United States Department of Agriculture / Forest Service

Rocky Mountain Research Station

General Technical Report RMRS-GTR-265

November 2011

Rocky Mountain Research Station 

Invasive Species Visionary White Paper
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Pearson, D. E.; Kim, M.; Butler, J., eds. 2011. Rocky Mountain Research Station 

invasive species visionary white paper. Gen. Tech. Rep. RMRS-GTR-265. Fort 

Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain 

Research Station. 37 p.

Abstract

Invasive species represent one of the single greatest threats to natural ecosystems and 

the services they provide. Effectively addressing the invasive species problem requires 

management that is based on sound research. We provide an overview of recent and 

ongoing invasive species research conducted by Rocky Mountain Research Station 

scientists in the Intermountain West in order to familiarize managers with the Station 

and its products. We also provide several links to continuously updated web sites 

and a periodic newsletter that covers Rocky Mountain Research Station’s invasives 

species research.

Keywords: invasive species, exotic, noxious, nonnative, pathogen, rehabilitation, 

restoration 
Executive Summary

This document contains an overview of invasive species research efforts by the Rocky 

Mountain Research Station (RMRS) to familiarize managers with the Station and its 

products.

Invasive plant, pathogen, invertebrate, and vertebrate species are among the greatest 

threats to forest, range, aquatic, and urban forest ecosystem health. Exotic species 

invasions in the United States cost an estimated $120 billion annually in lost revenues 

and mitigation. Expanding global trade increases both the introductions of invasive 

species and the costs associated with preventing introductions and managing new 

infestations. To address these threats, a comprehensive strategy is needed with a 

strong research component at its core.

Damaging impacts of exotic infestations include diminished productivity, decreased 

carrying capacity for livestock and wildlife, lowered recreational value, increased 

soil erosion, decreased water quality, and loss of native species. As native vegetation 

becomes displaced, further alterations in natural ecosystem processes occur, 

including changes in fire frequency and nutrient cycling. The impacts of invasive 

species can be exacerbated by human activities such as disturbance, fertilization, 

increasing CO2, and climate change. Exotic weeds are greatly reducing diversity and 

productivity of forests and rangelands; insects and pathogens are killing trees that are 

essential for ecosystem functions; and aquatic algae, invertebrates, and fish invaders 

are disrupting native fisheries and aquatic ecosystems.

Addressing the invasive species threat requires robust scientific understandings 

that can be used to fuel progressive management in the four action areas of: 

(1) prediction and prevention; (2) early detection and rapid response; (3) control and 

management; and (4) restoration and rehabilitation. This document describes RMRS’s 

invasive species research and its published works.

RMRS has the broad scientific expertise to conduct multidisciplinary research on 

invasive species issues with special emphasis on terrestrial and aquatic habitats 

throughout the Intermountain West. RMRS scientists provide ecological and 

biological information to help managers detect and eradicate new invaders that 

are still confined to limited areas. (For example, DNA tools are being developed 

to identify and screen for potentially invasive pathogens.) For well-established, 

widespread invasive species, RMRS contributes to the development and testing of 

landscape-scale mitigation strategies to prevent further spread into new areas and 

to manage invasive species to ecologically and socially acceptable levels using 

environmentally compatible tools and integrated control programs. (For instance, 

RMRS scientists are refining herbicide applications to improve the efficacy of weed 

control.) Additionally, RMRS, in collaboration with Montana State University’s 

quarantine facilities and entomologists from other countries, has established a very 

active biological control program that includes locating, screening, and introducing 

biological control agents with an emphasis on agent efficacy and post-release studies. 

Integrated research at RMRS provides management tools to restore and rehabilitate 

landscapes that have been degraded by diverse invasive species. RMRS scientists are 

working with university collaborators to develop seed mixes of native species that 

are competitive with exotic weeds to improve restoration and reduce weed invasion 

following management activities and wildfire.

RMRS scientists are extremely active in addressing all aspects of invasive species 

management. However, RMRS does not have a program area assigned to invasives 

research, so research in this area has been an ad-hoc effort by independent scientists. 

This document represents the physical manifestation of RMRS scientists gathering 

to evaluate invasive species research needs, collate current research efforts, and 

develop a common vehicle for disseminating research products.

i
Contents

Executive Summary...................................................................................i

Introduction...............................................................................................1

RMRS Invasive Species Program Overview ............................................3

RMRS Invasive Species Program Taxonomic Group Focus Areas..........6

I. Plants ............................................................................................6

II. Pathogens ...................................................................................13

III. Insects .......................................................................................27

IV. Aquatics .....................................................................................30

V. Terrestrial vertebrates ..............................................................33

RMRS Invasive Species Research Priorities and Future Directions ......37

ii
USDA Forest Service RMRS-GTR-265. 2011. 1

Introduction

Exotic species invasions have tremendous economic and ecological impacts around the 

world. In the United States, invasive species cost an estimated $120 billion annually in lost 

revenue and mitigation expenses. As a result, former Forest Service Chief Dale Bosworth 

identified exotic invasive species as one of the four primary threats to the nation’s forest and 

rangeland ecosystems. Within the Rocky Mountain region, invasive species have had particularly profound impacts. Exotic weeds are reducing diversity and productivity of forests 

and rangelands; insects and pathogens are killing trees that are essential for ecosystem functions; and aquatic algae, invertebrates, and fish invaders are disrupting native fisheries and 

aquatic ecosystems. To address these threats, a comprehensive strategy is needed that includes 

a strong research component at its core. Research is particularly crucial for the effective management of invasive species because the underlying causes of invasion arise from biological 

processes that are currently poorly understood. As a leader in resource management that oversees the largest body of public lands in the United States, Forest Service involvement will be 

essential to the successful management of invasive species and Forest Service Research and 

Development will play a critical role. The current document is an attempt by independent 

invasive species researchers within the Rocky Mountain Research Station (RMRS) to jointly 

assess invasive species research needs, collate current efforts within the Station, and develop 

a working group to better disseminate invasive species research products to and solicit input 

from our customers.

The Forest Service developed the National Strategy and Implementation Plan for Invasive 

Species Management (hereafter, National Strategy) in 2004 to provide a comprehensive framework for invasive species management with a stated goal to, “Reduce, minimize, or eliminate 

the potential for introduction, establishment, spread, and impact of invasive species across all 

landscapes and ownerships.” To achieve these ends, the National Strategy identifies four key 

program elements: (1) Prevention, (2) Early Detection and Rapid Response, (3) Control and 

Management, and (4) Rehabilitation and Restoration. Thus, the National Strategy establishes 

the necessary criteria for executing invasive species management and evaluating its success 

within the Forest Service, emphasizing on-the-ground management and control of invasive 

species as indicated by the stated Success and Accountability Measures for each of the four 

program areas. These accountability measures describe success in terms of preventing new 

introductions, reducing the number of acres infested with targeted invasive species, reducing 

rate of spread, and increasing the number of acres restored or rehabilitated to desired conditions. However, because the National Strategy focuses on management activities, it is not 

clear how Forest Service Research and Development (R&D) plays into this process and how 

to evaluate success of R&D in the context of these management goals. Research is critical 

to the successful management of invasive species, but its relationship to management must 

be clearly defined to properly evaluate its role in the National Strategy and invasive species 

management.

Research contributes to invasive species management by generating new information and 

ideas needed to advance both our understanding of invasion ecology and implementation of 

sound management, and by effectively communicating this information to those directly managing the resources. Understanding the role of Forest Service R&D in invasives management 

and restoration of impacted ecosystems requires understanding how R&D fits into the overall 

Forest Service framework. The United States Forest Service is divided into three branches: 

R&D, National Forest System (NFS), and State and Private Forestry (SPF). Each branch is 

autonomous in terms of oversight and budget, and each branch has a unique role in the management of our natural resources. R&D develops new knowledge to improve the management 

of our natural resources through the application of science. NFS directly oversees and manages the National Forests and National Grasslands. SPF provides information and consultation 

to state and private land managers with direct oversight of state and private lands, thereby 

acting as a liaison of information for management of lands not directly overseen by the Forest 

Service. For Forest Service invasives research and management to be successful, R&D must 

develop the critical new information and transfer this information to managers, while NFS and 
2 USDA Forest Service RMRS-GTR-265. 2011.

SPF must implement management approaches based on these research products to improve 

invasive species control on the ground.

The National Strategy defines goals and objectives in terms of management outcomes 

that are generated by NFS and SPF. Therefore, the unique role that research plays in supporting the successful implementation of the National Strategy must be explicitly defined in 

order to clearly identify research products and illustrate how research products provide critical information to managers for effective implementation, i.e., establish the critical linkages 

among research products and the ability of NFS and SPF to successfully address the goals of 

the National Strategy. To achieve these ends, invasive species scientists within RMRS and 

representatives from the NFS and SPF convened in Albuquerque, NM, in April 2006 to accomplish four key objectives: (1) identify critical information gaps within each of the four 

program areas of the National Strategy that must be filled before our clients can effectively 

manage invasive species within this region, (2) describe the research needs to fill the identified 

knowledge gaps, (3) identify research products and tools that are derived from the research 

efforts and explain how their application by managers can improve invasive species management, and (4) describe current research within RMRS that is directed toward the recognized 

information gaps. This approach allowed us to identify the research needs in a management 

context independent of ongoing research. We then assigned current research efforts to the corresponding critical information gaps to identify the resulting research products and potential 

management applications of these products that would fulfill the National Strategy objectives. 

Through this process, we were able to distinguish between research products and management products in the context of the appropriate linkage between research and management, 

addressing the shortfall of the National Strategy. Input from all RMRS scientists interested in 

or currently conducting invasives research was incorporated through this process along with 

input from stakeholders.

This effort also resulted in the development of an RMRS Invasive Species Working Group 

(ISWG). The RMRS ISWG was developed because there is no program area in the Station 

specifically designed to address invasive species issues. Hence, the ISWG is a collection of 

scientists across all RMRS Program Areas gathered for the purpose of evaluating, consolidating, and disseminating invasive species research within the Station.
USDA Forest Service RMRS-GTR-265. 2011. 3

RMRS Invasive Species Program Overview

The RMRS has scientific expertise in widely ranging disciplines and conducts multidisciplinary research on priority invasive species issues with special emphasis in terrestrial and 

aquatic habitats of the Intermountain West (Figure 1).

RMRS invasives research covers a wide array of diverse ecological and environmental 

gradients from arid southwest desert to mesic northern Rockies ecosystems and from low 

elevations of the Great Basin and Great Plains to high-elevation Rockies ecosystems. RMRS 

provides the basic ecological and biological information for managers to implement eradication programs for new invaders while the invaders are still confined to limited areas. For 

well-established, widespread invasive species, RMRS contributes to the development and 

testing of large-scale mitigation strategies to prevent further spread of invasives into new areas 

and to suppress their populations below ecological and economic thresholds of impact using 

environmentally compatible tools and integrated controlled programs.

The Rocky Mountain region is host to a number of invasive species. Some invasive species 

of great concern in this region include cheatgrass, leafy spurge, tansy ragwort, spotted and diffuse knapweed, saltcedar, white pine blister rust, 1,000 canker disease, rainbow/brook/brown 

trout, golden algae, and banded elm bark beetle.

RMRS research has renowned, multidisciplinary programs on diverse aspects of invasive 

species that span several decades (begun up to 75 years ago) with accompanying expertise, records, specimen collections, and long-term research plots. The RMRS staff works closely with 

land managers and other partners from domestic to international agencies and universities to 

incorporate scientific findings into land management plans. Tools and applications derived 

from science-based RMRS research are used to manage and restore forests and rangelands 

degraded by invasive species. Resource managers readily use these tools and applications to 

reduce this threat for protecting our natural resources.

Station Headquarters

Station Territory

Lab Location

Flagstaff

Provo

Ogden

Logan

Reno

Albuquerque

Fort Collins

Rapid City

Bozeman

Moscow Missoula

Boise
4 USDA Forest Service RMRS-GTR-265. 2011.

A few themes of RMRS invasive species research include: (1) assessing impacts (biological, economic, and social) of invasive species in natural ecosystems; (2) developing biological 

control methods for invasive plants; (3) assessing the role of disturbances and forest management practices on establishment and spread of invasive species; (4) determining basic biology, 

ecology, and genetics of invasive species and other affected species to facilitate predictions of 

future impact, management, and restoration; (5) testing treatments and methods for restoring 

or rehabilitating invaded ecosystems and evaluating treatment consequences to native species 

and ecosystem processes; (6) developing technologies for molecular identification and risk 

assessment models for predicting and detecting current and potential invasive species; and 

(7) developing user-friendly technology transfer tools (e.g., web-based tools for fire effects 

on invasive species) that synthesize science-based information for managing invasive species.

The prior report by Butler and colleagues (http://www.fs.fed.us/rm/pubs_other/rmrs_2009_

butler_j001.pdf) provides a comprehensive list of scientists working on invasive species 

issues that is tabulated by RMRS Program Area and FS R&D Invasives Overarching Priority 

Area along with contact information for each scientist and information on his or her research 

focus areas. The summary therein shows there are 13.4 scientist years of effort directed toward 

invasives research across the Station. However, a more direct way of assessing the strengths 

and weaknesses of the current program is perhaps to break out RMRS publications, which 

are the ultimate measure of research products, by taxonomic group and National Strategy 

category. Table 1 presents results from a simple search of the FS Treesearch database (http://

www.treesearch.fs.fed.us/) for invasive species-related publications produced by RMRS using the terms exotic and/or invasive. This search is not intended to be comprehensive. It 

probably underestimates actual publications, as the search terms are fairly simple. In fact, 

pathogen studies were not well represented from this search despite an abundance of work in 

this area because these search terms are not commonly used to describe pathogens. For this 

reason, the table also includes RMRS publications cited in the pathogen section of this document. The process of assigning publications to the various categories is also rather subjective. 

Despite the limitations, the results provide a representative index of real products from RMRS 

invasives research across the different taxonomic groups and National Strategy focus areas.

