Forest Resources 

of Isle Royale 

National Park 2010

Resource Bulletin

NRS-73

United States 

Department of Agriculture

Forest 

Service
Abstract

This publication provides a baseline overview of forest resources for Isle Royale National Park (Isle Royale) 

using data from the Forest Inventory and Analysis (FIA) Program of the U.S. Department of Agriculture, Forest 

Service. The availability of permanent FIA plots allows for the first-ever comparison of Isle Royale’s forest 

conditions (2006-2010) to reserved and non-reserved forest land within Michigan’s Laurentian Mixed ForestEcoprovince 212. Isle Royale’s prominent forest types, structure, and species composition reflect human 

and natural disturbances. FIA data suggest Isle Royale’s species-specific stand-size stocking, growth and 

mortality rates, tree densities, volume, live biomass, and aboveground and belowground carbon reflect a unique 

ecosystem due to a combination of factors: remote location in Lake Superior, disturbance legacy related to 

natural processes and mining exploration, absence of forest management for over eight decades, and 50 years 

of complex interactions between moose/wolf populations.

Acknowledgments

The authors would like to thank the many individuals who contributed both to the inventory and analysis of 

the forest resources of Isle Royale National Park and Michigan. The primary Isle Royale field crew and quality 

assurance staff of the 2010 inventory include Andrew Bird, Brady Boyce, Nathan Cochran, Ian Diffenderfer, 

Mike Downs, Ed Kloehn, Chris Lacosse, Steve Lorenz, Mark Majewsky, Jared Moilanen, Adam Morris, 

Charles Paulson, Greg Rekowski, Mick Reynolds, Sjana Schanning, Aimee Stephens, and Kris Williams. 

Data management personnel include Carol Alerich, James Blehm, Gary Brand, Mark Hatfield, Pat Miles, and 

Jay Solomakos. 

We would also like to thank the reviewers for their comments and suggestions. These were valuable 

for improving the clarity of using FIA data to describe and summarize the forest resources of Isle Royale 

National Park.

Published by: For additional copies:

U.S. FOREST SERVICE U.S. Forest Service

11 CAMPUS BLVD., SUITE 200 Publications Distribution

NEWTOWN SQUARE, PA 19073-3294 359 Main Road

Delaware, OH 43015-8640

January 2013 Fax: 740-368-0152

Visit our homepage at: http://www.nrs.fs.fed.us

Cover: Isle Royale shoreline. Photo by Bryan Murray, Michigan Technological University; used with permission.

Manuscript received for publication February 2012
Wilfred J. Previant, Linda M. Nagel, Scott A. Pugh, and Christopher W. Woodall

Contact author: 

Scott A. Pugh, spugh@fs.fed.us

906-482-6303 ext. 17

Wilfred J. Previant is a Ph.D. 

candidate in forest science 

at Michigan Technological 

University, Houghton, MI.

Linda M. Nagel is an associate 

professor at Michigan 

Technological University, 

Houghton, MI.

Scott A. Pugh is a forester with 

the Forest Inventory and Analysis 

(FIA) Program, Northern Research 

Station, Houghton, MI.

Christopher W. Woodall is a 

research forester with FIA, 

Northern Research Station, 

St. Paul, MN.

Forest Resources of Isle Royale 

National Park 2010

About the Authors

Contents

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

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Forest Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Forest Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Number of Trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Stocking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Biomass and Carbon . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Growth and Mortality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

Standing Dead Trees . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Isle Royale National Park FIA Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Isle Royale, Scoville Point. Photo by Karena Schmidt, Michigan Technological University; used with permission.
vi
1

INTRODUCTION

This publication provides an overview of the forest 

resources of Isle Royale National Park (Isle Royale). 

Population estimates are based upon 2010 inventory 

data from the Forest Inventory and Analysis (FIA) 

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

Service (USFS). To provide insights into Isle Royale’s 

ecological traits, traditional timber attributes (i.e., 

stocking, volume, and biomass) were incorporated 

with non-timber qualities (i.e., standing dead trees and 

carbon stocks). These findings, in turn, were compared 

to reserved and non-reserved forest land in Michigan’s 

Laurentian Mixed Forest-Ecoprovince 212. This resource 

bulletin is the first of its kind to investigate Isle Royale 

and is a result of the collaborative effort between 

Michigan Technological University and the USFS.

Introduction

Isle Royale aspen regeneration. Photo by Bryan Murray, Michigan Technological University; used with permission.

Isle Royale, aspen senescing with spruce and balsam fir understory. Photo by 

Auriel Fournier, Michigan Technological University; used with permission.

Isle Royale, paper birch decline. Photo by Bryan Murray, Michigan 

Technological University; used with permission.
2

BACKGROUND

Figure 1.—Ecoprovince 212- Laurentian Mixed Forest in Minnesota, Wisconsin, and Michigan. Inset of Isle Royale National Park depicts general FIA plot locations, 

Michigan, 2010.

FIA Plots on Isle Royale National Park 

FIA Plots 2010

Isle Royale National Park

0 10 Miles

Minnesota

Wisconsin

Michigan

Lake 

Michigan

Lake 

Superior

Ontario

0 225 Miles

Data Sources: Bailey’s Ecoregions 

and Subregions of the United States, 

Puerto Rico, and the U.S. Virgin Islands. 

U.S. Forest Service. 1994.

The Great Lake States

Isle Royale National Park

Ecoprovince 212

State Boundaries

Data Source: National Atlas of the 

United States. 2005.

Data Source: U.S. Forest Service. 2010.

Data Source: United States National 

Geological Survey. 1999.

Base Source: Michigan Geographic 

Data Library.

Projection: GCS - NAD83. Cartographer: Wilfred J. Previant, 

Michigan Technological University, 

January 2012.

Note: Depicted plot locations are approximate.
3

BACKGROUND

Background 

Isle Royale National Park is an archipelago in the 

northwest part of Lake Superior, juxtaposed between the 

northern edge of the temperate forest and the southern 

edge of the boreal forest (Rowe 1972). Part of Michigan’s 

Keweenaw County, Isle Royale encompasses more than 

450 islands, has a land base of about 230 square miles, 

and runs parallel to the shorelines of Minnesota and 

the province of Ontario, Canada. The main island is 

45 miles long and 9 miles wide; it is 14 miles from 

mainland Ontario, 16 miles from Grand Portage, MN, 

and 55 miles from Copper Harbor, MI (ESRI 2009). 

Elevation ranges from 602 to 1,362 feet above sea level 

(0 to 760 feet above Lake Superior); numerous inland 

lakes and bogs are located between the ridges orientated 

southwest-northeast (Albert 1995). Huber (1973) 

described the bedrock geology as uniform Precambrian 

volcanic lava flows with glacial deposits, kame moraines, 

and recessional moraines. Isle Royale has shallow soils in 

the northeast and deeper soils in the southwest. 

Wallace Lake watershed, located in the northeastern 

portion of Isle Royale, recorded an annual precipitation 

average of 29.9 inches and an annual daily temperature 

average of 37 °F for the years 1982-96 (Stottlemyer 

et al. 1998). Because the National Park Service (NPS) 

closes Isle Royale during the winter, we also attempted 

to find a suitable mainland proxy. The precipitation and 

temperature values are nearly identical to the nearby 

weather station in Thunder Bay, Ontario, for 1971-2000 

(http://climate.weatheroffice.gc.ca/).

Past Management 

The Isle Royale archipelago has not been notably 

disturbed by humans for the past 80 years, with little to 

no forest management practiced across the main island 

(Primmer 1938, Rakestraw 1965). However, the current 

forest diversity and structure of Isle Royale partially 

reflect the past disturbances of mining, fire, logging, and 

moose herbivory. 

In 1843-1900, Isle Royale was explored and mined for 

copper. Prospectors logged timber to support mining 

operations while also burning large areas of forest to 

expose the copper ore (Rakestraw 1965). The last large 

natural fires occurred in 1936 and 1948 in the central 

part of the main island and burned a combined 20 

percent of the main island (Janke et al. 1978). For 

the time period of 1931-1987, there were nearly 100 

documented lightning- and human-caused fires, but, 

with a few exceptions, each fire covered less than 1 acre 

(cf., Martin 1988; USDI 2004). 

