United States

Department of

Agriculture

Forest

Service

Northern

Research Station

General Technical 

Report NRS-7

AFTER THE BLOWDOWN:

A RESOURCE ASSESSMENT

OF THE BOUNDARY WATERS

CANOE AREA WILDERNESS, 

1999 - 2003

W. Keith Moser, Mark H. Hansen, Mark D. Nelson, Susan J. Crocker, 

Charles H. Perry, Bethany Schulz, Christopher W. Woodall, 

Linda M. Nagel, Manfred E. Mielke
Northern Research Station

U.S. Department of Agriculture – Forest Service

11 Campus Boulevard Suite 200

Newtown Square, PA 19073-3294

2007

www.nrs.fs.fed.us

Abstract

The Boundary Waters Canoe Area Wilderness (BWCAW) is an ecological 

and recreational treasure situated within the Superior National Forest 

in northern Minnesota, USA. It contains some of the last unspoiled 

remnants of the great North Woods of the Lake Superior region. A major 

storm hit the BWCAW on July 4, 1999. Known as the “Boundary WatersCanadian Derecho,” this rare type of storm lasted for more than 22 hours, 

traveled more than 1,300 miles, and produced wind speeds averaging 

almost 60 mph. Following the devastation of the windstorm, the Forest 

Inventory and Analysis unit of the Northern Research Station collaborated 

with the Eastern Region of the USDA Forest Service and the Minnesota 

Department of Natural Resources to sample this landscape and assess 

the effects of this catastrophic event.

Live-tree volume per acre estimates in the BWCAW were 29 percent 

lower for plots damaged by wind (796 cubic feet/acre) than for plots with 

no disturbance (1,128 cubic feet/acre). For the aspen/birch forest-type 

group and the hardwoods supergroup, volume per acre was signifi cantly 

lower in blowdown conditions than in conditions of no disturbance. Mean 

fuel loadings estimates indicate that blowdown areas had nearly twice 

the 100- and 1,000-hr+ fuels as the non-blowdown areas. The means 

of 10-, 100-, and 1,000-hr+ fuel loadings in BWCAW blowdown areas 

were higher than the means for these three classes in the BWCAW nonblowdown areas.

Almost every comparison between forest types showed a decline 

in overstory species diversity in blowdown areas compared to nonblowdown areas. Only aspen and other hardwoods and nonstocked 

forest-type groups showed a negligible change. When we examined 

understory diversity, measured by species richness, we found just the 

opposite: most of the blowdown sites showed increased diversity. The 

exceptions to this trend were in paper birch and balsam fi r forest types.
AFTER THE BLOWDOWN:

A RESOURCE ASSESSMENT

OF THE BOUNDARY WATERS

CANOE AREA WILDERNESS, 

1999 - 2003

W. Keith Moser, Mark H. Hansen, Mark D. Nelson, Susan J. Crocker, 

Charles H. Perry, Bethany Schulz, Christopher W. Woodall, 

Linda M. Nagel, Manfred E. Mielke

USDA Forest Service

Forest Inventory and Analysis, Northern Research Station, and

Northeastern Area, State and Private Forestry, St. Paul, Minnesota
Acknowledgments

This study would not have been possible without the support of the Superior National 

Forest; Northeastern Area, State and Private Forestry; and the Minnesota Department 

of Natural Resources. Some maps were provided by Dale Gormanson and 

Barry T. Wilson. 

Photographs are courtesy of Dave Hansen, University of Minnesota Agricultural 

Experiment Station.
The Boundary Waters Canoe Area Wilderness (BWCAW) is an ecological and 

recreational treasure within the Superior National Forest (SNF) in northern 

Minnesota that is comprised of a patchwork of lakes and forests. Portions of the 

BWCAW and neighboring Quetico Provincial Park in Ontario, Canada, contain 

some of the last unspoiled remnants of the great North Woods of the Lake Superior 

region. A resource assessment of the BWCAW presented both a challenge and an 

opportunity for the Northern Research Station’s Forest Inventory and Analysis (NRS 

FIA) program. This program was originally designed to provide strategic inventories 

of the forest resources for all 50 states. NRS FIA’s strength lies in its grid-based plot 

system, which provides accurate estimates over large areas, e.g., states.

Following the devastating windstorm in July 1999, there was a need to inventory 

the BWACW. NRS FIA collaborated with the Eastern Region of the USDA Forest 

Service and the Minnesota Department of Natural Resources to meet the challenge of 

sampling this landscape and assessing the effects of that catastrophe. The SNF funded 

a temporary intensifi cation of NRS FIA’s sampling scheme, allowing the collection 

of more data in the BWCAW than otherwise would have been possible. The goals of 

this report are to summarize some of the data collected and examine the impact of 

the windstorm on the BWCAW. The Forest Service’s Northeastern Area, State and 

Private Forestry provided funding for this report, which is a collaborative effort of 

the National Forest System, State and Private Forestry, NRS FIA, and the Minnesota 

Department of Natural Resources.

FOREWORD
CONTENTS

Foreword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

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

The Blowdown . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

 How Much was Standing: Standing Volume After the Blowdown . . . . . . . . . . . 4

 How Much was Blown Down: NRS FIA Assessment 

 of Down Woody Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

 Effects of Blowdown on Overstory and Understory Diversity . . . . . . . . . . . . . 12

The Resource After the Blowdown. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

 Forest Land Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

 Tree Number and Stand-size Class . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

 Volume. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

 Species Composition and Diversity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

 Why tree species diversity is important: forest health examples . . . . . . . . 25

 Composition and structure of selected forest types . . . . . . . . . . . . . . . . . . 25

 Diversity of overstory species. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

 Species composition and diversity of understory vegetation . . . . . . . . . . . 33

 Age . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

 Soil Resource of the BWCAW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

 Inventory Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

 Down Woody Material Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

 Geospatial Datasets and Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

References. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 51

Appendix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

INTRODUCTION

The Boundary Waters Canoe Area Wilderness 

Embedded in the Quetico-Superior region of northeastern Minnesota and southwestern Ontario, Canada, the Boundary Waters Canoe Area Wilderness (BWCAW) 

spans 1.1 million acres of the Superior National Forest (SNF) (Fig. 1). Forests and 

lakes form the predominant land cover of the BWCAW (Fig. 2). Numerous factors, 

including topography, species mix, and history (managed and unmanaged), and 

individual disturbances such as fi re, weather, and animal browsing have shaped 

BWCAW’s forests. The result is a mosaic of vegetation structures, species, 

and ages.

Figure 1. The Boundary 

Waters Canoe Area 

Wilderness, Superior National 

Forest in Minnesota.

Figure 2. Land cover within 

the Boundary Waters Canoe 

Area Wilderness (U.S. 

Geological Survey, National 

Land Cover Dataset of 2001).

Emergent herbaceous wetlands

Open water

Natural barren

Herbaceous

Deciduous forest

Evergreen forest

Mixed forest

Shrubland

Woody wetlands

PAGE 1
PAGE 2 INTRODUCTION

Located on the southern portion of the Canadian Shield, the BWCAW was shaped 

by glaciers that exposed bedrock and formed a multitude of lakes connected by 

streams and later by portages. Controlled fi rst by the Sioux and later by the Ojibwe 

peoples, the Boundary Waters area was occupied by the French, British and, after the 

Louisiana Purchase in 1803, the Americans. Two treaties, the fi rst with the British in 

1842 that fi xed the boundary between the United States and Canada and the second 

between the United States and the western Ojibwe in 1854, opened the region to 

exploration and settlement. There was some interest in gold mining but the real 

mineral wealth lay in various iron ores in the ground, resulting in extensive open-pit 

and deep-shaft mining activity which, in turn, led to the establishment of numerous 

settlements (Heinselman 1996).

By World War I, much of the land in the present BWCAW had been burned or 

logged. As a result, white pine, red pine, and white spruce declined in dominance 

while aspen, jack pine, balsam fi r, and black spruce became more prominent. As 

people became more interested in using the region’s wildlands for recreation and 

in exploiting its resources, conservation became a popular cause among many 

Minnesotans, resulting in successive withdrawals of land from management and 

development and the designation of much of it as the Superior National Forest 

in 1909 (Heinselman 1996). The strip of border country from Basswood Lake to 

Saganaga Lake, which contains some of the most ecologically interesting portions 

of the present BWCAW, was added to the Forest in 1936. Many administrative and 

policy initiatives affected the region in the intervening years, but the most signifi cant 

was the Wilderness Act of 1964, which designated the BWCAW as a unit of the 

National Wilderness Preservation System. This act recognized the “unique history 

and character” of the BWCAW and provided for special management considerations 

that have shaped the Boundary Waters to this day (Heinselman 1973). 

Today, the BWCAW is one of the most popular wilderness areas in the country, 

receiving hundreds of thousands of visitors each year. Lacking roads and motorized 

vehicles, most of the BWCAW is accessible only by foot, canoe, or kayak. With more 

than 1,500 miles of waterway, it is a popular backcountry destination (USDA Forest 

Service 2006).
THE BLOWDOWN

On July 4, 1999, a major storm event 

within the BWCAW, known as the 

Boundary Waters-Canadian Derecho, 

lasted for more than 22 hours, traveled 

more than 1,300 miles, and produced 

windspeeds averaging nearly 60 mph. The 

blowdown caused widespread devastation 

with casualties both in Canada and the 

United States. Moving from WSW to ENE, the storm entered the Arrowhead region 

of northeastern Minnesota in the early afternoon. Here, winds of 80 to 100 mph 

resulted in injuries to about 60 canoe campers and damage to tens of millions of trees 

within 477,000 acres of forest land on the SNF (USDA Forest Service 2002) in the 

course of leveling a swath 30 miles long and 4 to 12 miles wide. Such a storm can 

dramatically affect water quality, increase the potential for wildfi re, and signifi cantly 

infl uence forest composition. It was because of the latter that the Northern Research 

Station’s Forest Inventory and Analysis (NRS FIA) program was requested to 

intensify the sample of its inventory within the BWCAW.

PAGE 3
PAGE 4 THE BLOWDOWN

How Much was Standing: Standing Volume After the Blowdown

NRS FIA fi eld plot data were combined with geospatial datasets in a geographic 

information system to estimate the net cubic-foot volume of all live trees on forest 

land in the SNF, in BWCAW, in blowdown polygons, and within a 3-mile buffer 

surrounding the blowdown polygons (Fig. 3). Estimates were further stratifi ed 

by fi eld-level observations of plot-condition attributes, including softwoods 

vs. hardwoods, forest type, forest-type group, and disturbance codes (Table 1). 

Variances of these volume estimates, calculated under the assumption of simple 

random sampling, were used to determine 90-percent confi dence intervals. Paired 

comparisons of estimates, e.g., inside vs. outside blowdown polygons, were 

interpreted as being signifi cantly different when their respective confi dence intervals 

were not overlapping.

