or projected suitable fish habitat Opportunities for implementation Cost Barriers to implementation

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
126 USDA Forest Service RMRS-GTR-374. 2018 Table 5A.12—Adaptation options that address climate change effects on fisheries in the Greater Yellowstone Area subregion. Sensitivity to climatic variability and change: Warmer temperatures will increase stream temperature and risk of invasion by nonnative fish species. Adaptation strategy/approach: Manage nonnative fish populations to eliminate or reduce their impact on native fish. Strategy objective: Promote resilience, reduce stressors. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Encourage increased take/harvest of nonnatives, especially near long-term strongholds for natives. Remove nonnatives with manual or chemical techniques. Implement physical or electrical barriers to exclude nonnatives. Tactic effectiveness (risks) Low–moderate (need heavy harvest at the invasion front) Moderate–high Moderate–high Implementation urgency Mid term Near term Near term Where can tactics be applied? (geographic) Areas with heavy recreation and sport fishing; most effective at the front of invasions Where long-term suitable habitat for natives is available and non-natives are present Where long-term suitable habitat for natives is available and nonnatives are present Opportunities for implementation Cost Barriers to implementation

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 127 Table 5A.13—Adaptation options that address climate change effects on fisheries in the Greater Yellowstone Area subregion. Sensitivity to climatic variability and change: Higher temperatures will increase wildfire occurrence that can lead to erosion and mass wasting. Adaptation strategy/approach: Increase resilience to fire-related disturbance. Strategy objective: Promote resilience, reduce stressors. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Implement fuel treatments (thinning, prescribed burning) to reduce wildfire severity and size. Disconnect roads from stream networks to reduce erosion and sediment delivery to streams. Install erosion control structures following wildfires. Tactic effectiveness (risks) Moderate Moderate Moderate Implementation urgency Mid term Mid term Near term Where can tactics be applied? (geographic) Areas where canopy and surface fuels are high, adjacent to known native fish populations and habitat Areas adjacent to known native fish populations and habitat Where wildfire has occurred and erosion would affect known native fish populations and habitat Opportunities for implementation Areas that are already being targeted for fuel treatment, especially in the wildland-urban interface Cost Barriers to implementation

Chapter 5: Climate Vulnerability of Native Cold-Water Salmonids in the Northern Rockies Region
128 USDA Forest Service RMRS-GTR-374. 2018

Introduction

The projected rapid changes in climate will affect the 

unique vegetation assemblages of the Northern Rockies 

region in myriad ways, both directly through shifts in vegetation growth, mortality, and regeneration, and indirectly 

through changes in disturbance regimes and interactions 

with changes in other ecosystem processes, such as hydrology, snow dynamics, and exotic invasions (Bonan 2008; 

Hansen and Phillips 2015; Hansen et al. 2001; Notaro et 

al. 2007). These impacts, taken collectively, could change 

the way vegetation is managed by public land agencies in 

this area. Some species may be in danger of rapid decreases 

in abundance, while others may undergo range expansion 

(Landhäusser et al. 2010). New vegetation communities 

may form, while historical vegetation complexes may 

simply shift to other areas of the landscape or become 

rare. Juxtaposed with climate change concerns are the 

consequences of other land management policies and past 

activities, such as fire exclusion, fuels treatments, and grazing. A thorough assessment of the responses of vegetation 

to projected climate change is needed, along with an evaluation of the vulnerability of important species, communities, 

and vegetation-related resources that may be influenced by 

the effects, both direct and indirect, of climate change. This 

assessment must also account for past management actions 

and current vegetation conditions and their interactions with 

future climates.

This chapter addresses the potential impacts of climate 

change on forest vegetation in the Forest Service, U.S. 

Department of Agriculture (USFS) Northern Region and 

the Greater Yellowstone Area (GYA), hereafter called the 

Northern Rockies region (fig. 6.1). Then, based on the 

Chapter 6: Effects of Climate Change on 

Forest Vegetation in the Northern Rockies 

Region

Robert E. Keane, Mary Frances Mahalovich, Barry L. Bollenbacher, Mary E. 

Manning, Rachel A. Loehman, Terrie B. Jain, Lisa M. Holsinger, Andrew J. 

Larson, and Meredith M. Webster

Figure 6.1—The Northern 

Rockies (NR) assessment 

area that includes the 

Northern Region of the 

U.S. Forest Service and the 

Greater Yellowstone Area 

(Yellowstone National Park 

and surrounding areas). 

Presented are existing 

vegetation types by the five 

geographic sub-areas used 

to stratify assessments in this 

report. This map was created 

from the LANDFIRE Existing 

Vegetation Type map by 

aggregating the National 

Vegetation Classification 

Standard vegetation types 

into a set of vegetation types 

that has some meaning 

across the NR at this coarse 

scale. This map is intended 

to convey current vegetation 

of the NR.
USDA Forest Service RMRS-GTR-374. 2018 129

climate impacts assessment, we present an evaluation of the 

vulnerability of important tree species, vegetation types, 

and resources of concern to projected climate change effects. Last, we present various adaptation actions to address 

climate change vulnerabilities.

This chapter has six major sections. In the introductory 

section, we define terminology used throughout the chapter 

and provide background material on the details of the 

assessment including the scales, geographic areas, and pertinent information used to make our assessments. We discuss 

how to evaluate uncertainty in climate change projections 

and vegetation response. We also summarize the methods 

used to make projections of vegetation response to changing 

climate. The second section contains important ecological 

background information that was used to assess climate 

change impacts and projected climate change responses for 

17 tree species, 5 forest vegetation types, and 3 resources of 

concern. The third section presents information on the tree 

species, types, or resources of concern that are important 

when evaluating climate change responses. In the fourth 

section, we rate the vulnerability of the species, vegetation 

types, and resources of concern to climate change using 

information from the third section. In the fifth section, we 

discuss adaptation strategies and management actions that 

can be used to address likely impacts of climate change. The 

final section is a concluding discussion.

This chapter uses the best available information about 

climate change effects on vegetation in the Northern 

Rockies. We have integrated broad-scale modeling results 

with a detailed synthesis of climate change literature for the 

region. This chapter was written to aid land managers in addressing climate change effects on forest vegetation in land 

management planning and development of management 

strategies. This chapter does not include the detail needed 

to address climate change effects at the project level, but it 

does include valuable information and syntheses that can be 

used in project planning and in addressing broad concerns at 

large spatial scales.

Terminology

Climate

Evaluations of climatic trends can be confusing, mostly 

because weather and climate vary at different spatial 

and temporal scales. To reduce this confusion, it is often 

helpful to clearly define the terms and explain the scales 

that distinguish weather, climate variability, and climate 

change. Weather is the hourly, daily, weekly, or monthly 

summaries in temperature, precipitation, wind, humidity, 

and other atmospheric conditions observed at a given place 

or across a large region. Weather changes at relatively small 

temporal scales (quickly) and it can change significantly 

as one moves north or south, east or west, or up and down 

in elevation. Weather is difficult to predict more than a 

few days in advance. Climate is a statistical characterization of the weather, averaged over many years. The World 

Meteorological Organization defines it as the average 

30-year weather patterns of a region. Climate variability

is the variation in weather statistics over relatively broad 

regions and long time periods. Climate variability can be 

caused by underlying climatic processes, such as changes 

in patterns of ocean temperatures. The El Niño-Southern 

Oscillation (ENSO) and the Pacific Decadal Oscillation 

(PDO), for example, are two sources of climate variability 

in western North America (Newman et al. 2003). ENSO 

oscillations occur over 2- to 7-year periods (Gershunov and 

Barnett 1998), while PDO oscillations occur on a longer cycle (20–50 years) (Heyerdahl et al. 2002). External forcings, 

such as changes in solar radiation, large volcanic eruptions, 

and increasing concentrations of greenhouse gases in the atmosphere, also influence climate variability. Climate change

is a nonrandom change in climate that is measured over 

several decades or longer. It is technically defined as a statistically significant variation in either the mean state of the 

climate or in its variability, persisting for an extended period 

(decades or longer). Like climate variability, climate change 

may be due to natural internal processes or to external forcings. A climate scenario is a plausible and often simplified 

representation of one possible future climate, based on a 

consistent set of known principles about the climate system 

used as input to climate models.

Vegetation

Several general terms are used in vegetation ecology 

to describe how ecosystems respond to climate change 

(Intergovernmental Panel on Climate Change [IPCC] 2007). 

Adaptive capacity is the ability of a plant, species, or system 

to adjust to climate change (including climate variability 

and extremes) to moderate potential damages, to take advantage of opportunities, or to cope with the consequences. 

Exposure is the nature and degree to which a system is 

exposed to significant climate variations (Glick et al. 2010). 

Sensitivity is the degree to which a system is affected, either 

adversely or beneficially, by climate variability or change. 

The effect may be direct, such as crop yield decreases in response to a higher temperature, or indirect, such as damage 

caused by an increase in the frequency of coastal flooding 

due to sea-level rise. Resilience is the degree to which ecosystems can recover from one or more disturbances without 

a major shift in composition or function, whereas resistance

is the ability of an organism, population, community, or ecosystem to withstand perturbations without significant loss 

of structure or function (i.e., remain unchanged) (Holling 

1973; Seidl et al. 2016). From a management perspective, 

resistance includes (1) the degree to which communities are 

able to resist change, such as that from warming climates, 

and (2) the manipulation of the physical environment to 

counteract and resist physical and biological change (i.e., 

cutting, burning, harvest treatments). Vulnerability is the 

degree to which a system is susceptible to, and unable to 

cope with, the adverse effects of climate change, including 

associated climate variability and extremes. Vulnerability is 

a function of the character, magnitude, and rate of climate 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
130 USDA Forest Service RMRS-GTR-374. 2018

change and variation to which a system is exposed, its sensitivity, and its adaptive capacity.

Other terms describe how ecosystem processes that are 

affected by climate change will influence vegetation. In 

general, stressors are any physical, chemical, or biological entity that can induce an adverse ecosystem response. 

Stressors can arise from physical and biological alterations 

of natural disturbances, increased unmanaged demand for 

ecosystem services (such as recreation), alterations of the 

surrounding landscape, chemical alterations in regional air 

quality, or a legacy of past management actions (Joyce et al. 

2008).

Management

Climate change adaptation is an adjustment in natural or 

human systems in response to actual or expected climatic 

stimuli or their effects, which is intended to moderate harm 

or exploit beneficial opportunities (Spittlehouse and Stewart 

2004). Adaptation is often referred to as “preparedness,” 

and is based on scientifically supported strategic and tactical 

activities that support sustainable resource management. 

Adaptation addresses specific aspects of the sensitivity of 

resources to an altered climate. An adaptation tactic is a 

specific action described in management and planning documents that supports adaptation strategies and is implemented 

on the ground (e.g., reducing stem density and surface fuels 

in a dry mixed-conifer forest, or increasing culvert size on 

roads along a stream that is expected to have higher flood 

volumes) (Joyce et al. 2008; Millar et al. 2007a; West et al. 

2009). Assisted migration is deliberately planting species to 

colonize new habitats.

In an ideal sense, ecological restoration is defined as the 

practice of reestablishing historical plant and animal communities in a given area and the renewal of ecosystem and 

cultural functions necessary to maintain these communities 

now and into the future (Egan and Howell 2001). However, 

this ideal may be impossible to manage because: (1) little 

is known about historical conditions; (2) many key species 

may already be lost; (3) some efforts may be prohibitively 

expensive; and most importantly, (4) future climates will 

create novel ecosystems. As a result, The Society for 

Ecological Restoration has opted for a definition that states 

that ecological restoration is “the process of renewing and 

maintaining ecosystem health”.

The USFS manual (FSM) direction contained in FSM 

2020 includes objectives and a policy for restoration. The 

objectives of the USFS ecosystem restoration policy are to:

1. Restore and maintain ecosystems that have been 

damaged, degraded, or destroyed by reestablishing 

the composition, structure, pattern, and ecological 

processes.

2. Manage for resilient ecosystems that have a greater 

capacity to withstand stressors, absorb and recover 

from disturbances, and reorganize and renew 

themselves, especially under changing and uncertain 

environmental conditions.

3. Achieve long-term ecological sustainability and 

provide a broad range of ecosystem services to 

society.

The USFS emphasizes ecosystem restoration across all 

National Forest System lands with the goal of attaining 

resilient ecosystems. All strategic plans, including the USFS 

Strategic Plan, land and resource management plans, and 

area plans, must include goals and objectives to sustain the 

resilience and adaptive capacity of aquatic and terrestrial 

ecosystems by reestablishing, maintaining, or modifying 

their composition, structure, function, and connectivity. The 

goals and objectives must be established within this framework as defined by laws, Indian treaties and tribal values 

and desires, and regulations. The goals and objectives also 

must consider public values and desires, social concerns, 

economic sustainability, the historical range of variability, 

ecological integrity, current and likely future ecological 

capabilities, a range of climate and other environmental 

change projections, the best available scientific information, 

and technical and economic feasibility to achieve desired 

conditions for National Forest System lands. A primary element of an integrated approach is to identify and eliminate 

or reduce stressors that degrade or impair the ecosystem. 

Restoration activities should also take into account social 

and ecological influences at multiple scales and incorporate 

the concept of a dynamic system and ecological trajectory. 

Some ecosystems may have been altered to such an extent 

that reestablishing components of the historical range of 

variability may not be ecologically or economically possible. Therefore, goals and activities should focus on restoring 

the underlying processes that create functioning ecosystems.

Functional restoration, which is the restoration of abiotic 

and biotic processes in degraded ecosystems, focuses on 

the underlying processes that may be degraded, regardless of the structural condition of the ecosystem. Whereas 

ecological restoration tends to seek a historical reference 

condition, functional restoration focuses on the dynamic 

processes that drive structural and compositional patterns. 

Functional restoration aims to restore functions and improve 

structures with a long-term goal of restoring interactions 

between function and structure. It may be, however, that a 

functionally restored system will look very different from 

the historical reference condition in terms of structure and 

composition, and these disparities cannot be easily corrected 

because some threshold of degradation has been crossed or 

the environmental drivers, such as climate, that influenced 

structural and (especially) compositional development have 

changed.

Assessment Levels

This chapter uses three levels to assess the impacts of climate change on forest vegetation: species, vegetation types, 

and resource concerns. We selected these levels and their 

elements to ensure flexibility when considering the complex 

ecological concerns across the Northern Rockies. Not only 

did this structure facilitate consistent and comprehensive 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 131

assessments for the major management concerns identified 

in this chapter, but it also allows for the addition of new elements that may be identified in the future.

Species

At the finest level of assessment, we address climate 

change effects at the species or species group level. We allowed for the use of species groups by aggregating species 

by genera, guilds, plant functional types, or lifeforms. In 

this chapter we had only one species group: all cottonwood 

species (Populus trichocarpa, P. angustifolia, P. deltoides). 

This allows us to address regional concerns about important 

individual species or species groups that might be adversely 

affected by climate change. All tree species cannot be addressed, so the list of species and species groups included 

here represents only those species that are identified by the 

government agencies in the Northern Rockies as critical for 

addressing both management and climate change concerns.

Vegetation Types

Vegetation type assessment addresses climate change 

concerns at a coarse vegetation community type level so that 

future evaulations can be spatially described using a map or 

geographic information system layer. Five forest vegetation 

types are assessed to summarize potential climate change 

impacts: dry ponderosa pine (Pinus ponderosa)/Douglas-fir 

(Pseudotsuga menziesii) forests; western larch (Larix occidentalis) mixed mesic forests; mixed mesic western white 

pine (Pinus monticola), western redcedar (Thuja plicata), 

western hemlock (Tsuga heterophylla), and grand fir (Abies 

grandis) forests; lodgepole pine (Pinus contorta) mixed subalpine forests; and whitebark pine (Pinus albicaulis) mixed 

upper subalpine forests. These types are shown in both an 

existing vegetation map (fig. 6.1) and a potential vegetation 

map (fig. 6.2). Both maps and resultant categories were derived from LANDFIRE data (Rollins 2009), which covered 

the entire Northern Rockies region. Many of the estimated 

effects of climate change were based on evaluations of MC2 

model simulations (see MC2 section), and figure 6.3 portrays the MC2 vegetation types used to generate the model 

results in Appendix 6A. The potential vegetation type map 

and MC2 map can be used to estimate species assemblages 

in the absence of disturbance.

Resource Concerns

Three resource concerns related to forest vegetation are 

also addressed in this report. First, we considered the impact 

of climate change and vegetation response on landscape heterogeneity, defined as the diversity in landscape structure or 

patch characteristics. We assume that landscapes with high 

heterogeneity are more resilient to disturbance (Ahlqvist and 

Shortridge 2010; Oliver et al. 2010; Turner 1987). The second resource concern is timber production, as represented 

by timber volume. We attempted to address impacts of 

climate change on timber production solely via vegetation 

response, not from disturbance. Finally, we describe climate 

impacts on carbon reserves across the Northern Rockies. 

Resource specialists in the Northern Rockies region selected 

these resource concerns.

Geographic Stratification

The Northern Rockies region was stratified into five 

geographic subregions (fig. 6.1). The Western Rockies 

subregion includes northwestern Montana and northern 

Figure 6.2—Potential 

vegetation types for the 

entire NRAP assessment 

area by the five 

geographic subregions. 

This map was created 

from the LANDFIRE 

Biophysical settings 

map by aggregating the 

National Vegetation 

Classification Standard 

vegetation types into a 

set of vegetation types 

that has some meaning 

at this coarse scale.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
132 USDA Forest Service RMRS-GTR-374. 2018

and central Idaho. The Central Rockies subregion includes 

west-central Montana and all lands west of the Continental 

Divide and north to Canada. The Eastern Rockies subregion includes the Rocky Mountain Front and southwestern 

Montana. The GYA includes all lands that have been officially designated as part of this high-profile area, including 

Yellowstone National Park, Grand Teton National Park, 

the southern end of the Gallatin National Forest and the 

Beaverhead-Deerlodge National Forest, the western side 

of the Custer National Forest, and parts of the Shoshone, 

Bridger-Teton, Caribou, and Targhee National Forests. 

Last, the Grassland area includes all lands east of the 

Eastern Rockies subregion boundary to the eastern border 

of the USFS Northern Region.

The main purpose of dividing the assessment area into 

five subregions was to restrict climate change projections, 

impacts, and adaptation options to a specific part of the 

Northern Rockies region. The five subregions shown in 

figure 6.1 were included for all authors to standardize the 

spatial scales of their sections, but some authors of this 

chapter chose to evaluate climate change impacts at the 

national forest or finer scale. As a result, this chapter does 

not include formal sections for each subregion. Instead, the 

authors tuned their material to the subregion if the data and 

information allowed.

Uncertainty

Uncertainty is an expression of the degree to which 

something is unknown. Uncertainty can result from a lack 

of information or from a disagreement about what is known 

or even knowable. Uncertainty can also result from known 

and unknown errors. It may have many types of sources, 

from quantifiable errors in data to ambiguously defined concepts or terms, or uncertain projections of human behavior. 

Uncertainty can therefore be represented by quantitative 

measures, such as a range of values, or by qualitative statements, such as assessment of the judgment of a team of 

experts. Uncertainty differs from variability; variability is 

the actual range of a value or ecosystem variable.

All the climate models (global circulation models or 

GCMs) that predict rapidly warming climates have a high 

degree of uncertainty (IPCC 2007). Although there is little 

debate that atmospheric carbon dioxide (CO2) is increasing 

and that this increase will cause major changes in climate 

(IPCC 2007), there is a great deal of uncertainty about the 

magnitude and rate of climate change (Roe and Baker 2007; 

Stainforth et al. 2005). This uncertainty will almost undoubtedly increase as climate projections are made at finer 

resolutions, for different geographic areas, and for longer 

time periods (Knutti and Sedlacek 2013). The range of possible projections of future climate from GCMs (an increase 

in global average annual temperature of anywhere from 2.9 

to 14.4 oF ) is much greater than the variability of climate 

over the past two or three centuries (Stainforth et al. 2005), 

and the variability across GCMs is greater than the variability in the climate projections of each model. Because it is 

impossible to know whether society will respond to climate 

change by employing technological innovations to minimize 

CO2 emissions or to mitigate its effects, most GCMs also 

simulate a suite of scenarios that capture a range of possible strategies to deal with climate change, introducing 

yet another source of uncertainty. Moreover, it is the high 

variability of climate extremes, not the gradual change of 

Figure 6.3—The MC2 vegetation 

types for the assessment 

area by the five geographic 

subregions. This map was 

created from an MC2 

modeling effort (see appendix 

6A).

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 133

average climate, that will drive most ecosystem responses to 

the climate-mitigated disturbance and plant dynamics, and 

these rare, extreme events are the most difficult to predict 

(Easterling et al. 2000).

Yet another source of uncertainty in attempting to predict 

ecosystem change is introduced when we try to predict how 

the Earth’s vegetation and ecosystems will respond to highly 

uncertain climate change (Araujo et al. 2005). Mechanistic 

ecological simulation of climate, vegetation, and disturbance 

dynamics across landscapes is still in its infancy (Keane 

and Finney 2003; Sklar and Costanza 1991; Walker 1994). 

Many current ecosystem simulation models are missing the 

important direct interactions of disturbance, hydrology, and 

land use with climate that will surely dictate effects on plant 

distributions (Notaro et al. 2007). Little is known about the 

interactions among climate, vegetation, and disturbance, and 

interactions among different disturbance regimes (fire and 

beetles, for example) could create novel landscape behaviors. It is also difficult to determine how the critical plant 

and animal life cycle processes of reproduction, growth, 

and mortality will respond to changing climate (Gworek et 

al. 2007; Ibáñez et al. 2007; Keane et al. 2001; Lambrecht 

et al. 2007). These modeling uncertainties greatly increase 

as projections are made further into the future and at finer 

spatial scales (Xu et al. 2009).

Managers must account for these uncertainties when 

using the information in this report in any land management plan or analysis. Sometimes there is less uncertainty 

in implementing conventional restoration designs than in designing restoration or treatment plans that attempt to account 

for climate change impacts. For some areas or resources, 

such as the restoration of western larch ecosystems, addressing climate change in management plans may require 

only minor changes to current management practices. In 

other situations, major changes to current treatment designs 

may be needed, such as in ponderosa pine ecosystems. 

All climate effects will be manifested in different ways on 

different landscapes, and as a result, there is no magic “one 

size fits all” prescription that can be adopted everywhere. 

The decision to modify management actions to include 

climate change effects must always include an assessment of 

the uncertainty of that modification and, most importantly, 

local conditions.

Climate Change Assessment Techniques

Anticipating ongoing rapid climate change, ecologists 

are attempting to project the effects of those changes on 

myriad ecosystem processes across various scales (Clark 

et al. 2001; Joyce et al. 2014; Schumacher et al. 2006). 

Using traditional ecological field methods to explore climate 

change response may be difficult because of the complex 

interactions among ecological processes, disturbance, and 

climate at multiple temporal and spatial scales (McKenzie et 

al. 2014). It would simply be too costly and time-intensive 

to sample at the large spatial scales and long timespans need 

to quantify vegetation response (Keane and Finney 2003).

In general, there are four techniques to assess and project 

the effects of climate change on vegetation and other resource concerns. The first is expert opinion, and it involves 

having experts in the fields of climate change, ecology, and 

vegetation dynamics qualitatively assess what will happen 

to vegetation under various climate change scenarios. Most 

of the papers about climate change effects on vegetation 

used in this report were written by experts who have evaluated future climate projections and used their experience to 

deduce how vegetation will respond to different climates. 

Information from these papers was included in this report, 

but expert opinions were used only when there was no other 

information from the other assessment techniques.

The second technique is field assessment, where extensive field sampling or remote sensing projects monitor 

vegetation change in response to changing climate. Field 

sampling involves establishing plots in networks across 

the landscape, detecting change between plot measurements, and correlating these changes to climate data. Van 

Mantgem and Stephenson (2007), for example, related 

high tree mortalities to climate change using a network of 

monitoring plots. Demography studies track individuals 

over time, rather than using periodic plot-level inventories, 

to fully understand the role of climate relative to other risk 

factors such as competition, variation in physiology and 

function, and vulnerability to insects and pathogens. Such 

demography datasets are rare (Iverson and McKenzie 2013), 

but one study has tracked more than 27,000 individuals of 

40 species for about a decade to address interactions over 

an area of the southeastern United States (Clark et al. 2011). 

The only demographic dataset available for the Northern 

Rockies region is the USFS Forest Inventory and Analysis 

(FIA) database. The extensive FIA dataset has been summarized to describe vegetation shifts due to climate change 

elsewhere (McNulty et al. 1994) but not in the Northern 

Rockies region. Although field assessment techniques are 

the most reliable and most useful, they are often intractable 

(see previous paragraphs) because of the large areas and 

long time periods needed to properly sample vegetation 

at the appropriate scales to detect changes as a result of 

climate.

The third method involves the use of statistical analysis 

to create empirical models that project climate change 

response. Most of the studies that project the habitat, range, 

or occupational shifts of Northern Rockies tree species from 

climate warming use species distribution models (SDMs) 

to project future geographic ranges (Hansen and Phillips 

2015; Iverson and Prasad 2002; Warwell et al. 2007). SDMs, 

also called bioclimatic envelope models, niche models, and 

species envelope models, are developed by linking current 

climate with the current distribution of a species of interest 

by means of advanced statistical modeling (Guisan and 

Zimmermann 2000; Watling et al. 2012). Then, using the 

statistical model, a future species distribution is computed 

using projected future climate data as inputs rather than 

the past climate. However, SDMs are inherently flawed for 

projecting future species distributions in that they relate past 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
134 USDA Forest Service RMRS-GTR-374. 2018

species occurrence to climate, resulting in predictions of 

potential species habitat, not species distribution (Iverson 

and McKenzie 2013). The projected potential habitat is only 

reflective of the distribution of species today and does not 

relate climate to historical distributions. One of the biggest 

limitations to this approach is that many studies have now 

found that most species distributions are not in equilibrium 

with climate, thereby causing SDMs to miss those areas 

conducive to occupation by the species but where the species 

is currently absent. Moritz and Agudo (2013), for example, 

found many species in the fossil record existed over a wider 

range of climates than is recorded today.

Another limitation of empirical models is that the critical 

ecological processes, such as pollination, cone production, 

seed dispersal, seed germination, seedling establishment, 

tree growth, mycorrhizae influences, competitive interactions, disturbance, mutualism, and mortality, as well as 

the many disturbance processes, are not represented in 

SDMs, yet these are the main processes that control species 

abundance and presence (Iverson and McKenzie 2013; 

Watling et al. 2012). Dullinger et al. (2012), for example, 

found that range shifts predicted by SDMs retracted by more 

than 40 percent when seed dispersal was included in the 

prediction process. Girardin et al. (2008) found that process 

models were much better at projecting climate change effects on tree growth because they accounted for changes in 

soil moisture and growing season. Moreover, the climates 

used to develop SDMs represent a very small slice of time 

(50–100 years) relative to the long time periods that existing 

trees, such as the long-lived whitebark pine (>1,000 years 

of age), have survived on the landscape today, so SDMs 

cannot capture the climate for all stages in the life cycle of 

today’s trees. Most mature trees used to evaluate species 

occurrence in statistical models may have lived for hundreds 

to thousands of years and continued to survive despite major 

changes in climate. Along those same lines, one of the major 

problems of SDM modeling is that there is no sense of how 

long it will take for a species to be eliminated from one site 

and effectively populate a new site; because migration is 

a slow process, the timing of SDM model results are often 

incompatible with management timeframes. In addition, 

SDMs assume that the current distribution of the species is 

a consequence of climate alone, yet we know that fire exclusion, exotic diseases, and management actions have also 

influenced species occurrence (Gustafson 2013; Iverson and 

McKenzie 2013). Therefore, it is difficult to have confidence 

in SDM projections for fine-scale applications; they are 

informative, but not prognostic, especially on the short time 

scales of decades and half-centuries required by land management. This is especially true when addressing the high 

uncertainty of the GCM-derived climate used by the SDMs.

The last and perhaps the most effective technique uses 

simulation modeling to assess climate-mediated vegetation 

responses (Gustafson 2013; Iverson and McKenzie 2013; 

McKenzie et al. 2014). Here, future projections of climate 

are used as inputs to simple-to-complex ecological models 

to simulate the climate change effects (Baker 1989; He et 

al. 2008; Merriam et al. 1992; Perry and Millington 2008). 

A variety of existing models simulate ecological change at 

broad (global, regional) and fine (ecosystem, stand, point) 

scales (Bugmann 2001; Cramer et al. 2001). However, 

landscape-scale (40–400 square miles) models are perhaps 

the most critical for predicting effects of climate change 

because this is a key scale at which most ecosystem processes and links are manifested and the scale at which most 

management decisions are made (Cushman et al. 2007; 

Littell et al. 2011; McKenzie et al. 2014). Finer-scale stand 

models cannot incorporate important exogenous disturbance regimes because of their limited spatial extent, and 

coarse-scale dynamic global vegetation models (DGVMs) 

are unable to simulate important plant-, species- and 

canopy-level competition and disturbance effects, such as 

successional shifts, community dynamics, and differential 

disturbance effects among species (McKenzie et al. 2014).

To realistically model species composition changes, a 

mechanistic, process-driven simulation approach might be 

preferable to emphasize those physical drivers of vegetation 

dynamics that are directly related to climate (Gustafson 

2013). However, mechanistic model design is often overly 

complex and therefore currently intractable because of 

(1) overly detailed parameterization of life histories and 

physiologies for all species, (2) high complexity of many 

interacting disturbance factors, and (3) necessarily highresolution modeling over large areas (Lawler et al. 2006). 

Dynamic global vegetation models, such as the MC2 model 

used in this report (see next subsection), operate at scales 

from regional (hundreds of miles) to global (degrees of 

latitude and longitude). Although DGVMs are valuable for 

projections of climate change across large domains, these 

models aggregate species into lifeforms or plant functional 

types (PFTs) using structural or functional attributes, which 

may be useless to local managers (Bachelet et al. 2003; 

Bonan 2008; Neilson et al. 2005). Most of these models 

project shifts to more drought-tolerant and disturbancetolerant species or PFTs for future climates. This general 

shift in vegetation may be offset by physiological changes 

induced by CO2 fertilization, as suggested by a DGVM 

(MC1) that links water use efficiency to CO2-simulated 

expansion of forests into areas where the climate is currently 

too dry (Bachelet et al. 2003). This issue deserves further 

study to resolve the extent and duration of such mitigating 

effects of CO2; projected effects could differ substantially 

depending on how relationships are modeled.

To be effective at realistically predicting climate change 

effects, ecosystem models must simulate disturbances, 

vegetation, and climate, and also their interactions across 

multiple scales (Purves and Pacala 2008). Yet few models 

simulate ecosystem processes with the mechanistic detail 

needed to realistically represent important interactions 

among landscape processes, vegetation dynamics, disturbance regimes, and climate (Keane et al. 2015b; Riggs et al. 

2015). Direct interactions between climate and vegetation, 

for example, may be more realistically represented by 

simulating daily carbon (photosynthesis, respiration), water 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 135

(evapotranspiration), and nutrient (nitrogen, phosphorus) 

dynamics at the plant level than by simulating vegetation 

development annually using state-and-transition modeling 

approaches (Keane et al. 2015a). A fully mechanistic approach, however, may be difficult for both conceptual and 

computational reasons, and some simulated processes may 

always require a stochastic or empirical approach (Falk et 

al. 2007; McKenzie et al. 2014).

We used output from the DGVM MC2 to standardize 

our evaluation of change and vegetation responses for 

the Northern Rockies region. Output from this model is 

presented in Appendix 6A, and this output was used by all 

authors in developing the material on future climate effects 

on vegetation and in the vulnerability assessment. We did 

not use MC2 simulated species projections in the following 

sections.

MC2 Model

MC2 is a new implementation of the MC1 DGVM, 

which was created to assess the impacts of global climate 

change on ecosystem structure and function at a wide 

range of spatial scales from landscape to global (Bachelet 

et al. 2001; Peterman et al. 2014). MC2 is short for “MC1 

version 2.” MC1 was produced by combining physiologically based biogeographic rules, originally defined in the 

Mapped Atmosphere-Plant-Soil System (MAPSS) model 

(Neilson 1995), with biogeochemical processes packaged 

in a modified version of CENTURY (Parton et al. 1987) 

and a new fire disturbance model, MCFIRE (Lenihan 

et al. 1998, 2003). The three linked modules simulate 

biogeography (lifeform interpreter and vegetation classifier), biogeochemistry, and fire. The main functions of the 

biogeographic module are to (1) predict lifeforms, that is, 

the composition of deciduous-evergreen tree and C3-C4 

grass lifeform mixtures; and (2) classify those lifeforms and 

their associated biomass into different vegetation classes 

using a climatologic rule base. The biogeochemical module 

simulates monthly carbon and nutrient dynamics for a given 

ecosystem. Aboveground and belowground processes are 

modeled in detail and include plant production, soil organic 

matter decomposition, and water and nutrient cycling. 

Parameterization of this module is based on the lifeform 

composition of the ecosystems, which is updated annually 

by the biogeographic module. The fire module simulates the 

occurrence, behavior, and effects of severe fire. Allometric 

equations, keyed to the lifeform composition supplied by 

the biogeographic module, are used to convert aboveground 

biomass to fuel classes. Fire effects, specifically plant mortality and live and dead biomass consumption, are estimated 

as a function of simulated fire behavior (fire spread and fire 

line intensity) and vegetation structure. Fire effects feed 

back to the biogeochemical module to adjust levels of various carbon and nutrient pools to alter vegetation structure 

(e.g., leaf area index levels and woody vs. grass-dominated 

vegetation).

The MC2 model simulations were generated by Tim 

Sheehan (Conservation Biology Institute). Inputs to 

the MC2 model include soil (depth, texture, and bulk 

density), annual average atmospheric CO2 concentration, and monthly average climate variables (monthly 

precipitation, mean vapor pressure, and means of daily 

maximum and minimum temperatures). Historical climate 

data (1895–2008) were obtained from the PRISM group 

(Daly et al. 2008) and were upscaled to 30-arc-second 

resolution (~0.23 square mile). Soils data were derived 

from STATSGO (Soil Conservation Service 1991) by 

Kern (1995, 2000) and were scaled to the resolution of 

the climate data. Future climate projections were available from various GCMs, and we chose the MIROC 3.2 

medres (Hasumi and Emori 2004) based on its relatively 

high overall ranking according to Mote and Salathé 

(2010). GCM future projections were downscaled to 0.23 

square mile using the delta or anomaly method (Fowler et 

al. 2007). Anomalies between future and mean monthly 

historical (1971–2000) values were calculated to project 

estimates for each climate variable and each future month 

across the study area. We evaluated model output based on 

two greenhouse gas emissions scenarios described in the 

IPCC Special Report on Emissions Scenarios (Nakićenović

et al. 2000): A1B and A2. Future projections based on 

the most recent generation of emissions scenarios, the 

Representative Concentration Pathways, were not available across the entire Northern Rockies region, but the two 

generations of models are relatively similar in their estimates of global temperature change and spatial patterns of 

temperature and precipitation change (Knutti and Sedláček 

2013).

To evaluate potential climate effects on vegetation 

assemblages and disturbance regimes and the interaction with land management, we evaluated a suite of 

vegetation-related and fire occurrence variables output by 

the MC2 model under historical (1971–2000) conditions 

and future projections for mid-century and end-of-century. 

Specifically, we compared past vegetation distributions 

across the Northern Rockies with fire suppression and 

without, and made similar comparisons for two future 

years, 2050 and 2100, under both the A1B and the A2 

emissions scenario (Appendix 6A). Aboveground processes were examined by comparing the amount of carbon 

in live and dead biomass for three time periods (historical, 2030–2050, 2080–2100) and with and without fire 

suppression (Appendix 6A). Potential evapotranspiration 

was also evaluated to compare possible changes in aridity 

(over similar timespans and land management measures). 

Finally, projected changes in fire disturbance were 

examined by comparing estimated fire rotation and the 

percentage of the Northern Rockies burned by time period 

and suppression management (Appendix 6A).

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
136 USDA Forest Service RMRS-GTR-374. 2018

Forest Vegetation 

Responses to Climate

In general, many scientists expect the effects of climate 

change on forest vegetation to be primarily driven by vegetation responses to shifts in disturbance regimes, and then 

secondarily, through direct effects of vegetation interactions 

with climate through shifts in regeneration, growth, and 

mortality processes at both individual plant and community 

scales (Dale et al. 2001; Flannigan et al. 2009; Temperli et 

al. 2013). Most of the expected climate changes are reduced 

precipitation and increased temperatures (see chapter 3), 

resulting in a reduction in water available to trees and understory plants. These effects will be highly variable across 

time, from year to year and day to day, and across space, 

as the footprint of the new climate is manifested at fine to 

coarse scales. Trees will respond to projected reduced water 

availability, higher temperatures, and changes in growing 

season in diverse manners, but because trees cannot pick up 

their roots and move, any changes in vegetation composition 

and structure will be the result of changes in both the life 

cycle processes and responses of a plant to disturbance. This 

section discusses some possible general responses of trees 

and forest vegetation to projected climates.

Individual Plant

The effects of climate on forest vegetation can occur 

as both direct and indirect effects. Direct effects are the 

immediate and long-term impacts of increased temperature 

and decreasing water availability on vegetation life cycle 

processes, as discussed in detail throughout this document. 

But indirect effects, such as changes to fire, insect, and disease regimes, may be more important and long-lasting than 

direct effects.

In short, there are several important modes of response 

of plants to changing climates (Joyce and Birdsey 2000). 

The first is changes in productivity; plant productivity may 

increase in the future because of increasing temperatures, 

longer growing seasons, more variable precipitation, and 

CO2 fertilization (Aston 2010; Joyce 1995). Increases and 

decreases in productivity are related to changes in cone 

crops, tree vigor, and tree defenses. The window of successful seedling establishment will change (Ibáñez et al. 2007); 

increasing drought and high temperatures may narrow the 

time for effective regeneration in low- elevation Northern 

Rockies forests and widen the window in high elevation 

forests. Climate may directly cause tree mortality due to 

temperature or moisture stress on trees; there have been 

increases in tree mortality around the world from increasing temperatures and drought (Allen et al. 2010; Williams 

et al. 2010). This of course is related to productivity, but 

not entirely. Extreme climate events, such as late growingseason frosts and high winds causing blowdowns, may 

increase because of the predicted increases in climate variability (Notaro 2008), and these events may cause mortality

events (Joyce et al. 2014). There will also be disruptions 

in phenology as climates change; many plants may sustain 

considerable damage or mortality as phenological cues and 

events are mistimed with new climates (e.g., flowering occurring during dry portions of the growing season) (Cayan 

et al. 2001). Another related mode is the genetic limitation 

of the species or tree to respond to climate change (Hamrick 

2004); specialists may become maladapted to new climates 

(St. Clair and Howe 2007). Last, plants can respond to 

climate-mediated changes in disturbance in myriad ways 

(Aitken et al. 2008). This section deals only with those 

causal mechanisms that drive direct climate responses; the 

indirect climate-mediated disturbances and responses are 

detailed in a later section.

Direct effects of temperature on plant growth may 

increase both photosynthesis and respiration (Waring and 

Running 1998). Plant photosynthesis rates increase with 

temperature up to an optimum and then decline thereafter, 

with the optimum being species-dependent. If projected 

temperatures exceed the photosynthetic optima for Northern 

Rockies tree species, such as those in the lower elevation 

forests, then plant growth might suffer. However, there 

may be many portions of the Northern Rockies where 

temperature increases probably will not exceed optima, 

and there may be photosynthetic gains, such as in montane 

and subalpine areas. This, of course, depends on whether 

sufficient water is available to support increased photosynthesis. Respiration also increases with temperature; thus, 

photosynthetic gains may be lost through growth and maintenance respiration. Respiration occurs even when stomata 

are closed, so high temperatures coupled with low water 

availability may result in high respirational losses with few 

photosynthetic gains (Ryan et al. 1995).

Increased atmospheric CO2 levels may also directly 

modify ecophysiological growth processes. Oxygen and 

CO2 compete for active Rubisco (primary enzyme used in 

photosynthesis) sites. Higher atmospheric CO2 concentrations may increase internal leaf CO2 concentrations, thereby 

ensuring CO2 reaches most of the Rubisco sites, which can 

result in photosynthetic increases of 2 to 250 percent depending on site and species (Ehleringer and Cerling 1995). 

Conifers may also have increased water use efficiency in 

future water-limited environments, and increased water use 

efficiency may compensate for decreases in water availability and increase growth rates in water-rich environments 

(Waring and Running 1998). Water use efficiency is the ratio 

of water used for plant metabolism (photosynthesis and respiration) to the water lost to transpiration. With higher CO2

concentrations in the atmosphere, the plant would obtain 

more CO2 during the time the stomata are open, resulting in 

less loss through transpiration. Leaf biomass is usually the 

first to increase as plants attempt to optimize photosynthesis 

by growing more photosynthetically active tissue (i.e., more 

leaf area). However, increases in leaf area index are often 

transitory and greatly dependent on available nitrogen and 

water. Increases in leaf area might also result in greater 

rainfall interception, higher snow collection, and greater 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 137

canopy evaporation. Increased atmospheric CO2 levels and 

increasing temperatures can also interact to increase growth. 

Photosynthesis has temperature optima that differ by tree 

species, and warmer temperatures might be closer to the 

new temperature optima, especially during the cooler early 

growing season, perhaps resulting in faster growth.

Another major direct effect of warming temperatures is 

longer growing seasons (Cayan et al. 2001; McKenzie et 

al. 2008); that is, increases in temperatures often lengthen 

growing seasons for forest plants. There are concerns that 

future climates are projected to be highly variable, and the 

coupling of highly variable daily weather with highly variable growing seasons may increase the chances that plants 

will be more susceptible to adverse weather during fragile 

phenological stages (Hanninen 1995). Warm conditions in 

the early spring, for example, might stimulate bud burst and 

early growth, only to have these expanding tissues frozen by 

subsequent frost events. Plant phenological cues may be disrupted or triggered inappropriately because of high weather 

variability, and while this variability might result in minor 

damage for mature individuals, it may be fatal for seedlings. 

This may be especially true in localized frost pockets and 

narrow valleys that accumulate cold air, resulting in frequent 

frost during the early growing season. Warmer temperatures 

may reduce and perhaps eliminate growing season frosts in 

mountain valleys, thereby allowing more frost-susceptible 

species, such as ponderosa pine and western larch, to exist 

in traditional lodgepole pine, subalpine fir (Abies lasiocarpa), and Engelmann spruce (Picea engelmannii) habitats. 

Chmura et al. (2011) note that increased temperatures 

may result in decreased winter chilling that could result 

in delayed bud burst, reduced flowering, and lower seed 

germination. Winter dormancy prevents trees from growth 

flushes during warm winter periods, and future climates may 

trigger changes in winter dormancy and subject trees to high 

mortality during those cold snaps after the winter warming.

Snowpack dynamics are also directly influenced by 

changes in temperature and precipitation and declining 

snowpacks are expected under future climates (Mote et al. 

2005). Most of the water used by Northern Rockies trees 

usually comes from snowmelt (Waring and Running 1998), 

so the amount and duration of snowpack have the potential 

to influence regeneration and growth patterns of forest 

communities throughout the region. Warming temperatures 

may cause earlier snowmelt, leading to an earlier start of 

the growing season. However, earlier snowmelt could also 

result in longer periods of low soil water during the remaining part of the growing season, effectively shortening the 

growing season. Earlier snowmelt may also result in greater 

competition for water across the plants and species that 

make up the complex plant communities of the Northern 

Rockies. Plants with roots in the topmost layers of the soil 

might be able to more effectively capture the rainfall that 

used to occur as snowfall. This may favor grasses and some 

forbs over shrubs and trees (Daly et al. 2000). The lower 

snowpack may allow longer growing seasons in those 

subalpine and upper subalpine communities where cold and 

snowpack duration govern tree regeneration and growth; 

production and regeneration are likely to increase with 

decreasing snowpacks, especially in those high mountain 

environments where water is rarely limiting.

An indirect effect of climate change will be the shift in 

distribution of microsites that facilitate tree regeneration 

(Jones 2013). While effects of climate change at coarser 

scales mostly relate to tree growth and mortality, changes 

to microsite conditions will be likely to govern tree regeneration (Petrie et al. 2016). Microsites suitable for tree 

regeneration must be addressed in a spatial and temporal 

context. For example, conditions for tree establishment may 

be suitable all year on small microsites of up to 1.2 square 

yards, whereas larger microsites may be conducive to regeneration only during the spring. Researchers in Washington 

State found that even with major changes in climate, there 

probably will be ample microsites that are suitable for 

regeneration of trees (Little et al. 1994). In the Northern 

Rockies, however, projected climate changes will probably result in smaller and more ephemeral microsites for 

regeneration. The size, distribution, and duration of suitable 

microsites potentially will vary more each year and most regeneration might occur only during “wave” years (i.e., years 

with favorable weather conditions) where plentiful suitable 

microsites are widely available for long periods of time (see 

next subsection).

Climate change can also indirectly affect vegetation by 

altering mycorrhizae dynamics (Amaranthus et al. 1999). 

Nearly all Northern Rockies conifers depend on mycorrhizae for enhanced water use and nutrient absorption. Even 

whitebark pine, a species that lives in areas with the highest 

precipitation in the Northern Rockies, has a mutualistic 

relationship with several species of fungi (Mohatt et al. 

2008). Many trees, particularly those in the seedling and 

sapling stages, need mycorrhizae to survive, especially 

in areas of periodically severe water shortage (Walker et 

al. 1995). The migration of Northern Rockies tree species 

to more favorable sites in future climates may be entirely 

governed by the ability of the mycorrhizae to also populate 

these areas to allow or facilitate tree species establishment 

(Lankau et al. 2015). Allison and Treseder (2008) found 

warming increased fungal interactions, but drying caused 

significant decreases. Without viable populations of mycorrhizae, tree species movement might be significantly slowed 

or stopped. New microsite conditions created by predicted 

future climates may be inhospitable to mycorrhizae, but so 

little is known about how these fungi shift with climate that 

it is difficult to evaluate how they will respond to climate 

change (Fitter et al. 2000). Mycorrhizae responses to 

climate change after increased fire may be more important; 

fire may reduce the fungi in some areas. This may be especially true if the large, severe fires projected for the future 

actually occur (Stephens et al. 2014). Severe fires may kill 

all trees in a large burn, thereby eliminating the host for 

the mycorrhizae, and perhaps eventually the mycorrhizae 

themselves. Establishment of trees into these burned areas 

can be delayed for long periods, decades or even centuries, 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
138 USDA Forest Service RMRS-GTR-374. 2018

as mycorrhizae and trees revegetate the area together 

(Schowalter et al. 1997).

Perhaps the most important future indirect ecological 

concern is the role of today’s forest conditions and how they 

affect the ability of tree species to respond to future climate 

change. Ample research has shown that past and future 

human land use activities often result in ecological impacts 

that overwhelm any direct or indirect climate change effects 

(Moritz and Agudo 2013). Nearly a hundred years of fire 

suppression activities have resulted in increased tree regeneration and denser forest canopies, coupled with increases in 

duff, litter, and down dead woody fuels (Arno 1998; Ferry et 

al. 1995; Keane et al. 2002). Trees in these dense forests are 

in greater competition for the little water that is available for 

growth. As a result, trees in many fire-excluded stands are 

stressed, making them highly susceptible to mortality from 

secondary stressors, such as insect and disease outbreaks 

(Anderegg et al. 2012; Wikars and Schimmel 2001), drought 

(Allen et al. 2010), and fire (Hood et al. 2007). Increased 

tree densities may also foster increased severity of subsequent disturbances, resulting in more individuals dying and 

creating larger patches of mortality.

Another ecological concern closely related to fire 

exclusion is the current climate-mediated decline in forest 

communities that have recently become established as a 

result of fire exclusion. Some forests in the region, including the limber pine (Pinus flexilis) communities along 

the Rocky Mountain front, became established during the 

fire exclusion era but may now be declining in some portions of the Northern Rockies region because of increased 

drought and nonative disease (white pine blister rust). Other 

Northern Rockies forests, such as ponderosa pine, now 

have atypical forest compositions and structures due to the 

century of fire exclusion, and these now denser forests are 

stressed from both overcrowding and climate change (Millar 

et al. 2007b). Had fires been allowed to burn, there would 

probably be significantly less mortality, from either climate 

change or disturbance, compared to what we are experiencing today, and the mortality levels probably would not be 

projected to be as high in the future (Holsinger et al. 2014). 

Moreover, there are areas in the region where trees have 

encroached into dry grasslands (Arno and Gruell 1986), 

montane meadows, and subalpine forb fields (Butler 1986). 

Now, due to increased temperatures and decreased water 

availability, some of these recently established trees are 

dying. Examples include the limber pine expansion along 

the Rocky Mountain front (Taylor and Sturdevant 1998), 

Douglas-fir encroachment into dry prairie (Arno and Gruell 

1986), and subalpine fir encroachment into GYA forb fields 

(Bigler et al. 2005). There is concern as to whether climate 

change represents a threat to these modern forest types, 

which were probably rare in the historical record. Does 

increased vulnerability in 100-year-old limber pine forests 

really constitute a management concern? Or is the increase 

in mortality expected because the forests established in wet 

periods of the fire exclusion era?

Many forest species in the Northern Rockies region may 

respond to direct climate warming and drying by expanding 

their range into new habitats. Migrating to a new site has 

historically been the primary response of plants to climate 

change (Huntley 1991). Migration requires that the species 

be able to quickly occupy newly desirable sites of the future 

before other species get there or to outcompete other species 

once they are there. Neilson et al. (2005) detail four basic 

components of migration (moving to a new site): fecundity, 

dispersal, establishment, and growth. To be successful in the 

future, a species must produce enough seeds or propagules 

(fecundity) that are easily dispersed to new sites (dispersal), 

and the seedlings that become established on these sites 

must be able to grow (establishment) so that they can also 

produce ample propagules that are then dispersed even 

further (growth). As Davis et al. (2005) note, however, the 

species also must have the genetic capacity to migrate to 

the new climate and survive into maturity. Adapting in situ 

can take many forms, such as reducing leaf area to minimize transpiration losses, or surviving perturbations in the 

new disturbance regimes created by climate change. Most 

Northern Rockies tree species are long-lived and genetically plastic so that they can survive the wide fluctuations 

of weather in the future, but the ability to handle both deep 

drought and modified disturbance regimes may be the most 

important factor dictating future distributions of forest species (Allen et al. 2010).

