Illinois’ Forests

2005 

Resource Bulletin

NRS-29

2009

Northern

Research Station

United States 

Department of Agriculture

Forest

Service
Chris Albion

Tara Bauer

James Blehm

Brady Boyce

Joseph Boykin

Bill Burkman

Nathan Cochran

John Coulston

Jeffrey Dawson

Patrick Dayton

Ian Diffenderfer

Gianna Evans

Nick Giannettino

Trenton Girard

Dale Gormanson

Katrina Griffin

Ronald Hackett

Tracie Hamilton

Doug Hansen

Mark Hansen

Mark Hatfield

Glenda Hefty

John Hubsky

Brent Hummel

Hollister Hunt

Steve Hupe

Barb Johnson

Daniel Johnson

Travis Jones

Dan Kaisershot

Barb Knight

Ryan Kolling

Casey Krogstad

Cassandra Kurtz

Karlis Lazda

Earl Leatherberry

Dominic Lewer

Greg Liknes

Mike Long

Sean Maiers

Lisa Mahal

Amber Marshaus

Michael Mason

Dennis May

Jason McCall

Ron McRoberts

Pat Miles

Jerrod Moilanen

Adam Morris

Marc Much

Kevin Nimerfro

Benjamin Nurre

David Oaks

Stephen Ochs

Cassandra Olson

Shane Olson

Joe Perrone

Jay Perry

Emil Peter

John Phelps

Scott Pugh

Gerhard Raile

Michael Reichenberg

Paul Richards

Matthew Riederer

Travis Rymal

Jay Solomakos

Sarah Schmid

Matt Sedelbauer

Earl Sheehan

Willard Smith

Gary Stachowicz

Matt Swanson

Leland Swoger

Brad Totten

Brian Wall

Lacey Whitehouse

Dennis Wilson

Acknowledgments

The authors thank the following individuals whose dedication and hard work contributed to 

both the inventory and analysis of Illinois’ forest resources.

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

Published by: For additional copies:

USDA FOREST SERVICE USDA Forest Service

11 CAMPUS BLVD., SUITE 200 Publications Distribution

NEWTOWN SQUARE, PA 19073-3294 359 Main Road

Delaware, OH 43015-8640

January 2009 Fax: 740-368-0152

Manuscript received for publication 11 April 2008.

COVER PHOTO: Illinois landscape. Photo by Susan Crocker, U.S. Forest Service.

Note: Information including core tables, glossary, and sample/QA/QC methods will 

be included in a companion document, Illinois’ Forests 2005: Statistics and Quality 

Assurance, Resource Bulletin NRS-30, to be released as an Internet publication in 

tandem with this 5-year report. Data from the Illinois forest inventory can be accessed 

electronically at: http://www.nrs.fs.fed.us/fia/.
Illinois’ Forests

2005

Susan J. Crocker, Gary J. Brand, Brett J. Butler, David E. Haugen, 

Dick C. Little, Dacia M. Meneguzzo, Charles H. Perry, Ronald J. Piva, 

Barry T. Wilson, Christopher W. Woodall
Foreword

It is with satisfaction that we present Illinois’ statewide forest inventory 

report. This inventory was a cooperative effort led by the Forest Inventory 

and Analysis program of the Forest Service, U.S. Department of Agriculture, 

and the Illinois Council on Forestry Development representing Illinois’ forest 

resource interests.

Illinois has seen an increase of approximately 200,000 forested acres since 

the last inventory was conducted in 1998 and a gradual increase of roughly 

500,000 acres over the last 60 years. A full 40 percent of that gain has come 

in the last 10 years. This increase represents the hard work of the many 

organizations and landowners involved in expanding this valuable resource.

Concurrent to an evolving forest resource, many challenges have been 

identified. Our forests are increasing in volume and getting older. As these 

forests age, they face significant successional change. Shade tolerant species 

such as maples are gradually replacing predominantly oak forests, and nonnative invasive species are negatively impacting natural regeneration of oak 

species and other native forest types. The challenge begins when trying to 

identify management techniques to address these changes and adapt to new 

ones.

In addition to these challenges, Illinois’ forests face numerous threats, 

including those in the form of forest pests, parcelization, disease, and land 

conversion. With more than 90 percent of forest land in Illinois in private 

ownership, it is our responsibility to work with these landowners to devise 

and implement management strategies to address these developing threats 

across the entirety of Illinois’ forest resources.
The results of Illinois’ Forests 2005 will generate discussion and help the 

managers of this valuable resource to make responsible management 

decisions. We invite you to evaluate these results and engage our constituents 

in thoughtful discussion.

Michael R. Mason, Chief

Division of Forest Resources,

Office of Resource Conservation
Contents

Highlights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

On the Plus Side . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Areas of Concern . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Issues to Watch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

A Beginner’s Guide to Forest Inventory . . . . . . . . . . . . . . . . . . . . . . . . . . 6

 What is a tree? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

 What is a forest? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

 What is the difference between timberland, 

 reserved forest land, and other forest land? . . . . . . . . . . . . . . . . . 6

 How many trees are in Illinois? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

 How do we estimate a tree’s volume? . . . . . . . . . . . . . . . . . . . . . . . . . 7

 How much does a tree weigh? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

 How do we compare data from different inventories? . . . . . . . . . . . . 9

 A word of caution on suitability and availability... . . . . . . . . . . . . . . 9

Where are Illinois’ Forests? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

 Ecological Provinces of Illinois . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

 Distribution of Forest Land by Forest Type and Stand Size . . . . . . . 14

Forest Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Forest Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Trees on Nonforest land . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Biomass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Species Composition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Forest Density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

Diminishing Oaks, Maple Replacement . . . . . . . . . . . . . . . . . . . . . . . . . 36

Ownership . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

Riparian Forests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Average Annual Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

Average Annual Removals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Average Annual Mortality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
Forest Health . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

Down Woody Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

Tree Crowns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62

Ozone Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66

Forest Fragmentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70

Forest Invaders: Nonnative Invasive Plants . . . . . . . . . . . . . . . . . . . . . . 73

Insects and Diseases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

Emerald Ash Borer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83

Forest Products . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

Growing-stock Volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90

Sawtimber Volume and Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93

Timber Products Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

Data Sources and Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108

Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

­­­­

Highlights

 Since reaching an all-time low in 1924, the area of forest land has 

increased by 1.5 million acres.

 State legislation and participation in programs designed to promote 

sustainability and regeneration have contributed to the rise in the annual 

rate of increase in forest area.

 Trees cover 15 percent of the total land area in Illinois. 

 With over 2 billion trees representing nearly 100 different species, Illinois’ 

forests support a wide diversity of tree species.

 The State’s forests are growing at their highest rates since 1962.

 Average growing-stock volume per acre of timberland has increased 

threefold since 1948 and now totals 1,576 cubic feet per acre.

 As the volume of sawtimber continues to increase, sawtimber quality 

remains high.

 Illinois’ forests sequester an estimated 343 million tons of carbon.

 The condition of Illinois’ tree crowns indicates good forest health.

 Efforts to control the Asian longhorned beetle continue to be successful; 

no new infestations were found in 2004 or 2005.

On the Plus Side
­­­­

 Between 1998 and 2005, the number of trees on forest land decreased 

by 25 percent, or about a half billion trees, and live volume decreased 

by 36 percent.

 Illinois’ oak resource is characterized by an abundance of large, mature 

trees and a comparatively small sapling/seedling component.

 Thirty percent of total growing-stock mortality occurred in riparian forests. 

 Disease and old age were large contributors to the high mortality of 

American elm and black oak.

 Wildlife habitat provided by coarse woody debris is minimal due to a lack 

of large pieces of debris.

 Forest fragmentation is high throughout most of Illinois; the majority of 

interior forest land is within the Shawnee National Forest. 

 Nonnative invasive plants, including multiflora rose, garlic mustard, 

and bush honeysuckles, were found on 40 percent of sampled plots.

 Forest insects, disease, and drought continue to affect the health of 

Illinois’ forests. 

 Oak species are growing at a slower rate than non-oak species.

Areas of Concern
­­­­

Issues to Watch  High oak mortality, decreasing oak sapling/poletimber density, low oak 

regeneration, and understory maple dominance are indicative of a future 

shift in forest composition from oak/hickory dominated stands to maple 

dominated stands. 

 Forest land will soon undergo intergenerational transfers in ownership that 

may change future forest characteristics. 

 The emerald ash borer could have a significant impact on the health, 

structure, and composition of Illinois’ forests.

 Illinois’ forest product market appears to be shifting from high utilization 

of oak to increased demand for cottonwood.

Background

Above: Root structure; photo by Cassandra Olson, U.S. Forest Service. 

Inset: Common blue violet; photo by Susan Crocker, U.S. Forest Service. 
­­­­

BACKGROUND

We know a tree when we see one and we can agree on some common tree attributes. 

Trees are perennial woody plants with central stems and distinct crowns. In general, the 

Forest Inventory and Analysis (FIA) Program, of the Forest Service, U.S. Department 

of Agriculture, defines a tree as any perennial woody plant species that can attain a 

height of 15 feet at maturity. In Illinois, the problem is deciding which species should 

be classified as shrubs and which should be classified as trees. A complete list of the tree 

species measured in this inventory can be found in “Illinois’ Forests 2005: Statistics and 

Quality Assurance” (Resource Bulletin NRS-30), the companion to this document.

We know what a forest is, but where does the forest stop and the prairie begin? It’s an 

important question. Often, the gross area of forest land or rangeland determines the 

allocation of funding for certain State or Federal programs. Forest managers want more 

land classified as forest land and range managers want more land classified as prairie, but 

you have to draw the line somewhere.

FIA defines forest land as land at least 10 percent stocked by trees of any size or formerly 

having had such tree cover and not currently developed for nonforest uses. The area 

with trees must be at least 1 acre in size, and roadside, streamside, and shelterbelt strips 

of trees must be at least 120 feet wide to qualify as forest land.

From an FIA perspective, there are three types of forest land: timberland, reserved 

forest land, and other forest land. In Illinois, approximately 96 percent of forest land is 

timberland and 4 percent is reserved forest land.

 Timberland is unreserved forest land that meets minimum productivity 

requirements. 

 Reserved forest land is land withdrawn from timber utilization through legislation 

or administrative regulation. 

 Other forest land is commonly found on low-lying sites with poor soils where the 

forest is incapable of producing 20 cubic feet per acre per year at its peak. 

In Illinois inventories prior to 1998, only trees occurring on timberland plots were 

measured. Therefore, we cannot report volume on forest land for those inventories. The 

new annual inventory system facilitates the estimation and reporting of volume on all 

forest land, not just timberland. As these annual plots are remeasured in the coming 

years, we will also be able to report growth, removals, and mortality on all forest land. 

A Beginner’s Guide to Forest Inventory

What is a tree?

What is a forest?

What is the 

difference between 

timberland, reserved 

forest land, and other 

forest land?
­­­­

BACKGROUND

Trend reporting in this publication is necessarily limited to timberland except for the 

area of forest land on which individual tree measurements are not required. 

Illinois forest land contains approximately 570 million live trees that are at least 5 inches 

in diameter at breast height (d.b.h., 4.5 feet above the ground). We do not know the 

exact number because only a sample of trees was measured, roughly 1 out of every 26,000 

trees, or a total of 21,513 trees. These trees were measured on 1,004 forest plots (Fig. 1). 

For information on sampling errors, see the companion document, “Illinois’ Forests 2005: 

Statistics and Quality Assurance” (Resource Bulletin NRS-30).

Forest inventories typically express volume in cubic feet, but the reader may be more 

familiar with cords (a stack of wood 8 feet long, 4 feet wide, and 4 feet high). A cord 

of wood contains approximately 79 cubic feet of solid wood and 49 cubic feet of bark 

and air.

Volume can be precisely determined by immersing a tree in a pool of water and 

measuring the amount of water displaced. Less precise, but much cheaper and easier 

to do with living trees, is a method adopted by the Northern Research Station. In this 

method, several hundred trees were cut and detailed diameter measurements were taken 

along their lengths to accurately determine their volumes (Hahn 1984). Statistical tools 

were used to model this data by species group. Using these models, we can produce 

individual tree volume estimates based on species, diameter, and tree site index.

This method was also used to calculate sawtimber volumes. FIA reports sawtimber 

volumes in International 1/4-inch board foot scale as well as Doyle rule. To convert to 

the Scribner board foot scale, see Smith (1991).

Building on previous work, the U.S. Forest Service’s Forest Products Laboratory 

developed estimates of specific gravity for a number of tree species (U.S. For. Serv. 

1999). These specific gravities were applied to estimates of tree volume to determine 

merchantable tree biomass (the weight of the bole). To estimate live biomass, we have to 

add in the stump (Raile 1982), limbs, and bark (Hahn 1984). We do not currently report 

the live biomass of roots or foliage.

How many trees are 

in Illinois?

How do we estimate 

a tree’s volume?

How much does a 

tree weigh? 
­­­­

BACKGROUND

Figure 1.—Plot locations and 

inventory units associated with 

the current forest inventory, 

Illinois, 2005.

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P r a i r i e P r a i r i e

C l a y p a n C l a y p a n

S o u t h e r n S o u t h e r n

Chicago Metro Area

Moline

Alton

Peoria

Rockford

Decatur

Springfield

Waukegan

East Saint Louis

Champaign-Urbana

Carbondale

Depicted plot locations are approximate.

Projection: UTM Zone 16N, NAD 83.

Source: U.S. Forest Service, Forest Inventory and Analysis

Program, 2005 data. Geographic base data are provided

by the National Atlas of the USA and the Illinois Department of

Natural Resources. FIA data and mapping tools are

available online at http://www.fia.fs.fed.us/tools-data/.

Cartography: S.J. Crocker. July, 2007.

0 50

Miles

Legend

Plot locations

I n v e n t o r y U n i t s I n v e n t o r y U n i t s

Counties

Lakes and rivers

Public lands

Major cities

"
­­­­

BACKGROUND

Forest inventories report biomass as green or oven-dry weight. Green weight is the 

weight of a freshly cut tree; oven-dry weight is the weight of a tree with zero percent 

moisture content. On average, 1 ton of oven-dry biomass is equal to 1.9 tons of green 

biomass.

Data from new inventories is often compared with data from earlier inventories 

to determine trends in forest resources. However, for comparisons to be valid, the 

procedures used in the two inventories must be similar. As a result of FIA’s ongoing 

efforts to improve the efficiency and reliability of the inventory, several changes in 

procedures and definitions have occurred since the last Illinois inventory in 1998. While 

these changes will have little effect on statewide estimates of forest area, timber volume, 

and tree biomass, they may have significant effects on plot classification variables such as 

forest type and stand-size class. Some of these changes make it inappropriate to directly 

compare 2005 data tables with those published for the 1998 inventory. 

The biggest change between the two inventories was the change in plot design. A fixedradius subplot design was used in both the 1998 and 2005 inventories. However, the 

1998 inventory also included modeled plots, i.e., plots measured in 1985 and projected 

forward using the STEMS (Belcher et al. 1982) growth model. This process increases 

cost efficiency by reducing the number of undisturbed plots that are sent to the field 

for remeasurement. Disturbance was determined by comparing aerial photographs of 

the plots and looking for reductions in canopy cover. The idea was that parameters for 

the STEMS growth model could be fine-tuned using the measured, undisturbed plots 

and then applied to the remaining unmeasured, undisturbed plots. Unfortunately, the 

use of modeled plots introduced biased errors, so the current inventory includes full 

remeasurements. In other words, only field-measured plots are used for comparisons with 

the 1998 inventory in this publication. 

FIA does not attempt to identify which lands are suitable or available for timber 

harvesting, particularly since such suitability and availability is subject to changing laws, 

economic/market constraints, physical conditions, adjacency to human populations, and 

ownership objectives. The classification of land as timberland does not necessarily mean 

it is suitable or available for timber production. 

How do we compare 

data from different 

inventories?

A word of caution 

on suitability and 

availability
10

BACKGROUND

Nor is it safe to assume that forest owners plan regular harvests or intend to harvest 

at all. In response to FIA’s National Woodland Owner Survey, only 6 percent of 

landowners, owning 16 percent of Illinois’ private forest land, stated that they intend to 

harvest saw logs or pulpwood over the next 5 years. Many of Illinois’ private landowners 

own forest land for the aesthetic value it provides. Although most family forest owners in 

Illinois plan to do relatively little with their forest land in the near future, one in every 

ten acres is owned by someone who plans to either transfer their land to an heir or sell it 

within the next 5 years. 

Thus, forest inventory data alone are inadequate for determining the area of forest land 

available for timber production. Additional factors, like those provided above, need to 

be considered when estimating the timber base, and these factors may change with time.
11

BACKGROUND

Illinois spans three ecological provinces: the Eastern 

Broadleaf Forest, the Prairie Parkland, and the Lower 

Mississippi Riverine Forest (Fig. 2). 

The rolling hills and flat expanses of the Eastern Broadleaf 

Forest Province are dominated by a diverse mixture of 

broadleaf deciduous species. Relatively low precipitation 

in the area favors the drought resistance of the oak/hickory 

forest-type group (Bailey 1995). Major species include: 

white oak, red oak, black oak, shagbark hickory, and 

bitternut hickory. Maple, beech, and basswood increase in 

dominance in the northern portions of the province. In 

this area, sugar maple and American basswood dominate 

the maple/basswood forest type (Bailey 1995). 

The Prairie Parkland Province is characterized by an alternating pattern of prairie and 

deciduous forest. Forested portions of the province consist of uplands dominated by oak 

and hickory, and moist slopes and floodplains where eastern cottonwood and American 

elm are common species. Grasses are the predominant vegetation in prairies (Bailey 

1995).