Figure 3. Superior National 

Forest, Boundary Waters 

Canoe Area Wilderness, and 

blowdown areas, St. Louis, 

Lake, and Cook Counties, 

Minnesota.

How We Estimated It

Attribute Source Description

County Geographic St. Louis, Lake, Cook – political boundaries

SNF Geographic Superior National Forest – administrative boundary

BWCAW Geographic Boundary Waters Canoe Area Wilderness – 

 administrative boundary

Blowdown Geographic Polygon delineation of blowdown area classifi ed via 

 LandsatTM imagery

5-km (3-mile) buffer Geographic Area encompassed by 5-km (3-mile) buffer surrounding 

 blowdown polygons

Forest type Plot Jack pine type, aspen type

Forest-type group Plot White/red/jack pine group, aspen/birch group

Forest super group Plot Softwoods, hardwoods

Disturbance code Plot None (0), Unknown/not sure (70), Wind or weather 

 (50 or 52), Other

Table 1. Categories for 

estimating forest volume.
THE BLOWDOWN PAGE 5

What We Found Estimates of net cubic-foot (ft3

) volume per acre of all live trees on forest land did 

not differ signifi cantly between the BWCAW (1,066 ft3

/acre) and the remainder of 

SNF outside the BWCAW (990 ft3

/acre) (Fig. 4). Likewise, volume estimates within 

forest-type groups and forest types were not signifi cantly different between BWCAW 

and non-BWCAW portions of the SNF.

Figure 4. Forest volume 

within the Superior National 

Forest inside vs. outside the 

Boundary Waters Canoe Area 

Wilderness.

Forest type/group

Net volume (ft3/acre)

2,000

1,500

1,000

500

0

All

Softwoods

White/red/jack pine group

Jack pine type

Hardwoods

Aspen/birch group

Aspen type

SNF

Outside BWCAW

BWCAW

Error bars: 95 percent Confi dence Intervals
PAGE 6 THE BLOWDOWN

Within the 3-mile buffer area of the BWCAW (Fig. 5), estimates of volume per acre 

were signifi cantly lower for forest land with condition-level plot observations of wind 

damage than for undisturbed forest land, for all types/groups (707 vs. 1,154 ft3

/acre), 

softwoods (582 vs. 1,003 ft3

/acre), hardwoods (763 vs. 1,322 ft3/acre), and aspen/

birch group (748 vs. 1,282 ft3

/acre). Again, there were too few NRS FIA plots from 

other forest-type groups for comparisons of volume by condition damage code within 

the 3-mile buffer. Net volume (ft3/acre)

2,000

1,500

1,000

500

0

Forest type/group

All

Softwoods

White/red/jack pine group

Jack pine type

Hardwoods

Aspen/birch group

Aspen type

All plots

No disturbance

Wind damage

Error bars: 95 percent Confi dence Intervals

Figure 5. Forest volume within 

Boundary Waters Canoe Area 

Wilderness, inside a 3-mile 

(5 km) buffer surrounding and 

including blowdown polygons.
THE BLOWDOWN PAGE 7

What This Means Forest volume per acre did not differ signifi cantly between the BWCAW and the 

remainder of SNF. Therefore, per-acre volume of trees for all forest types was the 

same inside the BWCAW as it was in the Superior National Forest, but outside of the 

BWCAW. Looking just at forest land within the BWCAW, standing volume on forest 

land within the blowdown was signifi cantly lower than that outside the blowdown. 

While this was expected, it is interesting that not all blowdown plots were void of 

standing trees, nor was it consistent across forest types. This was due to different 

levels of wind damage across the landscape and differences in susceptibility to 

damage among forest types. Although both plot-level FIA data and remote sensingbased geospatial data were useful for comparing blowdown and non-blowdown forest 

volume, we favored a hybrid approach, using geospatial data to focus analyses on the 

vicinity of blowdown damage, coupled with analysis of FIA inventory data based on 

fi eld observations of wind damage.
PAGE 8 THE BLOWDOWN

How Much was Blown Down: NRS FIA Assessment of Down Woody Material

The BWCAW blowdown had substantial impacts on fuel and stand attributes 

at various spatial scales (Mattson and Shriner 2001). The amount of fuel in the 

BWCAW was increased substantially. This has increased the probability of wildfi re 

within or adjacent to the wilderness (Leuschen et al. 2000). It is estimated that the 

range in total woody fuel loadings increased from 4 to 20 tons/acre to 45 to 100 

tons/acre as a result of the blowdown. The estimated mean fuel loading in a typical 

BWCAW stand is 10 tons/acre (Leuschen et al. 2000). Assessing the down woody 

fuel loadings and fuel/stand relationships following a large-scale wind disturbance 

in the BWCAW helps describe not only the fuel loadings in the BWCAW and the 

surrounding forest ecosystem but also the ecosystem processes at work.

Estimates of mean fuel loadings for the three study strata indicate that blowdown 

areas have nearly twice the 100- and 1,000-hr+ fuels as the non-blowdown BWCA 

area (Fig. 6). The means of 10-, 100-, and 1,000-hr+ fuel loadings in BWCAW 

blowdown areas were higher than those for these three classes in both the BWCAW 

non-blowdown areas and the Laurentian mixed-forest ecosystem of the Lake States 

(Bailey 1995) (Ecoregion 212; see Figure 32) (ANOVA, all P < 0.1, Fig. 6).

The size and decay classes of 1,000-hr+ fuels did not differ among the three study 

strata (Tables 2 and 3, ANOVA, P > 0.4). Fuels in the 3- to 8-inch diameter class 

accounted for 83 percent of the total number of 1,000-hr+ pieces/acre in BWCAW 

blowdown areas (Table 2). Similarly, the Ecoregion 212 and non-blowdown areas 

of the BWCAW had 84 and 86 percent of the total number of 1,000-hr+ pieces. The 

difference in the mean number of 1,000-hr+ fuels was not signifi cant among the study 

strata for any decay class (Table 3). 

Trees per acre and tons of down woody fuels per acre were not strongly related 

among the three study strata (Fig. 3). However, BWCAW blowdown locations had 

higher mean fuel loadings (Fig. 7) when trees per acre were low (0 to 303 tons/acre) 

compared to non-blowdown areas and Ecoregion 212. When the number of standing 

trees per acre was high, all three areas had similar mean total fuel loadings. Logically, 

one would expect blowdown areas to have fewer standing trees and more fuels. Areas 

less affected by blowdown would retain more standing trees, with fewer down trees, 

resulting in lower fuel levels. These expectations are supported by the blowdown 

observations in Figure 7.

What We Found
THE BLOWDOWN PAGE 9

Figure 6. Mean fuel class 

estimates for forested NRS FIA 

plots (ANOVA, all P < 0.1).

Figure 7. Mean total fuel 

estimates for three study areas 

(ANOVA, all P < 0.0001).

Fuel class

Tons/acre

1-hr 10-hr 100-hr 1,000-hr+

14

12

10

8

6

4

2

0

Ecoregion 212

BWCAW Non-blowdown

BWCAW Blowdown

Trees/acre

0 to 303 304 to 606 607 to 910 911+

212 BWCAW Non-blowdown BWCAW Blowdown

Total fuels (tons/acre)

30

25

20

15

10

5

0
PAGE 10 THE BLOWDOWN

Table 2.—Mean 1,000-hr+ 

pieces/acre by diameter class 

and study area (ANOVA, 

P < 0.4) Percent Percent Percent

 Mean SE of total Mean SE of total Mean SE of total

 3-8 155 9.7 84 159.5 20.2 86 167.1 21.4 83

 8-13 25.9 2.4 14 25.1 3.6 14 31.6 4.5 16

 13-18 2.4 0.4 1 0.8 0.4 0 2.4 0.8 1

 19+ 0.8 0.4 0 0 0 0 0.8 0.4 0

Piece 

diameter 

(inches)

Ecoregion 212 BWCAW no damage BWCAW damage

Pieces per acre (no.)

Table 3.—Mean 1,000-hr+ 

pieces/acre by decay class and 

study area (ANOVA, P > 0.3)

 Percent Percent Percent

 Mean SE of total Mean SE of total Mean SE of total

 1 17 3 9 9 6 5 22 10 11

 2 44 5 24 38 10 20 48 10 24

 3 59 5 32 47 7 25 62 10 31

 4 42 4 23 40 6 22 35 6 17

 5 21 3 12 51 11 27 34 8 17

Decay 

class

Ecoregion 212 BWCAW no damage BWCAW damage

Pieces per acre (no.)
THE BLOWDOWN PAGE 11

Smaller diameter fuels decay quickly 

and disappear from wind-disturbed 

ecosystems, while larger fuels take longer 

to decay and thus remain in the ecosystem 

for longer periods. The greatest difference 

in fuel loadings among the study areas was 

for 100-hr fuels, which are the equivalent 

of large tree branches. The blowdown 

dramatically increased fuel loadings of 100-hr fuels compared to other fuel classes. 

Therefore, large-scale blowdowns may have the greatest effect on limbs and crowns, 

detaching them from standing trees rather than knocking down the entire bole. There 

were signifi cantly more 1,000-hr+ pieces in the BWCAW blowdown area, but the 

distribution of decay and size classes indicates that the accumulation of fuels from 

fallen trees is the same whether tree mortality was the result of normal processes, 

such as suppression mortality in Ecoregion 212, or large wind disturbances such as in 

the BWCAW blowdown.

In this study, we found no discernible relationship between total down woody fuel 

loadings and trees per acre. The amount of down woody fuel in Upper Great Lakes 

forests may be more dependent on successional trends and disturbance history (both 

natural and anthropogenic) than attributes for standing trees. Two stand development 

processes seem to confound correlations between these attributes and fuel loadings. 

First, some stands develop as a result of density-induced mortality and occasional 

individual-tree blowdowns (Canham and Loucks 1984, Frelich and Graumlich 1994). 

For these stands, a relatively constant amount of down woody materials can persist 

through all stages of stand development because of a balance between mortality and 

the decay of older woody materials. Other stands experience sudden stand-level 

disturbances, such as those observed in the blowdown areas of the BWCAW (see 

Canham and Loucks 1984, Frelich and Graumlich 1994, Peterson 2000, Woods 

2004). For these stands, sudden reductions in stand density simultaneously increase 

fuel loadings. Both processes (small wind disturbances and infrequent, large wind 

catastrophes) appear to be occurring in Upper Great Lakes forests.

What This Means
PAGE 12 THE BLOWDOWN

Effects of Blowdown on Overstory and Understory Diversity

Structural and species diversity is an important characteristic of most ecosystems, 

including the BWCAW. The pattern and intensity of disturbance infl uence both sitespecifi c and landscape diversity. Identifying and understanding the storm’s impact on 

diversity is an important research priority (Mattson and Shriner 2001).

Even with a limited number of plots, we observed two interesting patterns. Where 

we had comparable forest types in blowdown and non-blowdown conditions, nearly 

every one showed a decline in overstory species diversity when we compared plots 

with no disturbance to those with weather damage (wind) (Table 4). Only aspen and 

other hardwoods and nonstocked forest-type groups showed a negligible change. 