Another influence on the current conditions of Isle 

Royale’s forests is herbivory. White-tailed deer (Odocoileus 

virginianus) were once introduced in 1912 by the 

Michigan State Conservation Commission, but were last 

recorded in the 1930s (Shiras 1935). For survey years of 

1962-2009, the mean beaver (Castor canadensis) colony 

abundance was 149.9 (Romanski 2010), influencing 

vegetation dynamics of deciduous species associated with 

aquatic systems (Moen et al. 1990). The main herbivore 

on Isle Royale is moose (Alces alces), which arrived on Isle 

Royale in the early 1900s (Hickie 1936, Murie 1934). 

Wolves (Canis lupus) arrived in the 1940s and the resulting 

research into the dynamics of predator/prey populations 

made Isle Royale internationally famous (Peterson 1995). 

Within the past 50 years, the moose population has 

fluctuated between about 500 and 2,000 animals, and 

most Isle Royale vegetative investigations have focused 

on these changes and the resulting browsing pressure 

(http://www.isleroyalewolf.org). Research suggests that 

moose have impacted forest structure and diversity, tree 

densities, tree growth rates, tree regeneration success, and 

nitrogen cycling (McInnes et al. 1992, McLaren and Janke 

1996, McLaren and Peterson 1994, Pastor et al. 1998, 

Risenhoover and Maas 1987, Snyder and Janke 1976). 

Isle Royale’s geographic location, history, and ongoing research contributed to its authorization as a 

national park in 1931 by President Herbert Hoover, its 

establishment as a park in 1940 by President Franklin D. 

Roosevelt, its designation as wilderness in 1976 by the 

U.S. Congress, and its nomination as an International 

Biosphere Reserve in 1980 by the United Nations.
4

BACKGROUND

Efforts to Document Isle Royale 

Forest Resources

As a Biosphere Reserve, Isle Royale is considered 

globally important for the conservation of biological 

resources and the education, research, monitoring, 

and communication related to conservation issues. 

Past and current documentation of Isle Royale’s forest 

resources include using pollen counts to describe 

Holocene vegetation (Flakne 2003), General Land Office 

notes to reconstruct pre-settlement forest (Janke et al. 

1978), photographs to interpret succession following 

fire (Cooper 1913, 1928), vegetation sampling and 

classification to create cover-type maps (USDI 1999), 

and establishment of permanent plots to monitor forest 

health as part of the NPS Great Lakes Inventory and 

Monitoring Program (Sanders and Grochowski 2011). 

Although Isle Royale is globally recognized as a rare 

ecosystem, there is still a lack of quantitative information 

about it. In this resource bulletin, we use the 2010 FIA 

inventory to help describe the current forest conditions, 

provide a baseline for future inquiries, and discuss 

possible implications. Please refer to Isle Royale National 

Park FIA Methods section regarding sampling, annual 

inventories, and population estimates.

Ecoprovince 212 - Laurentian Mixed 

Forest Province

This bulletin is also the first attempt to highlight the 

uniqueness of Isle Royale’s FIA forest resources within 

a regional context. Previous Michigan FIA reports 

contain Isle Royale estimates (part of reserved forest 

land totals, discussed below), but no attempt has been 

made to separate and compare these values given similar 

ecological features (i.e., temperature, precipitation, 

geology, and vegetation).

An ecological region (Ecoregion) is a large-scale 

macroclimate that has predictable patterns and is 

associated with distinct geology (Bailey 1995, 2004, 

2009; Cleland et al. 2007). The daily and seasonal fluxes 

of moisture and solar radiation are the main parameters 

that distinguish ecoregions and are impacted by latitude, 

elevation, and continental/oceanic influences. 

Ecoregion designation starts at the broadest scale and 

has four domains: polar, dry, humid temperate, and 

humid tropical. These domains are subdivided into 

ecological provinces (Ecoprovince) that have a finer 

spatial scale and are delineated by specific daily and 

seasonal temperature fluxes, seasonal precipitation 

amounts, soil characteristics, and late-successional 

vegetation (Bailey 1995, 2004, 2009). Given Isle Royale’s 

position in northwestern Lake Superior, it is included 

in Ecoprovince 212, or the Laurentian Mixed Forest 

Province. In the United States, Ecoprovince 212 is made 

up of about 64.6 million acres (100,917 square miles) 

and includes the states of Minnesota, Wisconsin, and 

Michigan (Fig. 1; Cleland et al. 2007). It represents 

about 41 percent of the total area of these three states. 

The physiography of the Laurentian Mixed Forest 

Province varies from flat to hilly (elevation range 580 

to 1,725 feet above sea level) and reflects past glaciation 

with exposed bedrock, moraines, and glacial drift. The 

Great Lakes moderate the minimum and maximum 

temperatures, with an average temperature range of 

39 to 43 °F. Winters are moderately long and typically 

have continuous snow cover. Most precipitation occurs 

in the summer, with an average range of 27 to 34 

inches. The forest vegetation is a transition between 

southern deciduous and northern boreal species 

(Cleland et al. 2007).

Distinguishing between Forest Land, 

Timberland, Reserved Forest Land, 

and Other Forest Land

Forest land is land that is at least 10 percent stocked by 

live trees of any diameter size. It may include land that 

once had tree cover (formerly stocked), land that is not 

currently developed for nonforest uses, or land that will 

be naturally or artificiality regenerated. Forest land must 

be at least 1 acre in size and 120 feet wide. There is no 

minimum requirement for annual growth.
5

FOREST AREA

FIA has three categories of forest land:

•	 Timberland—forest land that is producing or is 

capable of producing crops in excess of 20 cubic feet/

acre/year of industrial wood in natural stands. Land is 

not withdrawn from timber utilization by statute or 

administrative regulation, and includes inaccessible 

and inoperable areas. 

•	 Reserved forest land—forest land that is withdrawn 

from timber utilization through statute without regard 

to productive status (e.g., some natural areas in state 

parks, national parks and lakeshores, and federal 

wilderness areas).

•	 Other forest land—forest land that is not capable of 

growing 20 cubic feet/acre/year due to site conditions 

and is not restricted from harvesting.

Forest Area

Background

Area estimates are the most basic and standard of all 

forest inventory attributes. Differences or changes 

between designated areas can be indicative of natural 

factors or human-caused changes. Summarizing forest 

characteristics provides valuable information about 

forest health, forest structure, sustainability, and 

unique features.

What we found

For the 2010 FIA inventory, Ecoprovince 212 in 

Michigan made up nearly 83 percent of Michigan’s total 

forest land (16.6 million acres: Table 1). Two percent of 

Michigan’s Ecoprovince 212 is reserved (375,503 acres) 

and includes nearly all of Michigan’s reserved forest land. 

Isle Royale’s area represents more than 36 percent of 

Ecoprovince 212 reserved forest land (138,497 acres). 

What this means

Ecoprovince 212-Laurentian Mixed Forest captures more 

than 80 percent of Michigan’s forest land, allowing us to 

make unique comparisons between Isle Royale, reserved, 

and non-reserved forest land. Isle Royale is a small 

component of Michigan’s overall forest area (less than 1 

percent), but represents more than a third of Michigan’s 

reserved forest land. This concentration of reserved 

forest land on Isle Royale, versus smaller parcels scattered 

throughout Michigan, strengthens comparisons between 

Isle Royale and Ecoprovince 212 non-reserved and 

reserved forest land. Additionally, Isle Royale’s isolation 

in Lake Superior minimizes the influence of surrounding 

a

Forest land (non-reserved) includes timberland.

b

Total is reserved and non-reserved forest land.

c

Isle Royale is included in Michigan’s Ecoprovince 212 reserved forest land.

d

Sampling error represents the 68-percent confidence interval around the estimate.

Table 1.—Area of forest land by category, Michigan, 2010

Forest land categorya Michigan (state totals)b Ecoprovince 212 (Michigan only) Isle Royalec

Sampling Sampling Sampling

Acres error (%)d Acres error (%)d Acres error (%)d

Timberland 19,386,095 0.5 15,954,513 0.5 -- --

Forest land (non-reserved) 19,624,601 0.5 16,192,151 0.5 -- --

Forest land (reserved) 378,867 8.4 375,503 8.4 138,497 13.5

Forest land (reserved and non-reserved) 20,003,467 0.4 16,567,653 0.4 138,497 13.5
6

FOREST TYPES

land changes (e.g., edge effect, threats from invasive 

plants, insects, and diseases). Future monitoring of 

both reserved and non-reserved forest land will provide 

valuable information about changes and trends in forest 

health, forest structure, and sustainability.