It is widely thought that warming climates will result in 

upward shifts in the elevational distribution of plant species. 

For example, Lenoir et al. (2008) found that some plant 

species have moved upward in elevation at a rate of 95 feet 

per decade. However, it is unclear whether such elevational 

shifts will drive long-term changes in forest communities, or if other predominating forces will outweigh these 

upward trends. For example, fire plays a dominant role in 

most Northern Rockies ecosystems, determining landscape 

structure and processes. Because even more wildfires are 

expected as climates change, effects of these large events 

may overwhelm any shifts in distributional ranges of forest species resulting from climate warming. Further, most 

plants in the region have slow migration rates, mostly 

because they are adapted to fire and as such rely more on 

regenerative organs (e.g., sprouting) than seed dispersal. 

Finally, implications of an upward elevational migration on 

forest communities need to be considered within a temporal 

and spatial context. That is, it may take a century or two 

for tree species to demonstrate significant elevational shifts 

due to long life cycles, old maturation ages, highly variable 

weather, and low dispersal potentials. The potential for tree 

species to migrate may be entirely different in each of the 

unique mountain ranges in the region, depending on a host 

of abiotic and biotic factors (e.g., precipitation levels, invasive species) and available colonizing species.

Most projections for the response of vegetation to climate 

shifts are for populations of species, not for communities. 

Little is known about how composition and abundance 

of biota will change at a community level in response to 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 139

climate shifts. Will new plant communities be dominated 

by generalist species that can exist across a wide variety of 

biophysical settings? Or will future communities be similar 

to historical analogs where fire-adapted species dominate? 

Will future communities be composed of species collections that were historically rare? Answers to these questions 

have important implications for future land management 

in that there is a great deal of synergy between plants and 

species in historical communities, such as interacting via 

root-grafting, sharing mycorrhizae, and relying on common 

pollinators, and future community composition may not 

have as many interactions. Moreover, future communities 

may not be as diverse because they may be dominated by a 

limited suite of species.

Climate change can affect important phases of the life 

cycle processes of plants: reproduction, regeneration, 

growth, and mortality. Moreover, it can affect plants at 

various scales from the needle to the tree to the forest, and 

over seconds to days to years to centuries (Eamus and Jarvis 

1989). The following subsections detail possible climate 

change effects by life cycle processes.

Reproduction

Cone and seed crops for many Northern Rockies trees 

could be both adversely and beneficially affected by climate 

change (Ibáñez et al. 2007; LaDeau and Clark 2001). Lowelevation xeric forests might have fewer and smaller cone 

crops because of increased stand density and water stress. 

Cone crops might also have a lower percentage of viable 

seed because of increased tree stress. The infrequency of 

cone crops coupled with low seed numbers may result in the 

lack of regeneration in recently burned areas, thereby causing a shift to nonforest vegetation.

The opposite might be true in higher, colder environments where increased temperatures will increase growing 

season length and thereby increase potential for more cone 

crops with greater number of seeds. Spruce-fir communities 

might produce so much seed that they may overwhelm regeneration of other conifers, especially after mixed-severity 

fires. Subalpine pine species such as whitebark and lodgepole pine have unique cone characteristics (whitebark pine 

cones facilitate seed dispersal by birds, whereas lodgepole 

pine cones may be serotinous and opened only by fire), so 

they may need to rely on disturbance for increased cone 

abundance.

An indirect result of the interaction of fire, vegetation, 

and climate is that as fire becomes frequent, some species, 

primarily trees, may be killed by fire before they reach 

reproductive maturity and may fail to set cones. Holsinger et 

al. (2014), for example, found that fires were projected to be 

so frequent in a western Montana watershed that lodgepole 

pine seedlings would be killed by fire before they were reproductively mature (around 15 years). Keane et al. (1990) 

found that ponderosa pine forests needed occasional interfire 

periods to be greater than 35 years to allow pine seedlings to 

grow above the lethal scorch height. If fire is too frequent, 

plants will not be able to grow to reproductive maturity or 

the reproductive organs might always be scorched by fire.

Climate warming and increased variability will also 

affect the phenology of cone crops, but effects may be minimal as plants adapt to new conditions. Some predict higher 

frost mortality of emerging cones due to an earlier onset of 

the growing season coupled with high daily temperature 

variability and lower flowering and seed germination 

because chilling requirements will not be met (Chmura et 

al. 2011). Others suggest that frequency and abundance of 

cone crops will be reduced in the future because of high 

tree stress from drought (Ibáñez et al. 2007). However, the 

increased productivity projected for many Northern Rockies 

forests may overwhelm minor losses from extreme weather 

events over the long run.

With changing climate, some tree species might be 

excluded from their current range because warmer temperatures may not allow chilling requirements for the seed 

(Shafer et al. 2001). The chilling requirement was a major 

evaluation factor in determining climate change vulnerability in Devine et al. (2012). Similarly, new climates may 

be asynchronous with the phenology of many tree species. 

Seed dispersal, for example, may occur at the driest and 

warmest times. Phenological keys may be out of sync in 

new climates, especially in a highly variable future, resulting in reduced flowering, growth, and reproduction. On the 

other hand, these phenological miscues may also occur in 

disturbance agents; highly variable weather may result in 

occasional deep frosts that kill beetle larvae, for example.

Regeneration

The life cycle phase in which most tree species are 

vulnerable to climate is regeneration (Solomon and West 

1993). Most tree species in the region reproduce by producing seeds that fall to the ground to germinate and grow into 

seedlings that then become mature trees. Microsite conditions needed for successful establishment are so demanding 

that seed germination and survival, especially for seeds that 

are wind dispersed, are rarely successful (Anderson and 

Winterton 1996). The successfully germinated seed produces a fragile radicle (embryonic root) that must penetrate 

the litter, then duff, then soil to put down a root system that 

will eventually feed the growing aboveground tissue. This 

penetration process demands moist soil conditions or the 

radicle and associated cotyledon (developing leaves) and 

hypocotyl (stem) will dry and die. To become a seedling, the 

seed requires suitable moisture conditions for long periods 

of time. Because few seeds become seedlings, many tree 

species often rely on high seed production to overcome mesic site conditions to ensure successful regeneration; of the 

millions of seed produced, perhaps at least some will land 

on moist microsites suitable for establishment. For dry xeric 

forests, most of the successful regeneration occurs in those 

wet years when soils are moist for a suitable time and solar 

insulation does not kill developing leaves and stems. These 

moist years are often called wave years, and the pulses of 

regeneration that occur in these years results in even-aged 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
140 USDA Forest Service RMRS-GTR-374. 2018

patches. Projected climate change is likely to decrease the 

frequency of these wave years, and on the driest sites, the 

frequency of wave years may be so low that no regeneration 

may occur, depending on the species. Planting on these 

newly dry sites may also be ineffective because of the short 

window of high soil moisture.

At the highest elevations, where the depth and duration 

of snow cover often governs tree regeneration, warming 

may enhance regeneration. Most years are moist enough for 

regeneration at high elevations, but snow remains on sites 

too long for successful regeneration in many years. With 

warming temperatures, snow is likely to melt earlier, giving 

more time for seedlings to survive and grow. Previous warm 

wave years in upper subalpine ecosystems are often dated 

by using seedling and sapling ages. Recent observations of 

invasions of subalpine meadows and balds by subalpine fir, 

alpine larch (Larix lyallii), and Engelmann spruce attest to a 

high number of sequential warm years over the last decade, 

which have facilitated regeneration in the high-mountain 

landscape (Butler 1986). Therefore, climate warming is 

expected to enhance regeneration at the subalpine and upper 

subalpine forest ecosystems.

Future climates and their high variability may also affect 

the ability of forest species to successfully germinate. Seed 

chilling requirements may not be met during mild winters, 

thereby reducing germination, and germination could be delayed until the driest parts of the growing season. Nitschke 

and Innes (2008) found that the chilling requirements were 

not being met for most low-elevation tree species in British 

Columbia. Soil temperatures may be too high, causing 

greater mortality of both germinants and established seedlings (Rochefort et al. 1994).

Climate change may also affect the dispersal properties 

of the reproductive propagules. Rodents that disperse seeds 

of ponderosa and western white pine, for example, may 

migrate or decline because of warmer, drier habitat conditions. Whitebark pine is dispersed by the Clark’s nutcracker 

(Nucifraga columbiana), which might shift habitats because 

of climate-mediated changes; nutcrackers usually nest in 

high elevation areas with ample snowpack (Tomback 1998), 

and these nesting habitats are predicted to decline in the 

future (Westerling et al. 2006). Longer and drier summers 

and falls also mean that seed dispersal may take place when 

the ground and litter are the driest and least hospitable for 

seed germination and establishment (Neilson et al. 2005). 

Human- and ungulate-mediated seed dispersal of exotic 

species could also be different in future climates; warmer, 

drier climates might reduce human and ungulate use to 

lower exotic seed dispersal. Changes in landscape spatial 

heterogeneity may also influence mechanisms of nonwind 

seed dispersal by shifting potential seed sources and changing patch sizes.

Growth and Mortality

Productivity potentially could increase in some 

Northern Rockies forests with warming climate, resulting 

in increased vigor and more resistance to stressors (Joyce 

1995). Worldwide, Lin et al. (2010) compute increases in 

biomass of more than 12 percent (20 percent in forests) with 

climate warming. However, Chmura et al. (2011) note that 

even with increased productivity, most forests will undergo 

reduced growth and survival as the climate interacts with the 

entire tree species life cycle.

Climate can adversely influence growth and mortality 

in many ways (Bugmann and Cramer 1998; Keane et al. 

2001). Projected decreases in water availability may result 

in shorter effective growing seasons and longer periods of 

continuous drought in the drier Northern Rockies forests 

(Williams et al. 2010). Longer drought might require 

Northern Rockies conifers to close stomata longer to conserve the little water available. Some xeric conifers, such 

as ponderosa pine and limber pine, have excellent stomatal 

control and are able to remain closed for long periods of 

time. Other conifers, such as Douglas-fir, have poor stomatal 

control, and this may drive leaf water potentials to extremely low values, which might result in intercellular cavitation, 

tissue damage, and perhaps plant mortality (Sala et al. 

2005). The projected increased temperatures will increase 

both maintenance and growth respiration, especially when 

stomata are closed. Increased respiration will require additional photosynthetic gains to counterbalance respiration 

losses, thus demanding even more water in a drier future. 

If photosynthetic production cannot exceed respiration demands, then the plant becomes stressed, thereby increasing 

the probability of mortality and susceptibility to insects and 

disease.

In the most mesic and montane ecosystems, a warming 

climate is likely to enhance growth and decrease mortality. 

Wu et al. (2011) found increases in plant growth for many 

forest and rangeland ecosystems with warming worldwide. 

Earlier growing seasons with ample moisture, such as 

that predicted for mesic montane forests in the Northern 

Rockies, will probably lead to increased productivity and 

greater growth. Although this increased biomass could result 

in additional foliar material to increase canopy bulk density 

and therefore result in higher crown fire potential, it could 

also result in higher growth rates for timber production and 

forage. This will be especially true in the higher mountain 

environments where cold temperatures, not moisture, limit 

tree growth. Longer, warmer growing seasons might result 

in higher productivities and greater biomass. The increased 

biomass will also increase competitive interactions between 

species, thereby favoring the more shade-tolerant individuals in the absence of disturbance. However, increased 

biomass could foster more-intense fires, and maybe 

greater insect and disease outbreaks, such that the more 

disturbance-tolerant species might ultimately inherit the 

landscape.

Genetics Concerns

It is widely accepted that climate limits species distributions. Climate is also a major environmental factor affecting 

plant phenotypes and a critical agent of natural selection, molding among-population genetic variation. Plant 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 141

adaptations to local environments have often developed a 

clinal or continuous response to abiotic and biotic factors 

such as temperature, frost-free periods, precipitation, fire, 

insects, and disease. More recently, ecotypic or a discontinuous response to environmental gradients is being recognized 

based on different soil or edaphic properties. The combination of clinal and ecotypic environmental gradients across 

the landscape enhances or limits plant survival and longterm persistence.

The hardiness of a plant is determined by its genetic 

background. Ecological genetics is a field of study investigating the genetic architecture, phenotypic plasticity 

(ability of an organism to change its phenotype in response 

to changes in the environment), and adaptive capacity of a 

species in the context of interactions among and between 

plant populations and environmental gradients. Ecological 

genetics and common garden studies are employed to study 

individual species. Well-designed common garden studies 

provide information on the adaptive strategy of a species 

(e.g., generalist, intermediate, or specialist; table 6.1) 

(Rehfeldt 1994). Processes that shape the genetic architecture of a species include natural selection, migration, genetic 

drift, and its mating system. Thus, the ability of plant populations to respond to climate change is influenced by the 

underlying patterns of genetic variation.

Molecular markers can reveal significant genetic diversity and divergence among populations associated with 

variation among populations (table 6.1). Past historical 

events affecting divergence among populations can be 

shaped by a variety of factors. Examples of abiotic factors 

are fire, glaciation (Hamrick 2004), and volcanic activity; 

for instance, range shifts east of the Cascades indicated 

ponderosa pine was replaced with lodgepole pine, and later 

repopulated by ponderosa pine after the Pleistocene (Hansen 

1942, 1947, 1949). Other factors include abiotic and biotic 

seed dispersal agents (for whitebark pine, limber pine, and 

ponderosa pine) (Lorenz and Sullivan 2009) and pollinator 

history. Plants that are insect-pollinated or rely on animaldispersed seed are more vulnerable to climate change 

because of the requirement for interaction with another 

organism.

Genetic diversity enables a species to adapt to changing 

environments, colonize new areas, occupy new ecological 

niches (USDA FS 2006), and produce substantial and robust 

progeny that persist in the long term (Ledig and Kitzmiller 

1992). The entire species does not adapt to environmental change over time, but populations within a species do. 

Species and populations of plants most vulnerable to climate 

change are rare species, genetic specialists, species with 

limited phenotypic plasticity, species or populations with 

low genetic variation, populations with low dispersal or 

colonization potential, populations at the trailing edge of 

climate change, populations at the upper elevational limit 

of their distribution, and populations threatened by habitat 

loss, fire, disease, or insects (Spittlehouse and Stewart 2004; 

St. Clair and Howe 2011). The underlying assumption about 

forest and rangeland species is that as climate continues to 

change, populations will become poorly adapted to their 

local climates, thus becoming stressed. But the ability of a 

species to respond to environmental change is closely tied 

to its adaptive strategy and the mechanisms that shape its 

genetic structure; therefore, this assumption may be false. 

Some species such as Douglas-fir, juniper (Juniperus spp.), 

and sagebrush (Artemisia spp.) may show range expansion 

in the future (Hansen and Phillips 2015).

Historical gene flow (seed and pollen movement) creates patterns of genetic differentiation that may allow some 

populations to be more predisposed to respond to climate 

change than others. Fragmentation is a critical issue for 

plant populations because isolation and the occurrence of a 

relatively few number of individuals can lead to inbreeding 

and loss of genetic diversity (Broadhurst et al. 2008; Potter 

et al. 2015). This field of study also informs research and 

management of the adaptive capacity and vulnerability to 

climate change (i.e., its direction and magnitude) of each 

species. Gene flow from adjacent populations that are more 

typical of future climates has the ability to increase the rate 

of adaptation by introducing genetic variation that is preadapted to warmer or drier climates (Aitken et al. 2008). A 

practical application of this field of study facilitates evaluating options for responding to environmental gradients and 

climate change, for example, choice of the appropriate 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

Table 6.1—Comparison of attributes characterizing a species’ adaptive strategy.a

Adaptive strategy

Attributes Specialist Generalist

Factor controlling phenotypic expression of adaptive traits Genotype Environment

Mechanisms for accommodating environmental heterogeneity Genetic variation Phenotypic 

plasticity

Range of environments where physiological processes function 

optimally Small Large

Slope of clines for adaptive traits Steep Flat

Partitioning of genetic variation in adaptive traits Largely among 

populations

Largely within 

populations

a Modified after Rehfeldt (1994).
142 USDA Forest Service RMRS-GTR-374. 2018

population or seed source to increase the likelihood of attaining a desired reforestation, restoration, or revegetation 

outcome.

Most species may not be able to adapt quickly enough 

to keep pace with projected migration rates of 328 to 3,280 

feet per year with climate change (Davis 1989; Malcolm et 

al. 2002). Davis and Shaw (2001) and Davis et al. (2005) 

suggest plant adaptation may be a more important factor in 

response to climate change due to the slow rates of plant 

migration impeded by population fragmentation as a result 

of land use patterns. Although Hamrick et al. (1992) and 

Hamrick (2004) suggest that long-lived species with high 

levels of genetic variation are well positioned for climate 

change, Etterson and Shaw (2001), Jump and Peñuelas 

(2005), and Parmesan (2006) argue that the ability of forest 

trees to adapt or migrate and follow climatic shifts may be 

restricted by their long lifespans, long generation intervals, 

and long juvenile phases.

Long-lived species often maintain high levels of genetic 

variation and gene flow, which facilitates their ability to 

evolve in response to changing climates (Hamrick 2004; 

Hamrick et al. 1992). Whitebark pine is an example of a 

long-lived species with high levels of genetic variation 

(Mahalovich and Hipkins 2011) and extensive gene flow 

(Richardson et al. 2002) attributed both to long-distance 

seed caching by Clark’s nutcracker and an outcrossed mating system involving wind pollination (Richardson et al. 

2002). Because plant populations are genetically adapted to 

local climates, the climatic tolerance of individual populations is often considerably narrower than the tolerance of the 

entire species.

Knowledge of the adaptation of Northern Rockies plant 

species is well documented for conifers (Rehfeldt 1994) but 

incomplete or lacking for other native plants. A species does 

not necessarily have only one adaptive strategy, though most 

do. Differences in adaptive strategy can be characterized by 

differences in variety (e.g., P. ponderosa var. ponderosa or 

Rocky Mountain ponderosa pine [P. ponderosa var. scopulorum]), elevation, and geography. For example, P. ponderosa

var. ponderosa is characterized as having an intermediate 

adaptive strategy; however, at high elevations (>5,000 feet), 

ponderosa pine has a specialist adaptive strategy. Rocky 

Mountain Douglas-fir (Pseudotsuga menziesii var. glauca) 

is characterized as having a specialist adaptive strategy; 

that is, its genetic variation is organized into numerous 

local populations, finely tuned to site-specific gradients. At 

higher elevations east of the Continental Divide, however, 

Douglas-fir has a generalist adaptive strategy; its genetic 

variation is organized into one or a few populations capable 

of surviving, growing, and reproducing over a broad range 

of environments (Rehfeldt 1989). Species possessing a generalist adaptive strategy are proposed to fare better than their 

intermediate and specialist counterparts in changing climate.

Patterns of adaptive variation for other native plants 

(e.g., shrubs, forbs, grasses, and sedges) are more complex, 

being both clinal and ecotypic. These species differ in 

lifeform (e.g., annual, biennial, and perennial) and ploidy 

level (number of copies of DNA, such as 4X, 6X, or 8X). 

The base ploidy level is 2X, where one copy of DNA is inherited on both the maternal and paternal sides. Grasses are 

hypothesized to be largely generalists and less vulnerable to 

climate change; however, ecotypic variation can overlay the 

generalist adaptive strategy. Forbs, which are largely insectpollinated, are more vulnerable to the changes in phenology 

and longer growing seasons expected with climate change.

Soil Responses

Each soil in the Northern Rockies region has an inherent ability to produce vegetation based on climate, parent 

material, topography, soil biology, and soil development 

(Armson 1977). Soil supports production of vegetation 

through interactions of nutrient cycling, soil hydrology, 

soil biology, physical support, and filtering (or buffering) 

(Attiwill and Leeper 1987). The quality and quantity of soil 

organic matter, the timing and amount of moisture, temperature, and acidity may all be altered by climate change, 

which will ultimately affect functional properties of soils 

and perhaps productivity (Bonan 2008).

Climate change affects the growth, mortality, and 

decomposition of vegetation, which in turn influence soil 

biology (Waring and Running 1998). Warmer temperatures, 

increased CO2, and longer growing season contribute to 

higher vegetative growth. Warmer temperatures, increased 

drought, and greater susceptibility to insects and disease 

may lead to increased mortality. Although higher temperatures will increase decomposition rates, the moisture 

required for decomposition may increase or decrease, leading to variable changes in decomposition rates (Davidson 

and Janssens 2006). Decomposition will increase with a 

combination of warmer temperature and higher moisture, 

whereas decomposition will decrease if summer droughts 

extend later (Rustad et al. 2000). Increased fire frequency 

and severity would generally reduce soil organic matter 

across large landscapes (Dooley and Treseder 2012).

Higher air temperatures will directly increase soil temperature. Increased vegetative cover would provide dense 

shade, thus decreasing soil temperature, whereas decreased 

vegetative cover would result in more heating at the soil surface. Dry soil, which is expected to be more common during 

future drought, would have wider temperature fluctuations 

than wet soil, which is buffered by the high heat capacity of 

water. In addition, if snow cover is lower but extreme cold 

periods continue to occur, soils will have lower minimum 

temperatures (Davidson and Janssens 2006).

The vulnerability of soils to future climate change is 

summarized in table 6.2. Effects will differ greatly, depending on local soil characteristics, the magnitude and trend of 

climate change, and vegetation response.

Stressors—Biotic and Abiotic Disturbances

A warming climate will rarely be the direct agent of 

change for Northern Rockies tree species and communities. 

Most of the changes in vegetation are likely to result from 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 143

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

Table 6.2—Assessment for soils to apply to vegetation concerns in the Northern Rockies.

Broad-scale climate 

change effect Ecosystem function

Current condition, 

existing stressors

Sensitivity to climatic 

variability and change

Expected effects 

of climate change

Risk assessment

Magnitude Likelihood

of effects of effects

Mainly changes in summer precipitationHigher summer temperatures

Available water (for vegetation)

Relative effective annual precipitation has been mapped for MT. Current condition has not been assessed for ID and ND. Existing stressors: extremes in water year (more frequent droughts), high stand densities.

Variable, depending on species, subregion and slope position. 

In western Northern Rockies, decreased precipitation is projected at low elevations; increased summer drought may result. High elevations may have increased precipitation. In eastern Northern Rockies, the higher interannual variation of precipitation would lead to years of increased drought. No trend projected for annual or seasonal precipitation.

High High

Increased atmospheric CO2

Nutrient cycling for vegetation production

Variable. Nitrogen is the most common nutrient deficiency, but other nutrients (phosphorus, potassium, boron) are also limiting. Existing stressors: severe fires, erosion.

Unknown.Potassium is easily lost on some metasediments, during whole-tree yarding.

Nitrogen, phosphorus, potassium and boron will become less available if soils become more acidic. Increased acidity of leachate would contribute to faster parent material decomposition, which would release inherent mineral nutrients in soil.

Unknown High

Soil temperature, moisture, and CO2

levels

Soil biota Most soils have healthy soil 

biota. Exceptions occur on abandoned roads and landings. Some stands have reduced biotic health from past management.Existing stressors: severe fires, erosion

Moderate Alteration of soil biota (fungi, 

microbes, nematodes) as well as the communities.

Variable Very high
144 USDA Forest Service RMRS-GTR-374. 2018

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region Broad-scale climate change effect Ecosystem function Current condition, existing stressors Sensitivity to climatic variability and change Expected effects of climate change Risk assessment Magnitude Likelihood of effects of effects Everything that contributes to increased fire and flood (e.g., more frequent high- intensity storms) Soil stability Little surface erosion occurs in the Northern Rockies Existing stressors: Most erosion occurs after severe wildfires or floods. Small amounts may occur in conjunction with roads, timber sales, grazing, and other land management activities. High—existing stressors will become more prevalent. Areas with decreased ground cover will be susceptible to increased surface erosion from wind and water. Moderate Very high Changes in spring and autumn precipitation (rain rather than snow, period of saturation longer) Slope stability Landslide prone areas have been mapped. Existing stressor: long period of saturation in some years. Variable Size and frequency of landslides will increase. Broad Very high Temperature, precipitation and CO2 concentrations Soil carbon storage and dynamics Soil is currently a major carbon storage pool and will continue to be a carbon sink as long as young stands continue to 

mature.Current stressors: periodic wildfires and insect outbreaks.

High in areas where disturbances become more prevalent.

If wildfire increases in frequency and extent as much as projected, this will maintain forests in younger age classes with less potential for carbon storage but higher carbon uptake.

Potentially 

high in 

drier forests

High in dry 

forests

Table 6.2(cont.)—Assessment for soils to apply to vegetation concerns in the Northern Rockies.
USDA Forest Service RMRS-GTR-374. 2018 145

responses to climate change-induced disturbance or to some 

combination of other climate-exacerbated stressors (Keane 

et al. 2015a). Climate change has marginally to severely 

altered disturbance regimes in the western United States 

(Liu et al. 2011). As we consider past climate variability and 

then add the projections in temperature and precipitation, 

there may be significant changes occurring across Northern 

Rockies forests because of a changing water balance and the 

role of disturbances such as wildfires, insects, and diseases. 

Whether it is invasive species (e.g., white pine blister rust; 

causal agent: Cronartium ribicola), drought, uncharacteristic 

wildfires, elevated native insect and disease levels, loss of 

historically fire-adapted tree species, unusually high forest 

densities compared to historical conditions, or some other 

combination of disturbance agents that serves to stress trees 

and forest ecosystems, recent research suggests that climate 

change is likely to further exacerbate those stressors and 

“stress complexes” (Iverson and McKenzie 2013). The following subsections present a short summary on four major 

classes of stressors important in the region. More-detailed 

summaries of disturbance responses and their interactions to 

climate change are presented in Chapter 8 of this report.

Wildland Fire

Wildland fire is pervasive throughout Northern Rockies 

forest ecosystems and was historically the dominant landscape disturbance in the region (Baker 2009; Barrows et 

al. 1977; Wellner 1970). Fire exclusion since the 1920s has 

disrupted annual occurrence, spatial extent, and cumulative 

area burned by wildfires. Climate change impacts to fire 

regimes are overlaid on a century of ecological changes to 

forest vegetation and fuels; thus, observed differences between current fire patterns and historical ones are a product 

of management legacies as well as anthropogenic changes to 

climate.

Wildland fire regimes, defined by fire frequency, annual 

area burned, severity, and pattern, are greatly influenced 

by variability in landscape environmental conditions 

including vegetation distribution, climate, weather, and 

topography (McKenzie et al. 2011). Climate and fuels are 

the two most important factors controlling patterns of fire 

within forest ecosystems. Climate controls the frequency of 

weather conditions that promote fire, whereas the amount 

and arrangement of fuels influence fire intensity and 

spread. These wildland fuels—the live and dead biomass 

that burns in fires—lose moisture and become flammable 

in the region’s typically warm and dry summers, during 

which there are ample sources of ignition from lightning 

strikes and humans. Therefore, the active fire season (period 

conducive to active burning) is in the summer, typically 

from late June through October, with shorter seasons at 

higher elevation sites where snowpack can persist well into 

July. Regionally, widespread fire years are correlated with 

drought (Heyerdahl et al. 2008). At large spatial scales, 

topography can influence the spatial pattern of fire spread. 

For example, in dissected mountainous areas, topographic 

features (e.g., barren slopes) can form barriers to fire spread 

(Grissino-Mayer et al. 2004), but where drainages are 

aligned with prevailing winds, topography can facilitate the 

spread of large fires (Sharples 2009).

Compositions and structures of forests in the Northern 

Rockies region are strongly determined by fire history. In 

general, fire regimes vary along environmental gradients, 

with fire frequency decreasing and fire severity increasing with elevation. For example, at the lowest and driest 

elevations, where forests are dominated by ponderosa pine, 

frequent surface fires historically consumed litter and dead 

wood and killed seedlings and smaller trees. Adaptive 

traits such as thick bark allowed mature ponderosa pines 

to survive many repeated fires over time and tree densities 

were kept low. Fire exclusion since the 1920s has increased 

surface fuel loads, tree densities, and ladder fuels, especially 

in low-elevation dry conifer forests (Schoennagel et al. 

2004). As a result, fires at the lowest and driest elevations 

may be larger and more intense, and may cause higher rates 

of tree mortality, than historical fire. But in mid- and higher 

elevation forests, where fires were historically infrequent 

because of relatively cold, wet conditions, fire exclusion has 

not affected the fire regimes (Romme and Despain 1989; 

Schoennagel et al. 2004). However, earlier onset of snowmelt, predicted to occur with changing regional climate, 

will reduce fuel moisture during fire season, making mid- to 

high-elevation forested systems flammable for longer periods of time (Miller et al. 2009). As these forested systems 

are not fuel-limited, fire occurrence and extent are likely to 

increase in the future (Littell et al. 2009, 2010; Westerling et 

al. 2006).

Insect Outbreaks

Regional insect activity and outbreaks are highly 

correlated with climate drivers, and potential climate 

change-induced insect activity will be an important influence on future forest composition and structure. The 

mountain pine beetle (Dendroctonus ponderosae) is an 

integral component of forest ecosystem processes because 

of its role in stand thinning and redistribution of resources 

and nutrients important for tree regeneration. It is also 

recognized as an aggressive and economically important 

forest insect responsible for tree mortality across large areas 

(Logan et al. 2003). Both bark beetle populations and their 

host trees are being influenced by changing climate. Many 

bark beetle life history traits that influence population success are temperature-dependent (Bentz and Jӧnsson 2015), 

and warming temperatures associated with climate change 

have directly influenced bark beetle-caused tree mortality in 

some areas of western North America (Safranyik et al. 2010; 

Weed et al. 2015). Host tree distribution across the Northern 

Rockies region, and tree vigor, which influences susceptibility to bark beetle attack (Chapman et al. 2012; Hart et 

al. 2013), will also be influenced as climate continues to 

change. Future bark beetle-caused tree mortality will therefore depend not only on the spatial distribution of live host 

trees and heterogeneity of future landscapes, as described in 

this chapter, but also on the ability of beetle populations and 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
146 USDA Forest Service RMRS-GTR-374. 2018

their associates to adapt to changing conditions when existing phenotypic plasticity is surpassed.

Pathogens

Forest diseases are found in all forest ecosystems of 

the Northern Rockies region. They are one of three major 

disturbance groups that affect ecosystem development and 

change, yet impacts of forest diseases on various resources 

and services in the region are difficult to estimate. The 

major groups of forest diseases in the region that affect 

ecosystems and ecosystem services are fungi and rusts 

(fungi that infect needles and causes damage and mortality, 

the most important being white pine blister rust), dwarf 

mistletoes (Arceuthobium spp.; a group of parasitic seed 

plants that are widespread across the region and that mostly 

cause reduced tree growth and productivity), root diseases (a 

major cause of growth loss and mortality), needle casts and 

blights (diseases that cause crown thinning and loss of lower 

branches), and abiotic diseases (damage to trees resulting 

from impacts of adverse environmental factors on tree 

physiology or structure).

Effects of climate changes on forest diseases are difficult 

to predict. Climate change can alter pathogens through 

direct effects on the development and survival of the 

pathogen, physiological changes in tree defenses, or indirect 

effects on the abundance of natural enemies, mutualists, and 

competitors (Ayres and Lombardero 2000). These dynamics 

are not well captured by GCMs because the ecology and impacts of pathogens are based on local site and environmental 

conditions. Epidemics also depend on local conditions for 

spread and infection to occur. Although models usually 

generate mean climatic conditions, it is often the extremes 

that have the greatest influence on pest conditions (Hepting 

1963), and these are also not well represented by GCMs. 

However, modeling efforts to date suggest that among the 

major Northern Rockies diseases, root disease is projected 

to cause the highest basal area loss as a percentage of total 

basal area in the region. Projected losses from root diseases 

ranged from zero percent on most national forests east of 

the Continental Divide to 15–19 percent on westside forests 

(Krist et al. 2014). Klopfenstein et al. (2009) used a subset 

of GCMs to predict how the geographic distribution of the 

climate envelope for Armillaria root rot (Armillaria solidipes, formerly A. ostoyae) and Douglas-fir could change 

in the interior northwestern United States. Their analysis 

suggests that Douglas-fir will have a considerably smaller 

geographic space that matches its current climate envelope 

and that this space will shift, while only minor changes are 

projected for A. solidipes. They suggest that areas where 

Douglas-fir is maladapted could increase, which could 

increase its susceptibility to Armillaria root rot. Climatemediated changes to forest tree diseases will be dictated 

by disease and host responses to new climates, and their 

interactions (Sturrock et al. 2010); the interactions among 

biotic diseases, abiotic stressors, and host status will drive 

future pathogen outbreaks. Predicted increases in temperature and drought will probably serve to increase pathogen 

populations in the future (Chakraborty et al. 2008). The 

role of pathogens as important disturbance agents is likely 

to increase in the future because they are able to migrate to 

new environments at a faster rate than trees.

Drought

Soil type and depth, aspect, and elevation all contribute 

to effective moisture availability for tree establishment 

and growth, producing patterns of forests in the Northern 

Rockies region. Additionally, the impact of stand condition 

on overall water balance and the effect of site and soil conditions on moisture availability are important to consider. 

The Natural Resources Conservation Service (NRCS) and 

the Natural Resource Information System of the Montana 

State Library have mapped the relative effective annual 

precipitation (REAP) for the State of Montana (Montana 

State Library and NRCS n.d.). REAP is an indicator of 

the amount of moisture available at a location, taking into 

account precipitation, slope and aspect, and soil properties. 

For example, two sites that receive the same amount of 

precipitation may have different effective precipitation due 

to unique soil and landform factors at each site. Depending 

on the geographic location within Montana and degree of 

slope, the actual precipitation for southerly aspects may be 

adjusted downward while northerly aspects may be adjusted 

upward.

Future climate change models indicate that the Northern 

Rockies region will have longer, drier summers and warmer 

conditions. Pioneer (seral) species such as ponderosa pine 

have the unique ability to establish on bare soil surfaces 

where high surface temperatures (>149 °F) exclude other 

species. One of the adaptations of these seral species is a 

capability for deep rooting, which allows the tree to find 

an adequate water supply and avoid extensive competition with shallow- and fibrous-rooted grasses and forbs. 

As the shade from these species limits sun-loving grasses 

and forbs, shade-tolerant tree species establish and grow. 

Grass and forb species usually have a shallower rooting 

characteristic that allows them to gather soil water from the 

nutrient-rich soil surface; in contrast, the overall rooting 

structure of shade-tolerant tree species in essence becomes 

much more competitive as succession progresses. In addition, the overall leaf surface area that develops over time 

on a given site increases. Lands dominated by grasses/

forbs or shrubs usually develop a maximum total leaf area 

of about 3.3 square feet per square foot of soil surface area. 

Forests can develop leaf areas in excess of 6.5 square feet 

per square foot of soil surface area. With increasing leaf area 

comes increased water transpiration, which can deplete the 

soil water storage capacity needed to keep trees hydrated 

throughout the summer. The additional canopy interception 

of rain and snow in dense forests, which directly evaporates 

into the atmosphere, further compounds this effect, reducing 

soil water recharge. The result is a water-stressed forest that 

not only becomes more susceptible to insects and disease, 

but also more prone to supporting severe wildfires because 

live fuel moisture is relatively low.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 147

Climate Change Assessments

This section contains the information that was used to 

assess vulnerability for all tree species, vegetation types, 

and resources of concern. There are four subsections for 

each item (e.g., tree species) to detail the (1) ecology, (2) 

disturbance interactions, (3) current and historical conditions, and (4) potential climate change responses. The 

first subsection presents important ecological information 

needed to understand how a species, type, or resource of 

concern might respond to future changes in climates, such 

as its drought- and shade-tolerance. The subsection on disturbance interactions contains information on those agents 

that affect the species, type, or concern, and important 

projections of how those disturbance agents might change 

in the future. Historical and current conditions are included 

as a subsection because any climate change response is 

greatly dependent on current status and past actions. Last, 

the anticipated climate change responses for the species, 

types, and concerns are included in perhaps the most important subsection. This material was ultimately the basis 

for evaluations of vulnerability or development of potential 

adaptation actions.

Most of the material in this section was taken from the 

literature, but substantial amounts of anecdotal and observational information were also included for context. However, 

due to imperfect knowledge across the evaluated entities 

and the high uncertainty in climate predictions and ecosystem responses, we admit that many of our projected climate 

change responses and resultant vulnerability assessments are 

based on our own professional experience. Moreover, some 

climate change response material may appear uneven across 

species, types, and concerns because detailed information is 

not available for all of them; for example, more information 

is available for timber tree species than nontimber species.

Tree Species

Most of the background information used in this subsection was synthesized from three primary sources. The 

Bollenbacher (2012) report presents characteristics of the 

major tree species of the Northern Rockies region, adapted 

from the autecological synthesis developed by Minore 

(1979). The commonly used silviculture reference edited 

by Burns and Honkala (1990) was used throughout, and the 

climate change report compiled by Devine et al. (2012) for 

the Pacific Northwest was also used for genetics and autecological information. Table 6.3 provides a general summary 

of ecological and genetic characteristics by tree species 

that will be important under future climate change. In this 

subsection, we attempted to integrate the genetic, morphological, ecological, and disturbance response characteristics 

summarized in table 6.3 to predict how a tree species would 

respond under future climate warming. We also integrated 

any material available in the literature to aid and support our 

predictions.

Discussion on climate change responses was synthesized 

from information in the literature and the MC2 modeling 

results (Appendix 6A) to evaluate the effects of climate 

change on important species, vegetation types, and resource 

concerns. This material forms the foundation for our vulnerability assessments and the adaptation strategies and tactics. 

Many of these climate change responses are based on the 

species characteristics and current ecosystem condition 

presented in this section.

The most astonishing finding in this section is that the 

literature is inconsistent on the response of tree species to 

future climate change. Results from SDM modeling are 

often, but not always, different from most other sources that 

include gap modeling, mechanistic ecosystem simulation, 

and field data summaries. As a result, we put less emphasis 

on the SDM results in our vulnerability assessment evaluations in Appendix 6B. Another finding is that the amount of 

climate change really matters. Most climate change studies 

predict few species changes after moderate warming (e.g., 

the B1, B2, A1B, and RCP 4.5 scenarios), but major species 

shifts under the most extreme emissions scenarios (e.g., the 

A1 and RCP 8.5 scenarios). Third, the timeframe used in the 

climate change study is also important. Management timeframes of 10 to 50 years are not long enough to effectively 

evaluate changes in fire, beetles, and tree growth. Ecosystem 

response to disturbance takes time, often two to five times 

the disturbance return interval. Last, climate change study 

results and subsequent ecosystem responses depend tremendously on the choice of GCMs used to simulate and quantify 

climate change. Some GCMs predict minor warming for 

the Northern Rockies region, while others predict major 

changes.

Based on a thorough review of the literature, we propose 

three basic modes of response to climate change for the major tree species of the region: modification, contraction, and 

expansion. First, the species could increase or decrease in 

productivity in situ within its current range due to increasing 

temperatures and adequate precipitation (acclimatization); 

for example, the majority of information seems to support 

the inference that most lands in the Northern Rockies region 

will increase in productivity (Aston 2010). Next, the species 

could die in those parts of its range where conditions will 

change enough to become inhospitable to that species (Allen 

et al. 2010) (contraction). Last, the species could migrate to 

areas that are more conducive to establishment and growth 

(Johnstone and Chapin 2003) (expansion). Any species can 

have multiple modes of response to climate change, and most 

species will respond to future climates via all three modes.

Application of these three modes to determine future species dynamics demands a thorough integration of variability 

and scale. For example, the ebb and flow of species migration demands a relatively long temporal scope to properly 

evaluate species range shifts (Prentice et al. 1991). A tree 

species could become established in a “new” environment 

made suitable by climate change, such as subalpine tree expansion into snow glades, but the great variability in climate 

may result in 1 year of drought or high snow that kills all 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
148 USDA Forest Service RMRS-GTR-374. 2018

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region Table 6.3—Summary of tree characteristics that indicate possible responses to future climate change. All fields are rated on a scale from one to five, with 1 generally indicating low levels and five generally indicating high levels of the variable (see specific notes below). Species Distributiona Tolerancesb Genetics Mycorrhizal dependencef Insect and disease exposureg Seed dissemination strategyh Shade Drought Fire Diversityc Geographic differentiationd Strategye Limber pine 1 1 5 2 3 3 I 4 4 5,4 Ponderosa pine–var. scopulorum 3 2 4 4 3 2 I 3 2 3,4 Ponderosa pine-var. ponderosa 3 2 4 5 3 2 I,S 3 4 3,4 Douglas-fir 4 4 4 4 2 2 S,G 3 3 3 Western larch 2 2 2 5 3 2 I 2 2 3 Western white pine 1 2 2 5 3 3 G 2 4 3,4 Aspen 2 1 4 1 5 2 G 2 3 3,2 Grand fir 2 4 2 2 2 2 G 2 4 3 Western redcedar 2 5 5 2 1 2 S 1 2 3 Western hemlock 2 5 5 2 2 2 S 2 2 3 Lodgepole pine 4 2 3 3 4 2 S 3 4 6 Whitebark pine 3 3 2 3 4 3 G 3 4 5 Subalpine fir 4 4 4 1 3 2 I 2 3 3 Engelmann spruce 3 4 4 2 3 2 I 2 2 3 Mountain hemlock 1 4 5 1 2 2 S 2 2 3 Alpine larch 1 1 5 1 2 3 S 3 1 3 Green ash 2 1 2 1 2 3 G 4 1 3

Cottonwood 2 1 4 3 3 3 G 3 2 1

a Distribution of 1 indicates narrow distribution in the Northern Rockies, while distribution of 5 indicates wide distribution.b Shade, drought, and fire tolerance of 1 indicates high intolerance, while 5 indicates high tolerance.c Genetic diversity of 1 indicates low diversity and 5 indicates high diversity.d Geographic differentiation of 1 indicates low genetic differentiation (narrow seed zones) and 5 indicates wide differentiation (large seed zones).e Genetic adaptive strategy of G indicates a generalist species (grows under wide range of conditions), I indicates an intermediate species (grows over a moderate range of conditions), and S 

indicates a specialist species (grows under a narrow range of conditions) (from Scott et al. 2013).

f Mycorrhizal dependence of 1 indicates that the species is not dependent on mycorrhizae, while 5 indicates that the species is highly dependent on mycorrhizae.g Insect/disease exposure of 1 indicates that the species is not susceptible to many damaging agents, while 5 indicates that the species is highly susceptible to insects and disease.h Seed dissemination is the primary means of seed dispersal where 1-water, 2-sprouts, 3-wind/gravity, 4-rodent, 5-bird, 6-serotinous.
USDA Forest Service RMRS-GTR-374. 2018 149

established seedlings. Conversely, 1 year of drought could 

kill many individuals in the grassland-woodland ecotone, 

but several wet years in a row might facilitate reestablishment of tree species into the high mortality zone. Further, 

the rate of climate change shifts will be governed by disturbance, not competition, so disturbance adaptations will be 

more important than climatic niches. Management actions, 

such as fire exclusion, may facilitate species expansion into 

areas that will eventually burn, causing extensive mortality.

All of the climate change response evaluations in this 

chapter have a high level of uncertainty; they are essentially 

best guesses from a wide variety of resource specialists and 

a review of the literature. The following information may 

provide a starting place, a possible prioritization, or assistance in addressing climate change in forest plans, but it 

is in no way accurate enough to provide valid predictions of 

what will happen in the future.

Limber Pine

Autecology

Limber pine (Pinus flexilis) is a shade-intolerant, early 

seral to pioneer species in the Northern Rockies (Steele 

1990). Its seeds are dispersed by rodents, but more importantly, by a bird (Clark’s nutcracker) that will cache limber 

pine seed anywhere there is microsite pattern that it uses 

for finding the seed (Lanner 1980; Lanner and Vander Wall 

1980). Limber pine has difficulty in competing with other 

encroaching species on more productive mesic sites and is 

often succeeded by Douglas-fir and subalpine fir. There is 

often little to no reproduction once tree densities are below 

10 trees per acre, mostly because of the lack of an effective 

pollination cloud, and those seeds that are produced have 

increased likelihood of inbreeding. Moreover, a minimum 

of 10 cone-bearing trees per acre is needed for dispersal by 

Clark’s nutcracker (McKinney et al. 2009). This tree species 

is very slow growing but long-lived, and some of the oldest 

trees in the region are limber pine.

Limber pine is a puzzling species in the context of 

ecosystem land management. It occupies xeric sites across 

a wide range of elevations (2,600 to 8,900 feet in elevation) 

in the Northern Rockies region that are often marginal for 

timber production (Jackson et al. 2010). Historically, it was 

often found on the margins between grasslands and forest 

ecosystems at the lower treeline on fire refugia (Steele 

1990). Because limber pine is easily killed by fire, the species was mostly found in fire-protected cove sites where fire 

was rare and of low severity, such as rocky outcrops, barren 

areas, and moist north slopes (Steele 1990). In these lower 

treeline areas, limber pine is often associated with Douglasfir, Rocky Mountain ponderosa pine, and quaking aspen 

(Populus tremuloides). On upland montane sites, it can 

often be found on limestone substrates and droughty soils, 

but in these areas it is associated with many other Northern 

Rockies conifers, especially lodgepole pine, subalpine fir, 

and Engelmann spruce (Langor 2007; Steele 1990). Limber 

pine seedlings are poor competitors with grass, but do well 

on rocky substrates and in shrub environments.

Limber pine is very tolerant of drought and can establish 

and grow in some of the most arid environments in the 

Northern Rockies region (Steele 1990) (table 6.3). It is 

associated with both ectomycorrhizae and arbuscular mycorrhizae that facilitate its ability to exist in extremely dry 

environments. Seedlings are very drought tolerant but have 

a low tolerance to competition, especially from herbaceous 

plants.

Genetically, limber pine has high outcrossing rates with 

average genetic diversity and average population differentiation (Devine et al. 2012). The fundamental and realized 

niche for limber pine is very broad in the region, indicating 

that this species has a generalist adaptive strategy with wide 

phenotypic plasticity.

Disturbance Interactions

As mentioned, the thin bark and low foliage of limber 

pine make the species highly susceptible to damage from 

wildland fire. Limber pine is also highly susceptible to white 

pine blister rust, and many communities suffer high mortality when the disease infects trees in a new region (Smith 

et al. 2013). Limber pine also facilitates the expansion 

of currant (Ribes spp.; an alternate host for the pathogen 

Cronartium ribicola) into traditional grasslands (Baumeister 

and Callaway 2006), thus increasing rust infections and 

mortality.

Other insects and pathogens are also impacting limber 

pine, but at a severity much lower than C. ribicola. Some 

researchers have detected mortality from mountain pine 

beetle in parts of the limber pine range (Jackson et al. 2010). 

Others have noted that limber pine stands on mesic sites 

may have severe dwarf mistletoe infections that could result 

in mortality levels similar to those observed from white pine 

blister rust. Porcupine (Erethizon dorsatum) damage is also 

prevalent east of the Continental Divide.

Historical and Current Conditions

With fire exclusion, limber pine has expanded its range 

from fire-protected cove sites into areas where it was historically restricted by frequent fires (Arno and Gruell 1983; 

Brown and Schoettle 2008). As a result of the diminished 

fire activity and active nutcracker caching, limber pine has 

expanded into grass and shrub rangelands, and this expansion has also allowed other species to inhabit historically 

nonforest areas (Jackson et al. 2010). Evidence suggests 

that limber pine can facilitate the establishment of other 

forest species, especially Douglas-fir, in rangeland settings 

(Baumeister and Callaway 2006). As a result, limber pine 

in the Northern Rockies region is currently occupying 

areas that were traditionally grasslands, and it is difficult to 

determine if this is inside or outside the range of variability 

of this ecosystem.

Ironically, the newly established limber pine forests 

throughout the Northern Rockies region are undergoing 

dramatic declines due to white pine blister rust, mountain 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
150 USDA Forest Service RMRS-GTR-374. 2018

pine beetle, and wind-caused red belt (Jackson et al. 2010; 

Langor 2007; Taylor and Sturdevant 1998). Increasing 

fires are also burning some of the stands that have become 

established since 1910. There is some white pine blister rust 

resistance in the species, but it is low, perhaps lower than 1 

in 100 individuals (Steele 1990).

Climate Change Responses

Some anticipate that warming temperatures on the east 

side of the region, along with increasing but more-variable 

precipitation, especially during the growing season, and 

waning snowpack will result in increased growth in many 

limber pine communities (Aston 2010). Increases in vigor 

are usually accompanied by larger cone crops, higher seed 

viability, greater number of seeds per cone, wider seed 

dispersal, and greater resistance to disease. Increased seed 

dispersal includes denser caching by birds and mammals, 

and probably more distant caching by Clark’s nutcracker. 

Increases in vigor might also extend to competitors of 

limber pine, so there could be increased competition from 

wind-dispersed conifers, especially on the more mesic portions of the limber pine range.

Warm temperatures, even with increased precipitation, 

could also result in drier conditions, especially for seed 

germination and seedling growth. Even if more seeds are 

cached by mammals and birds, the subsequent establishment of seedlings from the unclaimed caches might be 

low because of longer drought seasons and hotter ground 

temperatures. Any dispersal of limber pine seed to new 

areas, especially nonforested stands, might have limited 

regeneration success because of the lack of ectomycorrhizal 

associations and increased competition from grasses and 

dense shrubs (Coop and Schoettle 2009).

Disturbance interactions with warming climates are 

likely to be important to future limber pine dynamics. 

Increasing fire frequency and intensity may result in the 

burning of more limber pine stands, causing higher mortality (Coop and Schoettle 2009). Increased fire may stem the 

encroachment of limber pine into grasslands in areas where 

grazing is low. Warmer, drier conditions may also reduce 

blister rust infection by disrupting the blister rust cycle, especially during the late summer when Ribes species-to-pine 

infection occurs, and there may be fewer wave years where 

temperature and humidity are optimal for pine infection 

by white pine blister rust. Where precipitation is projected 

to increase, such as in the eastern portions of the Northern 

Rockies region, there may be higher rates of blister rust and 

dwarf mistletoe infection, which may cause higher limber 

pine mortality. Continued fire exclusion could enhance establishment of currant under mature limber pines and result 

in even greater white pine blister rust infection and mortality. Warmer temperatures also favor expansion of alternate 

host species such as currant, lousewort (Pedicularis spp.) 

and Indian paintbrush (Castilleja spp.) (Keane et al. 2015a).