When we examined understory diversity, measured by species richness, we found just 

the opposite: most of the blowdown sites showed increased diversity (Table 5). The 

exceptions were in paper birch and balsam fi r forest types.

Wind storms of similar magnitude to the storm in July 1999 can radically change the 

dynamics of a forest. Results suggest that some trees were damaged more heavily 

than others as large trees above the canopy may have been more susceptible to 

wind damage than trees just below the forest canopy. Such susceptibility would 

have reduced overstory diversity, as in the BWCAW. Yet this reduction increased 

opportunities for the understory vegetation community, probably due to the increased 

light level and reduced competition for soil moisture and nutrients. In the absence of 

further disturbances, overstory tree species again will dominate the site and return 

understory diversity to pre-1999 levels.

What We Found

What This Means
THE BLOWDOWN PAGE 13

Table 4. Shannon index for 

overstory species diversity, 

by disturbance category and 

forest type (N = 53 plots). All conifer forest types 1.12 1.03 -8

All hardwood forest types 1.25 1.01 -19

Aspen 1.29 1.28 0

Paper birch 1.34 1.00 -26

Sugar maple/beech/yellow birch 1.65

Other hardwoods and nonstocked 0.86 0.85 0

Balsam fi r 1.64 0.47 -71

Black spruce 0.95 0.78 -17

Eastern white pine 1.51

Jack pine 0.89

Northern white-cedar 0.89 1.05 18

White pine/red oak/white ash 2.09 1.75 -16

White spruce 1.36

Other pine/hardwood 1.55

Disturbance category

Percent

Forest type No disturbance Weather difference

Table 5. Understory species 

richness, by disturbance 

category and forest type 

(N = 53 plots). All conifer forest types 19.6 21.0 7

All hardwood forest types 19.1 20.1 6

Aspen 19.3 20.0 3

Paper birch 22.2 19.4 -12

Sugar maple/beech/yellow birch 21.0

Other hardwoods and nonstocked 12.3 25.0 103

Balsam fi r 30.0 22.0 -27

Black spruce 19.3 25.5 32

Eastern white pine 19.5

Jack pine 16.0

Northern white-cedar 20.0 20.5 3

White pine/red oak/white ash 17.0 17.0 0

White spruce 16.0

Other pine/hardwood 29.0

Disturbance category

Percent

Forest type No disturbance Weather difference

THE RESOURCE AFTER THE BLOWDOWN

Forest Land Area

The chief motivation for setting aside the BWCAW was to preserve the land from 

further exploitation. Along with the tremendous water resources, the structure and 

diversity of the forests are the foundation of the Boundary Waters region. Of the 

BWCAW’s 1.1 million acres, approximately 72 percent (783,000 acres) is forest 

land and 20 percent (190,000 acres) is open water. The forest land of the BWCAW 

is in a landscape diverse in geology, topography, disturbance history, and parcel 

size. Peninsulas, isthmuses, islands, lakes, ponds, rivers, and swamps create 

suitable conditions for numerous tree species in the North Woods. The forests of the 

Boundary Waters region vary by age, size, forest type, and forest-type group. NRS 

FIA defi nes a forest-type group as a collection of species grouped by co-occurrence, 

similar biological characteristics, or other factors.

About 51 percent of forest land is covered by softwood types (Fig. 8) such as black 

spruce and jack pine. The remaining 49 percent is dominated by hardwood forest 

types. Seventeen forest-type groups were recorded during the 1999-2003 inventory: 

jack pine; red pine; eastern white pine; balsam fi r; white spruce; black spruce; 

tamarack; northern white-cedar; white pine/red oak/white ash; other pine/hardwood; 

black ash/American elm/red maple; sugarberry/hackberry/elm/green ash; sugar 

maple/beech/yellow birch; elm/ash/locust; aspen; paper birch; and balsam poplar 

(Fig. 9). Seventy-one percent of total forest land area is represented by four forest 

types: paper birch (166,000 acres), aspen (164, 000 acres), black spruce (136,000 

acres), and jack pine (92,000 acres). Sixty-two percent of total paper birch area 

(103,000 acres), 45 percent of total aspen area (74,000 acres), and 45 percent of total 

jack pine area (41,000 acres) was in medium-diameter trees (Fig. 9). Many of the 

forest-type groups, e.g., red pine and eastern white pine, had the bulk of the acreage 

in the medium- and large-diameter stand-size classes. Prominent exceptions were 

balsam fi r, black spruce, tamarack, and black ash/American elm/red maple. Black 

spruce, which generally grows on sites that do not support rapid growth or large 

trees, has most of its acreage in the small and medium classes. This species generally 

averages 9 inches in diameter at maturity on good sites and 5 inches in diameter on 

poor sites. Tamarack can reach 20 inches in diameter on good sites but its average 

diameter is between 5 to 6 inches on nutrient-poor peatlands in northern Minnesota.

What We Found

PAGE 15
PAGE 16 THE RESOURCE AFTER THE BLOWDOWN

Figure 8. Forest land by forest 

type in the Boundary Waters 

Canoe Area Wilderness.

Figure 9. Area of forest land 

by forest type and stand-size 

class in the Boundary Waters 

Canoe Area Wilderness, 

1999-2003.

Forest Land

Softwoods

Hardwoods

Forest land area (thousand acres)

Jack pine

Red pine

Eastern white pine

Balsam fi r

White spruce

Black spruce

Tamarack

Northern white-cedar

White pine/

red oak/white ash

Other pine/hardwood

Black ash/

American elm/red maple

Sugar maple/

beech/yellow birch

Aspen

Paper Birch

Other hardwoods 

and nonstocked

Large diameter

Medium diameter

Small diameter

0 20 40 60 80 100
THE RESOURCE AFTER THE BLOWDOWN PAGE 17

Tree diameter is not an accurate indicator of tree age in the BWCAW. Although 

small trees are sometimes associated with young stands in many forest types, 

the combination of low site quality and short growing seasons in the BWCAW 

confounds analyses of age vs. tree size. Although the BWCAW has high species and 

structural diversity, large disturbances still drive forest composition and structure. 

This conclusion is based on the dominance of four forest types—aspen, jack pine, 

paper birch, and black spruce—that rapidly colonize areas that are opened up by 

disturbances such as fi re or windthrow. Nevertheless, disturbances are not consistent 

in their reach or impact; for example, a fi re does not uniformly burn every acre. 

Therefore, the patchy nature of disturbance creates a variety of stands of different age 

and species composition.

What This Means
PAGE 18 THE RESOURCE AFTER THE BLOWDOWN

Tree Number and Stand-size Class

An estimate of the number of trees in a forest can tell us something about its structure 

and often provides insight into the history of the stand. In general, productive 

sites with long growing seasons allow young trees to increase in diameter quickly. 

Therefore, a 9-inch tree with good crown position might be relatively young. 

However, in the BWCAW, where there is a short growing season and numerous 

low-productivity sites, a high number of medium-diameter stands does not always 

correlate with an abundance of middle-aged trees.

Stands generally start out with many small, young trees that become larger and less 

numerous as a result of competition-induced mortality. Therefore, a fully stocked 

stand with an average diameter less than 5 inches would have more trees per acre 

than a fully stocked stand where the average diameter exceeds 12 inches. Stand 

density is an important indicator of future stand dynamics because dense stands 

face higher competition for resources, e.g., light, water, and nutrients. Successful 

competition for resources helps determine species composition, growth rate, and 

general forest health. The combination of short growing seasons, low-productivity 

sites, and the presence of several species that tend to regenerate into dense stands 

of seedlings or sprouts and differentiate1

 slowly creates conditions for slow stand 

growth.

There were an estimated 455 million live trees in the BWCAW in 1999-2003 

(Fig. 10). The overall proportions were similar to those of the total forest area—

231 million trees (51 percent) were in the softwood species group versus 223 million 

trees in the hardwood-dominated forest types. There were more trees in mediumdiameter stands for both softwood and hardwood types. Hardwoods had more trees 

than softwoods in medium-diameter stands, while softwoods had more trees in smalldiameter stands (Fig. 10).

Most of the trees in the balsam fi r and black spruce forest types were in smalldiameter stands (Fig. 11 and Fig. 12a - Group A). Three of the four most prominent 

cover types (aspen, paper birch, and jack pine), had a preponderance of trees in 

the medium-diameter class (Fig. 11 and Fig. 12b - Group B). Finally, the red pine, 

eastern white pine (including white pine/red oak/white ash), white spruce, and 

northern white-cedar forest types had a plurality of trees in large-diameter stands 

(Fig. 11 and Fig. 12c - Group C).

What We Found

1

Differentiation is the process wherby groups of trees compete with each other, gain advantage, and 

grow (and die) at different rates. The ability of a tree species to respond to disturbance and gain 

advantage over its neighbors are two of the factors that determine whether that tree will become part 

of a future forest canopy.
THE RESOURCE AFTER THE BLOWDOWN PAGE 19

What This Means Each group of forest types represents a response to different disturbances. Group C 

consists of larger-diameter trees that likely are growing on a site that was previously 

disturbed. They probably are being replaced by younger and more shade-tolerant 

species. Group A is a mixture of two shade-tolerant forest types with different 

patterns of development. Black spruce can become established under closed canopies 

of shade intolerants but it also grows well in open sites. By contrast, balsam fi r 

generally becomes established under canopies of pines, aspen, or birch. Black spruce 

is found on wet sites that limit growth and extend the time that trees remain small in 

diameter. The medium-size trees of Group B (aspen, birch, jack pine) might represent 

the passage of time since the last disturbance. A century of fi re suppression means 

older trees have not been killed by wildfi re and the growing conditions that facilitate 

regeneration of these species have not been created.

140

120

100

80

60

40

20

0

Small diameter Medium diameter Large diameter

Stand-size class

Trees (millions)

Softwood forest types

Hardwood forest types

Figure 10. Number of all-live 

trees on forest land in the 

Boundary Waters Canoe Area 

Wilderness, 1999-2003.
PAGE 20 THE RESOURCE AFTER THE BLOWDOWN

Figure 12. Patterns of 

diameter distribution vs. 

number of trees in the 

BWCAW: (a) plurality in stands 

with smaller trees, (b) plurality 

in stands with medium-size 

trees, (c) plurality in stands with 

larger trees (compare to the 

actual distribution of trees by 

forest type and diameter class 

in Figure 11).

Figure 11. Number of trees in 

the Boundary Waters Canoe 

Area Wilderness, 1999-2003.

Jack pine

Red pine

Eastern white pine

Balsam fi r

White spruce

Black spruce

Tamarack

Northern white-cedar

White pine/

red oak/white ash

Other pine/hardwood

Black ash/

American elm/red maple

Sugar maple/

beech/yellow birch

Aspen

Paper Birch

Other hardwoods 

and nonstocked

Large diameter

Medium diameter

Small diameter

Trees (millions)

0 10 20 30 40 50 60 70 80

Number of trees

a.