Forest Types

Background

Forest types are a classification of forest land based on 

the species forming a plurality of live tree stocking. A 

specific forest type reflects historical events, both natural 

and human disturbances, as well as ongoing successional 

competition between species. Within stands of mixed 

tree-size classes and species, assignment of forest types is 

weighted toward the larger trees because they contribute 

more to stocking than smaller trees. The forest-type 

nomenclature reflects this dominance by indicating the 

presence or absence of a species (e.g., eastern white pine vs. 

eastern white pine/eastern hemlock). In some cases, forest 

types may be slightly misleading. Because Ecoprovince 

212, and specifically Isle Royale, occurs at the tension zone 

between temperate and boreal biomes, several species are 

at the edges of their respective ranges. The sugar maple/

beech/yellow birch forest type erroneously implies that 

American beech (Fagus grandifolia) occurs on Isle Royale 

and in the western Upper Peninsula of Michigan. To avoid 

confusion, this forest type has been changed to sugar 

maple/yellow birch throughout this publication. Refer to 

Burns and Honkala (1990) for additional information 

about the silvical characteristics of specific tree species. 

Lastly, the nonstocked forest type is land less than 10 

percent stocked with live trees. 

What we found

According to the 2010 inventory, Michigan has 56 forest 

types, with 47 occurring in Ecoprovince 212. There are 

21 reserved forest types and eight of these forest types 

occur on Isle Royale: paper birch, sugar maple/yellow 

birch, aspen, northern white-cedar, white spruce, black 

spruce, balsam fir, and eastern white pine/northern red 

oak/white ash. An estimated 80 percent of Isle Royale’s 

area is divided among the top four forest types; the three 

hardwood types (paper birch, sugar maple/yellow birch, 

and aspen) make up 67 percent of Isle Royale (Fig. 2, 

Table 2). The top four forest types by area, although not 

ranked in the same order, are the same on Isle Royale 

and in Ecoprovince 212 reserved (Fig. 3). 

Table 2.—Area and number of plots by Isle Royale forest types, Michigan, 2010

a

The eastern white pine/northern red oak/white ash is abbreviated as white pine/red oak/white ash forest type.

b

Sampling error represents the 68-percent confidence interval around the estimate.

Isle Royale forest typea Area Plots Sampling errorb Sampling errorb

Acres Number Percent Acres

Paper birch 41,892 12.4 26.6 11,160

Sugar maple/yellow birch 30,350 9.1 31.8 9,648

Aspen 19,970 5.8 37.3 7,455

Northern white-cedar 17,964 5.5 40.1 7,198

White spruce 11,348 3.5 48.0 5,443

Black spruce 6,946 2.0 67.7 4,702

Balsam fir 6,554 2.0 49.1 3,219

White pine/red oak/white ash 3,473 1.0 96.1 3,337

Total 138,497 41.4 13.5 18,642
7

FOREST TYPES

The age-class distribution indicates that Michigan’s nonreserved forest land is fairly young. Live trees under the 

age of 41 equate to 23 percent of the forested area, while 

trees under the age of 80 make up 80 percent of the 

forest land. The age-class distribution of reserved forest 

land, which includes Isle Royale, indicates relatively 

older conditions, with 4 percent of live trees under age 

40 and only 47 percent under age 80. In contrast, Isle 

Royale forest land resembles the non-reserved age-class 

distribution with 27 percent under age 40 and nearly 80 

percent under age 80 (Fig. 4).

Two forest types—aspen and paper birch—demonstrate 

how Isle Royale age distribution is more similar to nonreserved than reserved forest land. The vast majority 

of the aspen forest type is 80 years and younger on Isle 

Royale and non-reserved forest land (82 percent and 94 

percent, respectively), but only 47 percent on reserved 

forest lands (Fig. 5). With the paper birch forest type, 

83 percent of Isle Royale and 89 percent of non-reserved 

forest land is 80 years or younger, but only 65 percent of 

reserved forest land is that age (Fig. 6).

Paper birch 

Sugar maple/yellow birch 

Aspen 

Northern white-cedar 

White spruce 

Black spruce 

Balsam fir 

White pine/red oak/white ash 

13% 

8% 

3% 5% 

5% 30% 

14% 22% 

Sugar maple/yellow birch 

Paper birch 

Northern white-cedar 

Aspen 

Other 

Black spruce 

White spruce 

Balsam fir 

White pine/red oak/white ash 

22% 

2% 2% 3% 

4% 35% 

15% 10% 

7% 

Figure 2.—Distribution of eight forest types found on Isle Royale by area, 

Michigan, 2010. Note: the eastern white pine/northern red oak/white ash 

forest type is abbreviated as white pine/red oak/white ash.

Figure 3.—Distribution of prominent reserve forest types found in Michigan 

Ecoprovince 212 by area, Michigan, 2010. “Other” forest type includes jack 

pine, balsam fir, red pine, tamarack, northern red oak, red maple/lowland, 

eastern white pine/northern red oak/white ash, red maple/upland, nonstocked, 

willow, white oak/red oak/hickory, other hardwoods, and eastern white 

pine. Note: the eastern white pine/northern red oak/white ash forest type is 

abbreviated as white pine/red oak/white ash.

201-220

181-200

161-180

141-160

121-140

100-120

81-100

61-80

41-60

21-40

0-20

Stand-age Class (years)

Non-reserved 

Reserved 

Isle Royale

0 5 10 15 20 25 30 35 

Forest Land Area in Category (%) 

Figure 4.—Forest land by stand-age class, Michigan, 2010.

100-120

81-100

61-80

41-60

21-40

0-20

Stand-age Class (years)

Non-reserved 

Reserved 

Isle Royale

0 10 20 30 40 50 60 

Aspen Forest Type in Category (%) 

Figure 5.—Aspen forest type by stand-age class, Michigan, 2010.
8

NUMBER OF TREES

What this means

Fewer than half of the forest types across Michigan’s 

Ecoprovince 212 are within reserved forest lands. 

Because Isle Royale makes up 36 percent of reserved and 

less than 1 percent of Michigan’s Ecoprovince 212 forest 

land, all forest types except sugar maple/yellow birch are 

disproportionately represented on Isle Royale, making 

these Isle Royale forest types important contributors 

to overall reserved and non-reserved forest-type areas. 

Within the context of reserved forest lands, the forest 

types of paper birch, aspen, and white spruce are nearly 

exclusive to Isle Royale. 

On Isle Royale, the early-successional forest types 

of paper birch and aspen reflect past fire and wind 

disturbances. The proportional area of Isle Royale aspen 

forest type is similar to Michigan’s Ecoprovince 212 

reserved lands at 14 and 15 percent, respectively. The 

paper birch forest type is 30 percent of the area on Isle 

Royale and contributes 72.6 percent to reserved and 

17.5 percent to Michigan’s Ecoprovince 212 total forest 

land. Without any future major disturbances, these 

forest types will give way to late-successional forest types, 

potentially reducing the overall number of Isle Royale 

forest types. In the case of the paper birch forest type, a 

decline on Isle Royale could have a substantial impact 

on the total area of paper birch forest type found within 

Michigan Ecoprovince 212.

Aspen and paper birch represent about 45 percent of 

Isle Royale forest types, and the respective stand-age 

distributions indicate the majority of stands initiated 

between 40 and 100 years ago. As a result, they have 

a considerable influence on Isle Royale’s overall standage distribution. Although protection of Isle Royale 

began in the 1930s, the relative young age of aspen and 

paper birch forest types may have several causes. The 

stand-age distribution represents the last of the forestclearing mining fires at the turn of the 20th century, the 

1936 and 1948 fires, and the recent rapid increase in 

the moose population that inhibited regeneration and 

recruitment. Regeneration following these disturbances 

may have been hindered if there was not a suitable 

seedbed due to fire intensity, inadequate nearby seed 

sources, or heavy browsing. We should also note that 

overall stand-age distributions of reserved forest land 

would be significantly older if Isle Royale values were 

removed. The similarity in age classes between Isle 

Royale and Michigan’s non-reserved forest land indicates 

a common theme: most of today’s stands regenerated 

after large-scale disturbances, including the clearing of 

forests related to timber and mining exploitation.

Number of Trees

Background 

Forest land stand-size classification indicates the 

predominant diameter size of live trees that contribute 

to the majority of stocking. Forest types are categorized 

by stand-size classes while species are categorized by 

tree-size classes. The large-diameter stand-size class (or 

sawtimber tree-size) consists of softwoods 9.0 inches in 

diameter (at breast height, 4.5 feet or d.b.h.) and greater 

and hardwoods 11.0 inches in diameter and greater. The 

medium-diameter stand-size class (or poletimber treesize) includes softwoods 5.0 to 8.9 inches in diameter 

and hardwoods 5.0 to 10.9 inches in diameter. The 

small-diameter stand-size class (or sapling tree-size) 

includes saplings or trees between 1.0 and 4.9 inches 

in diameter.