Limber pine has an intermediate genetic adaptive strategy 

under changing climates largely driven by timing of pollen 

cloud dispersal (elevational effect) and seed dispersal by 

birds (Feldman et al. 1999). The species is highly adapted 

to populating the increasing burned areas projected for the 

future because of mammal- and corvid-mediated dispersal 

(Lanner and Vander Wall 1980). If future fires are larger 

and more severe, there may be less competition from other 

competing conifers, especially in the eastern portions of the 

Northern Rockies region along the timber-grassland ecotone. Limber pine has moderate genetic variation (capacity) 

in blister rust resistance, but major gene resistance to blister 

rust has not been identified in several studies of interior 

populations. There is probably little to no opportunity to 

hybridize with western white pine due to non-overlapping 

species distributions, and it will probably not hybridize with 

whitebark pine because the two species overlap only on 

limestone substrates. There is a high risk of loss of disjunct 

and isolated populations due to genetic drift, ineffective pollen cloud, and limited substrate availability.

Given all available information, limber pine responses to 

future climates may be minor and governed mostly by wildland fire and white pine blister rust. If fires increase, limber 

pine forests, some of which are already declining from 

rust, will suffer major declines, especially where they have 

encroached as a result of fire exclusion. Given its minor role 

in the Northern Rockies region prior to European settlement, 

we consider this species to be at most moderately vulnerable 

to climate change based on its high tolerance to drought 

and ability to populate severe environments, but high susceptibility to the introduced white pine blister rust and fire 

damage may put this species in peril.

Ponderosa Pine

Autecology

Ponderosa pine (Pinus ponderosa) shows distinct geographic variation over its range. The ponderosa variety (P. 

ponderosa var. ponderosa) ranges from the Fraser River 

drainage of southern British Columbia south through 

Washington and Oregon and into northern California (Oliver 

and Ryker 1990). In the Northern Rockies, it extends from 

the Canadian border to the central part of Montana on the 

west side of the Continental Divide. Rocky Mountain ponderosa pine (P. ponderosa var. scopulorum) extends east of 

the Continental Divide to North Dakota and South Dakota 

and south into Wyoming and farther. Within the wide range 

of both ponderosa pine variants, it is absent from several areas, including a large portion of southwestern Montana. This 

may be due to the lack of rainfall in the summer months, 

which prevents establishment except at higher elevations; 

however, it is also limited by the shorter growing season at 

these elevations.

In most of western Montana and Idaho, the upper 

elevational limit of the ponderosa variety is around 4,900 

feet, depending on latitude (Pfister et al. 1977). Moisture 

is the factor most often limiting growth, especially in the 

summer. Seasonal rainfall deficiency is evident from July 

and August precipitation (Fowells and Kirk 1945; Tarrant 

1953). The distribution of ponderosa pine on drier sites is 

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USDA Forest Service RMRS-GTR-374. 2018 151

closely related to supply of available soil moisture, which is 

closely related to soil texture and depth. Low temperatures, 

however, may dictate the success of ponderosa pine regeneration; seedlings of the species are highly susceptible to 

frost damage and the occurrence of frosts often excludes the 

pine from low valley settings, especially in frost pockets and 

cold air drainages (Shearer and Schmidt 1970).

Ponderosa pine is a shade-intolerant, drought-adapted 

species of the low-elevation dry forests of the Northern 

Rockies (Minore 1979) (table 6.3). It can be a climax species at the lower elevational limits of Northern Rockies 

coniferous forests, or a seral species in the higher elevation 

mesic forests, especially the Pacific variety. In dry climax 

forests, there is generally a mosaic of small even-aged 

groups. As a seral species, it is often associated with 

Douglas-fir, lodgepole pine, grand fir, and, in the northwestern Northern Rockies, western larch. Ponderosa pine is 

mostly intolerant of shade, but it is generally more tolerant 

than western larch and less tolerant than grand fir and western white pine. Although it reaches its greatest site indices 

on the mesic grand fir, western redcedar, and western 

hemlock sites (Cooper et al. 1991), it is rapidly replaced by 

a suite of more shade-tolerant competitors.

Ponderosa pine is a “drought avoider,” meaning it tolerates dry soil conditions by efficiently closing stomata to 

avoid water loss and xylem cavitation and stay alive during 

deep droughts (Sala et al. 2005) (table 6.3). This allows the 

species to tolerate intense drought better than its associates, 

specifically Douglas-fir, which is a “drought tolerator” 

and able to obtain water at lower moisture conditions. 

Although drought tolerators may be able to obtain water 

at lower moisture conditions, they may attempt to draw 

groundwater at such low soil water potentials that they experience extreme xylem cavitation, which may cause death. 

Ponderosa pine has been associated with several species of 

ectomycorrhizae, giving it a high capacity to survive in dry 

environments.

Cone crop periodicity varies greatly with ponderosa 

pine; observations indicate it is a poor seeder west of the 

Continental Divide and a fair seeder east of the divide. 

Throughout the region, natural regeneration is sporadic; it is 

best when there is a heavy seed crop followed by favorable 

weather during the next growing season (Heidmann 1983; 

Shearer and Schmidt 1970). Potter et al. (2015) performed 

molecular work that indicates that Rocky Mountain ponderosa pine is one of the most inbred conifers in the Northern 

Rockies, and its vulnerability could be further compromised 

with limited gene flow between populations. With cone crop 

periodicity or masting events that occur only every 7 to 

10 years, increasing natural regeneration problems may be 

developing on the east side of the Continental Divide. Soil 

texture, plant competition, and seedbed conditions have the 

greatest effect on seedling survival. Moisture stress reduces 

seed germination and limits seedling survival and growth. 

Competing vegetation deters seedlings. As mentioned, 

young seedlings (<36 days old) are susceptible to cold night 

temperatures and deep frosts, and occasionally the pine trees 

suffer winter desiccation in drying winds. Older seedlings 

(>110 days) can often withstand higher temperatures than 

Douglas-fir, grand fir, and Engelmann spruce, making it 

likely they will be more successful under future climates.

Ponderosa pine has a moderate potential for outcrossing with a high outcrossing rate. It has average genetic 

variation, but is weakly differentiated geographically. 

Although it has a strong population differentiation, it may be 

considered to be intermediate in adaptive strategy because 

both individuals and populations may be suited to diverse 

environments. There are steep clines (ecotypes or forms of 

species that exhibit gradual phenotypic and genetic differences over a geographic area as a result of environmental 

heterogeneity) in elevation, but gentle clines in latitude and 

longitude. There is high genetic variation between eastside 

and westside ponderosa pine in growth, survival, needle 

length, seasonal pattern of root growth, and ability to germinate under moisture stress (Oliver and Ryker 1990).

Disturbance Interactions

Fires have a profound effect on ponderosa pine where 

competing tree species are considerably less fire tolerant; this 

allows ponderosa pine to maintain dominance over large areas (Arno 1988; Steele et al. 1986). Fires historically allowed 

ponderosa pine to maintain its dominance across most of the 

low elevation savannas by killing competitors. Ponderosa 

pine has a great capacity to survive fire, better than nearly all 

of its competitors (Ryan and Reinhardt 1988).

There are about 108 species of insects that attack westside ponderosa pine and over 59 species that attack eastside 

ponderosa pine. The most damaging of the tree-killing 

insects are several species of Dendroctonus (Oliver and 

Ryker 1990). Among bark beetles, Ips species are second in 

destructiveness only to Dendroctonus. Ips are present naturally in all stands, where they usually breed in slash. Dwarf 

mistletoe is the most widespread disease on ponderosa pine 

but is rarely fatal in the region. Western pine shoot borer 

(Eucosma sonomana) is also a concern in the future.

Historical and Current Conditions

Ponderosa pine forests have been undergoing a severe 

decline due to the combination of logging and fire exclusion. Large pine trees in open pine savannas were harvested 

from nearly all but the most remote, inaccessible, or protected areas in the Northern Rockies region. Wildland fires 

have been excluded from remaining pine forests, causing 

advanced succession that was most rapid in the mesic habitat types (Arno 1988; Gruell et al. 1982). This has resulted 

in dense forests with overstories of stressed ponderosa pine 

and dense understories of its shade-tolerant competitors, 

most commonly Douglas-fir. There are often buildups of 

duff and litter, and an atypical accumulation of down dead 

woody fuels on the soil surface. The dense crowns, coupled 

with high surface fuel loadings, ensure that when these 

forests are burned by wildfires, the damage from the fire will 

be severe with high tree mortality, deep soil heating, high 

fuel consumption, and abundant smoke (Keane et al. 2002).

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
152 USDA Forest Service RMRS-GTR-374. 2018

Climate Change Responses

We expect ponderosa pine in the Northern Rockies 

region to handle increasing temperatures and deeper, 

longer droughts with only moderate difficulty. Its ability 

as a “drought avoider” to close stomata when soil water 

potential is low makes it the only forest species besides 

juniper to maintain its presence in many low elevation settings (Stout and Sala 2003). Morales et al. (2015) projected 

an 11-percent increase in the range of ponderosa pine in the 

western United States, and Nitschke and Innes (2008), using 

a gap modeling approach, projected the replacement of dry 

Douglas-fir dominated communities of British Columbia 

with ponderosa pine. Hansen et al. (2001) projected an expansion of ponderosa pine across the western United States 

and specifically in the Pacific Northwest, when most other 

tree species ranges were retracting in area. Rocky Mountain 

ponderosa pine is more intermediate in adaptive strategy 

than the ponderosa variety; it therefore has a high phenotypic plasticity and is better adapted to drought (table 6.3).

However, declining precipitation and variable spatial and 

temporal rainfall patterns may cause declines in ponderosa 

pine regeneration and range contractions, except in the 

eastern portions of the Northern Rockies region, where 

precipitation is expected to increase. Crimmins et al. (2011) 

estimated that ponderosa pine environments may rise more 

than 2,300 feet in elevation by 2050 in its range. Similarly, 

Gray and Hamann (2013) estimated ponderosa pine might 

move more than 1,600 feet northward and almost 1,000 

feet higher in elevation in the Northern Rockies by 2050. 

However, Franklin et al. (1991) projected future forests of 

ponderosa pine will cover about a third of its current range 

in landscapes of the eastern Cascades, and Bell et al. (2014) 

projected losses of more than 60 percent of its range by 

2090.

Increases in mountain pine beetle outbreaks, advancing 

competition resulting from fire exclusion, western pine 

shoot borer occurrence, and increases in fire severity and 

intensity will dictate the future of ponderosa pine in the 

Northern Rockies. If fires are too frequent, established 

regeneration will never grow above the lethal scorch 

height, and mature individuals will not become established. 

Increasing fire severity and occurrence could also eliminate 

many of the Northern Rockies relict ponderosa pine trees 

that provide the critical seed sources for populating future 

burns.

Douglas-fir

Autecology

Douglas-fir (Pseudotsuga menziesii) has been a major 

component of forests of western North American since 

the mid-Pleistocene era (Hermann and Lavender 1990). 

Only Rocky Mountain Douglas-fir (P. menziesii var. 

glauca) is found in the Northern Rockies. The range of 

this variety extends from central British Columbia through 

the Rocky Mountains into central Mexico. The range is 

fairly continuous in northern Idaho, western Montana, and 

northwestern Wyoming, with several outlying areas in eastcentral Montana and Wyoming. In the Northern Rockies, 

Douglas-fir grows in areas with maritime influence and 

mild climate in all seasons except a dry period in July and 

August. In the central Rocky Mountains, the winters are 

long and severe, and summers are hot and in some parts 

very dry. West of the Continental Divide in the region, the 

rainfall may be evenly divided between winter and summer. 

The altitudinal distribution of Douglas-fir increases from 

north to south, due to the effect of climate on the distribution. The limiting factors are temperature in the northern 

part of the range and moisture to the south. Thus, Douglasfir prefers southerly slopes in the northern part of its range, 

and northerly exposures in the southern part of its range 

(Pfister et al. 1977).

Douglas-fir in the Northern Rockies grows in pure 

stands on dry, cold sites, in both an even- and uneven-aged 

condition (Hermann and Lavender 1990). On other sites, 

the associated species are dependent on the climate, and by 

proxy, elevation and region. Montane low-elevation mesic 

Douglas-fir is often associated with western larch, western 

white pine, grand fir, western redcedar, and western hemlock, whereas on low-elevation xeric sites, Douglas-fir is 

associated with ponderosa pine, juniper, and quaking aspen. 

At upper elevational limits, the species is often found with 

lodgepole pine, subalpine fir, and Engelmann spruce. In rare 

cases it is found at the highest elevations associated with 

mountain hemlock (Tsuga mertensiana), whitebark pine, 

and alpine larch. Most of the Northern Rockies Douglas-fir 

forests are found on droughty sites, and the species is often 

associated with ponderosa pine; Douglas-fir is often the 

primary climax species whenever it is found with ponderosa 

pine (Keane 1985; Ryker and Losensky 1983; Steele and 

Geier-Hayers 1989). Again, proportion of other species 

growing with Douglas-fir varies widely depending on 

aspect, elevation, soil type, and history, particularly fire history, of the area.

Regeneration is most successful where Douglas-fir is 

seral, especially in the area of strong maritime influence in 

northern Idaho and western Montana, where it is associated 

with more montane species (e.g., grand fir, western redcedar, and western larch). Regeneration is poor where it has 

attained climax status in the cool, dry habitats (Ryker and 

Losensky 1983). Seedling growth the first year is relatively 

slow, limited generally by moisture, which triggers initiation 

of dormancy in midsummer. Competing vegetation may promote the establishment of a variety of seedlings by reducing 

temperature stress, but may inhibit seedling growth by competing strongly for moisture; this is most pronounced in the 

southern portion of the range. In the Rocky Mountains, it is 

a seral species in moist habitats and climax in the warmer, 

drier areas of its range.

In the interior portion of its Northern Rockies range, 

Douglas-fir ranks intermediate in shade tolerance, being 

more tolerant than western larch, ponderosa pine, lodgepole 

pine, and aspen (table 6.3). Old-growth Douglas-fir shows a 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 153

wide range of age classes, indicating it became established 

over long periods after major fires. It is gradually replaced 

by more tolerant western hemlock, western redcedar, and 

true fir on mesic montane sites. Douglas-fir tolerates drought 

better than nearly all of its competitors except for ponderosa 

pine. The species is a “drought tolerator” in that it keeps stomata open to extract soil water at extremely low soil water 

potentials, thereby subjecting it to potential xylem cavitation 

and potential death (Sala et al. 2005; Stout and Sala 2003).

The species exhibits a great deal of genetic differentiation, which is strongly associated with geographic or 

topographic features (Rehfeldt 1978). The pattern of genetic 

variation in growth and phenological traits among clines has 

been observed along north-south, east-west, and elevational 

transects. There is evidence of low genetic variation within 

local regions. For example, in southern Oregon, seed collected on the more xeric southerly aspects grew slower, 

set bud earlier, and had larger roots compared to seedlings 

grown from north-facing slopes. Seedlings from seed 

sources on southerly aspects have adaptive characteristics 

for a shorter growing season and drier soils and may survive 

under drought stress better than seedlings from seed sources 

on northerly aspects.

Disturbance Interactions

Douglas-fir has a great capacity to survive fire because of 

its thick corky bark and its deep main roots. The capacity of 

the species to form adventitious roots is another adaptation 

that has enabled Douglas-fir to survive fire. However, young 

Douglas-fir have thin bark and low height to live crown, 

greatly increasing mortality from fire (Ryan and Reinhardt 

1988). Ponderosa pine and western larch have better ability 

to survive fire across all life stages, so on sites with frequent 

fires where Douglas-fir is associated with other species, its 

cover is usually kept low by fire (Agee 1991). However, 

on cold, dry sites where the species is the indicated climax, 

frequent fire may create Douglas-fir savannas, especially 

east of the Continental Divide, such as in the high valleys of 

southwestern Montana.

Douglas-fir is subject to serious damage from a variety of agents that may increase under future climates 

(Hermann and Lavender 1990). Western spruce budworm 

(Choristoneura occidentalis) and Douglas-fir tussock moth 

(Orgyia pseudotsugata) are the most important insects 

affecting Douglas-fir. Both insects attack trees of all ages 

periodically throughout the range of interior Douglas-fir, 

often resulting in severe defoliation of stands. Many 

Douglas-fir stands in the central Northern Rockies are currently devastated by budworm and beetle. The Douglas-fir 

beetle (Dendroctonus pseudotsugae) is a destructive insect 

pest in old-growth stands of coastal and interior Douglas-fir. 

Armillaria and annosus (Heterobasidion annosum) root 

diseases may intensify in infection rate and widen in distribution to cause high tree mortality. Annosus root disease 

is particularly lethal in Douglas-fir (Hagle 2003). Of the 

many heart rot fungi (>300 species) attacking Douglasfir, the most damaging and widespread is red ring rot 

(Porodaedalea pini Murrill, 1905). Knots and scars resulting from fire, lightning, and falling trees are the main paths 

of infection. Losses from this heart rot far exceed those 

from any other decay. Other important heart rot fungi in the 

Northern Rockies are Fomitopsis officinalis, F. cajanderi, 

and Phaeolus schweinitzii.

Historical and Current Conditions

Historical frequent wildland fires kept Douglas-fir from 

becoming established on those dry sites where it was associated with ponderosa pine as frequent fires favored ponderosa 

pine establishment. It often became established after long 

interfire periods, such as during the Little Ice Age, and 

easily attained dominance if fire frequency was decreased. 

However, in the more montane portions of the Northern 

Rockies range of the species, Douglas-fir was often one of 

the major dominants, as it was a major competitor under 

historical mixed-severity fire regimes (Arno et al. 2000).

Today, though, cumulative effects of the fire exclusion 

era coupled with logging have allowed Douglas-fir to 

become the dominant species across its range, especially 

where it successionally replaced the historically dominant 

ponderosa pine forests (Arno and Gruell 1983; Arno et 

al. 2000; Gruell et al. 1982). As a result, we have seen an 

expansion of Douglas-fir into areas where fire was frequent 

historically, but also an increase in the density of the forests 

where it is associated with more mesic species. This has 

created large, contiguous areas where canopy fuels have increased and become denser, and surface fuels that have been 

converted from grass and shrubs to heavy down dead woody 

fuels (Keane et al. 2002). These conditions predispose many 

Douglas-fir forests to severe future fires. Moreover, these 

dense stand conditions have contributed to decreased vigor 

that predisposes the species to western spruce budworm and 

Douglas-fir beetle outbreaks. Many Douglas-fir forests of 

southwestern and central Montana are currently experiencing high budworm and beetle mortality.

Climate Change Responses

Several studies suggest that Douglas-fir will respond positively with future changes in climate. Morales et al. (2015) 

projected a 7-percent increase in the range of the species in 

the western United States by 2060. Soulé and Knapp (2013) 

found almost doubled radial growth in Douglas-fir in the 

western portions of the Northern Rockies in the latter half 

of the 20th century, but they attributed some of this increase 

to other factors such as CO2 fertilization. Rose and Burton 

(2009), using SDMs, projected that Douglas-fir forests in 

British Columbia will nearly triple in area by 2080, while 

Franklin et al. (1991) project no net loss of Douglas-fir habitat in the future in the Pacific Northwest. Using a gap model, 

Cumming and Burton (1996) also projected little change in 

the Douglas-fir zone in British Columbia.

However, it is likely that myriad factors will contribute 

to decline of Douglas-fir forests in some parts of the 

Northern Rockies region in the future. USFS Northern 

Region survey results from 2014 show significant increases 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
154 USDA Forest Service RMRS-GTR-374. 2018

in Douglas-fir 3-year seedling mortality (about 50 percent) 

due to increasing drought, high temperatures, and severe 

conditions, presumably related to climate change. In addition, Kemp (2015) found that natural postfire regeneration 

of Douglas-fir on sites that burned in 2000 and 2007 varied 

across gradients in elevation, aspect, and burn severity, 

and findings indicated that Douglas-fir regeneration was 

significantly reduced with increased heat loading (incoming solar radiation derived from site latitude, aspect, and 

slope). Specifically, the probability of successful Douglas-fir 

regeneration was lower at lower elevation sites and on sites 

with higher heat load (steep, southwest aspects). Likewise, 

Douglas-fir abundance was lower on sites at lower elevations and with higher heat loads.

On dry lower elevation southerly aspects in the southern 

Northern Rockies, ponderosa pine is likely to cope with 

moisture deficits better than Douglas-fir because it does not 

have the high potential for xylem cavitation (Stout and Sala 

2003). In addition, Douglas-fir might not have the genetic 

potential to rapidly migrate to more-suitable sites (Aitken et 

al. 2008). More importantly, a suite of insects and diseases 

is increasing in Northern Rockies Douglas-fir forests and 

creating heavy mortality, especially in southwestern portions 

of the region. The spruce budworm is killing many Douglasfir stands in southwestern Montana, while the Douglas-fir 

bark beetle is attacking stands in other parts of the Northern 

Region. Nitschke and Innes (2008) predict major losses of 

Douglas-fir from parts of British Columbia because of hot, 

dry conditions, while Shafer et al. (2001) predict major transitions in Douglas-fir in most of the U.S. Pacific Northwest, 

and raise some major concerns that the climate might be too 

warm to meet the chilling requirements of Douglas-fir seed. 

Using SDM approaches, Gray and Hamann (2013) projected 

that Douglas-fir will migrate more than 1,300 feet north and 

560 feet upwards in elevation by 2050, and Bell et al. (2014) 

projected losses of more than 40 percent of its range in the 

Northern Rockies by 2090.

Increases in wildland fires, coupled with adverse effects 

of the fire exclusion era in Northern Rockies forests, could 

also present some problems for Douglas-fir. Increasing fire 

danger in Douglas-fir stands with high canopy and surface 

fuels may promote wildland fires that kill the majority 

of Douglas-fir, even the most mature individuals. If fires 

increase in the future, regardless of fire suppression efforts, 

they may be so frequent that Douglas-fir seedlings cannot 

become established and grow to maturity.

Douglas-fir might be one of the Northern Rockies tree 

species most limited in range expansion because of its 

limited genetic diversity and structure (St. Clair and Howe 

2007). The species has a specialist genetic adaptive strategy 

at low-to-mid elevations and a more generalist strategy 

at higher elevations. With warming temperatures and a 

possible decrease in summer moisture conditions, Rocky 

Mountain Douglas-fir may contract from the driest portions 

of its range. Current natural regeneration failures may be 

exacerbated by reduced seed sources owing to large wildfires and hot and dry microclimate conditions, especially 

on southerly exposures at lower elevations. On moist sites 

(mixed mesic forest), mortality from root disease may increase because of increasing moisture stress.

Western Larch

Autecology

Western larch (Larix occidentalis) grows in the Upper 

Columbia River basin of northwestern Montana, and in 

northern and west-central Idaho (Schmidt and Shearer 

1990). It grows in the relatively moist-cool climatic zone. 

Limiting factors to western larch are low temperatures at the 

upper elevations, and lack of moisture at the lower extremes 

(Habeck 1990). Western larch grows on a wide variety 

of soils; most soils suitable for growth are deep and well 

drained. It is commonly found on valley bottoms, benches, 

and northeast-facing mountain slopes (Schmidt et al. 1976).

Western larch is adapted to extreme environmental 

heterogeneity, from maritime climates in the west and northwest to more continental climates, as westerly air masses 

move across the Bitterroot and Cabinet Mountains (Rehfeldt 

1982). At comparable elevations, the frost-free period in 

western Montana is 30 days shorter than in northern Idaho, 

and thus populations from western Montana are better 

adapted genetically to short frost-free growing seasons as 

compared to similar elevations in northern Idaho (Rehfeldt 

1995a). Moreover, as elevation increases and frost-free 

periods decrease, growth potential decreases. Early fall cold 

snaps are a major temperature factor affecting seedling and 

sapling survival, before resting buds have had an opportunity to fully lignify (Rehfeldt 1995b). Drought is another 

major climatic factor affecting mid-to-late season survival 

(Schmidt and Shearer1995). It is most likely to affect seedlings under heavy shade because of the heavy moisture use 

by the overstory and other competing vegetation. Zhang and 

Marshall (1994) and Zhang et al. (1994) characterize western larch as having low water use efficiency, as compared to 

other conifers in the Northern Rockies. Plants that have low 

water use efficiency tend to be larger in stature and produce 

more biomass, which may be trait-limiting in future warmer 

and more arid or variable-precipitation climates. The lower 

water use efficiency of western larch may explain its absence on xeric sites (Gower et al. 1995).

Cone and seed production in western larch is most 

prolific at ages older than 30 to 50 years, with seed crops 

occurring every 14 years in Idaho and every 10 years in 

Montana (Owens 2008). Good cone crops may occur in successive years if conditions are favorable (Owens and Molder 

1979). Spring frosts often reduce pollen, cone, and seed 

production in western larch, leading to sporadic seed years. 

Cone production is higher in stands that have larger crowns, 

such as stands that have been thinned (Shearer 1976). 

Cooler, wetter springs favor foliar diseases such as larch 

needle cast (Meria larisis); successive years of infection 

lead to reductions in available cone crops. Cone maturation 

follows elevation gradients; cones at lower elevations are 

generally mature in mid-August and seed dispersal occurs 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 155

into September. As such, seed may be available for dispersal 

during the fire season.

Seed germinates best on seedbeds exposed by burning 

or mechanical scarification (Antos and Shearer 1980; 

Beaufait et al. 1977; Schmidt 1969; Shearer 1976). 

Western larch seedlings survive poorly on undisturbed 

litter, humus, or sod or with heavy root competition; seedlings germinated on duff do not often survive (Beaufait 

et al. 1977). High solar irradiation is the most important 

physical factor affecting seedling survival (Shearer 1976). 

Southerly and west exposures are generally too severe for 

western larch seedlings to establish, particularly in drier 

sites at the lower elevational limits of its range. In the 

middle and northern portion of its ranges, western larch 

grows well on all exposures. Young seedlings grow fast on 

desirable sites. Only lodgepole pine is similar to western 

larch in seedling growth; Douglas-fir grows at about half 

the rate, and spruce and subalpine fir at about one-quarter 

the rate, of western larch. Site productivity has the most 

effect on height growth on western larch sites (Shearer 

1976).

Western larch is a long-lived early seral species. It is a 

fast-growing species with tall, open crowns, making the 

species easily able to outgrow all of its competitors on the 

more mesic sites (Milner 1992). It is also the most shadeintolerant conifer in the Northern Rockies (Minore 1979) 

(table 6.3); it can tolerate partial shading only in the seedling stage. Western larch is replaced through succession by 

all other conifers except for ponderosa pine. Western larch 

is moderately drought tolerant and can survive seasonal 

drought, but performs poorly when droughts last more than 

1 or 2 years. Douglas-fir is the most common associate, but 

others include ponderosa pine on lower drier sites; western 

hemlock, western redcedar, and western white pine on 

moist sites; and Engelmann spruce, subalpine fir, lodgepole 

pine, and mountain hemlock on cool, moist subalpine sites 

(Schmidt and Shearer 1990). It has been associated with 

mycorrhizal fungi in many portions of the region (Harvey 

et al. 1978).

Western larch has average genetic diversity with a weak 

population differentiation. Its low levels of differentiation 

indicate that it is more a generalist than a specialist. The 

species has a moderate outcrossing rate, and the patterns 

of genetic variation are mostly dominated by latitude and 

longitude. Populations need to be separated by 1,640 feet 

in elevation before genetic differentiation is expected.

Disturbance Interactions

Wildland fire is essential to the maintenance of western 

larch populations. Western larch depends on the opencanopy high light environments, and mineral soil seedbeds 

created by fire for successful, widespread regeneration 

(Schmidt et al. 1976). Western larch has unique characteristics that allow it to survive intense fire, including the 

thickest bark (Ryan and Reinhardt 1988), high crowns with 

high moisture contents, deep roots, and epicormic branch 

production (Fiedler and Lloyd 1995; Harrington 2012; 

Schmidt and Shearer 1995; Schmidt et al. 1976). Western 

larch is one of the few Northern Rockies tree species that 

has adapted to survive mixed-severity to stand-replacement fires (Hopkins et al. 2013; Marcoux et al. 2015). Tall 

surviving western larch can produce copious seeds that are 

wind dispersed across large burns to land on mineral soil 

seedbeds and ensure continued western larch domination 

(Stoehr 2000). However, if serotinous mature lodgepole 

pine trees occur with western larch, regeneration may be 

dominated by both species (e.g., Hopkins et al. 2013). 

Because western larch grows quicker and taller, it often 

outcompetes lodgepole pine to attain dominance (Pfister et 

al. 1977).

Western dwarf mistletoe (Arceuthobium campylopodum) is perhaps the most damaging disease-causing parasite 

of western larch (Schmidt and Shearer 1990). It can 

infect seedlings as young as 3 to 7 years old and continue 

throughout the life of the tree. In addition to killing treetops, reducing seed viability, creating conditions suitable 

for entry of other diseases and insects, and causing burls, 

brashness, and some mortality, it decreases height and diameter growth. Three other important diseases are found in 

western larch: needlecast caused by Hypodermella laricis, 

brown trunk rot, and red ring rot. The exotic larch casebearer (Coleophora laricella) and native western spruce 

budworm are currently the two most serious insect pests 

of western larch (Schmidt and Fellin 1973). However, neither of these agents causes substantial mortality. Western 

larch is susceptible to defoliation as a result of the recent 

western spruce budworm outbreak (DeNitto 2013). Larch 

needle cast results in substantial needle damage in cooler, 

moister springs. Episodic outbreaks of larch casebearer 

and western spruce budworm can also cause defoliation 

severe enough to reduce the current year’s tree growth 

(Schmidt et al. 1976) and disrupt cone production.

Historical and Current Conditions

The more mesic montane western portions of the region 

were often dominated by extensive western larch forests 

that had regenerated after major fires. The species dominated northwestern Montana and was the major timber 

species for most of the 1950s to 1970s. However, extensive 

logging as early as 1908 on USFS lands (Arno 2010) removed many of the large tall western larch that could have 

survived fire and cast seed across the landscape, and effective fire exclusion has removed the burned, mineral soil 

seedbeds where western larch can regenerate. Continued 

fire exclusion has served to increase forest density and 

surface fuel loads so that future fires may be more severe.

Climate Change Responses

Western larch is a species that is highly susceptible to 

climate warming. Most climate change studies predict 

major losses of western larch throughout the Northern 

Rockies. Morales et al. (2015) used an SDM approach to 

project a 41-percent loss of western larch in its range in 

the western United States, and Aston (2010) reports major 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
156 USDA Forest Service RMRS-GTR-374. 2018

expected declines in western larch habitat in the northern 

Rocky Mountains. Rehfeldt and Jaquish (2010) projected 

major shifts in western larch in the western portions of the 

Northern Rockies, with major losses in Montana and gains 

in Idaho. Nitschke and Innes (2008) used gap modeling 

approaches to simulate major losses in western larch in 

most of British Columbia. Coops and Waring (2011) suggest that western larch may invade many areas vacated 

by lodgepole pine in the future in some portions of the 

Pacific Northwest. In addition, considering western larch 

associates, competitive interactions among species may 

play a critical role in the current and projected distribution 

of tree species such as western larch (Thuiller et al. 2008). 

Although temperature-precipitation interactions tend to set 

the limits where species can successfully compete, temperature alone seems primarily responsible for adaptation 

of populations within those limits (Rehfeldt et al. 2014).

Western larch will probably migrate to more northerly 

and higher areas in the Northern Rockies, but not without 

surviving major fires. Gray and Hamann (2013) estimated 

western larch could migrate more than 500 miles northward and more than 1,100 feet higher in elevation in the 

region by 2050. Western larch has the ability to quickly 

take advantage of changes in productivity of colder sites, 

providing these areas burn and the western larch survives 

the fires to provide sufficient seed for colonization. 

Increasing fires may serve to return western larch to the 

Northern Rockies landscape, but managers may need to 

provide substantial assistance by planting western larch 

in burned areas before other species become established. 

Continued fire exclusion will probably result in major 

declines of western larch in the western portions of the 

region because increased competition will reduce vigor, 

making the trees more susceptible to damaging agents; 

surface and canopy fuel buildups will be so great that 

many relic western larch trees will die in uncharacteristically severe fires (Arno et al. 1997; Davis 1980; Norum 

1974). Keane et al. (1996) simulated major declines in the 

future for western larch under fire exclusion and moderate 

climate change, but found it increased as more fire was allowed to burn in the Glacier National Park landscape.

Western larch exhibits an intermediate adaptive strategy, and geographic clines for most adaptive traits are 

relatively flat (Rehfeldt 1994, 1995b). Populations from 

northerly latitudes and higher elevations exhibit the lowest growth potential, least tolerance to larch needle cast, 

and the lowest survival. Using a common garden study of 

143 populations, Rehfeldt (1995b) demonstrated that an 

increase of 9 °F would produce a mean annual temperature 

exceeding the current ecological distribution of the species. A molecular study using allozymes indicated low 

levels of genetic differentiation among populations from 

the inland Northwest (Fins and Steeb 1986). Evolutionary 

bottlenecks are commonly cited as a mechanism of 

reduced genetic differentiation among populations, and 

increased differentiation within populations.

Western larch may be highly susceptible to future 

changes in climate primarily because of its narrow geographic and elevational distribution in the region and its 

uncertain association with wildland fire. If wildland fires 

increase, western larch may have a distinct colonization 

advantage, providing fire mortality is low in those communities that have extensive fuel buildups from fire exclusion. 

However, if fires decrease and exclusion is continued, 

western larch may be outcompeted by its shade-tolerant 

competitors, and those seed-producing western larch that 

remain might be killed by severe fires created by abnormal 

fuel accumulations. If western larch is planted in those 

severely burned areas, the species will surely remain on 

the landscape in the future.

Western White Pine

Autecology

In the Interior West, western white pine (Pinus monticola) grows from near Quesnal Lake, British Columbia, 

south through the Selkirk Mountains of eastern Washington 

and northern Idaho and into the Bitterroot Mountains of 

western Montana (Graham 1990). Isolated populations are 

found as far east as Glacier National Park (Loehman et al. 

2011a). The climate of the interior portion of western white 

pine range is influenced by the Pacific Ocean; summers 

are dry and most of the precipitation occurs in the fall and 

winter. Western white pine is limited by moisture at lower 

elevations and temperatures at upper elevations. The southern boundary is limited by a balance of precipitation and 

evaporation.

Western white pine grows on diverse of soil types in 

the Northern Rockies (Harvey et al. 2008), but it primarily 

grows in areas where the upper soil layers are composed of 

loess or loess-like material. In this region, it generally grows 

at elevations of between 1,600 and 5,900 feet and where 

the topography is steep with V-shaped and round-bottomed 

valleys. It grows on a variety of slopes, but is common 

along moist creek bottoms, lower benches, and northerly 

slopes. Western white pine grows in association with a variety of species, and in the western hemlock/bride’s bonnet 

(Clintonia uniflora), western redcedar/bride’s bonnet, and 

grand fir/bride’s bonnet habitat types (Cooper et al. 1991).

Western white pine seeds require 20 to 120 days of cold, 

moist conditions before germination occurs. Seeds germinate in the spring when soil moisture is at field capacity 

from melting snow. Western white pine seedling establishment is favored by partial shade on severe to moderately 

severe sites (Graham 1990) but little to no shade on north 

slopes. Under full sun, germination begins earlier and ends 

earlier than in shaded conditions. Mineral soil surfaces are 

preferred over duff. Once established, western white pine 

grows best in full sunlight on all sites. Seedlings have low 

drought tolerance, and seedling mortality late in the first 

growing season is attributed to high surface temperatures 

on exposed sites, and drought in heavily shaded areas where 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 157

root penetration is slow. Early root and shoot development 

is not rapid.

Western white pine is almost always a seral species and 

is classified as intermediate in shade tolerance (Minore 

1979). It attains dominance in a stand only following wildfire or with silvicultural systems that favor it. It is tolerant 

of cold when it is dormant, and similar to lodgepole pine in 

cold tolerance.

Genetic variation of western white pine is high, with 

the greatest difference being among trees within a stand, 

although differences occur among stands and elevational 

zones. The adaptation of western white pine to different conditions (topographic, climatic, geographic, and 

edaphic) is governed more by phenotypic plasticity than by 

selective differences. The species has a high outcrossing 

rate and average genetic diversity with moderate genetic 

differentiation. It is a generalist species with broad climate 

and environmental tolerances (Devine et al. 2012).

Disturbance Interactions

Historically, western white pine forests mostly originated from wildfires, especially stand-replacement burns, 

but were also maintained by frequent low-severity fires 

(Barrett et al. 1991). The species, especially when mature, 

is more tolerant of heat and can better survive fire than 

nearly all of its shade-tolerant competitors. Its relatively 

thick bark and moderately flammable foliage make it 

intermediate in fire resistance among its conifer associates 

(Graham 1990). Native American burning was probably 

the primary source of fire that created the pure stands of 

western white pine in northern Idaho, but lightning was 

also important (Graham 1990).

The most prominent agent causing the severe declines 

in western white pine is white pine blister rust (Fins et 

al. 2002; Harvey et al. 2008). A combination of climate, 

extensive white pine blister rust, abundant alternate hosts, 

and susceptible western white pine caused significant 

losses in the recent past. Selection of naturally resistant 

trees as seed sources and planting of rust-resistant nursery 

stock can reduce losses. In the absence of blister rust, 

western white pine is long-lived, commonly surviving to 

300 to 400 years old.

The foremost root disease of western white pine is 

Armillaria root rot, which causes fading foliage, growth 

reduction, root-collar exudation of resin, dead and rotten 

roots, and black rhizomorphs. Annosus root disease and 

laminated root rot (Phellinus sulphurascens) also cause 

some mortality of individuals and groups. In periods of 

drought, pole blight, a physiological disorder, can occur 

in stands of the 40- to 100-year age class, causing yellow 

foliage and dead resinous areas on the trunk. Later, the 

top dies and, after a few years, the tree dies. The disease 

apparently is not caused by a primary pathogen but results 

from rootlet deterioration in certain soils, which restricts 

the uptake of water. Bark beetles are the most important 

insects that attack western white pine, and the most important species is the mountain pine beetle, which kills 

groups of trees, primarily in mature forests. The mountain 

pine beetle often attacks trees weakened by blister rust. 

Likewise, the red turpentine beetle (Dendroctonus valens) 

sometimes attacks weakened trees.

Historical and Current Conditions

Western white pine stands were once extensive across 

northern Idaho and parts of Montana, with large, tall 

pine trees dominating the montane landscapes (Harvey 

et al. 2008). As a result of logging, fire suppression, and 

extensive white pine blister rust infection, western white 

pine forests are nearly gone, and the species occurs only 

as scattered individuals in mixed-conifer stands (Fins et al. 

2002). This is truly an ecosystem in decline, and it may be 

doomed to extinction without active restoration.

Climate Change Responses

Western white pine presents a special challenge in forest management in the future. Recent studies have shown 

that western white pine might be the species best adapted 

to changes in climate in the northwestern portions of the 

Northern Rockies (Loehman et al. 2011a). Using SDMs, 

Gray and Hamann (2013) estimated western white pine 

could move almost 250 miles northward and 500 feet higher 

in elevation in the region by 2050. Its superior growth 

rates, ability to survive fire, and high timber value make it 

a species to promote in the creation of future forests with 

high resilience (Baumgartner et al. 1994; Graham 1990). It 

has the unique ability to disperse seeds into burned areas, 

which are likely to increase in the future, and the predicted 

increases in productivity where it occurs could mean that it 

might benefit more than any other tree species from changing climate, especially in the context of timber production. 

However, western white pine is currently ravaged by white 

pine blister rust, and it has not yet developed the genetic 

capacity to overcome the damaging effects of this exotic 

disease to populate future landscapes in the northwestern 

Northern Rockies (Fins et al. 2002). The species simply has 

not achieved a sufficient level of rust resistance to allow it to 

dominate future stands (Harvey et al. 2008). With white pine 

blister rust and its alternate hosts (e.g., currant) predicted to 

also increase in the future, creating a rust-resistant population of western white pine is critical to maintaining it in the 

mesic grand fir/western redcedar/western hemlock habitat 

types (Baumgartner et al. 1994). Without a comprehensive 

western white pine restoration program, there is little chance 

that this species will play an important role in the future.

Other issues may govern future western white pine 

dynamics. While wildland fire may increase growing space, 

thereby providing for high regeneration potential, there 

may be few western white pine trees to provide the seed 

source needed to regenerate these large burns. Further, in 

some portions of the Northern Rockies, the species may be 

highly dependent on ash cap soils (Graham 1990), which 

may prevent its migration to warmer sites. The species is 

also dependent on a unique assemblage of ectomycorrhizae 

whose availability in some areas might be reduced in the 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
158 USDA Forest Service RMRS-GTR-374. 2018

future; suitable substrate may not exist upslope so migration 

may not occur.

In summary, we deem western white pine to be highly 

predisposed to declines in the future due to the interacting 

effects of continued fire exclusion, low levels of white pine 

blister rust resistance in native populations, and rapid succession to more shade-tolerant conifer communities. While 

it may be a species of special interest for northwestern 

portions of the Northern Rockies, its populations and future 

under changing climates is especially precarious because 

of blister rust. Abundance of western white pine is currently low in isolated landscapes, and thus the magnitude 

of any decline may be large relative to current and past 

populations.

Quaking Aspen

Autecology

Quaking aspen (Populus tremuloides) is the most widely 

distributed native tree species in North America and is 

abundant in the mountains of western and southwestern 

Montana and northern Idaho (DeByle 1985; Perala 1990). 

Its habitat is limited primarily to areas of water surpluses 

(where annual precipitation exceeds evapotranspiration), 

and it is also limited by minimum or maximum growing 

season temperatures. Deterioration of aspen stands is often 

related to warmer summer temperatures (Perala 1983). 

Aspen grows on a variety of soils, but growth and development are strongly influenced by both physical and chemical 

properties of the soil. The best soils for aspen growth are 

usually well drained, loamy, and high in organic matter, 

calcium, magnesium, potassium, and nitrogen. Aspen has 

an important role in nutrient cycling because of its rapid 

growth and high nutrient demand. Aspen is limited by both 

shallow and deep water tables (>8.2 feet) because the roots 

need sufficient water and good aeration, especially during 

the growing season.

Compared to most conifer species, aspen is a short-lived, 

disturbance-maintained seral species (Mueggler 1985; 

Rogers 2002). It is shade-intolerant and aggressively sprouts 

following any disturbance (usually fire) that kills most of 

the live stems, thus stimulating vegetative reproduction (i.e., 

suckering) (Bartos 1978). Aspen reproduces primarily by 

asexual root sprouting. Parent trees (genets) produce stems/

trees (ramets), resulting in a clone or stand of genetically 

identical aspen stems (trees). Damage to parent trees alters 

the growth hormones (auxins and cytokinins) and stimulates 

a sprouting response (Perala 1990). Soil temperature is the 

most critical abiotic factor affecting suckering. Light is not 

needed for suckering but is needed for secondary growth. 

Eventually, most of the original root connections are severed 

as the ramets develop their own root systems to support 

nutrient uptake (Rogers et al. 2007; Shepperd and Smith 

1993). This reproductive strategy allows aspen to establish 

quickly on disturbed sites and outcompete conifers for soil 

moisture, nutrients, and light. In addition, the shared root 

system maintains overall stand vigor by allowing sharing 

of resources during the early stages of stand development 

(Mitton and Grant 1996; Romme et al. 1997).

Although there are a number of different aspen classifications (Mueggler 1988; Shepperd et al. 2001), it is 

widely recognized that aspen occurs as both stable climax 

communities and seral, disturbance-maintained communities 

(Mueggler 1985, 1988). Stable aspen communities occupy 

sites with both high soil moisture and solar radiation, which 

apparently preclude establishment of conifers for very long 

periods (or they never establish). Stable climax aspen communities do not require disturbance to maintain dominance. 

Seral aspen apparently occurs in two forms in the Northern 

Rockies. First, there are mesic stands in northwestern 

Montana and northern Idaho where aspen is a common 

seral component, but it rarely dominates stands unless there 

are several consecutive burns (Campbell and Bartos 2001; 

Cooper et al. 1991; DeByle 1985). The second seral type occurs in the drier forested areas in the region, such as east of 

the Continental Divide, especially in southwestern Montana. 

In these seral types, which are created by fire and sprouting, 

aspen occurs as the major stand component; these stands 

will eventually succeed to more shade-tolerant conifers 

(e.g., Douglas-fir, subalpine fir, and Engelmann spruce) in 

the absence of disturbance (DeByle 1985; Mueggler 1988).

Aspen has a high genetic diversity because it is essentially a transboreal broadleaf tree. It has weak genetic 

differentiation geographically, but strong differentiation at 

the population level. There is substantial phenotypic variation in the species, found both in the field and in genetic 

studies, as documented by varied leaf sizes, shapes, and 

phenologies.

Disturbance Interactions

Numerous factors other than competition will be important for quaking aspen under a changing climate. Perhaps 

the most important factor affecting aspen regeneration and 

distribution is browsing by ungulates, which frequently 

damage reproduction by browsing and by rubbing their 

antlers against the stems (Eisenberg et al. 2013; White et al. 

1998). Elk (Cervus elaphus) and moose (Alces alces) can 

also damage pole- and saw log-size trees by “barking” them 

with their incisors. Such injuries often expose individuals 

to secondary attack by insects or pathogens. Heavy use by 

overwintering ungulates can greatly reduce the number of 

aspen trees in localized areas. Cattle and sheep browsing is 

a serious problem in many areas of the Northern Rockies 

as livestock are allowed to range through recent aspen 

clearcuts. Mature aspen stands adjacent to livestock concentrations (water holes, salt blocks, and isolated stands in large 

open areas) often have root damage, are declining, and have 

few if any suckers present.

Fire can kill aspen stands (Bartos 1998), but it also 

creates conditions conducive to aspen regeneration and 

suckering by eliminating shade-tolerant conifers, which 

compete for light and eventually overtop and shade out 

aspen, leading to aspen decline (Campbell and Bartos 2001; 

Shepperd et al. 2001). Mature aspen trees may not survive 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 159

fire as well as the fire-adapted conifers of the region, but 

aspen is easily the most competitive after fire because it 

can aggressively regenerate from suckers (Shinneman et 

al. 2013). Aspen could do well in a warmer climate with 

increased fire frequency, but moisture will limit its success, with varying results (Anderegg et al. 2012; Hogg and 

Hurdle 1995; Kulakowski et al. 2013; Worrall et al. 2013).

Following disturbance, aspen normally dominates a site 

for 40 to 80 years. Natural thinning from disease, aging, 

and succession (shading) by competing conifers eventually 

reduces aspen abundance (Mueggler 1985; Rogers 2002). In 

central Utah, Shepperd et al. (2001) found that both regenerating and nonregenerating clones had stems of various age 

classes, which suggests that periodic sucker events occurred 

in these clones. In addition, they found that all of the nonregenerating clones had fewer roots than their regenerating 

neighbors, which indicates that root systems decline when 

clones are not periodically regenerating. Many aspen clones 

are known to be associated with ectomycorrhizae (Cripps 

and Miller 1993).

Aspen has low susceptibility to insect damage, except in 

urban plantings, but stem canker diseases have a significant 

impact on aspen ecosystems. Depending on the fungus, 

cankers may kill trees within a few years or persist for decades. Hypoxylon canker caused by Hypoxylon mammatum

is probably the most serious aspen disease east of the Rocky 

Mountains, killing 1 to 2 percent of the aspen annually 

(Perala 1990). Young trees are killed by small rodents and 

other mammals, particularly large ungulates (Eisenberg et 

al. 2013).

Historical and Current Conditions

Since around 1970, aspen has been in a period of general 

decline that is thought to be the result of wildfire exclusion, 

which has allowed plant succession to proceed toward conditions that ordinarily exclude aspen (Campbell and Bartos 

2001; Frey et al. 2004). Recent episodes of aspen dieback 

have been superimposed on this general decline. Dieback 

can be recognized by the suddenness of the impact, giving 

rise to the term “sudden aspen decline,” and by an epidemiology that begins with the death of branch tips, death of 

mature trees, and eventually death of entire clones (Frey et 

al. 2004). The dieback is suspected to be caused by drought.

Climate Change Responses

Aspen is a species that may experience both gains and 

losses under future climate, depending on local site conditions, particularly soil moisture. Seral aspen communities 

will respond differently from stable, climax aspen communities. Aspen communities on warmer, drier sites could 

have high mortality because of increasing water deficit. 

Ireland et al. (2014) found that drought was the major factor causing recent high mortality in southwestern aspen 

stands. In the boreal forests of western Canada, Hogg 

and Hurdle (1995) estimate that even with an 11-percent 

increase in precipitation, boreal forests in which aspen is a 

major component will decline due to drought stress. Sudden 

aspen decline has been associated with severe, prolonged 

drought, particularly in aspen stands that are on the fringe 

of aspen distribution (warmer and drier sites than those 

typically considered optimal for aspen persistence) (Frey et 

al. 2004). Recent research efforts have found that extreme 

weather events (e.g., drought, thaw-freeze events), insect 

defoliation, or pathogens, or a combination of these factors, 

have led to aspen mortality (Brandt et al. 2003; Candau et 

al. 2002; Hogg et al. 2002). Marchetti et al. (2011) found 

that aspen mortality from various insects and disease (e.g., 

Cytospora canker [Cytospora], bronze poplar borer [Agrilus 

liragus], and aspen bark beetles Trypophloeus populi and 

Procryphalus mucronatus) was greater in those stands that 

were drought-stressed and declining due to sudden aspen 

death. Further exacerbating the situation is that declining 

stands may have little or no regeneration because of intense 

ungulate herbivory, and those smaller stands that persist 

may be smaller and fewer with increased plant stress due to 

increased severity of summer droughts (Rogers et al. 2013). 

Growth may increase because photosynthetic rates appear 

to increase more in aspen than other tree species as atmospheric carbon increases, but this may be offset by increased 

atmospheric ozone, which reduces photosynthesis and may 

increase susceptibility to insects and disease.