Broad floodplains and low terraces typify the land form of the Lower Mississippi Riverine 

Forest Province (Bailey 1995). Vegetation is classified as bottomland deciduous forest 

and the primary forest-type groups are oak/gum/cypress and oak/hickory. Major species 

include Nuttall oak, water oak, cherrybark oak, cottonwood, sycamore, and baldcypress 

in the oak/gum/cypress group, and post oak, bur oak, and northern red oak in the 

oak/hickory group. Pecan, green ash, sweetgum and water tupelo are also present (Bailey 

1995; McNab and Avers 1996).

The greatest percentage of Illinois’ forest land is in 

southern Illinois, most of which is in the Shawnee 

National Forest (Fig. 3). There is also significant forest 

area in the western portion of the State along the 

borders of the Illinois and Mississippi Rivers.

Where are Illinois Forests?

Ecological Provinces 

of Illinois

Forest floor. Photo by Susan 

Crocker, U.S. Forest Service

Illinois hardwood stand. Photo by 

Susan Crocker, U.S. Forest Service
12

BACKGROUND

Figure 2.—Ecological 

provinces of Illinois (Bailey 

1995).

Projection: UTM Zone 16N, NAD83.

Source: U.S. Forest Service. Geographic base

data are provided by the National Atlas of the USA.

Cartography: S.J. Crocker. July, 2007.

0 50

Miles

Ecological Provinces

Lower Mississippi

Riverine Forest

Prairie Parkland

Eastern Broadleaf Forest
13

BACKGROUND

Figure 3.—Area of forest land 

as a percentage of county land 

area, Illinois, 2005. 

Projection: UTM Zone 16N, NAD83.

Source: U.S. Forest Service, Forest Inventory and

Analysis program, 2005 data. Geographic base data

are provided by the National Atlas of the USA. FIA data

and mapping tools are available online at

http://www.fia.fs.fed.us/tools-data/.

Cartography: S.J. Crocker. May, 2007.

0 50

Miles

Area of forest land

(percent of county land area)

0 - 9

10 - 19

20 - 29

30 - 39

40 - 73
14

BACKGROUND

Occupying 65 percent of forest land, oak/hickory is the predominant forest-type group 

in Illinois (Fig. 4; see Appendix for estimates of forest land area by county and foresttype group). Though oak/hickory is found throughout the State, this forest-type group is 

highly concentrated in west-central and southern Illinois. Elm/ash/cottonwood, which 

makes up 23 percent of forest land, is the second largest forest-type group. The top five 

forest types account for 71 percent of forest land (Fig. 5). The most common forest type 

in the State is white oak/red oak/hickory. 

Forest land in Illinois consists largely 

of stands with sawtimber-size trees. 

Sawtimber occupies 3.3 million acres, or 

72 percent of forest land (Fig. 6). Twenty 

percent of forest land is made up of 

poletimber and 8 percent contains sapling/

seedlings. Mature oak/hickory stands are 

the most prominent feature on Illinois 

forest land.

Distribution of Forest 

Land by Forest Type 

and Stand Size

White oak buds. Photo by Paul Bolstad, 

University of Minnesota, bugwood.org
15

BACKGROUND

Figure 4.—Distribution of forest 

land by forest-type group, 

Illinois, 2005.

Processing note: This map was produced by

linking plot data to MODIS satellite pixels (250 m)

using gradient nearest neighbor techniques. The

resulting image was resampled to 500 m pixels.

Projection: UTM Zone 16N, NAD83.

Source: U.S. Forest Service, Forest Inventory and Analysis

program, 2005 data. Geographic base data are provided by the

National Atlas of the USA. FIA data and mapping tools are

available online at http://www.fia.fs.fed.us/tools-data/.

Cartography: S.J. Crocker & B.T. Wilson. July, 2007.

Forest-type group

White/red/jack pine

Other softwoods

Oak/pine

Oak/hickory

Oak/gum/cypress

Elm/ash/cottonwood

Maple/beech/birch

Nonforest

0 50

Miles
16

BACKGROUND

Figure 5.—Distribution of forest 

land by forest type, Illinois, 

2005.

Figure 6.—Area of forest land 

by forest-type group and standsize class, Illinois, 2005.

0

500

1,000

1,500

2,000

2,500

Softwoods Other

hardwood

groups

Maple/

beech/birch

Elm/ash/

cottonwood

Oak/

hickory

Forest Land Area

(thousand acres)

Sawtimber

Poletimber

Sapling/seedling

Forest-type Group

Forest Type

15%

35%

13%

9%

1%

6%

5%

3%

10%

3%

White oak/red oak/hickory

Mixed upland hardwoods

Sugarberry/hackberry/elm/green ash

Silver maple/American elm

White oak

Sugar maple/beech/yellow birch

Softwoods

Oak/pine group

Lowland hardwoods

Other forest types
17

Forest Features

Above: Shawnee National Forest; photo by Susan Crocker, U.S. Forest Service. 

Inset: Monarch butterfly; photo by David Cappaert, Michigan State University, bugwood.org 
20

FOREST FEATURES

Estimates of forest area offer information on current status and trends. Fluctuations in 

area may indicate changing land use and/or forest health conditions. Monitoring these 

changes provides information essential for management and decisionmaking.

In the early 1800s, prior to European settlement, tall grass prairie and eastern deciduous 

forests were the dominant features on the Illinois landscape (Illinois State Nat. 

Surv. Div. 1960). Forests during this period spanned an estimated 13.8 million acres, 

approximately 40 percent of the total land area. For nearly 120 years (from 1800 to the 

1920s), forest area declined and in 1924 reached its lowest point with only 3 million 

acres of forest land (Telford 1926). A survey of Illinois’ forest resources in 1948 revealed 

an increase to 4 million acres. Since 1948, forest land has steadily risen and is currently 

an estimated 4.5 million acres, or about 13 percent of total land area (Fig. 7). The net 

gain in forest land has not occurred uniformly across the State. Rather, changes in forest 

area have varied by county; in some cases, counties have experienced losses greater than 

5 percent (Fig. 8). 

Illinois’ forest land began to increase in the 1960s and 1970s as a result of a declining 

farm economy. The reduced need for agricultural land fueled a reversion of pastures 

and marginal agricultural lands to forest land. A second increase in forest area occurred 

Forest Area

Background

What we found

What this means

Figure 7.—Area of forest land 

by inventory year, Illinois, 2005 

(error bars represent a 66-

percent confidence interval).

3,700

3,900

4,100

4,300

4,500

4,700

1940 1950 1960 1970 1980 1990 2000 2010

Inventory Year

Forest Land Area (thousand acres)
21

FOREST FEATURES

Figure 8.—Change in the area 

of forest land by county, Illinois, 

1985-2005.

during the latter half of the 1980s. This was due in large part to the success of state and 

national programs designed to promote well managed forests and forest regeneration. 

Since the Illinois Forestry Development Act of 1983, which granted cost-share 

assistance and favorable tax treatment for timber-producing forested lands with a forest 

management plan, the annual rate of increase in forest area has nearly doubled from 

0.2 percent between 1948 and 1985 to 0.3 percent between 1985 and 2005. The 

greatest increase occurred between 1998 and 2005, when the annual rate of increase 

was 0.6 percent.

Projection: UTM Zone 16N, NAD83.

Source: U.S. Forest Service, Forest Inventory and

Analysis program, 1985 - 2005 data. Geographic base

data are provided by the National Atlas of the USA.

FIA data and mapping tools are available online at

http://www.fia.fs.fed.us/tools-data/.

Cartography: S.J. Crocker. July, 2007.

0 50

Miles

Change in forest land area

1985 to 2005

(percent)

> 5% loss

0 - 5% loss

0 - 5% gain

> 5% gain
22

FOREST FEATURES

Many conditions that do not meet the definition of forest land also contain trees. While 

trees on nonforest conditions are not measured by FIA, the area of nonforest land with 

trees is mapped and recorded to generate estimates of the total area of treed land. 

Nonforest land with trees accounts for 2 percent of Illinois’ total land base (Fig. 9). The 

greatest percentages of nonforest land with trees are within the northern and southern 

tiers of the State (Fig. 10). There are several classes of nonforest land that contain trees. 

In Illinois, the urban and other with trees class has the largest area of nonforest land with 

trees (Fig. 11). However, a substantial portion is also found in pasture and rangeland 

with trees, and in wooded strips. Nonforest land with trees adds an additional 858,900 

acres of land to the total area of land with tree cover, or the area of treed land. Thus, 

nonforest land with trees and forest land form a combined total 5.3 million acres of treed 

land, which is equivalent to 15 percent of the total land area in the State. Even with the 

addition of nonforest land with trees, the southern tier remains the most heavily treed 

portion of Illinois (Fig. 10). Most counties show a net increase in the area of treed land 

when forest land and nonforest land with trees are combined. Counties with the greatest 

percent increase are concentrated in the northern half of the State, particularly in the 

Chicago metro area.

Figure 9.—Distribution of total 

land area by land use, Illinois, 

2005.

Trees on Nonforest Land

Background

What we found

2%

13%

5%

8%

2%

70%

Forest land

Nonforest land with trees

Cropland without trees

Other agriculture

Urban without trees

Water

Land Use
23

FOREST FEATURES

Figure 10.—Area of nonforest 

land with trees, total area 

of land with tree cover, and 

percent increase in area of tree 

cover by county, Illinois, 2005.

Projection: UTM Zone 16N, NAD83.

Source: U.S. Forest Service, Forest Inventory

and Analysis program, 2005 data. Geographic

base data are provided by the National Atlas of

the USA. FIA data and mapping tools are available

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

Cartography: S.J. Crocker. August, 2007.

0

1 - 25

25 - 50

50 - 100

< 100

0 100

Miles

0 - 9

10 - 19

20 - 29

30 - 39

40 - 73

Percent increase in area of tree cover

3 - 4

5 - 6

7 - 10

11 - 21

0 - 2

Area of nonforest land with trees

(percent of county land area)

Total area of land with tree cover

(percent of county land area)
24

FOREST FEATURES

Despite classification as nonforest, areas such as cropland, pastures, windbreaks, and 

urban areas often contain trees. While the number of trees on these nonforest conditions 

is insufficient to warrant classification as forest land, estimates of the area of nonforest 

land with trees provide additional information on the extent and distribution of treed 

land. Trees on nonforest conditions may be sparse, but they constitute a valuable 

resource that provides beneficial contributions to wildlife habitat, erosion control, 

protection from wind, improved water quality, carbon sequestration, aesthetics, and 

recreation. 

What this means

Figure 11.—Area of nonforest 

land with trees by land-use 

class, Illinois, 2005.

0 100 200 300 400 500

Christmas tree plantation

Reserved nonforest with trees

Cropland with trees

Pasture and rangeland with trees

Wooded strip

Idle farmland with trees

Marsh with trees

Narrow windbreak (< 120 ft)

Shelterbelt

Urban and other with trees

Area (thousand acres)

Nonforest Land Use
25

FOREST FEATURES

Biomass is a measure of the aboveground weight of live trees that is allocated among 

tree boles, stumps, tops, and limbs. Measurements of biomass provide estimates of the 

quantity and distribution of forest resources. Estimates of biomass are useful in analyses 

of questions related to carbon sequestration, meeting emissions reduction targets, fuel 

loadings in forest stands, and the availability and production of biofuels.

Illinois biomass has been increasing since 1985 (Fig. 12). Currently estimated at 210.6 

million dry tons, an average of 48 dry tons per acre, the distribution of biomass is similar 

to that of forest area. The majority of biomass is found in the southern tier of the State, 

primarily within the Shawnee National Forest (Fig. 13). Biomass on private timberland 

is currently about five times greater than biomass on public timberland; however, public 

timberland contains more biomass per acre (Fig. 12). Growing-stock trees contain 84 

percent of biomass; 11 percent is in nongrowing-stock trees, and 5 percent is in saplings 

(Fig. 14).

Illinois’ forests sequester 343 million tons of carbon. Live trees, which sequester 44 

percent of total carbon, are the State’s largest source of forest carbon (Fig. 15). Soil is 

another substantial carbon pool (33 percent). Additional carbon pools include live trees, 

below ground (8 percent); the forest floor (7 percent); down and dead wood (4 percent); 

standing dead trees (3 percent); and understory vegetation (1 percent).

Biomass

Background

What we found

0

10

20

30

40

50

60

70

1985 1998 2005

Inventory Year

Live Biomass (tons/acre)

Public Private

Figure 12.—Live biomass 

per acre of timberland by 

ownership and inventory year, 

Illinois, 1985 - 2005 (error 

bars represent a 66-percent 

confidence interval).
26

FOREST FEATURES

Figure 13.—Distribution of live 

biomass on forest land, Illinois, 

2005. 

Processing note: This map was produced by

linking plot data to MODIS satellite pixels (250 m)

using gradient nearest neighbor techniques. The

resulting image was resampled to 500 m pixels.

Projection: UTM Zone 16N, NAD83.

Source: U.S. Forest Service, Forest Inventory and

Analysis program, 2005 data. Geographic base

data are provided by the National Atlas of the USA.

FIA data and mapping tools are available online at

http://www.fia.fs.fed.us/tools-data/.

Cartography: S.J. Crocker & B.T. Wilson. July, 2007.

0 50

Miles

<

10 - 18

19 - 30

31 - 44

45 - 160

9

Live biomass on forest land

(oven-dry tons per acre)
27

FOREST FEATURES

The Illinois Forestry Development Act, participation in the Conservation Reserve 

Program, and reversion of agricultural lands to forest, have contributed to the statewide 

increase in total biomass. As holders of the majority of Illinois’ biomass, private forest 

landowners play an important role in sustaining this resource. The management of both 

public and private forest land has a strong effect on Illinois’ carbon sinks. As Illinois 

continues to become more involved in carbon trading, estimates of biomass and carbon 

sequestration by forests will become increasingly important.

What this means

Figure 14.—Distribution of live 

biomass on timberland by tree 

component, Illinois, 2005.

Figure 15.—Distribution of total 

carbon stock on timberland, 

Illinois, 2005.

44%

1%

3%

4%

33%

7%

8%

Live tree (aboveground)

Live tree (belowground)

Understory

Standing dead trees

Down and dead wood

Forest floor

Soil to 1 m

Ecosystem Pool

Tree Component

22%

8%

62%

5%

3% Growing-stock boles

Growing-stock stumps,

tops, and limbs

Nongrowing-stock boles

Nongrowing-stock

stumps, tops, and limbs

Saplings
28

FOREST FEATURES

Forest composition is constantly evolving. Influenced by the presence or absence of 

disturbances, such as timber management, recreation, wildfire, prescribed burning, 

extreme weather, and invasive species, the current state of tree species composition 

is a reflection of historical and environmental trends within a forest. As a result, the 

composition of species in a forest is an indicator of forest health, growth, succession, and 

the need for stand improvement, i.e., management. Knowledge of the distribution of 

species within a stand allows for the measurement and prediction of change.

Illinois’ forest land contains just over 2 billion trees (greater than 1 inch in d.b.h.) 

from nearly 100 different species. This number represents a 25 percent decrease in the 

number of trees between 1998 and 2005, equivalent to a loss of about a half billion trees. 

American elm, sugar maple, and black cherry are the most abundant species by number 

(Fig. 16). 

Live volume on forest land is an estimated 8 billion cubic feet. Most of this volume is 

found in the large-diameter size classes (Fig. 17). White oak remains the most dominant 

species (Fig. 18). Between 1998 and 2005, there were significant volume increases 

in silver maple, green ash, and American elm and a significant decrease in black oak 

volume.

Species Composition

Background

What we found

Figure 16.—Top 10 species on 

forest land by number of live 

trees, Illinois, 1998-2005.

0 50 100 150 200 250 300 350 400

American elm

Sugar maple

Black cherry

Hackberry

Green ash

Eastern hophornbeam

Sassaf ras

Slippery elm

Flowering dogwood

Shagbark hickory

Species

Number of Trees (millions)

1998

2005
29

FOREST FEATURES

Figure 17.—Live volume on 

forest land by stand-size class 

and inventory year, Illinois, 

1998-2005.

Figure 18.—Live volume 

on forest land for the 10 

most voluminous species, 

Illinois, 1998-2005 (error 

bars represent a 66-percent 

confidence interval).

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

Large diameter Medium diameter Small diameter

Stand-size Class

Live Volume (million ft 3

)

1998

2005

0 200 400 600 800 1,000 1,200

White oak

Silver maple

Black oak

Northern red oak

Eastern cottonwood

Shagbark hickory

Sycamore

Sugar maple

Green ash

American elm

Species

Live Volume (million ft3)

1998

2005
30

FOREST FEATURES

Illinois’ forests are composed of a diverse array of tree species. White oak, black oak, 

northern red oak, and silver maple are the most voluminous species in the State. The 

most abundant species, in terms of total number, are American elm and sugar maple, 

along with a host of predominantly understory species. While this is a reflection of 

variation in ecological roles, where species such as hackberry, eastern hophornbeam, and 

flowering dogwood are typically understory species and oaks and maples are dominant 

overstory species, it is also a sign of changing understory dynamics. Disturbance, 

particularly from harvesting and fire management, promotes oak regeneration. The 

absence of such disturbances has allowed shade-tolerant species to out-compete 

understory oaks. Thus, although oaks are fewer in number, their dominance in volume is 

due to high numbers of mature trees in the overstory. As these oaks continue to senesce, 

oak mortality will create gaps in the overstory that will likely be filled by maples and 

elms that now represent the majority of understory species.