The results indicate that a good deal of work has been conducted in the Station, but that 

research products are not evenly distributed across the categories. Invasive plants and pathogens have received the most attention and the bulk of the research has been done in the 

Table 1. Summary of the number of research publications produced by RMRS and its collaborators from 

1999 to 2011 that address each of the National Strategy areas for the six identified taxonomic groups. 

These results are not exhaustive but provide an estimation of the distribution of research products 

across taxa and National Strategy Areas. This table was generated by conducting a search in the FS 

Treesearch database using the keywords “exotic” and “invasive” for only RMRS for the period from 

1999-2011. The results were then assigned to the different categories based on taxonomic group and 

National Strategy Area based on title and abstract such that a paper could be counted in more than 

one category if it addressed more than one taxonomic group or subject area. All the specific papers 

tabulated here are not detailed in this document, but the following taxonomic sections give overviews 

of some of the key and more recent work in each area. Specific studies can be found by searching 

Treesearch or visiting the websites listed in Table 2.

Prediction and 

prevention

Early detection 

and rapid 

response

Control and 

management

Restoration and 

rehabilitation

Plants 62 19 97 106

Pathogens 29 12 98 27

Insects 4 2 4 3

Aquatic species 2 1 3 2

Terrestrial vertebrates 2 0 2 1

Totals 99 34 204 139
USDA Forest Service RMRS-GTR-265. 2011. 5

area of Control and Management and Restoration and Rehabilitation. Less work has been 

done in Prediction and Prevention and still less in Early Detection and Rapid Response. 

Taxonomically, the effort is very representative of the threats as most exotic pests in the Rocky 

Mountain West are invasive plants, and invasive pathogens present some of the greatest per 

capita risks. However, certain exotic insects present grave threats and there are substantial 

threats to aquatic ecosystems from exotic aquatic organisms. Clearly, there is a need for more 

work in the areas of Prediction and Prevention and Early Detection and Rapid Response, but 

Station efforts are quite strong in the areas of Control and Management and Restoration and 

Rehabilitation. The specific chapters that follow review and discuss some of these strengths 

and weaknesses in more detail and the final section comments on future invasives research at 

RMRS.

Dissemination of research results is a high priority for research and one of the key means 

by which the final success of the research cycle is achieved. Technical transfer efforts are discussed throughout the document in the appropriate sections and invasive species websites are 

compiled here in Table 2 for easy access. These websites provide a variety of products from 

overviews and updates of ongoing research to conference announcements, postings of the 

RMRS Invasives Species Newsletters, databases, and PDFs of published results.

Table 2. Websites related to RMRS invasives species research and national websites cited in this document.

Subject/title Internet location Primary author

Armillaria

http://forest.moscowfsl.wsu.edu/smp/

docs/docs/ART-GTR-draft_web.pdf G. I. McDonald et al.

Exotic forest pest info. sys. http://spfnic.fs.fed.us/exfor/

N. American Forest 

Comm.

Fire effects on weeds

http://www.fs.fed.us/fmi/products/

Zouhar_et_al_2007.html K. Zouhar

Gypsy moth

http://www.fs.fed.us/ne/

morgantown/4557/gmoth/ USDA FS

Invasive plants

http://www.fs.fed.us/rm/wildlife/

invasives/ D. E. Pearson

Leafy spurge http://www.team.ars.usda.gov/ J. L. Butler

RMRS Invasives Expertise directory

http://www.fs.fed.us/rm/pubs_other/

rmrs_2009_butler_j001.pdf J. L. Butler et al.

RMRS Invasive Species Working Group

http://www.rmrs.nau.edu/invasive_

species/ D. E. Pearson et al.

Rust diseases http://www.rms.nau.edu/rust/ B. G. Geils

Treesearch database http://www.treesearch.fs.fed.us/ USDA FS

White pines

http://www.fs.fed.us/rm/

highelevationwhitepines/index.htm A. W. Schoettle
6 USDA Forest Service RMRS-GTR-265. 2011.

RMRS Invasive Species Program 

Taxonomic Group Focus Areas

I. Plants

By Dean Pearson, Steve Sutherland, Jack Butler, Jane Smith, and Carolyn Sieg

Exotic plants dramatically impact natural communities and disrupt ecosystem services 

(Mack and others 2000). Although the bulk of current impacts are caused by relatively few 

exotic species, many additional exotics that are currently established at low levels are increasing in density and distribution and present substantial imminent threats. Additionally, 

new exotic plants will likely continue to be deliberately and accidentally introduced, which 

represents a potential pool of new invasive species. Managers have responded to the threat 

of invasive species in wildlands with a significant increase in the use of current management 

tools. However, many of the tools now being applied to wildland exotic plant management, 

such as herbicides and classical biocontrol, originated in intensive agricultural systems and 

are proving to be more challenging to apply over large areas in complex ecosystems (Pearson 

and Ortega 2009). Finally, exotic plant invasions are commonly exacerbated by disturbances 

such as wildfires, timber harvest, road building, burning, and grazing by livestock and native 

herbivores. The combined effects of multiple and interacting disturbances on populations of 

exotic plant species, especially in the face of projected climate change, are uncertain but potentially severe (Sieg and others 2010). Our National Grasslands are particularly threatened by 

invasive plants. Large areas of native grasslands are juxtaposed to intensive agricultural systems that serve as an almost continuous source of new invasive plants. Further, plant species 

widely sown as forage for livestock or roadside stabilization are invading native grasslands 

and adversely impacting wildlife habitat and overall biodiversity. Thus, extensive research is 

needed in all aspects of exotic plant invasions in the Intermountain West.

(1) Prevention. Given the continuing introduction of new invasive plants and expansion of 

current species, it is important to identify which new species present significant threats and 

which communities are most susceptible to invader impacts. This requires assessing both the 

causes of invasion, such as the attributes that determine invader establishment and success, 

and the conditions that determine community susceptibility. RMRS scientists are conducting 

research to identify attributes of successful plant invaders (Sieg and others 2003; Sutherland 

2004; Pearson and others in press; Ortega and others in press), evaluating biotic and abiotic 

factors that affect invasion into native communities by notorious invaders such as cheatgrass (Bromus tectorum) (Chambers and others 2007; Gundale and others 2008) and spotted 

knapweed (Centaurea stoebe; Ortega and Pearson 2005; Ortega and others in press; Pearson 

and others ongoing). One study is systematically sampling invaders across grasslands over a 

40,000 km2 areas in the native range of Turkey and the invaded range of Montana to examine 

the causes of invasion for over 20 species and quantitatively rank all invaders in the native 

range according to distribution and impact (Pearson and others ongoing). Station scientists 

and collaborators are also examining how disturbances such as wildfires (Smith and others 

2009b; Dodge and others 2008; Kuenzi and others 2008; Zouhar and others 2008; Fornwalt 

and others 2010) and management activities such as timber harvest (Wienk and others 2004; 

Sabo and others 2009; Wacker and Butler ongoing), salvage logging (Fornwalt ongoing), fuels 

treatments (Zouhar and others 2008; Owen and others 2009; Fornwalt ongoing), prescribed 

fire, and roads (Fowler and others 2008, Birdsall and others 2011) affect exotic plant invasions. Work is also underway to evaluate how community response to disturbance (resiliency) 

relates to community invasibility (Pearson and others ongoing). Recent studies are also revealing how biotic resistance from higher trophic levels may help prevent invasions (Pearson 

and others 2011 and ongoing). An important area for future research is developing strategies 

for locating and monitoring intact systems in order to target them for protection from invasion.
USDA Forest Service RMRS-GTR-265. 2011. 7

(2) Early Detection and Rapid Response. To reduce the spread and impact of invaders, it is 

necessary to understand how invaders disperse, determine where they are likely to establish 

and spread, develop monitoring protocols to detect new invasions, and create tools to rapidly 

control new populations. A priority in this regard is identifying non-invaded or little-invaded areas that can be protected from invasions. Thereafter, early detection provides the only 

real opportunity to locally eradicate new populations of invasives; however, because these 

new populations tend to grow exponentially, the window of opportunity is brief. RMRS staff 

are developing bioclimatic models to prioritize areas for preventing the spread of invaders 

(Warwell ongoing) and strategies for monitoring exotic species presence in Forest Inventory 

plots (Rudis and others 2006), on Forest Soil Disturbance monitoring plots (Page-Dumroese 

and others 2009a and 2009b), and on rangelands (Anderson and others 2004). Station scientists are examining the role of roads, trails, and canyons as dispersal corridors for new 

invaders (Butler ongoing; Fowler ongoing); assessing the role of native species in dispersing 

spotted knapweed seeds (Sutherland ongoing); and developing management tools, including 

herbicide application protocols for eradication of cheatgrass (Sutherland ongoing) and sickleweed (Falcaria vulgaris; Butler ongoing) and community-based action programs to control 

yellow starthistle (Centaurea solstitialis; Pendleton and Pendleton ongoing; Meyer ongoing). 

Although important research is currently underway on Early Detection and Rapid Response, 

we need more work in this area. In particular, there is a need for research that establishes the 

economical value of preventing invasions from expanding compared to managing and mitigating them once widely established. Currently, not enough research and management effort 

is put into addressing new invasions before native populations and communities are impacted. 

There is also a need for more spatial modeling research to prioritize areas for protection and 

additional work to develop methods for monitoring and eradicating new invasions. Finally, 

there is a need to develop remote sensing techniques such as aerial surveys to advance detection strategies.

(3) Control and Management. Once strong invaders become widespread, few tools can effectively suppress them over large regions. Moreover, because the ecosystems are so complex, 

the tools can sometimes result in unintended consequences such as when non-target species 

are affected or the target weed is replaced by another weed (Pearson and Ortega 2009). Thus, 

research is required to identify the circumstances where management intervention is appropriate, improve the effectiveness of current management tools, develop new tools, and refine the 

applications of weed management tools to maximize their effectiveness and minimize their 

side effects. RMRS scientists and collaborators help managers apply ecological concepts to 

the management of grass invasions (D’Antonio and others 2009) and are conducting experiments to better understand resistance to and persistence of invasions (McGlone and others 

in press). Station scientists are examining how plant community composition changes in response to invasion by saltcedar (Tamarix spp.; Johnson and others 2009), and leafy spurge 

(Euphorbia esula; Butler and Cogan 2004) and spotted knapweed (Ortega and Pearson 2005), 

as well as studying effects of invaders on system processes (Nosshi and others 2007; Butler 

ongoing; Chew ongoing) and animals (Ortega and others 2006; Pearson 2009, 2010; Finch ongoing) to determine required mitigation. Scientists are working to advance weed biocontrol by 

advocating for comprehensive support of biocontrol that includes more complete and formal 

evaluations of introduction outcomes (Maron and others 2010). They are working on biocontrol of cheatgrass using native fungal pathogens (Meyer and others 2008a, 2008b; Beckstead 

and others 2010; Pendleton ongoing), developing new biological control agents for other terrestrial and aquatic plants (Magana ongoing; Markin ongoing), evaluating the efficacy and 

safety of biological control agents for leafy spurge (Butler and others 2006; Wacker and Butler 

2006), spotted knapweed (Pearson and others 2000; Pearson and Callaway 2003, 2005, 2006, 

2008; Ortega and others 2004, 2006; Sturdevant and others 2006; Pearson and Fletcher 2008; 

Ortega and others in press; Pearson and others ongoing), and yellow starthistle (Centaurea 

solstitialis) (Birdsall and Markin 2010). They are also evaluating the efficacy of herbicides 

(Butler 1994; Crone and others 2009; Ortega and Pearson 2010, 2011) and cattle grazing for 

weed control (Medina ongoing), and conducting economic assessments to prioritize areas and 

resources for managing invasions (Jones ongoing). RMRS scientists are conducting numerous studies to determine the effects of management activities, including fire, Burned Area 
8 USDA Forest Service RMRS-GTR-265. 2011.

Recovery treatments, fuels treatments, and timber harvest (Zouhar and others 2008; Butler 

ongoing; Landres ongoing; Pendleton and Pendleton ongoing; Smith and others ongoing) on 

invasions.

(4) Rehabilitation and Restoration. The primary challenge in rehabilitating or restoring a 

site lies in identifying and reestablishing altered structural and functional components of the 

impacted community. Little is known about how the severity of ecosystem alterations impacts long-term sustainability, especially with regards to climate change. Even less is known 

regarding the restoration (requiring extensive management inputs)–rehabilitation (requiring 

intensive inputs) thresholds, or how they may change with time. Research is required to prioritize systems for restoration or rehabilitation, identify the residual effects of invaders following 

successful suppression, quantify the extent to which natural successional processes may restore systems, develop guidelines and approaches for reintroducing and reestablishing native 

species, and prevent re-infestation of the original invader(s) and secondary invasions. RMRS 

scientists are conducting research to quantify the effectiveness of various control measures at 

restoring native plant and animal communities and natural processes (Finch and others 2006; 

Smith and others 2006a, b, 2009a; Bateman and others 2008, 2009; Butler and Wacker 2010; 

Ortega and Pearson 2010, 2011; Finch and others in review; Chung ongoing; Collins-Merritt 

ongoing; Ortega and others ongoing) and to understand and prevent reinvasion and secondary invasion following weed control (Ortega and Pearson 2010, 2011; Pearson and others 

ongoing; Shaw ongoing). RMRS scientists are developing native seed mixes for seeding following exotic plant control and other management activities (Callaway and others ongoing), 

assessing the effectiveness of seeding in curtailing exotic species invasions following wildfires (Fornwalt 2009; Stella and others 2010; Peppin and others 2010), developing sources for 

native seed mixes (Butler ongoing; Shaw ongoing), and developing native seed propagation 

protocols (Meyer ongoing). Work is also being done to identify and propagate weed resistant 

genotypes of native species for use in restoration (Sutherland and others ongoing). Molecular 

markers are being used to determine historical population structure of plant species and inform target conditions for restoration (McArthur ongoing). Scientists are exploring how soil 

microorganisms affect shrub establishment in the presence of cheatgrass (Pendleton and others 2007), as well as the effect of herbicides used to treat cheatgrass on shrubs and associated 

mycorrhizae (Owens and others 2011). Research is also underway to understand human perspective on exotic plant management and restoration work (Raish ongoing). RMRS scientists 

have made a good start in the area of restoration research, but much more work is needed in 

developing restoration techniques, such as reseeding, and in understanding the factors inhibiting restoration, such as soil transformations and secondary invasions (Pearson and Ortega 

2009; Pearson and others ongoing).