Increased fire frequency, particularly on moist sites, is 

likely to favor aspen regeneration in the future by removing 

shading conifers, and younger stands (<40 years old) created 

by fire may be more resilient to drought. However, if future 

fires are severe, they may kill the shallow root systems and 

eliminate aspen. Increased herbivory on regenerating stands 

may occur as adjacent upland vegetation senesces and desiccates earlier in the growing season. Areas with mountain 

pine beetle-caused conifer mortality (especially in lodgepole 

pine) may release aspen, and it will regenerate once the 

conifer canopy is thinned or removed, again given sufficient 

soil moisture.

Grand Fir

Autecology

Grand fir (Abies grandis) is found on a wide variety of 

sites, including stream bottoms, and valley and mountain 

slopes of the northwestern United States and southern 

British Columbia (Foiles et al. 1990). Average precipitation 

in its range varies from 20 to 100 inches, but in northern 

Idaho the average is from 20 to 50 inches. The average 

growing season temperature is 57.2 to 66.2 °F. In the inland 

portion of its range, grand fir grows best on rich mineral 

soils of valley bottoms but also grows well on shallow 

exposed soils of mountain ridges if moisture is adequate 

(Antos 1972).

Grand fir is either a seral or climax species, depending on 

site moisture (Ferguson and Johnson 1996). On productive 

mesic sites, it grows rapidly to compete with other seral 

species in the overstory, but it is outcompeted by western 

redcedar and western hemlock. On drier sites where western 

redcedar and western hemlock are excluded because of 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
160 USDA Forest Service RMRS-GTR-374. 2018

drought, it is the most shade-tolerant species and can easily 

dominate the understory; it eventually assumes the dominant 

position in the climax condition. Grand fir is a major climax 

species in a variety of habitat types in Montana and northern 

Idaho, but it rarely grows in pure stands; one exception is 

on the Clearwater River drainage in north-central Idaho 

(Cooper et al. 1991; Pfister et al. 1977). In Montana and 

parts of Idaho, grand fir can also share dominance, even 

in the climax state, with subalpine fir, especially in narrow 

valley bottoms where subalpine fir can exert dominance in 

lower elevational zones (Antos 1972). In most of its range, 

grand fir is often associated with Douglas-fir, ponderosa 

pine, western larch, western white pine, and subalpine fir.

Grand fir has a high tolerance to shade but a low 

tolerance to drought, even though it can tolerate drought 

better than any of the conifers that may succeed it in the 

absence of disturbance (e.g., western redcedar and western 

hemlock). Grand fir forms associations with ectomycorrhizae and arbuscular mycorrhizae, which may allow it to 

outcompete some shade-tolerant conifers. It has a very low 

frost tolerance but can tolerate seasonally fluctuating water 

tables. It is monoecious and produces large, winged seed 

dispersed by wind. It has average levels of genetic diversity 

but weak geographic differentiation.

Disturbance Interactions

Grand fir is susceptible to fire damage in moist creek 

bottoms but is more resistant on dry hillsides where roots 

are deeper and bark is thicker (Ryan and Reinhardt 1988). 

Grand fir is less resistant to fire than western larch, ponderosa pine, and Douglas-fir but more resistant than subalpine 

fir, western hemlock, and Engelmann spruce. Most fires that 

burn grand fir sites are stand-replacement or mixed-severity, 

and these fires burn in fuels that generate sufficient heat to 

kill most grand fir trees (Arno 1980; Arno et al. 2000).

Grand fir is susceptible to heart rot and decay. Armillaria 

root rot and annosus root disease are common root diseases 

causing high tree mortality (Hagle et al. 2003). Numerous 

insects attack grand fir. The western spruce budworm and 

Douglas-fir tussock moth have caused widespread defoliation, topkill, and mortality in grand fir. The western balsam 

bark beetle (Dryocoetes confusus) and the fir engraver 

(Scolytus ventralis) are the principal bark beetles attacking 

grand fir (Foiles et al. 1990).

Historical and Current Conditions

Fire exclusion has increased grand fir on both dry and 

mesic sites, but increased tree densities have also stressed 

grand fir trees, contributing to increased fuel loadings, 

higher root rot, and greater insect damage and mortality. 

Historically, grand fir sites were probably dominated by 

western larch, western white pine, Douglas-fir, and ponderosa pine because of frequent fires, but these sites have 

since succeeded to the more shade-tolerant grand fir, and on 

the productive mesic sites, to western redcedar and western 

hemlock. Therefore, the condition of most grand fir stands 

depends on the last severe fire; if fire exclusion has caused 

grand fir to dominate in both the overstory and understory, 

then these stands are usually highly stressed because of increased root rot and insect agents. However, in earlier seral 

stands that have not yet experienced high grand fir regeneration, a rise in grand fir cover types is likely with continued 

fire exclusion.

Climate Change Responses

On xeric sites, increased drought and longer growing 

seasons will exacerbate grand fir stress from competition, 

resulting in high mortality mainly from insects and disease. 

Nitschke and Innes (2008), using a gap modeling approach, 

projected major declines in grand fir, and Coops and Waring 

(2011) used a mechanistic model to simulate a nearly 

50-percent decrease in the range of grand fir compared to 

historical distributions. Franklin et al. (1991) projected that 

grand fir will nearly disappear from the east slope of the 

Cascades.

Yet projections of increased productivity suggest 

increased grand fir populations on moderate sites (Aston 

2010). Urban et al. (1993) projected an expansion of grand 

fir forests into upland xeric sites of the Pacific Northwest. 

On mesic sites where grand fir is seral to western redcedar 

and western hemlock, the longer growing seasons coupled 

with higher temperatures may increase growth rates and 

regeneration success, thereby increasing tree density and 

competition and effectively reducing grand fir components. 

The opposite is true on those sites where grand fir is the indicated climax; grand fir will increase in both the overstory 

and understory in the absence of disturbance.

Disturbance, specifically fire, could be the major factor 

in the rearrangement of grand fir communities across the 

Northern Rockies landscape. Longer fire seasons and high 

fuel loadings from both fire exclusion and increased productivity will serve to foster large, severe fires that may reduce 

grand fir, especially on those sites where it is the indicated 

climax species (i.e., grand fir habitat types). Fire will reduce 

grand fir dominance at both landscape and stand scales.

In summary, although many grand fir forests are highly 

stressed from high tree densities, the species will probably 

tolerate changes in climate and remain on the landscape at 

levels that are closer to historical conditions rather than the 

high abundance observed now.

Western Redcedar

Autecology

The inland range of western redcedar (Thuja plicata) 

extends from the western slope of the Continental Divide in 

British Columbia south through the Selkirk Mountains into 

western Montana and northern Idaho (Minore 1990). The 

southern limit is Ravalli County and the eastern limit is near 

Lake McDonald in Glacier National Park. A few trees may 

exist east of the Continental Divide near St. Mary’s Lake 

(Pfister et al. 1977). Western redcedar is abundant in many 

forested swamps as well as sites that are too dry for western 

hemlock; it has better root penetration than western hemlock 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 161

(Habeck 1978). Western redcedar dominates wet ravines and 

poorly drained depressions. Where there is sufficient precipitation, low temperatures limit the range of the species. 

It is not resistant to frost and can be damaged by freezing 

temperatures in late spring and early fall.

Western redcedar occurs only in pure stands where fire 

has been excluded for a long time, or where fire has been 

used to maintain western redcedar dominance (Barrett 1988; 

Barrett and Arno 1991). It is commonly associated with a 

wide array of tree species: grand fir, western white pine, 

western hemlock, western larch, and ponderosa pine. Only 

western hemlock in the Northern Rockies is more shadetolerant than western redcedar, but western redcedar can 

be overtopped by Douglas-fir, grand fir, western hemlock, 

and western white pine (table 6.3). Its relative shade tolerance may be higher in warm than in cool areas, but western 

redcedar is very tolerant wherever it grows. Often present 

in all stages of forest succession, western redcedar can occupy pioneer, seral, and climax positions. In the Northern 

Rockies, however, most western redcedar stands are in the 

late seral-stages; it is usually considered a climax or near 

climax species. It has little tolerance to drought but can exist 

in seasonally wet areas, especially near riparian systems 

(Devine et al. 2012).

Western redcedar regenerates best on disturbed mineral 

soil, although scorched soil is not beneficial to its regeneration. Rotten wood that is in contact with the soil is a 

preferred seedbed in western redcedar groves. Western redcedar also propagates by clones, and clones tend to be more 

abundant than young trees established by seed. Establishing 

seedlings survive best in partial shade, as they are not 

tolerant of high soil temperatures or frost. Young branches 

are susceptible to sunscald. Roots of young seedlings grow 

more slowly than Douglas-fir roots but faster than western 

hemlock roots, and shoots have the longest growing period 

of any of the associated conifers.

Western redcedar has very low levels of genetic diversity, 

and this diversity is weakly distributed geographically and 

within populations. Clines are very gentle and seed zones 

narrow. This species cannot tolerate wide ranges of environmental conditions.

Disturbance Interactions

Relative to its associates, western redcedar is not as 

affected by damaging agents, but because it is long-lived, 

damaged trees are common (Minore 1990). Although western redcedar trees are somewhat wind-firm, especially on 

dry sites, the trees are often wind thrown in wetter environments. Western redcedar is less susceptible to fire damage 

than Engelmann spruce, western hemlock, grand fir, and 

subalpine fir in the Northern Rockies. Western redcedar is 

also less susceptible than other associated species to root 

pathogens. However, root disease still impacts western 

redcedars, and fungi eventually invade heartwood typically 

resistant to decay. In North America, the most important 

fungi attacking western redcedar are root, butt, and trunk 

rots, most importantly laminated root rot, honey fungus 

(Armillaria mellea), and stringy butt rot (Perenniporia 

subacida).

Historical and Current Conditions

Compared to historical distributions, there has not been a 

significant increase or decrease in western redcedar distribution in the Northern Rockies. However, western redcedar 

dominance has probably increased in those stands occupying mesic western redcedar sites due to fire exclusion.

Climate Change Responses

With warmer temperatures, mesic northern Rocky 

Mountain ecosystems may increase in productivity (Aston 

2010), and western redcedar may expand into more upland 

communities. Hamann and Wang (2006) projected that the 

western hemlock/cedar forests of British Columbia would 

double in range by 2050, and Urban et al. (1993), using 

gap modeling, simulated an expansion of western redcedar 

into upland western Oregon sites. Devine et al. (2012) rated 

western redcedar as having moderate vulnerability in the 

Pacific Northwest Region. With increased western redcedar 

productivity could come increased cone production and seed 

dispersal into new areas that might be more conducive to 

long-term seedling establishment.

Although warmer conditions in the future may benefit 

western redcedar, drier conditions in the future are likely 

to result in retraction of western redcedar to the warmer, 

wettest Northern Rockies sites; upland western redcedar 

stands might have high mortality from declining productivity. Woods et al. (2010) noted recent declines in western 

redcedar in British Columbia and attributed the decline 

to increased drought that decreased vigor and increased 

insect attacks and disease in western redcedar. Warming 

may also result in a loss of chilling required for western 

redcedar (Nitschke and Innes 2008), and the narrow genetic 

potential of western redcedar (Devine et al. 2012) may limit 

its expansion into new habitats. Using SDMs, Gray and 

Hamann (2013) estimated western redcedar might move 

400 miles northward and 1,000 feet higher in elevation in 

the Pacific Northwest by 2050. However, in some portions 

of the region, redcedar is mostly associated with ash cap 

soils, so despite the possible creation of new habitats by new 

climates, the potential of non-ash soils to sustain productive 

western redcedar may be limited.

It is uncertain how disturbance will affect western 

redcedar in the future. Fire can serve to maintain western 

redcedar communities if it burns at low severities and kills 

only seedlings and saplings. However, high-severity wildfires could eliminate seed sources. Continued fire exclusion 

may maintain current western redcedar distributions, but 

without proactive fuels treatments, wildfire that occurs after 

long periods of exclusion may burn with sufficient severity 

to cause extensive western redcedar mortality. Further, new 

warm-cold cycles may facilitate the injury called red belt 

and adversely affect young western redcedar, as evidenced 

by increased flagging during past dry seasons.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
162 USDA Forest Service RMRS-GTR-374. 2018

In summary, western redcedar may not be severely affected by future climate warming. The species may remain 

in its current range, and productivity may increase in some 

settings.

Western Hemlock

Autecology

The inland range of western hemlock (Tsuga heterophylla) includes the west side of the Continental Divide 

in Montana and Idaho, north to Prince George, British 

Columbia (Packee 1990). Western hemlock thrives in mild 

humid climates and in environments with abundant soil 

moisture throughout the growing season (Hann et al. 1994). 

Where the growing season is relatively dry, western hemlock is confined primarily to northerly aspects, moist stream 

bottoms, or seepage sites. Western hemlock grows on a 

variety of soil types, although it is a shallow-rooted species 

and does not develop a taproot. Abundant roots, especially 

fine roots, grow near the soil surface and are easily damaged 

by fire.

Western hemlock is considered very shade-tolerant and is 

perhaps the most shade-tolerant tree species in the Northern 

Rockies (table 6.3). It is a major climax or near-climax 

species in the region and is found with nearly all of the 

other conifer species, including western redcedar, grand fir, 

Douglas-fir, western larch, western white pine, lodgepole 

pine, and ponderosa pine. Seed germination and germinant 

survival occur when there is adequate moisture. Western 

hemlock can germinate on a variety of materials and in both 

organic and mineral seedbeds. Decaying logs and rotten 

wood are often favorable seedbeds; decayed logs have the 

added benefit of providing nutrients. Western hemlock is 

highly susceptible to drought and demands abundant water 

throughout the growing season (Baumgartner et al. 1994). It 

is associated with some ectomycorrhizae. Its seedlings are 

highly susceptible to frost.

Western hemlock has relatively low genetic diversity and 

low geographic differentiation. It has a high outcrossing rate 

and average heterozygosity (Devine et al. 2012). Growth 

rate is more related to soil conditions than to genetics.

Disturbance Interactions

A variety of root and bole pathogens cause significant 

damage and mortality in western hemlock. It is also very 

susceptible to fire damage because of its shallow roots and 

thin bark, and it is also susceptible to windthrow owing to 

shallow roots. On droughty sites, top dieback is common, 

and entire stands of western hemlock saplings have been 

killed in exceptionally dry years. Western hemlock is highly 

susceptible to annosus root disease and Indian paint fungus 

(Echinodontium tinctorium), but seems to have a high tolerance to Armillaria root rots (Packee 1990).

Historical and Current Conditions

The current distribution of western hemlock is similar 

to its historical distribution. However, most stands with 

western hemlock have become denser and the western 

hemlock component has increased in both the overstory and 

understory. Overly dense western hemlock stands may be 

declining in vigor, thereby becoming more susceptible to 

disease, insects, and abiotic perturbations (e.g., windthrow).

Climate Change Responses

In the past, western hemlock/western redcedar forests 

were associated with wetter conditions in the low elevation forests of the Northern Rockies, but this type declined 

as fires and drought increased (Gavin et al. 2007). Thus, 

increased drought and area burned may decrease western 

hemlock abundance and distribution. Several studies have 

projected contractions in western hemlock distribution. For 

example, Hansen et al. (2001) simulated major contractions 

in western hemlock range, and Franklin et al. (1991) project 

that western hemlock will occupy about half its current 

range on the western slopes of the Cascades. Shafer et al. 

(2001) noted that western hemlock may decrease in range 

because chilling requirements for the seeds will not be met. 

Using a mechanistic landscape model, Keane et al. (1996) 

simulated losses of western hemlock and western redcedar 

under moderate climate warming in Glacier National Park, 

mostly as a result of severe fires. Cumming and Burton 

(1996) projected minor changes in the western redcedarwestern hemlock zone in British Columbia under moderate 

warming. On the other hand, Hamann and Wang (2006) 

predicted that western hemlock would increase its range by 

more than 200 percent in British Columbia, and using gap 

modeling, Urban et al. (1993) simulated an expansion of 

western hemlock into upland western Oregon sites.

It is possible that western hemlock will maintain its 

current range under a changing climate. It may not have 

the diversity in growth habit that will allow it to expand 

its range into the more upland sites as temperatures warm. 

Because the species is dependent on ash cap soils, any 

migration may be relegated to those wetter and warmer sites 

without ash cap soils.

Lodgepole Pine

Autecology

Lodgepole pine (Pinus contorta) has wide ecological amplitude, but only the inland form (P. contorta var. latifolia) is 

found in the Northern Rockies (Lotan and Critchfield 1990). 

Lodgepole pine has the widest range of environmental tolerance of any conifer in North America (Lotan and Critchfield 

1990). It is relatively resistant to frost injury and can often 

survive in frost pockets where other species cannot (Pfister 

et al. 1977). In Montana, lodgepole pine does not grow on 

highly calcareous soils derived from dolomitic limestone 

(Lotan and Perry 1983). Lodgepole pine is primarily found 

on moist soils developed on colluviums from other types of 

limestone and calcareous glacial till. It grows well on gentle 

slopes and in basins, but it is also found on rough and rocky 

terrain, steep slopes and ridges, and bare gravel (Lotan and 

Critchfield 1990). Compared to other associated species, 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 163

lodgepole pine is intermediate in its needs for water, requiring more than Douglas-fir or ponderosa pine but less than 

spruce and subalpine fir in the region.

Lodgepole pine is intolerant of shade but highly tolerant 

of frost and drought (table 6.3). Occasionally seedlings 

become established under a forest canopy, but these individuals rarely do well and remain in a stunted form for long 

periods of time (decades to centuries). In the absence of fire, 

lodgepole pine is usually succeeded by its more tolerant 

associates, such as Douglas-fir in xeric environments and 

Engelmann spruce and subalpine fir in subalpine environments. Succession proceeds at variable rates, however, and 

is particularly slow in some high elevation forests (Arno 

et al. 1993). Lodgepole pine grows both in pure stands 

and in association with many conifers, primarily subalpine 

fir, spruce, Douglas-fir, and western larch (Steele et al. 

1983). Its successional role is dependent on environmental 

conditions and on competition. It is seral in most mesic 

Northern Rockies forest communities (Arno et al. 1986). 

However, on cool dry habitats, such as those found in the 

Greater Yellowstone Area and southeastern Idaho, it is 

dominant and tends to be persistent and form near-climax 

communities (Despain 1983). Its ability to remain on xeric 

landscapes is enhanced by its association with many types 

of mycorrhizae.

Lodgepole pine has a great ability to regenerate due to a 

combination of cone serotiny, high seed viability, early rapid 

growth, and ability to survive a wide variety of microsite 

and soil conditions (Hardy et al. 2000). The serotinous 

cone habit, where cones open only after being heated by 

wildland fire, is common in the Rocky Mountains, but in 

general, the highest serotiny is found in the northern parts 

of the region. Large quantities of stored seeds are available 

for regeneration after fire, and annual seedfall from nonserotinous cones helps in restocking in areas of relatively 

minor disturbance and maintaining lodgepole pine presence 

in mixed stands.

The best lodgepole germination occurs in full sunlight 

and on bare mineral soil or disturbed duff, with little competition. Adequate soil moisture is required for germination 

and survival, with the first few weeks being most critical. In 

southwestern Montana most of the season’s total germination occurs during the 2 weeks following snowmelt in late 

June when soil is saturated and temperatures most favorable. Drought is a common cause of mortality in first-year 

seedlings. Freezing temperatures may kill seedlings, but 

seedlings vary in frost resistance based on seed source. Frost 

heaving also causes mortality. Height growth begins earlier 

than in other associated species, except for other pines and 

western larch.

There is moderate genetic variation in strains of lodgepole pine, resulting in some strains growing well in cold 

climate and on poor sites. Lodgepole pine has an average 

genetic diversity but a weak differentiation across its 

Northern Rockies range and strong differentiation among 

populations. The species is a prolific seed producer and has 

a good cone crop at about 1- to 3-year intervals. It is wind 

pollinated and its seeds are wind dispersed.

Disturbance Interactions

Fire plays a critical role in lodgepole pine forest succession (Lotan et al. 1984). Typically, many Northern Rockies 

lodgepole pine forests originated from stand-replacement 

fires, but extensive fire scars in Northern Rockies lodgepole 

pine forests indicate the existence of a low-severity, nonlethal fire regime component in these forests, especially in 

many areas east of the Continental Divide (Arno et al. 1993; 

Stewart and Arno 1997). Lodgepole pine is apparently able 

to survive low-intensity fires quite well even though it has 

thin bark (Ryan and Reinhardt 1988). However, most lodgepole pine forests in the region have a mixed-severity fire 

regime in space and time, where all fire severity types are 

possible depending on available fuels, antecedent drought, 

and wind conditions (Arno et al. 2000). Consequently, 

lodgepole as a species will be well adapted to the fires of 

the future. Repeated fires, however, can eliminate lodgepole 

pine seed sources if the fires occur before existing lodgepole 

has become reproductively mature (approximately 10 

years). In most cases, lodgepole pine natural regeneration 

often overwhelms a burned site with abundant seed from 

serotinous cones and thereby excludes other species (Lotan 

and Perry 1983; Nyland 1998).

The mountain pine beetle is the most important insect 

pest and has played a significant role in the dynamics 

of lodgepole ecosystems (Roe and Amman 1970). Past 

research has tried to link fire, beetles, and lodgepole pine 

in a complex web of interactions (Geiszler et al. 1980). 

However, recent findings have shown that fire and beetles 

often act independently to influence lodgepole pine dynamics (Axelson et al. 2009; Moran and Corcoran 2012; 

Schoennagel et al. 2012).

Historical and Current Conditions

Advancing succession due to fire exclusion is contributing to replacement of lodgepole pine with subalpine fir in 

many areas of the Northern Rockies. Keane et al. (1994) 

found successional advancement of subalpine communities in the upper subalpine landscape of the Bob Marshall 

Wilderness increased from less than 8 percent of the landscape to more than 22 percent. Concurrent increases in burn 

areas are creating many new lodgepole stands and some 

may become dense thickets, but coupled with increased 

drought, these dense lodgepole stands may exacerbate 

stress from other factors, including competition, endemic 

insects and diseases, and wind. Warming temperatures have 

heightened bark beetle activity, resulting in more frequent 

and severe outbreaks that have devastated many mature 

lodgepole pine communities in the central Northern Rockies 

(Carroll et al. 2003).

Climate Change Responses

Longer drought periods and warmer temperatures in 

the lower, south-facing, drier lodgepole pine subalpine 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
164 USDA Forest Service RMRS-GTR-374. 2018

environments may cause decreased tree growth and regeneration potential, perhaps resulting in a transition to 

more-xeric trees species, such as Douglas-fir. Chhin et al. 

(2008) found that recent warming has decreased lodgepole 

pine growth rates in the foothill lodgepole pine communities 

of the low elevation forests in Alberta. Coops and Waring 

(2011) used process modeling to simulate minor declines 

with moderate warming in lodgepole pine in the Pacific 

Northwest (Oregon, Washington, and British Columbia), but 

major type conversions to other species with greater warming. Using an SDM approach, Hamann and Wang (2006) 

projected a net 50 percent loss of lodgepole pine in British 

Columbia under severe warming. Nigh (2014) projected 

that lodgepole pine heights may decrease by roughly 3 feet 

in moderate future warming, but the species has the genetic 

capacity to mitigate this height loss. In contrast, Rehfeldt 

et al. (1999) found substantial decline in lodgepole pine 

growth and height with minor changes in climate. Chhin 

et al. (2008) also found that decreases in lodgepole pine 

growth were correlated with high summertime temperatures, 

presumably related to summer drought. However, they also 

found that lodgepole pine growth increases with high fall 

temperatures. Gray and Hamann (2013) used SDM techniques and estimated lodgepole pine would move more than 

250 miles northward and more than 650 feet higher in elevation in the Northern Rockies by 2050. Bell et al. (2014), 

using SDMs, projected losses of more than 70 percent of its 

Northern Rockies range by 2090. Given that lodgepole pine 

is a generalist that is capable of regenerating and growing 

in a wide range of environments, it is likely that the decline 

of lodgepole pine from drier sites will occur only under extreme warming scenarios (e.g., RCP 8.5 and A2) over longer 

time periods.

Another possibility is that, in the higher elevational areas 

of the Northern Rockies subalpine, where seasonal drought 

is not a problem, warming climates may actually increase 

lodgepole pine productivity because of high precipitation 

(Aston 2010). Johnstone and Chapin (2003) show that 

lodgepole pine is not in equilibrium with current climate; 

thus the response of the species to climate shifts will be 

difficult to predict using SDM approaches. However, they 

found that there are places where lodgepole pine will be 

positively affected by climate change. Wang et al. (2006) 

projected major increases in lodgepole pine productivity 

under future climates with moderate warming, but major 

decreases and perhaps local extinctions under extreme 

warming. Romme and Turner (1991) projected increases 

in the lodgepole pine zone in the GYA under moderate 

warming.

A third possibility is that lodgepole pine will migrate into 

areas where it is currently excluded by harsh, cold, windy 

conditions, such as the upper subalpine and treeline. This 

relocation process will likely be catalyzed by fire, especially 

in those areas with high serotiny. Clark et al. (2017) found 

that under moderate warming, lodgepole pine would remain 

on the GYA landscape, but it would also expand into higher 

elevation environments historically occupied by whitebark 

pine. Most studies have projected the migration of lodgepole 

pine into the whitebark pine zone (Hamann and Wang 2006; 

Romme and Turner 1991).

Lodgepole pine is well adapted to increases in fire occurrence, depending on level of serotiny (Turner et al. 1999). 

Smithwick et al. (2009) simulated some positive increases 

in GYA lodgepole pine after fire and under climate change. 

If fire is too frequent, however, lodgepole may be eliminated 

from sites where fires reburn stands before established 

seedlings and saplings become reproductively mature. Clark 

et al. (2017) simulated major and rapid decreases in GYA 

lodgepole pine under high climate warming due to both 

inhospitable environments and too frequent fire.

In mesic subalpine sites, continued fire exclusion coupled 

with higher productivities will certainly heighten competitive interactions and put more lodgepole pine trees into 

stress, thereby increasing mortality, vulnerability to insects 

and disease, and canopy and surface fuels, and accelerating 

succession toward subalpine fir (Smithwick et al. 2009). 

Severe fires that then occur in these advanced successional 

communities could convert communities back to lodgepole 

pine, providing there is not a loss of seed source. Fire exclusion, especially in areas of high serotiny, might delay the 

expansion of lodgepole pine.

Projected increases in climatic conditions that facilitate 

mountain pine beetle outbreaks could reduce lodgepole 

pine populations and forest extents (Creeden et al. 2014; 

Gillette et al. 2014). Lodgepole pine is highly susceptible to 

bark beetle mortality, especially on those landscapes where 

fire exclusion has resulted in an abundance of mature hosts 

(Temperli et al. 2013). Bark beetle outbreaks will favor the 

more shade-tolerant, nonhost tree species, thereby creating 

dense stands that may be subject to severe crown fires after 

10 to 20 years. If beetle-killed stands burn, lodgepole pine 

can occupy the burned area only if viable seed sources 

remain. The varying levels of serotiny and beetle mortality 

will dictate future stand conditions in beetle-killed stands. 

Landscape heterogeneity is the only hedge against massive 

declines of lodgepole pine in the future (Logan and Powell 

2001).

In summary, lodgepole pine is expected to both expand 

and contract in range, but as long as fire remains on the 

landscape, the species is likely to maintain its presence in 

the Northern Rockies at roughly the same proportions as 

during the last 100 years, albeit in different areas. The species is highly exposed to any climate changes because of its 

wide range and diverse growing environments. But Soulé 

and Knapp (2013) suggest that the steep clines associated 

with lodgepole pine may be driven more by densitydependent selection than by environmental selection, so this 

species may be well adapted to future changes in climate. 

In addition, although the magnitude of climate effects is 

likely to be great for tree growth, it may be only moderate 

for species survival compared to other species. The likelihood of these effects is highly uncertain, primarily because 

of the uncertainty about fire frequency and severity, which 

determine the extent to which fire will continue to play its 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 165

role in the maintenance of lodgepole as a major component 

on future landscapes.

Whitebark Pine

Autecology

Whitebark pine (Pinus albicaulis) is an important 

component of high-elevation upper subalpine forests in the 

western United States and Canada (Arno and Hoff 1990). It 

is a keystone species because it supports unique community 

diversity, and it is a foundation species because of its roles in 

promoting community development and stability (Tomback 

and Achuff 2010; Tomback et al. 2001). More than 90 percent 

of whitebark pine forests occur on public lands in the United 

States and Canada, so maintaining whitebark pine communities requires a coordinated effort across Federal, State, and 

Provincial land management agencies (Keane et al. 2012).

Whitebark pine is a long-lived tree of moderate shade 

tolerance (Minore 1979) (table 6.3). It is common to find 

mature whitebark pine trees well over 400 years of age, 

especially on harsh growing sites; the oldest is more than 

1,275 years (Luckman et al. 1984). Well-formed, thrifty individuals often have smooth gray bark, especially in the tree 

crowns, which may appear whitish in bright sunlight (Arno 

and Hoff 1990). Whitebark pine is slow growing in both 

height and diameter, and it rarely grows faster than most of 

its competitors, except on the most severe sites (Arno and 

Hoff 1990). In general, whitebark pine grows where summers are short and cool and where most precipitation comes 

in the form of snow and sleet, with rain only in June through 

September. Whitebark pine survives strong winds, thunderstorms, and severe blizzards, and is one of the few upper 

subalpine species that can tolerate long periods of drought 

(Callaway et al. 1998).

Whitebark pine is a major component of high elevation 

forests throughout the upper subalpine and treeline zones in 

the Northern Rockies (Arno and Hoff 1990). Whitebark pine 

forests occur in two high mountain biophysical settings. 

On productive upper subalpine sites, whitebark pine is the 

major seral species that is replaced by the more shadetolerant subalpine fir, Engelmann spruce, and mountain 

hemlock, depending on geographic region (Arno 2001). 

These sites, referred to as “seral whitebark pine sites,” support upright, closed-canopy forests in the upper subalpine 

lower transition to treeline, just above or overlapping with 

the elevational limit of the shade-intolerant lodgepole pine 

(Pfister et al. 1977); the two pine species can often share 

dominance. Other minor species found with whitebark pine 

on these sites are Douglas-fir, limber pine, and alpine larch 

(Keane et al. 2012). Sites where whitebark pine is the only 

tree species able to successfully dominate high elevation 

settings (called climax whitebark pine sites) occur in the 

upper subalpine forests and at treeline on relatively dry, 

cold slopes. Other species, such as subalpine fir, spruce, and 

lodgepole pine, can occur on these sites, but as scattered 

individuals with truncated growth forms. Whitebark pine 

can also occur as krummholz, elfin forests, clusters, groves, 

tree islands, and timber atolls in the alpine treeline ecotone 

(Tomback 1989) and as a minor seral in lower subalpine 

sites (Cooper et al. 1991; Pfister et al. 1977).

Whitebark pine is eventually replaced, in the absence 

of fire, by the shade-tolerant subalpine fir, spruce, and 

mountain hemlock on the productive, seral whitebark pine 

sites (Arno and Hoff 1990). It can take 50 to 250 years for 

subalpine fir to replace whitebark pine in the overstory, 

depending on the local environment and fire history (Keane 

2001). Whitebark pine competes with lodgepole pine during 

early successional stages in the lower portions of its elevational range. Lodgepole pine usually has the competitive 

advantage over whitebark pine when it establishes from 

seed after a stand-replacing disturbance event because of its 

fast growth, serotiny, and copious seed production.

A bird (Clark’s nutcracker) and whitebark pine have 

coevolved into a mutualistic relationship that ensures their 

continued presence on the landscape (Tomback 1982, 1983). 

Whitebark pine has evolved a nearly exclusive dependence 

on nutcrackers to disperse its large wingless seeds, and in 

turn, nutcrackers utilize the large whitebark pine seeds as 

an important food source. The key behavior that benefits 

the whitebark pine is the tendency of nutcrackers to bury 

thousands of whitebark pine seeds each year as food stores 

in small clusters or “seed caches” across diverse forest 

terrain (Keane et al. 2012). Nutcrackers retrieve these seed 

caches primarily in spring and summer as an important food 

source for themselves and their young. However, not all 

seed caches may be recovered, particularly following a large 

cone crop. Snowmelt, spring rains, and summer showers 

stimulate seed germination, leading to whitebark pine regeneration. Although whitebark pine depends nearly exclusively 

on nutcrackers, nutcrackers often harvest and cache seeds of 

other large-seeded pines.

Whitebark pine is a genetically diverse species because 

of its dependence on bird-mediated seed dispersal (Keane et 

al. 2012). As a result, the species is highly adapted to exist 

across many environments, and is limited only by competition, even at the lowest elevations. It has only six seed zones 

across its entire range, so it is easily able to migrate across 

local landscapes to rapidly take advantage of newly burned 

areas. Whitebark pine has weak geographic differentiation 

in the Northern Rockies, but a moderate level of inbreeding. 

One concern in the future is that the breeding of rust resistance in future whitebark pine seedlings may compromise 

other important traits; Mahalovich et al. (2006) found lower 

cold tolerance in highly rust-resistant seedlings grown in the 

nursery.

Disturbance Interactions

Whitebark pine fire regimes are complex and variable 

in space and time, but in general, all three types of fire 

severities describe whitebark pine fire dynamics: nonlethal, 

stand-replacing, and mixed-severity (Morgan et al. 1994b). 

Some whitebark pine stands may undergo fire events that 

burn in low-intensity nonlethal surface fires (sometimes 

called underburns or low-severity fires) because of sparse 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
166 USDA Forest Service RMRS-GTR-374. 2018

surface and canopy fuel loadings and unique topographical 

settings. However, most fires in the upper subalpine burn in 

mixed-severity patterns that best facilitate continued existence of whitebark pine (Keane et al. 1994).

Mountain pine beetle is by far the most damaging insect 

in mature stands of whitebark pine. Much of the mature 

whitebark pine in the Northern Rockies was killed by this 

insect between 1909 and 1940. Epidemics evidently spread 

upward into the whitebark pine forest after the beetle became established in the lodgepole pine forests below. The 

GYA whitebark pine ecosystems have recently suffered one 

of the most severe mountain pine beetle mortality events in 

recorded history.

The principal disease of whitebark pine is the introduced 

white pine blister rust (Schwandt 2006). Blister rust is 

particularly destructive where the ranges of whitebark pine 

and blister rust coincide with currant, the alternate host of 

the rust. Where there is a source of inoculum from lowland 

forests, the spores that infect pine can be carried by wind to 

the trees, but cool, moist conditions are needed for infection 

in whitebark pine. Blister rust damage is severe and prevents tree development in many upper subalpine settings of 

northern Idaho and northwestern Montana. Whitebark pine 

has some resistance to the disease, and efforts at developing 

rust-resistant seed for regenerating burned and treated areas 

have been very successful.

Historical and Current Conditions

Whitebark pine has been declining since the early 20th

century from the combined effects of native mountain pine 

beetle outbreaks, contemporary fire exclusion policies, and 

the spread of the exotic white pine blister rust (Schwandt 

2006; Tomback and Achuff 2010). Losses of whitebark pine 

in some areas of the Northern Rockies exceed 80 percent 

(Keane et al. 2012). Whitebark pine is listed as endangered 

in Alberta, it is a candidate species for listing under the U.S. 

Endangered Species Act (USFWS 2011), and it is listed as 

endangered in Canada under the Federal Species at Risk 

Act. Within the last decade, major outbreaks of pine beetle 

and increasing damage and mortality from blister rust have 

resulted in cumulative whitebark pine losses that have altered high-elevation community composition and ecosystem 

processes in many regions of the United States and Canada.

Climate Change Responses

There is much disagreement in the research and management communities about the fate of whitebark pine as 

climates slowly warm. Some maintain that projected warmer 

conditions will severely reduce whitebark pine habitat and 

push whitebark pine “off the tops of mountains” (Lenoir 

et al. 2008) or restrict the species to north of the Canadian 

border (Koteen 1999; Schrag et al. 2007; Warwell et al. 

2007). This assumes that less hardy, shade-tolerant conifer 

species would establish in those higher elevation stands 

where whitebark pine currently dominates, and whitebark 

pine would “migrate” upslope to the limited areas above 

its current elevational range (Romme and Turner 1991). 

Bell et al. (2014), using SDMs, project minor losses (10–20 

percent) in whitebark pine range in the Northern Rockies 

by 2090. Others hold that climate-mediated changes in 

the disturbance regimes will serve to keep whitebark pine 

within its current range, albeit at lower levels (Loehman et 

al. 2011b). The fate of whitebark pine is uncertain because 

of high uncertainty in regional climate change predictions, 

the high genetic diversity and resilience of the species, and 

the localized changes in disturbance regimes and their interactions (Keane et al. 2015a).

Climate change has the potential to significantly impact 

whitebark pine ecosystems (Bartlein et al. 1997). Devine 

et al. (2012) rated whitebark pine the most vulnerable of 

all the Pacific Northwest tree species, primarily because of 

restricted range and white pine blister rust infections. Taking 

a historical perspective, however, we can see that whitebark 

pine was able to persist through many major climatic cycles 

in the past. Historical analogs of warmer climates in the paleoecological record indicate whitebark pine was maintained 

and even increased in some places under past warmer and 

drier climates in parts of its range (Whitlock and Bartlein 

1993; Whitlock et al. 2003). Whitebark pine can grow 

within a broad upper-elevation zone in the West; it just 

happens to grow best at high elevations where there is little 

competition from other tree species. For example, Arno et 

al. (1995) found that the elevational range of whitebark pine 

in the Bitterroot Mountains of Montana extended more than 

500 feet below its current lower elevation limits. Nitschke 

and Innes (2008) suggested that temperature alone would 

exclude whitebark pine from British Columbia landscapes. 

However, whitebark pine occupies the largest range of any 

five-needle pine in the United States and Canada—about 18 ̊ 

of latitude and 21 ̊ of longitude—indicating a great deal of 

tolerance to different climates (Tomback and Achuff 2010). 

Because it is bird dispersed, it is planted and grows in many 

environments and dies only from competition (Arno and 

Hoff 1990). Moreover, its longevity provides potential buffering against changing climates (Morris et al. 2008).

The same three responses of tree species to climatic 

change will occur for whitebark pine: Ranges will decline, 

stay the same, or expand. SDM studies have projected 

dramatic decreases in whitebark pine habitat over the next 

50 years (McDermid and Smith 2008; Warwell et al. 2007). 

Hamann and Wang (2006) projected a 100 percent decline 

in whitebark pine in British Columbia with high levels of 

warming. These models also predict that whitebark pine will 

probably make a transition to treeline environments that are 

above the current elevational range, but these transitional areas are much smaller than the traditional range of whitebark 

pine, thereby resulting in a net loss of the species. Climate 

can adversely affect growth and mortality of whitebark 

pine in many ways (Bugmann and Cramer 1998; Keane 

et al. 2001). Projected decreases in water availability may 

result in less water being available for some droughty sites. 

Longer drought might cause whitebark pine to shut their stomata longer to conserve the little water available, resulting 

in slow growth.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 167

However, many whitebark pine stands may have positive 

responses to warming climates. Anecdotal evidence shows 

that some whitebark pine forests are exhibiting abnormally 

high growth and more frequent cone crops with warmer 

summers and longer growing seasons. These observations 

are consistent with some region-based scenarios using computer modeling (Loehman et al. 2011b). Recent modeling 

efforts have shown that whitebark pine might be maintained 

on the landscape in the future, provided that projected 

increases in large, stand-replacement fires do occur and create large, competition-free burned areas (Clark et al. 2017; 

Loehman et al. 2011b). If tree dispersal enables range shifts 

to occur, this will lead to a new northern distributional range 

of whitebark pine (Hamann and Wang 2006; McKenney 

et al. 2007). Moreover, whitebark pine shows promise for 

being maintained in the Northern Rockies because of high 

levels of genetic diversity (Mahalovich and Hipkins 2011; 

Richardson et al. 2002), moderate to high heritabilities in 

key adaptive traits, demonstrated blister rust resistance 

(Hoff et al. 2001; Mahalovich et al. 2006), minimal inbreeding (Bower and Aitken 2007; Mahalovich and Hipkins 

2011), and generalist adaptive strategies.

Future climates may enhance growth of whitebark pine 

diameter and height and decrease mortality, especially in 

mesic seral whitebark pine forests. Earlier growing seasons 

with ample moisture, such as those projected for the upper subalpine forests, will result in increased productivity 

and greater growth. Longer, warmer growing seasons may 

also result in higher productivities and greater biomass, 

especially considering the high amounts of precipitation that 

currently fall in upper subalpine forests. The abundant moisture may enable longer growing seasons at high elevations. 

Increased biomass could result in higher growth rates for 

timber production and forage, especially in the widespread 

higher mountain areas where cold, not moisture, limits tree 

growth, creating potential for the inclusion of whitebark 

pine in the timber base. Increased biomass could also foster 

more intense, severe fires, and maybe insect and disease 

outbreaks, but more importantly, the increased biomass 

will probably increase cone crop abundance and frequency. 

However, this increased production may also heighten 

competitive interactions between whitebark pine and its 

associated species, thereby favoring the more shade-tolerant 

individuals in the absence of disturbance. If disturbances increase, however, the more fire-tolerant whitebark pine might 

inherit the landscape.

Whitebark pine cone and seed crops could be both 

adversely and beneficially affected by climate change. In 

high-elevation, historically cold environments, increased 

temperatures may increase growing seasons and thereby 

increase potential for more frequent and more abundant 

cone crops with greater numbers of seed. This is important 

because decreases in species abundance and associated cone 

production may be offset by climate-driven increases in 

cone crops. Warming and variability in climate will also affect the phenology of cone crops, but these impacts may be 

minimal as plants adapt to the new conditions. Some predict 

higher frost mortality of emerging cones due to earlier onset 

of the growing season, coupled with high daily temperature 

variability (Chmura et al. 2011). Others suggest that cone 

crops will be reduced in the future because of high tree 

stress from drought, resulting in less frequent and abundant 

cone crops. Many expect that changes in climate variability 

and timing will have low impact on species reproduction because whitebark pine is both drought-tolerant and 

cold-tolerant.

Perhaps the life stage most critical for whitebark pine 

is regeneration, where most species, but especially trees, 

are most susceptible to shifts in climate (Solomon and 

West 1993). The microsite conditions needed for successful regeneration are so demanding that seed germination, 

especially from seeds that are wind dispersed, is rarely 

successful (McCaughey and Tomback 2001). Bunn et 

al. (2003) emphasized the importance of accounting for 

microsite variability in assessing climate change response; 

high-elevation microsite changes, coupled with increased 

fire activity, could increase whitebark pine regeneration and 

growth as climates change. The depth and duration of snow 

cover often governs high-elevation tree regeneration. Most 

years are moist enough for regeneration, but snow remains 

on sites for a long time, thereby limiting the number of days 

that a seedling can actually photosynthesize and grow. If 

temperatures increase, then snow might melt earlier, giving 

more time for seedlings to survive and grow. Warm years 

often result in waves of regeneration and can be dated in 

upper subalpine ecosystems by using seedling and sapling 

tree ages (Little et al. 1994; Rochefort et al. 1994). Recent 

observations of invasions of subalpine meadows and balds 

by subalpine fir, alpine larch, and spruce are a testament to a 

high number of sequential warm years over the last decade, 

which have facilitated regeneration in the high mountain 

landscape. Moreover, there is often abundant precipitation 

in upper subalpine settings, and projections for the future 

indicate roughly the same amount, so seedling mortality 

from drought might continue to be minimal.

Many climate change studies consistently project drier 

conditions in the range of whitebark pine, which would 

result in large increases in the annual number and severity of 

wildfires and area burned (Flannigan et al. 2009; Krawchuk 

et al. 2009; Marlon et al. 2009). With increased fire, whitebark pine will have a unique opportunity to maintain its 

range or even increase in distribution in the future because 

it has bird-mediated seed dispersal mechanisms that can 

disseminate seed great distances into large, severe burns, 

well before wind can disperse the seeds of its competitors 

(Tomback 1977, 1982, 1989; Lorenz et al. 2008). Whitebark 

pine also has morphology that enables it to survive lowto moderate-severity fires (Ryan and Reinhardt 1988). 

Therefore, whitebark pine is uniquely positioned as a species that can increase under the more frequent fire regimes 

that result from warming climates. Further, nutcrackers may 

be harvesting seeds from trees that have survived blister 

rust, so there is some chance that seeds from unclaimed 

nutcracker caches may become blister rust-resistant trees. It 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
168 USDA Forest Service RMRS-GTR-374. 2018

is entirely possible that as long as wildland fire creates areas 

where birds will cache seeds and resultant seedlings can 

grow without competition, whitebark pine will continue to 

thrive throughout its range.

Current mountain pine beetle outbreaks are killing more 

whitebark pine than historical records indicate, and these outbreaks are probably a result of warmer winter temperatures 

that facilitate expansion of and establishment of beetle populations in the higher elevation whitebark pine zone (Logan 

and Powell 2001; Logan et al. 2003). A warmer climate may 

also accelerate the spread of blister rust (Koteen 1999).

In summary, whitebark pine is not expected to do well 

under future climates, not because it is poorly adapted to 

shifts in climate regimes, but rather because it is currently 

undergoing major declines from the exotic disease white 

pine blister rust that preclude its immediate regeneration in 

future burned areas. Moreover, the declines from white pine 

blister rust and mountain pine beetle have served to reduce 

whitebark pine populations to severely low levels, and now 

the nutcracker is acting more as a seed predator than a seed 

disperser (Keane and Parsons 2010). Climate shifts will 

only exacerbate this decline and complicate restoration efforts. Whitebark pine will be highly exposed to any climate 

changes because of its (1) confined distribution to the upper 

subalpine environments, (2) severely depressed populations, 

and (3) lack of ability to regenerate when populations are 

low because of nutcracker predation. The species has the 

genetic capacity to overcome both white pine blister rust 

and new climates to thrive over the next century, but only 

with extensive restoration efforts.

Subalpine Fir

Autecology

Subalpine fir (Abies lasiocarpa) grows in the coolest 

and wettest forest areas of the western continental United 

States (Alexander et al. 1990). Although widely distributed, 

it grows within a narrow range of mean temperatures (25 to 

40 °F); however, January temperatures average 5 to 25 °F. 

In contrast with other subalpine species, cool summers, cold 

winters, and deep winter snowpack are more important than 

precipitation in determining where subalpine fir grows.

Subalpine fir occupies the lower valleys to upper subalpine zone in the Northern Rockies. In the lower valley 

bottoms and footslopes, it is often associated with grand fir, 

western larch, Douglas-fir, western redcedar, and western 

white pine (Pfister et al. 1977). At the mid-subalpine, it 

is often associated with lodgepole pine, Douglas-fir, and 

Engelmann spruce; at the upper subalpine, it is associated 

with whitebark pine, alpine larch, mountain hemlock, and 

Engelmann spruce (Arno 2001). In the Rocky Mountains, 

subalpine fir is commonly found with Engelmann spruce, 

and the two together are often called spruce-fir forests 

(Moran-Palma and McTague 1997). The subalpine fir habitat types are probably the most common forest habitat types 

in the Northern Rockies (Pfister et al. 1977).

Subalpine fir is shade-tolerant, and is often the most 

shade-tolerant of all its associates, except for grand fir and 

mountain hemlock in isolated cases (Alexander et al. 1990; 

Minore 1979) (table 6.3). Although subalpine fir can grow 

under nearly all light conditions, seedling establishment 

and early survival are usually favored by partial shade 

(Knapp and Smith 1982). In the absence of grand fir and 

mountain hemlock, subalpine fir will survive under closedforest conditions with less light than Engelmann spruce. 

It may not compete well with the spruces, lodgepole pine, 

or interior Douglas-fir in the lower subalpine when light 

intensity exceeds 50 percent of full shade. Subalpine fir is 

quite intolerant of drought, and many seedlings can be killed 

if droughts are overly long or deep. The species is highly 

tolerant of frosts and can remain alive in seasonally wet 

conditions. Subalpine fir is usually the climax tree species 

in most subalpine areas of the Northern Rockies, although it 

sometimes shares climax status with spruce.

Subalpine fir is a prolific seed producer, often having 

large cone crops every 2 or 3 years (Alexander et al. 1990). 

Seeds usually drop in late fall, over snow in most places. 

The species is restricted to cold, humid habitats because 

of the low tolerance of seedlings to high temperatures and 

dry conditions (Knapp and Smith 1982); newly germinated 

subalpine fir seedlings rarely tolerate high solar radiation, 

and they are susceptible to heat girdling and drought (Little 

1992). Seedlings are also killed or damaged by spring 

frosts, competing vegetation, frost heaving, damping off, 

snowmold, birds, rodents, and trampling and browsing 

by large animals, but losses are not different than for any 

of the common associates of the species (Alexander et al. 

1990). However, the abundant seedfall of fir, coupled with 

cool conditions in the subalpine, often create dense mats of 

seedlings in stands that contain partial shade and overwhelm 

seedling establishment of all other species. Subalpine fir 

has average genetic diversity for a Northern Rockies tree 

species and weak geographic differentiation. There are 

strong clinal variations in phenological and morphological 

characteristics.

Disturbance Interactions

Subalpine fir is highly susceptible to fire damage because 

of thin bark, low-hanging dense foliage, and shallow roots 

(Ryan and Reinhardt 1988). Even the lowest severity fire 

can cause high mortality in subalpine fir. Frequent fires 

often eliminate subalpine fir from both the overstory and 

understory, thereby maintaining the more fire-adapted species of lodgepole pine, whitebark pine, western larch, and 

western white pine (Little et al. 1994; Murray et al. 1997; 

Wadleigh and Jenkins 1996). Invariably, some fir trees survive even the most severe fires in refugia, thereby providing 

a seed source for future stands (Murray et al. 1998; Veblen 

et al. 1994).

In spruce-fir forests, the most important insect pests 

are the western spruce budworm and western balsam bark 

beetle. The silver fir beetle (Pseudohylesinus sericeus) 

and the fir engraver may at times be destructive, but only 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 169

in local situations in the Northern Rockies. Fir broom rust 

(Melampsorella caryophyllacearum) and wood-rotting fungi 

are responsible for most disease losses, but root and butt rots 

may be important locally. Broom rust and wood rots weaken 

affected trees and predispose them to windthrow and 

windbreak. Decades of intense competition, coupled with a 

period of moderate to severe drought, often cause extensive 

mortality in subalpine fir stands. These high mortality events 

are often attributed to a complex of disease, insects, and 

other agents, but the underlying cause is low vigor in existing trees from overcompetition.