What this means

Illinois fall colors. Photo by Susan Crocker, U.S. Forest Service
31

FOREST FEATURES

Forest Density

Background

What we found

The density of a forest indicates the current phase of stand development and has 

implications for diameter growth, tree mortality, and yield. Density is typically measured 

in terms of number of trees or basal area per unit area. Stocking, a relative measure 

of density, represents the degree of tree occupancy required to fully utilize the growth 

potential of the land.

An average acre of Illinois timberland contains 

459 trees. Although the number of trees per acre 

of timberland increased from 1985 to 1998, the 

current estimate represents a significant decrease 

in density between 1998 and 2005 (Fig. 19). In 

contrast, live volume per acre of timberland has 

steadily increased since 1985 and now totals an 

estimated 1,751 cubic feet per acre (Fig. 20). 

Most of Illinois timberland is fully (40 percent) 

or moderately stocked (44 percent) (Fig. 21). 

Overstocked stands, which represent 3 percent of timberland, contain too many trees 

to support adequate tree growth and development. Poorly stocked stands that do not 

contain enough trees to fully utilize a site represent 12 percent of timberland area.

Central hardwoods, Illinois. Photo by 

Susan Crocker, U.S. Forest Service

0

100

200

300

400

500

600

700

1985 1998 2005

Inventory Year

Number of Live Trees per Acre

Figure 19.—Number of live 

trees per acre of timberland by 

inventory year, Illinois, 1985-

2005 (error bars represent a 

66-percent confidence interval).
32

FOREST FEATURES

Illinois’ overstory is currently dominated by oak, maple, hickory, and ash sawtimber 

(Table 1A). As a group, oaks make up the largest percentage of sawtimber density 

(28 percent), but represent only 7 percent of sapling/poletimber density (Fig. 22). 

In comparison, maple species make up a smaller percentage of sawtimber density 

(14 percent) and a larger portion of sapling/poletimber density (12 percent). Overall, 

there is much higher density in the smaller sapling and poletimber trees. American elm, 

sugar maple, black cherry, hackberry, and green ash have the highest sapling/poletimber 

densities. 

Figure 20.—Live volume per 

acre of timberland by inventory 

year, Illinois, 1985-2005 (error 

bars represent a 66-percent 

confidence interval).

Figure 21.—Area of timberland 

by stocking class, Illinois, 2005.

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

2,000

1985 1998 2005

Inventory Year

.

Volume (ft3/acre) Live-tree

0

5

10

15

20

25

30

35

40

45

50

Overstocked Fully stocked Medium

stocked

Poorly

stocked

Nonstocked

Stocking Class

Timberland Area (percent)
33

FOREST FEATURES

 Sawtimber density†

1985 1998 2005

Species estimate SE estimate SE estimate SE

Boxelder 0.5 a ± 0.08 0.6 ab ± 0.10 0.9 b ± 0.14

Red maple 0.4 a ± 0.07 0.7 b ± 0.11 0.5 b ± 0.12

Silver maple 1.4 a ± 0.16 2.2 b ± 0.24 3.0 c ± 0.39

Sugar maple 0.9 a ± 0.09 1.2 b ± 0.11 1.2 ab ± 0.15

Pignut hickory 0.8 a ± 0.07 1.1 b ± 0.10 1.3 b ± 0.14

Shagbark hickory 1.0 a ± 0.08 1.3 b ± 0.10 1.6 c ± 0.16

Mockernut hickory 0.6 a ± 0.06 0.8 b ± 0.08 0.4 c ± 0.08

Hackberry 0.5 a ± 0.07 0.8 b ± 0.09 1.2 c ± 0.13

White ash 0.9 a ± 0.08 1.1 b ± 0.10 0.8 a ± 0.12

Green ash 0.6 a ± 0.08 1.0 b ± 0.10 1.5 c ± 0.17

E. hophornbeam 0.0 a n/a 0.0 a n/a 0.0 a n/a

Black cherry 0.5 a ± 0.05 0.8 b ± 0.08 1.0 c ± 0.12

White oak 4.1 a ± 0.22 5.0 b ± 0.27 4.8 b ± 0.36

Shingle oak 0.4 a ± 0.05 0.8 b ± 0.08 0.9 b ± 0.12

Bur oak 0.6 a ± 0.08 0.7 a ± 0.10 0.8 b ± 0.14

Northern red oak 1.6 a ± 0.11 2.1 b ± 0.15 1.9 b ± 0.19

Black oak 3.0 a ± 0.19 3.5 b ± 0.22 2.9 a ± 0.25

Sassafras 0.1 a ± 0.03 0.2 ab ± 0.04 0.3 b ± 0.06

American elm 0.7 a ± 0.06 1.0 b ± 0.08 1.2 c ± 0.13

Slippery elm 0.4 a ± 0.04 0.4 a ± 0.05 0.5 a ± 0.08

All other species 9.4 a ± 0.38 12.2 b ± 0.49 13.6 c ± 0.71

Total 29.5 a ± 0.53 37.5 b ± 0.63 40.1 c ± 0.87

†

Sawtimber trees must be greater than 9 inches d.b.h. for softwoods and greater than 11 inches d.b.h. for 

hardwoods.

Table 1A.—Sawtimber density, expressed as number of live trees per acre on 

timberland, by inventory year, Illinois, 1985-2005 (Sampling errors [SE] represent a 

66-percent confidence interval. Sawtimber density estimates for a given species are 

not significantly different from one another if followed by the same letter). 
34

FOREST FEATURES

 Sapling/poletimber density†

1985 1998 2005

Species estimate SE estimate SE estimate SE

Boxelder 13.5 a ± 1.30 18.0 b ± 2.84 12.1 a ± 2.30

Red maple 7.9 a ± 1.30 10.2 a ± 3.40 4.6 b ± 0.96

Silver maple 12.8 a ± 1.41 7.9 b ± 1.52 7.3 b ± 1.28

Sugar maple 28.0 a ± 2.13 32.0 a ± 4.20 26.6 a ± 3.00

Pignut hickory 15.1 a ± 1.05 12.0 ab ± 2.92 9.5 b ± 1.13

Shagbark hickory 8.5 a ± 0.93 15.7 b ± 1.98 12.1 c ± 1.28

Mockernut hickory 11.0 a ± 1.07 8.2 b ± 1.70 3.8 c ± 0.68

Hackberry 15.6 a ± 1.18 28.6 b ± 3.49 22.3 c ± 2.22

White ash 15.2 a ± 1.14 16.9 a ± 2.19 7.7 b ± 1.15

Green ash 11.0 a ± 1.21 12.0 a ± 1.95 18.6 b ± 2.18

E. hophornbeam 18.1 a ± 1.58 25.0 b ± 3.53 19.0 ab ± 2.60

Black cherry 16.0 a ± 1.34 29.4 b ± 3.30 22.1 c ± 2.02

White oak 12.4 a ± 0.92 9.1 b ± 1.07 7.1 b ± 0.84

Shingle oak 7.1 a ± 0.72 15.7 b ± 3.90 8.1 a ± 1.36

Bur oak 1.1 a ± 0.22 1.6 ab ± 0.86 1.8 b ± 0.46

Northern red oak 4.1 a ± 0.47 3.6 a ± 0.81 3.2 a ± 0.50

Black oak 12.4 a ± 1.01 15.1 a ± 2.19 7.7 b ± 1.07

Sassafras 22.4 a ± 1.62 26.9 a ± 3.73 17.7 b ± 1.91

American elm 50.0 a ± 2.38 78.5 b ± 6.23 51.3 a ± 3.59

Slippery elm 28.0 a ± 1.55 23.5 a ± 2.94 15.3 b ± 1.69

All other species 140.3 a ± 4.28 159.3 b ± 9.46 129.5 c ± 6.36

Total 450.3 a ± 6.93 549.4 b ± 20.99 407.4 c ± 10.71

†

Sapling/poletimber trees range from 1.0 to 8.9 inches d.b.h. for softwooods and from 1.0 to 10.9 inches 

d.b.h. for hardwoods. 

Table 1B.—Sapling/poletimber density, expressed as number of live trees per acre 

on timberland, by inventory year, Illinois, 1985-2005 (Sampling errors [SE] represent 

a 66-percent confidence interval. Sapling/poletimber density estimates for a given 

species are not significantly different from one another if followed by the same letter). 
35

FOREST FEATURES

What this means

Figure 22.—Sapling/poletimber 

and sawtimber density for 

selected species on timberland 

by inventory year, Illinois, 

1985-2005.

0

5

10

15

20

25

30

35

1985 1998 2005 1985 1998 2005

Sapling/poletimber Density Sawtimber Density

Percent

Oaks

Maples

For the past 20 years, oaks have made up a large portion of the overstory. Presently, 

the density of American elm, silver maple, shagbark hickory, and green ash sawtimber 

is increasing, while the density of oak sawtimber is decreasing (Table 1A, Fig. 22). 

Individually, the density of most oak saplings and poletimber has remained fairly 

constant. Black oak, whose sapling/poletimber density dramatically fell between 1998 

and 2005, is a major exception (Table 1B). As a group, the density of oak saplings and 

poletimber has slowly decreased over time. 

The decrease in the number of trees per acre and the increase in live volume per acre are 

indicative of mature stands with adequate spacing and good growth. This is a result of 

the increased availability of growing space following a reduction in the overall number of 

trees. The stems that remain then face less competition for growing space and are able to 

grow more quickly. The existence of quality growth conditions is mirrored in the current 

levels of stocking, which show that the growing space available for tree development is 

fully utilized on the majority of forest acreage.

Evidence of possible succession to maple forest types is reflected in the changes in forest 

density among Illinois’ saplings, poletimber, and sawtimber trees. The density of oak 

sawtimber appears to be leveling off and it does not appear that oak will replace itself 

in the overstory. A lack of increasing oak density in the sapling/poletimber size classes 

coupled with decreasing oak sawtimber density and high maple sapling/poletimber 

density is an indication that future stands may include fewer oaks and more maples. 
36

FOREST FEATURES

Diminishing Oaks, Maple Replacement

Background

What we found

Oak/hickory forests are the predominant forest type on the Illinois landscape. The broad 

range of tree species and the structural variation within these forests contributes to their 

importance as a reservoir for biological diversity. Home to a number of mast-producing 

trees, many wildlife species are dependent on oak/hickory forests for the food and habitat 

they provide. 

With an average of fewer than 45 seedlings per acre of forest land, oaks represent a 

small component (7 percent) of the understory (Fig. 23A). Of all oak species, white and 

black oak seedlings are the most abundant, occurring over three times more often than 

red oak seedlings. Elm, ash, and maple have substantially more seedlings per acre than 

oaks. Similarly, oak saplings (which average fewer than seven saplings per acre of forest 

land) are far less abundant than other hardwood species (Fig. 23B). Regeneration of oak 

Figure 23.—Number of 

seedlings (A) and saplings 

(B) per acre of forest land for 

selected species, Illinois, 2005.

0

50

100

150

200

250

300

American elm

Green ash

Sugar maple

Hackberry

Boxelder

White ash

Silver maple

White oak

Black oak

Shagbark hickory

Shingle oak

Red maple

Red oak

Seedlings per Acre

Species

0

5

10

15

20

25

30

35

40

45

50

Species

Saplings per Acre

American elm

Sugar maple

Hackberry

Green ash

Boxelder

Shagbark hickory

Shingle oak

Black oak

White ash

White oak

Silver maple

Red maple

Red oak

A

B
37

FOREST FEATURES

within oak forests is poor (Fig. 24A, B). On average, the ratio of oak to non-oak species 

is 1 to 13 for both seedlings and saplings.

Figure 24.—Number of 

seedlings (A) and saplings (B) 

per acre for oak and non-oak 

species on oak and non-oak 

forest types, Illinois, 2005.

A

B

0

200

400

600

800

1,000

1,200

1,400

1,600

Oak Forest Types Non-oak Forest Types

Oak seedlings

Non-oak seedlings

Seedlings per Acre

0

50

100

150

200

250

Oak Forest Types Non-oak Forest Types

Oak saplings

Non-oak saplings

Saplings per Acre
38

FOREST FEATURES

A comparison of oaks and maples by diameter shows that the small-diameter classes 

are dominated by hard maples (primarily sugar maple), while the large-diameter classes 

consist mainly of black and shingle oaks in the other red oaks species group (Fig. 

25). Not surprisingly, the other red oak species group is the largest contributor to oak 

mortality; within this group, black oak has the highest mortality rate (Table 2). Ninetythree percent of oak growing-stock mortality occurred in trees where the d.b.h. was 11 

inches or greater. 

Figure 25.—Number of trees 

on forest land by diameter 

class for selected species 

groups, Illinois, 2005. 

0

10

20

30

40

50

60

70

80

90

1.0-2.9

3.0-4.9

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

21.0-22.923.0-24.9

25.0+

Select red oaks Other red oaks

Hard maple Soft maple

Diameter Class (inches)

Number of Trees (millions)

Table 2.—Average annual mortality for growing stock and sawtimber on timberland 

by selected species group, Illinois, 2005

Average annual Average annual

 Species group growing-stock mortality sawtimber mortality

(in thousand cubic feet/year) (in thousand board feet/year)

Select white oaks 2,846 9,863

Select red oaks 1,971 8,497

Other white oaks 924 4,079

Other red oaks 12,228 50,849

Hard maple 2,153 9,296

Soft maple 12,724 48,876
39

FOREST FEATURES

What this means

White oak. Photo by Paul Wray, Iowa State University, 

bugwood.org

Illinois’ oak resource is characterized by numerous large, mature trees and a 

comparatively small sapling/seedling component. Decreases in the frequency of 

beneficial disturbances including timber management and prescribed fire have 

contributed to suppression of oak seedlings and an increase in the abundance of non-oak 

seedlings and saplings. With an understory dominated by non-oak species such as sugar 

maple and with relatively few oak saplings available to move into the medium-diameter 

classes, it is likely that there will be a successional change in species dominance. Oak 

stands may eventually be dominated by more shade-tolerant species such as maples. 

With a largely mature oak resource, the future of oak in Illinois is uncertain. Maintaining 

a healthy oak resource will be dependent on successful seedling regeneration and sapling 

development.
­­­­40

FOREST FEATURES

Ownership

Background

What we found

FIA conducts the National Woodland Owner Survey (NWOS) to increase our 

understanding of who owns forest land, why they own it, and what they intend to do 

with it. It serves as the social complement to the inventory of the State’s biophysical 

forest resources and provides a more holistic understanding of the forest resources and 

the factors affecting them. 

Illinois’ forest land is predominantly held by private landowners. An estimated 206,000 

families and individuals own a total of 3.5 million acres, or 77 percent of forest land 

(Fig. 26). An additional 265,000 acres are owned by other private groups (e.g., 

corporations, associations, etc.). Collectively, private owners hold 82 percent of the 

State’s forests. Family forest owners generally own less than 10 acres of forest land 

(Fig. 27). However, family forest owners with landholdings greater than 10 acres own 

more than 55 percent of private forest land. The most common reasons for owning 

forest land are related to beauty and scenery, forest land as part of a farm, privacy, and 

as a family asset or legacy to pass on to heirs. Timber has been harvested on 11 percent 

of privately owned forest land in the past 5 years (Fig. 28). Four percent of family forest 

owners reported having a written forest management plan and 15 percent have sought 

management advice. Trespassing was rated as a significant concern by 46 percent of 

family forest owners. Other prevalent concerns were related to vandalism, dumping, 

property taxes, and owners’ abilities to keep their land intact for heirs. One in 10 acres of 

forest land is owned by someone who plans to transfer or sell it within the next 5 years. 

This is related, in part, to owner age; 49 percent of family forest land is owned by people 

65 or older (Fig. 29). 

Figure 26.—Area of forest land 

by ownership group, Illinois, 

2002-2004.

6%

8%

Ownership Group 4% 5%

Family and Individual

Business

Federal

State

Local

77%
­­­­41

FOREST FEATURES

Figure 27.—Area of family 

owned forests and number of 

family forest owners by size of 

landholdings, Illinois, 2002-

2004.

Size of Forest Landholdings (acres)

Acres

Owners

0

10

20

30

40

50

60

70

Percent

1-9 10-49 50-99 100-499 500+

Figure 28.—Area of family 

owned forests by recent (past 

5 years) forestry activity, 

Illinois, 2002-2004 (NTFPs are 

nontimber forest products; error 

bars represent a 66-percent 

confidence interval).

0 500 1,000 1,500 2,000 2,500

Activity

Forest Land Area (thousand acres)

Cost share

Public recreation

Private recreation

Posting land

Wildlife habitat improvement

Road/trail maintenance

Application of chemicals

Fire hazard reduction

Tree planting

Site preparation

Collection of NTFPs

Timber harvest
­­­­42

FOREST FEATURES

Private landholders are an important, diverse, and dynamic group of forest owners. 

Holding the majority of forest land, they have a substantial influence on the status, 

structure, and composition of Illinois’ forest resources. Based on the current age 

of family forest owners and their intended plans, forest land will soon undergo an 

intergenerational shift in ownership that will transfer a large portion of forest area to a 

new cohort of landowners. This change will influence how owners view, interact, and 

relate to their land, and may alter future forest characteristics.

What this means

Figure 29.—Area and number 

of family owned forests by age, 

Illinois, 2002-2004.

0

5

10

15

20

25

30

35

< 35 35-44 45-54 55-64 65-74 75+ No

Answer

Age (years)

Percent

Acres

Owners
­­­­43

FOREST FEATURES

Riparian Forests

Background

What we found

Largely located along river and stream borders, 

many riparian forests are oriented in long and 

narrow strips that do not meet FIA’s definition 

of forest land and are therefore not measured. 