100-120

81-100

61-80

41-60

21-40

0-20

Stand-age Class (years)

Non-reserved 

Reserved 

Isle Royale

Paper Birch Forest Type in Category (%) 

0 5 10 15 20 25 30 35 40 45 

Figure 6.—Paper birch forest type by stand-age class, Michigan, 2010.
9

NUMBER OF TREES

What we found

Isle Royale forest types are dominated by large- and 

medium-diameter stand-size classes (Table 3). The sugar 

maple/yellow birch forest type is composed entirely of 

the large-diameter stand-size class. Only the balsam fir 

forest type had higher stocking in small- diameter standsize classes.

Because forest types are a mix of different species of 

different sizes, how does non-reserved, reserved, and 

Isle Royale tree densities compare to that of species in 

Ecoprovince 212? Isle Royale has 20 tree species that 

equate to more than 97 million trees (greater than 1 

inch d.b.h.), or about 708 trees per acre (t.p.a.). When 

factoring in the sampling error, this overall density is 

comparable to Michigan’s Ecoprovince 212 non-reserved 

(741 t.p.a.) and reserved forest lands (614 t.p.a., Fig. 7). 

Both Isle Royale and reserved forest lands have higher 

stocking in large-diameter trees and lower stocking in 

smaller diameter trees when compared to non-reserved 

forest land.

Northern white-cedar is the most common species on 

Isle Royale, estimated at more than 25 million trees. 

The most common species following northern whitecedar are white spruce (Picea glauca, 17.8 million trees), 

balsam fir (Abies balsamea, 14.9), paper birch (Betula 

papyrifera, 12.8), yellow birch (Betula alleghaniensis, 

6.9), black spruce (Picea mariana, 5.4), sugar maple 

(Acer saccharum, 5.0), black ash (Fraxinus nigra, 3.3), 

eastern white pine (Pinus strobus, 2.7), and quaking 

aspen (Populus tremuloides, 2.0). Nearly 2 million trees 

are divided among the following species: pin cherry 

(Prunus pensylvanica), jack pine, white ash (Fraxinus 

americana), chokecherry (Prunus virginiana), tamarack 

(Larix laricina), red maple (Acer rubrum), willow spp. 

(Salix spp.), American mountain-ash (Sorbus americana), 

green ash (Fraxinus pennsylvanica), and balsam poplar 

(Populus balsamifera). 

Not reserved 

Reserved 

Isle Royale

0 

100 

200 

300 

400 

500 

600 

700 

800 

900 

Total Large diameter Medium diameter Small diameter 

Trees per Acre 

Stand-size Classes 

Figure 7.—Trees per acre by stand-size class, Michigan, 2010. Error bars 

represent the 68-percent confidence interval around the estimate.

Table 3.—Stocking (trees at least 1 inch d.b.h.) by stand-size class of Isle Royale forest types, Michigan, 2010

a

The eastern white pine/northern red oak/white ash is abbreviated as white pine/red oak/white ash forest type. 

b

Sampling error represents the 68-percent confidence interval around the estimate.

Isle Royale forest typea Total Large diameter Medium diameter Small diameter

Thousand Sampling Thousand Sampling Thousand Sampling Thousand Sampling

trees error (%)b trees error (%)b trees error (%)b trees error (%)b

Paper birch 25,011 32.4 6,735 43.5 16,281 45.3 1,996 100.3

Sugar maple/yellow birch 19,633 37.9 19,633 37.9 - - - -

Northern white-cedar 14,983 44.7 8,738 60.8 2,424 69.6 3,821 100.3

Aspen 11,235 44.6 2,161 62.6 7,564 61.4 1,511 96.1

Balsam fir 9,260 74.0 - - 960 96.1 8,300 81.9

White spruce 7,462 52.2 6,337 59.1 1,125 96.1 - -

Black spruce 5,944 75.5 5,944 75.5 - - - -

White pine/red oak/white ash 4,553 96.1 - - 4,553 96.1 - -

Total 98,082 17.1 49,547 22.2 32,906 30.4 15,628 51.9
10

NUMBER OF TREES

Nearly all the prominent species have saplings that make 

up more than 71 percent of the total stocking by tree size 

(Fig. 8). Only paper birch (46 percent) and quaking aspen 

(13 percent) have lower values. Quaking aspen is the only 

species where sawtimber (55 percent) exceeds poletimber 

stocking (32 percent). Although the aspen forest type is 

the fourth largest on Isle Royale, the species itself is the 

tenth most common. Overall, conifer species are more 

common in small-diameter classes than deciduous species.

1996). Without a major disturbance (i.e., fire and/or 

windthrow) that provides regeneration and recruitment 

opportunities, paper birch and aspen will likely continue 

to decline in numbers.

Although there is considerable sampling error with 

balsam fir, the stocking pattern of this third most 

common species may be a result of severe moose 

browsing, the pattern and frequency of windthrow and 

fire disturbance, and the presence of both temperate and 

boreal species on Isle Royale. According to McLaren 

and Janke (1996), balsam fir (and to some extent, white 

spruce) had lower densities on the southwest end of Isle 

Royale while densities were higher on the northeast end. 

They attributed the higher densities and basal area to the 

1936 and 1948 fires (creation of suitable seedbeds), more 

frequent windstorms (increased sunlight availability), 

and reduced competition because moose favor the 

palatable species of aspen, paper birch, and hazel (Corylus 

cornuta). Observations support these findings, with 

the northeast end of Isle Royale resembling a dog-hair 

thicket (Charles Paulson and Suzanne Sanders, pers. 

comm.).

What will Isle Royale forest types and species 

distribution look like in the future? With the 

combination of infrequent natural disturbances and 

constant browsing pressure, the current low stocking of 

small-diameter paper birch and quaking aspen may not 

be sufficient to become future seed sources. Conversely, 

northern white-cedar’s abundance and low palatability 

may mean an increase in stocking. Previous findings on 

Isle Royale indicated that when northern white-cedar 

was an available food source, it made up less than 1 

percent of a moose’s diet (Aldous and Kreftling 1946). 

In general, as mortality impacts overstory species and 

creates gap openings, one would expect shade-tolerant 

and non-palatable species to increase in frequency. 

Under this scenario, Isle Royale will gradually shift to 

conifer species.

Saplings 

Poletimber-size 

Sawtimber-size 

0 10 20 30 

Northern white-cedar 

White spruce 

Balsam fir 

Paper birch 

Yellow birch 

Black spruce 

Sugar maple 

Black ash 

Eastern white pine 

Quaking aspen 

Number of Trees (million) 

Species 

Figure 8.—Number of live trees (at least 1 inch d.b.h.) on Isle Royale by treesize class and species, Michigan, 2010. Error bars represent the 68-percent 

confidence interval around the total estimate of selected prominent species. 

Not shown are pin cherry, jack pine, white ash, chokecherry, tamarack, red 

maple, willow spp., American mountain-ash, green ash, and balsam poplar.

What this means

The patterns of overall tree density, species frequency, 

and species distribution by tree size tell an intriguing 

story. Two pioneer tree species—paper birch and quaking 

aspen— require significant disturbance for regeneration. 

The low stocking values in the sapling class, combined 

with mortality rates (see Growth and Mortality section), 

would suggest that paper birch and aspen have not 

experienced a disturbance since the early- to mid-1900s 

(Cooper 1928, Janke et al. 1978; McLaren and Janke 
11

STOCKING

Stocking

Background

Stocking is defined as the degree of occupancy of land by 

live trees, measured by basal area and/or the number of 

trees in a stand by size or age and spacing, compared to 

the basal area and/or number of trees required to fully use 

the growth potential of the land. If a stand is overstocked, 

it may indicate an increased probability of forest health 

problems and lower growth rates; a poorly stocked 

stand may indicate poor site quality or a stand that is 

converting back to a forested condition following a major 

disturbance.