Historical and Current Conditions

Effects of 100 years of fire exclusion have not yet become manifest in most subalpine fir ecosystems because of 

historically infrequent fire and slow successional advancement. However, abundance of subalpine fir cover types has 

increased in many subalpine and upper subalpine landscapes 

(Keane et al. 1994), and many stands that had low subalpine 

fir components now have fir dominating the understory and 

encroaching in the overstory. Increased stand density has 

resulted in many stands becoming stressed from competitive interactions, heightening susceptibility to disturbances. 

Recent dry, droughty conditions have led to high-elevation 

subalpine fir mortality of undetermined origin called subalpine fir die-off, usually attributed to a complex of causal 

mechanisms such as drought, greater competition, higher 

temperatures, and increasing diseases. Therefore, as fire is 

progressively kept off the subalpine landscape, the subalpine 

fir stands that replaced the pine communities will progressively decline in vigor and be more susceptible to fire, 

insects, and diseases. A concern is that if these overly dense, 

unhealthy stands continue to escape fire, the seed sources 

of the fire-adapted pines will be eliminated, and high elevation sites may be converted to grass and shrublands (Keane 

2001). Another concern is that as fire is excluded from these 

dense forests, canopy and surface fuels will accumulate to 

such levels that, when they are burned, fires will be of extremely high severities (Keane 2001; Morgan et al. 1994b).

Climate Change Responses

It is challenging to predict responses of subalpine fir to 

future climate change. It is a species that is highly adapted 

to moist growing conditions, so it is likely to respond 

poorly to increasing temperatures and drought (Alexander 

et al. 1990). On the other hand, it is a fierce competitor 

that can outcompete all subalpine tree species for shade, 

and it is a species that has a diverse range throughout the 

Northern Rockies. Subalpine fir could expand its range into 

the treeline, become more or less productive in its current 

range, and decline in productivity and occurrence in those 

areas that become inhospitable for the species, presumably the warmer, drier portions of its current range. Most 

paleo-reconstructions over the Holocene show subalpine 

fir dominated during periods of cold, moist conditions but 

declined in extent as climates warmed (Brunelle et al. 2005; 

Whitlock 1993, 2004). Hamann and Wang (2006) projected 

that future losses of subalpine fir from drought will exceed 

gains from range expansion, resulting in a 97-percent 

decrease in the range of the species in British Columbia. 

Romme and Turner (1991) estimated major to minor losses 

in subalpine fir in the future in the GYA, depending on 

degree of warming, and Bell et al. (2014) modeled little 

loss of subalpine fir in the Northern Rockies. Using SDM 

techniques, Crimmins et al. (2011) estimated that the 

subalpine fir/spruce zone would move upward in elevation 

by 300 feet by 2050. Woodward et al. (1994) suggested 

that subalpine fir will produce less frequent and lower cone 

crops in the future. However, seedling establishment may 

be the bottleneck for subalpine fir in the future; the species 

needs long periods of high moisture for seeds to germinate 

and seedlings to thrive (Urban et al. 1993), and years that 

meet these conditions may be less frequent in the future in 

the lower subalpine.

In those areas with abundant precipitation, longer 

growing seasons and reduced snowpacks may increase 

regenerative success of subalpine fir, especially in subalpine 

areas where snow pack historically controlled regenerative 

success (Means 1990; Urban et al. 1993). These areas constitute most of the range of fir in the subalpine to treeline. 

Little and Peterson (1991) found that most fir regeneration 

occurred in low snow years because there were more 

suitable microsites. Villalba et al. (1994) found subalpine 

fir growth was positively correlated with increasing summertime temperature. Higher productivity in these subalpine 

forests may also increase cone crops, tree growth, and 

species densities. Denser stands may eventually result in 

high competitive stress, making these fir stands even more 

vulnerable to high mortality from insects, disease, and abiotic factors, and therefore less resilient. However, declines 

in whitebark pine and lodgepole pine from beetle- and rustcaused mortality may facilitate fir regeneration and growth, 

resulting in more fir trees and more stands dominated by 

subalpine fir.

Those Northern Rockies areas in high-elevation (treeline) 

settings may have an increase in subalpine fir as the heavy 

snow and cold conditions that precluded fir regeneration at 

treeline become less frequent (Cayan et al. 2001; Rochefort 

et al. 1994). However, the decline of whitebark pine trees 

that act as nurse crops to facilitate subalpine fir establishment may contribute to the inability of the fir to establish in 

the high elevation settings. Establishment of populations at 

the upper subalpine and treeline may be possible only when 

fire is absent long enough to allow enough subalpine fir to 

gain reproductive maturity; then sufficient seed can be dispersed over enough years to ensure suitable environmental 

conditions for seedling establishment (Little and Peterson 

1991; Little et al. 1994).

Increases in wildland fire would decrease subalpine fir 

throughout the Northern Rockies, and those decreases would 

be much more extensive and steeper than any resulting from 

direct climate change effects. Frequent fires would favor 

nearly all of the associates of subalpine fir because it is the 

least adapted to survive fire (Arno and Hoff 1990; Keane 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
170 USDA Forest Service RMRS-GTR-374. 2018

2001). Little et al. (1994) found limited subalpine fir regeneration over 30 years after a fire at Mount Rainier, but those 

regeneration events that did occur happened after low snow 

years. Heusser (1998) found that subalpine fir increased in 

growth with warmer temperatures during the spring of the 

growth year, but growth was negatively correlated with high 

summer temperatures the previous years.

In summary, the future of subalpine fir will depend 

on both the future level of fire and the degree of climatic 

warming. Subalpine fir is likely to be a species that shifts 

across the high mountain landscape, with gains in expansion 

balancing losses of contraction (caused directly by changes 

in climate). However, future increases in fire, disease, and 

insects may limit its abundance. Fir is an aggressive competitor, so gains in the species through advanced succession 

in the upper subalpine will probably be balanced by or 

exceed losses from the drier, lower subalpine caused by fire, 

drought, and pathogens.

Engelmann Spruce

Autecology

Engelmann spruce (Picea engelmannii) is widely distributed in the western United States and is a major component 

of the high-elevation Northern Rockies forests (Alexander 

and Shepperd 1990). It grows in humid climates with long, 

cold winters and short, cool summers, and occupies one of 

the highest and coldest environments of the western United 

States. The range of mean annual temperature in which this 

species occurs is narrow considering its wide distribution. 

Engelmann spruce grows best on moderately deep, welldrained, loamy sands and silts and clay loam soils from a 

variety of volcanic and sedimentary materials. It also grows 

well on glacial and alluvial soils where the water table is 

accessible.

Engelmann spruce is rated as shade tolerant, but it is less 

shade tolerant than its major associate, subalpine fir (Minore 

1979) (table 6.3). It is more shade enduring than interior 

Douglas-fir, western white pine, lodgepole pine, quaking 

aspen, western larch, or ponderosa pine (Alexander and 

Shepperd 1990). The species does not tolerate drought well 

and it is perhaps the least adapted to drought conditions of 

the subalpine tree species (Alexander and Shepperd 1990). 

It is highly frost tolerant and one of the few upper subalpine 

species that can tolerate seasonal standing water. It is associated with mycorrhizae but does not seem to be dependent on 

the fungi for survival. It is wind pollinated and its seeds are 

wind dispersed.

In the Northern Rockies, Engelmann spruce is mostly 

associated with subalpine fir but grows with many other 

tree species, including mountain hemlock, whitebark pine, 

western larch, Douglas-fir, quaking aspen, lodgepole pine, 

limber pine, and western hemlock. In most upland subalpine 

Northern Rockies sites, Engelmann spruce is a minor species associated with subalpine fir in later seral communities. 

It is often found in the upper subalpine as scattered individuals with the greatest height and diameter (Arno 2001). 

Pure Engelmann spruce communities are found in wet areas 

and riparian settings, and in severe frost pockets where all 

frost-sensitive tree species are excluded.

Spruce seeds germinate in a variety of substrates, including duff, litter, and decomposed humus, and seedlings 

have best initial survival on duff seedbeds, rather than on 

mineral soil. Engelmann spruce has low tolerance to high 

temperatures and drought, especially in the first 5 years of 

establishment. Due to its slow initial root penetration and 

sensitivity to heat in the succulent stage, drought and heat 

girdling kill many first-year spruce seedlings. Drought 

losses can continue to be significant during the first 5 years 

of seedling development, especially during prolonged 

summer dry periods (Alexander and Shepperd 1990). After 

establishment, adequate soil moisture, cool temperatures, 

and shade favor survival.

Engelmann spruce is similar to subalpine fir in that it has 

an average genetic diversity with weak geographic differentiation. It is considered intermediate in its adaptive strategy, 

being neither a generalist nor a specialist. Populations show 

habitat specificity. Engelmann spruce has a high outcrossing 

rate and possesses the ability to cross with white spruce 

(Picea glauca).

Disturbance Interactions

Engelmann spruce is highly susceptible to fire injury and 

death, but some spruce survive severe burns because of their 

large size (Bigler et al. 2005; Wadleigh and Jenkins 1996). 

The species can survive fire better than its primary associate, 

subalpine fir (Ryan and Reinhardt 1988). Surviving large 

spruce trees can provide abundant seed in burned areas, but 

rarely do these seeds germinate to create forests dominated 

by Engelmann spruce; these spruce-dominated forests occur 

only in seasonally wet habitats (Pfister et al. 1977).

Engelmann spruce is susceptible to windthrow, especially 

after any cutting in old-growth forests. The spruce beetle 

(Dendroctonus rufipennis) is the most serious insect pest 

of Engelmann spruce. It is restricted largely to mature and 

overmature spruce, and epidemics have occurred throughout 

recorded history. The western spruce budworm also attacks 

Engelmann spruce.

Historical and Current Conditions

It is difficult to determine recent trends in Engelmann 

spruce forests across the Northern Rockies because the species is rarely the dominant component in a stand. One would 

expect that advancing succession under a century of fire 

exclusion has increased spruce in the subalpine and upper 

subalpine. However, logging and fire have reduced spruce 

in lower elevation areas, where it occurs in seasonally wet 

areas and frost pockets.

Climate Change Responses

Similar to subalpine fir, some losses of Engelmann 

spruce are likely in the drier portions of its range, especially 

in those seasonal moist sites that will be mostly dry in the 

future. Liang et al. (2015) found that major mortality events 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 171

have occurred in Engelmann spruce over the last 20 years 

because of increased drought, presumably related to changing climate. Alberto et al. (2013) found that this species had 

lower growth the year following warm, dry years in the U.S. 

Cascades. Using SDMs, Morales et al. (2015) projected a 

47 percent contraction in Engelmann spruce in the northern 

Rocky Mountains by 2060, and Hamann and Wang (2006) 

projected a 27-percent decrease in the range of Engelmann 

spruce in British Columbia by 2050. Gray and Hamann 

(2013) estimated Engelmann spruce would move 230 miles 

northward and 550 feet higher in elevation in the Northern 

Rockies by 2050. Using SDMs for the southwestern United 

States, Notaro et al. (2012) projected that Engelmann spruce 

would disappear by 2050. Using gap modeling, Burton 

and Cumming (1995) projected a precipitous collapse of 

Engelmann spruce in the mesic forests of British Columbia. 

Coops and Waring (2011) used mechanistic modeling 

to simulate a retraction in spruce range of more than 50 

percent.

Engelmann spruce may be the first species to become 

established in high elevation areas where snow precluded 

conifer regeneration historically, but where there now may be 

a seasonal wetland or subalpine wet meadow (Schauer et al. 

1998). Jump and Peñuelas (2005) note that Engelmann spruce 

has the genetic capacity to adapt to large swings in climate 

in situ by taking advantage of shifts in microsites. Due to the 

great seed dispersal ability and tall stature of the species, it is 

able to disseminate into previously unforested areas, such as 

glades, meadows, and balds, to expand its range. Whitlock 

(2000) found increased spruce regeneration during the warmest periods of the past several centuries, and Luckman et al. 

(1984) found Engelmann spruce growth positively correlated 

with increasing summertime temperature. Various SDM approaches project minor changes in the spruce-fir subalpine 

zone (Bell et al. 2014; Crimmins et al. 2011).

Engelmann spruce is poorly adapted to fire, and thus 

major declines are expected with the projected increases in 

area burned. But these declines may be offset by increased 

regeneration on burned areas with mineral soil substrates. 

Continued fire suppression activities may maintain spruce 

on the landscape, but this species may persist at lower 

abundance because of increased drought. Fire suppression 

may also ensure the demise of Engelmann spruce in that, 

when fires eventually burn, the severities may be so great 

that they kill all spruce seed sources. In addition, Bentz et 

al. (2010) noted that future climates are likely to be more 

conducive to the spruce beetle, and Stout and Sala (2003) 

suggested that future climates may foster more spruce budworm events, leading perhaps to further declines in spruce.

In summary, Engelmann spruce is a species that is 

highly sensitive to climate but likely to persist in future 

Northern Rockies landscapes because of the superior 

ability of the species to seed into new areas, especially 

burned areas, and ability to remain in the high mountain 

landscape. Projected increases in subalpine productivity 

will also serve to keep spruce on the Northern Rockies 

landscape.

Mountain Hemlock

Autecology

Mountain hemlock (Tsuga mertensiana) is usually found 

on cold, wet, snowy upper subalpine sites, where it grows 

slowly and sometimes lives to be more than 800 years old. 

The species is apparently limited by late snowmelt, short 

growing seasons, and cool summer temperatures throughout much of its range in the Pacific Northwest. Earlier 

snowmelt, higher summer temperatures, and lower summer 

precipitation in the lower portions of its range produce 

conditions under which growth is limited (West et al. 2009). 

Areas occupied by mountain hemlock generally have a cool 

to cold maritime climate that includes mild to cold winters, 

a short, warm to cool growing season, and moderate to high 

precipitation. The presence of mountain hemlock in the 

Rocky Mountains is closely correlated with the eastward 

penetration of moist maritime air masses (Woodward et al. 

1994). Mountain hemlock occurs in mixed upper subalpine 

stands in the western portions of the Northern Rockies, 

often relegated to the moist north slopes.

Mountain hemlock is considered highly tolerant of 

shade and other forms of competition, and it is probably 

more tolerant than any of its Northern Rockies associates, 

even subalpine fir in some places (Minore 1979). Mountain 

hemlock is considered a minor climax species in most 

of its limited habitats; mountain hemlock often succeeds 

lodgepole pine or subalpine fir (Means 1990). The species 

has a low tolerance to drought but a high tolerance to frost 

and standing water. It is wind pollinated, and the seeds are 

wind dispersed.

Mountain hemlock has large cone crops about every 3 

years. It reaches reproductive maturity quickly by around 

20 years of age, and most of the seedfall occurs during 

the fall months. It has average genetic diversity and weak 

geographic differentiation, but moderate population 

differentiation.

Disturbance Interactions

Mountain hemlock is considered susceptible to fire because it often retains branches almost to the ground, grows 

in clusters, and often has shallow roots spread throughout 

well-developed forest floors that dry out in the summer 

(Dickman and Cook 1989). It has thick bark and can 

withstand some low-intensity fire, but overall, it will often 

succumb to fire damage over time. Fire is a rare visitor to 

these mesic, cold stands, so any increase in fire frequency 

will reduce mountain hemlock populations.

The most striking damage to mountain hemlock is probably that caused by laminated root rot. This fungus spreads 

from centers of infection along tree roots so that all trees 

are killed in circular areas that expand radially. Mountain 

hemlock is the species most susceptible to root rot in subalpine forests (Means 1990).

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
172 USDA Forest Service RMRS-GTR-374. 2018

Historical and Current Conditions

There have been few evaluations of mountain hemlock 

distributions in the Northern Rockies, and thus it is difficult to gauge trends in this species over the last century. 

The fire exclusion era has advanced succession in those 

subalpine sites where mountain hemlock can be found, 

thereby increasing the numbers and density of the species. 

These dense forests are probably not currently stressed 

because of high productivity in these areas. Mountain 

hemlock has a limited range in the region, so any significant warming and drying could drive the species to local 

extinction.

Climate Change Responses

With warming climate in western North America, existing mountain hemlock forests will probably increase in 

productivity, especially in the upper and lower elevational 

boundaries of the mountain hemlock zone (Means 1990). 

Near Mount Baker, Washington, ring width of mountain 

hemlock increased with increasing monthly temperatures in 

the preceding 12 months, decreasing winter precipitation, 

and decreasing snow depth, implying that productivity should increase with predicted temperature increases 

(Woodward et al. 1994). Graumlich et al. (1989) estimated 

that productivity increased 60 percent in the last century in 

four high-elevation stands in Washington, three of which 

contained 48 to 96 percent mountain hemlock. They related 

this increase most strongly to the increase in growing 

season temperature during this period (about 2.7 °F). West 

et al. (2009) projected increases in growth and productivity of mountain hemlock throughout much of its range in 

Washington and northern Oregon, but increased summer 

drought stress will reduce productivity in mountain hemlock 

forests of southern Oregon and near the lower elevation limit of the species. Peters and Lovejoy (1992) estimated that 

if mean annual temperatures increase 4.5 °F, the mountain 

hemlock zone may be shifted 1,800 feet higher in elevation 

and decrease as a proportion of forestland from 9 percent to 

2 percent in Oregon. An increase of 9.0 °F may induce an 

upward shift of 3,700 feet, which is above all but the tallest 

peaks, effectively eliminating the species from the Northern 

Rockies (Means 1990). Woodward et al. (1994) speculated 

the mountain hemlock will produce less frequent and lower 

cone crops in the warm future.

In summary, the high productivity of mountain hemlock 

sites in the western Northern Rockies may mitigate the 

potential decline of mountain hemlock over the next 50 

years. Local shifts of the species are likely to occur where 

it is established in droughty low-elevation areas of Idaho 

and western Montana, but overall, the species might be 

somewhat stable under climate warming. It might even 

increase in productivity and make range expansions into the 

lower treeline. The species is not highly exposed to climate 

changes because of its limited range in the region and its 

somewhat confined niche. The magnitude of climate effects 

on mountain hemlock responses will be great, but mostly 

positive, and the likelihood of these effects has a high uncertainty, primarily because of the uncertain role that fire will 

play in the dynamics of mountain hemlock populations in 

future landscapes.

Alpine Larch

Autecology

Alpine larch (Larix lyallii) is a deciduous conifer that 

occupies the highest and most remote environments in 

the Northern Rockies, growing in and near treeline on 

high mountains across the inland Pacific Northwest (Arno 

1990). In the Rocky Mountains, alpine larch extends from 

the Salmon River Mountains of central Idaho northward to 

Lake Louise in Banff National Park, Alberta (Arno 1990). 

Within this distribution, alpine larch is common in the 

highest areas of the Bitterroot, Anaconda-Pintler, Whitefish, 

and Cabinet Ranges of western Montana. It is also found in 

lower abundance in isolated stands atop many other ranges 

and peaks in western Montana and northern Idaho (Arno 

and Habeck 1972). Alpine larch grows in cold, snowy, and 

generally moist climates where for more than half of the 

year, mean temperatures are below freezing. Mean annual 

precipitation for most alpine larch sites is between 32 and 

75 inches, the larger amount being more prevalent near the 

crest of the Cascades; most stands in the Montana Bitterroot 

Range receive 39 to 59 inches. About 75 percent of this 

precipitation is snow and sleet. Ridgetop alpine larch stands 

are exposed to violent winds; most alpine larch stands annually experience winds reaching hurricane velocity or more, 

especially during thunderstorms or during the passage of 

frontal systems.

Alpine larch is perhaps the most drought-susceptible 

conifer in the Northern Rockies because of its reliance on 

subsurface water during the dry summer months (Arno 

1990). It achieves its best growth in high cirque basins and 

near the base of talus slopes where the soils are kept moist 

throughout the summer by aerated seep water. It can also 

tolerate boggy wet meadow sites having very acidic organic 

soils. The species is most abundant on cool, north-facing 

slopes and high basins, where it forms the uppermost band 

of forest. It also covers broad ridgetops and grows locally 

under relatively moist soil conditions on south-facing 

slopes. The Northern Rockies may have a droughty period 

for a few weeks in late summer, but the effect is minor in 

most alpine larch sites; however, dry surface soils may prevent seedling establishment in certain years.

Alpine larch is the most shade-intolerant conifer growing 

at high-elevation Northern Rockies sites and is classified 

as very intolerant (Minore 1979) (table 6.3). Its evergreen 

associates attain their best development in forests below 

the lower limits of larch. An exception is whitebark pine, 

another treeline inhabitant, which is most abundant on 

warm exposures and microsites and thus tends to complement rather than compete with larch. Alpine larch grows 

mostly in pure stands, but it can be found with whitebark 

pine, subalpine fir, and Engelmann spruce near their upper 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 173

limits. Alpine larch roots extend deep into fissures in the 

rocky substrate. Trees are well anchored by a large taproot 

and large lateral roots and are very windfirm. Alpine larch 

is easily replaced by subalpine fir in most upper subalpine 

sites, but the species can act as a climax species in the lower 

treeline (Arno and Habeck 1972).

Alpine larch is one of the few deciduous conifers in the 

Northern Rockies, and as a result, it has a high capacity to 

survive wind, ice, and desiccation damage during the winter 

because the needles are off the trees. The species also has an 

evergreen sapling stage that allows it to quickly take advantage of the short growing season in the early summer after 

snowmelt (Arno and Habeck 1972). Alpine larch seedlings 

are frost-tolerant. Mature trees produce good cone crops 

every fifth year, and these seeds drop in early fall. It is assumed that alpine larch has an average genetic diversity and 

weak geographic differentiation, but little genetic work has 

been done on this species.

Disturbance Interactions

Fire is an occasional but localized visitor in alpine larch 

stands, causing injury or death in most cases. Large fires are 

infrequent in the cool, moist, and rocky sites where alpine 

larch occurs, and fire spreads poorly on these sites because 

of light and discontinuous fuels. Unlike its thick-barked, 

fire-resistant relative western larch, alpine larch has thin 

bark, has low resistance to surface fire, and often dies after 

low-intensity fires (Ryan 1998).

Powerful winds in alpine larch stands often damage 

crowns, in conjunction with loads of clinging ice or wet 

snow (Arno and Habeck 1972). Nevertheless, the deciduous 

habit and supple limbs of this tree make it more resistant 

to wind damage than its associates. Death usually occurs 

when advanced heart rot has so weakened the bole that high 

winds break off the trunk. Brown trunk rot produces the 

only conks commonly found on living trunks (Arno 1990); 

this fungus is evidently the source of most heart rot. Snow 

avalanches and snowslides are an important source of damage in many stands, but again, this species is better adapted 

to survive these disturbances than its evergreen associates.

Historical and Current Conditions

This species is rarely studied, and as a result, very little is 

known about its population trends in the Northern Rockies. 

Our best guess is that alpine larch populations have stayed 

roughly the same across most of its range in the region over 

the last 100 years. There have been some losses from fire in 

some areas, especially the Bitterroot Mountains of Montana, 

but there have also been gains. Recent anecdotal observations indicate that alpine larch has been increasing in ribbon 

forests, glades, and high-elevation open areas where snow 

accumulated historically; over the last two decades, these 

areas have been clear of snow enough of the year to foster 

alpine larch regeneration.

Climate Change Responses

We think alpine larch has a high potential to decrease in 

both productivity and abundance with climate change. On 

the one hand, alpine larch is a shade- and drought-intolerant 

species, so it does not do well in areas of increasing dryness and competition (Arno and Habeck 1972). Its high 

demand for subsurface water during the growing season is 

apparently the main factor limiting its range in the Northern 

Rockies (Arno 1990), making it highly susceptible to increasing drought in the future. Alpine larch growth is highly 

correlated with high snowpack, especially in April, which is 

usually indicative of high subalpine moisture throughout the 

year (Colenutt and Luckman 1991; Peterson and Peterson 

1994). The lack of summertime groundwater would be 

more likely in the southern part of the species range in the 

Northern Rockies, specifically western Montana and central 

Idaho.

On the other hand, alpine larch can produce copious 

amounts of seed that may land on upper subalpine and timberline areas that were historically covered with snow for 

most of the year but in the future may be sufficiently snowfree to allow wind-dispersed seed to germinate and grow 

into viable seedlings. There is ample anecdotal evidence 

documenting alpine larch encroachment into ribbon forests, 

glades, and snowfields. These seedlings could become 

mature trees, provided there is sufficient moisture. With 

higher rates of productivity in a warming climate, seedlings 

and trees may have greater growth and cone production. 

However, short-term increases in alpine larch regeneration 

may be offset by the high variability in drought in the upper subalpine, which may eventually cause declines in the 

larch. Another possibility is that the more shade-tolerant 

subalpine conifers, such as spruce and subalpine fir, might 

become established in these new open areas and outcompete 

alpine larch for dominance. Along those same lines, the 

more drought-tolerant whitebark pine may also become established in the snow-free areas and survive the anticipated 

long droughts.

Although alpine larch apparently lacks the morphological, ecophysiological, and genetic capacity to adapt to 

new environments, it does have the ability to genetically 

intergrade with western larch to produce hybrids that may 

be more tolerant of drought and competition (Carlson et 

al. 1990). Moreover, its superior seed dispersal capability 

may allow it to become established in treeline areas made 

environmentally favorable by climate change, mainly from 

decreasing snowpacks and higher temperatures. These areas, 

however, may be significantly smaller and more isolated 

than areas in its current range, where it will decline because 

of lack of water.

Alpine larch is not well adapted to survive wildland fire 

(Arno 1990), and as its existing range becomes drier and 

fires become more probable, it is expected that more alpine 

larch will burn, providing there are sufficient fuels. Those 

upper subalpine forests that are co-dominated by whitebark 

pine and alpine larch are probably the most susceptible of 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
174 USDA Forest Service RMRS-GTR-374. 2018

subalpine larch habitats to increases in fire. Rocks, scree, 

and fuel-free areas protect many alpine larch communities, 

so it may be years before fire, or the more shade-tolerant 

competitors, invade pure alpine larch woodlands (Arno 

and Habeck 1972). Although alpine larch does not seem to 

be impacted by major insects and pathogens (Arno 1990), 

future climates may increase the possibility that insects and 

diseases that were relatively minor in the past could become 

more significant in the future, especially in timberline environments where damaging agents were depressed by cold 

(Woods et al. 2010).

In summary, alpine larch is one of the most susceptible 

tree species in the Northern Rockies region to climatic shifts 

that result in increasing drought and fire. Its exposure to 

climate change is likely to be high because upper subalpine 

areas may experience the greatest climatic change (Luce 

et al. 2013). Due to its specialized habitat, alpine larch has 

the highest risk for major range shifts, and impacts to the 

species may be great if there are insufficient environments 

created upslope.

Green Ash

Autecology

Green ash (Fraxinus pennsylvanica) is the most widely 

distributed of all the American ashes (Kennedy 1990), 

but primarily occurs in the eastern and central United 

States. In the Northern Rockies, green ash is restricted to 

the northern Great Plains, which is the northwestern edge 

of its range (Girard et al. 1987; Lesica 2009). Naturally a 

moist bottomland or streambank tree, it is well adapted to 

climatic extremes and has been widely planted in the Plains 

States and Canada. It is probably the most adaptable of all 

the ashes, growing naturally on a range of sites, from clay 

soils subject to frequent flooding and overflow, to sandy or 

silty soils where the amount of available moisture may be 

limited. In the northern Great Plains, green ash grows best 

on fertile, moist, well-drained alluvial soils, primarily along 

river bottomlands and woody draws. It also occurs in broad 

upland depressions and ridges, which have subsurface water 

early in the growing season (Girard et al. 1987; Lesica 2003; 

Lesica and Marlow 2013). Natural stands of green ash are 

almost completely confined to bottomlands, but the species 

grows well when planted on moist upland soils. It lines the 

watercourses in the western parts of its range where rainfall 

is insufficient to support upland growth.

Green ash varies from intolerant to moderately shadetolerant in woody draws. It is an early-seral species, 

colonizing alluvial soils. It regenerates from seed when exotic grass (which inhibits germination through competition 

for soil moisture) is absent or has low cover (Lesica 2003; 

Lesica and Marlow 2013). It also regenerates vegetatively 

through stump sprouting. Uresk and Boldt (1986) reported 

90-percent sprouting success following trunk removal in an 

experimental study in North Dakota. Lesica (2009) found 

that stump sprouts can achieve full tree height in 20 years. 

Although green ash is generally drought-tolerant, prolonged 

drought may affect regeneration success because it is at 

the most arid edge of its range (Severson and Boldt 1978). 

Kennedy (1990) found that a population from the arid, 

northwestern part of the green ash range was more droughtresistant than one from the moister central Great Plains and 

northeast.

Disturbance Interactions

Green ash is easily killed by fire, but stumps of most 

size classes of green ash sprout readily after both fire and 

mechanical trunk or stem removal (Lesica 2009). The 

species has several insect and disease agents; it is particularly susceptible to white stringy heartroot (Perenniporia

fraxinophila), which weakens the plant and makes it more 

susceptible to wind or ice breakage (Lesica and Marlow 

2013).

Historical and Current Conditions

Very little is known about the range expansion or contraction of green ash. However, green ash in the Northern 

Rockies is at the northwestern (most arid) edge of its range 

(Lesica 2009), and evidence suggests that many of the green 

ash communities on the western fringe of the northern Great 

Plains are declining (Boldt et al. 1978; Lesica 1989, 2001).

Climate Change Responses

Green ash has a broad ecological amplitude and can 

survive droughty conditions, but it grows optimally on moist 

sites. As soil moisture declines with a warmer, drier climate, 

marginal sites may become less favorable for regeneration 

and survival of young green ash trees. With increases in 

fire frequency, there will probably be increased vegetative 

regeneration and decreased production of seedlings following fire; fire often kills green ash seed on or near the 

soil surface, restricting seedling recruitment to surviving 

seed-producing trees. Green ash may benefit from increased 

temperatures because seedling and mature tree growth 

may increase with increasing soil temperatures. However, 

those green ash populations associated with moist upland 

microsites (e.g., northeast-facing residual snow-loaded 

depressions) may suffer severe drought stress as snowpack 

declines and melts sooner, and regeneration may decrease, 

eventually resulting in loss of those communities.

Most mature green ash communities are somewhat 

resistant to wildland fire, given that the species can sprout 

afterward, so the projected increases in fire in the future may 

not impact most green ash stands, especially the moist communities. Low-severity fires might promote regeneration 

by thinning stands and stimulating sprouting; green ash has 

both root crown and epicormic sprouts, and both are typical 

following fire events, especially in the woody draws and 

riparian areas of the Great Plains. High-severity fires, however, may result in mortality. Browsing pressure on green 

ash communities is also likely to increase with increased 

drought, as upland grasses and forbs desiccate and senesce 

earlier, or are replaced by invasive, less palatable species.

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Cottonwood

Autecology

Black cottonwood (Populus trichocarpa) is the largest of 

the American poplars and the largest hardwood tree in western North America (Debell 1990). Narrowleaf cottonwood 

(P. angustifolia) and black cottonwood grow primarily on 

seasonally wet to moist open canopy sites (typically along 

streams and rivers) in the western portions of the Northern 

Rockies. Plains cottonwood (Populus deltoides) occurs in 

eastern Montana and the Dakotas portion of the region. All 

three species typically occupy fluvial surfaces along floodplains of streams and rivers.

Cottonwoods typically dominate riparian communities 

on alluvial sites at low to mid-elevations. Various riparian 

shrubs (e.g., willows [Salix spp.], alder [Alnus spp.)], birch 

[Betula spp.], dogwood [Cornus spp.)]) and a variety of 

graminoids and forbs occur in the understory of cottonwood stands (Merigliano 2005). Cottonwood is very shade 

intolerant, and conifers (e.g., Douglas-fir, Rocky Mountain 

juniper [Juniperus scopulorum], ponderosa pine, Engelmann 

spruce, subalpine fir) may encroach and become dominant 

in upland cottonwood forests (typically on river and stream 

terraces). The species is also drought intolerant, and requires 

an accessible water table (i.e., free, unbound water) during most of the growing season (Rood et al. 2003). Older 

cottonwood individuals can reach very deep water tables. 

Plains cottonwood is probably more able to extract water in 

the unsaturated zone once the water table has dropped below 

the extent of the roots (Merritt et al. 2010). The finer textured soils in the northern Great Plains hold more water, but 

it is harder to extract due to the finer soil texture. However, 

plains cottonwood has apparently adapted to extract water 

and is likely to be more resilient to drought than the other 

species.

For all three species of cottonwood, high streamflows are 

required for successful seedling establishment; the associated scouring action and deposition of fresh alluvium creates 

optimal surfaces for germination. All species of cottonwood 

are prolific seed producers, and the windborne seeds disperse widely once the catkins have matured and seeds are 

released. Seeds are viable for only about 2 weeks, and thus 

timing of seed release and recession of flood flows is essential to successful germination (Malanson and Butler 1991). 

Black and narrowleaf cottonwood seedlings are usually 

established on a yearly basis, depending on flood frequency, 

timing, and duration. Plains cottonwood establishment is 

less frequent and more episodic because flows are more 

variable in both magnitude and frequency. Scott et al. (1997) 

found that about 72 percent of the plains cottonwoods along 

the Missouri River of eastern Montana established after a 

very large flood event (flow >1,800 cubic yards per second 

with a recurrence interval of 9.3 years). High numbers of 

seedlings become established in the first year after a flood, 

but they naturally thin out up to several years later, if they 

have not been scoured away by high flow events. The young 

seedlings and saplings that survive are frequently injured 

and sometimes killed by unseasonably early or late frosts 

(Debell 1990).

Disturbance Interactions

Cottonwood is mildly fire tolerant owing to its thick 

bark, high branches, and foliage that is too moist to burn 

in most years. It is considered a weak stump sprouter, but 

unlike aspen, cottonwood rarely regenerates from suckers 

(Brown 1996). Gom and Rood (1999) found that black and 

narrowleaf cottonwood were more successful at coppice 

(stump) sprouting and suckering than plains cottonwood. 

Cottonwood is able to survive low-intensity fires in the short 

term, but fire injuries can lead to the introduction of diseases 

that weaken and perhaps kill the tree (Borman and Larson 

2002).

Although several insects attack cottonwood, none has 

yet been reported as a pest of economic significance. Tent 

caterpillars (Malacosoma spp.) are the most important 

foliar feeders that affect the Northern Rockies. At least 70 

fungal species cause decay in cottonwood, but only 6 fungi 

cause significant losses; 2 of these—brown stringy heart 

rot (Spongipellis delectans) and yellow laminated butt rot 

(Pholiota populnea)—cause 92 percent of the loss. Russian 

olive (Elaeagnus angustifolia) and saltcedar (Tamarix ramosissima) are aggressive invasive trees that often outcompete 

plains cottonwood, particularly during or following drought 

(Shafroth et al. 2002). These species, along with invasive 

herbaceous species, are a threat to cottonwoods in general.

Historical and Current Conditions

Black cottonwood was common throughout the 

Columbia River watershed in Lewis and Clark’s day, and 

can still be found today, but it is greatly reduced in extent.

Climate Change Responses

As snowpack declines and melts earlier with warming 

temperatures, there will be reduced, attenuated river flows 

(loss of extreme high and low flows), along with a possible 

shift in timing of peakflows to earlier in the season, before 

cottonwood seed is viable for germination. These shifts 

in timing, magnitude, and variability may result in both 

decreased germination and establishment of young cottonwoods (Whited et al. 2007). Human demand for water is 

likely to increase in the future, which will probably result in 

creation of additional diversions and reservoir expansions. 

Any alteration of hydrologic flow regime (i.e., timing, magnitude, and duration) will affect both floodplain interaction 

and water available to cottonwoods, which in turn may reduce recruitment and establishment of seedlings (Auble and 

Scott 1998; Beschta and Ripple 2005). Decreased streamflows and floodplain interactions may result in a conversion 

of streamside vegetation from cottonwood to upland species, 

along with reduced growth and regeneration (recruitment) 

and increased mortality of cottonwood (Beschta and Ripple 

2005). Upland conifers (e.g., Engelmann spruce, lodgepole 

pine, and Douglas-fir) typically establish once the stream 

and local water table have dropped, and they can shade out 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
176 USDA Forest Service RMRS-GTR-374. 2018

the remaining cottonwoods. In addition to competition from 

upland conifers, there may be increased browsing pressure 

on cottonwoods, which will further contribute to declines in 

cottonwood regeneration and recruitment.

Plains cottonwood may be more persistent under a 

changing climate because of greater plant-available soil water in the unsaturated zone (as a result of finer textured soils) 

in its habitat. Black and narrowleaf cottonwood typically 

occur in coarser substrate, which will become much drier 

as flows are lower and recede earlier than in the past, or are 

attenuated due to diversions. Seedling and sapling mortality 

may increase in these species. Plains cottonwood regeneration occurs with episodic flooding, whereas black and 

narrowleaf cottonwood regenerate with 1- to 3-year bankfull 

flow return intervals (typically an annual recruitment cycle); 

therefore, plains cottonwood will probably be better adapted 

to irregular flows that may occur with climate change. Black 

and narrowleaf cottonwood are likely to be at greater risk 

to changing climate because of soil water characteristics in 

their habitats and their narrow amplitude in terms of germination and flood events on specific fluvial surfaces.

Vegetation Types

Vegetation types are broad species assemblages that are 

used to identify the geographic distribution of vegetation in 

the Northern Rockies. Vegetation types are different from 

species in that species can be a major to minor component in 

a vegetation type, but vegetation types can be composed of 

a number of species. Here we describe generally the likely 

response of forest vegetation types in the Northern Rockies 

to climate change. This section is less detailed than the section on species because readers can refer to the individual 

species for each vegetation type as presented in the previous 

section.

Dry Ponderosa Pine-Douglas-fir Forests

Ecology

Dry ponderosa pine and Douglas-fir forests are the driest 

forests in the Northern Rockies. These forests are relatively 

rare in northern Idaho, more common in western Montana, 

and prominent in central and eastern Montana where moisture is most limited. They are often found at the foothills of 

mountain ranges in the region, but also in extensive flatlands 

bordering perennial grasslands and shrublands. Historically, 

frequent fires often maintained pure to mixed ponderosa 

pine woodlands and savannas in areas currently occupied by 

this type. However, fire exclusion has led to increased tree 

density and abundance of Douglas-fir, making these forests 

susceptible to uncharacteristically severe fire.

Disturbance Interactions

These forests recover from disturbance by slowly shifting 

from fire-tolerant pioneer species to less fire-tolerant and 

shade-tolerant “climax” species over time. This successional 

process can occur over 200 to 1,000 years. Ponderosa pine 

is often able to colonize the hot dry surface conditions 

of a disturbed site. Over time, as it matures, it provides a 

shaded environment where less heat-tolerant Douglas-fir 

can establish. In a frequent low-severity fire regime, the 

thick-barked ponderosa pine survives fire, whereas the 

thinner barked Douglas-fir and ponderosa pine seedlings do 

not. If frequent fires are sustained, the ponderosa pine forest 

can develop into large patches of open-grown old growth, 

intermixed with relatively small openings that can persist 

for centuries. During a cool wet climatic period, or through 

fire suppression, Douglas-fir or denser ponderosa pine can 

become established. The increased biomass and structural 

heterogeneity of these denser forests allow fires to develop 

into active crown fires that return the site to the initial stand 

establishment phase. If fires burn these areas again, forest 

establishment may be limited because of loss of seed source, 

limited soil moisture, and high surface temperature.

Historical and Current Conditions

A century of fire exclusion, coupled with extensive 

logging and grazing, has changed these open dry woodlands to closed, dense forests that are often dominated by 

Douglas-fir.

Climate Change Responses

This vegetation type may be reduced in some areas of its 

current range under a changing climate because of dry, hot 

conditions. However, this type may expand into the mixed 

mesic forest type (next subsection), especially on south 

slopes, as drought increases. This forest type will probably 

be the most dynamic in the future, with many of the current 

areas of this type seeing losses in Douglas-fir, balanced 

by gains in ponderosa pine. Dry Douglas-fir communities 

that are currently too cool to support ponderosa pine may 

support more ponderosa pine with warming climate. Fire 

exclusion in this type has increased forest density and accumulation of surface fuels; both conditions are likely to 

support high-severity fires in the next century (Keane et al. 

2002).

Western Larch Mixed Mesic Forests

Ecology

Western larch mixed-conifer forests, found in northern 

Idaho and northwestern Montana, evolved under a combination of moist air masses from the west and cold air masses 

from Canada, resulting in a patchy forest condition with a 

mixture of western larch, ponderosa pine, lodgepole pine, 

Douglas-fir, and spruce subalpine forests. Western larch 

is most prominent on cooler, moist topographic positions 

(Touzel 2013); thus, the influence of a warming climate 

may change the potential distribution of western larch to the 

more northerly aspects with soils most capable of retaining 

needed moisture during the growing season (Rehfeldt and 

Jaquish 2010).

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 177

Disturbance Interactions

These forests evolved under a mixed-severity fire regime, 

which produced a diverse pattern of shade-intolerant western larch, ponderosa pine, lodgepole pine, and Douglas-fir. 

High-severity fire was more common on moist and cool 

sites, and produced very large burn patches, often with 

legacy western larch (Marcoux et al. 2015). Under fire exclusion, many of these forests have become denser, putting 

them at risk to high-severity fire (Arno 2010; Harrington 

2012; Hopkins et al. 2013).

Historical and Current Conditions

In the past, wildland fire maintained extensive stands of 

western larch across Montana and Idaho. Due to its great 

value as a timber species, many older stands of western 

larch were harvested across much of the Northern Rockies, 

and these forests were often planted back to western larch 

after extensive site treatments. With fire exclusion, succession advanced and western larch was replaced with mixed 

stands of lodgepole pine, Douglas-fir, and grand fir.

Climate Change Responses

The western larch mixed-conifer forests of northern 

Idaho and northwestern Montana are a forest type that has 

been changing and is likely to continue to change. Fire 

exclusion, coupled with climate change, will probably 

continue to reduce western larch and increase the more 

shade-tolerant Douglas-fir, grand fir, and subalpine fir in 

some areas. Continued fire exclusion will result in further 

accumulation of surface and canopy fuels, and coupled 

with hotter and drier conditions with climate change, will 

put these forests at risk of high-severity fire. High mortality 

of the seed-bearing western larch and ponderosa pine may 

result.

Some attributes of this cover type may serve to make it 

more resilient in the future. Western larch is not susceptible 

to the wide range of insects and diseases common to its 

associated tree species, and it has the best ability to survive 

fire of all its tree associates. As such, it makes an excellent 

candidate to feature in management to increase resilience. 

However, western larch mixed mesic forests are one of our 

most vulnerable forests to climate change impacts, mainly 

because past land management has made natural western 

larch forests susceptible to the damaging effects of uncharacteristically high-severity wildfires. Management of these 

forest types to create stand and landscape conditions within 

the historical range of variability are likely to increase resilience to climate change.

Mixed Mesic Western White Pine-Western 

Redcedar-Western Hemlock-Grand Fir Forests

Ecology

Moist forests within the Northern Rockies range from 

500 to 1,750 feet and occasionally occur at 1,900 feet 

(Jain and Graham 2005). These forests are influenced by 

a maritime climate with wet winters and dry summers. 

Precipitation ranges from 20 to 91 inches and predominantly 

occurs from November to May. A defining characteristic 

of these forests is a layer of fine-textured ash (up to 24 

inches thick) that caps the residual soils. In addition, these 

forests are characterized by complex topography, including 

dissected slopes and varying degrees of slope angle, all 

of which influence soil development and ash cap depth. 

Disturbance is another important component of these forests 

that contributes to creating vegetative mosaics. Thus, the 

combination of disturbance, topography, moisture and temperature regimes, parent material, soil weathering, and ash 

cap depth results in productive vegetation that is complex in 

composition and structure. For example, up to 10 different 

tree species can occupy a given square yard of this forest 

type (Jain and Graham 2005).

The nine primary tree species that grow together in this 

wet forest type, outside of riparian areas, are ponderosa 

pine, western larch, Douglas-fir, grand fir, western white 

pine, western redcedar, western hemlock, lodgepole pine, 

and Engelmann spruce. The niche that these species occupies varies by habitats. For example, western redcedar 

is a mid-seral species in western hemlock types but is late 

seral on western redcedar riparian and upland habitat types. 

The genetic adaptive capacity and autecological characteristics of individual trees species and their tolerances to 

light, moisture, temperature, and disturbance is also highly 

variable among the different tree species in this forest type 

(Minore 1979). Some species are better adapted to regenerating in shade (western hemlock and western redcedar), 

whereas other species can regenerate in a wide range of 

conditions (western white pine). Some have a stronger 

competitive capacity than other species when growing 

together; for example, western larch cannot compete with 

western hemlock. Some are drought-tolerant (ponderosa 

pine, western larch, and western white pine), and others are 

drought-intolerant (western hemlock).

Disturbance Interactions

Natural disturbances (snow, ice, insects, disease, and 

fire), when combined, create heterogeneity in patch sizes, 

forest structures, and composition in this forest type. Ice 

and snow create small gaps and openings, reducing forest 

densities and altering species composition. Native insects 

(e.g., bark beetles) and diseases (e.g., Armillaria root rot 

and dwarf mistletoes) infect and kill the very old or stressed 

individuals, and tend to diversify vegetation communities 

(Hessburg et al. 1994). A mixed-severity fire regime also 

plays a role in creating a mosaic of forest compositions and 

structures. Historically, nonlethal surface fires occurred 

at relatively frequent intervals (every 15 to 25 years) in a 

quarter of the area of this forest type. Lethal crown fires 

burned about a quarter of the area at intervals of 20 to 150 

years, occasionally extending to 300 years. A mixed-severity 

fire regime characterized the rest of the moist forests, with 

return intervals of 20 to 150 years. Fires typically started 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
178 USDA Forest Service RMRS-GTR-374. 2018

burning in July and were usually out by early September 

(Hann et al. 1997).

Historical and Current Conditions

In addition to white pine blister rust and salvage that removed most of the western white pine, harvesting removed 

the early-seral, shade-intolerant species (e.g., ponderosa 

pine and western larch) that were resistant to fire and other 

disturbances. Partial canopy removal and minimal soil surface disturbance in these harvests were ideal for Douglas-fir 

and grand fir, which regenerated aggressively, in contrast 

with the shade-intolerant pines and larch species. Fire exclusion also prevented the creation of canopy openings and 

receptive seedbeds for the regeneration of pine and larch. 

Similar to the dry forests, high canopies (>165 feet) of western white pine, western larch, and ponderosa pine and other 

early and mid-seral species are currently absent. In their 

place, the present forest structure and composition (grand 

fir and Douglas-fir) favor the compression of nutrients, 

microbial processes, and root activity toward the soil surface 

(Harvey et al. 2008). When wildfires occur, surface organic 

layers can be consumed, decreasing the nutrition and 

microbial processes important for sustaining these forests. 

In general, the lack of the early seral species and historical 

structures most likely have altered the disturbance regimes 

that sustained these forests.

Climate Change Responses

Habitat types are not static but reflect the operational environment that supports a particular set of plant species. As 

the moist forests experience climate change, the competition 

among species and how these forests evolve will be particularly dynamic. Thus, any discussion concerning climate 

change and an individual tree species that grows in moist 

mixed-conifer (and dry mixed-conifer) forest must be placed 

within the context of species cohorts, the adaptive capacity 

of an individual tree species, the interaction of disturbance, 

and how environmental niches change over time and space. 

For example, if future moisture regimes no longer support 

the current distribution of western hemlock, the remaining 

species that thrive on the upland western redcedar habitat 

types are likely to become dominant (Graham 1990). How 

disturbance changes (intensity, extent, and return interval) 

with a warming climate can also influence the subsequent 

effects on particular tree species. In a drier climate, western 

redcedar may become the late-seral species in what we consider to be western hemlock habitat types.

Lodgepole Pine Mixed Subalpine Forests

Ecology

Lodgepole pine forests straddling and occurring east 

of the Continental Divide are associated with the cold 

continental air mass that influenced their development. The 

higher elevations combined with the relatively dry cold 

climate associated with this type exclude many of the warm 

and moisture-dependent tree species found on the west side 

of the Continental Divide. Aspen, which is often associated 

with moisture seeps, swales, and other moist sites within 

this type, is released from conifer suppression by fire. 

Disturbance is needed to maintain aspen in this type and 

to keep seral lodgepole pine communities from becoming 

dense with subalpine fir.

Disturbance interactions. Lodgepole pine mixed 

subalpine forests in the Northern Rockies evolved with 

both high-severity and mixed-severity fire regimes. Mixedseverity fire regimes were common in central Montana on 

flatter slope positions and produced a diverse pattern of 

various-sized patches of different ages and tree sizes. Standreplacing fire return intervals were 100 to 500 years (Fischer 

and Clayton 1983). However, stands reaching 60 to 80 years 

of age often suffered severe mortality from mountain pine 

beetle, creating snags and down fuel (Jenkins et al. 2008).

Historical and Current Conditions

This forest type was probably the most extensive in the 

Northern Rockies, with vast subalpine areas dominated by 

even-aged and multiaged stands of lodgepole pine, mixed 

with aspen, created by mixed-severity fire. Subalpine fir has 

probably increased as a result of fire exclusion, but more 

importantly, most of this type is currently dominated by 

large, mature lodgepole pine. Landscapes of these mature 

forests have fostered the large mountain pine beetle outbreak observed in many parts of the region (Central Rockies 

and GYA).

Climate Change Responses

This type will probably expand and contract, but provided that fire is not excluded from these areas, it is not likely 

to change substantially in a warmer climate.

Whitebark Pine Mixed Upper 

Subalpine Forests

Ecology

Perhaps the most threatened forest type, whitebark pine 

mixed upper subalpine forests are associated with high 

elevations, and the distribution of this type is primarily influenced by the cold continental air masses in Montana and 

higher elevations in northern Idaho. In this type, whitebark 

pine is found with subalpine fir, Engelmann spruce, and 

mountain hemlock, and subalpine larch in the area west of 

the Continental Divide. This type occurs on about 5 million acres in the Northern Rockies, primarily on the higher 

ridges and mountaintops. At the lower elevations within 

the range of this type, whitebark pine typically serves as a 

minor early-seral species in mixed-conifer stands. At the 

uppermost elevations, whitebark pine can serve as a major 

climax species.