RMRS scientists have developed several important websites (see also Table 2) to help 

communicate research results to customers related to these overall products (RMRS Invasive 

Species Working Group http://www.rmrs.nau.edu/invasive_species//), the ecology of biological invasions and their management (Pearson and Ortega, http://www.fs.fed.us/rm/wildlife/

invasives/), and leafy spurge management (Butler, http://www.team.ars.usda.gov/). RMRS 

is also providing information on interactions between fire and exotic plants through literature reviews of more than 100 invasive plant species in the Fire Effects Information System 

(http://www.fs.fed.us/database/feis/plants/weed/weedpage.html) and is informing managers 

on a national scale through a “Rainbow Series” literature review on fire and exotic plants 

(http://www.fs.fed.us/fmi/products/Zouhar_et_al_2007.html, and Zouhar and others 2008). 

Quantitative analysis of knowledge gaps, such as that regarding fire and exotic plants (http://

www.fs.fed.us/fmi/products/Zouhar_et_al_2007_pdfs/Chap12.pdf), can provide guidance for 

future research in the Intermountain West and nationally.

Literature Cited

Anderson, G.L.; Kirby, D.; Kline, D.; Butler, J.; Kazmer, D. 2004. Rapid field assessment 

of rangelands using COAST digital imaging system. In: Proceedings of the 19th Biennial 

Workshop on Color Photography Videography and Airborne Imaging for Resource 
USDA Forest Service RMRS-GTR-265. 2011. 9

Assessment. October 6-8, 2003; Logan, UT; American Society for Photogrammetry and 

Remote Sensing.

Bateman, Heather L.; Chung-MacCoubrey, Alice; Finch, Deborah M.; Snell, Howard L.; 

Hawksworth, David L. 2008. Impacts of non-native plant removal on vertebrates along the 

Middle Rio Grande (New Mexico). Ecological Restoration 26(3):193-195.

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Butler, J.L.; Cogan, D.R. 2004. Leafy spurge effects on patterns of plant species richness. 

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control of leafy spurge. Rangeland Ecology and Management 63:553-563.

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Dodge, R.S.; Fulé, P.Z.; Sieg, C.H. 2008. Dalmatian toadflax (Linaria dalmatica) response to 

wildfire in a southwestern USA forest. Ecoscience 15:213-222.

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of roads and prescribed fire in Arizona ponderosa pine forests. Rangeland Ecology and 

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forb, spotted knapweed. Northwest Science 83(4):348-360.

Johnson, T.D.; Kolb, T.E.; Median, A.L. 2009. Do riparian plant community characteristics 

differ between Tamarix (L.) invaded and non-invaded sites on the Upper Verde River, 

Arizona? Biological Invasions. doi: 10.1007/s10530-009-9658-2.

Kuenzi, A.M.; Fulé, P.Z.; Sieg, C.H. 2008. Effects of fire severity and pre-fire stand treatment 

on plant community recovery after a large wildfire. Forest Ecology and Management 

255:855-865.

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Biotic invasions: Causes, epidemiology, global consequences, and control. Ecological 

Applications 10:689-710.

McGlone, C.M.; Sieg, C.H.; Kolb, T.E. 2011. Invasion resistance and persistence: Established 

plants win, even with disturbance and high propagule pressure. Biological Invasions 

13:291-304.

Meyer, S.E.; Beckstead, J.; Allen, P.S.; Smith, D.C. 2008. A seed bank pathogen causes 

seedborne disease: Pyrenophora semeniperda on undispersed grass seeds in western North 

America. Canadian Journal of Plant Pathology 30:525-533.

Meyer, S.E.; Nelson, D.L.; Clement, S.; Beckstead, J. 2008. Cheatgrass (Bromus tectorum) 

biocontrol using indigenous fungal pathogens. In: Kitchen, S.G.; Pendleton, R.L.; Monoco, 

T.A.; Vernon, J., comps. Proceedings—Shrublands Under Fire: Disturbance and Recovery 

in a Changing World. June 6-8; Cedar City, UT. Proc. RMRS-P-52. Fort Collins, CO: U.S. 

Department of Agriculture, Forest Service, Rocky Mountain Research Station: 61-67.

Nosshi, M.I.; Butler, J.L.; Trlica, M.J. 2007. Soil nitrogen mineralization not affected by grass 

species traits. Soil Biology and Biochemistry 39:1031-1039.

Ortega, Y.K.; McKelvey, K.S.; Six, D.L. 2006. Invasion of an exotic forb impacts reproductive 

success and site fidelity of a migratory songbird. Oecologia 149:340-351.

Ortega, Y.K.; Pearson, D.E. 2005. Strong versus weak invaders of natural plant communities: 

Assessing invasibility and impact. Ecological Applications 15:651-661.

Ortega, Y.K.; Pearson, D.E. 2010. Effects of picloram application on community dominants 

vary with initial levels of spotted knapweed (Centaurea stoebe) invasion. Invasive Plant 

Science and Management 3:70-80.

Ortega, Y.K.; Pearson, D.E. 2011. Long-term effects of weed control with picloram along a 

gradient of spotted knapweed invasion. Rangeland Ecology and Management 64:67-77.

Ortega, Y.K.; Pearson, D.E.; McKelvey, K.S. 2004. Effects of biological control agents and 

exotic plant invasion on deer mouse populations. Ecological Applications 14:241-253.

Ortega, Y.K.; Pearson, D.E.; Waller, L.P.; Sturdevant, J.J.; Maron, J.M. In press. Populationlevel compensation impedes biological control of an invasive forb and indirect release of 

a native grass. Ecology.

Owen, S.M.; Sieg, C.H.; Gehring, C.A. 2011. Rehabilitating Downy Brome (Bromus 

tectorum)-invaded shrublands using imazapic and seeding with native shrubs. Invasive 

Plant Science and Management 4:223-233.

Owen, S.M.; Sieg, C.H.; Gehring, C.A.; Bowker, M.A. 2009. Above- and belowground 

responses to tree thinning depend on the treatment of tree debris. Forest Ecology and 

Management 259:71-80.

Page-Dumroese, D.S.; Abbott, A.M.; Rice, T.M. 2009a. Forest soil disturbance monitoring 

protocol Vol. I Rapid Assessment. Gen. Tech. Rep. WO-82a. Washington, DC: U.S. 

Department of Agriculture, Forest Service. 31 p.
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Page-Dumroese, D.S.; Abbott, A.M.; Rice, T.M. 2009b. Forest soil disturbance monitoring 

Protocol Vol. I Rapid Assessment. Gen. Tech. Rep. WO-82b. Washington, DC: U.S. 

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Pearson, D.E. 2009. Invasive plant architecture alters trophic interactions by changing predator 

abundance and behavior. Oecologia 159:549-558.

Pearson, D.E. 2010. Trait- and density-mediated indirect interactions initiated by an exotic 

invasive plant acting as an autogenic ecosystem engineer. American Naturalist 176:394-403.

Pearson, D.E.; Callaway, R.M. 2003. Indirect effects of host-specific biological control agents. 

Trends in Ecology and Evolution 18(9):456-461.

Pearson, D.E.; Callaway, R.M. 2005. Indirect nontarget effects of host-specific biological 

control agents: Implications for biological control. Biological Control 35:288-298.

Pearson, D.E.; Callaway, R.M. 2006. Biological control agents elevate hantavirus by 

subsidizing mice. Ecology Letters 9:443-450.

Pearson, D.E.; Callaway, R.M. 2008. Weed biocontrol insects reduce native plant recruitment 

through second-order apparent competition. Ecological Applications 18:1489-1500.

Pearson, D.E.; Callaway, R.M.; Maron, J.L. 2011. Biotic resistance via granivory: 

Establishment by invasive, naturalized and native asters reflects generalist preference. 

Ecology 92:1748-1757.

Pearson, D.E.; Fletcher, R.J., Jr. 2008. Mitigating exotic impacts: Restoring native deer mouse 

populations elevated by an exotic food subsidy. Ecological Applications 18(2):321-334.

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biological control agent on deer mouse ecology. Oecologia 122(1):121-128.

Pearson, D.E.; Ortega, Y.K. 2009. Managing invasive plants in natural areas: Moving beyond 

weed control. In: R.V. Kingley, ed. Weeds: Management, Economic Impacts and Biology. 

New York, Nova Publishers: 1-21.

Pearson, D.E.; Ortega, Y.K.; Sears, S. In press. Darwin’s naturalization hypothesis up-close: 

intermountain grassland invaders differ morphologically and phenologically from native 

community dominants. Biological Invasions.

Pendleton, R.L.; Pendleton, B.K.; Warren, S.D.; Johansen, J.R.; St. Clair, L.L. 2007. 

Shrub establishment in the presence of cheatgrass: The effect of soil microorganisms. 

In: Sosebbe, R.E.; Wester, D.B.; Britton, C.M.; McArthur, E.D.; Kitchen, S.G., comps. 

Proceedings: Shrubland Dynamics—Fire and Water. August 10-12, 2004; Lubbock, TX. 

Proc. RMRS-P-47. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Rocky Mountain Research Station: 136-141.

Peppin, D.; Fulé, P.Z.; Sieg, C.H.; Beyers, J.; Hunter, M.E. 2010. Post-wildfire seeding 

in forests of the western United States: An evidence-based review. Forest Ecology and 

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on standing crop of understory plant species in ponderosa pine stands in northern Arizona, 

USA. Forest Ecology and Management 257:1656-1662.

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nest-site selection and nest survival in response to fuel reduction in a southwestern riparian 

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2009b. Post-wildfire recovery of riparian vegetation during a period of water scarcity in 

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breeding bird habitat in the Rio Grande Bosque. In: Aguirre-Bravo, C.; Pellicane, Patrick 

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seeding following three high-severity wildfires. International Journal of Wildland Fire

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Cyphocleonus achates and its potential impact on spotted knapweed. Gen. Tech. Rep. U.S. 

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Euphorbia species. Rangeland Ecology and Management 59:468-474.

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Department of Agriculture, Forest Service, Rocky Mountain Research Station. 355 p.
USDA Forest Service RMRS-GTR-265. 2011. 13

II. Pathogens

By Ned B. Klopfenstein and Brian W. Geils

Invasive fungal pathogens have caused immeasurably large ecological and economic 

damage to forests. It is well known that invasive fungal pathogens can cause devastating 

forest diseases (e.g., white pine blister rust, chestnut blight, Dutch elm disease, dogwood 

anthracnose, butternut canker, Scleroderris canker of pines, sudden oak death, pine pitch canker) (Maloy 1997; Anagnostakis 1987; Brasier and Buck 2001; Daughtrey and others 1996; 

Furnier and others 1999; Hamelin and others 1998; Davidson and others 2003; Gordon and 

others 2001). Furthermore, invasive pathogenic fungi have disrupted many forest ecosystems 

and threaten to eliminate some tree species (Liebhold and others 1995). RMRS research has 

historically emphasized white pine blister rust, caused by Cronartium ribicola, because of 

the extensive damage to five-needled white pines that are a keystone species to many forest 

ecosystems in the Interior West since its introduction to North America in the late 1800s. 

However, this disease continues to spread to new areas and environments. RMRS scientists 

are instrumental in providing synthesized information concerning research on invasive species, including white pine blister rust (Geils and others 2010; Hunt and others 2010; Kim 

and others 2010c; Richardson and others 2010a; Zambino 2010). Another emerging invasive 

pathogen in the Rocky Mountain region and elsewhere is Geosmithia morbida, the cause of 

1,000 cankers disease. This disease can cause mortality of walnut trees (Juglans spp.) and is 

transmitted by the walnut twig beetle, Pityophthorus juglandis (Tisserat and others 2009). In 

recent years, RMRS has not had the resources to address this disease. Currently, a research 

group from Colorado State University is evaluating methods to prevent movement of the 

pathogen and insect vector.

In 2006, the USDA Forest Service R&D Invasive Species Strategic Program Area obtained 

input from a formal peer review of diverse user groups in order to develop long-term planning for the program. The Invasive Species Strategy was revised to reflect this guidance, 

and research efforts were prioritized to address the future challenges to managers. As a result of this process, a publication series was produced (Dix and Britton 2010) that includes 

12 visionary papers developed to address future invasive species research issues and priorities. RMRS scientists who work on invasive pathogens contributed to papers on overarching 

priorities (Britton and others 2010) and invasive plant pathogens (Klopfenstein and others 

2010). Similarly, a summary of invasive species research and an expertise directory for the 

RMRS was recently published (Butler and others 2009), which included a section on invasive 

pathogen research (Klopfenstein and Geils 2009). RMRS has also contributed to regional forest pathology groups, such as Western International Forest Disease Work Conference, which 

cover diverse aspects of invasive pathogens (Geils 2004b). In another review paper, several 

authors from Federal and State institutions produced a collaborative review on impacts of 

non-native invasive species on U.S. forests (Moser and others 2009). This review addresses ecological, economic, and social impacts of invasive species such as pathogens, insects, 

plants, and aquatic organisms in forests. Recommendations for policy and management were 

provided.

RMRS research programs have developed critical information for four key areas of invasive pathogens and microbes.

(1) Prediction and Prevention. Because invasive pathogens are virtually impossible to eradicate after establishment, predicting and preventing them is the most efficacious method to 

minimize impacts. However, considerable baseline information on precise distributions of 

hosts and pathogens and interactions with the environment is needed to develop effective 

prediction tools. When compiling inventories of pathogenic fungi, it is important to include 

pathogens that cause only minor disease problems, because invasive pathogens frequently 

cause only minor damage in the area of their origin. Also, representative samples are needed 

for pathogens that are widespread, because subspecies groups may exist that have distinct 

ecological behavior. Surveys of existing fungi of forests and nurseries are difficult to conduct because numerous species exist, fungal taxonomy is constantly changing, and species 

are difficult to identify accurately. However, DNA-based diagnostics provide a reliable and 
14 USDA Forest Service RMRS-GTR-265. 2011.

cost-effective means to survey existing pathogens (or hosts) within a region (Hoff and others 

2004b). Because of the diverse utility of DNA-based characterization, it is extremely shortsighted to preclude DNA-based approaches from any pathogen survey.