What we found

Within Isle Royale, 85 percent of the area is considered 

medium or fully stocked. This area compares favorably 

to reserved forest land (80 percent) and non-reserved 

forest land in Michigan’s Ecoprovince 212 (84 percent, 

Fig. 9). Only two Isle Royale forest types were considered 

overstocked: balsam fir (24 percent) and sugar maple/

yellow birch (23 percent, Fig. 10). This stocking pattern 

was also seen in reserved forest land, but did not carry 

over to non-reserved forest land, because overstocking 

rates for balsam fir (9 percent) and sugar maple/yellow 

birch (7 percent) were much lower. The Isle Royale 

balsam fir forest type was also the most varied in stocking 

because each stocking category was represented.

What this means

The high percentage of fully and medium stocked 

forest land in Isle Royale is beneficial for maintaining 

forest health. Although lower stocking levels would be 

expected on poorer quality sites (e.g., wetter soils of 

northern white-cedar), it was not evident on Isle Royale. 

The sugar maple/yellow birch forest type tends to have 

higher stocking values given the shade tolerance of the 

compositional species (i.e., sugar maple), while the 

stocking variability of the balsam fir forest type can be 

attributed to sampling error, balsam fir’s shade tolerance, 

past disturbance regimes, influence of moose, and ability 

to exist on a variety of sites.

Poorly stocked 

Medium stocked 

Fully stocked 

Overstocked 

0 20 40 60 80 100 

Not reserved 

Reserved 

Isle Royale

Forest Land (%) 

Ecoprovince 212 Categories 

Overstocked 

Fully stocked 

Medium stocked 

Poorly stocked 

0 20 40 60 80 100 

Balsam fir 

White spruce 

Black spruce 

Northern white-cedar 

White pine/red oak/white ash 

Sugar maple/yellow birch 

Aspen 

Paper birch 

Isle Royale Forest Land (%) 

Forest Types 

Figure 10.—Percentage of Isle Royale forest land by stocking class and forest 

type, Michigan, 2010. Note: the eastern white pine/northern red oak/white ash 

forest type is abbreviated as white pine/red oak/white ash.

Figure 9.—Percentage of forest land by stocking class within Michigan’s 

Ecoprovince 212, Michigan, 2010. “Nonstocked” category not shown.
12

VOLUME

Volume

Background

Volume is similar to stocking because it characterizes 

forest resources and is easily compared between species 

and forest types. Volume also incorporates net growth, 

removals, and mortality. Estimates of live-tree volumes 

are in cubic feet and include all live trees at least 

5 inches d.b.h. 

What we found

On Isle Royale forest land, there are about 243 million 

cubic feet of growing stock, or about 1,575 cubic feet /

acre. Northern white-cedar (25 percent), paper birch 

(21 percent), yellow birch (16 percent), white spruce (15 

percent), and quaking aspen (13 percent) contribute 89 

percent of this total volume (Fig. 11). 

Michigan’s Ecoprovince 212 non-reserved forest 

lands have an estimated 25.3 billion cubic feet (1,567 

cubic feet/acre); reserved forest lands have about 830 

million cubic feet (2,211 cubic feet/acre). The top 

five species contributing to total volume estimates for 

Ecoprovince 212 non-reserved forest land are sugar 

0 20 40 60 80 

Northern whitecedar

Paper birch 

Yellow birch 

White spruce 

Quaking aspen 

Black spruce 

Sugar maple 

Balsam fir 

Other 

Eastern white pine 

Volume (millions ft3) 

Tree Species 

Figure 11.—Volume estimates of growing stock on Isle Royale forest land 

by species, Michigan, 2010. Error bars represent the 68-percent confidence 

interval around the estimate. “Other” includes tamarack, jack pine, red maple, 

black ash, green ash, balsam poplar, pin cherry, willow spp., and American 

mountain-ash.

maple (17 percent), red maple (13 percent), northern 

white-cedar (10 percent), red pine (8 percent), and 

quaking aspen (6 percent). On reserved forest land, 58 

percent of the volume can be attributed to sugar maple 

(17 percent), northern white-cedar (12 percent), eastern 

hemlock (10 percent), yellow birch (10 percent), and 

paper birch (9 percent).

Overall, Isle Royale contributes nearly 2 percent to the 

total forest land volume of Michigan’s Ecoprovince 212, 

although this varies by species. For example, paper birch 

represents more than 8 percent of the total paper birch 

volume within Michigan’s Ecoprovince 212. Yellow birch 

and white spruce contribute 6 percent to total volume 

estimates, respectively. Although Isle Royale makes up 

less than 1 percent of Michigan’s Ecoprovince 212 forest 

land, northern white-cedar, quaking aspen, balsam fir, 

and black spruce disproportionately contribute at least 1 

percent to total volume estimates.

Of Isle Royale’s high volume species (northern whitecedar, paper birch, yellow birch, white spruce, and 

quaking aspen), 70 percent of this volume is contained 

within the sawtimber-size class. This percentage is similar 

to other reserved forest land for these same species. 

However, about 58 percent of Michigan’s non-reserved 

forest land volume is categorized as sawtimber-size 

diameter. Comparing each species’ proportional volume 

of poletimber-size classes to sawtimber-size classes 

indicates that Isle Royale and reserved forest land allocate 

more volume in the sawtimber-size trees of northern 

white-cedar, yellow birch, and quaking aspen (Fig. 12).

Isle Royale, Daisy 

Farm yellow 

lady slipper. 

Photo by Karena 

Schmidt, Michigan 

Technological 

University; used 

with permission.
13

BIOMASS AND CARBON

Poletimber Sawtimber 

Not reserved

Reserved

Isle Royale

White spruce

Not reserved

Reserved

Isle Royale

Northern white-cedar

Not reserved

Reserved

Isle Royale

Yellow birch

Not reserved

Reserved

Isle Royale

Paper birch

Not reserved

Reserved

Isle Royale

Quaking aspen

0 10 20 30 40 50 60 70 80 90 100 

Species Volume in Land Category (%) 

Select Species by Land Category

Figure 12.—Prominent species volume by tree size for each land category, 

Michigan, 2010.

What this means

Volume is an important component of forest structure 

because it is a function of tree height and diameter. 

Areas or species that have disproportionate contributions 

indicate bigger (d.b.h.), taller, and older trees. The 

volumes and respective contributions of paper birch, 

yellow birch, and white spruce to Michigan’s forest 

resources reflect the fully stocked stands of medium- and 

large-diameter trees on Isle Royale. As these mediumstocked stands shift to large-diameter stand-classes and 

as older and larger trees senesce, changes in volume 

estimates will have a potentially substantial impact on 

Isle Royale’s forest resources.

Biomass and Carbon

Background

The topics of biomass and carbon are drawing much 

public interest. Biomass estimates are valuable in 

determining fuel availability, fuel loading, carbon 

allocation, carbon sequestration, and changes in carbon 

pools. The ability of an individual tree or forest to act as 

a carbon sink is important because of global and regional 

climate change concerns. Because about half of a tree’s 

biomass is carbon, understanding forest carbon stocks is 

critical to carbon credit markets, management strategies, 

and carbon cycle dynamics.

Biomass estimates include bole volume plus bark and 

branches of all live trees 1 inch in diameter and greater, 

and are reported in oven-dry short tons (tons). Carbon 

is reported as short tons (tons) and uses five categories, 

or pools, for classification. Following standards based 

on the U.S. National Greenhouse Gas Inventory, forest 

carbon pools are delineated as live aboveground, live 

belowground, dead wood, litter, and organic soil (U.S. 

EPA 2010). Generally, trends in biomass and carbon 

follow those in volume.

What we found 

On Isle Royale, live aboveground biomass is an estimated 

5.4 million tons, which averages to 38.9 tons/acre. 

This biomass distribution was concentrated in the two 

largest forest types by area: sugar maple/yellow birch (36 

percent) and paper birch (29 percent, Fig. 13). Per acre 

averages were similar across non-reserved and reserved 

forest land (39.1 and 52.7 tons/acre, respectively). 

The per acre average of the sugar maple/yellow birch 

forest type was consistently greater than overall averages 

(Table 4). Although non-reserved and reserved biomass in 

Michigan’s Ecoprovince 212 were not concentrated into 

as few forest types as on Isle Royale, sugar maple/yellow 

birch contributed 28 percent to non-reserved biomass 

and 50 percent to reserved biomass. Also, although Isle 
14

BIOMASS AND CARBON

Royale’s total biomass contribution to Michigan’s overall 

biomass volume was equal to the land mass ratio (less 

than 1 percent), 14 percent of Michigan’s paper birch 

forest type biomass was attributed to Isle Royale. 