DiameterDiameterDiameter

Number of trees Number of trees

b. c.
THE RESOURCE AFTER THE BLOWDOWN PAGE 21

How much space does a tree occupy? The answer 

is determined using tree size; stem volume is a 

measure of tree size. The volume of all the trees 

in a forest is a function of the age of the species 

present, the productivity of the site, and growing 

conditions. Growing conditions include weather, 

disturbances, or other stressors. A forest with good 

site productivity, favorable growing conditions, 

and suitable species likely will have greater 

volume than it would on a poor site with a high 

level of disturbance and unsuitable species.

In 1999-2003, all live-tree volume on forest land in the BWCAW was an estimated 

832 million cubic feet (Fig. 13). Hardwoods accounted for 47 percent and softwoods 

accounted for 53 percent. Of this volume, 383 million cubic feet were in largediameter stands, 400 million cubic feet were in medium-diameter stands, and 49 

million cubic feet were in small-diameter stands. Seventy-two percent of total 

volume was in fi ve forest types: jack pine (94 million cubic feet/11 percent), eastern 

white pine (84 million cubic feet/10 percent), black spruce (84 million cubic feet/10 

percent), aspen (199 million cubic feet/24 percent), and paper birch (144 million 

cubic feet/17 percent) (Fig. 14).

Several forest types had most of their total volume in a particular stand-size class. 

Tamarack had all of its volume in medium- or small-diameter stands (Fig. 14). The 

volumes of elm/ash/locust and balsam poplar volume were mostly in mediumdiameter stands. Ninety-four percent of red pine was in the large-diameter class and 

eastern white pine also had an overwhelming proportion of its total volume in largediameter stands (Fig. 14). Both pines are capable of great size. White pine/red oak/

white ash and northern white-cedar both had more than 70 percent of their volume in 

large-diameter stands.

There are three stand-size classes: small-diameter trees (Fig. 15a - Class A), mediumsize trees (Fig. 15b - Class B), and large-diameter trees (Fig. 15c - Class C). Most of 

the trees in jack pine stands were in medium-size stands, but there was more volume 

in large-diameter stands. Balsam fi r and black spruce had more trees in smalldiameter stands, though there was more volume in medium stands.

Volume

What We Found
PAGE 22 THE RESOURCE AFTER THE BLOWDOWN

Seven species make up the bulk of total volume: quaking aspen, paper birch, northern 

white-cedar, eastern white pine, red pine, jack pine, and black spruce (Fig. 16). 

Monocultures are rare in the BWCAW. For example, quaking aspen is found in every 

major forest type; its proportion of total volume ranges from 4 percent of the sugar 

maple/beech/yellow birch type to nearly two-thirds of the aspen type. Paper birch 

also is found in many forest types. Most of the softwood species are commonly found 

in softwood forest types. Most of the hardwood types contain more species than 

softwood types. 

Two primary dynamics shape forest composition in the BWCAW: (1) pioneer 

species such as aspen or jack pine occupy gaps created by disturbances, and (2) 

late successional species like balsam fi r start out in the understory. In the absence 

of disturbance, these species move into the overstory and eventually dominate the 

canopy. Shade-intolerant species establish in shade-tolerant forest types when a local 

disturbance creates gaps. While jack pine, paper birch, and aspen are opportunistic 

colonizers, continued lack of fi re will progressively reduce the ecological 

opportunities for these species to establish and thrive.

What This Means

Figure 13. Net volume of 

all-live trees in the Boundary 

Waters Canoe Area 

Wilderness, 1999-2003.

0-500

501-1,000

1,001-1,500

1,501-2,000

2,001+

Net cubic foot volume/acre
THE RESOURCE AFTER THE BLOWDOWN PAGE 23

Figure 14. Volume of all-live 

trees on forest land in the 

Boundary Waters Canoe Area 

Wilderness, 1999–2003.

Figure 15. Patterns of 

diameter distribution vs. alllive volume of trees in the 

Boundary Waters Canoe Area 

Wilderness: (a) plurality in 

stands with smaller trees, (b) 

plurality in stands with mediumsize trees, (c) plurality in stands 

with larger trees (compare to 

the actual distribution of trees 

by forest type and diameter 

class in Figure 14).

Jack pine

Red pine

Eastern white pine

Balsam fi r

White spruce

Black spruce

Tamarack

Northern white-cedar

White pine/

red oak/white ash

Other pine/hardwood

Black ash/

American elm/red maple

Sugar maple/

beech/yellow birch

Aspen

Paper Birch

Other hardwoods 

and nonstocked

Volume of all live trees (million ft3)

0 20 40 60 80 100 120 140

Large diameter

Medium diameter

Small diameter

All-live volume

a.

DiameterDiameterDiameter

All-live volume All-live volume

b. c.
PAGE 24 THE RESOURCE AFTER THE BLOWDOWN

Figure 16. Volume of all-live 

trees, Boundary Waters Canoe 

Area Wilderness, 1999-2003.

Jack pine

Red pine

Eastern white pine

Balsam fir

White spruce

Black spruce

Tamarack

Northern white-cedar

White pine / red oak / white ash

Other pine / hardwood

Black ash / American elm / red maple

Sugarberry/hackberry / elm / green ash

Sugar maple / beech / yellow birch

Elm / ash / locust

Aspen

Paper birch

Balsam poplar

Non stocked Balsam fir

Tamarack

White spruce

Black spruce

Jack pine

Red pine

Eastern white pine

Northern white-cedar

Red maple

Sugar maple

Yellow birch

Paper birch

Black ash

Green ash

Balsam poplar

Bigtooth aspen

Quaking aspen

Northern red oak

0

20

40

60

80

100

120

140

Balsam fir

Tamarack

White spruce

Black spruce

Jack pine

Red pine

Eastern white pine

Northern white-cedar

Red maple

Sugar maple

Yellow birch

Paper birch

Black ash

Green ash

Balsam poplar

Bigtooth aspen

Quaking aspen

Northern red oak

Forest type

Volume of all-live trees (million ft3

)

Species
THE RESOURCE AFTER THE BLOWDOWN PAGE 25

Species Composition and Diversity

Why tree-species diversity is important: forest health examples

A forest that includes a range of species, tree sizes, and ages can provide a variety of 

habitats for wildlife as well as a range of recreation and aesthetic experiences. Forest 

diversity infl uences and is infl uenced by forest health. For example, eastern spruce 

budworm, one of the most destructive insect defoliators in North America, defoliates 

millions of balsam fi r and spruce trees annually. The budworm defoliates only new 

growth; feeding affects growth rates and trees will die after 7 years of defoliation. 

Since 1949, spruce budworm has defoliated balsam fi r and white spruce in Minnesota 

every year but 1966. Black spruce is rarely defoliated and only when growing in 

association with balsam fi r or white spruce. In the BWCAW, balsam fi r and white 

spruce were defoliated 39 of the past 56 years. The most recent period of sustained 

defoliation occurred from 1983 to 1995; virtually all balsam fi r and white spruce in 

the BWCAW were affected. 

The forest tent caterpillar (FTC) has defoliated aspen 15 of the last 56 years. 

Repeated years of aspen defoliation can result in dieback and, in combination with 

drought, can cause tree mortality. Birch is occasionally defoliated by the FTC and 

is especially hard hit by drought and damage by the bronze birch borer and birch 

leaf miner. Old age also is a contributing factor. The most recent years of sustained 

defoliation occurred in 2000-2004.

Composition and structure of selected forest types

Jack pine, paper birch, and aspen. Three early successional forest types that rely 

on stand-replacing disturbances such as fi re are jack pine, paper birch, and aspen 

(Fig. 17). 

Figure 17. Location of 

selected forest types in the 

Boundary Waters Canoe Area 

Wilderness, 1999-2003.

Jack pine

Other softwoods

Eastern white pine

Black spruce

Other hardwoods

Forest type

Aspen

Paper birch
PAGE 26 THE RESOURCE AFTER THE BLOWDOWN

One of the most widespread conifers in northern North America, jack pine depends 

on fi re to prepare sites for regeneration and to open its serotinous cones. Large jack 

pine trees are somewhat fi re resistant but not as much as red pine or southern yellow 

pines. Paper birch, another early successional species, is a widespread hardwood 

tree that is valued by Native Americans. Pioneer species can be an indication of past 

disturbances, so they can help us determine stand history in the BWCAW. Quaking 

aspen is a widespread, aggressive colonizer of disturbed landscapes noted for its 

prolifi c sprouting and for its bright yellow leaves in the fall. Aspen represents a high 

proportion of total volume and total forest land area; its presence frequently points 

to the past occurrence of large disturbances. All three species can co-occur and 

frequently regenerate after the same disturbances (Heinselman 1973).

Not surprisingly, the all-live volume in jack pine stands was dominated by jack 

pine trees (Fig. 18). However, it is interesting that aspen and paper birch, and black 

spruce, a more shade-tolerant and presumably late successional species, also had 

signifi cant volume in the jack pine forest type. Black spruce becomes established 

after fi res (Heinselman 1973) but also may have established under a jack pine 

overstory. In the absence of disturbance, black spruce may succeed jack pine as the 

dominant species in the overstory.

All-live volume in the paper birch forest type inside the BWCAW totaled 144 million 

cubic feet, of which 54 percent was paper birch (Fig. 19). Quaking aspen had 21.7 

million cubic feet of volume in the paper birch type. Black spruce and northern 

white-cedar, two later successional species, had 20.3 and 7.3 million cubic feet of 

volume, respectively.

In the aspen forest type there were 182 million cubic feet of all-live volume. Sixtyeight percent or 124.1 million cubic feet resulted from the presence of quaking aspen 

(Fig. 20). The principal co-occurring species was paper birch (27.3 million cubic 

feet); jack pine volume was also high with 7.0 million cubic feet. There were 14.9 

million cubic feet of black spruce volume and 6.2 million cubic feet of balsam fi r 

volume in this forest type.

What We Found
THE RESOURCE AFTER THE BLOWDOWN PAGE 27

Jack pine is an important early successional species in the BWCAW. The presence 

of this species as well as that of aspen and paper birch points to a stand-initiating 

disturbance, probably fi re. All three forest types had signifi cant volumes of later 

successional species, particularly in the smaller diameter classes. This characteristic 

hints at the presence or absence of fi re. For example, having balsam fi r as an 

understory companion to jack pine suggests that fi re has not occurred since the stand 

was fi rst regenerated. Balsam fi r is one of few understory species that are likely to be 

much younger than the pioneer species in the overstory (Heinselman 1973). The data 

suggest that, in the absence of fi re, these more shade-tolerant species will grow into 

the canopy and create the understory conditions that will favor only shade-tolerant 

advance regeneration.

What This Means

Figure 18. All-live volume 

in the jack pine forest type, 

Boundary Waters Canoe Area 

Wilderness, 1999-2003.