Prediction of invasive pathogens requires an understanding of (1) current geographic distributions of forest pathogens and hosts; (2) genetic relationships among pathogen species, 

subspecies, and populations; (3) potential for intraspecific or interspecific hybridization to 

create novel pathogens with unique biological behavior; (4) genetic relationships among host 

species, subspecies, and populations; (5) environmental factors (e.g., temperature, moisture, 

soil types) that are suitable for survival, growth, and reproduction of forest hosts and pathogens; (6) how changing climate will affect the suitable climate space for forest hosts and 

pathogens; and (7) pathways of pathogen movement and introduction.

Concepts to examine the genetic structure of hosts and pathogens at the landscape level 

have been developed (Klopfenstein and others 2001; Lundquist 2005b; Lundquist and Hamelin 

2005a, 2005b; Lundquist and Klopfenstein 2001; Richardson and others 2005). DNA-based 

analyses are currently underway to examine the genetic relationship of white pine blister rust 

pathogens worldwide (Richardson others 2010b). Such studies will evaluate risks associated 

with new introductions and seek the evolutionary and/or geographic origin of white pine blister rust that was introduced to North America. Studies on the distribution of genetic groups 

of Armillaria spp., root-rot pathogens of diverse trees, are providing a framework to predict 

potentially invasive pathogens and hybrids (Hanna and others 2007b; Hanna and others 2009). 

Studies are ongoing to examine the distribution and genetic relationships among Armillaria

spp. in the Northern Hemisphere (Cannon and others 2008).

Recently, considerable interest has developed on eucalypt rust (Puccinia psidii), also 

known as guava rust, ohia rust, or myrtle rust. Eucalypt rust has been introduced to Hawaii, 

where it poses a current threat to myrtaceous trees, which represent ~80% of the native forest 

in Hawaii. This pathogen is also the subject of worldwide concern, because of its capacity to 

infect eucalypts. Collaborative work with Universidade Federal de Viçosa (Viçosa, Brazil), 

Washington State University, the University of Hawaii, Forest Health Protection-Region 5, 

Western Wildland Environmental Threat Assessment Center, and RMRS is examining the 

population genetic structure of the eucalypt rust in Brazil, the putative origin of this rust, and 

other countries where the rust has been found. One goal of this project is to identify eucalypt 

rust populations that pose additional threat to Hawaiian forest and eucalypts (Cannon and 

others 2010; Graca and others 2010). Other evaluations were performed to assess the invasive 

risk of western gall rust (caused by Peridermium harknessii) to Pinus radiata in New Zealand 

(Ramsfield and others 2007). In addition, RMRS scientists were instrumental in developing a 

response plan for Scots pine blister rust, caused by a potentially invasive pathogen that is not 

yet present in the United States. (Geils and others 2009)

Other factors, such as climate and means of dispersal, must also be considered when predicting potentially invasive pathogens. Studies are underway that will use climate variables to 

predict areas with suitable climate space for invasive pathogens and evaluate potential effects 

of climate change (Klopfenstein and others 2009a). Other studies have investigated the possible mode of transport for invasive pathogens (Frank and others 2004, 2008; Geils 2004a).

(2) Early Detection and Rapid Response. Early detection of forest pathogens is dependent on identification to species, subspecies, and population level. Taxonomic identification 

of forest pathogens is largely dependent on herbaria and culture collections that allow comparisons among microbes. RMRS has a Forest Pathology Herbarium under the supervision of 

B.W. Geils. In addition, over 10,000 living culture archives of forest pathogens, endophytes, 

decomposers, and potential biological control agents are housed in the Forestry Sciences 

Laboratory in Moscow, Idaho. Because most forest pathogens and associated fungi cannot be 

easily detected or identified, techniques are needed to detect and identify forest pathogens and 

associated fungi (Kim and others 2005). DNA-based diagnostic methods were developed and/

or applied for root rot fungi (Hanna and others 2007a; Kim and Klopfenstein 2011; Kim and 

others 2000, 2001, 2006, 2010a, 2010b, 2011; Klopfenstein and others 2009b; Stewart and 

others 2006), white pine blister rust (McDonald and others 2006; Zambino 2002; Zambino and 

others 2007a), powdery mildew pathogens (Mmbaga and others 2000, 2004), endophytes, and 

potential biological control agents (Hoff and others 2004a, 2004b; Stewart and others 2006). 
USDA Forest Service RMRS-GTR-265. 2011. 15

RMRS research has contributed over 500 diagnostic DNA sequences to national databases 

to help in the identification of forest pathogens and microbes. These DNA-based diagnostic 

tools allow surveys of the present distributions of pathogens and microbes. These surveys are 

necessary to recognize an introduced pathogen and allow predictions of potentially invasive 

pathogens and microbes. Furthermore, such DNA-based diagnostic tools can be adapted for 

screening procedures designed to prevent movement of invasive pathogens and microbes.

One striking example of the need for DNA-based identification is associated with a conifer 

nursery (Stewart and others 2006). In this situation, isolates of Fusarium commune are highly 

pathogenic to Douglas-fir (Pseudotsuga menziseii), but morphologically indistinguishable 

from nonpathogenic Fusarium oxysporum. However, multiple DNA-based techniques were 

developed to detect and identify the pathogenic Fusarium species (Stewart and others 2006). 

Because nurseries represent a primary route by which invasive pathogens are spread, it is critical that DNA-based tools are used to survey pathogens that exist in nursery settings.

The utility of DNA-based diagnostics was also demonstrated with the white pine blister rust 

pathogen, C. ribicola. In North America, this pathogen was long assumed to utilize only Ribes

spp. as its alternate (telial) host. Recently, natural infections of C. ribicola were found on three 

other alternate host species, Pedicularis racemosa, Pedicularis bracteosa, and Castilleja miniata (McDonald and others 2006; Zambino and others 2007a). The C. ribicola telia on these 

non-Ribes alternate hosts are morphologically indistinguishable from those produced by C. 

coleosporioides, an endemic pathogen that causes stalactiform rust on lodgepole pine (Pinus

contorta) and utilizes Pedicularis spp. and Castilleja spp. as alternate hosts (Farr and others 

1995; Vogler and Bruns 1998). Thus, DNA-based diagnostics were essential to recognize 

natural C. ribicola infection of non-Ribes alternate hosts in North America. Understanding the 

pathogen ecology and host utilization is essential to managing and predicting ecological behavior of invasive pathogens. RMRS scientists prepared a synthesis of molecular approaches 

for investigating white pine blister rust pathosystems (Richardson and others 2010a).

The fungal genus Armillaria is associated with diverse tree species worldwide. However, 

some Armillaria species are virulent pathogens, while others exhibit low pathogenicity and 

play beneficial roles in forest ecosystems. Thus, accurate identification of Armillaria species 

is a critical component of surveys of forest pathogens. Because many Armillaria species are 

difficult to identify by morphology, DNA-based techniques were developed to help identify 

Armillaria species (Kim and others 2000, 2001, 2006). These techniques were used to identify Armillaria species collected in a survey of Armillaria spp. in the inland northwestern 

United States. Surprisingly, an area in south-central Idaho was identified where the primary 

pathogenic Armillaria species (A. solidipes = A. ostoyae) was not found, even though suitable 

habitat types, suitable host trees, and other Armillaria species were present (McDonald and 

others 1987). Based on this information it appears that any introduction of A. solidipes into 

south-central Idaho represents an invasive species risk. This situation also emphasizes the 

key role of DNA-based diagnostic methods for pathogen surveys, without which this unique 

phenomenon would remain unrecognized.

(3) Control and Management. Because of the enormous and growing impacts of white pine 

blister rust, considerable research in RMRS has be devoted to control and management of this 

disease that impacts diverse forest ecosystems that comprise several species of five-needled 

white pines (Geils 2001, 2003; Hoff and others 2001; Kendall and Keane 2001; McCaughey 

and Schmidt 2001; Schoettle 2004a; Tomback and others 2001a; Zambino and McDonald 

2003). Continuing studies have documented the spread of white pine blister rust (Geils 2000; 

Geils and others 2003; Kearns and Jacobi 2007) and the development of hazard rating systems (Van Arsdale and others 2006). Additional studies have been conducted on infection 

episodes of comandra rust, a related native rust disease, on lodgepole pine (Jacobi and others 

2002). A white pine blister rust model has been developed that simulates the life cycle of the 

pathogen and resulting tree mortality (McDonald and others 1981), and further developments 

of this model are still in use as an extension to the Forest Vegetation Simulator (FVS; http://

www.fs.fed.us/foresthealth/technology/wpbr_model.shtml). Research on disease resistance 

has contributed to breeding programs of western white pine and eastern white pine (Hudgins 

and others 2005; Jurgens and others 2003; McDonald and others 2004; Woo and others 2001, 

2002, 2004a, 2004b), and genetic research has evaluated the impact of resistance breeding 
16 USDA Forest Service RMRS-GTR-265. 2011.

on the genetic diversity of western white pine (Kim and others 2003). Research by RMRS 

scientists to assess resistance in limber pine and Rocky Mountain bristlecone pine is ongoing 

(Sniezko and others 2008; Vogler and others 2006; Schoettle and others 2007; Schoettle and 

others 2009). Methods to identify genetic markers for rust resistance have been developed 

for other tree species (Tabor and others 2000). Because the white pine blister rust pathogen 

requires an alternate host to complete its lifecycle, research has documented the distribution 

and role of Ribes spp. in this disease (Van Arsdel and Geils 2004; Zambino 2010). Recently, 

other alternate hosts of white pine blister rust were confirmed in North America (McDonald 

and others 2006; Zambino and others 2007a). This finding may significantly impact our 

understanding of risks posed by this disease (Kearns and others 2004; Zambino and others 

2006, 2007b). Genetic research is assessing whether the blister rust pathogen is changing in 

a manner that could affect disease development, potential risks of new introductions, and genetic relationships among pathogen populations (Hamelin and others 2000; McDonald 2000; 

Richardson 2006; Richardson and others 2007, 2008a).

Other research is being directed toward developing proactive approaches in management 

of high-elevation white pines to reduce the impact of white pine blister rust (Schoettle 2004b; 

Schoettle and Sniezko 2007; Schoettle and others 2007; Schoettle and others 2009). This 

new intervention paradigm moves past the idea of protecting the hosts from exposure to the 

established non-native invader and shifts toward facilitating naturalization by preparing the 

landscape to sustain ecosystem function into the future in the presence of the invasive. For 

white pine blister rust, this means facilitating evolution of genetic resistance in the pine host 

to the non-native pathogen. Positioning the ecosystem for greater resilience upon invasion 

is especially important for traditionally minimally managed ecosystems where the risk of 

ecological impacts is high. These ecosystems may be remote but they are not out of reach for 

invasion by non-native organisms.

Science information has been synthesized for various users and forest managers. A website established by B.W. Geils entitled “The Peridium” contains diverse information about 

rust diseases and their management (http://www.rms.nau.edu/rust/). A website developed by 

A.W. Schoettle is devoted to high-elevation white pines, their ecosystems, and the factors 

that threaten them (http://www.fs.fed.us/rm/highelevationwhitepines/index.htm). Information 

about whitebark pine was also compiled in book form (Tomback and others 2001b). In addition, B.W. Geils has established an RMRS database that contains comprehensive historical 

publications related to white pine blister rust. USDA research on biological control of native 

and invasive pathogens was also summarized (Klopfenstein and others 2000).

Other pathogens, such as Armillaria spp. and other root pathogens, have the potential to 

behave as invasive pathogens following disturbances, such as fire or fuels treatment. Sciencebased syntheses have developed reports and online tools to guide managers in the application 

of fuels treatments and potential impacts on root disease (Armillaria Response Tool http://

forest.moscowfsl.wsu.edu/fuels/art/; Rippy and others 2005; McDonald and others 2005). A 

number of studies have developed methods and models to evaluate the effects of diseaseinduced disturbances at various landscape scales (Kallas and others 2003; Lundquist 2000, 

2005a; Lundquist and Beatty 2002; Lundquist and Hamelin 2005a, 2005b; Lundquist and 

Lindner 2000; Lundquist and Negron 2000; Lundquist and Sommerfeld 2002; Reich and 

Lundquist 2005). Other studies have developed methods to assess non-timber impacts of disease (Lundquist and Ward 2005; Stubblefield and others 2005).

(4) Rehabilitation and Restoration. Information has been compiled for restoration of forest 

ecosystems impacted by white pine blister rust (Arno and others 2001; Burns and others 2008; 

Conklin and others 2009; Fins and others 2002; Harvey and others 2008; Keane 2001; Keane 

and Arno 2001; McCaughey and Tomback 2001; Neuenschwander and others 1999; Tomback 

and others 2001b; Wagner and others 2000). Science synthesis reports have been developed to 

demonstrate how molecular genetic tools can contribute to rehabilitation and restoration (Kim 

and others 2005; Richardson and others 2005). RMRS research has been active in defining 

host populations that are affected by white pine blister rust, such as white bark pine (DekkerRobertson and Bruederle 2001; Richardson 2001; Richardson and others 2002a), western 

white pine (Kim and others 2003, 2011), and limber pine (Schoettle and Rochelle 2000). 