Forest land live biomass can be broken into four 

categories: belowground for saplings and trees, tops/

limbs/stumps, saplings, and boles. On Isle Royale, tree 

boles contributed 57 percent of the total biomass, while 

belowground (i.e., roots) biomass was the same as the 

live-tree tops/limbs/stumps value at 17 percent (Fig. 14).

Isle Royale’s forests have more than 16 million tons of 

carbon or about 119 tons/acre. The largest component is 

organic matter in mineral soil, contributing 67 percent 

(11 million tons, Fig. 15). Live aboveground and 

belowground carbon was 3.3 million tons, or 20 percent 

Tops/limbs/stumps 

Saplings 

Belowground 

Boles 

17% 

9% 

17% 

57% 

Figure 14.—Percentage of live-tree biomass (tons) on Isle Royale by 

aboveground and belowground components, Michigan, 2010. Saplings include 

trees at least 1 but less than 5 inches d.b.h. Stumps are from ground level to 

1 foot in height. Belowground represents live saplings and trees. Boles are 

merchantable portions from 5 inch d.b.h. to a 4-inch top.

of the carbon on Isle Royale. For comparison, nonreserved and reserved forest land contains 1,690.8 and 

45.5 million tons of carbon, respectively. This averages to 

105.8 and 121.5 tons/acre for non-reserved and reserved 

forest land, respectively. The organic matter in soil was 

also similar in Isle Royale and reserved and non-reserved 

forest land (59 and 64 percent, respectively).

The northern white-cedar forest type covers the fourth 

largest area on Isle Royale (10 percent) but contains the 

third most carbon (17 percent, Fig. 16). The majority 

of this contribution is from carbon from organic matter 

within mineral soil. Although the prominent forest types 

of Isle Royale typically had organic soil amounts between 

65 and 70 percent, sugar maple/yellow birch had 50 

percent (Fig. 17).

Sugar maple/yellow birch 

Paper birch 

Aspen 

Northern white-cedar 

Other 

9% 

9% 

17% 

36% 

29% 

Figure 13.—Percentage of live-tree aboveground biomass by forest type on 

Isle Royale, Michigan, 2010. “Other” forest types include white spruce, black 

spruce, balsam fir, and eastern white pine/northern red oak/white ash.

Table 4.—Live aboveground tree (minimum 1 inch d.b.h.) biomass by forest type and Ecoprovince 212 forest land regions, Michigan, 2010

a

Sampling error represents the 68-percent confidence interval around the estimate.

Michigan’s Ecoprovince 212 Isle Royale

Forest type Non-reserved Reserved

Dry tons Dry tons Dry tons 

Million sampling Dry tons/ Million sampling Dry tons/ Million sampling Dry tons/

dry tons error (%)a acre dry tons error (%)a acre dry tons error (%)a acre

Sugar maple/yellow birch 177.9 2.8 53.0 9.9 15.9 74.8 1.9 32.5 63.7

Paper birch 8.7 11.9 36.5 2.4 24.3 40.9 1.6 28.8 37.8

Aspen 72.9 4.1 29.4 0.7 34.0 26.4 0.5 38.9 25.5

Northern white-cedar 48.4 5.0 38.2 1.3 30.6 34.2 0.5 44.0 26.6

Other 325.3 1.8 36.8 5.6 19.4 45.6 0.9 39.3 31.3

Total 633.2 0.9 39.1 19.8 10.0 52.7 5.4 15.7 38.9
15

BIOMASS AND CARBON

Soil organic 

Aboveground (live) 

Litter 

Dead wood 

Belowground (live) 

9% 

4% 3% 

67% 

17% 

22%

17%

25%

11%

10%

15%

Aspen 

White spruce 

Paper birch 

Sugar maple/yellow birch 

Northern white-cedar 

Black spruce 

Balsam fir 

White pine/red oak/white ash 

2% 

6% 

7% 

Figure 15.—Isle Royale forest land carbon stock (tons) by component as 

classified by Intergovernmental Panel on Climate Change (IPCC), Michigan, 

2010. Litter includes leaves and small woody debris (branches less than 3 

inches in diameter). Mineral soil occurs below the O horizon.

Figure 16.—Isle Royale forest land carbon stock by forest type as classified 

by IPCC, Michigan, 2010. Note: the eastern white pine/northern red oak/white 

ash forest type is abbreviated as white pine/red oak/white ash.

Aboveground (live) 

Belowground (live) 

Dead wood 

Litter 

Organic soil 

0 25 50 75 100

White pine/red oak/white ash 

Balsam fir 

Black spruce 

Aspen 

White spruce 

Sugar maple/yellow birch 

Northern white-cedar 

Paper birch 

Proportion of Carbon by Pool (%)

Forest Types 

Figure 17.—Isle Royale forest type carbon stock by component as classified 

by IPCC, Michigan, 2010. Note: the eastern white pine/northern red oak/white 

ash forest type is abbreviated as white pine/red oak/white ash.

What this means

Tree boles contain the greatest amount of Isle Royale’s 

total biomass, and the majority of the biomass is found 

in sugar maple/yellow birch and paper birch forest 

types. Future increases in biomass will be a result of trees 

making the transition from small-diameter to largediameter stand-size classes. Isle Royale biomass stocks 

will increase at a slower rate compared to Ecoprovince 

212 non-reserved forest land because Isle Royale has less 

area allocated to small-diameter stand-size classes. 

Estimates of live aboveground and belowground 

biomass help us understand carbon pools within and 

between areas, but the forest soils typically contain 

most of ecosystem carbon. Forest soils that have higher 

moisture content tend to have more carbon per acre 

as water impedes microbial decay rates, allowing 

carbon allocation rates to exceed carbon release due 

to decomposition (Schlesinger and Andrews 2000, 

Trumbore 2000). This is evident in the northern whitecedar forest type and the higher amounts of stored 

carbon on a per acre basis. 

Additionally, stand structure and age can act as a 

surrogate for carbon allocation and sequestration rates as 

a function of time from a previous disturbance (Pan et al. 

2011). In other words, following a recent disturbance, 

the vigorous growth of a young stand will accumulate 

carbon at a faster rate than an established forest, yet will 

have lower overall carbon amounts. 

Conversely, large-diameter stands reflect a longer time 

since disturbance. These stands can have larger carbon 

pools but may sequester carbon at lower annual rates. 

On Isle Royale, no active management or documented 

large-scale disturbance has occurred since the 1930s 

and 1940s, and those areas were concentrated on the 

northeast side of the island (Janke et al. 1978). In 

the case of sugar maple/yellow birch, located on the 

southwest part of Isle Royale, the large-diameter standsize classes within fully stocked stands contributed to 

higher aboveground carbon than other forest types. 
16

GROWTH AND MORTALITY

Growth and Mortality

Background

Growth and mortality analysis provides information 

on forest dynamics related to succession, disturbance, 

productivity, sustainability, forest health, competition, 

and biotic and abiotic factors. Average annual net growth 

(growth including ingrowth minus mortality and cull) is 

computed by measuring trees at two points in time and 

determining the average annual change in volume over 

that period. Although species dependent, a lower growth 

rate (the percentage of annual net growth to current 

volume) is generally indicated by a percentage less than 

or equal to 1.0. Moderate growth rates range from 1.0 

to 3.0 percent; high growth rates exceed 3.0 percent. 

Negative values indicate mortality is exceeding growth.

Some factors that cause mortality are native and invasive 

plant competition, insects, disease, wind, fire, drought, 

floods, and air pollution (this mortality analysis does 

not include harvesting or land conversion). Mortality 

may have single or multiple causes that may arise from 

one incident or over multiple years. For example, a 

lightning strike may weaken a tree’s defense and make 

it susceptible to a pest attack that then takes several 

years to cause mortality. Although the true cause 

may be undetermined, mortality is a concern when it 

surpasses the growth and regeneration rates of the forest, 

increasing fuel loads. Similar to annual net growth, the 

average annual mortality of the forest is compared to the 

current standing volume. Also species dependent, lower 

mortality rates are less than or equal to 1.0 percent. 

Moderate rates of mortality range between 1.0 and 3.0 

percent; high mortality rates exceed 3.0 percent.