Disturbance Interactions

Whitebark pine and its associates developed under both a 

stand-replacing fire regime on steep north slopes, and under 

a mixed-severity fire regime on other aspects and flatter 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 179

slope positions. Various sized patches are common within 

the range, with density depending on moisture availability. 

The future could bring more-intense fire that could further 

threaten whitebark pine distribution.

There have been three outbreaks of mountain pine beetle 

in the Northern Rockies over the last 100 years. The first 

one in the 1920s–1930s killed significant areas of whitebark 

pine (Tomback et al. 2001). Snags from this outbreak can 

still be seen today. Another major outbreak occurred in the 

early 1980s, but the largest outbreak started in the mid2000s and has continued, especially in the GYA.

Historical and Current Conditions

More than 14 percent of the Northern Rockies could 

have consisted of whitebark pine forests, with late-seral 

mixed fir-spruce patches mixed throughout, prior to 1910. 

However, with extensive white pine blister rust epidemics 

and mountain pine beetle outbreaks over the last several 

decades, the upper subalpine landscape has slowly shifted 

from whitebark pine to more spruce and fir and nonforest 

vegetation in some places (Tomback et al. 2001).

Climate Change Responses

There may be substantial change in the upper subalpine 

forests over the next century. However, that change will 

probably be driven by whitebark pine mortality from white 

pine blister rust rather than climate change, and the changes 

will primarily be in forest composition and structure rather 

than distribution. Over the last 40 years, whitebark pine 

has become a minor component of this forest type in many 

parts of the western Northern Rockies because of white pine 

blister rust, allowing subalpine fir to become dominant in 

both the overstory and understory. Although the GYA has 

yet to have massive die-offs from white pine blister rust, 

it has not escaped recent mountain pine beetle outbreaks, 

and the whitebark pine mortality rates in cone-bearing 

trees from these outbreaks exceed 50 percent in most areas. 

Recent fires in the upper subalpine have served to reset the 

successional clock to the earliest seral stages of shrub and 

herbaceous communities, but whitebark pine regeneration 

levels are low in these burns because of low population levels (Leirfallom et al. 2015). Clark’s nutcracker apparently is 

eating most of the seeds from the few remaining whitebark 

pine trees and not enough of their seed caches go unclaimed 

to germinate and grow into trees (Keane and Parsons 

2010). This has served to keep recently burned areas in the 

shrub/herb stage for long periods, which may allow time 

for other wind-dispersed tree species to populate the burn. 

Thus, whitebark pine may continue to decline in this type, 

and species dominance is likely to shift to subalpine fir, 

Engelmann spruce, and lodgepole pine.

Most of the range shifts of this forest type will probably 

be in wilderness areas, as about 50 percent of this type is 

found in wilderness (Keane 2000). Many Northern Rockies 

wilderness areas have lands that are above the elevations 

at which this type occurs, so there are potential areas for 

this type to expand. Wildland fire will be the catalyst for 

any range shifts in this forest type. Continued fire exclusion 

may seem appropriate for whitebark pine types, but it is 

contraindicated in many situations. Most whitebark pine 

will eventually succumb to white pine blister rust; thus, suppressing fire does not necessarily protect it. Fire is needed 

to create conditions in which whitebark pine can become 

established and grow to maturity. If fires are suppressed 

and no rust-resistant trees are planted, then whitebark pine 

is likely to remain a minor component of this forest type. 

However, if wildland fires occur and burned areas are planted with rust-resistant trees, then whitebark pine may become 

more abundant in the high elevation settings of the Northern 

Rockies. Therefore, land management is likely to be more 

critical than climate in dictating the future composition and 

extent of this forest type.

Resources of Concern

Landscape Heterogeneity

Background

Historically, most Northern Rockies landscapes were 

shaped by disturbance regimes interacting with vegetation 

and climate creating shifting mosaics of diverse vegetation 

assemblages. Wildfire was the primary sculptor of historical 

landscape composition and structure, especially at lower 

elevations (including ignitions by Native Americans and 

lightning), with other disturbances (mountain pine beetle 

outbreaks, root rot pockets, windthrow) woven into the 

patchwork of forestlands. Forest patterns were constantly 

shifting over time and space at rates governed by interactions among vegetation, disturbance, and climate, resulting 

in different patch sizes, shapes, and distributions. Therefore, 

understanding the variability and scale of disturbance and 

succession is critical to quantifying historical landscape 

heterogeneity, which in turn affects biological diversity and 

ecosystem resilience.

High landscape heterogeneity creates diverse biological 

structure and composition, which are considered more resilient and resistant to disturbances (Bannerman 1997; Cohn 

et al. 2015; Haire and McGarigal 2010; Turner 1987). For 

example, the effects of mountain pine beetle outbreaks are 

less severe in landscapes with diverse age structures of host 

tree species (Schoettle and Sniezko 2007). Heterogeneous 

landscapes also promote population stability (Oliver et al. 

2010) because fluctuations in plant and animal population 

are less when landscape structure is diverse (Turner et al. 

1993). Heterogeneous landscapes may also have more corridors, buffers, and refugia for wildlife and plant migration.

During the past 100 years, land management practices 

have altered the temporal and spatial characteristics of 

Northern Rockies landscapes. Timber management has 

modified patch shape and structure at lower elevation, 

and fire exclusion has changed patch size and diversity. 

Fire exclusion has in many cases created landscapes with 

large contiguous patches of old, dense stands with high 

surface and canopy fuel accumulations (Keane et al. 2002), 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
180 USDA Forest Service RMRS-GTR-374. 2018

although some areas with frequent disturbance (e.g., 

frequently burned ponderosa pine forest) are also homogeneous compared to presettlement montane forests (Romme 

2005). Because we have directly or indirectly managed for 

late seral conditions, some Northern Rockies landscapes 

are highly susceptible to insects and disease, owing to low 

tree vigor from intense competition, and have an abundance 

of live and dead fuels that will contribute to the severity of 

future wildfires.

Climate Change Responses

Many current Northern Rockies landscapes have less 

ability to buffer potential climate change effects because of 

widespread increases in the density of shade-tolerant species 

in forests, although some landscapes, especially in subalpine 

forests, still have structures and compositions similar to 

those observed in the historical record. Recent wildfires, 

restoration activities, and timber harvest have helped return 

some heterogeneity, especially in wilderness areas and 

national parks. However, most Northern Rockies landscapes 

are outside their historical range and variability (HRV) in 

landscape structure, making it challenging to implement effective climate change adaptation.

Landscape heterogeneity may increase if climatemediated changes in disturbance regimes increase (Funk 

and Saunders 2014). During the past 20 years, wildfire 

area burned and mountain pine beetle outbreaks have both 

increased, replacing late seral forests with younger age and 

size classes and thereby increasing heterogeneity. Continued 

increases in wildfires and other disturbances are projected in 

a warmer climate (Bentz et al. 2010; Marlon et al. 2009), so 

projected declines in biodiversity (e.g., Botkin et al. 2007) 

could be balanced by gains in landscape heterogeneity 

(Kappelle et al. 1999).

Continued fire exclusion in a warmer climate may promote 

late seral forests that would be stressed from competition 

and drought (van Mantgem and Stephenson 2007). Wildfires 

that will eventually burn these landscapes may become large 

and burn more severely, thereby creating large patches of 

homogeneous postburn conditions (Flannigan et al. 2005, 

2009). These fires may also create semipermanent shrublands 

and grasslands in areas that have become too dry for conifer 

establishment or where seed sources are eliminated (Fulé 

et al. 2004). However, some have found a high degree of 

heterogeneity in severity and vegetation conditions following 

large fires (Collins and Stephens 2010; Keane et al. 2008). 

Although the size, shape, and distribution of forest management treatments are a concern for landscape heterogeneity, 

the effects of management on landscape properties may be 

overwhelmed by other disturbances.

Is there an appropriate level of heterogeneity for 

Northern Rockies landscapes? How can management 

facilitate landscape heterogeneity and minimize adverse 

climate change effects? Mechanistic ecosystem models can 

be used to simulate landscape structure and composition in 

the future and to understand effects of management actions 

(Keane 2013), but cannot generate heterogeneity metrics as 

design criteria for ecosystems. Using the HRV of landscape 

characteristics is a more straightforward and useful approach 

(Keane 2013; Morgan et al. 1994a; Nonaka and Spies 2005) 

(box 6.1). The HRV of landscape metrics may not represent 

future conditions (Millar 1997; Millar and Woolfenden 

1999), but does provide an estimate of landscape conditions 

under which ecosystems have developed over the last 1,000 

years, conditions that produced functional, heterogeneous 

ecosystems (Landres et al. 1999). It is preferable to first use 

HRV as a reference for landscape heterogeneity (Keane et 

al. 2015b), then ecological models can be parameterized 

for historical conditions and used to generate a set of useful 

landscape metrics (Keane 2012).

Timber Production

Background

The area managed for timber production as one of the 

objectives for management is about 8,700 out of 34,000 

square miles of forested lands throughout the USFS 

Northern Region. This area includes approximately 2,600 

square miles in northern Idaho, 4,250 square miles in 

western Montana, 1,400 square miles in central and eastern 

Montana, and 450 square miles in the Greater Yellowstone 

portion of the Northern Region.

During the 1970s and 1980s, an average of 98 square 

miles were harvested each year, which amounted to about 

1,900 square miles that had some type of harvest treatment implemented to meet various management objectives 

including timber production. From 1990 through 2014, an 

average of 39 square miles were harvested each year, which 

amounted to about 970 square miles. Recent harvest during 

2014 of 32 square miles may be more typical of current and 

near-term future harvest levels.

The species composition of timber harvests has fluctuated 

during the past 45 years, as harvest has often followed some 

disturbance agent such as mountain pine beetle in western 

white pine and lodgepole pine, spruce beetle in Engelmann 

spruce, white pine blister rust in western white pine, root 

disease in Douglas-fir and grand fir, Douglas-fir beetle and 

spruce budworm in Douglas-fir, and wildfire in a variety 

of species types. The current percentage of acreage in each 

of the major species composition groups within the lands 

suitable for timber production across the Northern Region 

is 6 percent ponderosa pine, 13 percent dry Douglas-fir, 27 

percent lodgepole pine, 6 percent western larch, 12 percent 

mixed subalpine fir and Engelmann spruce, and 35 percent 

mixed western white pine, grand fir, western hemlock, moist 

site Douglas-fir, and western redcedar forests.

Many of the current timber harvests in mixed mesic types 

of northern Idaho and western Montana are removing grand 

fir, Douglas-fir, and western hemlock, and replanting western white pine, western larch, and ponderosa pine. Other 

harvests involve removal of lodgepole pine and replanting 

of western larch. Thinning in ponderosa pine and dry 

Douglas-fir forests is also common. Within eastern Montana 

and the GYA, harvesting is concentrated on mountain pine 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 181

beetle-susceptible or dead lodgepole pine and ponderosa 

pine, and thinning in ponderosa pine and dry forest Douglasfir forests is also common.

Climate Change Responses

With increasing temperatures and the potential for increases in forest productivity (Aston 2010; Joyce 1995) and 

biomass accumulation (Lin et al. 2010) will probably come 

potential increases in timber production for most Northern 

Rockies forests (Garcia-Gonzalo et al. 2007). Productivity 

increases are projected to be substantial because most 

forested lands in the region are in the mesic montane, 

subalpine, and upper subalpine. The increase in biomass 

might result in higher basal areas, greater timber value, and 

increased regeneration (Sohngen et al. 2001). However, 

these mesic temperate forests might also become denser, 

which may result in decreased vigor that may offset gains in 

productivity from climate alone. Depressed vigor might also 

increase susceptibility to insects and disease; because insect 

and disease outbreaks are projected to increase in severity 

and frequency, there may be some major timber losses from 

forest pathogen and insect mortality (Joyce et al. 2008). 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

Box 6.1—Using Historical Range and Variability to Assess and Adapt to Climate Change 

To effectively implement ecosystem-based management, land managers often find it necessary to obtain a reference 

or benchmark to represent the conditions that describe fully functional ecosystems (Cissel et al. 1994; Laughlin et al. 

2004). Contemporary conditions can be evaluated against this reference to determine status, trend, and magnitude 

of change, and to design treatments that provide society with valuable ecosystem services while returning declining 

ecosystems to a more sustainable condition (Hessburg et al. 1999; Swetnam et al. 1999). Reference conditions 

are assumed to represent the dynamic character of ecosystems and landscapes, varying across time and space 

(Swanson et al. 1994; Watt 1947). 

The concept of historical range and variability (HRV) was introduced in the 1990s to describe past spatial and 

temporal variability of ecosystems (Landres et al. 1999), providing a spatial and temporal foundation for planning 

and management. HRV has sometimes been equated with “target” conditions (Harrod et al. 1999), although targets 

can be subjective and somewhat arbitrary; they may represent only one possible situation from a range of potential 

conditions (Keane et al. 2009). HRV encompasses a full range of conditions that have occurred across multiple 

spatiotemporal scales. 

HRV represents a broad historical envelope of possible ecosystem conditions—burned area, vegetation cover type 

area, patch size distribution—that can provide a time series of reference conditions. This assumes that 

(1) ecosystems are dynamic, not static, and their responses to changing processes are represented by past 

variability; (2) ecosystems are complex and have a range of conditions within which they are self-sustaining, and 

beyond this range they make a transition to disequilibrium (Egan and Howell 2001); (3) historical conditions can 

serve as a proxy for ecosystem health; (4) the time and space domains that define HRV are sufficient to quantify 

observed variation; and (5) the ecological characteristics being assessed for the ecosystem or landscapes match the 

management objective (Keane et al. 2009). 

The use of HRV has been challenged because a warmer climate may permanently alter the environment of 

ecosystems beyond what was observed under historical conditions (Millar et al. 2007a). In particular, disturbance 

processes, plant species distribution, and hydrologic dynamics may be permanently changed (Notaro et al. 2007). 

However, a critical evaluation of possible alternatives suggests that HRV might still be the most viable approach in 

the near term because it has relatively low uncertainty. 

An alternative to HRV is forecasting future variations of landscapes under changing climates by using complex 

empirical and mechanistic models. However, the range of projections for future climate from the commonly used 

global climate models may be greater than the variability of climate over the past three centuries (Stainforth et al. 

2005). This uncertainty increases when we factor in projected responses to climate change through technological 

advances, behavioral adaptations, and population growth (Schneider et al. 2007). Moreover, the variability of 

climate extremes, not the gradual change of average climate, will drive most ecosystem response to climatemediated disturbance and plant dynamics (Smith 2011) that are difficult to project. Uncertainty will also increase as 

climate projections are extrapolated to the finer scales and longer time periods needed to quantify future range and 

variability (FRV) for landscapes (Araujo et al. 2005; Keane et al. 2009).

Given these cumulative uncertainties, time series of HRV may have lower uncertainty than simulated projections 

of future conditions, especially because large variations in past climates are already captured in the time series. It 

may be prudent to wait until simulation technology has improved enough to create credible FRV landscape pattern 

and composition, a process that may require decades. In the meantime, attaining HRV would be a significant 

improvement in the functionality of most ecosystems in the Northern Rockies, and would be unlikely to result in 

negative outcomes from a management perspective. As with any approach to reference conditions, HRV is useful as 

a guide, not a target, for restoration and other management activities.
182 USDA Forest Service RMRS-GTR-374. 2018

There will also be an increase in potential mortality from 

wildland fire with increased fuel, drier conditions, and longer fire seasons, and this might facilitate even more timber 

losses. Future timber harvests from mature timberland might 

be a race against losses from increased insects, disease, and 

fire. The greatest climate change impacts on commercial 

forestry may come from changes in the disturbance regimes 

rather than changes in productivity (Kirilenko and Sedjo 

2007).

There are other considerations in addressing how timber 

resources in the Northern Rockies region will change with 

warming climates. First, most of the roads on Northern 

Rockies lands are in drier, lower elevation forests where 

productivity may decline and more trees are projected to die 

from drought. Fewer roads are in the subalpine and upper 

subalpine where productivities and associated timber values 

are likely to increase, resulting in limited ability to transport 

timber to markets. Creation of new roads is expensive, 

risky, and environmentally damaging. These higher lands 

are distant from timber markets and sawmills, and are also 

more topographically complex and steep, thereby limiting 

the potential for mechanized timber removal while increasing harvesting costs. These higher elevation lands are also 

where most of the threatened and endangered plant and 

animal species are found, especially grizzly bear (Ursus 

arctos), Canada lynx (Lynx canadensis), and wolverine 

(Gulo gulo), making it more difficult to implement timber 

harvest projects in these sensitive areas. If increases in 

insects, diseases, and fire are realized, the quality of timber 

will probably be reduced, and the value of the timber for 

building material will drop dramatically (Gillette et al. 

2014; Kirilenko and Sedjo 2007; Spittlehouse and Stewart 

2004). Longer fire seasons will probably mean there will be 

less time to perform forestry tasks, such as inventory, sale 

layout, and cruising. This may also mean that less agency 

money will be spent on forestry projects, such as ecosystem 

restoration, fuels treatments, and timber harvest sales, and 

more money will be spent on fire suppression activities. As 

the risk of uncharacteristic fire severity due to uncharacteristically high forest density increases, there will most likely 

be reductions in timber production opportunities, especially 

in dry forest areas that may be lost and converted to grass 

and shrub lands (Allen et al. 2010).

Timber species will also shift in the future. Increases in 

temperature and soil moisture deficits may result in shifts 

of desirable timber species, such as western larch, to species compositions that are susceptible to root disease, such 

as Douglas-fir and grand fir. Any increases in production 

at mid- and higher elevations from warming temperatures 

could be offset by losses from root disease because of continued fire exclusion. Land management efforts that create 

late-seral, shade-tolerant communities, namely fire exclusion and some fuels treatments, will increase the risk that 

standing timber will be affected by damaging agents before 

it can be harvested.

Many new forest practices, harvesting techniques, and 

markets are being proposed to offset carbon emissions from 

fossil fuels with carbon emissions from harvested biomass 

(Kirilenko and Sedjo 2007). Most of these new technologies 

will result in better utilization of timber resources and a more 

diverse and vibrant timber market. Biomass burning for energy, for example, could provide a market for noncommercial 

material removed from proposed fuels treatments. Slash piles 

could have value as biomass for energy. A more diverse market for wood products would surely enhance potential timber 

harvests in the region, but it is essential that any proposed 

cutting activity be done in an ecological context, especially 

in this time of rapidly changing climates. Proposed harvesting activities must address a wide diversity of issues, such as 

landscape character, species mix, successional dynamics, and 

fuels, to ensure these activities are effective and to minimize 

the long-term environmental impact.

It is essential that ecological principles be used to design 

harvest treatments of the future to ensure the creation of 

resistant, resilient forests that can withstand major impacts 

of climate change. Designing fuels treatments without 

considering ecosystem restoration concerns, for example, 

might create forests that are highly susceptible to insects and 

disease or fire. Favoring shade-tolerant, fire-susceptible species over fire-tolerant, sun-loving, early-seral tree species is 

ecologically inconsistent and likely to create landscapes that 

are intolerant of future climate change.

One proposed management alternative, carbon sequestration (see next subsection), might be cause for concern. The 

main assumption of most carbon sequestration options is to 

maximize biomass to sequester carbon from the atmosphere 

and put it into timber products to offset fossil fuel burning. 

The problem is that this approach must recognize the role 

of disturbance to be effective in the long term. Many studies have shown that the most resilient forests are ones with 

suboptimal carbon sequestration.

Again, the major issue related to climate change and 

timber production in the near term is loss from disturbance. 

The anticipated increases in drought, severe large wildfires, 

root disease, other diseases such as white pine blister rust, 

and insect damage such as that from large-scale bark beetle 

outbreaks, need to be addressed throughout the Northern 

Rockies. Tactics to increase landscape heterogeneity overall 

and reduce forest density in the dry forest types will be key 

climate change responses in the near term. Adjusting species 

composition and distribution may help sustain long-term 

timber production.

Carbon Sequestration

Background

North American forests are considered important carbon 

sinks and currently offset about 13 percent of annual continental fossil fuel emissions (Pacala et al. 2007). Size and 

persistence of forest carbon sinks depend on land use, land 

management, and environmental factors such as vegetation 

composition, structure, and distribution, climate, and disturbance processes including wildfire.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 183

Vegetated landscapes play an important role in storing 

carbon in the form of plant and animal materials (both live 

and dead), aboveground and in soils. Forests store carbon in 

soils (about 45 percent of total storage), aboveground and 

belowground live biomass (about 42 percent), dead wood 

(about 8 percent), and litter (about 5 percent) (Bonan 2008; 

Pan et al. 2011). Because forests contain large reservoirs 

of carbon (i.e., carbon sinks) and facilitate flows of carbon 

from the atmosphere to the biosphere (i.e., carbon sequestration), they are an important component of the global carbon 

cycle and are thought to have the potential to mitigate 

climate change (Ingerson 2007; Pan et al. 2011). The carbon 

sequestration potential of Earth’s forests is about 33 percent 

of global anthropogenic emissions from fossil fuels and land 

use (Denman 2007). Carbon typically accumulates in woody 

biomass and soils for decades to centuries until a disturbance event releases this stored carbon into the atmosphere 

(Goward et al. 2008). Disturbance and decomposition are 

recognized as primary mechanisms that shift ecosystems 

from carbon sinks to carbon sources (Baldocchi 2008), 

and wildfire in forested ecosystems is one of the primary 

disturbances that regulates patterns of carbon storage and 

release (Kasischke et al. 2000a,b). Forest insect outbreaks 

can also release carbon through decomposition of needles 

and other fine fuels from attacked trees (Kurz et al. 2008). 

The amount and rate of carbon release from a disturbance 

event depends on the extent and severity of the disturbance, 

as well as predisturbance site conditions and productivity 

(Bigler et al. 2005; Falk et al. 2007). In the case of both 

wildfires and insect outbreaks, although long intervals 

between events can allow carbon to accumulate for years 

to centuries, probability of disturbance increases with time 

(Clark 1989). Changing climate, in combination with other 

ecosystem stressors such as disturbance, may be sufficient 

to cause structural or functional changes in ecosystems, and 

thus fundamentally alter carbon dynamics of landscapes.

Although long intervals between disturbance events, 

such as wildfires or insect outbreaks, can allow carbon to 

accumulate for years to centuries, probability of disturbance 

increases with time (Goward et al. 2008; Loehman et al. 

2014). Thus, disturbance-prone forests will eventually move 

stored carbon to the atmosphere, regardless of management 

strategies designed to limit or prevent disturbance events. 

However, unless structural or functional ecosystem shifts 

occur, net carbon balance in disturbance-adapted systems 

at steady state is zero when assessed over long time periods 

and at landscape scales. This is significant to management 

for two reasons: (1) disturbance-prone ecosystems cannot be managed to increase stored carbon over historical 

amounts without limiting the occurrence and magnitude of 

disturbance events; and (2) major shifts in vegetation composition, distribution, and structure resulting from climate 

change will result in different patterns of carbon storage on 

the landscape as compared with the historical period. Thus, 

it is important to develop expectations for landscape carbon 

storage potential in the context of projected climate change 

effects on both disturbance dynamics and vegetation patterns, and the relationships between them.

Climate Change Responses

As described in chapter 8, future warmer, drier conditions are likely to result in more frequent, larger wildfires, 

and greater annual area burned, which will serve to move 

carbon from biomass storage to the atmosphere. Warmer 

temperatures and increased drought stress are also projected 

to increase the area susceptible to or affected by beetle 

outbreaks. Regrowth of forests following disturbance may 

be delayed if the climatic conditions stress remaining or 

reestablishing species. Disturbance events in combination 

with additional climate-caused stressors may also result in 

functional transitions, such as a shift from forests to montane woodland or grassland-dominated vegetation types, 

which would probably result in less stored carbon. Frequent 

fires may also maintain open woodlands and savannas that 

might sequester less carbon than forests, but these carbon 

pools may be more stable and resilient to climate shifts.

Strategies that aim to manage carbon resources should 

consider the following:

1. Is the system disturbance-prone? If so, is it reasonable 

to expect the system to accumulate carbon over 

historical (steady-state) levels, especially given future 

climatic conditions that may increase the frequency, 

severity, and magnitude of disturbance events?

2. What are appropriate temporal and spatial scales 

over which to measure carbon storage? For example, 

in forests with multicentury disturbance cycles, 

it may take hundreds of years for forests to attain 

pre-disturbance levels of carbon, but this does not 

mean that they have become carbon sources at the 

appropriate, ecological scale of measurement.

3. Can potential future disturbance events be managed? 

For example, will it be possible to suppress or exclude 

wildfires from the system in the future, and at what 

economic or ecological costs?

4. Can additional stressors (e.g., drought stress, invasive 

weeds, and other management activities) be mitigated, 

to help maintain existing vegetation communities?

5. How might the system change with changing climate 

and disturbance? For example, are future climatic 

conditions conducive to persistence of forests, or will 

conditions become too warm or dry for the current 

dominant species?

6. Do planned carbon accounting methods assess 

ecological benefits of natural disturbance processes 

in carbon-equivalent units so that they can be 

weighed against carbon losses from disturbance? For 

example, wildfires confer many important ecological 

benefits not measurable in carbon units (e.g., nutrient 

release and redistribution and stimulation of plant 

growth, increased productivity in soil systems from 

decomposition of burned material, initiation of 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
184 USDA Forest Service RMRS-GTR-374. 2018

vegetation succession and forest regeneration, and 

increased availability of resources for surviving trees) 

that may actually increase carbon sequestration rates.

Two complementary activities, monitoring and modeling, 

can improve our understanding of cross-scale ecological 

drivers and responses to disturbance (Loehman et al. 2014). 

Monitoring programs can be used to quantify long-term 

carbon dynamics before and after disturbance, evaluate 

responses of ecosystems to changes in climate, and identify 

shifts in ecosystem patterns and processes emergent under 

changing climates. Monitoring data can also be used to 

provide inputs to, calibrate, and validate models. Models, 

in turn, can be used to simulate emergent environmental 

patterns, compare effects of potential treatments, identify 

vulnerable landscapes or ecosystem components, and bridge 

gaps between landscape-scale ecological processes and 

variables measured in small areas and over short periods 

of time. There is room for improvement on both fronts, as 

described previously in this chapter. Although it may be 

tempting to meet policy-driven goals of increased carbon 

storage via management strategies designed to exclude 

or limit the extent and magnitude of disturbance events 

(e.g., wildfires), it is important to remember that native 

disturbance processes confer many important ecological 

benefits not measurable in carbon units (see item 6). Thus, 

it will be important to develop accounting methods that can 

assess ecological benefits in carbon-equivalent units so that 

they can be weighed against carbon losses from disturbance.

Vulnerability Assessment

All items in each of the three levels of assessment were 

rated as to their vulnerability to climate change using the 

same rubric employed across all chapters in this report 

(table 6.4), and the results are summarized in detail in 

Appendix 6B. We populated a table with information for the 

eight categories in table 6.4 using a thorough consideration 

of five factors: climate, disturbance, life history, dependencies, and other stressors. For climate, we considered whether 

the species, vegetation type, or resource concern was sensitive to changes in direct effects of climate (temperature 

and precipitation) or indirect effects of climate (e.g., soil 

moisture, snowpack, seasonality of flows, climatic water 

deficit, altered flow regimes, and stream temperature). For 

example, we asked, “Does the system inhabit a relatively 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

Table 6.4—Categories used to assess the vulnerability of species, vegetation types, and resource concerns in this chapter. 

Evaluation category Description Example

Habitat, ecosystem 

function, or species

Specific biophysical or social entity of interest Whitebark pine

Broad-scale climate change 

effect

Overarching change in climate that is 

expected to affect a resource

Warming temperatures

Current condition, existing 

stressors

Current status of resource relative to desired 

conditions, including factors that are reducing 

the quality or quantity of the resource

Reduced abundance, wildland fire, mountain 

pine beetle, white-pine blister rust

Sensitivity to climatic 

variability and change

Specific sensitivity of a habitat, species, or 

ecosystem function that responds to climate 

Low ability to compete with encroaching 

conifers

Expected effects of climate 

change

How specific habitat, species, or ecosystem 

function is expected to respond to climate 

change (develop inferences from model 

projections and known responses to climatic 

variability)

Regeneration may be reduced by combination 

of warming and low seed availability

Adaptive capacity Ability to adjust to climate change, to 

moderate potential damages, or to cope with 

the consequences; usually more appropriate 

for species than for systems and processes

Variable: unable to compete with other tree 

species, but bird-mediated seed dispersal 

allows quick colonization of burned over areas

Exposure The extent to which each species’ physical 

environment will change expressed as low, 

moderate, or high

High

Risk assessment,

magnitude of effects 

Estimate of the magnitude of climate change 

effects expressed as low, moderate, or high by 

time period 

Moderate

Risk assessment,

likelihood of effects 

Estimate of the likelihood that climate change 

effects will occur expressed as low, moderate, 

or high by time period

High
USDA Forest Service RMRS-GTR-374. 2018 185

narrow climatic zone, or does it experience large changes 

in composition or structure with small climatic changes?” 

We also considered both direct sensitivity to climate change 

(e.g., ecophysiology and life history) and indirect sensitivity to climate change (e.g., ecological relationships such 

as competition, dispersal, and migration). Vulnerability to 

disturbance was assessed in reference to whether the species, type, or concern was sensitive to major disturbances, 

primarily wildland fire, insect outbreaks, drought, and 

pathogens. Disturbances are major catalysts for vegetation change and can combine with climate stressors and 

nonclimate stressors to create a broader stress complex with 

multiple interactions. Life history aspects of the species and 

vegetation type were considered to address the impact of the 

growth rate, susceptibility to mortality, longevity, and reproductive strategy of a species, all of which may influence 

sensitivity to climate change. Species with long lifespans 

may have lower vulnerability than short-lived species. We 

also addressed the dependence of species on other ecosystem processes or landscape elements. Riparian species, for 

example, are dependent on wet conditions. Last, nonclimate 

stressors, such as land use, grazing, timber harvest, and fire 

exclusion were integrated into our assessment.

The vulnerability assessment in Appendix 6B is further 

summarized in table 6.5 for only the tree species included 

in this report. We ranked each species by subregion (fig. 

6.1) and removed those species that did not occur in a given 

subregion. We also included the rankings of two other efforts for comparison purposes. The Devine et al. (2012) 

report assessed vulnerability for tree species in the Pacific 

Northwest, and the Hansen and Phillips (2015) effort assessed vulnerability for some Northern Rockies tree species 

using SDMs. This information is presented as a means of 

helping land managers to integrate climate change impacts 

into their planning documents and analyses.

Adaptation Strategies 

and Tactics

This chapter documents what could happen to Northern 

Rockies forest resources under potential future climates. 

Land managers need options for adapting to climate change 

and mitigating any adverse impacts incurred as a result of 

changing climate. Adaptation can be defined as initiatives 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

Table 6.5—Final tree species vulnerability ratings (1 = lowest vulnerability) for the entire Northern Rockies (NR), and the 

five subregions of the NR. Also included are ratings from the Pacific Northwest in Devine et al. (2012) report and from 

the northern Rocky Mountains in Hansen and Phillips (2015). 

Tree species NR West Central East GYA Grass

Devine et al. 

(2012) 

Hansen and 

Phillips (2015)

Alpine larch 1 2 1 NAa NA NA 4 NRTb

Whitebark pine 2 1 2 1 1 NA 1 1

Western white pine 3 5 3 NA NA NA 13 NRT

Western larch 4 6 4 NA NA NA 12 8

Douglas-fir 5 8 8 2 2 1 11 9

Western redcedar 6 4 5 NA NA NA 15 7

Western hemlock 7 3 6 NA NA NA 10 6

Grand fir 8 7 7 NA NA NA 5 11

Engelmann spruce 9 9 11 3 4 5 3 5

Subalpine fir 10 10 12 4 5 6 2 4

Lodgepole pine 11 11 10 5 6 7 8 3

Mountain hemlock 12 3 9 NA NA NA 7 2

Cottonwood 13 12 13 6 3 2 17 NRT

Quaking Aspen 14 13 14 8 7 3 6 NRT

Limber pine 15 NA 15 7 8 4 18 NRT

Ponderosa pine-west 16 14 16 NA NA NA 14 10

Ponderosa pine-east 17 NA NA 8 9 8 NRT 10

Green ash 18 NA NA 9 10 9 19 NRT

a NA = Not applicable.

b NRT = Not rated.
186 USDA Forest Service RMRS-GTR-374. 2018

and measures to reduce the vulnerability of natural and 

human systems against actual or expected climate change 

effects (IPCC 2007). Adaptation actions range from the simple, such as doing nothing or increasing the harvest rotation 

age, to the complex, such as implementing fuels treatments 

to reduce the risk of high-severity fire in ecosystems with 

rare plants (Spittlehouse and Stewart 2003). Most land 

managers have the tools, knowledge, and resources to begin 

to address climate change, but as Swanston and Janowiak 

(2012) note, managers need to expand their thinking to consider new issues, spatial scales, timing, and prioritization of 

efforts. For example, managers need to account for the high 

variability and trend of climate in the design of alternative 

land management actions.

There are some fundamental principles that can serve as 

starting points in the development of adaptation approaches 

(Joyce et al. 2008; Millar et al. 2007a; West et al. 2009). First, 

it will be increasingly important to prioritize management actions based on both the vulnerability of resources and on the 

likelihood that actions to reduce vulnerability will be effective 

(i.e., prioritization). Next, adaptive management principles 

provide a decisionmaking framework that maintains flexibility and incorporates new knowledge and experience over time 

(i.e., adaptive management). Management actions that result 

in a wide variety of benefits under multiple scenarios but have 

little or no risk may be the first places to look for near-term 

implementation (i.e., low-hanging fruit). Where vulnerability 

to a particular resource is high, precautionary actions to 

reduce risk in the near term, even with existing uncertainty, 

may be essential (i.e, triage). It is important to remember that 

climate change is much more than increasing temperatures; 

increasing climate variability across all components of climate, such as precipitation, humidity, and radiation, will lead 

to equal or greater impacts that will need to be addressed (i.e., 

increased uncertainty). Last, many adaptation actions are often complementary with other land management actions, and 

any actions to adapt forests to future conditions may also help 

restore these forests to healthy conditions (i.e., multiple objectives). When designing adaptation actions, it is important to 

address and integrate these principles to maximize efficiency.

The concepts of resistance, resilience, and response serve 

as the fundamental options for managers to consider when 

responding to climate change using adaptation (Millar et al. 

2007a; Swanston and Janowiak 2012). Resistance options

improve the defenses of an ecosystem against anticipated 

climate change responses or directly defend the ecosystem against disturbance to maintain current conditions. 

Resistance actions are often effective in the short term, but 

resistance options are likely to require greater effort over 

the long term as the climate shifts further from historical 

norms. Moreover, there is a real risk that the ecosystem 

will undergo irreversible change because of large climatic 

shifts, thereby rendering all resistance activities ineffective. Resilience options allow some change, but emphasize 

a quick return to prior conditions after a disturbance. 

Resilience actions are also short-term and should be used for 

high-value resources or areas that are buffered from climate 

change impacts. Response options intentionally accommodate change and allow ecosystems to adaptively respond to 

changing and new conditions. A wide range of actions exists 

under this option, all working to influence ways in which 

ecosystems adapt to future conditions.

Resistance, resilience, and response options serve as the 

broadest and most widely applicable level of a continuum 

of management responses to climate change. Along this 

continuum, adaptation actions become increasingly specific 

from options to strategies to tactics. Adaptation strategies

describe how adaptation options could be employed, but 

they are still broad and general in their application across 

ecosystems.Tactics are more-specific adaptation responses, 

and they can provide prescriptive directions on how actions 

can be applied on the ground.

There are many broad strategies and associated tactics 

that can be used to adapt to climate change impacts in the 

Northern Rockies region, and the major ones that were 

identified by managers and scientists in a series of workshops in fall 2015 are detailed in table 6.6 and described 

next. Adaptation tactics for all Northern Rockies species, 

vegetation types, and resource concerns discussed in this 

chapter are summarized in table 6.7. Adaptation tactics were 

designed at different scales and levels of organization. Some 

involve Northern Rockies managers at the highest levels 

of agency organization, and others apply to ecologists, 

silviculturists, and resource specialists at the lower levels 

of organization. Some tactics concern multiple species or 

resources, while others are specific to just one entity. These 

tactics were designed so that Northern Rockies managers 

can use these recommendations to directly address climate 

change impacts in their planning and implementation of 

any action, specifically National Environmental Policy Act 

analysis.

As in other adaptation efforts, many tactics developed 

by Northern Rockies managers were focused on protecting 

forests from severe disturbance, mainly fire (table 6.6). 

For example, managers identified promoting disturbanceresilient forest structure and species as key strategies. 

Both thinning and prescribed fire can be used to reduce 

forest density and promote disturbance-resilient species. 

Disturbance-resilient species can also be planted. Managers 

recognized the importance of promoting and planting siteadapted species, specifically western larch and western 

white pine on moist sites, ponderosa pine on dry sites, 

Douglas-fir on extremely dry sites, and lodgepole pine on 

harsh sites that are difficult to regenerate.

Preparing for disturbance will also be important under 

a changing climate. Tree regeneration after severe fire 

may be more limited in the future with increased drought. 

Promoting legacy trees of disturbance-resilient species may 

help to increase postfire regeneration. Managers may also 

want to increase seed collection and ensure that adequate 

nursery stock is available for post-disturbance planting.

Another theme in the adaptation strategies and tactics 

developed by Northern Rockies managers was promoting 

diversity, including species diversity, genetic diversity, and 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 187

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

Table 6.6—Adaptation options that address climate change effects on forested vegetation in the Northern Rockies.

Sensitivity to climatic variability and change: The frequency and scale of disturbance will likely increase with climate change.Adaptation strategy/approach: Promote disturbance-resilient species, including western larch and western white pine on moist sites, ponderosa pine on dry sites, Douglas-fir on extremely dry sites, and lodgepole pine on harsh sites that are difficult to regenerate.

Specific tactic – A Specific tactic – B Specific tactic – C

Tactic Thin to favor disturbance-resilient species. Plant disturbance-resilient species. Promote disturbance-resilient species with 

prescribed fire and/or natural fire use.

Where can tactics be applied? On sites most likely to be affected by 

wildfire

On sites most likely to be affected by wildfire

On sites most likely to be affected by wildfire

Sensitivity to climatic variability and change: Increasing temperatures with climate change will lead to increased moisture stress and fire.Adaptation strategy/approach: Reduce forest density and maintain low densities.

Specific tactic – A Specific tactic – B Specific tactic – C

Tactic Conduct thinning treatments (precommercial and commercial). Use prescribed fire to maintain structure and promote fire-tolerant conifer species. Use regeneration and planting to influence forest structure.Where can tactics be applied? Dense stands with low risk of root disease 

problems 

Dense stands Where there are no opportunities for 

thinning because of species or stand condition

Sensitivity to climatic variability and change: Areas with limited species and genetic diversity will likely be more susceptible to climate change stressors.Adaptation strategy/approach: Promote species and genetic diversity.

Specific tactic – A Specific tactic – B Specific tactic – C

Tactic Plant potential microsites with mix of 

species (hedge your bets).

Maintain species diversity during thinning. Interplant to supplement natural 

regeneration and genetic diversity.

Where can tactics be applied?

In sufficiently large openings on sites most at risk for drought stress

In dense or overstocked stands on sites more at risk for drought stress and where sufficient diversity exists for thinning

In sufficiently large openings on sites most at risk for drought stress
188 USDA Forest Service RMRS-GTR-374. 2018

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region Table 6.6 (cont.)—Adaptation options that address climate change effects on forested vegetation in the Northern Rockies. Sensitivity to climatic variability and change: Increasing temperatures with climate change will lead to longer growing seasons, increased drought stress, and increased fire. Adaptation strategy/approach: Promote ecosystem resilience. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Promote legacy trees of western larch, Douglas-fir, western white pine, Engelmann spruce, whitebark pine, and subalpine larch for regeneration and wildlife habitat. Collect seed for post-wildfire reforestation and other planting needs, especially for subalpine larch, whitebark pine, and high- elevation western larch. Promote landscape heterogeneity and create connectivity at multiple scales. Where can tactics be applied? On dense spruce, fir, and lodgepole pine sites Where species of interest occur At broad spatial scales Sensitivity to climatic variability and change: Climate change will likely lead to increased disturbance, increased moisture deficits, and species distribution shifts. Adaptation strategy/approach: Increase knowledge for agency land managers and stakeholders. Specific tactic – A Specific tactic – B Specific Ttactic – C Tactic Determine what connectivity means for different species and guilds. Track tree species regeneration and distribution. Improve integration between wildlife managers and forest ecologists, and between research and management. Where can tactics be applied? All lands All lands All lands Specific tactic – D Specific tactic – E Specific tactic – F Tactic Monitor blister rust resistance within planted white pine stands, and try to 

understand the relationship between infection rates and climatic drivers (e.g., fog).

Identify other resource management goals (not directly related to stand structure and composition) that may modify management strategies for forest vegetation, such as water yield, snow retention, and wildlife habitat.

Support the adaptive management research framework; develop consistent monitoring framework that can capture long-term change.

Where can tactics be applied? On sites planted with white pine Federal lands Federal lands
USDA Forest Service RMRS-GTR-374. 2018 189 Table 6.6 (cont.)—Adaptation options that address climate change effects on forested vegetation in the Northern Rockies. Sensitivity to climatic variability and change: Climate change will likely lead to increased whitebark pine mortality through increased mountain pine beetle activity, fire, and white-pine blister rust. There will also likely be a loss of site conditions that support whitebark pine. Adaptation strategy/approach: Promote resilient whitebark pine communities. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Identify sites that are less likely to be affected by climate change (refugia), and focus on those sites for restoration. Implement a variety of management strat- egies and options to promote whitebark pine, including fire management, planting at lower elevations, and removing other dominant species (e.g., lodgepole pine, spruce and fir). Plant genetically-selected seedlings to promote blister rust resistance. Where can tactics be applied? Federal lands Federal lands Federal lands Sensitivity to climatic variability and change: Climate change will lead to increased risk of stand-replacing wildfire, mortality from drought, and loss of large ponderosa pine individuals in ponderosa pine forests. Adaptation strategy/approach: Decrease density within stands, and increase structural diversity across the landscape. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Reduce density by thinning, prescribed fire, and wildfire use, with density and structural goals based on past and pre- dicted future conditions. Promote age class and structural diversity across the landscape, through regenera- tion harvest, thinning, prescribed fire and wildfire use. Monitor establishment, survival and de- velopment of ponderosa by age class and in different topoedaphic conditions using Forest Inventory and Analysis data and project-level stocking exams. Where can tactics be applied? Ponderosa pine, Douglas-fir forests In locations where activities are allowed Ponderosa pine, Douglas-fir forests Sensitivity to climatic variability and change: Climate change stressors cross boundaries, forcing agencies to coordinate and work across boundaries. Adaptation strategy/approach: Work across jurisdictions at a larger scales. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Align budgets and priorities for program of work with neighboring lands. Communicate about projects adjacent to other lands, and coordinate on the ground. Work across boundaries to preserve roads, trails, and access with increasing fire and flood events. Where can tactics be applied? All lands All lands All lands

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
190 USDA Forest Service RMRS-GTR-374. 2018 Table 6.6 (cont.)—Adaptation options that address climate change effects on forested vegetation in the Northern Rockies. Sensitivity to climatic variability and change: The vigor and extent of quaking aspen may be reduced with increased frequency of disturbance and drought under changing climate. Adaptation strategy/approach: Restore and promote the health and vigor of aspen clones. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Manage ungulates during the regeneration phase (e.g., with slash barriers, increased hunting pressure, grazing management, and salt block placement). Remove conifers around aspen, at multiple scales and using multiple tools (i.e., hand and commercial treatments). Monitor the extent and condition of aspen clones to determine the effect of disturbance frequency on aspen survival, effects of sudden aspen decline, and incidence of new clones; this may lead to strategic protection measures for specific clones. Where can tactics be applied? Wherever aspen regeneration prescriptions are applied Wherever aspen occurs outside of protected areas Wherever aspen occurs Sensitivity to climatic variability and change: The distribution of subalpine forests is likely to shift as a result of increasing temperatures with climate change. Adaptation strategy/approach: Monitor and detect change in seedling survival, species composition, and mortality of mature trees in subalpine forests. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Install and analyze additional plots to gather trend information over time, targeting areas where changes are expected. Use Forest Inventory and Analysis plot information to determine trends in subalpine forests. Expand reforestation monitoring and post- treatment monitoring. Where can tactics be applied? Federal lands All lands In reforestation or treatment locations

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 191 Table 6.7—Management recommendations for each of the evaluated species, vegetation types, and resource concerns. Habitat, ecosystem function, or species Primary adaptive tactics Restoration potential Further management recommendations Species Limber pine Promote rust resistance while preserving genetic diversity; monitor mortality rates and distributions; evaluate which stands need treatment to ensure conservation of species; determine impact of fire exclusion era. Low to moderate – the main drawback is the exotic disease white-pine blister rust. Most management actions should be to increase rust resistance in native populations. Initiate rust-resistant programs; identify plus trees; collect cones and determine rust resistance; map limber pine populations and identify those stands that have become established before and after the fire exclusion era. Ponderosa pine Restore fire to historically fire-dominated stands; reduce fuel loadings to mitigate uncharacteristic fire severities; use HRV as guide to design and conduct restoration treatments. Moderate to high – reintroducing fire or fire surrogates into fire-excluded stands is the first step; addressing where to plant in the future is the next. Reduce or eliminate Douglas-fir in fire-excluded stands; remove competition through thinnings and prescribed burns; monitor lower treeline in SW Montana and central Idaho to evaluate potential ponderosa pine increases. Douglas-fir Reduce competition and increase vigor; keep stand density low; replace Douglas-fir with ponderosa pine, western white pine, and western larch in areas where root disease is a concern; emphasize ponderosa pine on lower elevation dry forests. Moderate to high – mitigating effects of the fire exclusion era is the first step; might be more difficult in cool, dry environs. Keep stocking low; change species composition on sites where root disease and soil moisture deficits will be increasing; concentrate planting on the higher elevation, mesic sites and avoid planting in the lower treeline. Western larch Restore declining larch stands from adverse fire exclusion effects; prioritize northerly aspects and ash cap soils for treatment; reduce competition; manage larch more intensively on more xeric sites where larch may not be the species to plant on south slopes even though current climate may be suitable. Reduce forest density in all successional stages to provide larch with better chance to utilize soil moisture. Moderate to high in west region; moderate in central region. Cut to remove more shade-tolerant species using group selections and thinnings; consider planting options on north slopes where long term persistence will have highest potential; consider genetic stock with best adaptive traits for drought and moisture stress compatibility; maintain stocking and structure diversity to favor moisture regime for larch in all successional stages and to be more able to cope with fire; consider most intensive management for larch on sites with least moisture deficits. Western white pine Promote rust resistance. Moderate in west region; low to moderate in central region, mainly due to the devastating effects of rust mortality. Increased planting of blister rust resistant material; thinning dense stands to increase young pine vigor. Aspen Restore quasi-historical fire regimes; prioritize areas were aspen already exist albeit at lower than historical levels. Moderate for all NR. Plant aspen where it is now absent but once flourished; manage aspen at the landscape level by ensuring mix of age classes and successional stages. Grand fir Foster landscape heterogeneity; ensure age class structure is near HRV. High in the west and central regions. Low priority for restoration; no need to spend valuable restoration dollars restoring this forest unless it is locally declining.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
192 USDA Forest Service RMRS-GTR-374. 2018

Table 6.7(cont.)—Management recommendations for each of the evaluated species, vegetation types, and resource concerns.

Habitat, ecosystem function, or species Primary adaptive tactics Restoration potential Further management recommendations

Species (cont.)Western redcedar Ensure high landscape heterogeneity; 

multiple age classes 

High in west and central NR regions Low priority for restoration; no need to spend valuable 

restoration dollars restoring this forest unless it is locally declining.

Western hemlock Maintain diversity of age classes and high 

landscape diversity

High in west and central NR regions Low priority for restoration; no need to spend valuable 

restoration dollars restoring this forest unless it is locally declining.

Lodgepole pine Perhaps the most important subalpine 

species to manage for mixed age classes and successional stages that approximate HRV 

Moderate to high in most if its NR range

Allow managed fires to burn in moderate years.

Whitebark pine Most climate change adaptation strategies 

are detailed in Keane et al. (2015a): promote rust resistance; conserve genetic diversity; implement treatments on the higher stands in project areas; plant rustresistant seedlings in old or recent burns.

Low to moderate in most of its range primarily due to the devastating effects of blister rust

Follow Keane et al. (2010) rangewide strategy: protect rust-resistant plus trees; promote rust resistance; implement prescribed burn and mechanical cuttings to reduce competition; plant and direct-seed blister rust resistant seedlings on burn and treated areas; cold hardy and drought tolerant material.

Subalpine fir Populations can best be modified by 

wildfire suppression efforts at local scales. 

High in most of the NR Low priority for climate impact mitigation; no need to 

spend valuable restoration dollars restoring this forest unless it is locally declining.

Engelmann spruce Populations can best be modified by 

wildfire suppression efforts at local scales; planting may be warranted in areas with declining populations.

High in most of the NR; moderate in those low elevation wetland stands

Low priority for climate change adaptation actions; no need to spend valuable restoration dollars conserving this forest unless it is declining locally

Mountain hemlock Increased fire suppression efforts will 

increase populations if needed. 

Moderate to high in west and central regions of NR

Although this species may have low priority for mitigating adverse climate change effects, it is important to monitor so it does not go locally extinct.

Alpine larch Preserve genetic diversity by collecting 

and storing seed. 

Low to moderate across most of its range

Monitor changes in alpine larch populations; document

Green ash Reduce grazing; increasing fire 

suppression and grazing can be used to modify ash populations along with planting in areas where populations are critically low.

High in the eastern NR Plant in recently burned areas where it last existed. 