Understanding of population dynamics and capacity for regeneration is critical to sustaining 
USDA Forest Service RMRS-GTR-265. 2011. 17

healthy ecosystems and restoring impacted ecosystems (Coop and Schoettle 2009; Coop and 

others 2010; Richardson and others 2002b). Fire-scar and tree-recruitment chronologies have 

been developed from two limber and bristlecone pine sites in Colorado (Brown and Schoettle 

2008). Population structures in both sites document relationships with disturbances and 

changes in climate and land use over the past several centuries, and they provide the longest 

such records yet developed for this area of North America. A population genetic model parameterized for the high elevation white pines is being constructed to examine the effects of white 

pine blister rust on the ecological and evolutionary dynamic of rust resistance in the pines 

(Antolin and others 2009; Schoettle and others 2010). Incorporation of these natural disturbance regimes with management intervention is critical to the long-term sustainability of the 

host population in the presence of the invasive species (Coop and Schoettle 2009). Lessons 

learned from long-term research toward enhancing natural recovery of impacted ecosystems 

has been synthesized for management professionals (McDonald and others 2005; McDonald 

and Hoff 2001; Zambino and McDonald 2003).

Genetic conservation is an important strategy for sustaining white pines threatened by 

white pine blister rust and other stressors. RMRS scientists and cooperators are developing 

and applying molecular and quantitative tools for investigating genetic diversity, correlations 

among adaptive traits, and disease resistance in several species of white pines. Kim and others 

(2011) examined the range-wide genetic diversity of western white pine (Pinus monticola) 

populations across the western United States. In related studies, Richardson and others (2009) 

demonstrated that spatial patterns of western white pine derived from molecular and quantitative genetic data were congruent with regional climates. Issues related to the conservation of 

limber pine have been addressed by Schoettle and others (2008).

Ongoing research is addressing how climate change will further threaten forest ecosystems that are at risk from white pine blister rust (Richardson and others 2008b; Warwell and 

others 2007, 2008). Influences of other disturbances such as mountain pine beetle epidemics 

and climate change on management of white pine blister rust impacts is also being explored 

(Schoettle and others 2008).

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McDonald, G.I.; Richardson, B.A.; Zambino, P.J.; Klopfenstein, N.B.; Kim, M.-S. 2006. 

Pedicularis and Castilleja are natural hosts of Cronartium ribicola in North America: A 

first report. Forest Pathology 36:73-82.

McDonald, G.I.; Tanimoto, P.D.; Rice, T.M.; Hall, D.E.; Stewart, J.E.; Zambino, P.J.; Tonn, 

J.R.; Klopfenstein, N.B.; Kim, M.-S. 2005. Root disease analyzer—Armillaria. Res. 

Note. RMRS-RN-23-13WWW. Fort Collins, CO: U.S. Department of Agriculture, Forest 

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McDonald, G.I.; Zambino, P.J.; Klopfenstein, N.B. 2005. Naturalization of host-dependent 

microbes after introduction into terrestrial ecosystems: Evolutionary epidemiology of white 

pine blister rust. Chapter 5. In: Lundquist, J.E.; Hamelin, R.C., eds. Forest Pathology—

From Molecules to Landscapes. St. Paul, MN: American Phytopathological Society Press: 

41-57.
USDA Forest Service RMRS-GTR-265. 2011. 23

McDonald, G.; Zambino, P.; Sniezko, R. 2004. Breeding rust-resistant five-needle pines in the 

western United States: Lessons from the past and a look to the future. In: Sniezko, R.A.; 

Samman, S.; Schlarbaum, S.E.; Kriebel, H.B., eds. Breeding and genetic resources of fiveneedled pines: Growth, adaptability, and pest resistance. Proc. RMRS-P-32. Fort Collins, 

CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 

259 p.

Mmbaga, M.T.; Klopfenstein, N.B.; Kim, M.-S. 2000. Molecular genetic analysis of powdery 

mildew pathogens of dogwood. In: Bryson, J.L., ed. and comp. Proceedings of the Southern 

Nursery Association Research Conference 45:236-242.

Mmbaga, M.T.; Klopfenstein, N.B.; Kim, M.-S.; Mmbaga, N.C. 2004. PCR-based 

identification of Erysiphe pulchra and Phyllactinia guttata from Cornus florida using ITSspecific primers. Forest Pathology 34:321-328.

Moser, K.W.; Barnard, E.L.; Billings, R.F.; Crocker, S.J.; Dix, M.E.; Gray, A.N.; Ice, G.G.; 

Kim, M.-S.; Reid, R.; Rodman, S.U.; McWilliams, W.H. 2009. Impacts of nonnative 

invasive species on U.S. forests and recommendations for policy and management. Journal 

of Forestry 107:320-327.

Neuenschwander, L.F.; Byler, J.W.; Harvey, A.E.; McDonald, G.I.; Ortiz, D.S.; Osborne, H.L.; 

Snyder, G.C.; Zack, A. 1999. White pine in the American West: A vanishing species—

Can we save it? Gen. Tech. Rep. RMRS-GTR-35. Fort Collins, CO: U.S. Department of 

Agriculture, Forest Service, Rocky Mountain Research Station. 22 p.

Ramsfield, T.D.; Kriticos, D.J.; Vogler, D.R.; Geils, B.W. 2007. Western gall rust—A threat 

to Pinus radiata in New Zealand. New Zealand Journal of Forestry Science 37:143-152.

Reich, R.M.; Lundquist, J.E. 2005. Use of spatial statistics in assessing forest diseases. In: 

Lundquist, J.E.; Hamelin, R.C., eds. Forest Pathology—From Genes to Landscapes. St. 

Paul, MN: American Phytopathological Society Press: 127-143.

Richardson, B.A. 2001. Gene flow and genetic structure of whitebark pine (Pinus albicaulis): 

Inferences into bird-dispersed seed movement and biogeography. Thesis. University of 

Idaho, Moscow. 55 p.

Richardson, B.A. 2006. The white pine blister rust pathosystem: Assessing Cronartium ribicola

genetic structure among different hosts and environments. Dissertation. Washington State 

University, Pullman.

Richardson, B.A.; Brunsfeld, S.J.; Klopfenstein, N.B. 2002a. DNA from bird-dispersed seed 

and wind disseminated pollen provides insights into postglacial colonization and population 

genetic structure of whitebark pine (Pinus albicaulis). Molecular Ecology 11:214-227.

Richardson, B.A.; Ekramoddoulah, A.K.M.; Liu, J.-J.; Kim, M.-S.; Klopfenstein, N.B. 

2010a. Current and future molecular approaches to investigate the white pine blister rust 

pathosystem. Forest Pathology 40:314-331.

Richardson, B.A.; Kim, M.-S.; Klopfenstein, N.B.; Ota, Y.; Woo, K.S., Hamelin, R.C. 2010b. 

Tracking the footsteps of an invasive plant pathogen: Intercontinental phylogeographic 

structure of the white-pine-blister-rust fungus, Cronartium ribicola. In: Noshad, D.; Noh, 

E.W.; King, J.; Sniezko, R.A., eds. Breeding and genetic resources of five-needle pines. 

Proceedings IUFRO Working Party 2.02.15. September 22-26, 2008; Yangyang, Korea. 

Korea Forest Research Institute: 56-60.

Richardson, B.A.; Klopfenstein, N.B.; Brunsfeld, S.J. 2002b. Assessing Clark’s nutcracker 

seed-caching flights using maternally inherited mitochondrial DNA of whitebark pine. 

Canadian Journal of Forest Research 32:1103-1107.

Richardson, B.A.; Klopfenstein, N.B.; Peever, T.L. 2005. Assessing forest-pathogen 

interactions at the population level. Chapter 3. In: Lundquist, J.E.; Hamelin, R.C., eds. Forest 

Pathology—From Molecules to Landscapes. St. Paul, MN: American Phytopathological 

Society Press: 21-30.

Richardson, B.A.; Klopfenstein, N.B.; Zambino, P.J.; McDonald, G.I.; Geils, B.W.; Carris, 

L.M. 2008a. The influence of host resistance on the genetic structure of the white pine 
24 USDA Forest Service RMRS-GTR-265. 2011.

blister rust fungus, Cronartium ribicola, in western North America. Phytopathology 

98:413-420.

Richardson, B.A.; Rehfeldt, G.E.; Kim, M.-S. 2009. Congruent climate-related genecological 

responses from molecular markers and quantitative traits for western white pine (Pinus 

monticola). International Journal of Plant Science 170:1120-1131.

Richardson, B.A.; Warwell, M.V.; Kim, M.-S.; Klopfenstein, N.B.; McDonald, G.I. 2008b. 

Integration of population genetic structure and plant response to climate change: Sustaining 

genetic resources through evaluation of projected threats. In: Proceedings of Advances in 

Threat assessment and Their Application to Forest and Rangeland Management. July 18-

20, 2006; Boulder, CO: 35-65.

Richardson, B.A.; Zambino, P.J.; Klopfenstein, N.B.; McDonald, G.I.; Carris, L.M. 2007. 

Assessing host specialization among aecial and telia hosts of the white pine blister rust 

fungus, Cronartium ribicola. Canadian Journal of Botany 85:299-306.

Rippy, R.C.; Stewart, J.E.; Zambino, P.J.; Tirocke, J.M.; Kim, M.-S.; Klopfenstein, N.B.; 

Thies, W.G. 2005. Root disease considerations for fuels treatments in western forests. Gen. 

Tech. Rep. RMRS-GTR-141. Fort Collins, CO: U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Research Station. 32 p.

Schoettle, A.W. 2004a. Ecological roles of five-needle pines in Colorado: Potential 

consequences of their loss. In: Sniezko, R.A.; Samman, S.; Schlarbaum, S.E.; Kriebel, 

H.B., eds. Breeding and genetic resources of five-needle pines: Growth, adaptability, and 

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Schoettle, A.W. 2004b. Developing proactive management options to sustain bristlecone and 

limber pine ecosystems in the presence of a non-native pathogen. In: Shepperd, W.D.; 

Eskew, L.G., comps. Silviculture in special places: Proceedings of the National Silviculture 

Workshop. September 8-11, 2003; Granby, CO. Proc. RMRS-P-34. Fort Collins, CO: U.S. 

Department of Agriculture, Forest Service, Rocky Mountain Research Station: 46-155. 

Available: http://www.fs.fed.us/rm/pubs/rmrs_p034/rmrs_p034_146_155.pdf.

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Schoettle, A.W.; Burns, K.S.; Costello, S.; Witcosky, J.; Howell, B.; Connor, J. 2008. A race 

against beetles: Conservation of limber pine. Nutcracker Notes 14:11-12.

Schoettle, A.W.; Rochelle, S.G. 2000. Morphological variation of Pinus flexilis (Pinaceae), a 

bird-dispersed pine, across a range of elevations. American Journal of Botany 87:1797-1806.

Schoettle, A.W.; Sniezko, R.A. 2007. Proactive intervention to sustain high-elevation pine 

ecosystems threatened by white pine blister rust. Journal of Forest Research 12:327-336.

Schoettle, A.W.; Sniezko, R.A.; Burns, K.S. 2009. Sustaining Pinus flexilis ecosystems of the 

southern Rocky Mountains (USA) in the presence of Cronartium ribicola and Dendroctonus 

ponderosae in a changing climate. In: Noshad, D.; Noh, E.; King, J.; Sniezko, R.A., eds. 

Breeding and Genetic Resources of Five-Needle Pines Conference, IUFRO Working Party 

2.02.15. September 22-26, 2008; Yangyang, Republic of Korea, Korea Forest Research 

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Schoettle, A.W.; Sniezko, R.A.; Burns, K.S.; Freeman, F. 2007. Preparing the landscape 

for invasion–Early intervention approaches for threatened high elevation white pine 

ecosystems. In: Goheen, E.M.; Sniezko, R.A., tech. coords. Proceedings of the conference 

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Northwest Region: 72-75. Available: http://www.fs.fed.us/r6/nr/fid/wbpine/proc.shtml.

Sniezko, R.A.; Kegley, A.; Danchok, R.; Schoettle, A.W.; Burns, K.S.; Conklin, D. 2008. 

Cronartium ribicola resistance in whitebark pine, southwestern white pine, limber pine 

and Rocky Mountain bristlecone pine—Preliminary screening results from first tests at 
USDA Forest Service RMRS-GTR-265. 2011. 25

Dorena GRC. In: McWilliams, M.G., comp. Proceedings of the 55th Western International 

Forest Disease Work Conference; October 15-19, 2007; Sedona, AZ. Salem, OR: Oregon 

Department of Forestry: 84-86.

Stewart, J.E.; Kim, M.-S.; James, R.L.; Dumroese, R.K.; Klopfenstein, N.B. 2006. Molecular 

characterization of highly virulent isolates of Fusarium oxysporum from a conifer nursery. 

Phytopathology 96:1124-1133.

Stubblefield (Holte), C.H.; Lundquist, J.E.; van der Kamp, B. 2005. Forest disease impacts 

of wildlife: Beneficial? In: Lundquist, J.E.; Hamelin, R.C., eds. Forest Pathology—From 

Genes to Landscapes. St. Paul, MN: American Phytopathological Society Press: 95-103.

Tabor, G.M.; Kubisiak, T.; Klopfenstein, N.B.; Hall, R.B.; McNabb, H.S., Jr. 2000. Bulk 

segregant analysis identifies molecular markers linked to Melampsora medusae resistance 

in Populus deltoides. Phytopathology 90:1039-1042.

Tisserat, N.; Cranshaw, W.; Leatherman, D.; Utley, C.; Alexander, K. 2009. Black walnut 

mortality in Colorado caused by the walnut twig beetle and thousand cankers disease. 

Online. Plant Health Progress doi:10.1094/PHP-2009-0811-01-RS.

Tomback, D.F.; Arno, S.F.; Keane, R.E. 2001a. The compelling case for management 

intervention. Chapter 1. In: Tomback, D.F.; Arno, S.F.; Keane, R.E., eds. Whitebark Pine 

Communities—Ecology and Restoration. Washington, DC: Island Press: 3-25.

Tomback, D.F.; Arno, S.F.; Keane, R.E., eds. 2001b. Whitebark Pine Communities—Ecology 

and Restoration. Washington, DC: Island Press. 440 p.

Van Arsdel, E.P.; Geils, B.W. 2004. The Ribes of Colorado and New Mexico and their rust 

fungi. FHTET-04-13, Fort Collins, CO: U.S. Department of Agriculture, Forest Service, 

Forest Health Technology Enterprise Team. 32 p.