What we found

Average annual net growth of live trees on Isle Royale 

was 2.6 million cubic feet for the 2010 inventory. The 

average annual net growth of northern white-cedar and 

white spruce actually exceeded Isle Royale’s total (2.9 

million cubic feet) because paper birch and quaking 

aspen had negative average annual net growth (1.2 

Paper birch

-4,000 -2,000 0 2,000 4,000 

Isle Royale total 

Northern white-cedar 

White spruce 

Yellow birch 

Black spruce 

Sugar maple 

Eastern white pine 

Balsam fir 

Quaking aspen 

Annual Net Growth of Live Trees (thousand ft3) 

Tree Species 

Figure 18.—Average annual net growth for live trees (at least 5 inches d.b.h.) 

on Isle Royale by species, Michigan, 2010. Error bars represent the 68-percent 

confidence interval around the estimate of selected prominent species.

million cubic). The sampling error at the 68-percent 

confidence interval does introduce high amounts 

of variability, so some caution should be used when 

interpreting these results (Fig. 18).

This annual net growth estimate for Isle Royale is about 

1.1 percent of all live-tree volume and is considered a 

moderate rate of growth (Fig. 19). Of the top nine species 

by volume, three species had moderate growth rates 

(balsam fir, black spruce, and northern white-cedar), three 

species had high growth rates (sugar maple, white spruce, 

and eastern white pine), one species exhibited slow growth 

(yellow birch), and two species had mortality exceeding 

growth (paper birch at -2.0 and quaking aspen at -0.7). As 

with the variability in the average annual net growth of all 

live trees, caution should be used with these results.

The average annual mortality volume of Isle Royale 

was 3.8 million cubic feet, of which two species made 

up 80 percent (paper birch at 1.9 and quaking aspen 

at 1.2 million cubic feet). Of the prominent species by 

volume, sugar maple and eastern white pine did not have 

any annual mortality for the 2010 inventory (Fig. 20). 

The ratio of average annual mortality to current volume 

of Isle Royale was 1.6 percent, indicating a moderate 

rate of mortality (Fig. 21). Of the prominent species 

experiencing mortality, four species showed a lower rate 

of mortality (yellow birch, black spruce, white spruce, 

and northern white-cedar), balsam fir had a moderate 
17

GROWTH AND MORTALITY

3.6 

3.2 

3.1 

2.8 

2.1 

1.1 

1.0 

0.9 

-0.7 

-2.0 

-8 -6 -4 -2 0 2 4 6 8 

Eastern white pine 

White spruce 

Sugar maple 

Northern white-cedar 

Black spruce 

Isle Royale total 

Balsam fir 

Yellow birch 

Quaking aspen 

Average Annual Net Growth to Volume (%) 

Tree Species 

Paper birch 

0 1,000 2,000 3,000 4,000 5,000 

Isle Royale total 

Paper birch 

Quaking aspen 

White spruce 

Yellow birch 

Balsam fir 

Northern white-cedar 

Black spruce 

Annual Mortality of Trees (thousand ft3) 

Tree Species 

3.9 

2.3 

1.9 

1.6 

0.8 

0.4 

0.3 

0.2 

0.0 1.0 2.0 3.0 4.0 5.0 

Quaking aspen 

Balsam fir 

Paper birch 

Isle Royale total 

White spruce 

Black spruce 

Yellow birch 

Northern white-cedar 

Average Annual Mortality to Volume (%) 

Tree Species 

Figure 19.—Ratio (percent) of average annual net growth to current volume 

of live trees (at least 5 inches d.b.h.) on Isle Royale, Michigan, 2010. Error bars 

represent the 68-percent confidence interval around the estimate of selected 

prominent species.

Figure 20.—Average annual mortality of trees (at least 5 inches d.b.h.) on 

Isle Royale by species, Michigan, 2010. Error bars represent the 68-percent 

confidence interval around the estimate of selected prominent species.

Figure 21.—Ratio (percent) of average mortality to current volume of live 

trees (at least 5 inches d.b.h.) on Isle Royale, Michigan, 2010. Error bars 

represent the 68-percent confidence interval around the estimate of selected 

prominent species.

2.2 

0.5 

1.1 

1.0 

1.4 

1.6 

0.0 0.5 1.0 1.5 2.0 2.5 

Non-reserve annual 

net growth 

Reserve annual net growth 

ISRO annual net growth 

Non-reserve annual 

mortality 

Reserve annual mortality 

ISRO annual mortality 

Average Annual Mortality and Net Growth to Volume (%) 

Ecoprovince 212 

Figure 22.—Ratio (percent) of average annual mortality and net growth to 

current volume of live trees (at least 5 inches d.b.h.) on Isle Royale (ISRO), and 

Ecoprovince 212 reserved, and non-reserved forest lands, Michigan, 2010. 

Error bars represent the 68-percent confidence interval around the the estimate 

of forest land categories.

rate of mortality, and two species had a high rate of 

mortality (paper birch and quaking aspen).

How does Isle Royale’s ratio of average annual net 

growth and mortality to current volume compare to 

non-reserved forest land in Michigan’s Ecoprovince 212? 

Although there are differences between Isle Royale and 

non-reserved forest land, growth and mortality rates both 

fall in the moderate category with rates between 1.0 and 

3.0 percent (Fig. 22).

What this means

Isle Royale’s annual net growth is considered moderate 

for all live trees, although it is lower than that of nonreserved forest lands. This rate was negatively influenced 

by the pioneer species of paper birch and quaking aspen 

because these two species are becoming overmature and 

recruitment stocking is relatively low. White spruce, 

sugar maple, and northern white-cedar exhibited the 

greatest level of annual net growth, which may be 

attributed to at least two reasons: little to no moose 

browse pressure and canopy-gap creation by senescing 

paper birch and quaking aspen that allows mid- to 

shade-tolerant species to reach the upper canopy.

Although Isle Royale’s mortality rate was higher than 

that of non-reserved forest lands, it is still considered 

moderate. One important distinction between Isle 

Royale and non-reserved forest lands is that non-reserved 
18

STANDING DEAD TREES

forests are actively managed, allowing for the removal of 

live trees that may potentially die between inventories. 

Quaking aspen and paper birch provide the majority of 

mortality volume on Isle Royale due to their advanced 

age, although balsam fir did exhibit the second highest 

average annual mortality to volume (2.3 percent). This 

moderate rate may have at least two factors: long-term 

moose browse pressure and, while undocumented on 

Isle Royale, the spruce budworm attack in the late 

1990s and mid to late 2000s in Michigan’s forest lands 

(Pugh et al. 2009).

Standing Dead Trees

Background

Snags, or standing dead trees, reflect stand succession 

and are key components of wildlife habitat, structural 

diversity, and carbon storage. The frequency of 

standing dead trees per area, total volume by species, 

and aboveground biomass by species are some of the 

common measurements for understanding the value of 

standing dead trees. To be considered a standing dead 

tree, the tree must have a d.b.h. of at least 5 inches and 

be at least 4.5 feet tall.

What we found

The standing dead trees on Isle Royale are estimated at 

about 4.7 million. Paper birch and quaking aspen made 

up 74 percent of this value (Fig. 23). Of the prominent 

species, only sugar maple had no estimated standing 

dead trees. Standing dead trees on Isle Royale averaged 

33.7 t.p.a., with paper birch the most abundant at 18.5 

t.p.a. Quaking aspen averaged about 6 t.p.a., while 

balsam fir, white spruce, black spruce, and northern 

white-cedar averaged between 1 and 3 t.p.a. The overall 

frequency of standing dead trees is inversely related to 

tree diameter with about 88 percent of standing dead 

trees between 5 and 14.9 inches d.b.h. and about 12 

percent larger than 15 inches d.b.h. (Fig. 24). 

Paper birch 

Quaking aspen 

Balsam fir 

White spruce 

Northern white-cedar 

Black spruce 

Yellow birch

9% 

7% 

3% 1% 

5% 56% 

19% 

Paper birch 

Quaking aspen 

Spruce-fir 

Other 

0 200 400 600 800 1,000 1,200 1,400 

Standing Dead (in thousands) 

19.0-20.9 

17.0-18.9 

15.0-16.9 

29.0-30.9 

23.0-24.9 

21.0-22.9 

13.0-14.9 

11.0-12.9 

9.0-10.9 

7.0-8.9 

5.0-6.9 

Diameter Classes (at d.b.h.) 

Figure 23.—Distribution of standing dead trees (at least 5 inches d.b.h.) 

by species on Isle Royale, Michigan, 2010.

Figure 24.—Trees species distribution of standing dead trees by diameter class 

on Isle Royale, Michigan, 2010. “Spruce-fir” indicates balsam fir, black spruce, 

and white spruce. “Other” indicates yellow birch, eastern white pine, jack pine, 

and northern white-cedar.