However, there are a number of riparian forests 

that do meet the FIA definition of forest land. By 

combining a portion of mesic physiographic classes 

(narrow flood plains/bottomlands, broad flood 

plains/bottomlands, other mesic) and all hydric 

classes (swamps/bogs, etc.), we can derive coarse 

estimates of the size, structure, and composition of 

Illinois’ riparian forests.

Riparian forests total an estimated 992,500 acres 

and account for 22 percent of Illinois’ forest 

land (Table 3). A mapped distribution of riparian forests using U.S. Fish and Wildlife 

Service’s National Wetlands Inventory data shows that much of these forests are 

concentrated along rivers and streams in the southern tier of Illinois (Fig. 30). FIA data 

indicates that 74 percent of riparian forest land is in narrow floodplains and bottomlands 

that are less than a quarter mile wide. 

Riparian forest along the Cache River, 

Illinois. Photo by Susan Crocker, U.S. 

Forest Service

Table 3.—Area of forest land (in acres) in riparian physiographic classes by stand 

size, Illinois, 2005

Stand-size class

Large

diameter

Medium

diameter

Small

diameter

Non-

 Physiographic class stocked Total

 Narrow flood plains/bottomlands 443,184 128,700 53,432 1,674 626,991

 Broad flood plains/bottomlands 199,212 29,019 8,564 1,569 238,364

 Other mesic 23,635 0 6,017 1,504 31,156

 Swamps/bogs 14,025 8,347 0 0 22,372

 Small drains 43,959 11,374 7,841 1,490 64,665

 Bays and wet pocosins 9,032 0 0 0 9,032

 Total 733,047 177,440 75,854 6,237 992,580
­­­­44

FOREST FEATURES

Figure 30.—Distribution of 

riparian forest types (from the 

U.S. Fish and Wildlife Service’s 

National Wetlands Inventory), 

Illinois, 2005.

Projection: UTM Zone 16N, NAD83.

Source: U.S. Fish and Wildlife Service, National

Wetlands Inventory. Geographic base data are

provided by the National Atlas of the USA.

Cartography: S.J. Crocker. October, 2007.

0 50

Miles

Legend

Freshwater forested/shrub wetland
­­­­45

FOREST FEATURES

Figure 31.—Top 12 species, 

by number of trees, in riparian 

physiographic classes on 

forest land, Illinois, 2005 (error 

bars represent a 66-percent 

confidence interval).

0 10 20 30 40 50 60

American elm

Green ash

Silver maple

Hackberry

Boxelder

Water tupelo

Red maple

Sugar maple

Black cherry

Slippery elm

Black willow

Black walnut

Species

Number of Trees (millions)

Illinois’ riparian forests currently 

contain an estimated 352.3 

million live trees, an average of 

355 trees per acre of riparian forest 

land. Nearly 70 tree species were 

identified; the most commonly 

observed species were American 

elm, green ash, silver maple, 

hackberry, and boxelder (Fig. 31). 

These five species account for half 

of the total number of trees on 

riparian forest land. Estimates of 

volume show that riparian forests 

contain 2.1 billion cubic feet, or 26 percent of the State’s total live volume on forest 

land. Silver maple (29 percent of total riparian volume), eastern cottonwood 

(9 percent), green ash (7 percent), hackberry and sycamore (5 percent each) have 

the greatest percentage of volume in riparian forests.

Thirty-eight percent of total mortality of growing stock on timberland occurred in 

riparian forests. Species with considerable mortality include: red maple (6.3 million 

cubic feet), silver maple (3.6 million cubic feet), American elm (3.3 million cubic feet), 

hackberry (2 million cubic feet), green ash (1.3 million cubic feet), and pin oak 

(474,500 cubic feet).

Bald cypress swamp, Cache River State Natural Area, 

Illinois. Photo by Susan Crocker, U.S. Forest Service.
­­­­46

FOREST FEATURES

Riparian forests contain a diverse number of species, but only a handful of those species 

are dominant. Surprisingly, many of these dominant species, e.g. American elm, green 

ash, silver maple, and hackberry, are experiencing high mortality. Some of this mortality 

can be attributed to severe flooding, particularly from the Mississippi flood of 1993. 

However, insects and diseases are also important contributors. For example, much of the 

mortality of American elm is due to Dutch elm disease (DED). Additionally, the emerald 

ash borer (EAB) is a major threat to green ash, the second most abundant species in 

volume and number of trees. Riparian forest corridors may play an important role in the 

dispersal of EAB. In combination with adverse weather and old age, continued spread of 

DED and EAB could change the structure and composition of riparian forests. 

What this means
­­­­47

FOREST FEATURES

Average Annual Growth

Background

What we found

Figure 32.—Average annual 

net growth of growing stock on 

timberland by inventory year, 

Illinois, 1962 to 2005.

0

50

100

150

200

250

300

350

1950 1960 1970 1980 1990 2000 2010

Inventory Year

Average Annual Growth

(million ft3/yr)

A stand’s capacity for growth, i.e., for trees 

to increase in volume, is an indication of 

the overall condition of the stand and more 

specifically of tree vigor, forest health, and 

successional stage. Forest growth is measured 

as average annual net growth, where net 

growth is equivalent to gross growth minus 

mortality. Average annual net growth represents 

an average for the annual change in volume 

between the two most recent inventories, 1998 

and 2005 for this report.

Since 1962, average annual net growth of 

growing stock has been on the rise (Fig. 32). Net 

growth averaged 327 million cubic feet per year 

between 1998 and 2005. Nearly all of that growth (98 percent) was in hardwoods. Silver 

maple had the highest growth rate, followed by eastern cottonwood, white oak, and 

northern red oak (Fig. 33). Collectively, Illinois’ major oak species (white, northern red, 

bur, and black oak) account for 23 percent of total growth. The bulk of growth occurred 

in large-diameter stands (Fig. 34). Ninety-four percent of net growth in white, northern 

red, bur and black oaks was in large-diameter stands.

Understory vegetation. Photo by 

Susan Crocker, U.S. Forest Service
­­­­48

FOREST FEATURES

Figure 33.—Average annual 

net growth of growing stock 

on timberland for the top 12 

species, Illinois, 1998 to 2005.

Figure 34.—Average annual 

net growth of growing stock on 

timberland by stand-size class, 

Illinois, 1998 to 2005.

0 5 10 15 20 25 30 35 40

Silver maple

Eastern cottonwood

White oak

Northern red oak

Bur oak

Sycamore

Black oak

Hackberry

Sugar maple

Black walnut

White ash

American elm

Species

Average Annual Growth (million ft3/yr)

0

50

100

150

200

250

300

Large diameter Medium diameter Small diameter

Stand-size Class

Average Annual Growth

(million ft3/yr)
­­­­49

FOREST FEATURES

Illinois’ forests are growing at their highest rates since 1962. The preponderance of this 

growth is occurring within large-diameter stands, which indicates that mature trees 

are continuing to increase in volume. While sustained growth of large-diameter oak 

increases its availability for commercial wood products, growth of other species in a 

variety of size classes suggests that in the future oak may not be as dominant as it is today.

Growth, removals, and mortality data are collected only on trees 5 inches in d.b.h. or 

greater. As a result, growth rates reported here provide information on trends in the 

overstory, but do not reflect potential changes in understory growth.

What this means

Height measurement. Photo by Cassandra Olson, 

U.S. Forest Service

Field crew member measuring tree diameter. 

Photo by Cassandra Olson, U.S. Forest Service
­­­­50

FOREST FEATURES

Average Annual Removals

Background

What we found

Figure 35.—Average annual 

removals of growing stock on 

timberland by inventory year, 

Illinois, 1962 to 2005 (error 

bars represent a 66-percent 

confidence interval).

Trees are removed from timberland to meet a 

variety of management objectives. Changes in the 

quantity of growing stock removed helps to identify 

trends in land use change and forest management. 

Because removals are generally recorded on a limited 

number of plots, the estimates for removals show 

greater variance than those for growth, mortality, or 

area. Like forest growth, the rate at which trees are 

removed represents the annual average of removals 

that occurred between 1998 and 2005.

Growing-stock removal rates began a rapid climb during the 1960s, reaching a peak in 

the early 1980s (Fig. 35). Since 1985, the rate at which growing stock was removed from 

timberland has decreased. Currently, growing stock is removed at an average of 60.6 

million cubic feet per year. Eighty-seven percent of growing-stock removals occurred on 

private land. Hardwoods account for virtually all of total removals; softwood removals 

total 43,000 cubic feet per year and represent less than 0.1 percent of total removals. 

White oak and eastern cottonwood had the highest annual removals, each averaging 

8.9 million cubic feet per year (Fig. 36). Oak species account for 36 percent of annual 

removals.

Tree felling. Photo by U.S. Forest 

Service, Northeastern Area archives, 

bugwood.org

0

10

20

30

40

50

60

70

80

90

100

1950 1960 1970 1980 1990 2000 2010

Inventory Year

Average Annual Removals

(million ft3/yr)
­­­­51

FOREST FEATURES

What this means

Figure 36.—Average annual 

removals of growing stock 

on timberland for the top 10 

species by inventory year, 

Illinois, 1985 to 2005 (error 

bars represent a 66-percent 

confidence interval).

Wood products represent an important industry in Illinois. Changing market demands 

and market values can influence the rate of tree removals and the species being removed. 

Black oak was the only species to show a significant change (decrease) in removals 

between inventory cycles. Perhaps the most important trend is an apparent change in 

which species are being removed. Illinois’ forest products market seems to be moving 

away from high utilization of oak and the demand for cottonwood is increasing.

-1 2 5 8 11 14 17

1985 to 1998

1998 to 2005

Species

Average Annual Removals (million ft3/yr)

White oak

Eastern cottonwood

Black oak

Northern red oak

Sycamore

Hackberry

Shagbark hickory

White ash

Silver maple

Sweetgum
­­­­52

FOREST FEATURES

Average Annual Mortality

Background

What we found

What this means

Forest health, vigor, and the rate of accretion and depletion are all influenced by tree 

mortality. Mortality can be caused by insects, disease, adverse weather, succession, 

competition, fire, old age, or human or animal activity, and is often the result of a 

combination of these factors. Tree volume lost as a result of land clearing or harvesting 

is not included in mortality estimates. Growing-stock mortality estimates represent the 

average cubic-foot volume of sound wood in growing-stock trees that died each year as 

an average for the years between inventories (1998 and 2005 in this report).

Since the 1960s, the rate of growing-stock mortality has continued to grow with 

each inventory (Fig. 37). Average annual mortality of growing stock on timberland 

is currently an estimated 86.7 million cubic feet per year, roughly 1.3 percent of total 

growing stock volume. American elm, black oak, and red maple have the highest rates 

of mortality; all three species experienced significant increases in mortality since 1998 

(Fig. 38). A closer look at elm mortality shows that 27 percent of elms were infected 

with disease; 72 percent of elm damage agents were unknown/other. 

Increasing mortality reflects the growing maturity of Illinois’ forests. As the bulk of the 

State’s forests are made up of large-diameter stands, much of the mortality may be the 

result of senescence. However, elm mortality is largely due to the continued spread of 

DED. Black oak mortality is related to oak wilt and old age. As oak is a major overstory 

component and does not appear to be replacing itself in the overstory, oak mortality has 

implications for the future composition of Illinois’ forests. As American elm and maples 

now occupy the majority of the poletimber density, high elm mortality makes maples 

likely candidates to replace oaks in the overstory.
­­­­53

FOREST FEATURES

Figure 37.—Average annual 

mortality of growing stock on 

timberland by inventory year, 

Illinois, 1962 to 2005. 

0

10

20

30

40

50

60

70

80

90

100

1950 1960 1970 1980 1990 2000 2010

Inventory Year

Average Annual Mortality

(million ft3/yr)

Figure 38.—Average annual 

mortality of growing stock on 

timberland for the top seven 

species by inventory year, 

Illinois, 1985 to 2005 (error 

bars represent a 66-percent 

confidence interval).

0 5 10 15 20

American elm

Black oak

Red maple

Sycamore

Silver maple

Slippery elm

White ash

Species

1985 to 1998

1998 to 2005

Average Annual Mortality (million ft3/yr)

Forest Health

Above: Flowering dogwood; photo by Susan Crocker, U.S. Forest Service. 

Inset: White-tailed deer; photo by U.S. Forest Service archives, bugwood.org.
­­­­56

FOREST HEALTH

Down Woody Materials

Background

What we found

Down woody materials including fallen trees and branches fulfill a critical ecological 

niche in Illinois’ forests. They provide valuable wildlife habitat in the form of coarse 

woody debris and contribute to forest fire hazards via surface woody fuels. 

In Illinois, the fuel loadings of down woody materials (fuel-hour classes) are not 

exceedingly high and are not significantly different from fuel loadings in neighboring 

states; for fuel-hour definitions, see Woodall and Monleon (2008) (Fig. 39). The 

distribution of coarse woody debris by size class seems to be heavily skewed (76 percent) 

towards pieces less than 8 inches in diameter at point of intersection with plot sampling 

transects (Fig. 40A). Decay class distribution appears to be fairly uniform across the 

State, except for decay class 3 logs (33 percent) (Fig. 40B). Coarse woody pieces in 

decay class 3 are typified by moderately decayed logs that are structurally sound, missing 

most of their bark, and have extensive sapwood decay. There is no strong trend in 

coarse woody debris volume per acre among classes of live density (basal area per acre). 

However, stands with the highest coarse woody debris volumes also had the lowest 

standing live density (Fig. 41). 

Figure 39.—Estimates of mean 

fuel loadings by fuel-hour 

class on forest land for Illinois, 

Indiana, and Iowa, 2005 (error 

bars represent a 66-percent 

confidence interval).

0

5

10

15

20

25

1-hr 10-hr 100-hr 1000+-hr

Fuel-hour Class

Amount of Fuel (tons/acre)

Indiana

Illinois

Iowa
­­­­57

FOREST HEALTH

Figure 40.—Mean distribution 

of coarse woody debris (pieces 

per acre) by (A) size class 

(inches) and (B) decay class 

(1 – least decayed, 5 – most 

decayed) on forest land, 

Illinois, 2005.

Coarse Woody

Diameter (inches)

76%

20%

3% 1%

3.0 - 7.9

8.0 - 12.9

13.0 - 17.9

18.0+

Decay Class 7%

29%

33%

25%

6%

1

2

3

4

5

A

B

Coarse woody debris. Photo by David Stephens, 

bugwood.org
­­­­58

FOREST HEALTH

What this means Down woody fuel loadings in Illinois’ forests are low and, in general, they are not very 

different from those in neighboring states. Only in times of extreme drought would these 

low fuel amounts pose a hazard. Coarse woody debris volumes are also relatively low and 

are represented by small, moderately decayed pieces. The lack of large pieces of debris is 

a good indication that coarse woody debris is not a significant source of wildlife habitat. 

Because fuel loadings are not exceedingly high across Illinois, the danger of wildfire is 

outweighed by the benefit of down woody material for wildlife habitat and carbon sinks.

0

100

200

300

400

500

600

700

800

900

1,000

0.0 - 30.1 -

60.0

60.1 -

90.0

90.1 -

120.0

120.1+

30.0

Basal Area (ft2/acre)

Coarse Woody Debris Volume

(ft3/acre)

Figure 41.—Estimates of 

mean coarse woody debris 

volumes by stand density on 

forest land, Illinois, 2005 (error 

bars represent a 66-percent 

confidence interval).
­­­­59

FOREST HEALTH

Soils

Background

What we found

Rich soils are the foundation of productive forest land. The soil inventory illustrates 

the unique niches that different forests now occupy to maximize their competitive 

advantage. As an initial inventory, the collected data also provide critical baseline 

information to document changes in forest health resulting from natural or human 

influences.

Field data were collected from 2001 to 2005. Only forest-type groups with more than 

five samples are considered. The forest floor is thicker under the oak/hickory forest-type 

group than under elm/ash/cottonwood (3.38 and 2.67 cm, respectively, Fig. 42), but the 

elm/ash/cottonwood forest-type group occurs in soils with greater depths to restrictive 

layers.

Differences in the coarse fragment content and bulk density of soils under elm/ash/

cottonwood and oak/hickory stands were also found. Oak/hickory forest-type groups 

are found over more coarse subsoil (10 to 20 cm) than subsoil found under elm/ash/

cottonwood stands (4.79 and 1.40 percent coarse fragments, respectively). The bulk 

density of mineral soil in both the 0 to 10 and 10 to 20 cm layer is higher under the 

oak/hickory forest-type group. 

The pH of the surface mineral soil is higher under elm/ash/cottonwood than under 

oak/hickory (Table 4). Additionally, the Ca2+, Mg2+, K+ and Na+ content of the soil is 

significantly higher under elm/ash/cottonwood than under oak/hickory. This consistency 

leads to higher amounts of exchangeable cations (ECEC) under the elm/ash/cottonwood 

forest-type group. This is true in both samples (0 to 10 and 10 to 20 cm). Interestingly, 

Al3+ stocks are lower in elm/ash/cottonwood than in oak/hickory.

The adjusted Soil Quality Index (SQI) is a new metric that combines the distinct 

physical and chemical properties of the soil into a single, integrative assessment that 

ranges from 0 to 100 (Amacher et al. 2007). By linking SQI values to plot locations, it is 

possible to evaluate the influence of parent material on soil quality. In Illinois, the lowest 

quality soils are found on soils formed from colluvium (Fig. 43); this is true in both the 

0 to 10 and 10 to 20 cm layers. 
60

FOREST HEALTH

Figure 43.—Adjusted Soil 

Quality Index (SQI) for the 

0 to 10 cm layer, Illinois, 2005 

(error bars represent a 66-

percent confidence interval).