Cottonwood Foster high variability in river flows to 

increase seedling establishment potential; eliminate competition.

Moderate to high Prioritize the most mesic sites first; allow fire to burn in 

areas that are not too dense; conduct cuttings to remove conifer competition.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 193 Table 6.7(cont.)—Management recommendations for each of the evaluated species, vegetation types, and resource concerns. Vegetation types Dry ponderosa pine- Douglas-fir forests Create less dense forests with composition related to moisture deficit tolerance. High everywhere in dry settings Manage density and appropriate composition related to projected moisture limited sites Western larch mixed mesic forests Create a greater landscape heterogeneity forest pattern that may limit the extent of large uncharacteristically severe disturbances using mechanical and prescribed fire as tools; greater moisture deficits, less available moisture for trees will require consideration of appropriate species distribution and forest density in the future; create within stand structure diversity and more open conditions to allow larch to maintain dominance. High in western portion of the region Manage pattern of the forest to increase the diversity of successional stages and arrangement; tools in areas suitable for timber production will include timber harvest and prescribed burning, and areas in roadless areas will be restored with wildfire for resource benefit with some planting where seed source is absent due to large fires; maintain stocking levels to favor larch moisture relationship in all successional stages and to be able to better cope with fire; manage species composition less susceptible to root disease especially in northern Idaho; manage larch in lynx habitat knowing that larch needs more open conditions to maintain dominance over the long term in a stand. Mixed mesic western white pine-western redcedar-western hemlock-grand fir forests Attempt to emphasize the restoration of western white pine while also maintaining landscape heterogeneities similar to historical conditions; promote rust resistance and plan treated and burned areas with pine seedlings. Moderate because of blister rust Monitor local conditions to evaluate losses or gains in the four species so management options can be adjusted. Lodgepole pine mixed subalpine forests High in most ares Again, manage pattern to increase the diversity of successional stages and arrangement; roadless areas need wildfire for resource benefit; planting to lodgepole may be needed where seed source is absent due to large fires; manage species composition in lynx habitat knowing that returning natural fire regimes will reduce subalpine fir populations. Whitebark pine mixed upper subalpine forests Most climate change adaptation strategies are detailed in Keane et al. 2015a: most important – create landscape heterogeneity in composition and size classes; also promote rust resistance; conserve genetic diversity; implement treatments on the higher stands in project areas; plant rust-resistant seedlings in old or recent burns. Low to moderate in most of its range primarily due to blister rust Follow Keane et al. (2010) rangewide strategy: protect rust-resistant plus trees; promote rust resistance; implement prescribed burn and mechanical cuttings to reduce competition; plant and direct-seed blister rust resistant seedlings on burn and treated areas; cold hardy and drought tolerant material.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
194 USDA Forest Service RMRS-GTR-374. 2018 Table 6.7(cont.)—Management recommendations for each of the evaluated species, vegetation types, and resource concerns. Resource concerns Landscape heterogeneity Design restoration and climate change treatments at multiple scales, especially the landscape scale; allow wildfires to burn. Moderate Landscape heterogeneity should be evaluated periodically to determine trends and magnitudes. Timber production Thinning and planting western larch, ponderosa pine and western white pine on appropriate habitats will be important to long-term timber production to enable the forest to better cope with disturbance such as fire and root disease, manage density within dry forest settings. High in western portion of region for larch and western white pine. High for ponderosa pine everywhere. Manage landscapes for species composition, structure and pattern best able to cope with moisture deficits and disturbance, especially root disease, bark beetles and fire. Manage dry forest settings to be more open grown ponderosa pine compared to current dense mixed Douglas-fir forests. Increase percent of ponderosa pine, western larch and western white pine on mixed mesic settings to cope with increase in fire and root disease. Manage for a diversity of lodgepole pine, spruce, subalpine fir, larch and whitebark pine in higher elevations considering increasing soil moisture deficits. Manage for a diversity of successional stages (landscape heterogeneity) in a pattern that will better cope with disturbance agents. Carbon sequestration Carbon can be best sequestered by embracing ecosystem management and restoring landscapes and ecosystems; carbon sequestration is a side effect of an ecosystem treatment, not the objective. N/A The best management approach for managing carbon sequestration is to foster a timber management program that emphasizes an ecosystem approach.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 195

landscape diversity. Increasing diversity is a “hedge your 

bets” strategy that reduces risk of major forest loss. Areas 

with low species and genetic diversity are likely to be more 

susceptible to the stressors associated with climate change; 

thus, promoting species and genetic diversity, through plantings and in thinning treatments, is likely to increase forest 

resilience to changing climate. Promoting heterogeneity of 

species and structure across the landscape is also expected 

to increase resilience to wildfire, insects, and disease.

There is a lot of uncertainty associated with climate 

change, and managers identified several ways to increase knowledge and manage in the face of uncertainty. 

Implementation of an adaptive management framework can 

help managers deal with uncertainty and adjust management 

over time. In the context of climate change adaptation, 

adaptive management involves: definition of management 

goals, objectives and timeframes; analyzing vulnerabilities; 

determining priorities; developing adaptation strategies and 

tactics; implementing plans and projects; and monitoring, 

reviewing, and adjusting (Millar et al. 2014). Development 

of a consistent monitoring framework that can capture 

ecosystem changes with shifting climate is a key component 

of the adaptive management framework. For example, 

tracking tree species regeneration and distribution will help 

managers determine how species are responding to climatic 

changes and ways to adjust management accordingly (e.g., 

guidelines for planting). Integration between research and 

management and across resource areas (e.g., forest management and wildlife) will also be key in implementation of 

the adaptive management framework to ensure that the best 

available science is being considered in on-the-ground management and that management approaches do not conflict 

(e.g., effects of a particular thinning treatment on wildlife).

Managers also identified adaptation strategies and 

tactics to maintain particular species or community types 

of concern. For example, climate change is likely to lead 

to increased whitebark pine mortality through increased 

mountain pine beetle activity, fire, and white pine blister 

rust. There will probably also be a loss of site conditions 

that support whitebark pine. To promote resilient whitebark 

pine communities, managers may want to focus restoration 

efforts on sites less likely to be affected by climate change 

(i.e., refugia). A variety of management strategies can be 

implemented to promote whitebark pine, including fire 

management, planting at lower elevations, and removing 

other dominant species (e.g., lodgepole pine, spruce, and 

fir). Genetically selected seedlings can also be planted to 

promote blister rust resistance.

Finally, managers recognized that stressors associated 

with climate change cross boundaries, making it increasingly important that agencies coordinate and work across 

boundaries. Agencies can coordinate by aligning budgets 

and priorities for programs of work, communicating about 

projects adjacent to other lands, and working across boundaries to maintain roads, trails, and access that are likely to be 

more frequently impacted by fire and flood events under a 

changing climate.

Discussion

Given the high uncertainties in predicting climate, 

vegetation, and disturbance responses to increasing CO2, 

we think that assessing vegetation change and vulnerabilities is currently more of an educated guess based on 

inconsistent and contradictory studies rather than a highly 

confident evaluation of comprehensive scientific investigation. Many of the techniques used to predict tree species 

response to climate change in the literature present only 

one possible future out of seemingly unlimited possibilities. 

These predictions would change if a new climate change 

scenario were used, if new data were augmented with existing data, if new variables were included in the analysis, if 

simulation parameters were modified, or if new algorithms 

were included in existing models. Moreover, there are still 

many unknowns in ecosystem science, and if we link those 

unknowns to the unknowns in climate systems, these uncertainties would certainly swamp any educated guesses that 

we might have. Consequently, these projections and assessments must be interpreted in the context of high uncertainty.

One important lesson that we learned while writing 

this chapter is that climate change is only one of the many 

challenges facing land managers, and some of these other 

challenges might be more important than mitigating climate 

change. We found that successfully mitigating ecosystem 

impacts from past management actions, such as fire exclusion and introductions of exotic species, will also mitigate 

climate change impacts. Restoring fire-prone ecosystems 

declining due to fire exclusion, for example, might successfully solve two issues: It would increase ecosystem health 

and create resilient forests that could thrive under future 

climate changes. These fire-dominated forests have already 

experienced great variation in past climate and clearly have 

broad amplitudes of resilience with respect to climate. In another example, fostering greater rust-resistance in our native 

five-needle pines may allow us to create forests that are less 

vulnerable to changes in climate. There will be places in the 

Northern Rockies where the primary challenge will be climate change impacts, such as drought at the lower treeline, 

but overall, we think that the best approach is to integrate 

climate change considerations into current management 

actions rather than conducting management actions for the 

sole purpose of climate change mitigation. Ecosystem restoration, as a prime example, could be the best approach for 

preparing for climate change.

The main question then is: How do we restore ecosystems in the Northern Rockies? Managers need reference 

conditions at the stand and landscape scales to prioritize, 

plan, design, and implement effective restoration activities. This becomes somewhat problematic when we need 

that reference to include the trend and variability of future 

climate. Considering the high uncertainty of future climate 

and vegetation projections, and knowing the resilience of 

fire-adapted species, we suggest that any conclusions about 

the infeasibility of ecosystem restoration under changing 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
196 USDA Forest Service RMRS-GTR-374. 2018

climates are imprudent. It may be more prudent to wait 

until simulation technology has improved to include credible pattern and process interactions with realistic regional 

climate dynamics for the future so that we base decisions 

about the restoration of ecosystems on better information. 

But improving ecosystem models may take decades before 

simulations can be used to predict species and landscape 

response to climate change with reasonable accuracy. While 

we wait, we lose valuable populations and rust-resistant 

trees, and our options for restoration diminish greatly. Even 

with climate change, restoration activities will probably be 

appropriate considering the high genetic variation across 

the range of forest species, which provides the foundation 

for adaptation (Bower and Aitken 2006, 2008; Mahalovich 

and Hipkins 2011; Rehfeldt et al. 1999). Therefore, we think 

that the current emphasis on ecosystem restoration in the 

Northern Rockies will lead to more-resilient ecosystems for 

the future. Until we have realistic models and less uncertain 

climate change projections, we desperately need a construct 

to use as a reference for restoration. Using historical data to 

guide future management actions may entail less uncertainty 

than building new references based on uncertain climate 

change projections. Therefore, we think that historical 

ranges and variability may provide sufficient reference conditions in the future.

We think that the concept of HRV still has a valid place 

in land management, at least for the near future. Landscape 

models can be used to simulate fire regimes and their 

interaction with climate and vegetation to create HRV time 

series that can be used as reference conditions to assess, 

plan, evaluate, design, and implement ecosystem restoration treatments. HRV should be used only to guide land 

management—not as a target on which to evaluate success 

or failure. There are few measures of ecosystem health that 

match the scale, scope, flexibility, and robustness of HRV 

analysis. HRV might provide a useful, though not ideal, reference for land management over the next several decades 

until simulation modeling advances to a level where models 

can forecast both accurate climate and climate responses by 

the ecosystems.

Conclusions

Climate change is one of many challenges facing land 

managers, and some of these other challenges might be 

more important than climate change. In addition, mitigating 

past ecosystem damage (e.g., fire exclusion and nonnative 

introductions) is a climate-smart practice. For example, 

restoring fire-prone ecosystems can both improve ecosystem 

function and create forests that will be resilient in a warmer 

climate. Fire-prone forests have already withstood variation 

in past climate and have broad amplitudes of resilience 

with respect to climate. There will be places in the Northern 

Rockies region where climate change will be the primary 

challenge (e.g., drought at lower treeline), but integrating 

climate change considerations into current management 

operations is preferable to a climate-centric management 

strategy.

Multiresource monitoring will be critical for managing 

ecosystems in the future, building on existing monitoring 

systems but with additional elements to accommodate the 

effects of climate change (Janowiak et al. 2014). Although 

costly in terms of money and personnel, an extensive monitoring system will save money in the long run by evaluating 

the effectiveness of adaptation tactics and providing a means 

to adjust them. Without monitoring, it will be impossible 

to know the magnitude and trend of climate effects on 

vegetation, or if actions proposed in this document (see 

section on adaptation strategies and tactics) are useful for 

planning and management. Monitoring data can also be used 

to provide inputs to calibrate and validate models. Models, 

in turn, can be used to simulate emergent environmental 

patterns, compare effects of potential treatments, identify 

vulnerable landscapes or ecosystem components, and bridge 

gaps between large-scale ecological processes and variables 

measured in small areas and over short periods of time. 

Therefore, any future land management planning will be 

complete only if a plan for monitoring proposed actions is 

included.

Acknowledgments

We acknowledge Art Zack, Megan Strom, Chris Schnepf, 

Paul Zambino, and Kevin Greenleaf from the U.S. Forest 

Service for technical reviews. We thank Gregg DiNitto, Paul 

Zambino, Blakey Lockman, Marcus Jackson, Joel Egan, 

Sandra Kegley, and Brytten Steed of U.S. Forest Service 

Forest Health and Protection, and Barbara Bentz, U.S. 

Forest Service Rocky Mountain Research Station, for additions to the disturbance sections. This work was partially 

funded by the Rocky Mountain Research Station Fire, Fuels 

and Smoke Program and U.S. Forest Service Office of 

Sustainability and Climate.

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Appendix 6—Vegetation Model Output, Vulnerability 

Assessment Descriptions, and Adaptation Options for 

Forest Vegetation in the Northern Rockies.

Appendix 6A—Dynamic Global Vegetation Model (MC2) Output for the Northern 

Rockies.

The following figures show output from the MC2 dynamic global vegetation model for the Northern Rockies region, 

including vegetation type distribution (figs. 6A.1–6A.4), carbon (6A.5, 6A.6), potential evapotranspiration (6A.7), and fire 

rotation (6A.8). See Chapter 6 for further information on the MC2 model and model simulation details.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

Figure 6A.1—Maps of MC2 

vegetation type distributions 

for three time spans (historical, 

2030–2050, and 2080–2100) 

and with and without fire 

suppression. Vegetation types 

are abbreviated as follows: B 

= boreal; M = maritime; S = 

subtropical; SA = subalpine; 

T = temperate; and ENF = 

evergreen needleleaf forest; 

ENW = evergreen needleleaf 

woodland; F = forest; MF = 

mixed forest; MW = mixed 

woodland; DBF = deciduous 

broadleaf forest; and DBW 

= deciduous broadleaf 

woodland.
214 USDA Forest Service RMRS-GTR-374. 2018

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

Figure 6A.2—MC2 Vegetation type distributions as proportion of the landscape for each subregion, 

where 2A = Western Rockies; 2B = Central Rockies; 2C = Eastern Rockies; 2D = Grassland; 2E = 

Greater Yellowstone Area; and vegetation type acronyms are: ENF = evergreen needleleaf forest; ENW 

= evergreen needleleaf woodland; F = forest; MF = mixed forest; MW = mixed woodland; DBF = 

deciduous broadleaf forest; and DBW = deciduous broadleaf woodland.

2A
USDA Forest Service RMRS-GTR-374. 2018 215

2B

Figure 6A.2—Continued.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
216 USDA Forest Service RMRS-GTR-374. 2018

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

Figure 6A.2—Continued.

2C
USDA Forest Service RMRS-GTR-374. 2018 217

Figure 6A.2—Continued.

2D

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
218 USDA Forest Service RMRS-GTR-374. 2018

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

2E

Figure 6A.2—Continued.
USDA Forest Service RMRS-GTR-374. 2018 219

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

Figure 6A.3—Potential vegetation type distributions as proportion of the landscape for each subregion where vegetation types are 

abbreviated as follows: Ponderosa pine-Douglas-fir = dry ponderosa pine and Douglas-fir forests; eastern grasslands = eastern 

grasslands; lodgepole pine-aspen = lodgepole pine and aspen mixed conifer forests; mixed mesic = mixed mesic white pine, cedar, 

hemlock, grand fir forests; montane shrubs = montane shrubs; Palouse = Palouse (western grassland); riparian = riparian; sagebrush 

dominated = sagebrush-dominated systems; larch mixed conifer = western larch mixed conifer forests; whitebark pine-spruce-fir = 

whitebark pine-spruce-fir forests; woodland = woodland; and exotics = exotics.
220 USDA Forest Service RMRS-GTR-374. 2018

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

Figure 6A.4—Existing vegetation type distributions as proportions of the landscape for each subregion, where vegetation types are 

abbreviated as follows: Ponderosa pine-Douglas-fir = dry ponderosa pine and Douglas-fir forests; eastern grasslands = eastern 

grasslands; lodgepole pine-aspen = lodgepole pine and aspen mixed conifer forests; mixed mesic = mixed mesic white pine, cedar, 

hemlock, grand fir forests; montane shrubs = montane shrubs; Palouse = Palouse (western grassland); riparian = riparian; sagebrush 

dominated = sagebrush-dominated systems; larch mixed conifer = western larch mixed conifer forests; whitebark pine-spruce-fir = 

whitebark pine-spruce-fir forests; woodland = woodland; and exotics = exotics.
USDA Forest Service RMRS-GTR-374. 2018 221

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

Figure 6A.5—Maps of aboveground live carbon averaged across each of three time spans 

(historical, 2030–2050, and 2080–2100) and with and without fire suppression, for the 

A1B and A2 emission scenarios.
222 USDA Forest Service RMRS-GTR-374. 2018

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

Figure 6A.6—Maps of aboveground dead carbon averaged across each of three time 

spans (historical, 2030–2050, and 2080–2100) and with and without fire suppression, 

for the A1B and A2 emission scenarios.
USDA Forest Service RMRS-GTR-374. 2018 223

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

Figure 6A.7—Maps of potential evapotranspiration (PET) averaged across each of three 

time spans (historical, 2020–2050, and 2070–2100) and with and without fire 

suppression, for the A1B and A2 emission scenarios.
224 USDA Forest Service RMRS-GTR-374. 2018

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

Figure 6A.8—Maps of annual fire rotation averaged across each of three time spans (historical, 

2020–2050, 2080–2100) and with and without fire suppression, for the A1B and A2 emission 

scenarios.
USDA Forest Service RMRS-GTR-374. 2018 225

Appendix 6B—Climate Change Vulnerability Assessments and Ratings for Tree 

Species, Forest Vegetation Types and Forest Resources of Concern.

The following tables describe climate change vulnerability assessments for tree species, forest vegetation types, and 

forest resource concerns (table 6B.1), and risk assessment and vulnerability ratings for the same species, vegetation types, 

and resources of concern (table 6B.2). See Chapter 6 for further discussion of climate change vulnerabilities for forest 

vegetation.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
226 USDA Forest Service RMRS-GTR-374. 2018 Table 6B.1—Vulnerability assessment for the three scales of analysis (species, vegetation type, resource concern) for vegetation of the Northern Rockies (NR). Habitat, ecosystem function, or species Broad-scale climate change effect Current condition, existing stressors Sensitivity to climatic variability and change Expected effects of climate change Species Limber pine Warming temperatures, eastern portion of Northern Rockies anticipated increase in precipitation, less snow pack, variable precipitation during growing season. Reduced abundance due to white pine blister rust infections, mountain pine beetle outbreaks, continued fire exclusion, and on wetter sites, limber pine dwarf mistletoe can cause mortality. Shade intolerant, early-seral to pioneer species following fire or tree removal; difficulty in competing with other encroaching species on more productive sites; little to no reproduction at low tree densities (lack of effective pollination cloud) and those seeds that are produced have increased likelihood of inbreeding; minimum of 10 cone- bearing trees per acre is needed for dispersal by birds (i.e., corvids). Increased growth; larger seed crops; increased seed dispersal into burned areas due to bird dispersal; lower seed germination due to warmer, drier conditions; loss of ectomycorrhizal associations, increased competition from wind-dispersed conifers; less blister rust infection due to higher temperatures and lower relative humidity disrupting the blister rust cycle; except in wave years; higher blister rust and dwarf mistletoe infections on eastside where precipitation is projected to increase; large and intense wildfires could threaten seed sources. Ponderosa pine

—

var. scopulorum

Increasing temperatures; deeper and longer droughts; increasing fire severity and occurrence; shorter growing seasons and longer dormant seasons.

Higher than historical tree densities. 

Generalist adaptive strategy; high phenotypic plasticity; early- to mid-seral species; moderate shade tolerance; well-adapted to drought.

Decreases in dwarf mistletoe and western gull rust damage; competitive capacity will increase; fire effects uncertain; more highly vulnerable to loss of disjunct and isolated populations, as compared to var. ponderosa; declining precipitation and variable spatial and temporal pattern may cause declines in regeneration, except in eastern portion of northern region where precipitation is expected to increase; increases in mountain pine beetle outbreaks; advancing competition, increasing western pine shoot borer occurrence; large and intense wildfires could threaten seed sources.

Ponderosa pine

—

var. ponderosa

Minor cold hardiness issues at lower elevations.

Precipitation pattern may favor regeneration; increases in pine beetle (western and mountain) Lophodermiumsp. Elytroderma, Armillaria root rot, Mycosphaerella pini; extreme fire behavior; competition from grand fir and Douglas-fir.

Intermediate adaptive strategy at low to mid elevations; specialist adaptive strategy at higher elevations; moderate phenotypic plasticity; early- to mid-seral species; little shade tolerance; less adapted to drought.

Competitive capacity will increase; increasing fires may have both beneficial and detrimental effects (high uncertainty); dwarf mistletoe and western gull rust may decrease; loss of disjunct and isolated populations on edges of range; limited ectomycorrhizae availability at higher elevations; suitable substrates may not exist upslope, impedes both natural and artificial regeneration; large and intense wildfires could threaten seed sources.

Douglas-fir Increase in 

temperature causing increase in soil moisture deficits and less available water especially at lower elevation dry sites.

Increase in tree density has increased risk of mortality from a large fire standpoint and will also limit regeneration and species distribution locally; root disease a major cause of mortality in northern Idaho and western Montana.

Sensitive to increasing temperatures and increasing soil moisture deficits, this will predispose Douglas-fir to other related mortality agents such as insect and disease. 

At lower elevation southerly aspects expect ponderosa pine to be better able to cope with moisture deficits and disturbance such as fire, spruce bud worm; less seed source due fire size and due to cone production problems with spruce bud worm; mesic sites expect increase in mortality due to root disease; higher elevation southerly slopes may provide increased climate suitability for Douglas-fir; large and intense wildfires could threaten seed sources.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 227 Western larch Increase in temperature causing increase in evaporative demand and soil moisture deficits. Increase in forest density has increased mortality risk from a fire standpoint, especially existing large larch trees; past selective harvest and lack of fire have reduced species distribution and density, especially very large individuals. Very sensitive to changes in temperature; spring frosts often reduce pollen, cone and seed production that leads to sporadic seed years; very sensitive to warm temperatures to establish regeneration on high energy, southerly slopes; rising temperatures and increasing soil moisture deficits will affect potential distribution; increasing amount of fire will likely benefit larch as long as it is not in overly dense forest conditions with poor vigor leading to loss of seed source after fire. Range expansion and/or shift to more northerly aspects; reduction of size/age diversity of trees; larger fires may facilitate larch regeneration because the larger larch trees may provide seed on burned areas; increased drought on drier sites may exacerbate competition stress caused by invading shade tolerant species. Western white pine Warming temperatures; longer growing seasons; increased fire; increases in drought. Local rates of blister rust infection may hold steady but remains highly susceptible to wave years of infection; increases in Armillaria root rot, mountain pine beetle (endemic—depends on white pine population size and tree size), Lophodermium nitens, Lecanosticta aciocola severe needle blight on- going issue with cool-wet protracted springs; potential seed sources vulnerable to fire damage; critical thresholds for regeneration establishment may be possible resulting in ineffective pollen cloud, no seed production and higher probability of inbreeding. Early spring frost and cold hardiness may not be physiologically in tune as individuals migrate upslope; moisture: lower elevation ecotones (<25” per year precipitation threshold); moderate shade- tolerance; early- to mid-seral good competitive ability; up to 3 years seed viability in soil bank; generalist adaptive strategy; high phenotypic plasticity. Increased growth; increased abundance with less grand fir provided there is a seed source or planting; less blister rust infection due to high temperatures and lower relative humidity except for wave years; if seed source exists, fire will increase growing space providing for regeneration potential; the species is dependent on ash cap on many sites, which may prevent migration to wetter/warmer sites; limited ectomycorrhizae availability at higher elevations; suitable substrate may not exist upslope so migration may not be expedited; both natural and artificial regeneration may occur with drought; pole blight may occur. Table 6B.1—Continued.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
228 USDA Forest Service RMRS-GTR-374. 2018 Quaking Aspen Warming temperatures, decreasing snowpack, increase in severity and frequency of wildfires. Although there are stable climax aspen communities, most aspen is a fire-maintained, early seral component of a forested community; stands are declining in number and size; stressors include competition with and shading by conifers, typically due to fire exclusion, domestic and native ungulate herbivory, and increasing temperature coupled with declining precipitation; reduction of soil moisture may cause severe water stress, which reduces aspen’s ability to survive (e.g., sudden aspen decline) and to reproduce both vegetatively and by seed, thereby reducing genetic variability. Sensitivity varies based on site characteristics, primarily soil moisture and solar radiation; it is mostly shade-intolerant; ubiquitous across most of North America; aspen is most persistent on sites with high solar radiation coupled with moist to wet soils; it does not tolerate extended drought; highly fire adapted and regenerates abundantly after stand-replacing fire, although it can regenerate in conifer dominated stands in some settings; it will persist or possibly increase with warmer temperatures as long as there is sufficient soil moisture; fringe communities may succumb to sudden aspen decline with long-term and severe water deficit, which will kill the roots. Communities on warmer, drier sites could decrease due to water deficit; some stands may have significant mortality with little or no regeneration due to herbivory; sudden aspen decline has been associated with severe, prolonged drought, particularly in aspen stands that are on the fringe of the species’ distribution (warmer and drier sites than those typically considered optimal for aspen persistence); fewer and smaller stands and of those that persist, there will be increased plant stress due to increased severity of summer droughts; increased fire frequency may likely favor aspen regeneration by removing shading conifers; younger stands (<40 years old) may be more resilient to drought and frequent fires could favor aspen on moister sites; severe fire may kill shallow root systems and eliminate aspen in some hotter and drier sites; growth may increase because photosynthetic rates appear to increase more in aspen than other tree species as atmospheric carbon increases, but this may be offset by increased drought stress and increased atmospheric ozone, which reduces photosynthesis and may increase susceptibility to insects and disease; higher herbivory (browsing) on regenerating stands is possible as adjacent upland vegetation senesces and desiccates earlier in the growing season; areas with mountain pine beetle-caused conifer mortality (especially in lodgepole pine) may release aspen and regenerate once the conifer canopy is removed; conifers use more water than aspen, so more aspen stands mean more streamflow; aspen forms natural fuel breaks that can be used effectively in fire management; pathological rotation is short-lived. Grand fir Increasing drought; longer growing seasons; increased fire and disease; highly variable weather. Fire exclusion has increased grand fir in dry and mesic sites, but increased tree densities have also stressed fir trees, contributing to increased fuel loadings, higher root rot, and greater insect damage and mortality. Late-seral, shade tolerant species highly susceptible to fire; usually exists in areas where competition and tree density is high so most trees are stressed; highly stressed trees are more susceptible to climatic fluctuations and trends. On xeric sites, increased drought and longer growing seasons will exacerbate stress from competition, resulting in high mortality mainly from insects and disease; longer fire seasons and high fuel loadings from exclusion will also reduce this species; on mesic sites, longer growing seasons coupled with higher temperatures may increase growth rates and regeneration success, thereby increasing tree density and competition; fire will reduce grand fir dominance at across the landscape. Western redcedar Longer growing seasons; warmer temperatures; highly variable weather; enhanced warm and cold cycles; early frosts. Root and butt diseases: low susceptibly to pathogens. Generalist adaptive strategy; high phenotypic plasticity; high shade-tolerance; long-lived; seed production good; vegetative potential. Increased growth rate; fire adds uncertainty; warm/cold cycle may facilitate red-belt and adversely affect western redcedar (early warming followed by early frost); cedar flagging from dry seasons (entire branch is shed, interferes with seed production); ash cap dependent, which may prevent it to migrate to wetter/warmer sites.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 229 Western hemlock Longer growing seasons; warmer temperatures; highly variable weather; early frosts during the growing stage. Confined to the moister portions of northern Rockies; susceptible to annosus root rot, Echinodontium tinctorium; High tolerance to Armillaria root rot. Provisionally tends to be a generalist adaptive strategy; high shade tolerance; needs ample moisture; susceptible to spring frost; very good competitor; high seed producer; seed viability only lasts one year in soil bank; susceptible to acid rain; ash cap dependent. May stay the same and potentially not change its current distribution; vulnerable to water deficits so declines are possible on the drier sites; since the species is ash cap dependent, migration may be retarded to wetter/warmer sites without ash cap soils. Lodgepole pine Increasing temperatures; longer droughty periods; increasing fire occurrence, frequency, and severity; increased productivity. Advancing succession due to fire exclusion is contributing to declines in lodgepole pine in many areas; current increases in burn areas are creating many new lodgepole stands and some may become dense thickets; increased drought may exacerbate stress from other factors including competition, endemic insects and diseases, and wind; warming temperatures may heighten bark beetle activity resulting in more frequent and severe epidemics. Shade-intolerant conifer that has a wide climatic amplitude in subalpine areas; exists on a wide variety of soil types and may be the only species to inhabit infertile and well drained sites; moderately drought tolerant; reproductive success depends on level of serotiny; well adapted to colonize post-burn environments; highly susceptible to bark beetles, especially when in stress from endogenous and exogenous factors such as competition, fire damage, and drought. Longer drought periods and warmer temperatures may decrease growth and regeneration on the driest sites (lower elevation lodgepole stands); well adapted to increases in fire occurrence and size depending on level of serotiny, but it may be eliminated from sites where fires reburn stands before established seedlings and saplings become reproductively mature. In mesic subalpine sites, continued fire exclusion coupled with higher productivities will heighten competitive interactions and put more lodgepole pine into stress thereby increasing mortality, insect and disease vulnerability, canopy and surface fuels, and accelerating succession toward subalpine fir; conversely, increasing fire could expand lodgepole pine occurrence, even when fires are large and severe; increasing insect (i.e., bark beetles) outbreaks may further acceleration toward non-host, shade-tolerant species. Subalpine fir Increased disturbance frequency and severity; highly variable weather and climate; decreasing snowpacks; lengthening growing seasons. Fire exclusion has increased abundance of this species on many subalpine and upper subalpine landscapes; many current stands have high densities and trees may be stressed from competitive interactions resulting in increasing susceptibility to disturbances; increasing drought could further exacerbate competitive stress and increase mortality. Highly vulnerable to subtle changes in climate; shade-tolerant species that is an aggressive competitor in subalpine areas; uniquely adapted to quickly occupy gaps in subalpine forest canopies; relatively intolerant of drought; unable to mature when seasonal drought is common; not adapted to disturbance, especially fire, with high mortality even after low severity fires; frequent cone crops. Longer growing seasons and reduced snowpacks will increase regenerative success, especially in those high- elevation areas where snow historically controlled regenerative success; higher productivity in subalpine forests may increase regeneration and species densities, eventually resulting in high competitive stress making these fir stands vulnerable to high mortality and therefore less resilient; declines of the species on drier sites may result from new drought regimes reducing regeneration success; increases of the species on moister sites will result from increased regeneration and competitive advantages; fir may gain in upper subalpine and timberline environments that are controlled by snow dynamics; subalpine fir could also increase as it replaces rust- and beetle-killed whitebark pine, yet whitebark pine can also act as a nurse crop to facilitate subalpine fir establishment; increased fire would decrease fir; the future of subalpine fir depends on both fire suppression levels and climatic responses. Table 6B.1—Continued.

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Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region Engelmann spruce Increased disturbance frequency and severity; highly variable weather and climate; decreasing snowpacks; lengthening growing seasons. Spruce is usually associated with fir in the NR; it occurs as a minor to major component of many subalpine stands and only dominates in wetland or special land types; fire exclusion has increased abundance of this species on many subalpine and upper subalpine landscapes; many current stands have high densities and trees may be stressed from competitive interactions resulting in increasing susceptibility to disturbances; increasing drought could further exacerbate competitive stress and increase mortality. Spruce is highly susceptible to changes in climate; it is not as an aggressive competitor and often is only a minor portion of a stand; it is highly vulnerable to drought; it can quickly regenerate in severely burned microsites providing there are seed sources; highly susceptible to windthrow and wind damage. Losses of spruce in the drier portions of its range, especially in those seasonal moist sites that will now be dry; not well adapted to fire so major declines are expected in burned areas, but these declines may be offset by increased regeneration on burned areas with mineral soil substrates; continued suppression activities may maintain spruce on the landscape but it may be at lower levels due to increased drought; it may increase in the upper subalpine when snowpacks become consistently lower and soil becomes drier thereby allowing spruce to encroach into glades, meadows, and balds. Whitebark pine Warming temperatures, lower snowpacks, highly variable weather, increasing fires in both intensity and severity, increasing insect and disease outbreak frequencies and 

severities; increase in populations of mountain pine beetles through possible univoltism shifts.

Reduced abundance due to white pine blister rust infections, mountain pine beetle outbreaks, and continued fire exclusion; survival due to cold hardiness in seedlings and saplings in frost pockets and swales.

Inability to compete with encroaching conifers due to low growth rates, moderate shade intolerance, and seed dispersal characteristics. Little to no reproduction may occur once tree densities are low; long-lived species that lasts through climate epochs.

On many upper subalpine sites there may be increased growth, larger seed crops, increased seed dispersal into increasing areas being burned due to bird-mediated dispersal providing there are adequate seed sources; lower seed germination due to warmer, drier conditions; possible loss of ectomycorrhizal associations; lack of suitable substrates (suitable soils) as species moves upslope; increased competition from wind-dispersed, shade tolerant conifers with fire exclusion; less infection due to higher temperatures and lower relative humidity, disrupting the highly variable blister rust cycle except in wave years; increased fire may provide caching habitat for nutcrackers that allow decades of development in the absence of competition from fir and spruce; losses in whitebark pine due to increased beetles, rust, and fire; may be offset by increases in growth, cone crops, and abundant regeneration in burned areas, but management actions are needed to augment natural regeneration by planting and direct seedling rust-resistant pine.

Table 6B.1—Continued.
USDA Forest Service RMRS-GTR-374. 2018 231 Alpine larch Warming temperatures; longer growing seasons; smaller snowpacks; less summer water; possible summer droughts; increased fire. Found in moist upper subalpine cove sites with abundant above and belowground moisture; exists in mixed stands of whitebark pine and sometimes subalpine fir; can form extensive stands in sub-irrigated upper subalpine areas. Very shade intolerant; intergrades with western larch; while this species is quite sensitive to shifts in climate, it may initially increase because it may colonize upper subalpine non-forest sites quicker than other species, but the newly established individuals may be unable to survive to maturity as drought and temperatures increase, climates become more variable, and fires increase in the upper subalpine; susceptible to damage from fire. Increased growth rates; greater ability to populate upper subalpine and treeline ecotones because of wind-aided seed dispersal and evergreen regenerative properties; increased fire may reduce many stands that historically were too wet to burn; on mesic sites, enhanced growing environment may increase competition from other more competitive, shade-tolerant conifers; lack of whitebark pine seed caching because of depressed cone crops may favor alpine larch dominance in areas that currently lack trees (e.g., treeline, subalpine balds, meadows, glades); on xeric sites, lack of summer groundwater may contribute to higher water stress and lower growth rates; years with deep droughts may kill established regeneration; alpine larch may decline in those areas with lower water availability and declining groundwater flow. Green ash Warming temperatures, decreasing snowpack, increase in severity and frequency of wildfires. Domestic and native ungulate herbivory has affected both structure and composition of these communities. Green ash has broad ecological amplitude and can survive droughty conditions, but persists optimally in moist sites; as soil moisture declines, marginal sites may become less favorable for regeneration and survival of young trees; there will probably be increased vegetative regeneration and decreased production of seedlings following fire—fire often kills green ash seed on or near the soil surface, restricting seedling recruitment to surviving seed producing trees. Green ash may benefit from increased temperatures; seedling growth may increase with increasing soil temperatures; after increased fires, green ash has both root crown and epicormic sprouts, and both are typical following disturbances such as fire; fire may be very important in woody draws and riparian areas of the Great Plains; woody draws are long and narrow, so even though they are more moist than surrounding uplands, they can burn during frequent fires in surrounding grasslands. Low-severity fires might promote regeneration by thinning stands and stimulating sprouting (the primary response to fire); browsing pressure will likely increase with increased drought, as upland grasses and forbs desiccate and senesce earlier, or are replaced by invasive, less palatable species. Table 6B.1—Continued.

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Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region Cottonwood Warming temperatures; decreasing snowpack; increase in severity and frequency of wildfires. There has been a reduction in area due to conversion and development of floodplains; composition and structure of cottonwood forests have been altered due to changes in flow regimes; structural alteration (typically simplification) of the channel (e.g., levees, bank-armoring structures) has likely contributed to channel widening, or channel incision and loss of floodplain interaction; nonnative trees that are more drought tolerant are already present along rivers and streams in eastern Montana; increased drought stress will likely favor these species over cottonwood; additional stressors include roads, along with domestic and native ungulate browsing (particularly on young cottonwoods). All species of cottonwood require saturated, but aerobic substrates and full sunlight to germinate and persist; any alteration of hydrologic flow regime (e.g., timing, magnitude and duration) will affect floodplain interaction and plant available water that may reduce recruitment and establishment of seedlings (cottonwoods regenerate primarily by seed); decreased streamflows and floodplain interaction may result in a shift in streamside vegetation to upland species, along with reduced growth and regeneration, and increased mortality of cottonwood; because cottonwoods are shade intolerant (require full sunlight), any conifers that establish on the drier fluvial surfaces will grow tall enough to eventually shade out the cottonwoods; as snowpacks decline and melt earlier, peakflows will be reduced and variation in discharge will decline, leading to a loss of various fluvial (depositional) surfaces along the stream, on which cottonwood germinate; the system becomes less complex; there may be fewer recruitment events; in addition, there may be a shift in timing of peakflows to earlier in the season, before cottonwood seed is viable for germination, resulting in both decreased germination and 

establishment of young cottonwoods; increased demand for water (additional diversions, reservoir expansions) and increased browsing pressure (adjacent upland vegetation senesces and desiccates earlier in the growing season) may also lead to a decline in cottonwood; sizes of cottonwood forests may decrease as these fluvial surfaces are less frequently inundated; there may be little to no recruitment of young cottonwoods. 

Timing of flooding is critical to germination success, and establishment of young (sapling, pole) cottonwoods both diminished; this will vary based on winter snowpack, and amount and timing of snowmelt (and associated peakflows); seedlings establish on moist to wet bare mineral soil, typically on stream bars, in full sunlight; as the snowpack declines and melts earlier, there will be reduced, more stabilized flows (loss of extreme high and/or low flows) and/or a shift in timing of peakflows to earlier in the season, before cottonwood seed is viable for germination); with earlier peakflows and less discharge, germination success is diminished; increased demand for water (additional diversions, reservoir expansions) and increased browsing pressure (as adjacent upland vegetation senesces and desiccates earlier in the growing season) will also likely lead to a decline in cottonwood.

Table 6B.1—Continued.
USDA Forest Service RMRS-GTR-374. 2018 233 Vegetation types Dry ponderosa pine and Douglas-fir forests Increase in temperature, causing increase in soil moisture deficits and less available water especially at lower elevation dry sites. Increased density has put at risk increased mortality from a fire- severity standpoint, root disease a major cause of mortality in northern Idaho and western Montana. Sensitive to increasing temperatures and increasing soil moisture deficits; this will predispose Douglas-fir to other related mortality agents such as insects and disease; this may give ponderosa pine an advantage on these settings At lower elevation southerly aspects, expect ponderosa pine to be better able to cope with moisture deficits and disturbance such as fire, spruce budworm; less seed source due to fire size and cone production problems with spruce budworm; mesic sites expect increase in mortality due to root disease; higher elevation southerly slopes may provide increased climate suitability for Douglas-fir, whereas ponderosa pine will be favored at lower elevations; patches size will increase due to severe fire if density reductions are not implemented. Western larch mixed- conifer forests Increase in temperatures will likely rearrange current species associations on higher-energy slope positions Larch forests have been reduced in extent due to successional effect from fire suppression, and preferential harvest; forest density increases have been substantial, and it now exists in uncharacteristic dense forest conditions in many areas. In northern Idaho, forest density (and productivity) was a bit denser due to warm mesic climate and deep ash capped soils. In areas once dominated in northern Idaho by western larch, western white pine, and ponderosa pine, they are now dominated by mixed grand fir and moist-site Douglas-fir forests. The spatial pattern of forest structure has been homogenized in many areas, leading to a continuous horizontal fuel profile atypical of historic landscape structure in many areas once typical of mixed-severity regime. Larch is sensitive to changes in temperature; very sensitive to warm temperatures to establish regeneration on high energy, southerly slopes; rising temperatures and increasing soil moisture deficits will affect potential distribution and pattern of larch forests especially on high energy aspects. Increasing amount of fire will likely benefit larch as long as it is not in overly dense forest conditions with poor vigor with continuous horizontal fuel profile across landscapes. Larch is highly vulnerable to increase in temperature and uncharacteristic fires in dense forest settings; the loss of large tree structure and larch regeneration success could be a major effect due to the current lack of heterogeneity and patch densities; this is especially true for high-energy topographic locations; increases in soil moisture deficits could retract the range of western large to more northerly slopes with deep soils; cone production could be positively affected with increasing temperatures, which could cause cone maturation to be earlier and could mean earlier fire seasons may still be timed with cone production and seed cast after fire. Adaptation ability for cone production and seeding distance and regeneration ability may be reduced if connectivity is reduced due to very large and more frequent severe fires occurring. High forest density and low landscape pattern diversity compared to HRV may put at risk medium, large, and old-growth larch stands due to increasing moisture deficits and stand replacing fire. Simplification of within- and between-patch structure due to increased fire severity and size could lead to loss of diversity and loss of important wildlife habitat such as cavity nesting habitat for birds and mammals. In northern Idaho, the change in species composition of the forest to more intolerant to shade species has resulted in a forest much more susceptible to wide spread root disease mortality. These areas involve millions of acres on which less carbon sequestration will take place given the relatively novel species composition of today’s forests. Given the likely increase in soil moisture deficits in the future, root disease effects are not likely to reduce; lower tree densities of reproductively mature larch and loss of connectivity between populations will increase inbreeding depression as a result of disruption of an effective pollen cloud. Table 6B.1—Continued.

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Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region Lodgepole pine and aspen mixed conifer forests Increasing temperatures; longer droughty periods; increasing fire occurrence, frequency, and severity; increased productivity. Many stands of this type are succeeding to subalpine fir- spruce due to fire exclusion; aspen has been declining due to lack of fire and increasing drought; healthiest areas are in wilderness. This type is more sensitive to management actions than climate in that continued fire exclusion will ensure their decline; this type thrives with fire and will even survive insect and disease outbreaks if fire is present on the landscape. This cover type could expand in the future with increasing fires and warming of the subalpine; disturbances may eliminate competing conifers and facilitate serotiny-aided lodgepole pine regeneration; aspen may decline on the drier parts of its range, but could increase and make major advances into the subalpine as fires burn competing conifers and temperatures moderate creating favorable climates; if fires are too frequent, this cover type may be replaced by semi-permanent shrub-herb, but as long as fire return intervals are greater than the reproductive age, lodgepole and aspen should prevail; as fires increase, more areas in this type will be early seral, creating more heterogeneous landscapes with more patches of pine and fir mixed with aspen. Mixed mesic white pine, cedar, hemlock grand fir forests Increasing temperatures; more drought; more fires. This type is limited to the northwestern portions of the Northern Rockies and much of this area has had management activities (harvest); western white pine occurrence has been severely reduced by blister rust but has shown increases in some portions of this type; unharvested stands are becoming more dense creating conditions that favor rot, insects, and disease damage. This type includes a fire-tolerant, fast-growing, early-seral species (western white pine) with a collection of late-seral, shade- tolerant, highly competitive species so the type may actually not change in coverage as fires facilitate conversion to pine on these sites. Western white pine may become a more dominant feature of this type; declines in cedar and hemlock are possible; moisture changes are probably not limiting on these sites as much as the dependence on ash cap soils; major gains in the type are probably not possible because of the limited distribution of ash cap soils in some areas and the decrease in moisture outside of the current type’s range. Similar to other types, the distribution of seral types may be more heterogeneous due to fire, but the long period of fire exclusion might foster atypical high-severity fires that might burn entire landscapes in some areas, and this might result in homogeneous pine stands providing sufficient rust resistance and seed sources. Whitebark pine- spruce-fir forests Declining snowpacks; increasing fire; increasing 

temperatures.

This type is probably increasing from effective fire exclusion; losses in whitebark pine are successionally replaced by fir-spruce; the low-elevation spruce-fir types are becoming more dense and crowded.

This type might not be as sensitive as other more xeric sites to direct climate change impacts, because there is abundant water, and predicted increases in both regeneration and growth may actually increase its climate resilience; increasing fires may cause a shift to more early seral communities and if whitebark pine populations were not experiencing rust outbreaks, these early seral communities would probably be dominated by whitebark pine.

This type may contract in the future due to several interacting factors; whitebark pine will continue to decline due to rust and beetle outbreaks, spruce-fir forest may decline due to increased fire and reduced soil water; this site could be replaced by lodgepole-aspen in drier locations; if agencies plant and conduct restoration activities, whitebark pine could make major gains into the increasing burned areas, thereby replacing spruce-fir and limiting the contraction of this type; low-elevation sprucefir stands are probably going to move towards the western larch/mixed conifer type because of prolonged droughts and increasing temperatures, especially after fires.

Table 6B.1—Continued.
USDA Forest Service RMRS-GTR-374. 2018 235 Resource concerns Landscape heterogeneity Increased productivity causing accelerated succession; increases in disturbance frequency and extent; highly variable drought intensity and extent; migration of species to new habitats; changes in magnitude, season, and variability of water availability. Ninety years of fire exclusion coupled with past management activities (e.g., grazing) has reduced landscape heterogeneity. Landscape heterogeneity is highly susceptible to subtle shifts in climate because it is the reflection of the interaction of vegetation dynamics with disturbance regimes, topography, and land use. Small changes in climate may facilitate large changes in disturbances or vegetation dynamics causing new landscape mosaics. Increased fire across most of the NR may both increase and decrease landscape heterogeneity. Wildfires and wildland fire use fires may create patchworks of fire severity types across burned areas that will increase heterogeneity and therefore landscape resilience, but some fires may burn fire-excluded landscapes with high severities causing atypical large patches of high plant mortality that may decrease heterogeneity. While large, severely burned patches occurred in historical fires, the frequency and size of these patches may be different today. The highly variable species migration rates into areas with new climates may increase heterogeneity, but the rapidly changing climates may only facilitate generalist species thereby decreasing heterogeneity. Timber production Increase in temperature, causing increase in soil moisture deficits and less available water that larch need, will shift species composition to root disease prone species particularly Douglas- fir and grand fir. Higher temperatures likely to extend fire season and to reduce forest inventory on areas suitable for timber production. Some increase in productivity may occur at mid to higher elevations; however, increase in fire may reduce timber production opportunities. Composition shift causing reduced productivity is likely in the western portion of the region on root disease-prone sites and in southerly exposures. Risk of uncharacteristic fire severity very high due to uncharacteristic high forest density which will reduce timber production opportunities, especially in dry forest areas. Sensitivity is high in northern Idaho and southerly exposures due to increasing moisture deficits and increase in uncharacteristic disturbance such as severity and extent of fire and root disease. Expect some increase in production at mid and higher elevations due to warming temperatures. This could be offset overall by losses due to root disease and increase in fire severity across the areas suitable for timber productions. Less production (sequestration) anticipated in northern Idaho if current species compositions are not changed. Table 6B.1—Continued.