Balsam fir

White spruce

Black spruce

Jack pine

Red pine

Eastern white pine

Northern white-cedar

Red maple

Paper birch

Balsam poplar

Bigtooth aspen

Quaking aspen

Northern red oak

5.0-6.9

7.0-8.9

9.0-10.9

11.0-12.9

13.0-14.9

15.0-16.9

17.0-18.9

19.0-20.9

0

2,000,000

4,000,000

6,000,000

8,000,000

10,000,000

12,000,000

14,000,000

16,000,000

18,000,000

5.0-6.9

7.0-8.9

9.0-10.9

11.0-12.9

13.0-14.9

15.0-16.9

17.0-18.9

19.0-20.9

Species

Diameter class 

(inches)

All-live volume (ft3

)
PAGE 28 THE RESOURCE AFTER THE BLOWDOWN

Figure 19. All-live volume in 

the paper birch forest type, 

Boundary Waters Canoe Area 

Wilderness, 1999-2003.

Figure 20. All-live volume 

in the aspen forest type, 

Boundary Waters Canoe Area 

Wilderness, 1999-2003.

Balsam fir

Tamarack (native)

White spruce

Black spruce

Jack pine

Red pine

Eastern white pine

Northern white-cedar

Red maple

Sugar maple

Yellow birch

Paper birch

Green ash

Bigtooth aspen

Quaking aspen 5.0-6.9

9.0-10.9

13.0-14.9

17.0-18.9

0

4,000,000

8,000,000

12,000,000

16,000,000

20,000,000 5.0-6.9

7.0-8.9

9.0-10.9

11.0-12.9

13.0-14.9

15.0-16.9

17.0-18.9

19.0-20.9

19.0-20.9

15.0-16.9

11.0-12.9

7.0-8.9

Balsam fir

White spruce

Black spruce

Jack pine

Red pine

Eastern white pine

Northern white-cedar

Red maple

Sugar maple

Paper birch

Black ash

Green ash

Bigtooth aspen

Quaking aspen 5.0-6.9

7.0-8.9

9.0-10.9

11.0-12.9

13.0-14.9

15.0-16.9

17.0-18.9

19.0-22.9

23.0-26.9

0

5,000,000

10,000,000

15,000,000

20,000,000

25,000,000

5.0-6.9

7.0-8.9

9.0-10.9

11.0-12.9

13.0-14.9

15.0-16.9

17.0-18.9

19.0-22.9

23.0-26.9

Species

All-live volume (ft3

)

Species Diameter class 

(inches)

All-live volume (ft3

)

Diameter class 

(inches)
THE RESOURCE AFTER THE BLOWDOWN PAGE 29

What We Found

Eastern white pine. Majestic eastern white pines, emergent above the forested 

canopy, offer one of the most evocative images within the BWCAW. White pine 

forest land is abundant in area (Fig. 9) and volume (Fig. 14). Eastern white pine and 

red pine once covered about 20 percent of the area in the BWCAW (Ayres 1899). 

Because white pine is somewhat resistant to fi re, its presence can be tied to periods 

of disturbance. Due to logging and uncontrolled fi res (natural and human caused), it 

occupies much less area today.

Most eastern white pine stands are 61 to 100 years old (Fig. 21). Most of the 

remaining volume falls into the 21 to 40 and 161 to 180 age groups. The large 

presence of paper birch and aspen in the 61 to 100 year age group suggests that the 

forest type was established by a signifi cant disturbance not repeated in subsequent 

years.

Figure 21. All-live volume in 

the eastern white pine forest 

type, Boundary Waters Canoe 

Area Wilderness, 1999-2003.

Balsam fir

White spruce

Black spruce

Jack pine

Red pine

Eastern white pine

Northern white-cedar

Red maple

Paper birch

Quaking aspen

0-20 years

21-40 years

41-60 years

61-80 years

81-100 years

100-120 years

121-140 years

141-160 years

161-180 years

0

5,000,000

10,000,000

15,000,000

20,000,000

25,000,000

0-20 years

21-40 years

41-60 years

61-80 years

81-100 years

100-120 years

121-140 years

141-160 years

161-180 years

Species

All-live volume (ft3

)

Age class (years)
PAGE 30 THE RESOURCE AFTER THE BLOWDOWN

Late successional forest type: sugar maple/birch/beech. A variation of the maple/

birch/beech forest type is common in the eastern portion of the BWCAW, where 

red maple (A. rubrum) is the largest component. The forest type has a fairly varied 

composition (Fig. 22). In addition to red maple there were signifi cant volumes of 

paper birch, bigtooth aspen, eastern white pine, black spruce, and jack pine. The 

oldest age class for all four forest types was 61 to 80 years. Judging from the fact that 

thin-barked red maple was able to establish, these data suggest that fi re was limited 

from 1920 to 1960. This gap fi ts neatly into Heinselman’s (1973) period of fi re 

suppression in the North Woods.

As we have observed with other forest types, there apparently was a gap in the 

normal disturbance regime, allowing the maple/birch/beech forest type to become 

established. The range of age classes in this type is striking in its limited extent, 

particularly when considering the range of potential maximum ages of the BWCAW’s 

forests.

Diversity resulting from the interaction between factors such as site, species, and 

disturbance history is a recurring theme in nearly every acre of forest land in the 

BWCAW. One example concerns eastern white pine. Because the bulk of the white 

pine volume was in the 61 to 100 year age class and mature white pine is moderately 

fi re resistant, it is likely that disturbances between 1899 to 1942 created conditions 

suited to white pine and its cohorts. The presence of red pine, birches, and aspen 

in similar age classes also suggest a fi re origin of the stand. Because of the relative 

fi re resistance of mature pines with thick bark, fi re does not necessarily result in 

the initiation of a new stand (Heinselman 1973). A fi re might not kill the overstory 

(releasing growing space) but would kill seedlings in the understory. The reason for 

the lack of young stands might be that the overstory density reached a point where 

any seedling that did germinate was unable to survive under the canopy.

What This Means

What This Means

What We Found
THE RESOURCE AFTER THE BLOWDOWN PAGE 31

Figure 22. All-live volume 

in the sugar maple/yellow 

birch/beech forest type, 

Boundary Waters Canoe Area 

Wilderness, 1999-2003.

Balsam fir

White spruce

Black spruce

Jack pine

Red pine

Eastern white pine

Red maple

Paper birch

Bigtooth aspen

Quaking aspen

Northern red oak

0-40 years

41-60 years

61-80 years

0

500,000

1,000,000

1,500,000

2,000,000

2,500,000

3,000,000

3,500,000

4,000,000

4,500,000

5,000,000

0-40 years

41-60 years

61-80 years

Species

All-live volume (ft3

)

Age class 

(years)

Diversity of overstory species

One measure of diversity is the number of species in a plot, stand, or region. This 

“species richness” treats species’ presence equally, whether there are 2 trees or 2,000. 

By contrast, the Shannon diversity index measures a combination of the number 

of species and the evenness or distribution of those species (Magurran 2003). A 

forest with 10 species where 90 percent of the area is occupied by a single species 

will have a lower Shannon index than a forest with 10 species where each of the 

species occupies a roughly equal proportion of the forest area. As in our example, the 

absolute magnitude of the index is not important; its value is as a relative index for 

comparing different landscapes (Peet 1975).

There are pockets of high and low tree species diversity in BWCAW forests. When 

estimates of the overstory Shannon diversity index were compared to overstory basal 

area (Table 6), the diversity index appeared to stabilize after the basal area reached 

a certain threshold. For example, jack pine diversity appeared to stabilize around 

1.2 after a basal area of 30 square feet per acre. There were no trends for diversity 

vs. age (Table 7). Aspen and paper birch diversity appear to be consistent across age 

classes unlike jack pine diversity, which increased as age increased and black spruce 

diversity, which declined with age. 

What We Found
PAGE 32 THE RESOURCE AFTER THE BLOWDOWN

Table 6. Average Shannon 

diversity index of overstory 

tree species, by forest type 

and overstory basal area, 

Boundary Waters Canoe Area 

Wilderness, 1999-2003.

Aspen -- -- -- 1.3 -- 1.7 1.3 1.1 1.5 -- 1.2 -- 1.5 --

Black spruce -- -- 1.6 0.9 0.7 -- 0.7 1.0 0.7 1.0 -- -- -- --

Eastern white pine -- -- -- -- -- -- -- 1.5 -- -- -- -- -- 1.5

Jack pine 0.3 -- -- -- -- 1.3 -- -- -- -- -- -- 0.7 --

Paper birch -- 0.5 1.2 1.2 1.2 0.9 0.8 1.4 1.2 -- -- 1.1 -- --

White pine/red oak/

 white ash -- -- -- -- 1.7 2.1 -- -- -- -- -- -- -- --

Forest type

Overstory basal area (ft2

/acre)

 10 20 30 40 50 60 70 80 90 100 110 120 130 160

Table 7. Average Shannon 

diversity index of overstory 

tree species, by forest type 

and average stand age class, 

Boundary Waters Canoe Area 

Wilderness, 1999-2003.

Aspen -- 1.32 1.43 0.69 1.21 1.22 1.53 1.28 -- --

Balsam fi r -- -- -- 1.64 -- -- -- -- -- 0.47 --

Black spruce -- -- -- 1.15 0.95 1.32 0.33 -- 0.16 -- 0.86

Eastern white pine -- -- -- -- -- -- -- 1.53 1.49 -- --

Jack pine -- 0.35 -- 0.61 -- -- -- -- 2.00 -- --

Paper birch 0.89 -- -- -- 1.23 1.18 1.19 1.05 -- -- --

Forest type

Average stand age (years)

 0 10 30 40 50 60 70 80 90 100 110

What This Means Although site or climatic factors can limit the number of species on a particular site, 

diversity often is infl uenced by each tree species’ competitive abilities, the collective 

associations of tree species, and site productivity or human interactions that attempt 

to direct a forest toward a particular structure or species mix. Given that the overstory 

diversity of each forest type is stable by basal area but varies by age, except for aspen 

and paper birch, we can conclude that time since the last major disturbance is the 

primary driver of diversity in the BWCAW.
THE RESOURCE AFTER THE BLOWDOWN PAGE 33

Species composition and diversity of understory vegetation

Understory species composition. Understory vegetation is an important component 

of forested ecosystems. Changes in the diversity and abundance of vascular plant 

species can indicate stress, e.g., pollution or forest degradation. Another indicator of 

disturbance is an increase in the number of exotic species, many of which are early 

colonizers (pioneer) species.