On Isle Royale, there are about 34 million cubic feet of 

volume and 0.8 million tons of biomass of standing dead 

trees, which averages to about 246 cubic/acre (6 tons/

acre). As found with standing dead trees, paper birch 

and quaking aspen combined represent 67 percent of the 

volume and 71 percent of the biomass of standing dead 

trees found on Isle Royale. When compared to nonreserved forest land in Michigan’s Ecoprovince 212, per 

acre values are 89 cubic feet of volume and 0.02 tons of 

biomass of standing dead trees.

What this means

Paper birch and quaking aspen on Isle Royale are the 

dominant standing dead species in regards to frequency, 
19

ISLE ROYALE NATIONAL PARK FIA METHODS

diameter distribution, volume, biomass, and proportion 

of standing dead to live basal area. These patterns again 

reflect the successional events that initially created high 

populations across wide areas of both quaking aspen and 

paper birch that are now senescing. Additionally, the 

relatively low values per acre found on Michigan’s nonreserved forest land reflect management that typically 

removes low vigor trees.

Isle Royale National Park 

FIA Methods

The national FIA plot design consists of a series of 

permanent plots randomly located in a matrix of 

hexagonal cells (Overton et al. 1990). Each plot consists 

of four fixed-radius subplots covering about 0.17 

total acres. Since 1999, FIA has implemented annual 

inventories in which about 20 percent of the plots are 

visited each year (Smith 2002). After 5 years of data 

collection, analysis and reports are completed based upon 

this set of data, or cycle, of plots. Each additional year 

of remeasurements creates an annual moving window of 

5-year cycles and reports. The last year of the cycle is used 

to identify the full set of plots. In this report, the cycle of 

plots measured from 2006 through 2010 are collectively 

labeled the 2010 inventory. 

The national standard sampling intensity is about one plot 

per 6,000 acres. However, Michigan had triple intensity 

sampling in 2006 through 2007 (one plot per 2,000 acres). 

The average area represented per plot in the 2010 inventory 

for Michigan is about 2,755 acres of land, noncensus 

water, and inland census water. For the 2010 inventory, 

44 plots on Isle Royale and 10,682 plots in Michigan were 

measured. Experienced field crews measure many condition 

variables (e.g., forest type, stand size, and stand age) and 

tree-level attributes (e.g., species, diameter, and height) that 

are used to estimate additional attributes (e.g., volume, 

biomass, carbon, net growth, and mortality) across regions 

(e.g., national forests and states) with associated measures of 

reliability (U.S. Forest Service 2007, 2011).

The quality of the estimates is affected by sampling, 

measurement, prediction, and nonresponse error. Several 

times within this report, sampling error (SE) is used 

as the primary measure of the reliability of an estimate 

and is based on one standard error. This error indicates 

that 68 percent of the time (two out of three chances), 

while using the same methods, a complete inventory 

of the entire population would have been within the 

limits indicated. For example, the 2010 FIA inventory 

estimates the Isle Royale paper birch forest type has 

41,892 acres (SE 26.64 percent) with 25,011,488 live 

trees (SE 32.41 percent) 1-inch d.b.h. or larger. For 

the individual attributes, the SE is ± 11,160 acres and 

± 8,106,223 trees. For additional information about 

sampling design, sampling error, and specific limitations 

with FIA population estimates, refer to Bechtold and 

Patterson (2005).

These population estimates are available to the public 

via the U.S. Forest Service FIA DataMart, an online 

database (http://apps.fs.fed.us/fiadb-downloads/

datamart.html). Woudenberg et al. (2010) provides 

documentation on database structure, calculations of 

population estimates, and explanations of codes and 

table attributes. Results for this publication were taken 

from 2006-2010 USFS FIA data accessed via the USFS 

EVALIDator 4.01 (http://apps.fs.fed.us/Evalidator/

tmattribute.jsp). More information on usage can be 

found online at http://fia.fs.fed.us/tools-data/other/

default.asp.

Isle Royale, Rock 

Harbor black morel. 

Photo by Karena 

Schmidt, Michigan 

Technological 

University; used 

with permission.
20
21

SUMMARY

Summary

This report is the first-ever attempt to use FIA data to 

provide baseline quantitative information about the 

forest resources of Isle Royale National Park. This FIA 

bulletin reflects a unique application of using timber 

and non-timber attributes for reserved forest lands. With 

the national permanent plot system, the FIA 5-year 

remeasurement cycle allows for the opportunity to 

further monitor Isle Royale’s forest dynamics. 

The forest conditions of Isle Royale (2010 inventory) 

are compared to those of Michigan’s Ecoprovince 212 

reserved and non-reserved forest lands. Isle Royale 

represents 36 percent of Michigan’s reserved forest land 

and less than 1 percent of non-reserved land. Isle Royale’s 

four prominent forest types (paper birch, sugar maple/

yellow birch, aspen, and northern white-cedar) and four 

tree species (northern white-cedar, white spruce, balsam 

fir, and paper birch) are important contributors to 

Michigan’s overall forest resources. 

Human-caused and natural fires between 1847 and 1948 

on Isle Royale created large tracts of early-successional 

species (i.e., paper birch and trembling aspen), 

while current vegetative disturbances following the 

establishment of the park (post-1930) can be somewhat 

attributed to the arrival of moose. These factors have 

resulted in similarities and differences between Isle 

Royale and non-reserved forest land in Michigan’s 

Ecoprovince 212. Isle Royale’s per acre estimates of 

tree densities, volume, live biomass, and aboveground 

and belowground carbon were similar to those found 

in Michigan’s non-reserved and reserved forest land. 

Stand-age structure was more similar between Isle Royale 

and Michigan’s non-reserved forest land than reserved 

forest land. 

However, important differences in species-specific 

stand-size stocking, growth, and mortality were detected. 

About 85 percent of Isle Royale’s stands are considered 

medium to large in diameter, with balsam fir providing a 

notable amount of stocking in small-diameter stand size. 

The low stocking values of small-diameter deciduous 

species (i.e., paper birch, trembling aspen, yellow birch, 

sugar maple, and black ash) may also be inadequate for 

self-replacement, allowing Isle Royale to gradually shift 

to conifer species. This transition is supported by the 

average annual net growth of both white spruce and 

northern white-cedar exceeding Isle Royale’s total. 

Although growth and mortality rates on Isle Royale and 

non-reserved forest land were considered moderate, 

differences were found when looking at individual 

species. Mortality exceeded growth for both paper birch 

and trembling aspen on Isle Royale, with nearly 75 

percent of the standing dead trees attributed to these 

species. These patterns again reflect the successional 

events that initially created large populations across wide 

areas of both quaking aspen and paper birch that are 

now senescing. Conversely, the relatively low values per 

acre found on Michigan’s non-reserved forest land reflect 

management that typically removes low vigor trees.

Overall, FIA data suggest Isle Royale’s forests are a 

unique ecosystem due to a combination of factors: 

existence of boreal and temperate biomes, remote 

location in Lake Superior, disturbance legacy related 

to natural processes and mining exploration, absence 

of forest management for over eight decades, and 50 

years of complex interactions between moose/wolf 

populations. 

Isle Royale, archipelago. Photo by Linda Nagel, Michigan Technological 

University; used with permission.

Isle Royale, 

Lake Richie 

hepatica flower 

and lycopodium. 

Photo by Karena 

Schmidt, Michigan 

Technological 

University; used 

with permission.
22

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24 p.

This publication provides a baseline overview of forest resources for Isle Royale National 

Park (Isle Royale) using data from the Forest Inventory and Analysis (FIA) Program of 

the U.S. Department of Agriculture, Forest Service. The availability of permanent FIA 

plots allows for the first-ever comparison of Isle Royale’s forest conditions (2006-2010) 

to reserved and non-reserved forest land within Michigan’s Laurentian Mixed ForestEcoprovince 212. Isle Royale’s prominent forest types, structure, and species composition 

reflect human and natural disturbances. FIA data suggest Isle Royale’s species-specific 

stand-size stocking, growth and mortality rates, tree densities, volume, live biomass, and 

aboveground and belowground carbon reflect a unique ecosystem due to a combination of 

factors: remote location in Lake Superior, disturbance legacy related to natural processes 

and mining exploration, absence of forest management for more than eight decades, and 50 

years of complex interactions between moose/wolf populations.

KEY WORDS: reserved forest land, inventory, forest area, volume, mortality, growth, forest 

health, biomass, carbon, disturbance, ecoprovince, succession

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