Adjusted SQI (0-100)

Parent Material

Till

Outwash

Loess

Colluvium

Alluvium

0 10 20 30 40 50 60 70 80 90

Table 4.—Selected chemical properties of forest soils, Illinois, 2005 Forest-floor Thickness (cm)

Forest-type Group

4.0

3.0

2.0

1.0

0.0

Elm/ash/cottonwood Oak/hickory

Figure 42.—Forest-floor 

thickness by forest-type 

group, Illinois, 2005 (error 

bars represent a 66-percent 

confidence interval). 

Soil layer and 

forest-type group

No. of 

samples

pH in

H2

O

Ca2+ Mg2+ K+ Na+ S Al3+ ECEC

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

0 - 10 cm

Elm/ash/cottonwood 11 6.5 3,032 485 175 56 18 22 20

Oak/hickory 29 5.7 1,574 276 112 11 8 36 11

10 - 20 cm

Elm/ash/cottonwood 11 6.6 2,800 440 148 76 12 31 19

Oak/hickory 28 5.5 1,115 249 78 12 8 88 9
61

FOREST HEALTH

What this means The forest floor results from the slow accumulation of organic matter. Carbon, the 

primary component of soil organic matter, has a number of important functions 

including increasing water holding capacity, retaining nutrients by cation exchange (e.g., 

Ca2+, Mg2+, K+), releasing other nutrients as it decays (e.g., N, P, and S), and capturing 

potential toxic agents (e.g., Hg) (McBride 1994). Carbon is also inventoried to track 

the sequestration of certain greenhouse gases. It traps nutrients and improves water 

holding capacity. Thicker forest floors indicate greater carbon storage and can also be 

viewed as a fire hazard. The differences in forest-floor thickness are likely related to the 

greater amount of moisture available to support decomposition in elm/ash/cottonwood 

stands. There may also be differences in tissue quality. Hill et al. (1992) observed that 

cottonwood leaves decayed more quickly than the oak species they sampled.

Bulk density, which measures the mass of dry soil in 

a fixed volume, is an important physical property of 

soil. Trees have greater difficulty rooting in soils with 

higher bulk densities, and there is less pore space 

available for air and water exchange. Soil texture 

affects bulk density; sandy soils tend to have higher 

bulk densities than finer textured soils like silts, clays, 

and loams.

Effective cation exchange capacity (ECEC) is the sum 

of five key mineral elements: Na+, K+, Ca2+, Mg2+, and 

Al3+. High ECEC values are associated with higher 

fertility. In Illinois, the oak-hickory forest-type group 

was found on sites with low relative fertility. 

Soil profile. Photo by Phil Crawl, 

U.S. Forest Service, bugwood.org
62

FOREST HEALTH

Tree Crowns

Background

What we found

Crown condition is an indicator of general 

tree health. Vigorous tree growth is associated 

with full, dense crowns (Schomaker 2003). 

Conversely, sparse crowns suggest poor growth 

conditions resulting from disturbances such as 

disease, insect activity, and adverse weather, 

or from unfavorable site conditions such as 

nutrient deficiency, overcrowding, and moisture 

stress or excess.

Five of the main components of crown 

condition are crown density, foliar transparency, 

uncompacted live crown ratio, crown dieback, 

and crown vigor. Crown density is an estimate of crown fullness and represents the 

amount of branches, foliage, and reproductive structures that block light through the 

crown (U.S. For. Serv. 2007a). The amount of light visible through the live, normally 

foliated portion of the crown is defined as foliar transparency. Uncompacted crown ratio 

is the percentage of total tree height that supports live foliage. Dieback is a measure of 

twig and branch mortality within the crown. Crown vigor is an estimate of the crown 

condition and health of saplings. Determination of crown vigor is based on estimates of 

crown ratio, dieback, and condition of foliage (U.S. For. Serv. 2007a). 

Overall, Illinois’ tree crowns are in good condition. The majority of trees have high 

crown ratios and crown densities, low foliar transparencies, and relatively little dieback. 

Established critical thresholds for crown condition show that trees are most susceptible 

to mortality within 1 year when hardwoods have greater than 30 percent dieback (20 

percent for softwoods), and crown densities less than 30 percent (for both hardwoods 

and softwoods) (Steinman 2000). In Illinois, 5 percent of trees have more than 30 

percent dieback and only 6 percent of trees have a crown density lower than 30 percent. 

Additionally, trees are considered to be generally unhealthy when foliar transparency 

exceeds 40 percent (Coulston 2005). Estimates of transparency show that 4 percent 

of trees have greater than 40 percent transparency. Crown density, which serves as an 

indicator of expected tree growth, was more than 30 percent for 94 percent of the trees 

in Illinois. 

Tree crowns. Photo by Susan Crocker, 

U.S. Forest Service
63

FOREST HEALTH

While the majority of trees were healthy, some species did exhibit notable trends in 

crown condition. Sugar maple, hackberry, and pignut hickory have some of the highest 

mean crown ratios. White ash, black cherry, and American elm have some of the highest 

mean transparencies and the greatest amounts of dieback (Fig 44).

The severity of dieback is categorized as none (0 to 5 percent), light (6 to 20 percent), 

moderate (21 to 50 percent), or severe (51 to 100 percent). Eighty-six percent of 

trees had no dieback, 11 percent had light dieback, and only 3 percent of crowns had 

moderate or severe dieback. Black cherry, silver maple, white ash, and sugar maple had 

the greatest proportion of dieback in the moderate and severe classes (Fig. 45). 

Sixty-five percent of saplings are in vigor class 1 (good), 33 percent are in vigor class 2 

(average), and 2 percent are in vigor class 3 (poor) (Fig. 46).

Figure 44.—Mean crown 

ratio, mean foliar transparency 

and mean crown dieback for 

selected species (calculated for 

trees 5 inches d.b.h. or larger), 

Illinois, 2005.

0 20 40 60 80

Silver maple

Hackberry

Pignut hickory

Sugar maple

Boxelder

American elm

Black cherry

White oak

Green ash

Black oak

White ash

Sassafras

Percent

Crown Ratio Transparency Dieback

Species
64

FOREST HEALTH

0 20 40 60 80 100

Black cherry

Boxelder

American elm

Black oak

Sassafras

Silver maple

White ash

Sugar maple

White oak

Hackberry

Green ash

Pignut hickory

Percent

None Light Moderate Severe

Species

Figure 45.—Percentage of 

species dieback by severity for 

selected species (calculated for 

trees 5 inches d.b.h. or larger), 

Illinois, 2005.

Figure 46.—Distribution of 

saplings by vigor class, Illinois, 

2005.

2%

65%

33%

Class 1

Class 2

Class 3

Vigor Class
65

FOREST HEALTH

Crown condition is an assessment of current tree conditions, but it also serves as a 

measure of site quality, stand density, and the degree and influence of external stresses. 

Measurements from crown variables indicate that there are no major problems affecting 

tree condition in Illinois. Moreover, high density and crown ratio, and low transparency 

and dieback show that most of Illinois’ trees exhibit increased potential for survival, 

reproduction, nutrient storage, and carbon fixation (U.S. For. Serv. 2007a). 

What this means

Yellow-poplar. Photo by Susan Crocker, 

U.S. Forest Service
66

FOREST HEALTH

Ozone Damage

Background

What we found

Ozone is a naturally occurring component of both the upper and lower atmosphere. 

Ground level ozone pollution results largely from industrial processes and automotive 

engines (U.S. For. Ser. 2007b). As a result, ozone levels are often higher in and 

downwind of major industrial and urban centers, and when temperatures are warm. 

Elevated concentrations of ground-level ozone can adversely affect forested landscapes, 

causing direct foliar injury and reduced photosynthetic activity (Coulston et al. 2004). 

Prolonged exposure to high levels of ozone reduces tree growth, weakens tree defenses 

(increasing vulnerability to insects and disease), and may lead to changes in forest 

composition, regeneration, and productivity. 

Plant response to ozone is monitored using bioindicator plants (biomonitoring) that 

exhibit increased sensitivity to ambient levels of pollution (Coulston et al. 2003). 

The use of bioindicator plants provides an indirect measure of air quality, identifying 

conditions that are favorable for the occurrence of ozone injury. In 1994, as part of a 

national ozone biomonitoring program, FIA and the Forest Service’s Forest Health 

Monitoring (FHM) Program initiated bioindicator surveys. Ozone bioindicator data was 

first collected in Illinois in 1997. The national ozone grid that instituted permanent 

biosite plots was established in 2002.

During the 2005 inventory, 153 biosites were sampled for ozone injury; 44 percent 

of these plots contained plants with injury (Table 5). Only 2 percent of evaluated 

bioindicator plants had ozone damage. For each biosite, the severity and amount of 

ozone damage was used to calculate a biosite index. Index values are grouped into four 

categories that describe plant response and identify the degree of risk or possible impacts 

to a forest due to ambient ozone exposure (Table 6) (Smith et al. 2007). Ninety-two 

percent of biosites fall into the no risk category, 6 percent show light risk, and just over 1 

percent of biosites are in the moderate or high risk categories (Fig. 47).

Eight species of bioindicator plants were evaluated in Illinois: black cherry, white 

ash, sassafras, sweetgum, yellow-poplar, milkweed, blackberry, and spreading dogbane. 

Ozone damage was recorded on all species except sweetgum. Milkweed had the greatest 

percentage of recorded damage. 
67

FOREST HEALTH

Ozone damage on yellow-poplar. Photo by U.S. 

Forest Service, Region 8 archives, bugwood.org

Table 6.—Classification scheme for Biosite Indexa (Smith et al. 2007)

a

The categorizations of the biosite index are subjective and based solely on expert opinion.

b

Relative ozone air quality from a plant’s perspective. See EPA-456/F-99-002 July 1999; 

http://www.airnow.gov.

c

According to the EPA’s Proposed Guidelines for Ecological Risk Assessment (Federal Register 61(175): 

47552-47631).

Biosite

Index

Bioindicator 

response

Assumption 

of risk Possible impact Relative air qualityb

0 to < 5 Little or no

 foliar injury None

Visible injury to

highly sensitive 

species, e.g., 

black cherry

Good

5 to < 15 Light

foliar injury Low

Visible injury to 

moderately sensitive 

species, e.g., 

yellow poplar

Moderate

15 to < 25 Moderate 

foliar injury Moderate

Visible and

invisible injury.

Tree-level responsec

Unhealthy for

sensitive species

≥ 25 Severe

foliar injury High

Visible and invisible

injury. Ecosystemlevel responsec

Unhealthy

Table 5.—Ozone bioindicator data, Illinois, 2005

Parameter 2001 2002 2003 2004 2005

Biosites (no.) 43 27 27 28 28

Biosites with injury (%) 33 19 56 61 61

Plants evaluated (no.) 2,919 2,703 1,951 2,205 2,436

Plants with injury (no.) 64 22 66 73 44
68

FOREST HEALTH

Ground-level ozone exposure is reported using the SUM06 index. This index, recorded 

for a 24-hour period over a 3-month growing season, represents the sum of all average, 

hourly ozone concentrations greater than 0.06 parts per million (ppm) (Coulston et 

al. 2004). Leaf damage can occur after exposure to ozone levels above 8 ppm-hours. 

Seedling growth (in natural forest stands) can be affected at levels between 10 and 15 

ppm-hours (Heck and Cowling 1997). Yearly SUM06 values were averaged for the 

survey period. Most of Illinois was exposed to ozone levels between 10 and 20 ppm-hours 

(Fig. 48). The highest ozone concentrations were recorded over southwestern Illinois, 

from the greater St. Louis metro to portions of the Shawnee National Forest. 

92%

6%

1% 1%

0 to < 5 - No Risk

5 to < 15 - Low Risk

15 to < 25 - Moderate Risk

 ≥ 25 - High Risk

Biosite Index

Figure 47.—Number of biosites 

by biosite index value, Illinois, 

2005.
69

FOREST HEALTH

What this means

Figure 48.—Mean observed 

ground-level ozone exposure 

reported as SUM06, Illinois, 

2005.

The majority of Illinois’ forests are exposed to moderate concentrations of ground-level 

ozone. With relatively few recorded plant injuries and light damage severity, the risk 

from ozone is considered low throughout most of the State. Forests in southwestern 

Illinois have the highest exposure to elevated concentrations of ozone and are at higher 

risk of ozone damage. The potential for reduced growth and decreased forest health 

increases with continued exposure to high ozone levels. Ozone-induced stress will have 

the greatest impact on ozone-sensitive species (e.g., black cherry and yellow-poplar), 

particularly those down wind of major urban areas. Adverse effects on more dominant 

species such as oaks and maples will be less severe as a result of increased tolerance to 

ozone.

O n t a r i o

0 200

Miles

Projection: Albers Equal Area Conic, NAD83.

Sources: U.S. Environmental Protection Agency,

2001-2005; J. Coulston, U.S. Forest Service,

Knoxville, TN. Geographic base data are provided

by the National Atlas of the USA and Environmental

Systems Research Institute (ESRI), 2005.

Cartography: S.J. Crocker. February, 2008.

Mean SUM06 (2001-2005)

(ppm - hours)

0 - 8

8.1 - 10

10.1 - 15

15.1 - 20

20.1 - 25

25 +
70

FOREST HEALTH

Forest Fragmentation

Background

What we found

Forest fragmentation has been called “the most serious threat to biological diversity” 

(Wilcox and Murphy 1985). Forman (1995) defines fragmentation as “the breaking up 

of large habitat or land areas into smaller parcels.” This results in a loss of interior forest 

and an increase in edge habitat, which has many negative effects on the remaining 

vegetation and wildlife. Some of the harmful consequences of fragmentation are a loss 

of biodiversity, increased populations of invasive and nonnative species, and changes in 

biotic and abiotic conditions (Haynes 2003). 

Fragmentation occurs naturally from disturbances such as wildfire, wind, and flooding, or 

as the result of human activities such as conversion to agriculture or urban development/

sprawl (Haynes 2003). Human disturbance has a more severe impact on the remaining 

forest because it occurs more frequently and results in more permanent land-use changes 

than natural disturbance events (Haynes 2003). Conversion to agriculture is primarily 

responsible for the small size and fragmented condition of the remaining forest in Illinois 

(Heske et al. 1999). For example, in the east-central part of the State, most forest 

remnants are small woodlots on farms; the largest areas of forest are found along rivers 

(Heske et al. 1999).

National Land Cover Dataset (NLCD) imagery from 2001 (Vogelmann et al. 2001) was 

used to create a fragmentation map of Illinois using techniques developed by Riitters et 

al. (2002). Riitters et al. used NLCD imagery to produce maps of forest versus nonforest 

cover, forest density, and forest connectivity, and then analyzed the corresponding pixel 

values from each map to create a fragmentation map. During the analysis, an output 

pixel was assigned to one of five classes:

• Interior forest – continuous forest canopy

• Edge – junction between forest and nonforest areas

• Patch – small forest area surrounded by mostly or all nonforest area

• Nonforest – nonforest land cover

• Water/barren land – open water or naturally barren land

Forested pixels from the forest versus nonforest cover map were placed in one of three 

forest classes (interior, edge, or patch); nonforested pixels were assigned to a “nonforest” 

class. In addition, pixels classified as “open water” or “bare rock/sand/clay” in the original 

NLCD imagery were placed in a “water/barren land” class in the fragmentation map and 

were not considered a cause of fragmentation. 
71

FOREST HEALTH

What this means

Using this method, 81 percent of pixels were classified as nonforest, 17 percent fell 

in a forested class, and the remaining 2 percent were identified as “water/barren land” 

(Fig. 49). Further breakdown of all pixels shows that 7 percent were classified as interior 

forest, 7 percent as edge, and 3 percent as patch. 

Results show that interior and edge classes have the same proportion of forest. This 

implies that forest land in Illinois is heavily fragmented. Again, this is primarily due 

to agriculture; however, nonforest wetland and urban development are also causes of 

fragmentation according to land-cover data. The majority of interior forest land is 

concentrated in the southern tip of the State, or in riparian areas along rivers (Fig. 50). 

The remaining landscape contains a high proportion of edge habitat and many small, 

isolated patches of forest land. This type of fragmented landscape lacks the continuous 

forest habitat required by many species of plants and wildlife, and can result in loss of 

biodiversity and even extinction (Forman 1995). While edge habitat may benefit certain 

species, it also has many negative effects, such as increased predation of bird nests and 

prey species (Heske et al. 1999), and declines in native plant and wildlife populations 

(Collinge 1996).

Figure 49.—Distribution of 

landscape patterns derived 

from National Land Cover 

Dataset classification, Illinois, 

2001.

81%

2% 7% 3%

7%

Interior

Patch

Edge

Nonforest

Water

Land Cover Class
72

FOREST HEALTH

Figure 50.—Map of landscape 

patterns derived from 

National Land Cover Dataset 

classification, Illinois, 2001.

0 50

Miles

Processing note: This map was produced by applying

techniques adapted from Riitters et al. (2002) to the

2001 National Land Cover Dataset image of the state of Illinois.

Projection: UTM Zone 16 N, NAD83.

Source: National Land Cover Dataset, 2001 data.

Geographic base data are provided by the National Atlas of the USA.

Cartography: D. Meneguzzo. July, 2007.