Van Arsdale, E.P.; Geils, B.W.; Zambino, P.J. 2006. Epidemiology for hazard rating of white 

pine blister rust. In: Guyon, J.C., comp. Proceedings of the 53rd Western International 

Forest Disease Work Conference. August 26-29, 2005; Jackson, WY: 49-64.

Vogler, D.R.; Bruns, T.D. 1998. Phylogenetic relationships among the pine stem rust fungi 

(Cronartium and Peridermium spp.). Mycologia 90:244-257.

Vogler, D.R.; Delfino-Mix, A.; Schoettle, A.W. 2006. White pine blister rust in high-elevation 

white pines: Screening for simply inherited, hypersensitive resistance. In: Guyon, J.C., 

comp. Proceedings of the 53rd Western International Forest Disease Work Conference. 

September 26-30, 2005; Jackson, WY. Ogden, UT: U.S. Department of Agriculture, Forest 

Service, Intermountain Region: 73-82.

Wagner, M.R.; Block, W.M.; Geils, B.W.; Wenger, K.F. 2000. Restoration ecology: A new 

forest management approach or another merit badge for foresters. Journal of Forestry 

98:22-27.

Warwell, M.V.; Rehfeldt, G.E.; Crookston, N.L. 2007. Modeling contemporary climate profiles 

and predicting their response to global warming for whitebark pine (Pinus albicaulis). 

In: Goheen, E.M.; Sniezko, R.A., coords. Proceedings of the conference Whitebark Pine: 

A Pacific Coast Perspective. August 27-31, 2006: Ashland, OR. R6-NR-FHP-2007-01. 

Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Region: 

139-142.

Warwell, M.V.; Rehfeldt, G.E.; Crookston, N.L. 2008. Modeling species’ realized climatic 

niche space and predicting their response to global warming for several western forest 

species with small geographic distributions. In: Proceedings of Advances in Threat 

Assessment and Their Application to Forest and Rangeland Management. July 18-20, 

2006; Boulder, CO: 36-59.

Woo, K.-S.; Fins, L.; McDonald, G.I. 2004a. Genetic and environmentally related variation in 

needle morphology of blister rust resistant and nonresistant Pinus monticola. In: Sniezko, 

R.A.; Samman, S.; Schlarbaum, S.E.; Kriebel, H.B., eds. Breeding and genetic resources 

of five-needled pines: Growth, adaptability, and pest resistance. Proc. RMRS-P-32. Fort 

Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research 

Station: 148-153.
26 USDA Forest Service RMRS-GTR-265. 2011.

Woo, K.-S.; Fins, L.; McDonald, G.I.; Wenny, D.L.; Eramian, A. 2002. Effects or nursery 

environment on needle morphology of Pinus monticola Dougl. and implications for tree 

improvement programs. New Forests 24:113-129.

Woo, K.-S.; Fins, L.; McDonald, G.I.; Wiese, M.V. 2001. Differences in needle morphology 

between blister rust resistant and susceptible western white pine stocks. Canadian Journal 

of Forest Research 31:1880-1886.

Woo, K.-S.; McDonald, G.I.; Fins, L. 2004b. Influence of seedling physiology on expression 

of blister rust resistance in needles of western white pine. In: Sniezko, R.A.; Samman, 

S.; Schlarbaum, S.E.; Kriebel, H.B., eds. Breeding and genetic resources of five-needled 

pines: Growth, adaptability, and pest resistance. Proc. RMRS-P-32. Fort Collins, CO: U.S. 

Department of Agriculture, Forest Service, Rocky Mountain Research Station: 250-254.

Zambino, P.J. 2002. Dry grinding at near-ambient temperatures for extracting DNA from rust 

and other fungal spores. BioTechniques 33:48-51.

Zambino, P.J. 2010. Biology and pathology of Ribes and their implications for management 

of white pine blister rust. Forest Pathology 40:264-291.

Zambino, P.J.; McDonald, G.I. 2003. Resistance to white pine blister rust in North American 

five-needle pines and Ribes and its implications. In: Geils, B.W., comp. 2004. Proceedings 

of the 51st Western International Forest Disease Work Conference; August 18-22, 2003; 

Grants Pass, OR. Flagstaff, AZ: 111-125.

Zambino, P.J.; McDonald, G.I.; Richardson, B.A. 2007a. First report of the white pine blister 

rust fungus, Cronartium ribicola, on Pedicularis bracteosa. Plant Disease 91:467.

Zambino, P.J.; Richardson, B.A.; McDonald, G.I.; Klopfenstein, N.B.; Kim, M.-S. 2006. NonRibes alternate hosts of white pine blister rust: What this discovery means to whitebark 

pine. Nutcracker Notes Issue 10:6-7.

Zambino, P.J.; Richardson, B.A.; McDonald, G.I.; Klopfenstein, N.B.; Kim, M.-S. 2007b. 

A paradigm shift for white pine blister rusts: Non-Ribes alternate hosts for Cronartium

ribicola in North America. In: Proceedings of the 53rd Western International Forest Disease 

Work Conference. September 22-30, 2005; Jackson, WY: 161-163.
USDA Forest Service RMRS-GTR-265. 2011. 27

III. Insects

By Jose F. Negrón

RMRS research on insect pests focuses mostly on conifer pests. There is a long history 

of invasive insects causing significant impacts, mortality, and changes in forest ecosystem 

structure in North America. Perhaps the most evident example is the introduction of the gypsy 

moth, Lymantria dispar, into eastern North America in the 1860s (Forbush and Frenald 1896). 

Although not well understood, it has caused shifts in forest structure and significant resources 

have been spent in management and control efforts that continue today (http://www.fs.fed.us/

ne/morgantown/4557/gmoth/). The smaller European elm bark beetle, Scolytus multistriatus, 

was introduced into North America in the early 1900s (Chapman 1910). Coupled with Dutch 

elm disease, for which the insect is the primary vector (Readio 1935), it has caused the devastation of native elms across North America (Bloomfield 1979). The Asian longhorned beetle, 

Anoplophora glabripennis, and the emerald ash borer, Agrilus planipennis, are more recent 

introductions (Nowak and others 2001; Poland and McCullough 2006). The former has killed 

numerous maples, elms, and willows in New York and Chicago and the latter is destroying 

extensive areas of ash in Michigan and across the Midwest. The Sirex woodwasp, Sirex noctilio, which attacks several species of pines, was detected in 2004 (Hoebeke and others 2005) 

and is considered established in parts of Pennsylvania, New York, and Michigan (http://www.

invasivespeciesinfo.gov/animals/sirexwasp.shtml). In the Rocky Mountain Region, the first 

detection of the banded elm bark beetle, Scolytus schevyrewi, occurred in 2003 (Negrón and 

others 2005). The insect utilizes various species of elms as hosts and tree mortality has been 

reported particularly in conjunction with drought. A number of other exotic bark beetles are 

established in North America (Wood 1982). Although none have been agents of extensive 

mortality, their ecological implications are not well known. Some other recent introductions 

to North America include the pine shoot beetle, Tomicus piniperda; the redhaired pine bark 

beetle, Hylurgus ligniperda; and the Mediterranean pine engraver, Orthotomicus erosus (Lee 

and others 2010). The mountain pine beetle, Dendroctonus ponderosae, a native disturbance 

agent in pine forests of western North America, is currently expanding its range into new areas 

of British Columbia and Alberta (Carroll and others 2004). Although there is evidence of historical mountain pine beetle outbreaks in high elevation five needle pine forests (Perkins and 

Roberts 2003), current trends in beetle-caused tree mortality appear unprecedented. Increasing 

temperature associated with climate change as it directly influences the insect is one important 

factor in mountain pine beetle range expansion and shifts in outbreak dynamics (Carroll and 

others 2004). Due to their extreme sensitivity to temperature, all forest insects will be directly 

affected by temperature increases. Moreover, climate change affects on forest insects may 

also manifest indirectly through affects to host trees. In addition to predicted changes in the 

geographic distribution of many tree species, climate change will also affect tree physiology 

and thus interactions with their herbivore predators (Mattson 1980; Zvereva and Kozlov 2006; 

McKenney and others 2007). Therefore, in a changing climate, many forest insects currently 

considered native may soon become invasive as their habitat changes.

Building a successful invasive species research program in entomology at the Rocky 

Mountain Research Station needs to be linked to the National Strategy and Implementation 

Plan for Invasive Species Management and must address the four national program elements:

(1) Prevention. There is some understanding of the major exotic species of concern that could 

impact our western forests. Pathway and risk assessments, such as the Exotic Forest Pest 

Information System for North America (http://spfnic.fs.fed.us/exfor/), have been initiated to 

identify priority insects. International commercial activities and unregulated transport of firewood are primary pathways for the movement of invasive insects; therefore, it is imperative to 

design educational programs that build public awareness of the problem. Climate change will 

affect host response, the likelihood of establishment of invasive insects, and the range expansion of native insects into new areas. The examination of how climate change may influence 

these processes is of utmost importance. At RMRS, studies are underway to examine how 

climate change will influence range expansion of mountain pine beetle and other bark beetles.
28 USDA Forest Service RMRS-GTR-265. 2011.

(2) Early Detection and Rapid Response. Between 1985 and 2000 there were almost 7,000 

records of interception of exotic bark beetles by USDA APHIS (Haack 2001). These numbers 

will increase as worldwide commerce continues to expand. Tools in support of programs 

aimed at the early detection of insects such as the identification of pheromones or attractants 

for detection and monitoring will streamline and increase the efficiency of these programs. At 

RMRS, in cooperation with the PSW Research Station, we have been studying the chemical 

ecology of the banded elm bark beetle (Negrón and others 2005; Lee and others 2002). We 

continue to witness a precipitous decline in taxonomic expertise in wood-boring insects, and 

the available scientists are unable to address the demand for this service. This raises the need 

for developing taxonomic tools that can be used by personnel of agencies responsible for 

detection at ports of entry. In cooperation with APHIS, Colorado State University, and Forest 

Health, the RMRS has developed an image-based key to the Bark Beetle Genera of North 

America (Mercado 2010). Also in Cooperation with Colorado State University, at RMRS we 

are finalizing a “Revision of the Species in the Genus Hylurgops LeConte,” which includes 

potentially important exotic species (Mercado, unpublished data).

(3) Control and Management. Available control strategies against established invasive 

insects are laborious, expensive, unsustainable, and of unknown efficacy. Streamlined approaches need to be developed to mitigate potential impacts, and just as importantly treatment 

success needs to be evaluated. As not every infestation can be targeted for control, decision 

support systems are needed to identify proper circumstances in which active management 

is warranted. Exploration of biological control approaches for managing invasive insects 

needs to continue. At RMRS, the work on range expansion of bark beetles will partly address 

the identification of new areas where management approaches may be needed. Scientists at 

RMRS also have the expertise to develop biological control programs targeted at potentially 

damaging exotic insects.

(4) Rehabilitation and Restoration. The identification of native host plant material resistant to invasive insects will be needed for use in re-vegetation programs of affected areas. 

In cases that this is not possible, identifying alternative plants and trees that could be used to 

restore affected ecosystems while minimizing ecological impacts will also be needed. Finally, 

we will need to develop long-term cultural control approaches for restoring affected areas. 

Implementation of these programs should be followed by an assessment of their efficacy.

Literature Cited

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Carroll, A.; Taylor, S.; Régnière, J.; Safranyik, L. 2004. Effects of climate change on range 

expansion by the mountain pine beetle in British Columbia. In: Shore, T.L.; Brooks, J.E.; 

Stone, J.E., eds. Mountain Pine Beetle Symposium: Challenges and Solutions. Victoria, 

British Columbia: Inf. Rep. BC-X-399. Victoria, British Columbia: Canadian Forest 

Service: 223-232.

Chapman, J.W. 1910. The introduction of a European scolytid (The smaller elm bark beetle, 

Scolytus multistriatus Marsh) into Massachusetts. Psyche 17:63-68.

Forbush, E.H.; Fernald, C.H. 1896. The Gypsy Moth. Porthetria dispar (Linn.). A report of 

the work of destroying the insect in the Commonwealth of Massachusetts, together with 

an account of its history and habits both in Massachusetts and Europe. Boston: Wright & 

Potter Printing Co.

Haack, R.A. 2001. Intercepted Scolytidae (Coleoptera) at U.S. ports of entry: 1985-2000. 

Integrated Pest Management Review 6:253-282.

Hoebeke, E.R.; Haugen, D.A.; Haack, R.A. 2005. Sirex noctilio: Discovery of a Palearctic 

siricid woodwasp in New York. Newsletter of the Michigan Entomological Society 

50:24-25.

Lee, J.C.; Hamud, S.M.; Negrón, J.F.; Witcosky, J.J.; Seybold, S.J. 2010. Semiochemicalmediated flight strategies of two invasive elm bark beetles: A potential factor in competitive 

displacement. Environmental Entomology 39:642-652.
USDA Forest Service RMRS-GTR-265. 2011. 29

Mattson, W.J. 1980. Herbivory in relation to plant nitrogen content. Annual Review of Ecology 

and Systematics 11:119-161.

McDonald, G.; Zambino, P.; Sniezko, R. 2004. Breeding rust-resistant five-needle pines in the 

western United States: Lessons from the past and a look to the future. In: Sniezko, R.A.; 

Samman, S.; Schlarbaum, S.E.; Kriebel, H.B., eds. Breeding and genetic resources of fiveneedle pines: Growth, adaptability, and pest resistance. Proc. RMRS-P-32. Fort Collins, 

CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 

259 p.

McKenney, D.W.; Pedlar, J.H.; Lawrence, K.; Campbell, K.; Hutchinson, M.F. 2007. Potential 

impacts of climate change on the distribution of North American trees. BioScience 

57:939-948.

Mercado, J.M. 2010. Bark beetle genera of North America. 2010. Online. Available: www.

lucidcentral.org. [Accessed: July 20, 2010.]