Of the 214 species in understory vegetation plots, 167 were in hardwood forest types 

and 165 in softwood forest types. Forty-seven were only in softwood types while 

49 were only in hardwood types. In softwood forest types (Fig. 23), 4 of the top 15 

understory vegetation species (5 in hardwood types (Fig. 24)) were regenerating 

trees, that is, young seedlings that will grow into the canopy should growing space 

become available. There were six species of woody shrubs in softwood types and 

four in hardwood forest types. Of the remaining understory vegetation species, 

four were herbaceous species, including large-leaved aster, Eurybia macrophylla, 

and one was a forb, Aralia nudicaulis or wild sarsaparilla. Although they varied in 

importance, whether in hardwood or softwood forest types, the 15 most common 

species were largely the same. The only difference was the presence of quaking 

aspen (Populus tremuloides) in hardwood forests and late low blueberry (Vaccinium 

angustifolium) in softwood forest types.

The BWCAW landscape is dominated by four fi re-infl uenced forest types: jack pine, 

quaking aspen, paper birch, and black spruce. Given the importance of past fi res in 

regenerating these forest types and a history of fi re suppression, it is not surprising 

to fi nd nearly identical species in the softwood and hardwood types. In such early 

successional forest types, the time since the stand-initiating disturbance, soils, and 

climate have the most signifi cant infl uence on species composition.

What We Found

What This Means
PAGE 34 THE RESOURCE AFTER THE BLOWDOWN

Figure 23. Top 15 understory 

species in softwood forest 

types based on the number 

of plots with at least one 

instance of the species, 

Boundary Waters Canoe Area 

Wilderness, 1999-2003.

Figure 24. Top 15 understory 

species in hardwood forest 

types based on the number 

of plots with at least one 

instance of the species, 

Boundary Waters Canoe Area 

Wilderness, 1999-2003.
THE RESOURCE AFTER THE BLOWDOWN PAGE 35

Understory species diversity. The overstory infl uences the presence, vigor, and 

composition of tree and other plant species in the understory. An open canopy 

allows maximum sunlight to reach the forest fl oor as well as minimum overstory 

competition for soil moisture, which favors certain plant species. This type of 

overstory provides less protection from the elements than a dense canopy, which 

shuts out more light and provides increased root competition, which again favors 

certain species. Depending on forest type, there might be an increase or decrease in 

diversity as the overstory basal area increases.

We compared the number of species with forest type and overstory basal-area 

class. Shade-intolerant pioneer species allow more light through their canopies. 

A completely open canopy might resemble open grassland, with the majority of 

biomass in a relatively limited suite of species. Understory diversity was higher at 

lower basal areas of shade-tolerant forest types and at higher basal areas for shadeintolerant forest types, e.g., aspen and birch (Table 8).

Although a limited number of samples precludes fi rm conclusions about species and 

forest types, we found interesting trends. First, early successional forests have more 

species in the understory than late successional forests with the same overstory basal 

area, because the early successional canopy lets in more light. In some inconclusive 

instances, forest types such as aspen had slightly higher species richness. Another 

implication is that the number of understory species varied little over most of the 

forest types and basal areas. This suggests that overall regional productivity and 

climate, as well as the disturbance regime, infl uenced understory diversity more than 

the forest type in the overstory.

What We Found

What This Means

Table 8. Understory species 

richness, by forest type and 

basal area, Boundary Waters 

Canoe Area Wilderness, 

1999-2003

Aspen -- -- -- 9 -- 20 20 20.5 16 -- 25 -- 22 --

Black spruce -- -- 16 28 18 -- 23 16 15.5 25 -- -- -- --

Eastern white pine -- -- -- -- -- -- -- 17 -- -- -- -- -- 22

Jack pine 15 -- -- -- -- 18.5 -- -- -- -- -- -- 12 --

Paper birch -- 18 17 22 20 18 20 23 21 -- -- 19 -- --

White pine/red oak/

white ash -- -- -- -- 17 17 -- -- -- -- -- -- -- --

Forest type

Basal area (ft2

/acre)

 10 20 30 40 50 60 70 80 90 100 110 120 130 160
PAGE 36 THE RESOURCE AFTER THE BLOWDOWN

Invasive species. The spread of nonnative 

invasive plants threatens species diversity 

and productivity throughout North America 

and the world. Intentionally or not, hundreds 

of nonnative species have been introduced to 

the United States. One of the most important 

benefi ts of protected areas like BWCAW 

is that humans have a minimum impact on 

native plant communities.

Six species of nonnative invasive understory plants were found on NRS FIA plots 

in the BWCAW and more than half were grasses. Included were Poa trivialis

(six occurrences), Poa pratensis and Sonchus oleraceus (two each) and Humulus

lupulus, Lychnis coronaria, and Rosa rugosa (one each). Despite many homesteads 

and in-holdings in the BWCAW, there does not seem to be a great number of 

invasive species. However, offi cials with the SNF found evidence of other invasive 

species, including orange and yellow hawkweeds (Hieracium aurantiacum and H. 

caespitosum) and spotted knapweed (Centaurea maculosa) (Bruce Anderson, SNF, 

pers. comm.).

Invasive species can alter ecosystem processes and structure. Although we did not 

fi nd numerous invasive plant species in the BWCAW, more time must be devoted to 

identifying such species as the number of people visiting the region increases, thus 

increasing the transport and spread of nonnative invasive species.

What We Found

What This Means
THE RESOURCE AFTER THE BLOWDOWN PAGE 37

The age of a forest tells a story about the land’s productivity, its disturbance history, 

and the events and interactions among its constituent parts. Age can infl uence rate 

of growth, suitability for a particular species of wildlife, or potential for economic 

use, and also alter susceptibility and response to disturbance. Expectations about the 

relationships between age and species composition, age and size, and age and growth 

rate are based on ecological knowledge. The age structure of the BWCAW refl ects 

the impact of at least two factors: exclusion from harvesting of certain areas and 

infl uence of past disturbances such as wind storms, insects and disease attacks, and 

fi re regimes. 

Age is a diffi cult variable to interpret using NRS FIA data. The age of a stand is 

estimated from tree cores of two or three dominant or codominant trees in the 

overstory and may not represent the age of the stand as a whole. It is tempting to 

use tree size as a surrogate for tree age, particularly when not all trees are sampled. 

The NRS FIA stand-size variable provides a coarse surrogate for stages of stand 

development (McWilliams et al. 2002), but it is based solely on tree diameter, which, 

in turn, can be infl uenced by tree density, site conditions, disturbance history and 

species, and other factors. For example, a fast-growing 40-year-old aspen stand might 

have a greater average diameter than an 80-year-old black spruce stand. For these 

reasons, care is needed when looking at size alone.

The youngest stands apparently predominate in the east-central and western portions 

of the BWCAW, while the older stands are more prominent in the central and 

northwestern portions (Fig. 25). Looking at total forest land area, some of the foresttype groups like jack pine have signifi cant amounts of acreage in each age class, 

refl ecting more frequent stand-initiating past disturbances (Fig. 26). Other types seem 

to have been initiated at one time.

Black spruce had the most even distribution of volume among age classes (Fig. 27). 

Except for the 0- to 20-year age class, which would have been expected to have little 

biomass, the proportion of volume roughly matches the proportion by area (Fig. 26). 

Red pine had a much higher proportion of its volume in older stands (81+ years). 

The two most prominent species, quaking aspen and paper birch, had most of their 

biomass in the 40- to 80-year age classes (Fig. 27). Of interest is how many forest 

types have most of their total volume in these classes, particularly among hardwood 

forest types. Of the 17 forest types in the BWCAW, 10 have at least 60 percent of 

their volume in these age classes.

Age

What We Found
PAGE 38 THE RESOURCE AFTER THE BLOWDOWN

Ecological preservation, wildlife habitat, and wilderness recreation are not the only 

benefi ts provided by the BWCAW. Another benefi t comes from the opportunity for 

carbon sequestration, an ecological function whereby growing vegetation captures 

and stores carbon, resulting in reduced levels of atmospheric carbon, which is a 

greenhouse gas. As we look to forests in the North Woods as reservoirs of carbon 

storage, we need to understand age-class and species mix, both of which strongly 

infl uence carbon accumulation, to understand the disturbance history that created 

these age- and species-mixes.

Heinselman (1973) defi ned the natural fi re rotation as the average time required for 

a natural fi re regime to burn an area equivalent to the total area of an ecosystem. 

This concept is valuable in comparing disturbance patterns in different ecosystems 

and attempting to understand the degree to which many plant species depend on 

fi re. Heinselman estimated a presettlement fi re rotation of 122 years, settlement fi re 

rotation of 87 years, and a fi re-rotation value of 2,000 years for the 61-year span 

of fi re suppression between 1911 and 1972—a dramatic change. This period of fi re 

suppression is evident in the high proportion of 40- to 80-year-old volume in the 

BWCAW. On the basis of these data alone, we conclude that: (1) stand-replacing 

disturbances have not occurred for some time, and (2) if such disturbances do not 

occur in the future, there will be a change in forest type as the shade intolerants reach 

the canopy and outlive the early successional aspen and birch. 

What This Means

Figure 25. Stand age in the 

Boundary Waters Canoe Area 

Wilderness, 1999-2003.

Stand age (years)

0-20

21-40

41-60

61-80

81-100

101+
THE RESOURCE AFTER THE BLOWDOWN PAGE 39

Figure 26. Total forest-land 

area of the Boundary Waters 

Canoe Area Wilderness, 

1999-2003.

Figure 27. All-live volume in 

the Boundary Waters Canoe 

Area Wilderness, 1999-2003.

Jack pine

Red pine

Eastern white pine

Balsam fi r

White spruce

Black spruce

Tamarack

Northern white-cedar

White pine/

red oak/white ash

Other pine/hardwood

Black ash/

American elm/red maple

Sugar maple/

beech/yellow birch

Aspen

Paper Birch

Other hardwoods 

and nonstocked

0 20 40 60 80 100 120

0-20

21-40

41-60

61-80

81-100

101+

All-live volume (million ft3)

Forest type

Jack pine

Red pine

Eastern white pine

Balsam fi r

White spruce

Black spruce

Tamarack

Northern white-cedar

White pine/

red oak/white ash

Other pine/hardwood

Black ash/

American elm/red maple

Sugar maple/

beech/yellow birch

Aspen

Paper Birch

Other hardwoods 

and nonstocked

Forest land (thousand acres)

0 10 20 30 40 50 60 70 80 90

0-20

21-40

41-60

61-80

81-100

101+

Forest type
PAGE 40 THE RESOURCE AFTER THE BLOWDOWN

Soil Resource of the BWCAW

Climate and soils have a profound infl uence on the forests of the BWCAW. 

Inventory and assessment of the forest soils provide critical baseline information on 

forest health and productivity, especially in light of continued natural and human 

disturbance. The forests of the BWCAW are underlain largely by inceptisols, entisols, 

and histosols (Fig. 28). Inceptisols are diverse and relatively young soils that have not 

experienced extreme weathering or major accumulation of metal oxides. They occur 

across a range of climates and vegetative communities. Entisols are mineral soils that 

might only have the beginnings of a soil horizon. In Minnesota, they are common 

in river bottoms and outwash sands. Histosols generally have a high organic matter 

content in the upper 30 inches; these are the marsh and bog soils found in ancient 

glacial lake beds across the northern part of the State (Anderson et al. 2001, Brady 

1990, Spurr and Barnes 1980, USDA Natural Resource Conservation Service 1999). 