Fragmentation Category

Water/barren land

Interior forest

Nonforest

Patch

Edge
73

FOREST HEALTH

Forest Invaders: Nonnative Invasive Plants

Background

What we found

Nonnative invasive plants are becoming increasingly abundant in native forest 

ecosystems. Their abundance in introduced environments can be attributed to high 

adaptability, the availability of disturbed habitats, and a lack of natural enemies, 

which allows them to outcompete and displace native species (Pimentel et al. 2000). 

Nonnative invasive plants are a major concern because they alter natural plant 

communities and processes, threaten biodiversity, and contribute to a decrease in 

sustainability, productivity, and wildlife habitat. 

Data on nonnative invasive understory plants was collected on 731 Phase 2 plots 

sampled between 2004 and 2006, and 46 vegetative diversity (Phase 3) plots sampled 

between 2001 and 2004. Nonnative invasive understory plants were identified on 296 

Phase 2 plots and 27 Phase 3 plots. Information on invasive tree species was collected 

on all 1,004 forested Phase 2 plots sampled between 2001 and 2005. Sixteen different 

nonnative invasive species were found in Illinois (Table 7). Some plots had as many as 

seven different species; however, 72 percent of plots had one or two species per plot 

(Fig. 51).

 Species Scientific name Number of occurrences

 Multiflora rose Rosa multiflora 498

 Nonnative bush honeysuckles Lonicera spp. 276

 Japanese honeysuckle Lonicera japonica 196

 Garlic mustard Alliaria petiolata 135

 Common buckthorn Rhamnus cathartica 58

 Common/Lesser burdock Arctium minus 40

 Autumn olive Elaeagnus umbellata 39

 Japanese barberry Berberis thunbergii 33

 Reed canary grass Phalaris arundiacea 32

 Japanese stiltgrass Microstegium vimineum 8

 Ailanthus Ailanthus altissima 3

 Amur honeysuckle Lonicera maackii 3

 Dame’s rocket Hesperis matronalis 3

 Phragmites Phragmites australis 3

 Oriental bittersweet Celastrus orbiculatus 1

 Glossy buckthorn Frangula alnus 1

 Total 1,329

Table 7.—Occurrence of invasive plants on forest land, Illinois, 2001-2006
74

FOREST HEALTH

Multiflora rose (Rosa multiflora), nonnative bush honeysuckles (Lonicera spp.), Japanese 

honeysuckle (Lonicera japonica), and garlic mustard (Alliaria petiolata) were the most 

commonly observed invasive plants (Table 7). Multiflora rose (Fig. 52) and nonnative 

bush honeysuckles (Fig. 53) are widely distributed across the entire State. By contrast, 

the distribution of garlic mustard and Japanese honeysuckle is narrow (Fig. 54). 

Garlic mustard was generally limited to the northern half of Illinois, while Japanese 

honeysuckle dominated the lower half of the State.

On each Phase 2 plot where a nonnative invasive plant species was identified, the 

percentage of invasive plant cover on the forested portion of the subplot was recorded. 

The majority of invasive species encountered represented less than 10 percent of the 

plant cover (Fig. 55). 

Figure 51.—Distribution of 

nonnative invasive understory 

plants observed on Phase 2 

and Phase 3 plots (n=323), 

Illinois, 2001-2006.

0

20

40

60

80

100

120

140

1 2 3 4 5 6 7

Number of Species Per Plot

Number of Inventory Plots

Phase 3 vegetation sampling. Photo by 

Cassandra Olson, U.S. Forest Service
75

FOREST HEALTH

Figure 52.—Distribution of 

plots containing multiflora rose 

(Rosa multiflora), Illinois, 2001-

2006.

Depicted plot locations are approximate.

Photos: James H. Miller, U.S. Forest Service, Bugwood.org.

Projection: UTM Zone 16N, NAD 83.

Source: U.S. Forest Service, Forest Inventory and Analysis

Program, 2001 - 2006 data. Geographic base data are provided

by the National Atlas of the USA and the Illinois Department of

Natural Resources. FIA data and mapping tools are

available online at http://www.fia.fs.fed.us/tools-data/.

Cartography: S.J. Crocker. July, 2007.

0 50

Miles

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Chicago Metro Area

Moline

Alton

Peoria

Rockford

Decatur

Springfield

Waukegan

East Saint Louis

Champaign-Urbana

Carbondale

!(

Legend

Major cities

Shawnee National Forest

Multiflora rose
76

FOREST HEALTH

Figure 53.—Distribution of 

plots containing nonnative bush 

honeysuckles (Lonicera spp.), 

Illinois, 2001-2006.

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Chicago Metro Area

Moline

Alton

Peoria

Rockford

Decatur

Springfield

Waukegan

East Saint Louis

Champaign-Urbana

Carbondale

Depicted plot locations are approximate.

Photos: R. Old (top), P. Breen (mid.), L. Mehrhoff (bott.), Bugwood.org.

Projection: UTM Zone 16N, NAD 83.

Source: U.S. Forest Service, Forest Inventory and Analysis

Program, 2001 - 2006 data. Geographic base data are provided

by the National Atlas of the USA and the Illinois Department of

Natural Resources. FIA data and mapping tools are

available online at http://www.fia.fs.fed.us/tools-data/.

Cartography: S.J. Crocker. July, 2007.

0 50

Miles

Legend

Major cities

Shawnee National Forest

!( Non-native bush honeysuckles
77

FOREST HEALTH

Figure 54.—Distribution 

of plots containing garlic 

mustard (Alliaria petiolata) 

and Japanese honeysuckle 

(Lonicera japonica), Illinois, 

2001-2006.

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")

Chicago Metro Area

Moline

Alton

Peoria

Rockford

Decatur

Springfield

Waukegan

East Saint Louis

Champaign-Urbana

Carbondale

Depicted plot locations are approximate.

Photos: D. Cappaert (top), T. Bodner (bottom), Bugwood.org.

Projection: UTM Zone 16N, NAD 83.

Source: U.S. Forest Service, Forest Inventory and Analysis

Program, 2001 - 2006 data. Geographic base data are provided

by the National Atlas of the USA and the Illinois Department of

Natural Resources. FIA data and mapping tools are

available online at http://www.fia.fs.fed.us/tools-data/.

Cartography: S.J. Crocker. July, 2007. 0 50

Miles

Japanese honeysuckle

Major cities

Shawnee National Forest

Legend

Garlic mustard and

Japanese honeysuckle ")

!( Garlic mustard

!(
78

FOREST HEALTH

Figure 55.—Occurrence of 

the top four nonnative invasive 

plants (as a percentage of total 

occurrence by species) by 

percentage of total plant cover 

on a subplot, Illinois, 2001-

2006.

Preliminary data shows that nonnative invasive plants are widely distributed across 

Illinois. The extent to which these species cause harm has not yet been determined. 

However, as the spread of nonnative species continues, the number and abundance of 

native plant species will decline, resulting in a loss of overall species diversity and a 

reduction in the value and health of Illinois’ forests.

What this means

0

5

10

15

20

25

30

35

< 1 1 - 5 6 - 10 11 - 25 26 - 50 51 - 75 75 - 100

Percent of Total Plant Cover

Percent Occurrence

Multiflora rose

Nonnative bush honeysuckles

Garlic mustard

Japanese honeysuckle

All other encountered species

Common buckthorn. Photo by Chris Evans, River to River 

CWMA, bugwood.org
79

FOREST HEALTH

Insects and Diseases

Background

What we found

Insect and disease activity helps shape the structure and composition of forests. 

Monitoring the status of these organisms is an important part of assessing the current 

state of and changing trends in Illinois’ forests, and also provides a valuable means of 

maintaining healthy, vigorous forests and managing future forest resources.

Native Insects 

A number of native insects were active during 

the survey period. Eastern tent caterpillar 

(Malacosoma americanum) caused heavy 

defoliation of black cherry trees in many 

counties throughout Illinois in 2001 and 2002 

(Fig. 56). After a wet spring and an increase in 

parasitic insect density, caterpillar populations 

crashed in 2003. Eastern tent caterpillar began 

to build again in 2005, causing heavy defoliation 

in Illinois’ southern tier. In contrast, a viral 

infection caused populations of the forest tent 

caterpillar (Malacosoma disstria) to remain at low levels from 2003 to 2005, following a 

2002 outbreak that resulted in heavy defoliation in southeastern Illinois. Moderate to 

heavy infestations of the bagworm moth (Thyridopteryx ephemeraeformis) damaged white 

pine, spruce, and juniper trees across the central and southern thirds of Illinois between 

2002 and 2004. Populations of the fall webworm (Hyphantria cunea) declined in 2005, 

following 3 years of heavy infestation in west-central and south-central Illinois. 

Nonnative Insects 

Populations of Japanese beetle (Popillia japonica) increased dramatically in 2002. By 

2005, infestations of this beetle were heavy throughout most counties in the northern 

two-thirds of the State. Since the first moth catch in 1973, gypsy moth (Lymantria dispar) 

populations have varied from year to year. Though gypsy moth has become established 

in northeastern counties of Illinois, there was little discernable defoliation between 2001 

and 2005 (Fig. 57). Over the course of the survey period, eradication efforts targeted 

at the Asian longhorned beetle (Anoplophora glabripennis) yielded a continual decrease 

in the number of new infestations; no new infestations were identified in 2005. Asian 

longhorned beetle was declared eradicated from Illinois in 2008. 

Eastern tent caterpillar. Photo by 

Susan Crocker, U.S. Forest Service
80

FOREST HEALTH

Figure 56.—Counties with 

eastern tent caterpillar 

infestations, Illinois, 2001-2002.

Projection: UTM Zone 16N, NAD83.

Sources: U.S. Forest Service, Northeastern Area,

State and Private Forestry and the Illinois Department

of Natural Resources. Geographic base data are

provided by the National Atlas of the USA.

Cartography: S.J. Crocker. February, 2008.

0 50

Miles

Eastern Tent Caterpillar

Infestation Severity

2001-2002

Light

Moderate to heavy
81

FOREST HEALTH

Figure 57.—Distribution of 

gypsy moth based on positive 

trap catch, Illinois, 2001-2005.

Projection: UTM Zone 16N, NAD83.

Sources: Illinois Department of Agriculture;

APHIS PPQ; U.S. Forest Service, Northeastern

Area State and Private Forestry. Geographic base

data are provided by the National Atlas of the USA.

Cartography: S.J. Crocker. February, 2008.

0 50

Miles

Gypsy Moth

Infestation Status

2001 - 2005

Found but not established

Established / Quarantined
82

FOREST HEALTH

What this means

Diseases

Oak wilt, caused by the fungus Ceratocystis fagacearum, continues to be an important 

source of oak mortality. All species of oak are susceptible to oak wilt, but the disease 

occurs more frequently and progresses more rapidly in red oak species. The incidence of 

DED continues to increase each year. Forty-five counties in Illinois reported moderate 

to heavy elm mortality in 2005. Trees are often killed before they reach sawtimber-size; 

consequently, aging stands present a future health risk (Haugen 1998). Leaf tatters, a 

sporadic problem in Illinois for approximately 15 years, continued to plague white oak 

and hackberry fairly consistently throughout the survey period. This condition, which 

halts the development of leaf tissue between major veins, is believed to be caused by 

herbicidal drift. In 2005, a cool, wet spring contributed to moderate to severe sycamore 

anthracnose (Apiognomonia veneta) in 23 northern counties. Ash decline, in moderate to 

high severity, was reported in eight counties in 2005.

Emerging Threats

In addition to existing pest problems, Illinois’ forests are at risk for exotic introductions 

of EAB and sudden oak death. Sudden oak death is caused by the fungal-like pathogen 

Phytophthora ramorum. Susceptible species include a variety of oaks, Douglas-fir, and 

Rhododendron spp. (O’Brien et al. 2002). Established populations of P. ramorum are 

known to occur only on the West Coast; however, transportation of infected nursery 

stock has introduced the pathogen to nurseries in a number of eastern and southern 

states. All Illinois samples collected during the survey period tested negative for 

P. ramorum.

Abiotic Factors

Extreme drought stretched across west-central and northwestern Illinois in 2005; 

during this period, southern Illinois experienced moderate to severe drought conditions. 

By the fall of 2005, drought conditions in the northern portion of the State were severe 

to extreme.

During the survey period, Illinois’ forests were affected by native and nonnative insects, 

disease, and drought. These stressors create weakened trees that are vulnerable to 

secondary attack by other insects and diseases or are the direct cause of tree mortality. In 

combination, there may be significant impacts to tree growth and increased risk of forest 

fire. While efforts to eradicate Asian longhorned beetle have proven successful, Illinois’ 

forests face serious risk from other exotic introductions, primarily EAB which could have 

dramatic implications for the future composition of Illinois’ forests. 
83

FOREST HEALTH

Emerald Ash Borer

Background

What we found

Emerald ash borer (EAB) (Agrilus planipennis) has been the source of widespread decline 

and mortality of ash trees in the north-central region of the U.S. since its discovery in 

Michigan in 2002. An exotic wood-boring beetle, EAB is a pest of all major species of 

ash, including green, white, black, and blue ash, and all ash cultivars (Cappaert et al. 

2005). Although surveys conducted in 2005 did not reveal evidence of the beetle, EAB 

was detected in northeastern Illinois in 2006. EAB is believed to have been present in 

Illinois for 3 to 5 years prior to its discovery there. 

Illinois forest land contains an estimated 130.1 million ash trees (greater than 1 inch in 

diameter). Total live ash volume on forest land is 424.3 million cubic feet. Ash is widely 

distributed across the State (Fig 58). Dense pockets of ash are located in northeastern 

corner and in the southern tier. Ash is present on nearly 2 million acres, or 44 percent of 

Illinois forest land (Fig. 59). It is rarely the most abundant species in a stand; in general, 

ash makes up less than 25 percent of total live-tree basal area. Nearly 30 percent of ash 

trees are in floodplains (Fig. 60).

Twenty-five percent of Illinois forest land is dominated by ash forest types. The 

understory of these stands is composed largely of American elm, boxelder, hackberry, and 

green ash saplings, and silver maple, green ash and American elm poletimber (Fig. 61). 

The majority of understory volume in ash dominated stands is in silver maple (Fig. 62).

Emerald ash borer. Photo by David Cappaert, 

Michigan State University, bugwood.org
84

FOREST HEALTH

Figure 58.—Ash density on 

forest land, Illinois, 2005.

Processing note: This map was produced by

linking plot data to MODIS satellite pixels (250 m)

using gradient nearest neighbor techniques. The

resulting image was resampled to 500 m pixels.

Projection: UTM Zone 16N, NAD83.

Source: U.S. Forest Service, Forest Inventory and

Analysis program, 2005 data. Geographic base

data are provided by the National Atlas of the USA.

FIA data and mapping tools are available online at

http://www.fia.fs.fed.us/tools-data/.

Cartography: S.J. Crocker & B.T. Wilson. July, 2007.

0 50

Miles

< 5

5 - 14

15 - 29

30 - 49

< 50

Density of ash

(trees per acre)
85

FOREST HEALTH

Figure 59.—Presence of ash 

on forest land, as a percentage 

of stand basal area (BA), 

Illinois, 2005.

Figure 60.—Number of live ash 

on forest land by species and 

physiographic condition class, 

Illinois, 2005.

0

500

1,000

1,500

2,000

2,500

3,000

No ash 0.1-25.0 25.1-50.0 50.1-75.0 75.1-100.0

Ash BA per Acre/Total Live BA per Acre (percent)

Forest Land Area

(thousand acres)

Physiographic Condition Class

Xeric Mesic Floodplains Hydric

Number of Ash Trees (millions)

Pumpkin ash

Green ash

Black ash

White ash

0

15

30

45

60
86

FOREST HEALTH

Figure 61.—Top eight 

understory species in stands 

with an ash forest type by 

number of trees and diameter 

class, Illinois, 2005.

Figure 62.—Live volume of 

understory species (trees 5.0 

to 10.9 inches d.b.h.) in stands 

with an ash forest type, Illinois, 

2005.

0

5

10

15

20

25

30

35

40

American

elm

Boxelder Hackberry Green ash Silver

maple

Black

willow

Black

cherry

Saplings - 1.0 to 4.9 d.b.h. Poletimber - 5.0 to 10.9 d.b.h.

Species

Number of Trees (millions)

0

10

20

30

40

50

60

70

80

Silver

maple

Green ash Hackberry American

elm

Boxelder Black

willow

Red maple Black

cherry

Species

Live Volume (million ft3

)
87

FOREST HEALTH

What this means Ash is an important component of Illinois’ forest resource. An abundant species in 

woodland and riparian forests, ash is also widely planted in urban and suburban areas. 

The entirety of Illinois’ ash resource is at risk for widespread mortality related to EAB. 

Substantial mortality of ash would have a significant impact on statewide forest resources 

and related industries such as timber, wood products, recreation, and nurseries. Species 

composition and forest structure would likely undergo change as ash stands give way 

to maple stands. Sanitation and removal of ash in non-ash forest types may result in 

similar conversions. Additionally, the loss of ash in riparian zones would have a major 

effect on species diversity, erosion, water quality, and food and habitat availability 

for macroinvertebrates. Overall, EAB may have an impact similar to that of DED or 

chestnut blight.

Forest Products

Above and inset: Log pile in a mixed oak stand; photo by Eli Sagor, University of Minnesota, bugwood.org 
90

FOREST PRODUCTS

Growing-stock Volume

Background

What we found

Growing-stock volume is the amount of sound wood in live, commercial tree species; 

trees must be at least 5 inches in d.b.h. or greater and free of defect. This measure has 

traditionally been used to ascertain wood volume available for commercial use. Estimates 

of the volume of growing stock are important considerations in economic planning and 

when evaluating forest sustainability.