Negrón, J.F.; Witcosky, J.J.; Cain, R.J.; LaBonte, J.R.; Duerr, D.A., II; Mcelwey, S.J.; Lee, 

J.C.; Seybold, S.J. 2005. The banded elm bark beetle: A new threat to elms in North 

America. American Entomologist 51:84-94.

Nowak, D.J.; Pasek, J.E.; Sequeira, R.A.; Crane, D.E.; Mastro, V.C. 2001. Potential effect of 

Anoplophora glabripennis (Coleoptera: Cerambycidae) on urban trees in the United States. 

Journal of Economic Entomology 94:116-122.

Perkins, D.L.; Roberts, D.W. 2003. Predictive models of whitebark pine mortality from 

mountain pine beetle. Forest Ecology Management 174:495-510.

Poland, T.M.; McCullough, D.G. 2006. Emerald ash borer: Invasion of the urban forest and 

the threat to North America’s ash resource. Journal of Forestry 104:118-124.

Readio, P.A. 1935. The entomological phases of Dutch elm disease. Journal Economic 

Entomology 28:341-353.

Wood, S.L. 1982. The bark and ambrosia beetles of North and Central America (Coleoptera: 

Scolytidae), a taxonomic monograph. Great Basin Naturalist Memoirs, No. 6. 1359 p.

Zvereva, E.L.; Kozlov, M.V. 2006. Consequences of simultaneous elevation of carbon dioxide 

and temperature for plant-herbivore interactions: A metaanalysis. Global Change Biology 

12:27-41.
30 USDA Forest Service RMRS-GTR-265. 2011.

IV. Aquatics

By Michael K. Young

The problem of invasive aquatic species has long been recognized by scientists at the 

Rocky Mountain Research Station. Fausch and others (2006, 2009) recently overviewed this 

issue. A point that often distinguishes nonnative aquatic species from nonnatives in other environments is that the presence of some species is frequently prized by managers and the public. 

For example, many sport fisheries in the Rocky Mountains are based on angling for nonnative 

brook trout, brown trout, or rainbow trout, which have been implicated in the loss of native 

cutthroat trout and bull trout (Dunham and others 2002; Rieman and others 2006). In some 

cases, “native” cutthroat trout are regularly introduced into previously fishless waters where 

they may displace other aquatic species, such as some native amphibians (Dunham and others 

2004). The sometimes conflicting societal desires for protecting native species and providing 

recreational opportunities presents managers with many challenges, which are intensified by 

the increasing urbanization of the Rocky Mountains, growing demands for water, and altered 

precipitation and streamflow patterns driven by climate change. Thus, prioritizing where to 

conduct native species conservation—based on species habitat requirements, the ecological, 

evolutionary, and social value of particular populations, and habitat distribution and dynamics—represents a knowledge gap that needs to be addressed, for example with the group of 

decision models applied to systematic conservation planning (Peterson and others 2008).

Furthermore, much of the research on aquatic invasive species has focused on nonnative 

salmonid fishes. Little work has been done by RMRS on invasive algae. Given climate change 

forecasts for reduced late summer stream flows and warming temperatures, future waves of 

nonnative species invasions are likely to include coolwater and warmwater species of fishes 

that arrive via connected river networks or human-assisted transport e.g., smallmouth bass 

throughout the Pacific Northwest (Sharma and others 2009). Moreover, large numbers of other kinds of invasive aquatic organisms—crayfish, mussels, amphibians, macroinvertebrates, 

and nonindigenous pathogens—are already present or likely to appear. Little work in any of 

the four core areas has been done with respect to these taxa, although this may become a management and research priority in the near future.

(1) Prevention. The prevention and prediction of invasions of nonnative aquatic species are 

critical concerns of managers. Rocky Mountain Research Station scientists have contributed 

to providing information that addresses aspects of prevention and prediction. For example, 

because rivers and streams are linear networks, strategically placed barriers to fish movements 

can create upstream refuges for native fish. A critical issue is how the size and characteristics of the upstream network are related to long-term persistence of native fish populations 

(Peterson and others ongoing), which dictates where barriers to nonnative fish migrations 

should be placed. Yet perhaps as or more important to persistence of native fish populations 

is the retention of connectivity between different populations. This connectivity might permit demographic support for marginally productive populations from stronger ones or the 

re-founding of populations lost after environmental catastrophes. Hence, the management 

problem is not just where to build a barrier to fish movement, but whether to build one at 

all. To that end, researchers have constructed a decision model that quantifies the tradeoffs 

between the invasion of a nonnative species, brook trout, and the retention of migratory pathways for a native species, west slope cutthroat trout (Peterson and others 2008). Constructing 

similar models for other sets of native and nonnative species, and conducting the field research supporting this work, would assist managers in other parts of the Rocky Mountains.

Less work has been directed at predicting which nonnative aquatic species are likely to appear. This is in part because many nonnative sport fishes have already been widely distributed 

by management agencies and have access to many waters throughout the Rocky Mountains. 

Moreover, although stocking of nonnative species in waters containing native species has 

greatly declined, illegal transfers by anglers have increased in recent decades. Thus the suite 

of nonnative fishes likely to appear is well known, but whether they will successfully invade 

new or accessible waters is not. Recent and ongoing research (Rich and others 2003; Rieman 

and others 2006; Benjamin and others 2007; Wenger and others ongoing; Neville and others 
USDA Forest Service RMRS-GTR-265. 2011. 31

ongoing) is identifying how environmental characteristics (e.g., hydrologic regime, stream 

valley configuration, water temperature, land management, natural disturbance, and climate 

change) influence invasion success by brook trout. Similar work needs to be undertaken for 

other species.

(2) Early Detection and Rapid Response. A focus of aquatic species research in RMRS 

has been quantifying detectability of fish species during sampling (Peterson and others 2004, 

2005; Young and Schmetterling 2004; Rosenberger and Dunham 2005; Schmetterling and 

Young ongoing; Thurow and others ongoing). The objective of this work was to improve the 

reliability of electrofishing-based estimates of the presence or abundance of certain species of 

salmonid fishes, primarily federally threatened bull trout. Tailoring this work to address the 

presence or abundance of nonnative species such as brook trout, brown trout, or rainbow trout 

would be relatively straightforward but has yet to be done.

There remain two key problems with respect to early detection of nonnative fish species. 

First, using electrofishing-based sampling to establish presence tends to be labor-intensive and 

expensive, making it unlikely that large numbers of waters will be surveyed annually. Thus, 

early detection of invasions of nonnative fishes is unlikely unless particular sites are already 

being monitored for other purposes. Second, hybridization of native species with nonnative 

ones, such as bull trout with brook trout or westslope cutthroat trout with rainbow trout, is 

a great concern for managers. The loss of genetic integrity of populations of native species 

may be driven by the movements of hybridized individuals (Hitt and others 2003) that are 

often difficult to recognize during field sampling. Presently, genetic assessments of these fish 

are neither timely nor inexpensive enough to permit their use for monitoring the status of 

invasions of hybridized fish. Hence, a key management need is a cost-effective, broad-scale 

assessment of fish community composition and genetic status.

(3) Control and Management. Research on the control and management of nonnative aquatic species was mentioned in conjunction with prevention, although relatively little work has 

directly addressed eradication or suppression of nonnative species. An exception has been the 

preliminary study on the effectiveness of pheromone-based removals of brook trout (Young 

and others 2003; Lamansky and others 2009). This research is modeled after insect control 

practices that rely on pheromone traps or lures. Refinement of this approach for brook trout 

and its extension to other species, as well as work on mechanical control of other nonnative 

fishes (Rinne and others ongoing) would fill a large void for managers, who at present have 

few tools for the effective control of nonnative fishes.

(4) Rehabilitation and Restoration. Rehabilitating or restoring populations of native species 

following nonnative species removal has not been a focus of research or a widely expressed 

management need because populations have been reestablished following long-used fish 

stocking protocols. Nevertheless, research in this area may be required if restoring population characteristics such as genetic diversity or life history complexity become restoration 

targets. A potentially controversial problem that is largely unstudied involves habitat restoration, much of which is completed under the guise of improving habitat for fish species. Yet 

it is unknown whether such activities favor native or nonnative species. Similar work on the 

effects of natural disturbance, e.g., severe fire, debris torrents, and floods, indicated that native 

fishes responded more favorably following disturbance than did nonnative fishes (Sestrich 

and others in prep; Rinne and others in prep), suggesting that more stable, “restored” habitats 

may prove detrimental to native fishes when nonnative fishes are present (Dunham and others 2003; Rinne and others in prep). More comprehensive research on community responses 

to natural disturbance and human manipulation of freshwater habitats is necessary to satisfy 

information needs of managers.

Literature Cited

Dunham, J.B.; Adams, S.B.; Schroeter, R.E.; Novinger, D.C. 2002. Alien invasions in aquatic 

ecosystems: Toward an understanding of brook trout invasions and potential impacts on 

inland cutthroat trout in western North America. Reviews in Fish Biology and Fisheries 

12:373-391.
32 USDA Forest Service RMRS-GTR-265. 2011.

Fausch, K.D.; Rieman, B.E.; Dunham, J.B.; Young, M.K.; Peterson, D.P. 2009. Invasion versus 

isolation: Trade-offs in managing native salmonids with barriers to upstream movement. 

Conservation Biology 23:859-870.

Lamansky, J.A., Jr.; Keeley, E.R.; Young, M.K.; Meyer, K.A. 2009. The use of hoop nets 

seeded with mature brook trout to capture conspecifics. North American Journal of 

Fisheries Management 29:10-17.

Peterson, D.P.; Rieman, B.E.; Dunham, J.B.; Fausch, K.D.; Young, M.K. 2008. Analysis of 

tradeoffs between threats of invasion by nonnative brook trout (Salvelinus fontinalis) and 

intentional isolation for native westslope cutthroat trout (Oncorhynchus clarkii lewisi). 

Canadian Journal of Fisheries and Aquatic Sciences 65:557-573.

Sharma, S.; Herborg, L.-M.; Therriault, T.W. 2009. Predicting introduction, establishment and 

potential impacts of smallmouth bass. Diversity and Distributions 15:831-840.
USDA Forest Service RMRS-GTR-265. 2011. 33

V. Terrestrial vertebrates

By Dean Pearson and Deborah Finch

Within the Interior West, terrestrial vertebrates do not represent a large number of invasive 

species relative to invasive weeds, aquatic vertebrates, and invertebrates. However, several 

invasive terrestrial vertebrate species do cause substantial economic and ecological damage in 

the U.S. and in this region (Pimental 2000, 2007; Bergman and others 2002; Finch and others 

2010). About 28 species of mammals have been introduced into the U.S.; these include dogs 

(Canis familiaris), cats (Felis catus), horses (Equus caballus), burros (E. asinus), cattle (Bos 

taurus), sheep (Ovis aries), pigs (Sus scrofa), goats (Capra hirus), deer (Cervus spp.), rats 

and other small mammals (Drost and Fellers 1995; Layne 1997). In the Interior West, released 

burros and horses graze heavily on native vegetation, facilitating invasion by exotic annuals. 

Many invasive mammal species in the Interior West have escaped or were released into the 

wild; some have become pests by preying on native animals, by spreading diseases to native 

animals, by grazing on crops and native vegetation, by increasing soil erosion, or by damaging 

structures (Pimental 2007; Finch and others 2010).

Approximately 100 of the 1,000 bird species in the United States are exotic (Temple 1992; 

EPA 2005). Of the introduced bird species, only 5% are considered beneficial whereas the 

majority are considered pests. The most serious pest bird in the Interior West and throughout 

the United States is the exotic common pigeon (Columba livia), which inhabits most cities 

(Robbins 1995). Pigeons defecate on buildings, streets, sidewalks, statues, and cars; and they 

feed on grain. Pigeons act as reservoirs and vectors for human and livestock diseases, such as 

parrot fever, ornithosis, histoplasmosis, and encephalitis (Weber 1979; Long 1981). Another 

very recently introduced and expanding dove is the Eurasian Collared Dove (Streptopelia 

decaocto). This species has invaded North America at a record pace. In 1982, it arrived in 

Florida and has since rapidly spread to places as far as Montana and Alaska. The invasiveness 

of this species has raised concern over its potential impacts on native species, particularly 

related species such as the Mourning Dove, but currently very little is known about its impacts on natives. Some birds damage crops. Exotic European starlings (Sturnus vulgaris) are 

common throughout the Interior West where they cost millions in reduced grain production 

and displace native birds. Another exotic urban bird, the house sparrow (Passer domesticus) 

was introduced in 1853 to control the canker worm, but by 1900, it had become a pest. House 

sparrows damage plants in residential and public areas, consume wheat, corn, and fruit, and 

harass and displace native birds (Pimental 2000).

About 53 amphibians and reptile species have been introduced into the United States 

(Pimental 2000). Perhaps the most significant amphibian pest in the Interior West is the 

bullfrog (Rana catesbeiana). Originally native to eastern North America, the bullfrog has 

been introduced widely in the West. Bullfrogs are broadly generalist consumers implicated 

in the decline of native ranid frogs and the Mexican gartersnake (Thamnophis eques) (Rosen 

and Schwalbe 1995). Bullfrogs may expose native amphibians to increased levels of risk by 

spreading the chytrid fungus (Batrachochytrium dendrobatidis). Bullfrogs are suspected to be 

significant predators of hatchling and juvenile western pond turtles. Some invasive terrestrial 

animal species are exotic like European wild pigs, nutrias, rock doves, and European starlings, 

but many are native species like brown-headed cowbirds, common ravens, and red foxes 

that have expanded into new habitats. Anthropogenic factors contributing to native species 

becoming invasive include: direct human introductions into new regions (bull frogs, eastern 

fox squirrels), habitat alterations (coyotes, brown-headed cowbirds), food subsidies (common 

ravens), facilitation by introduced exotics (brown-headed cowbirds), artificial habitats such 

as telephone poles used for nesting (common ravens), and suppression of large predators that 

may facilitate range expansions (red foxes, raccoons). At present, there are relatively few 

studies within RMRS examining these issues as they relate to terrestrial vertebrate invaders.