The peaty or “hemist” type of histosols are common in northern Minnesota, where 

the cool climate slows decomposition. The nature of histosols makes it diffi cult to 

obtain consistently accurate volume measurements in the fi eld. Accordingly, density 

and chemistry data from this soil type are limited.

Soils data were collected from 2001-2003 (Table 9). Because data were limited, 

it was diffi cult to compare soils under different forest-type groups. Therefore, we 

considered only a few forest-type groups with more than fi ve samples. Coniferous 

forest-type groups were found on deeper soils than the aspen/birch forest-type 

group (Fig. 29). The forest fl oors2

 under softwood forest-type groups in Minnesota 

are thicker than those under hardwood forest-type groups (Miles et al. 2007), but 

the small number of samples limits our ability to draw a similar conclusion in the 

BWCAW. The relative carbon content of the forest fl oor is consistent across foresttype groups (Fig. 30). The white/red/jack pine forest-type group has lower soil pH 

(0-4 in) than the aspen/birch forest-type group (Fig. 31). The calcium:aluminum 

ratio is lowest in the white/red/jack pine forest-type group (Table 9), suggesting that 

these forest-type groups are underlain by poor quality soils. Under certain conditions, 

aluminum can be toxic to plants.

Softwood forests tend to accumulate greater amounts of forest fl oor than hardwood 

stands because of the chemical properties of the litter itself. Softwood needles tend to 

have lower nutrient content and thus break down more slowly than hardwood leaves. 

The difference also may be related to outbreaks of exotic earthworms that consume 

hardwood litter. These outbreaks are known to adversely affect rare plants, nutrient 

cycling, and the broader plant community (Bohlen et al. 2004a, b; Gundale 2002; 

Hale et al. 2005; Pritchett and Fisher 1987).

2

FIA defi nes the forest fl oor as the entire thickness of organic material overlying the mineral soil, 

consisting of the litter and the duff (humus) (O’Neill et al., 2005).
THE RESOURCE AFTER THE BLOWDOWN PAGE 41

The low soil pH, high aluminum, and low ECEC are related to the chemistry of the 

coniferous litter. Coniferous litter is more acidic than deciduous litter (Pritchett and 

Fisher 1987), so low pH leachate percolates through the soil profi le. The hydrogen 

ions tend to displace the native minerals useful for plant growth and lower the pH 

of the mineral soil (Brady 1990). Aluminum is increasingly mobilized as soil pH 

decreases (McBride 1994). These are natural processes that can lead to the formation 

of spodosols.

Figure 28. Soil orders in 

Minnesota. In northeastern 

Minnesota, forests are 

concentrated on alfi sols and 

inceptisols. Entisols and 

histosols also are prominent 

forest soils.
PAGE 42 THE RESOURCE AFTER THE BLOWDOWN

Table 9. Selected chemical 

properties of the mineral soil, 

Boundary Waters Canoe Area 

Wilderness, 2001-2003.

Layer and 

forest type group

pH Org. C Ex. Ca Ex. Al ECEC

 (%) (mg/kg) (mg/kg) (cmol+/kg)

Forest fl oor 

 White/red/jack pine 14 39.82 

 Spruce/fi r 10 34.99 

 Aspen/birch 21 39.47 

Mineral soil (0-10 cm) 

 White/red/jack pine 6 4.23a

 6.91 482.62a 399.34a 7.96

 Spruce/fi r 6 4.65ab 3.65 551.79ab 241.53ab 6.16

 Aspen/birch 12 4.70b

 4.03 900.95b 131.74b 8.19

Mineral soil (10-20 cm) 

 White/red/jack pine 4 5.06 3.55 387.07 91.77 3.80

 Spruce/fi r 5 5.12 2.22 587.97 126.22 5.16

 Aspen/birch 9 4.90 2.09 292.77 160.83 3.83

No. 

samples

Superscripts are used to indicate which means are statistically similar. All observations are statistically 

similar in those groups without any superscripts.

Figure 29. Depth to subsoil, 

Boundary Waters Canoe Area 

Wildnerness, 2001-2003. Error 

bars represent 1 standard 

error.

Forest type group

Depth to subsoil (cm)

White/red/jack

pine

Spruce/fi r Aspen/birch

30

25

20

15

10

5

0
THE RESOURCE AFTER THE BLOWDOWN PAGE 43

Figure 30. Organic carbon 

in the forest fl oor, Boundary 

Waters Canoe Area 

Wilderness, 2001-2003. Error 

bars represent 1 standard 

error.

Figure 31. pH of the 

mineral soil (0 to 4 inches), 

Boundary Waters Canoe Area 

Wilderness, 2001-2003. Error 

bars represent 1 standard 

error.

Forest type group

Soil pH

White/red/jack

pine

Spruce/fi r Aspen/birch

5.5

5.0

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

Forest type group

Organic C (percent)

White/red/jack

pine

Spruce/fi r Aspen/birch

50

45

40

35

30

25

20

15

10

5

0

SUMMARY

Heinselman (1973) emphasized that a variety of disturbances, interacting with 

variation in landscapes and species, has resulted in incredible diversity in the 

BWCAW. Formed by a complex interplay of disturbance, land, and climate, the 

forests of the BWCAW contain a variety of stand structures, species mixes, and 

densities that provide us with a myriad of wilderness experiences.

Diversity, particularly structural diversity, is threatened by the suppression of these 

disturbances. Efforts have been made to reestablish fi re as a tool for shaping stand 

structure and composition, but the large-scale, irregular wildfi res that played such a 

prominent role in shaping the current state of the forests are unlikely to occur again.

Wind damage, at both small and large scales, can radically alter the forest. We have 

seen how the dramatic changes caused by the 1999 windstorm have affected the 

BWCAW’s forests with respect to volume, composition, structure, and diversity. 

The dramatic increase in down woody material increases the risk of catastrophic fi re, 

particularly in the short term, until such fuels are reduced.

As we continue into the 21st century, areas like the BWCAW not only have 

ecological value but also offer recreational and spiritual refuges from the rapid pace 

of modern life. The BWCAW, while changing at a pace far different from that of 

landscapes outside its boundaries, continues to change. In fact, the BWCAW of 

the 22nd century may be far different from what we see today depending on the 

frequency of disturbances that nature and humans cause.

PAGE 45

DATA

Inventory Plots

The plot and tree measurements presented here are from measurements on 211 forest 

inventory plots between September 1998 and August 2003 as part of the national 

inventory conducted by the USDA Forest Service’s Forest Inventory and Analysis 

(FIA) program (Table 10) (Bechtold and Patterson 2005). These permanent sample 

plots are located systematically at an intensity of approximately one plot every 3,000 

acres. The data used in this study were restricted to plots in the Boundary Waters 

Canoe Area Wilderness, Superior National Forest, Minnesota, and further restricted 

to plots that were entirely on forest land. Complete documentation of the plot design 

and all measurements can be found at http://socrates.lv-hrc.nevada.edu/fi a/dab/

databandindex.html. 

Tree measurements used include species, diameter (stem diameter outside bark 

measured at 4.5 feet to the last 0.1 inch), height (total tree height measured to 

the nearest foot), and tree location (determined through distance and azimuth 

measurements from a fi xed point on the plot). Height was measured only on trees 5 

inches or larger in diameter. Only measurements from live trees were considered.

On Forest Health Monitoring or Phase 3 (P3) plots, NRS FIA measures an additional 

suite of variables: soil characteristics, down woody material, understory vegetation, 

and crown characteristics. The SNF provided support to upgrade all Phase 2 (P2) 

plots to P3 plots in 2000 and 2001.

NRS FIA database tables were queried to obtain plot data within the three 

northeastern Minnesota counties (Cook, Lake, and St. Louis) that encompass the 

SNF. Phase 2 plots from 1999 to 2003 (MN cycle 12, subcycles 1-5) were queried. 

Because many of these plots are located outside the bounds of the SNF, BWCAW, 

and the 1999 blowdown, subsequent queries and analyses are constrained using 

geospatial overlays.

Table 10. Northern Forest 

Inventory and Analysis plot 

counts for the Boundary Waters 

Canoe Area Wilderness, 

1999-2003.

 Year Cycle Subcycle P2 P3

 1999 12 1 22 

 2000 12 2 24 3

 2001 12 3 0 55

 2002 12 4 0 50

 2003 12 5 54 3

PAGE 47
PAGE 48 DATA

Down Woody Material Sampling

Between 2001 and 2003, FIA sampled 317 P3 plots in forests of the Upper Great 

Lakes, with 89 plots in the BWCAW (34 in blowdown and 55 in nonblowdown 

areas) and 228 plots in the greater forest ecosystem outside the BWCAW (Ecoregion 

212) (Fig. 19). We followed the down woody material sampling protocol detailed in 

Woodall and Williams (2005).

There were three study areas: (1) the greater forest ecosystem outside the BWCAW 

(Ecoregion 212), (2) inside the BWCAW in nonblowdown areas, and (3) inside 

the BWCAW in blowdown areas. Bailey (1995) delineated the forest ecosystem 

occupying the lake-swamp-morainic plains and lowlands of the Great Lakes and 

New England regions as the Laurentian Mixed Forest ecosystem (Ecoregion 212). 

In the Great Lakes area, the Ecoregion 212 stretches from the Canadian border in 

northwestern Minnesota across the northern areas of Wisconsin and Michigan 

(Fig. 32). All study plots were classifi ed as inside or outside BWCAW blowdown 

areas by overlaying plot locations on coarse-scale sketch maps provided by the 

Minnesota Department of Natural Resources (Befort 2005).

Figure 32. Approximate plot 

locations (perturbed due to 

privacy laws) for study plots in 

the 212 ecosystem (gray area) 

and Boundary Waters Canoe 

Area Wilderness (boundary 

within inset). Data sources: 

National Atlas of the USA, 

ESRI Maps, and the USDA 

Forest Service.
DATA PAGE 49

Geospatial Datasets and Analysis

Geographic information system (GIS) polygon 

delineations of the SNF, BWCAW, and the 

1999 blowdown were obtained from the SNF. A 

3-mile buffer surrounding blowdown polygons 

was created to identify the blowdown vicinity, 

within which some subsequent analyses were 

constrained. GIS layers of inventory plot 

center locations were created based on global 

positioning system (GPS) coordinates obtained 

during fi eld data collection. The location of plots 

relative to geospatial datasets was determined 

via spatial join functions. Tabular attributes 

were added to NRS FIA plot tables, indicating 

whether each plot location occurred inside or 

outside each geographic area of interest (SNF, 

BWCAW, blowdown polygon, 3-mile buffer). Subsequent tabular estimates of 

volume incorporated categorical attributes resulting from these spatial joins (Nelson 

and Moser 2007).