Growing-stock volume has risen steadily since 1948 with the sharpest increase occurring 

between 1998 and 2005. The current estimate of growing-stock volume on timberland is 

6.8 billion cubic feet (Fig. 63). More than one-fourth of this volume is in trees that are 

21 inches in d.b.h. or larger. Average growing-stock volume per acre has also increased; 

the current average of 1,576 cubic feet per acre is nearly three times the average in 

1948 (Fig. 64). White oak, which accounts for more than 12 percent of growing-stock 

volume, is the most voluminous species on Illinois timberland (Fig. 65). Silver maple, 

black oak, and red oak also have significant volume in growing stock. Most species have 

experienced a net gain in volume since 1985. Black oak, which significantly decreased 

between the 1998 and 2005 inventories, is an exception. Volume increases were most 

significant in the middle diameter classes and in trees 29 inches or greater (Fig. 66).

Figure 63.—Growing-stock 

volume on timberland by 

inventory year, Illinois, 1948-

2005 (error bars represent a 

66-percent confidence interval).

0

1

2

3

4

5

6

7

8

1940 1950 1960 1970 1980 1990 2000 2010

Inventory Year

Growing-stock Volume

.. (billion ft3

)
91

FOREST PRODUCTS

Figure 64.—Growing-stock 

volume per acre of timberland 

by inventory year, Illinois, 1948-

2005.

Figure 65.—Growing-stock 

volume on timberland for the 

top 12 species by inventory 

year, Illinois, 1985-2005 (error 

bars represent a 66-percent 

confidence interval).

0

200

400

600

800

1,000

1,200

1,400

1,600

1,800

1948 1962 1985 1998 2005

Growing-stock Volume (ft3/acre)

Inventory Year

0 200 400 600 800 1,000

White oak

Silver maple

Black oak

Red oak

Eastern cottonwood

Shagbark hickory

Sycamore

Sugar maple

Green ash

Black walnut

American elm

Pignut hickory 1985

1998

2005

Species

Growing-stock Volume (million ft3)
92

FOREST PRODUCTS

Rising growing-stock volume can be attributed to the growth of current hardwood 

stands, increasing timberland area, relatively low mortality rates (particularly between 

1962 and 1985), and decreasing removal rates. The majority of timberland is dominated 

by mature oaks. Therefore, significant volume in oak growing stock is not a surprise. 

While Illinois’ growing-stock volume appears healthy and stable, the future of Illinois 

timberland is likely to include an increase in mortality as mature stands senesce.

What this means

0

100

200

300

400

500

600

700

800

900

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

21.0-22.9

23.0-24.9

25.0-26.9

27.0-28.9

29.0+

2005

1998

1985

Diameter Class (inches)

Growing-stock Volume

(million ft3

)

Figure 66.—Growing-stock 

volume on timberland by 

diameter class and inventory 

year, Illinois, 1985-2005 (error 

bars represent a 66-percent 

confidence interval).
93

FOREST PRODUCTS

Sawtimber Volume and Quality

Background

What we found

Sawtimber trees are live trees of commercial species that contain either one 12-foot or 

two noncontiguous 8-foot logs that are free of defect. Hardwoods must be at least 11 

inches d.b.h. and softwoods must be 9 inches d.b.h. to qualify as sawtimber. Sawtimber 

volume is defined as the net volume of the saw log portion of live sawtimber, measured 

in board feet, from a 1-foot stump to minimum top diameter (9 inches for hardwoods 

and 7 inches for softwoods). Estimates of sawtimber volume are used to determine the 

monetary value of wood volume and to identify the quantity of merchantable wood 

availability.

Sawtimber volume has more than tripled since 1962 and is currently estimated at 25.3 

billion board feet (Fig. 67). Half of the volume of sawtimber is in seven hardwood 

species: white oak, black oak, silver maple, northern red oak, eastern cottonwood, 

shagbark hickory, and American sycamore (Fig. 68). Collectively, almost 30 percent of 

sawtimber volume is made up of mature oaks. Species like American elm and green ash 

account for a relatively small percentage of sawtimber volume. 

Most species groups increased in sawtimber volume between 1998 and 2005 (Fig. 69). 

Oaks showed the least growth in sawtimber. Volume in the select white oaks and the 

select red oaks increased by less than 10 percent and declined in the other white oaks 

and the other red oaks groups, which contain post oak and black oak, respectively. 

0

5

10

15

20

25

30

1940 1950 1960 1970 1980 1990 2000 2010

Inventory Year

Sawtimber Volume

(billion board feet)

Figure 67.—Sawtimber volume 

on timberland by inventory 

year, Illinois, 1948-2005 (error 

bars represent a 66-percent 

confidence interval).
94

FOREST PRODUCTS

Figure 68.—Sawtimber volume 

on timberland by species, 

Illinois, 2005.

Figure 69.—Changes 

in sawtimber volume on 

timberland for major species 

groups, Illinois, 1998 to 2005.

0 2 4 6 8 10 12 14 16

White oak

Silver maple

Black oak

Northern red oak

Eastern cottonwood

Sycamore

Shagbark hickory

Sugar maple

Green ash

American elm

Species

Sawtimber Volume (percent)

-10 10 30 50 70 90

Select red oaks

Select white oaks

Other red oaks

Other white oaks

Ash

Cottonwood and aspen

Hickory

Hard maple

Soft maple

Other eastern soft hardwoods

Black walnut

Other eastern hard hardwoods

Change in Sawtimber Volume

from 1998 to 2005 (percent)

Species Group
95

FOREST PRODUCTS

The quality of Illinois’ sawtimber has remained constant over the past 20 years 

(Fig. 70). Sawtimber quality is determined using a grading system that incorporates 

factors including diameter, log length, and the cull portion of the saw log. Tree grade is 

based on a scale of 1 to 3, with grade 1 representing the highest quality and grade 3 the 

lowest. Generally, around 20 percent of Illinois sawtimber is in grade 1.

The majority of Illinois’ forests are maturing. Mature stands are more likely to succumb 

to windthrow, insects, and disease pathogens. The relatively small area of poletimber 

and sapling/seedling stands may be related to how timber is harvested in much of the 

State. Often, mature timber is removed as single, scattered trees or in small groups. The 

lack of significant disturbance may not open hardwood stands to progressive seedling 

development because smaller trees in the understory are generally outcompeted by 

larger, canopy-dominant trees. Exceptions include species such as sugar maple, which are 

tolerant of understory conditions and can take advantage of small gaps in the canopy. 

The current trend in changing sawtimber volume indicates that oaks have lower growth 

rates than species like maple, walnut, and sycamore. Relatively large increases in these 

non-oak species reflect the likely species mixture for the next generation of overstory 

trees. 

Figure 70.—Sawtimber volume 

on timberland by tree grade, 

Illinois, 2005.

What this means

0

10

20

30

40

50

60

70

80

90

100

1985 1998 2005

Grade 1 Grade 2 Grade 3

Inventory Year

Sawtimber Volume

(percent)
96

FOREST PRODUCTS

Timber Products Output

Background

What we found

The harvesting and processing of timber products produces a stream of income shared 

by timber owners, managers, marketers, loggers, truckers, and processors. Illinois’ forestrelated manufacturing industries employ over 32,000 people, with gross annual payroll 

earnings of more than $1.1 billion (U.S. Census Bur. 2005). Wood products, according 

to the Illinois Department of Commerce and Economic Opportunity, form the State’s 

24th largest export sector, grossing more than $37 million in 2004 (Little 2007). Not 

included in this figure are logs or sawn materials that were grown in Illinois and were 

shipped from other states to foreign markets. To better manage the State’s forests, it is 

important to know the species, amounts, and locations of timber being harvested.

Surveys of Illinois’ wood-processing mills are conducted periodically to estimate the 

amount of wood volume that is converted into products. The last survey was conducted 

in 2003 and, for this report, is supplemented by the most recent surveys conducted in 

surrounding states that processed wood harvested from Illinois. Thirty-four million cubic 

feet of industrial roundwood was harvested from Illinois. The majority of this volume, 

almost 23 million cubic feet, was processed in-state by 89 saw mills and 1 handle mill. 

One million cubic feet of the industrial roundwood processed in Illinois came from other 

States. Almost one-third, or 11 million cubic feet, of the industrial roundwood harvested 

from Illinois was exported to other states for processing.

Saw logs accounted for 91 percent of the total industrial roundwood harvested, 

followed by pulpwood at 4 percent and mine timbers at 2 percent (Fig. 71). Other 

industrial roundwood products harvested included veneer, handles, and cooperage. 

The red oak and white oak groups combined made up 55 percent of the total industrial 

roundwood harvest (Fig. 72). Other important species groups harvested were soft maple, 

cottonwood, hickory, and ash. Softwoods made up less than 1 percent of the total 

volume harvested; most of this was shipped to out-of-state pulp mills.

In the process of harvesting industrial roundwood, 26 million cubic feet of harvest 

residues were left on the ground. Without a prominent pulpwood market in the State, 

much of the upper tree bole goes unused as it is too small for saw logs or veneer logs. The 

processing of industrial roundwood in the State’s primary wood-using mills generated 

another 15 million cubic feet of wood and bark residues. Only 6 percent of the mill 

residues were not used for fiber products, fuelwood, mulch, small dimension lumber, or 

other uses (Fig. 73).
97

FOREST PRODUCTS

Figure 71.—Industrial 

roundwood production by 

product, Illinois, 2005.

Figure 72.—Industrial 

roundwood production by 

species group, Illinois, 2005.

2% 91%

1%

1%

4%

1%

Saw logs

Veneer logs

Pulpwood

Cooperage

Handles

Mine timbers

Industrial Roundwood 

Production

0

2

4

6

8

10

12

Red oak

group

White oak

group

Soft Cotton- Hickory Ash Hard Black

walnut

Other

hardwoods

Softwoods

maple

Species Group

Industrial Roundwood Production

(million ft3

)

wood maple
98

FOREST PRODUCTS

Nearly all of the wood-processing facilities in Illinois are sawmills processing state-grown 

saw logs. These mills offer woodland owners an outlet to sell timber and provide jobs 

in some of the State’s rural areas. The demand for wood products is likely to increase, 

placing a greater demand on the resource. An important consideration for the future of 

Illinois’ primary wood-products industry is its ability to retain and process the industrial 

roundwood harvested, leading to value-added production in the State. Currently, almost 

one-third of the industrial roundwood harvested in Illinois is sent to other states for 

processing, providing less benefit to the Illinois economy. Another important issue is 

the volume of residues that are generated in the State that go unused. Better utilization 

of the resource and the use of logging slash and mill residues for industrial fuelwood at 

cogeneration facilities are possible solutions for this problem.

What this means

Type of Residue

46%

19%

7%

22%

6%

Fiber products

Industrial fuel

Domestic fuel

Other uses

Not used

Figure 73.—Disposition of mill 

residues generated by primary 

wood-using mills, Illinois, 2005.
99

Data Sources and Techniques

Above: Illinois fall colors; photo by Susan Crocker, U.S. Forest Service. 

Inset: Northern cardinal; photo by Johnny N. Dell, bugwood.org 
102

DATA SOURCES AND TECHNIQUES

Forest Inventory

Information on the condition and status of forests in Illinois was obtained from the 

Northern Research Station’s Forest Inventory and Analysis (NRS-FIA) Program. 

Previous inventories of Illinois’ forest resources were completed in 1948, 1962, 1985, 

and 1998.

Since the 1998 inventory, several changes in FIA methods have improved the quality 

of the inventory. The most significant change between inventories has been the shift 

from periodic to annual inventory. Historically, FIA inventoried each state on a cycle 

that averaged about 12 years. However, the need for timely and consistent data across 

large geographical regions along with national legislative mandates resulted in FIA 

implementing an annual inventory program. Annual inventory was initiated in Illinois 

in 2001.

With the NRS-FIA annual inventory system, approximately one-fifth of all field plots are 

measured each year. The entire inventory is completed within 5 years. After this initial 

5-year period, NRS-FIA will report and analyze results using a moving 5-year average. 

For example, NRS-FIA will be able to generate inventory results for 2002 through 2006 

or for 2003 through 2007. 

Other significant changes between inventories include implementing new remotesensing technology, a new field-plot configuration and sample design, and gathering 

additional remotely sensed and field data. The use of new remote-sensing technology 

allows NRS-FIA to use classifications of Multi-Resolution Land Characterization 

(MRLC) data and other remote-sensing products to stratify the total area of Illinois and 

to improve estimates. 

New algorithms were used for the 2005 inventory to assign forest type and stand-size 

class to each condition observed on a plot. These algorithms are being used nationwide 

by FIA to provide consistency from state to state. As a result, changes in forest type 

and stand-size class will reflect actual changes in the forest and not changes due to 

differences between algorithms. The list of recognized forest types, groupings of these 

forest types for reporting purposes, models used to assign stocking values to individual 

trees, definition of nonstocked (stands with a stocking value of less than 10 percent for 

live trees), and names given to the forest types changed with the new algorithms. As 

a result, comparisons between the published 2005 results and those published for the 

1998 inventory may be invalid. Contact NRS-FIA for additional information on the 

algorithms used in both inventories.
103

DATA SOURCES AND TECHNIQUES

Phase 1

Phase 2

Sampling Phases

The 2005 Illinois inventory was conducted in three phases. In the first phase, satellite 

imagery was used to stratify the State and aerial photography was used to select 

plots for measurement. The second phase entailed measuring the traditional suite of 

mensurational variables and the third phase focused on a suite of variables related to 

forest health.

Land that could not be sampled included private tracts where field personnel were 

unable to obtain permission to measure a plot and plots that were inaccessible because 

of a hazard or danger to field personnel. The methods used in preparing this report were 

adjusted to account for such sites.

For the Illinois inventory, FIA used a classification of satellite imagery for stratification. 

The imagery was used to form two initial strata: forest and nonforest. Pixels within 60 m 

(2 pixel widths) of a forest/nonforest boundary formed two additional strata: forest edge 

and nonforest edge. Forest pixels within 60 m of the boundary on the forest side were 

classified as forest edge and pixels within 60 m of the boundary on the nonforest side 

were classified as nonforest edge. All strata were divided into public or private ownership 

based on information available in the Protected Lands Database (DellaSala et al. 2001). 

The estimated population total for a variable is the sum across all strata of the product 

of each stratum’s area (from the pixel count) and the variable’s mean per unit area (from 

plot measurements) for the stratum.

Phase 2 of the inventory consisted of the measurement of the annual sample of Illinois 

field plots. Current FIA precision standards for annual inventories require a sampling 

intensity of one plot for approximately every 6,000 acres. FIA has divided the entire area 

of the United States into nonoverlapping hexagons, each of which contains 5,937 acres 

(McRoberts 1999). An array of field plots was established by selecting one plot from 

each hexagon based on the following rules: 1) if a FHM plot (Mangold 1998) fell within 

a hexagon, it was selected; 2) if no FHM plot fell within a hexagon, the existing NRSFIA plot nearest the hexagon center was selected; and 3) if neither FHM nor existing 

NRS-FIA plots fell within the hexagon, a new NRS-FIA plot was established in the 

hexagon (McRoberts 1999). This array of plots is designated the Federal base sample and 

is considered an equal probability sample; its measurement in Illinois is funded by the 

Federal Government.
104

DATA SOURCES AND TECHNIQUES

The total Federal base sample of plots was systematically divided into five 

interpenetrating, nonoverlapping subsamples or panels. Each year, the plots in a single 

panel are measured; panels are selected on a 5-year, rotating basis (McRoberts 1999). 

For estimation purposes, the measurement of each panel of plots can be considered an 

independent systematic sample of all land in a State. Field crews measure vegetation on 

plots forested at the time of the last inventory and on plots currently classified as forest 

by trained photointerpreters using aerial photographs or digital orthoquads.

NRS-FIA has two categories of field-plot measurements: Phase 2 field plots (standard 

FIA plots) and Phase 3 plots (forest health plots) to optimize our ability to collect 

data when available for measurement. Both types of plots are uniformly distributed 

geographically and temporally. Phase 3 plots are measured with the full suite of FHM 

vegetative and health variables (Mangold 1998) as well as the full suite of measures 

associated with Phase 2 plots. Phase 3 plots must be measured between June 1 and 

August 30 to accommodate the additional measurement of nonwoody, understory 

vegetation; ground cover; soils; and other variables. On Phase 2 plots, only variables that 

can be measured throughout the year are collected. Results of the 2005 annual inventory 

are based on field measurement of 1,004 forested Phase 2 plots and 84 forested Phase 3 

plots. 

The national FIA four-subplot cluster configuration (Fig. 74) was first used for data 

collection in Illinois in 2001 and will be used in subsequent years. The national plot 

Phase 3

Figure 74.—Current NRS-FIA 

field-plot design.

MAGNETIC

1

4 3

2

Plot

center

NMAGNETIC

N
105

DATA SOURCES AND TECHNIQUES

configuration requires mapping all forest conditions on each plot. Due to the small 

sample size each year, precision associated with estimates of components of change such 

as mortality will be relatively high. Consequently, we report estimates of components of 

change only after multiple annual panels have been measured. With completion of the 

annual inventory in 2005, the full range of change estimates is now available. 

The overall plot layout for the new configuration consists of four subplots. The centers 

of subplots 2, 3, and 4 are located 120 feet from the center of subplot 1. The azimuths to 

subplots 2, 3, and 4 are 0, 120, and 240 degrees, respectively, from the center of subplot 1. 