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Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region Carbon sequestration Increased fire; increasing drought; productivity gains and losses. Past policies of fire exclusion have created late-seral landscapes that sequester little carbon; past timber activities may have created younger stands that sequester more carbon; increasing disturbance (fire, insect, disease) has caused short-term losses in carbon sequestration. Carbon sequestration is very sensitive to climate change impacts on vegetation and disturbance. Rates of carbon sequestration are going to largely be dependent on the rate of burning in the future and the gains and losses of productivity; productivity gains and losses need to be evaluated at large spatial and temporal scales to understand future carbon dynamics. Fire exclusion will tend to push most ecosystems into later successional stages where sequestration rates are minimal; burning from controlled and uncontrolled wildfires and prescribed burning will cause short-term losses but the high productivity of the developing early-seral stands may increase sequestration for decades; sites that were historically dry will probably experience decreases in production and carbon sequestration in the future, and mesic sites with abundant water (e.g., subalpine, upper subalpine) may experience increases in productivity. Table 6B.1—Continued.
USDA Forest Service RMRS-GTR-374. 2018 237 Table 6B.2—Risk assessment and vulnerability ratings for species, vegetation types, and resources of concern. Habitat, ecosystem function, or species Adaptive capacity Exposure Risk assessment magnitude of effects Risk assessment likelihood of effects Northern Rockies vulnerability ranking Species Limber pine Intermediate adaptive strategy largely driving by timing of pollen cloud dispersal (elevational effect); highly adapted to populating the burned areas predicted for the future due both to wind and corvid-mediated dispersal; poor competitor on more productive sites, if future fires are larger and more severe, there will be less competition from other subalpine conifers; possesses moderate genetic variation (capacity) in blister rust resistance; major gene resistance to blister rust has not been identified in several studies of interior populations, warmer temperatures favor expansion of alternate host species (currant, lousewort and Indian paintbrush); little to no opportunity to hybridize with western white pine due to non-overlapping species distributions, cannot hybridize with whitebark pine; very high risk of loss of disjunct and isolated populations due to genetic drift, ineffective pollen cloud, and substrate availability. High Moderate Moderate 15 Ponderosa pine var. scopulorum Generalist adaptive strategy; high phenotypic plasticity; better adapted to drought. Moderate Low Low 17 Ponderosa pine var. ponderosa Intermediate adaptive strategy at low to mid elevations Specialist adaptive strategy at higher elevations; moderate phenotypic plasticity; less adapted to drought. Moderate Moderate Moderate 16 Douglas-fir Specialist adaptive strategy at low to mid elevations, generalist adaptive strategy at higher elevations; no opportunity of hybridizing with coastal Douglas-fir subspecies because distributions do not overlap; highly adaptive to a large range of moisture and temperature gradients. In moist forest settings, Douglas- fir is limited to a relatively short-lived seral species due to the influence of two root diseases; With warming temperatures and a possible decrease in summer moisture drought conditions, Rocky Mountain Douglas-fir may increase along with an increase in associated stressors; vulnerable to uncharacteristic fire behavior and severity due to increased densities; increase in susceptibility to Douglas-fir bark beetle mortality uncertain but probably an increased activity; moderate change in species distribution expected away from driest margins. High potential for natural regeneration failure due to reduced seed source from large wildfires and difficult micro climate especially on southerly exposures at lower elevations with increasing moisture deficits expected. On moist sites (mixed mesic forest), increases in root disease mortality due to increasing moisture stress on sites where western white pine, ponderosa pine and larch occurred historically. Less carbon sequestration expected in Douglas-fir in those forest setting; there is a high likelihood of change in local distribution due to moisture deficits and fire severity and a high probability of carbon sequestration in northern Idaho if Douglas-fir remains a dominant species in mixed mesic forests. High High High 5

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Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region Western larch Intermediate adaptive strategy, low capacity to regenerate with increasing moisture deficits on higher energy slopes. Larch is adapted to warm-moist and cool-moist settings. It does best on northerly cool aspects. It is a prolific light seed-cone producer but in sporadic years. High adaptive capacity on lower- energy slopes; wind disperses seed further than many associates, so it can take advantage of newly opened areas due to harvest or fire as an early seral species; larch has few insect and disease stressors unlike associates and is adapted to fairly frequent mixed-severity fire; it can be a dominant, long-lived seral tree species on lower-energy slopes; potential serious reductions in extent of larch on higher energy-slope positions. High High Very High 4 Western white pine Generalist adaptive strategy, high phenotypic plasticity; cold hardiness may influence distribution; lack of abundance may influence its role in the moist forest ecosystem; especially adapted to future climates in the mesic regions of the NR; there could be major expansions into historical ranges and the subalpine as rust resistance increases in western white pine populations. Moderate High High 3 Quaking aspen Aspen has the widest distribution of all trees in this report; it is circumpolar across multiple continents; it is highly susceptible to many insect and diseases; with a warmer climate, gypsy moth may have greater impacts and cause possible mortality; aspen distribution may shift upslope or to northeast (cooler, moister) aspects if drought and repeated fire causes mortality on the warmer, drier sites. Riparian aspen communities will likely persist or increase in extent, particularly if the sites remain moist throughout the growing season and increased fire burns the riparian zone, killing conifers. Fire will favor aspen, but prolonged drought will cause mortality. Younger aged stands (<40 years) may be more resilient to drought; long-distance dispersal by light seed may enhance its ability to colonize recently burned areas; this will vary based on winter snowpack, and amount and time of melt (and associated peakflows) but only if there is sufficient moisture. Moderate Moderate High 14 Grand fir Generalist adaptive strategy, only differences are racial (blue and green race); increases in disease, insects, and fire may reduce populations. Low Moderate Moderate 8 Western redcedar Generalist adaptive strategy; high phenotypic plasticity; cold/warm cycles 

early in spring or winter may cause red belt.

Moderate Moderate Moderate 6

Western hemlock Inferred or putative generalist adaptive strategy; information limited 

concerning western hemlock; susceptible to early frost.

Moderate Moderate Moderate 7

Lodgepole pine Specialist adaptive strategy; especially adapted to occupy post-burn 

landscapes that may be more common in the future; highly susceptible to increasing bark beetle outbreaks, especially on landscapes dominated by mature individuals. Varying levels of serotiny allow the species to occupy new upper subalpine environments while also regenerating after fire; its intolerance of deep droughts may reduce its capacity along the xeric edges of its current range; Heterogeneity across broad landscapes may mitigate adverse impacts from fire and mountain pine beetles.

Moderate Moderate Moderate 11

Table 6B.2

—Continued.
USDA Forest Service RMRS-GTR-374. 2018 239 Subalpine fir Generalist adaptive strategy; increasing fire will reduce subalpine fir populations to historical levels; fire exclusion may foster subalpine fir encroachment into larch, lodgepole pine, and whitebark pine late seral stands; increasing subalpine temperatures may increase fir growth and accelerate succession toward fir-dominated stands, however, as competition increases, warmer climate may facilitate increased mortality from insects and disease as trees become more stressed from high stem densities. Low Moderate Moderate 10 Engelmann spruce Intermediate adaptive strategy with opportunities to hybridize with white spruce; hybrids may be more suited to future climates, and hybridization is another key driver in speciation. Low Moderate Moderate 9 Mountain hemlock Increasing fire will reduce populations, especially where trees are smaller or in dense stands; potential to move to higher elevations; sensitive to low soil moisture in drier locations. Hybridizes with western hemlock to some extent. Should be able to persist across the landscape, perhaps in more scattered patches. Low Moderate Moderate 12 Whitebark pine Highly adapted to populating the greater burned areas predicted for the future due to bird-mediated dispersal; if future fires are larger, more severe, there will be less competition from other subalpine conifers; ability to survive fire better than its competitors; moderately shade tolerant so it can exist in competition with limited cone crops; delayed germination adaptation may mitigate warmer, drier conditions; possesses moderate to high genetic variation (capacity) in adaptive traits (blister rust resistance, late winter cold hardiness and drought tolerance), as well as phenotypic plasticity to respond to climate change. Warmer temperatures favor expansion of alternate host species (currant, lousewort and Indian paintbrush). No opportunity to hybridize with another stone pine and cannot cross with western white or limber pine where species distributions overlap; high risk and loss of disjunct and isolated populations; more drought tolerant than its associates; long distance bird dispersal will increase regeneration potential as more of the landscape burns. High High High 2 Alpine larch Its specific habitat requirements may make it difficult for alpine larch to remain on the landscape over the long term; short-term gains in alpine larch encroachment in upper subalpine and treeline glades and meadows may be lost in those years with deep drought; effective, long-term establishment of alpine larch may depend on the ability of seed dispersal to find those areas with sufficient moisture to maintain the species. High High High 1 Table 6B.2

—Continued.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
240 USDA Forest Service RMRS-GTR-374. 2018

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region Green ash Since green ash communities are already fire adapted (most associated species display some fire tolerance and/or postfire sprouting ability), increased fire will likely not affect most of the moister communities. However, those communities associated with either ephemeral drainages (e.g., woody draws) or moist upland microsites (e.g., northeast-facing depressions) may experience more drought stress as snowpack declines and melts sooner, and regeneration may decrease, eventually resulting in loss of those communities. Moderate Moderate High 18 Cottonwood Plains cottonwood may be more persistent due to greater plant available soil water in the unsaturated zone (as a result of finer textured soils). Black and narrowleaf cottonwood typically occur in coarser substrate, which will become more droughty as flows are lower and recede earlier than in the past, or are attenuated due to diversions. Seedling and sapling mortality may increase in these species. Plains cottonwood regeneration occurs with episodic flooding, whereas black and narrowleaf cottonwood typically regenerate with 1–3 year bankfull flow return intervals; therefore, plains cottonwood will likely be more adapted to irregular flows (in timing, magnitude and duration) that may occur with climate change. Moderate Moderate Moderate to High 13 Vegetation Types Dry ponderosa pine and Douglas-fir forests Douglas-fir highly adaptive to a large range of moisture and temperature gradients. Ponderosa pine adapted to settings that are moisture limited and can grow well where moisture is less limited such in association currently with grand fir; exposure of Douglas-fir to increasing moisture deficits may change composition to more ponderosa pine; increasing moisture deficits will give ponderosa pine the advantage on dry forest settings due to fire, insect and disease. High High High 3 Western larch mixed conifer forests Larch forests thrive on northerly cool aspects locations in the Region; it is a prolific light seed cone producer but in sporadic years, may seed longer distances than many associates, so can take advance of newly opened areas due to harvest or fire as an early-seral species; larch has few insect and disease stressors unlike associates, and is adapted to fairly frequent 

fire; it can out-dominate long lived seral tree species, and due to the large diameters it can attain, is important to many cavity nesters as habitat when it reaches ages over 200 years in patches large enough and connected enough to provide functional habitat; exposure on southerly aspects; warming temperatures and possible decreased summer moisture and associated drought may decrease distribution of western larch, which could mean that it will retreat to low-energy northerly slope settings; distribution of larch in patches on high-energy slopes would be reduced significantly; serious reduction in extent of larch in patches on higher-energy slope positions in the long run.

High High Very High 2

Table 6B.2

—Continued.
USDA Forest Service RMRS-GTR-374. 2018 241 Lodgepole pine and aspen mixed conifer forests This type has the capacity to absorb climate changes and either remain constant or expand into the upper subalpine; losses in aspen due to drought may be offset by gains in lodgepole pine, especially after fire; there may be long-term migrations of this type to higher elevation areas with increasing disturbance. High Moderate High 4 Mixed mesic white pine, cedar, hemlock grand fir forests This type may have the capacity to remain intact with changing climates; it may not be able to expand due to ash cap; increasing fire will favor western white pine, and fire exclusion will favor the shade-tolerant species; drier sites may see grand fir becoming more common than cedar or hemlock. Low Moderate Low 5 Whitebark pine- spruce-fir forests This type may have the capacity to respond favorably to changes in climate, but depressed populations of whitebark pine coupled with increasing fire may result in short-term losses of this type; however, if rust-resistant whitebark pine are planted and restoration activities are implemented, whitebark pine can easily dominate on these sites, especially if fires are large and severe, and whitebark pine may be able to make advances into the treeline; continued fire exclusion will probably aid in keeping this type somewhat static, and it may encroach on lower treeline sites if no fires are allowed High High High 1 Resource Concerns Landscape heterogeneity Because heterogeneity is an expression of disturbance, vegetation, and climate interactions, it depends on other factors to determine its adaptive capacity. High Moderate High NA Timber production Productivity could increase at higher elevation sites. Productivity in northern Idaho will likely decrease on southerly aspects due to root disease reducing productivity of alternate species unless western larch, ponderosa pine and western white pine are aggressively restored; high exposure due to species composition changes and risk to increased disturbance. High Moderate to high in north Idaho High in north Idaho NA Carbon sequestration All ecosystems have an inherent capability to store carbon, and the rate and capacity of carbon storage depends on plant productivity and disturbance; maximum levels of productivity depend on climate, whereas the instantaneous levels of productivity depend on successional stage or time since disturbance.Modeling studies have shown that many areas will increase productivity and increase sequestration rate and magnitude; the delicate balance between disturbance and climate coupled with land management will dictate where sequestration will increase and where it will decrease; it is important to know that over the long term (centuries), sequestration is near zero (disturbance and respiration losses are balanced by productivity gains). High High Moderate NA Table 6B.2

—Continued.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
242 USDA Forest Service RMRS-GTR-374. 2018

Appendix 6C—Adaptation Options for Forest Vegetation in the Northern Rockies.

The following tables describe climate change sensitivities and adaptation strategies and tactics for forest vegetation, 

developed in a series of workshops as a part of the Northern Rockies Adaptation Partnership. Tables are organized by 

subregion within the Northern Rockies. See Chapter 6 for summary tables and discussion of adaptation options for forest 

vegetation.

Table 6C.1—Adaptation options that address climate change effects on forest vegetation in the Central Rockies subregion.

Sensitivity to climatic variability and change: Aspen will be lost with increasing drought and lack of disturbance.Adaptation strategy/approach: Increase aspen populations.Strategy objective: Increase aspen populations.

Specific tactic – A Specific tactic – B Specific tactic – C Specific tactic – D

Tactic Actively decrease impact 

of ungulate browsing through an increase in predation of ungulates.

Increase fire disturbance. Develop techniques to 

successfully artificially regenerate aspen; improve drought tolerance with genetic selection of droughttolerant mother trees and identify and target areas most likely to successfully regenerate or provide favorable planting habitat.

Protect existing aspen populations and regeneration treatments from browsing.

Tactic effectiveness (risks)

High where ungulates concentrate

Implementation urgency Where can tactics be applied? (geographic)Opportunities for implementationCostBarriers to implementation

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 243 Table 6C.2—Adaptation options that address climate change effects on forest vegetation in the Central Rockies subregion. Sensitivity to climatic variability and change: Known unknowns and unknown unknowns. Adaptation strategy/approach: Increase knowledge and implement adaptive management. Strategy objective: Increase knowledge. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Monitor blister rust resistance within planted white pine stands, and try to understand the relationship between infection rates and climatic/weather drivers like fog. Identify other resource management goals (not directly related to stand structure and composition) that may modify management strategies for forest vegetation, such as water yield, snow retention, and wildlife habitat. Support the adaptive management research framework through a partnership between Region 1 and Rocky Mountain Research Station to evaluate management treatments and how they contribute to resiliency. Develop monitoring framework that will be consistently be implemented so that long- term change can be captured. Tactic effectiveness (risks) Implementation urgency Where can tactics be applied? (geographic) Opportunities for implementation Cost Barriers to implementation

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
244 USDA Forest Service RMRS-GTR-374. 2018 Table 6C.3—Adaptation options that address climate change effects on forest vegetation in the Central Rockies subregion. Sensitivity to climatic variability and change: Potential shifts in lodgepole pine ecosystems with changing climate. Adaptation strategy/approach: Promote resilience by maintaining age-size class composition at the stand and landscape level. Strategy objective: Maintain lodgepole pine on the landscape. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Identify areas appropriate for wildfire use and increase flexibility in how we manage fire; emphasize modified suppression and resource benefit fire; allow moderate season fires to burn. Proactively treat stands with prescribed fire to reduce fire and insect mortality and increase individual tree vigor. Implement silvicultural mechanical treatments. Tactic effectiveness (risks) Other unintended consequences could lower it from high to moderate. Highly variable depending on scale, district expertise, and landscape position. Highly variable depending on scale. Implementation urgency High/near term Where can tactics be applied? (geographic) Implement Wildland Fire Decision Support System forest wide Opportunities for implementation Highly dependent on other resource concerns and political and social issues. Cost Barriers to implementation Integration between forest and fire team Prescribed fire air quality restrictions limit what we can do; other resource constraints (e.g., lynx) Other resource constraints (e.g., thermal cover, lynx habitat, marten and wolverine)

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 245 Table 6C.4—Adaptation options that address climate change effects on forest vegetation in the Central Rockies subregion. Sensitivity to climatic variability and change: Homogenization of the ponderosa forest type across the landscape resulting in: increase in density causing associated increase in risk of severe stand replacing fires; increased risk of mortality from drought; loss of ponderosa pine on stressful sites; loss of large ponderosa pine and large ponderosa snag recruitment; and reduced water yield. Adaptation strategy/approach: Decrease the density within ponderosa pine-Douglas-fir stands, and increase structural. Strategy Objective: Develop resilience to fire, moisture and stress. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Reduce stand density with thinning, pre- scribed fire, and wildland fire use, with density and structural goals based on past and predicted future conditions. Promote age class and structural diver- sity across the landscape, through re- generation harvest, thinning, prescribed fire, and wildland fire use. Monitor establishment, survival and develop- ment of ponderosa by age class and in differ- ent conditions (e.g., aspect, heat load and soil moisture) using Forest Inventory and Analysis data and project-level stocking exams. Tactic effectiveness (risks) Thinning = high, prescribed fire = high, wildland fire use = moderate High where implemented High Implementation urgency Near-term in wildland urban interface areas. Mid term elsewhere Near-term in wildland urban interface areas. Mid term elsewhere Long term Where can tactics be applied? (geo- graphic) Ponderosa pine – Douglas-fir forests Harvesting and thinning on non-re- served lands; prescribed fire and man- aged wildfire where approved. Ponderosa pine – Douglas-fir forests Opportunities for implementation Work with collaborators on private and state land to include the wildland urban interface; work with other organizations to get funding and do work on private lands. Work with collaborators on private and state land to include the wildland urban interface; work with other orga- nizations to get funding and do work on private lands. Forest Inventory and Analysis; restoration and resiliency report; forest regeneration reports; adapting Common Stand Exam protocols. Cost Varies by treatment Varies by treatment Inexpensive Barriers to imple- mentation Some: cost, litigation None

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
246 USDA Forest Service RMRS-GTR-374. 2018 Table 6C.5—Adaptation options that address climate change effects on forest vegetation in the Central Rockies subregion. Sensitivity to climatic variability and change: Changing moisture regimes with changing climate. Adaptation strategy/approach: Replace plant association group-habitat typing with an index based on biophysical variables. Strategy objective: Increase knowledge; plant associations are not expected to remain the same under climate change. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Identify a set of biophysical predictors related to habitat types, site productivity, vegetation composition, and structure. Possible predictors include landform, soil depth, texture, type (specifically ash cap soil), actual evapotranspiration, potential evapotranspiration and water balance deficit. Predict site productivity based on biophysical predictors; make concept operationally implementable so it can be used to aid in planting decisions, and aid understanding of long-term effects of management and long-term goals for a site. Project into the future based on climate change models. Tactic effectiveness (risks) Unknown Unknown Unknown Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) Opportunities for implementation Cost Barriers to implementation

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 247 Table 6C.6—Adaptation options that address climate change effects on forest vegetation in the Central Rockies subregion. Sensitivity to climatic variability and change: Subalpine forest shifts as a result of climate change. Adaptation strategy/approach: Monitor and detect change through measurement of seedling survival, species composition and mortality of mature trees. Strategy objective: Increase knowledge on climate-induced subalpine forest shifts. Specific tactic – A Specific tactic – B Tactic Install and analyze additional plots where trend information is needed over time; more intensified grid plots could also be installed. Initiate the use of Forest Inventory and Analysis plot information. Tactic effectiveness (risks) High Moderate to low, depending on how fast changes are occurring Implementation urgency High—need to know now Already part of regional strategy Where can tactics be applied? (geographic) Target areas of risk where we expect to see changes, focusing on disturbance areas; in especially sensitive forests such as whitebark pine Large enough geographic area that information can be statistically meaningful Opportunities for implementation Very few because of lack of funding, but protocols and analysis tools already established Already paid for, and existing expertise and knowledge are available Cost High based on information needs; many plots needed Minimal Barriers to implementation Need training and oversight of data collection; need to have consistent, replicable protocol in order to be able to detect change; lack of immediate and long term funding Difficult to get data updates in a timely manner; getting non-Forest Service data is difficult

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
248 USDA Forest Service RMRS-GTR-374. 2018 Table 6C.6 (cont.)—Adaptation options that address climate change effects on forest vegetation in the Central Rockies subregion. Sensitivity to climatic variability and change: Subalpine forest shifts as a result of climate change. Adaptation Strategy / Approach: Monitor and detect change through measurement of seedling survival, species composition and mortality of mature trees. Strategy Objective: Increase knowledge on climate-induced subalpine forest shifts. Specific Tactic – C Specific Tactic – D Tactic Expand reforestation monitoring to include additional monitoring and different electronic formats. Implement pre- and post-treatment monitoring over time to be able to determine if treatments are meeting objectives. Tactic effectiveness (risks) High High Implementation urgency High Moderate Where can tactics be applied? (geographic) Everywhere we are planting sensitive vegetation types Treated areas Opportunities for implementation Often doing it anyway, and methodology is already in place; need to make sure we are collecting right data in the right electronic format Existing systems Cost Low unless data collection becomes arduous Moderate to high; depends on number of plots, length of time to monitor, what data is being collected; less expensive than intensifying grid across landscape. Barriers to implementation Need to establish protocols, conduct training, identify a location for data storage and determine who would do the analysis; lack of immediate and long-term funding Lack of immediate and long-term funding; lack of training and oversight; lack of treatments to monitor

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 249 Table 6C.7—Adaptation options that address climate change effects on forest vegetation in the Central Rockies subregion. Sensitivity to climatic variability and change: Subalpine forest shifts as a result of climate change. Adaptation strategy/approach: Promote resilience of subalpine forests to climate-induced shifts. Strategy objective: Create conditions that will be resilient to perturbations. Specific tactic – A Specific tactic – B Tactic Identify areas appropriate for managed wildfire; increase the flexibility of how we manage fire and de-emphasize suppression. Artificially regenerate seedlings with higher levels of rust resistance than the natural population. Tactic effectiveness (risks) Other unintended consequences could lower it from high to moderate High at site scale; low across large landscapes Implementation urgency High, near term High, near term Where can tactics be applied? (geographic) Highly dependent on other resource concerns and political and social issues; problematic in areas with mixed ownership Have process established to develop rust-resistant seedlings; coordinate with tree improvement and nursery to continue to improve rust-resistant sources Opportunities for implementation All lands: Federal, State, communities, universities All lands: Federal, State, communities, universities Cost Inexpensive Moderately expensive; cost of seedlings high Barriers to implementation Integration between forest and fire team; sociopolitical environment and backlash; lack of public support; decline in air quality Access; cost; unable to plant in wilderness or research natural areas

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
250 USDA Forest Service RMRS-GTR-374. 2018 Table 6C.7 (cont.)—Adaptation options that address climate change effects on forest vegetation in the Central subregion. Sensitivity to climatic variability and change: Subalpine forest shifts as a result of climate change. Adaptation Strategy / Approach: Promote resilience of subalpine forests to climate-induced shifts. Strategy Objective: Create conditions that will be resilient to perturbations. Specific Tactic – C Specific Tactic – D Specific Tactic – E Tactic Proactively treat with prescribed burn or mechanical thinning to reduce the risk of fire and insect mortality; increase individual tree vigor to establish the desired species composition and establish appropriate patch sizes. Implement a broad review of most current literature, develop a regional library, and implement a climate change information system. Educate the public on the need to increase resilience and develop a cohesive broader message. Tactic effectiveness (risks) Highly variable depending on scale, district expertise, and landscape position High if used Low Implementation urgency Moderate-mid term High, near term Low, long term Where can tactics be applied? (geographic) All National Opportunities for implementation All lands: Federal, State, communities, universities National Cost Low to high depending on the combination of treatment, objectives, and local conditions Barriers to implementation This type is not far from historic conditions, so there is not as much reason to restore; more complex and difficult to access; window for treatment is narrow

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 251 Table 6C.8—Adaptation options that address climate change effects on forest vegetation in the Central Rockies subregion. Sensitivity to climatic variability and change: Homogenization of the larch forest type across the landscape, resulting in increased density and associated increase risk of severe stand-replacing fires, increased risk of mortality from drought, loss of western larch on stressful sites, loss of large larch, large larch snag recruitment across the landscape, and reduced water yield. Adaptation strategy/approach: Decrease density within stands, and increase structural diversity across the landscape. Strategy objective: Develop resilience to fire and moisture stress. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Reduce density with thinning, prescribed fire, and wildland fire use. Promote age class and structural diversity across the landscape, through regeneration harvest, thinning, prescribed fire and managed wildfire. Monitor establishment and survival of western larch by age class across different aspects/heat load/soil moisture. Use Forest Inventory and Analysis data to capture regeneration success by topographical position. Tactic effectiveness (risks) Thinning = high; prescribed fire = moderate; wildland fire use = low when first implemented, moderate over time High where implemented High Implementation urgency Where can tactics be applied? (geographic) Opportunities for implementation Cost Barriers to implementation

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
252 USDA Forest Service RMRS-GTR-374. 2018 Table 6C.8 (cont.)—Adaptation options that address climate change effects on forest vegetation in the Central subregion. Sensitivity to climatic variability and change: Homogenization of the larch forest type across the landscape resulting in increased density and associated increase risk of severe stand-replacing fires, increased risk of mortality from drought, loss of western larch on stressful sites, loss of large larch, large larch snag recruitment across the landscape, and reduced water yield. Adaptation Strategy / Approach: Decrease density within stands, and increase structural diversity across the landscape. Strategy Objective: Develop resilience to fire and moisture stress. Specific Tactic – D Specific Tactic – E Tactic Prioritize management for larch on landscape facets where monitoring indicates it is going to persist (e.g., on north aspects, but not southern aspects, or by habitat types). Maintain and promote large diameter western larch across the landscape, so that large diameter snags, larch seed sources, and wildlife habitats are also maintained. Tactic effectiveness (risks) High High if A and B are implemented Implementation urgency Where can tactics be applied? (geographic) Opportunities for implementation Cost Barriers to implementation

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 253 Table 6C.9—Adaptation options that address climate change effects on forest vegetation in the Central Rockies subregion. Sensitivity to climatic variability and change: High density of mixed-mesic white pine, cedar, hemlock, grand fir forests stands, leading to lower carbon sequestration because of lower density of some species (western larch, ponderosa pine and western white pine) and increased shade-tolerant species. High densities increase susceptibility to wildfire. Heart rot and root rot in cedar and hemlock decreases carbon sequestration and timber values. Adaptation strategy/approach: Promote diversity in species composition and structure at multiple spatial scales (within stands and across the landscape). Strategy objective: Promote resilience and increase carbon sequestration. Specific tactic – A Specific tactic – B Specific tactic – C Specific tactic – D Specific tactic – E Tactic Conduct regeneration harvest and planting to promote shade-intolerant tree species (western larch, ponderosa pine, white pine, birch) and rust-resistant white pine. Promote western white pine. Conduct density management thinning to retain shade-intolerant trees and develop large trees across the landscape; prune younger western white pine to promote resistance to blister rust. Increase knowledge on how the different tree densities and species compositions within this group function as habitats and how the mosaic of stands influences connectivity for wildlife. Develop a site- related prioritization approach for implementing management tactics. Tactic effectiveness (risks) High High High Unknown High Implementation urgency Mid-term Where can tactics be applied? (geographic) Within this vegetation type Opportunities for implementation Cost Barriers to implementation

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
254 USDA Forest Service RMRS-GTR-374. 2018 Table 6C.10—Adaptation options that address climate change effects on forest vegetation in the Central Rockies subregion. Sensitivity to climatic variability and change: Whitebark pine mortality from increased mountain pine beetle outbreaks, fire, and blister rust and shifts/loss of site conditions that support whitebark pine. Adaptation strategy/approach: Restore whitebark pine. Strategy objective: Increase rust-resistant regeneration and cone-bearing trees. Specific Tactic – A Specific Tactic – B Tactic Assess condition; save seed sources; grow rust-resistant seedlings; collect seed; plant seedlings; monitor activities; prioritize treatment; and conduct research (mirror Keane range- wide restoration strategy). Identify sites that are likely to not be as heavily affected (refugia), and focus on those sites for restoration. Tactic effectiveness (risks) Implementation urgency Where can tactics be applied? (geographic) Opportunities for implementation Cost Cost of planting is high Barriers to implementation The majority of whitebark pine is in wilderness or other protected areas, or in roadless areas with limited access. Thus, the ability to treat directly is limited. Need comprehensive long-term planning and commitment at multiple levels.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 255 Table 6C.11—Adaptation options that address climate change effects on forest vegetation in the Eastern Rockies subregion. Sensitivity to climatic variability and change: Increased frequency of disturbance, drought, browsing, and livestock trampling may reduce vigor and extent of aspen, even given the upward trend of aspen in pine forests that have extensive beetle-caused mortality. Adaptation strategy/approach: Maintain and restore/promote the health and vigor of clones (specific key stressors include repeat disturbance, conifer com- petition, browse/trampling). Strategy objective: Maintain the current population trend, promote resilience, reduce stressors/threats, and increase knowledge. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Actively manage ungulates during regeneration phase through slash barriers, increase in hunting pres- sure, grazing management, and salt block placement. Implement conifer removal on mul- tiple scales and through hand and commercial treatments. Monitor extent and condition of aspen clones to determine the effect of disturbance frequency on aspen survival, effects of sudden aspen decline, and incidence of new clones; potentially imple- ment strategic protection measures for specific clones. Tactic effectiveness (risks) High Highest Moderate to high Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) Wherever aspen regeneration pre- scriptions are applied Wherever aspen occurs outside of protected areas Wherever aspen occurs Opportunities for imple- mentation Rocky Mountain Elk Foundation, permittees Rocky Mountain Elk Foundation Rocky Mountain Elk Foundation Cost Varies by tool Expensive – fencing Inexpensive – grazing management Inexpensive Moderate Barriers to implementation Some – litigation, scale and timing to be effective (staffing capacity), priority, permittees Some – litigation, scale and timing to be effective (staffing capacity), priority None

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
256 USDA Forest Service RMRS-GTR-374. 2018 Table 6C.12—Adaptation options that address climate change effects on forest vegetation in the Eastern Rockies subregion. Sensitivity to climatic variability and change: Ability of Douglas-fir to develop stands with large, old-growth structure in face of fire, drought, beetles, spruce budworm and limited cone production. Adaptation strategy/approach: Establish age-class and structural diversity to promote landscape heterogeneity, which could provide appropriate amounts and distribution of large tree structure. Strategy objective: Promote resilience, and reduce stressors and threats. Specific tactic – A Specific tactic – B Specific tactic – C Specific tactic – D Tactic Manage stand-scale disturbance through thinning, prescribed fire, and managed wildfire to accelerate the development of large tree structure. Manage landscape disturbance to achieve heterogeneity in structural diversity. Identify critical stands with high value and large diameter for direct protection from fire and insects; protect using pesticides, stand manipulation, fire protection, and windthrow monitoring. Improve cone production in key seed collection areas through fertilizer, pesticides and stand manipulation. Tactic effectiveness (risks) High – thinning Moderate – fire Moderate–high High Moderate Implementation urgency Near–mid term Near–mid term Near term Near term Where can tactics be applied? (geographic) Throughout species range Throughout species range Throughout species range Throughout species range Opportunities for implementation Forest plan; restoration committees Forest plan; restoration committees Coordinate with wildlife priorities Inland Empire Cooperatives Cost Inexpensive Inexpensive Inexpensive Inexpensive–moderate Barriers to implementation Some – litigation, scale and timing to be effective (staffing capacity), priority Some – litigation, scale and timing to be effective (staffing capacity), priority None None

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 257 Table 6C.13—Adaptation options that address climate change effects on forest vegetation in the Eastern Rockies subregion. Sensitivity to climatic variability and change: Limited ability of limber pine to persist and regenerate in the face of frequent fires, blister rust, and mountain pine beetle; challenges include uncertainties in genetic variation and geographically disjunct populations. Adaptation strategy/approach: Maintain viable populations of limber pine in suitable environments. Strategy objective: Promote resilience, reduce impacts of stressors/threat, increase knowledge, engage coordination. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Address information gaps on current location, potential habitat and stand condition through coordination with other groups. Address genetic data gaps by establishing a breeding program that includes rust- resistance screening, seed zones and drought tolerance through coordination with other groups. Conduct stand treatments to promote resilience over a wide geographic area; protect remaining trees with pesticides and stand thinning, and establish a planting program to achieve scattered, mature individuals. Tactic effectiveness (risks) High High High at local stand scale Moderate at population level Implementation urgency Near term Near term Near term: improve resilience of existing stands Mid term: planting (answer genetic questions first) Where can tactics be applied? (geographic) Forest plans, Region 1 broad-scale monitoring strategy Inland Empire Cooperatives Forest plans, restoration committees Opportunities for implementation All lands: Federal, State, communities, universities All lands: Federal, State, communities, universities All lands: Federal, State, communities, universities Cost Moderate Moderate Inexpensive Barriers to implementation None None Some – litigation, scale and timing to be effective (staffing capacity), priority

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
258 USDA Forest Service RMRS-GTR-374. 2018 Table 6C.14—Adaptation options that address climate change effects on forest vegetation in the Eastern Rockies subregion. Sensitivity to climatic variability and change: Small, fragmented populations of eastside ponderosa pine are vulnerable to loss of regeneration capability following repeated disturbance, especially in ecotone sites. Adaptation strategy/approach: Maintain genetic diversity, population viability, increase resilience, and promote big-tree structure. Strategy objective: Promote resilience, reduce stressors/threats, and facilitate transition. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Manage stand-scale disturbance through thinning, prescribed fire, and managed wildfire to accelerate the development of large tree structure and facilitate the transition to a savanna ecotone. Develop seed collection and reforestation strategies to address potential loss of genetic variability due to disjunct populations and shortened mean return interval of severe disturbances. Identify critical stands with high value and large diameter for direct protection from fire and insects; protect with pesticides, stand manipulation and fire protection. Tactic effectiveness (risks) High High High Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) Low-elevation ecotones; suitable ponderosa pine sites Low-elevation ecotones; suitable ponderosa pine sites Low-elevation ecotones; suitable ponderosa pine sites Opportunities for implementation Forest management; coordination with fire management Forest management; Inland Empire Cooperatives Forest management; wildlife habitat priorities Cost Inexpensive Inexpensive-moderate Inexpensive Barriers to implementation Some – litigation, scale and timing to be effective (staffing capacity), priority None Some – litigation, scale and timing to be effective (staffing capacity), priority

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 259 Table 6C.15—Adaptation options that address climate change effects on forest vegetation in the Greater Yellowstone Area subregion. Sensitivity to climatic variability and change: Climate change forces us to work across boundaries. Stressors cross boundaries. The public expects coordination. Adaptation strategy/approach: Work across jurisdictions at larger scales. Strategy objective: Encourage coordination. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Align budgets/priorities for program of work for neighboring lands (e.g., constrained budget forces cooperation for invasive species strategies). Communicate about adjacent projects and coordinate on the ground; develop memorandum of understanding for adjacent projects. Preserve roads, trails, and access despite increased fire and flood events. Tactic effectiveness (risks) High (if we succeed) High High Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) Greater Yellowstone Area Greater Yellowstone Area Greater Yellowstone Area Opportunities for implementation All lands: Federal, State, communities, universities All lands: Federal, State, communities, universities All lands: Federal, State, communities, universities Cost Inexpensive Inexpensive Moderately expensive Barriers to implementation Major barriers: politics Some barriers: politics, time, lack of priority, distance, travel budget Major barriers: shrinking budget, staffing

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
260 USDA Forest Service RMRS-GTR-374. 2018 Table 6C.16—Adaptation options that address climate change effects on forest vegetation in the Greater Yellowstone Area subregion. Sensitivity to climatic variability and change: Increased fire and disease, and interactions with the wildland-urban interface. Adaptation strategy/approach: Increase the resilience of forest stands to disturbance, and protect people from potential risks of increased fire. Strategy objective: Manage fires in a way to protect the wildland-urban interface. Specific tactic – A Specific tactic – B Specific tactic – C Specific tactic – D Tactic Create buffer zones between fire and residential development, and implement thinning. Influence development zoning in high risk areas with local government and insurance companies. Increase forest diversity through heterogeneity of species composition, age class and structure. Promote education and communication about responsible land owner tactics. Tactic effectiveness (risks) Moderate – intense fires cross boundaries, having unintended impacts on resources and cultural landscapes High (if we can do it) Moderate – large fires, climate change Moderate Implementation urgency Where can tactics be applied? (geographic) Opportunities for implementation Cost Barriers to implementation Land designation 

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 261 Table 6C.17—Adaptation options that address climate change effects on forest vegetation in the Greater Yellowstone Area subregion. Sensitivity to climatic variability and change: Increased impacts from fire, insects, disease, climate, and increased competition. Adaptation strategy/approach: Promote resilient whitebark pine communities. Strategy objective: Maintain whitebark pine on the landscape. Specific tactic – A Specific tactic – B Specific tactic – C Specific tactic – D Tactic Actively remove other dominant tree species, such as lodgepole pine, spruce, and fir. Prioritize management for populations with high survival potential. Implement a variety of management strategies/options, such as control sites, fire management, and possibly planting at lower elevations. Replant screened, grafted, genetically-selected seedlings to promote blister rust resistance. Tactic effectiveness (risks) Unknown – Not sure if it will work. See barriers. Moderate – uncertainty, models not considering all factors Moderate – see barriers Moderate – see barriers Implementation urgency Near term Near term to long term – more information needed Near term Near term Where can tactics be applied? (geographic) Where we have access; road, management designation Greater Yellowstone Area Greater Yellowstone Area Where we have access and permission Opportunities for implementation Overall whitebark pine strategies, investment strategy niches, Greater Yellowstone Coordinating Committee (GYCC) Overall whitebark pine strategies, investment strategy niches, GYCC Overall whitebark pine strategies, investment strategy niches, GYCC We already have the trees and selected planting locations Cost Moderately expensive Inexpensive Expensive Moderately expensive Barriers to implementation Major barriers: limited by wilderness designations, road access, litigation, compliance Major barriers: limited by wilderness designations, road access, litigation, cost Major barriers: limited by wilderness designations, road access, litigation, cost Some barriers: ideal places, access, cost

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
262 USDA Forest Service RMRS-GTR-374. 2018 Table 6C.18—Adaptation options that address climate change effects on forest vegetation in the Western Rockies subregion. Sensitivity to climatic variability and change: Increased impacts from moisture stress and fire. Adaptation strategy/approach: Actively reduce density and maintain low densities. Strategy objective: Promote forest resilience through density management. Specific tactic – A Specific tactic – B Specific Tactic – C Tactic Implement pre-commercial and commercial thinning. Conduct prescribed fires. Influence stand density with planting. Tactic effectiveness (risks) High Moderate – depends on stand conditions High Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) Be cautious with root disease-sensitive species and sites Applied to maintain fire-tolerant conifer species and maintaining structure Apply where opportunities for thinning are negligible due to species or stand condition Opportunities for implementation Cost Inexpensive Inexpensive Inexpensive Barriers to implementation Some, barriers greater for Federal lands. There are thinning restrictions due to lynx. Some, barriers greater for Federal lands Some, barriers greater for Federal lands

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 263 Table 6C.19—Adaptation options that address climate change effects on forest vegetation in the Western Rockies subregion. Sensitivity to climatic variability and change: Increased frequency and scale of disturbances such as fire and drought. Adaptation strategy/approach: Promote disturbance-resilient species, such as ponderosa pine, western larch, western white pine, Douglas-fir, and lodgepole pine. Strategy objective: Promote forest vegetation resilience to disturbance. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Promote thinning to favor disturbance-resilient species. Promote planting of disturbance-resilient species. Promote resilient species with prescribed fire and/or natural fire use. Tactic effectiveness (risks) High High Moderate Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) Western larch and western white pine on moist sites, ponderosa pine on dry sites, Douglas-fir on extremely dry sites, and lodgepole pine on harsh, difficult-to-regenerate sites Western larch and western white pine on moist sites, ponderosa pine on dry sites, Douglas-fir on extremely dry sites, and lodgepole pine on harsh, difficult- to-regenerate sites Western larch and western white pine on moist sites, ponderosa pine on dry sites, Douglas-fir on extremely dry sites, and lodgepole pine on harsh, difficult-to- regenerate sites Opportunities for implementation Any place management is feasible and allowed Any place management is feasible and allowed Any place management is feasible and allowed Cost Inexpensive Inexpensive Inexpensive Barriers to implementation Scale will vary because of budgetary limitations Scale will vary because of budgetary limitations Scale will vary because of budgetary limitations. Natural fire may not occur where or when manageable.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
264 USDA Forest Service RMRS-GTR-374. 2018 Table 6C.20—Adaptation options that address climate change effects on forest vegetation in the Western Rockies subregion. Sensitivity to climatic variability and change: Increasing disturbance, moisture deficits, stress due to densities, and longer growing seasons. Adaptation strategy/approach: Increase knowledge on current issues, strategies, and future goals. Strategy objective: Increase knowledge for agency land managers and stakeholders. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Address definition of connectivity, including species guilds and scale, and identify existing and historical conditions in order to develop desired conditions. Share knowledge on tree species migration at fine and broad scales, and track regeneration success, species distribution at the fine scale, species transfer zones, habitat type, and soil type. Share knowledge on fire regimes in spruce-fir forests and increase collaboration with the Rocky Mountain Research Station. Tactic effectiveness (risks) High High High Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) Landscape Landscape Landscape Opportunities for implementation All lands: Federal, State, communities, and universities All lands: Federal, State, communities, and universities All lands: Federal, State, communities, and universities Cost Inexpensive Inexpensive Moderately expensive Barriers to implementation Funding, lack of understanding Funding, lack of understanding Funding, lack of understanding

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 265 Table 6C.21—Adaptation options that address climate change effects on forest vegetation in the Western Rockies subregion. Sensitivity to climatic variability and change: Increasing disturbance, moisture deficits, stress due to densities, and longer growing seasons. Adaptation strategy/approach: Increase knowledge on current issues, strategies, and future goals. Strategy objective: Increase knowledge for agency land managers and stakeholders. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Address how to manage conservation areas, such as research natural areas and roadless wilderness. Promote the important components within these areas and desired conditions. Communicate the accurate mapping of important species such as whitebark pine. Address the desired conditions at the landscape level and also for important wildlife habitat by tackling the “how much is enough?” question. Tactic effectiveness (risks) Moderate High High Implementation urgency Mid term Near term Near term Where can tactics be applied? (geographic) Program level Program and national forest level Program and national forest level Opportunities for implementation Rocky Mountain Research Station, The Nature Conservancy, Wilderness Society, universities, tribes, conservation partners Universities, conservation partners, state heritage programs Rocky Mountain Research Station, universities, tribes, conservation partners Cost Moderate Moderate Moderate Barriers to implementation Time Time Time

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
266 USDA Forest Service RMRS-GTR-374. 2018 Table 6C.22—Adaptation options that address climate change effects on forest vegetation in the Western Rockies subregion. Sensitivity to climatic variability and change: Increasing disturbance, moisture deficits, stress due to densities, and longer growing seasons. Adaptation strategy/approach: Increase knowledge on current issues, strategies, and future goals. Strategy objective: Increase knowledge for agency land managers and stakeholders. Specific tactic – A Specific tactic – B Tactic Increase awareness on the role of root disease in carbon sequestration by publishing root disease data. Communicate the need for improved integration between wildlife managers and forest ecologists, and between research and management. Conduct an annual meeting with Rocky Mountain Research Station on management needs for research. Tactic effectiveness (risks) High Implementation urgency Near term Where can tactics be applied? (geographic) Program/Region 1 and Rocky Mountain Research Station Opportunities for implementation Program/Region 1 and Rocky Mountain Research Station Cost Inexpensive Barriers to implementation Lack of time and impetus to do it

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 267 Table 6C.23—Adaptation options that address climate change effects on forest vegetation in the Western Rockies subregion. Sensitivity to climatic variability and change: Increasing disturbance, moisture deficits, stress due to densities, and longer growing seasons. Adaptation strategy/spproach: Promote resilience in forest vegetation. Strategy objective: Promote resilience by reducing stressors and facilitating transitions. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Reduce forest densities to increase fire resilience in lodgepole pine and whitebark pine sites with pre- commercial thinning. Reduce forest densities to increase fire resilience in lodgepole pine and whitebark pine sites with commercial thinning. Promote appropriate density conditions and landscape heterogeneity within mapped lynx habitat in spruce-fir forests. Tactic effectiveness (risks) High High Moderate Implementation urgency Near term Near term Mid term Where can tactics be applied? (geographic) Higher elevations Higher elevations Higher elevations Opportunities for implementation Whitebark Pine Ecosystem Foundation, Forest Health Protection, programmatic National Environmental Policy Act work, stewardship contracting Whitebark Pine Ecosystem Foundation, Forest Health Protection, programmatic National Environmental Policy Act work Rocky Mountain Research Station, State fish and game, U.S. Fish and Wildlife Service, fire management Cost Moderate Moderate Moderate Barriers to implementation Endangered species (lynx), lack of available funding, access and short operating season, management limitations within roadless wilderness, and potential litigation Endangered species (lynx), lack of available funding, access and short operating season, management limitations within roadless wilderness, and potential litigation Knowledge gaps in desired conditions

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
268 USDA Forest Service RMRS-GTR-374. 2018 Table 6C.24—Adaptation options that address climate change effects on forest vegetation in the Western Rockies subregion. Sensitivity to climatic variability and change: Increasing disturbance, moisture deficits, stress due to densities, and longer growing seasons. Adaptation strategy/approach: Promote resilience in forest vegetation. Strategy objective: Promote resilience by reducing stressors and facilitating transitions. Specific tactic – D Specific tactic – E Specific tactic – F Tactic Promote legacy trees of western larch, Douglas-fir, western white pine, Engelmann spruce, whitebark pine, and alpine larch. Establish seed collection and seed bank needs for alpine larch, whitebark pine, and high-elevation western larch. Coordinate with other land managers/owners on post-wildfire reforestation and planting of whitebark pine. Promote landscape heterogeneity and create connectivity at multiple scales through strategic placement of treatment units. Increase patch size/treatments and cross-ownership boundary coordination. Tactic effectiveness (risks) High High Moderate Implementation urgency Near term Near term Mid term Where can tactics be applied? (geographic) Within dense spruce-fir-lodgepole pine sites Where these species occur Landscape Opportunities for implementation National forest plan desired conditions and project Whitebark Pine Ecosystem Foundation, volunteers (e.g., backcountry horseman and stakeholders), Forest Health Protection National forest plan desired conditions and project Cost Inexpensive, can be done in conjunction with project Expensive because of remote location/poor access, but volunteers can help reduce costs Moderately expensive Barriers to implementation None other than lack of these trees in some areas and windthrow risk Budget (to reduce this barrier, solicit partners); wilderness/roadless policy limitations Some barriers, knowledge gaps in desired conditions.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 269 Table 6C.25—Adaptation options that address climate change effects on forest vegetation in the Western Rockies subregion. Sensitivity to climatic variability and change: Increasing disturbance, moisture deficits, stress due to densities, and longer growing seasons. Adaptation strategy/approach: Promote resilience in forest vegetation. Strategy objective: Promote resilience by reducing stressors and facilitating transitions. Specific tactic – G Specific tactic – H Specific tactic – I Tactic Promote rapid response and assessment for postfire reforestation. Implement a triage approach to soil moisture conditions (e.g., loess soil mapping) for prioritizing areas for western white pine and whitebark pine. Protect high value trees (plus other trees, cone producers, and rare species) via management actions, including pheromones and seed orchards. Tactic effectiveness (risks) High High High Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) Throughout zone Throughout zone Throughout zone Opportunities for implementation Burned area emergency response Intermountain Forest Tree Nutrition Cooperative, Natural Resources Conservation Service, Rocky Mountain Research Station Whitebark Pine Ecosystem Foundation, volunteers, Forest Health Protection Cost Moderate Moderate Moderate Barriers to implementation Burned Area Emergency Response does not fund planting; commitment from forests; lack of strategy Funding; lack of understanding of utility by forests Funding

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
270 USDA Forest Service RMRS-GTR-374. 2018 Table 6C.26—Adaptation options that address climate change effects on forest vegetation in the Western Rockies subregion. Sensitivity to climatic variability and change: Accelerated root disease mortality due to climate stressors. Adaptation strategy/approach: Reduce dominance of root disease sensitive species (e.g., Douglas-fir and grand fir) on root disease-prone sites. Strategy Objective: Facilitate transition. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Regenerate and plant with species less susceptible to root disease. Thin out root disease-susceptible species where less root disease-susceptible species are abundant. Conduct a hot prescribed burn, followed by a re-burn. Tactic effectiveness (risks) High Moderate Unknown Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) Root disease-prone sites with current root disease losses and where management is allowed Root disease-prone sites; in areas where management is allowed; where adequate, less susceptible species are present and current losses are low Root disease prone sites and in areas where management is allowed Opportunities for implementation Cost Inexpensive Inexpensive Inexpensive Barriers to implementation Where losses are severe and timber value may not cover cost of site preparation May not be highest priority 5-year regeneration requirement

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 271 Table 6C.27—Adaptation options that address climate change effects on forest vegetation in the Western Rockies subregion. Sensitivity to climatic variability and change: Sites with limited species and genetic diversity are more likely to be impacted by climate change and climate- related stressors. Adaptation strategy/approach: Work across jurisdictions at larger spatial scales. Strategy objective: Promote resilience. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Plant potential microsites with a mix of species to push the envelope and hedge bets. Maintain species diversity during thinning. Interplant to supplement natural regeneration and genetic diversity. Tactic effectiveness (risks) Moderate High Moderate Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) In sufficiently large openings (from harvest, fire, or in understocked stands) on sites most at risk for drought stress Dense or overstocked stands on sites more at risk for drought stress and where sufficient diversity exists for thinning. In sufficiently large openings (from harvest, fire, or in understocked stands) on sites most at risk for drought stress. Opportunities for implementation Cost Inexpensive Inexpensive Inexpensive Barriers to implementation Openings are lacking because of limited timber harvest and fire suppression. Insufficient funding. Thinning restrictions due to lynx. Openings are lacking because of limited timber harvest and fire suppression.

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
272 USDA Forest Service RMRS-GTR-374. 2018 Table 6C.28—Adaptation options that address climate change effects on forest vegetation in the Western Rockies subregion. Sensitivity to climatic variability and change: Increasing moisture demands and drought stress in moisture-demanding species (western hemlock and western redcedar) on upland sites. Adaptation strategy/approach: Minimize the effects to the stand from the affected species (western hemlock and western redcedar). Strategy objective: Promote resilience and facilitate transition. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Implement pre-commercial thinning to limit dominance of these species on drought-prone sites. Encourage regeneration harvest and planting with a more diverse species mix. Preserve road and trail access despite increased fire and flood events. Tactic effectiveness (risks) Moderate High Moderate Implementation urgency Near term Near term Mid term Where can tactics be applied? (geographic) Opportunities for implementation Cost Barriers to implementation

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region
USDA Forest Service RMRS-GTR-374. 2018 273 Table 6C.29—Adaptation options that address climate change effects on forest vegetation in the Western Rockies subregion. Sensitivity to climatic variability and change: Western white pine is resilient but underrepresented. Adaptation strategy/approach: Increase presence of western white pine. Strategy objective: Promote resilience and facilitate transition. Specific tactic – A Specific tactic – B Specific tactic – C Tactic Implement planting of blister rust- resistant western white pine. Implement blister rust pruning. Retain existing natural white pine when thinning, harvesting, and burning. Tactic effectiveness (risks) High High Thinning/harvest – high Burning – moderate Implementation urgency Near term Near term Near term Where can tactics be applied? (geographic) Western redcedar, western hemlock and moist grand fir habitat types (and on moister microsites of drier habitat types) Stands with moderate infection, but low infection above pruning height; may be critical if thinning Where western white pine is present Opportunities for implementation Cost Inexpensive Inexpensive Inexpensive Barriers to implementation Openings are lacking because of limited timber harvest and fire suppression. Insufficient funds and access More difficult on steep slopes, where fire is needed for site preparation

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region

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