REFERENCES

Anderson, J.L.; Bell, J.C.; Cooper, T.H.; Grigal, D.F. 2001. Soils and landscapes 

of Minnesota. St. Paul, MN: University of Minnesota Extension Service. 

[Available online at: www.extension.umn.edu/distribution/cropsystems/

DC2331.html]. Accessed 22 August 2006.

Ayres, H.B. 1899. Timber conditions of the pine region of Minnesota: Part I. Forest 

reserves. Washington, DC: U.S. Geological Survey, 21st Annual Report: 679-

689. 

Bailey, R.G. 1995. Description of the ecoregions of the United States. Misc. Publ. 

1391. Washington, DC: U.S. Department of Agriculture, Forest Service. 

Bechtold, W.A.; Patterson, P.L., eds. 2005. Forest Inventory and Analysis national 

sample design and estimation procedures. Gen. Tech. Rep. SRS-GTR-80. 

Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern 

Research Station. 85 p.

Befort, B. 2005. Sketch map of BWCAW blowdown affected areas. St. Paul, MN: 

Minnesota Department of Natural Resources.

Bohlen, P.J.; Groffman, P.M.; Fahey, T.J.; Fisk, M.C.; Suarez, E.; Pelletier, D.M.; 

Fahey, R.T. 2004a. Ecosystem consequences of exotic earthworm invasion in 

north temperate forests. Ecosystems. 7(1): 1-12.

Bohlen, P.J.; Scheu, S.; Hale, C.M.; McLean, M.A.; Migge, S.; Groffman, P.M.; 

Parkinson, D. 2004b. Non-native invasive earthworms as agents of change in 

northern temperate forests. Frontiers in Ecology and Environment. 2(8): 

427-435.

Brady, N.C. 1990. The nature and properties of soils. 10th ed. New York, NY: 

Macmillan. 639 p.

Canham, C.D.; Loucks, O.L. 1984. Catastrophic windthrow in the presettlement 

forests of Wisconsin. Ecology. 65: 803-809.

Frelich, L.E.; Graumlich, L.J. 1994. Age-class distribution and spatial patterns in an 

old-growth hemlock-hardwood forest. Canadian Journal of Forest Research. 

24: 1939-1947.

Gundale, M.J. 2002. Infl uence of exotic earthworms on the soil organic horizon and 

the rare fern Botrychium mormo. Conservation Biology. 16(6): 1555-1561.

Hale, C.M.; Frelich, L.E.; Reich, P.B. 2005. Exotic European earthworm invasion 

dynamics in northern hardwood forests of Minnesota, USA. Ecological 

Applications. 15(3): 848-860.

Heinselman, M.L. 1973. Fire in the virgin forests of the Boundary Waters Canoe 

Area, Minnesota. Quaternary Research. 3: 329-382.

Heinselman, M.L. 1996. The Boundary Waters wilderness ecosystem. Minneapolis, 

MN: University of Minnesota Press.

Leuschen, T.; Wordell, T.; Finney, M.; Anderson, D.; Aunan, T.; Tine, P. 2000. 

Fuel risk assessment of the blowdown in the Boundary Waters Canoe Area 

Wilderness and adjacent lands. Duluth, MN: U.S. Department of Agriculture, 

Forest Service, Superior National Forest. 

PAGE 51
PAGE 52 REFERENCES

Magurran, A.E. 2003. Measuring biological diversity. Oxford: Blackwell.

Mattson, W.J.; Shriner, D.S., eds. 2001. Northern Minnesota Independence Day 

storm: a research needs assessment. Gen. Tech. Rep. NC-216. St. Paul, MN: 

U.S. Department of Agriculture, Forest Service, North Central Research 

Station. 65 p.

McWilliams, W.H.; O’Brien, R.A.; Reese, G.C.; Waddell, K.L. 2002. Distribution 

and abundance of oaks in North America. Chapter 2. In: McShea, W.J.; Healy, 

W.M., eds. The ecology and management of oaks for wildlife. [New York, 

NY]: Johns Hopkins Press: 13-33.

McBride, M.B. 1994. Environmental chemistry of soils. New York, NY: Oxford 

University Press. 406 p.

Miles, Patrick D.; Jacobson, Keith; Brand, Gary J.; Jepsen, Ed; Meneguzzo, Dacio; 

Mielke, Manfred E.; Olson, Cassandra; Perry, Charles H. (Hobie); Piva, Ron; 

Wilson, Barry Tyler; Woodall, Christopher. 2007. Minnesota’s forests 1999-

2003 (Part A). Resour. Bull. NRS-12A. Newtown Square, PA: U.S. Department 

of Agriculture, Forest Service, Northern Research Station. 92 p.

Nelson, M.D.; Moser, W.K. 2007. Integrating remote sensing and forest inventory 

data for assessing the BWCAC blowdown. In: Greer, J.D., ed. New remote 

sensing technologies for resource managers: procedings of the eleventh Forest 

Service remote sensing applications conference; 2006 April 24-28; Salt Lake 

City, UT. CD-ROM, American Society for Photogrammetry and Remote 

Sensing: 8 p.

O’Neill, K.P.; Amacher, M.C.; Perry, C.H. 2005. Soils as an indicator of forest health: 

a guide to the collection, analysis, and interpretation of soil indicator data in 

the Forest Inventory and Analysis program. Gen. Tech. Rep. NC-258. St. Paul, 

MN: U.S. Department of Agriculture, Forest Service, North Central Research 

Station. 53 p.

Peet, R.K. 1975. Relative diversity indices. Ecology 56(2): 496-498.

Peterson, C.J. 2000. Catastrophic wind damage to North American forests and the 

potential impact of climate change. Science of the Total Environment. 262: 

287-311.

Pritchett, W.L.; Fisher, R.F. 1987. Properties and management of forest soils. 2d ed. 

New York, NY: John Wiley and Sons.

Spurr, S.H.; Barnes, B.V. 1980. Forest ecology. New York, NY: John Wiley and Sons. 

687 p.

USDA, Forest Service. 2001. Final environmental impact statement for the Boundary 

Waters Canoe Area Wilderness fuel treatments. Milwaukee, WI: U.S. 

Department of Agriculture, Forest Service, Superior National Forest, Eastern 

Region. Vol. 1.

USDA, Forest Service. 2002. After the storm: a progress report, July 2002. 

Milwaukee, WI: U.S. Department of Agriculture, Forest Service, Superior 

National Forest, Eastern Region. [http://www.fs.fed.us/r9/forests/superior/

storm_recovery/afterstorm/.] Accessed 6 April 2006.
REFERENCES PAGE 53

USDA, Forest Service. 2006. History of the Boundary Waters Canoe Area 

Wilderness. Milwaukee, WI: U.S. Department of Agriculture, Forest Service, 

Superior National Forest, Eastern Region. [http://www.fs.fed.us/r9/forests/

superior/bwcaw/bwhist.php.] Accessed 6 April 2006.

USDA, Natural Resources Conservation Service. 1999. Soil taxonomy: a basic 

system of soil classifi cation for making and interpreting soil surveys. Agric. 

Handb. 436. Washington, DC: U.S. Department of Agriculture. 869 p.

Woodall, C.W.; Williams, M.S. 2005. Sample protocol, estimation procedures, 

and analytical guidelines for the down woody materials indicator of the 

FIA program. Gen. Tech. Rep. NC-256. St. Paul, MN: U.S. Department of 

Agriculture, Forest Service, North Central Research Station. 47 p.

Woods, K.D. 2004. Intermediate disturbance in a late-successional hemlock-northern 

hardwood forest. Journal of Ecology. 92: 464-476.
APPENDIX

Forest Inventory and Analysis defi nes forest land as treed land at least 1 acre in 

size, at least 120 feet in width, and possessing a minimum of 10-percent stocking 

of live trees. FIA separates forest land by two criteria: is the forest land productive 

or unproductive, and is the forest land reserved or unreserved? Combining these 

criteria, we defi ne three components of forest land: (1) timberland—forest land that 

is not restricted from harvesting by statute, administrative regulation, or designation 

and is capable of growing trees at a rate of at least 20 cubic feet per acre per year at 

maximum annual increment; (2) reserved forest land—land that is restricted from 

harvesting by statute, administrative regulation, or designation (state and national 

parks, Federal wilderness areas, etc.); and (3) other forest land—low-productivity 

forest land that is not capable of growing trees at a rate of 20 cubic feet per acre per 

year. Because the Boundary Waters Canoe Area Wilderness has been designated 

as a wilderness area, all of the forest land within the BWCAW is considered to be 

reserved.

The FIA defi nes stand-size class as a function of the predominant (based on stocking) 

diameter class of live trees within the condition. Large-diameter trees are at least 11.0 

inches in diameter for hardwoods and at least 9.0 inches in diameter for softwoods. 

Medium-diameter trees are at least 5.0 inches in diameter, but not as large as largediameter trees. Small-diameter trees are less than 5.0 inches in diameter. A stand that 

is assigned to one of these three categories still might contain trees in one or both of 

the other two categories.

PAGE 54
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call 202-720-5964 (voice and TDD). USDA is an equal opportunity provider and employer.

About the Authors

W. Keith Moser, Mark H. 

Hansen, Mark D. Nelson, 

Susan J. Crocker, Charles 

H. Perry, and Christopher 

W. Woodall are with the 

Northern Research Station’s 

Forest Inventory and 

Analysis program in 

St. Paul, Minnesota. 

Bethany Schulz is with 

the Pacifi c Northwest 

Research Station’s Forest 

Inventory Analysis program 

in Anchorage, Alaska. 

Linda M. Nagel is with 

Michigan Technological 

University in Houghton, 

Michigan.

Manfred E. Mielke is with 

State and Private Forestry’s 

Northeastern Area in 

St. Paul, Minnesota. 

Moser, W. Keith; Hansen, Mark H.; Nelson, Mark D.; Crocker, Susan J.; 

 Perry, Charles H.; Schulz, Bethany; Woodall, Christopher W.; 

 Nagel, Linda M.; Mielke, Manfred E. 2007. After the blowdown: 

 a resource assessment of the Boundary Waters Canoe Area 

 Wilderness, 1999-2003. Gen. Tech. Rep. NRS-7. Newtown Square, 

 PA: U.S. Department of Agriculture, Forest Service, Northern Research 

 Station. 54 p.

 The Boundary Waters Canoe Area Wilderness (BWCAW) was struck 

by a major windstorm on July 4, 1999. Estimated volume in blowdown 

areas was up to 29 percent less than in non-blowdown areas. Mean 

down woody fuel loadings were twice as high in blowdown areas 

than in non-blowdown areas. Overstory species diversity declined 

in blowdown areas, but understory diversity, measured by species 

richness, increased. Windstorms, like wildfi re, are part of the historic 

disturbance regime in the Boundary Waters–Quetico region.

KEY WORDS: Boundary Waters, wilderness, Derecho, blowdown
Capitalizing on the strengths of existing science capacity in the 

Northeast and Midwest to attain a more integrated cohesive 

landscape scale research program