(1) Prevention. Europe is the main source of North American exotic vertebrates. Recent studies suggest that new introductions of exotic mammals and birds from Europe to North America 

peaked in the mid 19th century and have since declined to very low levels (Jeschke and Strayer 

2005). This suggests that most such introductions have already occurred or that contemporary 
34 USDA Forest Service RMRS-GTR-265. 2011.

laws are reasonably effective at preventing new exotic mammal and bird introductions. 

However, within the Rocky Mountain Region, certain exotic and native North American invaders are still expanding into new locations, e.g., Eurasian collared doves, European wild 

boars, bull frogs, common ravens, and brown-headed cowbirds. Research can contribute to 

addressing this problem by developing new understanding of the factors facilitating expansion 

of these invaders (Finch and others 2010). RMRS Scientist Deborah Finch led the recovery 

team for the southwestern willow flycatcher, a species often parasitized by cowbirds. The 

recovery plan included steps for preventing cowbird parasitism. Past RMRS research has 

documented the link between anthropogenic disturbance and brown-headed cowbird invasion 

(Tewksbury and others 1999). Current research is underway to determine the habitat and landscape factors influencing the presence and distribution of cowbirds, their hosts, host selection, 

and host reproductive success (Finch ongoing). However, current RMRS research examining 

the potential range expansion of other animal invaders is limited or absent.

(2) Early Detection and Rapid Response. Given the continued expansion of extant invaders, 

such as bull frogs and Eurasian Collared Doves, into new locations, development of methods 

to monitor for nascent foci of vertebrate invaders and rapidly address them is warranted. Past 

and current RMRS research has clarified the role of habitat in influencing where brown-headed cowbirds are present or absent and where hosts are not affected or are severely affected in 

southwestern river systems (Finch 1982, 1983; Finch and Stoleson 2000; Schweitzer and others 1998; Brodhead and others 2007). Other invasive species research in this area is lacking, 

however, but is justified based on increasing rates of new introductions of invasive species, 

including invasive vertebrates (Finch and others 2010). Climate change is likely to influence 

the movement or spread of some invasive vertebrates. Finch and others (2010) advocate research to detect migration of invasives into new areas as habitats shift in response to changing 

climates.

(3) Control and Management. Effective management of invasive vertebrates requires 

(1) understanding the biological and ecological factors that determine invader success so management can target those causal factors for control and (2) identifying the invader’s impacts 

on native species to ensure that management actions effectively mitigate invader impacts. 

Past RMRS research has documented how variation in managed habitats impacts the distribution of brown-headed cowbirds and their hosts and influences which hosts are selected to be 

parasitized (Finch 1982, 1983; Finch and Stoleson 2000; Schweitzer and others 1996, 1998; 

Brodhead and others 2007). Such information is valuable in designing habitat management 

approaches that will limit cowbird brood parasitism. Current RMRS research is evaluating 

the impacts of brown-headed cowbirds on native birds to determine whether host species may 

need active intervention (Finch, ongoing). Other collaborative studies are evaluating factors 

that determine brown-headed cowbird success (e.g., Tewksbury and others 2006). Research is 

needed to determine mechanisms for invader success and quantify invader impacts for other 

species, such as bull frogs, that have increasing impacts in the Interior West. In addition, studies of invasive urban species are needed to determine the extent they will need to be managed 

in rapidly expanding urban environments such as Phoenix, Denver, and Las Vegas.

(4) Rehabilitation and Restoration. Rehabilitating and restoring native communities impacted by invasive terrestrial vertebrates requires understanding the invader’s impacts and the 

capacities of native species to recover from these impacts once the invader has been effectively controlled or removed. RMRS research in this area is currently limited to studies evaluating 

whether cowbird abundance and impacts on hosts increase or decrease after restoration and 

whether restoration for other purposes (e.g., fuel reduction) has benefits in controlling cowbird parasitism (Finch ongoing). Additional research is needed for other invasive terrestrial 

animal species, especially in habitats where restoration is beneficial in controlling damage 

and also to determine whether restoration for other purposes has incidental effects, positive or 

negative, on invasive vertebrates.
USDA Forest Service RMRS-GTR-265. 2011. 35

Literature Cited

Bergman, D.; Chandler, M.; Locklear, A. 2002. The economic impact of invasive species 

to Wildlife Services’ cooperators. In: Clark, L.; Hone, J.; Shivik, J.A.; Watkins, 

R.A.; VerCauteren, K.C.; Yoder, J.K., eds. Human conflicts with wildlife: economic 

considerations. Proceedings of the Third NWRC Special Symposium. National Wildlife 

Research Center, Fort Collins, CO.

Brodhead, Katherine M.; Stoleson, Scott H.; Finch, Deborah M. 2007. Southwestern willow 

flycatchers (Empidonax traillii extimus) in a grazed landscape: factors influencing brood 

parasitism. The Auk 124(4):1213-1228.

Drost, C.A.; Fellers, G.M. 1995. Non-native animals on public lands. In: LaRoe, E.T.; Farris, 

G.S.; Puckett, C.E.; Doran, P.D.; Mac, M.J., eds. Our living resources: A report to the 

nation on the distribution, abundance, and health of U.S. plants, animals and ecosystems. 

Washington, DC: U.S. Department of the Interior, National Biological Service.

Environmental Protection Agency [EPA]. 2005. Final list of bird species to which the 

Migratory Bird Treaty Act does not apply. Federal Register March 15, 2005. 70:49.

Finch, D.M. 1982. Rejection of cowbird eggs by crissal thrashers. Auk 99:719-724.

Finch, D.M. 1983. Brood parasitism of the Abert’s towhee: Timing, frequency, and effects. 

Condor 85:355-359.

Finch, D.M.; Stoleson, S.H., eds. 2000. Status, ecology, and conservation of the southwestern 

willow flycatcher. Gen. Tech. Rep. RMRS-GTR-60. Ogden, UT: U.S. Department of 

Agriculture, Forest Service, Rocky Mountain Research Station. 131 p.

Finch, Deborah M.; Pearson, Dean; Wunderle, Joseph; Arendt, Wayne. 2010. Terrestrial 

animals as invaders and as species at risk from invasions. In: Dix, M.E.; Britton, K., eds. A 

dynamic invasive species research vision: Opportunities and priorities 2009-29. Gen. Tech. 

Rep. WO-79. Washington, DC: U.S. Department of Agriculture, Forest Service Research 

and Development: 43-54.

Jeschke, J.M.; Strayer, D.L. 2005. Invasion success of vertebrates in Europe and North 

America. Proceedings of the National Academy Science USA 102:7198-7202.

Layne, J.N. 1997. Non-indigenous mammals. In: Simberloff, D.; Schmitz, D.C.; Brown, T.C., 

eds. Strangers in Paradise. Washington, DC: Island Press: 157-186.

Long, J.L. 1981. Introduced birds of the world: The worldwide history, distribution, and 

influence of birds introduced to new environments. New York: Universe Books.

Ortega, Y.K.; Pearson, D.E.; Waller, L.P.; Sturdevant, N.J.; Maron, J.M. In press. Populationlevel compensation impedes biological control of an invasive forb and indirect release of 

a native grass. Ecology

Pimental, D.; Lach, L.; Zuniga, R.; Morrison, D. 2000. Environmental and economic costs of 

nonindigenous species in the United States. BioScience 53:53-65.

Pimental, David. 2007. Environmental and economic costs of vertebrate species invasions 

into the United States. Lincoln, NE: U.S. Department of Agriculture, National Wildlife 

Research Center Symposia, Managing Vertebrate Invasive Species. University of Nebraska.

Robbins, C.S. 1995. Non-native birds. In: LaRoe, E.T.; Farris, G.S.; Puckett, C.E.; Doran, P.D.; 

Mac, M.J., eds. Our living resources: A report to the nation on the distribution, abundance, 

and health of U.S. plants, animals and ecosystems. Washington, DC: U.S. Department of 

the Interior, National Biological Service: 437-440.

Rosen, P.C.; Schwalbe, C.R. 1995. Bullfrogs: Introduced predators in southwestern wetlands. 

In: LaRoe, E.T.; Farris, G.S.; Puckett, C.E.; Doran, P.D.; Mac, M.J., eds. Our living 

resources: A report to the nation on the distribution, abundance, and health of U.S. plants, 

animals, and ecosystems. Washington, DC: U.S. Department of the Interior, National 

Biological Service: 452-454.
36 USDA Forest Service RMRS-GTR-265. 2011.

Schweitzer, S.H.; Finch, D.M.; Leslie, D.M., Jr. 1998. The brown-headed cowbird and its 

riparian-dependent hosts in New Mexico. Gen. Tech. Rep. RMRS-GTR-1. Fort Collins, 

CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 

23 p.

Schweitzer, S.H.; Finch, D.M.; Leslie, David M., Jr. 1996. Reducing impacts of brood 

parasitism by brown-headed cowbirds on riparian-nesting migratory songbirds. In: Desired 

future conditions for Southwestern riparian ecosystems: Bringing interests and concerns 

together. September 18-22, 1995; Albuquerque, NM. Gen. Tech. Rep. RM-272: Fort 

Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and 

Range Experiment Station: 267-276.

Temple, S.A. 1992. Exotic birds, a growing problem with no easy solution. The Auk 

109:395-397.

Tewksbury, J.J.; Gardner, L.; Gardner, S.; Lloyd, J.D.; Saab, V.; Martin, T.E. 2006. Tests 

of landscape influence: Nest predation and brood parasitism in fragmented ecosystems. 

Ecology 87:759-768.

Tewksbury, J.J.; Martin, T.E.; Hejl, S.J.; Redman, T.S.; Wheeler, F.J. 1999. Cowbirds in a 

western valley: Effects of landscape structure, vegetation, and host density. Studies in 

Avian Biology 18:23-33.

Weber, W.J. 1979. Health hazards from pigeons, starlings and English sparrows: Diseases and 

parasites associated with pigeons, starlings, and English sparrows which affect domestic 

animals. Fresno, CA: Thomson Publications.
USDA Forest Service RMRS-GTR-265. 2011. 37

RMRS Invasive Species Research 

Priorities and Future Directions

Presently, RMRS invasives research is conducted independent of other FS research stations because it focuses on issues and to some extent species largely unique to the region. 

Currently, 13.4 scientists (or scientist years) from six of the seven RMRS Programs (Air, 

Water, and Aquatic Environment; Fire, Fuel, and Smoke; Forest and Woodland Ecosystems; 

Grassland, Shrubland, and Desert Ecosystems; Human Dimensions; and Wildlife and 

Terrestrial Ecosystems) are conducting research on invasive species (Butler and others 2009). 

Since there is no RMRS program explicitly assigned to address invasive species issues, invasive species research in the Station has historically been ad-hoc with little coordination or 

communication across the Station regarding invasives research and with individual scientists 

struggling to obtain research support. To address this problem, and as a synergistic outcome 

of the Albuquerque Workshop that resulted in the current document, a group of scientists dedicated to invasive species research organized into the RMRS Invasive Species Working Group 

(ISWG). The ISWG is a cross-program multidisciplinary team formed to better integrate 

invasive species research across the Station with an emphasis on communicating research 

products to our customers. To date, the ISWG has developed two synthesis papers to summarize current RMRS research activities on invasive species: Butler and others (2009) and the 

current document. It has also established a website (http://www.rmrs.nau.edu/invasive_species) to disseminate research information and foster technology transfer, and it publishes a 

periodic newsletter (current and previous issues are located on the website) to familiarize 

and update customers with RMRS activities on invasive species and provide customers with 

contact information for feedback. It is hoped this collaborative effort will allow the Station to 

improve invasives management consistent with recommendations from the previous National 

Invasive Species Strategic Program Area Review. The establishment of this working group 

also provides a potential mechanism for building collaborations with other state and national 

invasive species efforts.

The organization of the RMRS ISWG has proven extremely valuable to date. It has not only 

greatly improved outreach efforts by the Station—it also holds the potential to facilitate more 

coordinated efforts on invasive species research and improve future research. For instance, 

the external review of the FS R&D invasive species research strategy (the National Invasive 

Species Strategic Program Area Review) recommended that FS expand its proactive research 

role (Prediction & Prevention, Detection & Rapid Response), while clearly maintaining its 

reactive research role (Management & Mitigation, Restoration & Rehabilitation). In response, 

the FS R&D research strategy emphasizes the following four overarching research priorities: 

(1) Quantifying invasive species biology, ecology, interaction, and impacts; (2) Predicting and 

prioritizing invasive species; (3) Identifying and detecting invasive species; and (4) Managing 

invasive species and altered systems. The RMRS invasives research has recognized strengths 

in overarching research priorities (1) and (4) and RMRS has recently produced significant 

advances in research priority areas (2) and (3). Proactive research is critical because it is much 

more economically efficient and logistically feasible. For this reason, these research areas 

warrant further expansion, and significant efforts are needed for education, training, and outreach. The ISWG recognizes these priorities as appropriate future directions and is committed 

to advancing invasive research and outreach to meet these objectives.

Literature Cited

Butler, J.; Pearson, D.; Kim, M.-S., tech. eds. 2009. Invasive species working group: Research 

summary and expertise directory. Fort Collins, CO: U.S. Department of Agriculture, Forest 

Service, Rocky Mountain Research Station. 20 p. Available: http://www.treesearch.fs.fed.

us/pubs/34540.

Also available online at http://www.fs.fed.us/rm/pubs/rmrs_gtr265.pdf.
Federal Recycling Program Printed on Recycled Paper

The Rocky Mountain Research Station develops scientific information 

and technology to improve management, protection, and use of the 

forests and rangelands. Research is designed to meet the needs of 

the National Forest managers, Federal and State agencies, public and 

private organizations, academic institutions, industry, and individuals. 

Studies accelerate solutions to problems involving ecosystems, range, 

forests, water, recreation, fire, resource inventory, land reclamation, 

community sustainability, forest engineering technology, multiple use 

economics, wildlife and fish habitat, and forest insects and diseases. 

Studies are conducted cooperatively, and applications may be found 

worldwide.

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