The center of the new plot is located at the same point as the center of the previous plot 

if a previous plot existed at the same location. Trees with a d.b.h. of 5 inches or larger 

are measured on a 24-foot-radius (1/24 acre) circular subplot. All trees 1 to 4.9 inches 

in diameter are measured on a 6.8-foot-radius (1/300 acre) circular microplot located 

12 feet east of the center of each of the four subplots. Seedlings (trees less than 1 inch 

d.b.h. and at least 6 inches tall [softwood species] or 12 inches tall [hardwood species]) 

are counted but not individually measured on this same microplot. Forest conditions on 

the four subplots are recorded. Factors that differentiate forest conditions are changes in 

forest type, stand-size class, land use, ownership, and density. Each condition that occurs 

anywhere on any subplot is identified, described, and mapped if the area of the condition 

meets or exceeds 1 acre in size. 

Field plot measurements are combined with Phase 1 estimates in the data compilation 

and table production process. However, other tabular data can be generated at the Forest 

Inventory and Analysis Data Center webpage at http://www.fia.fs.fed.us/tools-data/. 

For additional information, contact: Program Manager, Forest Inventory and Analysis, 

Northern Research Station, 1992 Folwell Avenue, St. Paul, MN 55108 or State Forester, 

Illinois Department of Natural Resources, Office of Resource Conservation, Division of 

Forest Resources, 1 Natural Resource Way, Springfield, IL 62702-1271.
106

DATA SOURCES AND TECHNIQUES

Information about family forest owners is collected annually through the U.S. Forest 

Service’s National Woodland Owner Survey (NWOS). The NWOS was designed to 

increase our understanding of owner demographics and motivation (Butler et al 2005). 

Individuals and private groups identified as woodland owners by FIA are invited to 

participate in the NWOS. Each year, questionnaires are mailed to 20 percent of private 

owners, with more detailed questionnaires sent out in years that end in 2 or 7 to coincide 

with national census, inventory, and assessment programs. Data presented here are 

based on survey responses from 201 randomly selected families and individuals who own 

forest land in Illinois. For additional information about the NWOS, visit: www.fia.fs.fed.

us/nwos.

National Woodland Owner Survey

Insects and Disease

Timber Products Output Inventory

This study was a cooperative effort of the Illinois Department of Natural Resources, 

Southern Illinois University (SIU), and NRS-FIA. Using a questionnaire designed 

to determine the size and composition of Illinois’ forest products industry, its use of 

roundwood (round sections cut from trees), and its generation and disposition of wood 

residues, SIU personnel contacted via mail and telephone all primary wood-using 

mills in the State. Completed questionnaires were sent to NRS-FIA for editing and 

processing. As part of data editing and processing, all industrial roundwood volumes 

reported on the questionnaires were converted to standard units of measure using 

regional conversion factors. 

Information about the insects and diseases affecting Illinois’ forests was gathered from 

the U.S. Forest Service, Northeastern Area State and Private Forestry (www.na.fs.fed.

us), the national Forest Health Monitoring (FHM) program (fhm.fs.fed.us/), and the 

Illinois Department of Agriculture (www.agr.state.il.us/index.html).
107

DATA SOURCES AND TECHNIQUES

National Land Cover Data Imagery

Mapping Procedures

Maps in this report were constructed using (1) categorical coloring of Illinois counties 

according to forest attributes (such as forest land area); (2) a variation of the k-nearestneighbor (KNN) technique to apply information from forest inventory plots to remotely 

sensed MODIS imagery (250 m pixel size) based on the spectral characterization of 

pixels and additional geospatial information; or (3) colored dots to represent plot 

attributes at approximate plot locations.

Derived from Landsat Thematic Mapper satellite data (30-m pixel), the National Land 

Cover Dataset (NLCD) is a land cover classification scheme (21 classes) applied across 

the United States by the U.S. Geological Survey (USGS) and the U.S. Environmental 

Protection Agency (EPA). The NLCD was developed from data acquired by the MRLC 

Consortium, a partnership of Federal agencies that produce or use land-cover data. 

Partners include the USGS, EPA, U.S. Forest Service, and National Oceanic and 

Atmospheric Administration.
108

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112

Appendix

(Continued on next page)

Area of Forest Land (in acres) by County and Forest-Type Group, Illinois, 2005.

Forest-type Group

White/ Loblolly/ Exotic Oak/ Elm/ash/ Maple/ Exotic

red/jack shortleaf Pinyon/ soft- Oak/ Oak/ gum/ cotton- beech/ Aspen/ hard- NonCounty Total pine pine juniper woods pine hickory cypress wood birch birch woods stocked

Adams 87,032 0 0 7,127 0 0 73,538 0 6,367 0 0 0 0

Alexander 55,049 0 0 0 0 0 35,470 2,382 17,197 0 0 0 0

Bond 44,558 0 0 0 0 0 26,100 0 18,458 0 0 0 0

Boone 3,177 0 0 0 0 0 0 0 3,177 0 0 0 0

Brown 64,925 0 0 0 0 5,893 50,027 0 7,436 0 0 0 1,569

Bureau 32,534 0 0 0 0 0 21,776 0 7,194 3,563 0 0 0

Calhoun 69,930 0 0 0 0 0 38,699 0 25,215 6,017 0 0 0

Carroll 52,887 6,659 0 0 0 0 23,284 0 14,617 6,836 0 0 1,490

Cass 45,518 7,127 0 0 0 0 18,673 4,419 13,825 0 0 0 1,473

Champaign 5,893 0 0 0 0 0 4,419 0 1,473 0 0 0 0

Christian 19,334 0 0 0 0 0 1,065 0 16,468 1,801 0 0 0

Clark 69,466 0 0 0 0 0 51,524 0 17,942 0 0 0 0

Clay 38,184 0 0 0 0 0 30,620 0 6,017 1,548 0 0 0

Clinton 20,526 0 0 0 0 0 6,017 6,017 8,493 0 0 0 0

Coles 39,729 0 0 0 0 0 36,166 0 3,563 0 0 0 0

Cook 57,144 0 0 0 0 0 41,105 0 8,934 3,966 0 0 3,139

Crawford 56,083 0 0 0 0 0 27,444 0 15,247 13,393 0 0 0

Cumberland 7,550 0 0 0 0 0 6,046 0 0 0 0 0 1,504

DeKalb 2,982 0 0 0 0 0 2,982 0 0 0 0 0 0

De Witt 11,300 0 0 0 0 0 8,163 0 3,137 0 0 0 0

Douglas 13,019 0 0 0 0 0 7,933 0 5,086 0 0 0 0

DuPage 11,121 0 0 0 0 0 8,059 0 3,062 0 0 0 0

Edgar 4,451 0 0 0 0 0 1,490 0 0 1,480 0 0 1,480

Edwards 19,800 0 0 0 0 0 5,154 0 10,152 4,494 0 0 0

Effingham 51,217 0 0 0 0 6,017 36,380 0 1,533 7,286 0 0 0

Fayette 101,640 0 0 0 0 0 59,142 0 39,668 2,830 0 0 0

Franklin 49,909 0 0 0 0 0 33,192 0 10,020 6,696 0 0 0

Fulton 127,189 0 0 0 0 0 114,839 0 9,369 2,981 0 0 0

Gallatin 43,255 0 1,832 0 0 0 10,197 0 31,226 0 0 0 0

Greene 34,416 0 0 0 0 0 20,779 0 8,480 5,157 0 0 0

Grundy 8,372 0 0 0 0 0 1,490 0 6,881 0 0 0 0

Hamilton 65,009 0 0 0 0 0 41,548 0 16,960 6,501 0 0 0

Hancock 53,909 0 0 0 0 0 42,049 0 7,366 4,494 0 0 0

Hardin 60,794 0 6,111 0 0 0 46,204 0 903 7,576 0 0 0

Henderson 45,079 0 0 0 0 1,155 32,427 0 11,497 0 0 0 0

Henry 31,283 0 0 0 0 0 21,908 0 8,426 949 0 0 0

Iroquois 20,517 0 0 0 0 0 7,127 0 13,390 0 0 0 0

Jackson 107,853 0 2,037 0 0 4,673 73,883 2,997 24,263 0 0 0 0

Jasper 26,124 0 0 0 0 0 24,590 0 1,533 0 0 0 0

Jefferson 71,511 0 0 0 0 0 42,805 938 27,768 0 0 0 0

Jersey 57,822 0 0 0 0 0 47,491 0 1,248 9,083 0 0 0

Jo Daviess 75,047 0 0 9,527 0 6,278 39,201 0 6,354 12,197 0 0 1,490

Johnson 101,379 0 0 7,329 0 0 69,364 0 15,684 7,329 0 0 1,674

Kane 16,858 0 0 0 1,782 0 10,489 0 4,588 0 0 0 0

Kankakee 18,724 0 0 0 0 0 13,379 0 5,345 0 0 0 0

Kendall 4,526 0 0 0 0 0 4,472 0 54 0 0 0 0

Knox 54,696 0 0 0 0 0 41,865 0 5,591 7,239 0 0 0

Lake 33,162 6,278 0 0 0 0 14,995 0 10,399 1,490 0 0 0

La Salle 49,432 0 0 0 0 0 21,876 0 8,644 18,912 0 0 0

Lawrence 30,925 0 0 0 0 0 14,438 0 16,487 0 0 0 0

Lee 10,461 0 0 0 0 0 5,116 0 5,345 0 0 0 0

Area of Forest Land (in acres) by County and Forest-Type Group, Illinois, 2005.
113

Livingston 12,407 0 0 0 0 0 12,407 0 0 0 0 0 0

Logan 13,963 0 0 0 0 0 12,472 0 0 0 0 0 1,490

McDonough 35,602 0 0 0 0 0 35,602 0 0 0 0 0 0

McHenry 54,992 0 0 0 5,345 0 32,855 0 16,792 0 0 0 0

McLean 17,990 0 0 0 0 0 7,383 0 7,334 3,272 0 0 0

Macon 23,984 0 0 0 0 0 7,326 0 16,657 0 0 0 0

Macoupin 94,126 0 0 0 0 0 83,076 0 11,050 0 0 0 0

Madison 67,808 0 0 0 0 0 46,965 0 20,844 0 0 0 0

Marion 92,216 0 0 0 0 0 70,523 0 15,755 5,939 0 0 0

Marshall 27,065 0 0 0 0 0 11,724 0 1,087 14,254 0 0 0

Mason 22,433 7,933 0 0 0 0 5,893 0 7,127 0 0 1,480 0

Massac 36,995 0 0 0 0 2,997 24,995 7,329 1,674 0 0 0 0

Menard 20,480 0 0 0 0 0 13,276 0 333 6,872 0 0 0

Mercer 36,746 0 0 0 5,345 0 20,925 0 7,127 3,349 0 0 0

Monroe 42,869 0 0 0 0 0 22,564 0 20,305 0 0 0 0

Montgomery 50,510 0 0 0 0 336 43,602 0 0 6,573 0 0 0

Morgan 49,087 0 0 0 0 0 37,231 0 11,856 0 0 0 0

Moultrie 5,345 0 0 0 0 0 5,345 0 0 0 0 0 0

Ogle 44,117 4,472 0 0 0 0 30,141 0 0 9,504 0 0 0

Peoria 68,881 0 0 0 0 0 60,605 0 2,384 5,893 0 0 0

Perry 49,929 0 7,107 0 0 0 31,924 0 7,329 3,570 0 0 0

Piatt 5,893 0 0 0 0 0 0 0 5,893 0 0 0 0

Pike 130,368 0 0 0 0 0 106,392 0 23,977 0 0 0 0

Pope 172,051 3,746 11,981 2,811 0 5,994 121,085 6,696 10,794 8,944 0 0 0

Pulaski 50,044 0 0 0 0 0 25,692 0 20,900 3,452 0 0 0

Putnam 16,125 0 0 0 0 0 5,910 0 10,215 0 0 0 0

Randolph 102,370 0 0 0 0 6,696 62,187 0 29,081 4,405 0 0 0

Richland 29,623 0 0 0 0 0 23,489 0 6,134 0 0 0 0

Rock Island 46,538 0 0 0 0 0 21,044 0 10,282 13,828 1,383 0 0

St. Clair 62,945 0 0 0 0 0 23,574 0 39,372 0 0 0 0

Saline 54,814 0 190 0 0 0 45,890 0 8,734 0 0 0 0

Sangamon 43,285 0 0 0 0 0 13,232 0 24,160 5,893 0 0 0

Schuyler 104,848 0 0 0 0 0 63,375 0 16,854 24,619 0 0 0

Scott 8,874 0 0 0 0 0 8,874 0 0 0 0 0 0

Shelby 49,337 0 0 0 0 0 43,065 0 4,768 1,504 0 0 0

Stark 5,606 0 0 0 0 0 0 0 5,606 0 0 0 0

Stephenson 27,273 0 0 0 0 0 27,273 0 0 0 0 0 0

Tazewell 25,063 0 0 0 0 0 10,570 0 5,893 8,600 0 0 0

Union 106,747 0 0 1,626 0 0 81,165 0 6,121 17,835 0 0 0

Vermilion 40,252 0 0 0 0 0 30,518 0 5,315 4,419 0 0 0

Wabash 349 0 0 0 0 0 349 0 0 0 0 0 0

Warren 27,719 0 0 0 0 0 19,056 0 2,770 1,029 0 0 4,864

Washington 42,605 0 0 0 0 0 29,626 0 12,979 0 0 0 0

Wayne 75,152 0 0 0 0 0 36,579 6,191 20,232 12,150 0 0 0

White 52,603 0 0 0 0 994 25,792 0 19,937 5,881 0 0 0

Whiteside 21,737 3,263 0 0 0 0 4,472 0 6,619 5,893 0 0 1,490

Will 36,412 0 0 0 0 0 17,918 0 18,494 0 0 0 0

Williamson 80,832 0 313 3,035 0 3,348 38,641 5,536 29,959 0 0 0 0

Winnebago 19,537 0 0 0 0 0 7,127 0 5,345 7,065 0 0 0

Woodford 35,385 0 0 0 0 0 5,893 0 8,909 20,583 0 0 0

Total 4,525,231 39,478 29,570 31,454 12,472 44,379 2,932,619 42,504 1,019,078 349,147 1,383 1,480 21,666

Forest-type Group

White/ Loblolly/ Exotic Oak/ Elm/ash/ Maple/ Exotic

red/jack shortleaf Pinyon/ soft- Oak/ Oak/ gum/ cotton- beech/ Aspen/ hard- NonCounty Total pine pine juniper woods pine hickory cypress wood birch birch woods stocked

Area of Forest Land (in acres) by County and Forest-Type Group, Illinois, 2005. (Continued from previous page)
114

Susan J. Crocker is a 

Forester with the Forest 

Inventory and Analysis 

Program, Northern 

Research Station, 

St. Paul, Minnesota.

Gary J. Brand is a 

Research Forester with 

the Forest Inventory 

and Analysis Program, 

Northern Research 

Station, St. Paul, 

Minnesota.

Brett J. Butler is a 

Research Social 

Scientist with the 

Forest Inventory and 

Analysis Program, 

Northern Research 

Station, Amherst, 

Massachusetts.

David E. Haugen is a 

Forester with the Forest 

Inventory and Analysis 

Program, Northern 

Research Station, 

St. Paul, Minnesota.

Dick C. Little is Council 

Liaison through the 

University of Illinois—

Urbana-Champaign 

with the Illinois Forestry 

Development Council, 

Springfield, Illinois.

Dacia M. Meneguzzo 

is a Forester with the 

Forest Inventory and 

Analysis Program, 

Northern Research 

Station, St. Paul, 

Minnesota.

Charles H. Perry 

is a Research Soil 

Scientist with the Forest 

Inventory and Analysis 

Program, Northern 

Research Station, 

St. Paul, Minnesota.

Ronald J. Piva is a 

Forester with the Forest 

Inventory and Analysis 

Program, Northern 

Research Station, 

St. Paul, Minnesota.

Barry T. Wilson is a 

Research Forester with 

the Forest Inventory 

and Analysis Program, 

Northern Research 

Station, St. Paul, 

Minnesota.

Christopher W. 

Woodall is a Research 

Forester with the Forest 

Inventory and Analysis 

Program, Northern 

Research Station, 

St. Paul, Minnesota.

About the Authors
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Printed on recycled paper

Crocker, Susan J.; Brand, Gary J.; Butler, Brett J.; Haugen, David E.; Little, Dick 

C.; Meneguzzo, Dacia M.; Perry, Charles H.; Piva, Ronald J.; Wilson, Barry T.; 

Woodall, Christopher W. 2009. Illinois’ Forests 2005. Resour. Bull. NRS-29. 

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

Research Station. 114 p.

The first full, annualized inventory of Illinois’ forests reports more than 4.5 

million acres of forest land with an average of 459 trees per acre. Forest land 

is dominated by oak/hickory forest types, which occupy 65 percent of total 

forest land area. Seventy-two percent of forest land consists of sawtimber, 

20 percent contains poletimber, and 8 percent contains sapling/seedlings. 

The volume of growing stock on timberland has been rising since 1948 

and currently totals 6.8 billion cubic feet. The average annual net growth of 

growing stock from 1998 to 2005 is 327 million cubic feet per year. Additional 

information on forest attributes, changing land use patterns, timber products, 

and forest health is included in this report.

KEY WORDS: inventory, forest statistics, forest land, volume, biomass, riparian, 

growth, removals, mortality, forest health, Illinois
Capitalizing on the strengths of existing science capacity in 

the Northeast and Midwest to attain a more integrated, 

cohesive, landscape-scale research program