Iowa’s Forests

1999-2003 Part A

Resource Bulletin

NC-266A

2006

North Central 

Research Station

United States 

Department of Agriculture

Forest

Service
Iowa’s landscape is dominated by agriculture, but beyond the fields of corn 

and soybeans lie 2.7 million acres of hardwood forests owned largely by 

138,000 private landowners. Iowa’s forests provide critical wildlife habitat, 

conserve our valuable soils, and protect our streams, rivers, and lakes. Iowa’s 

forests employ over 20,000 Iowans in the wood products industry, providing 

over $1 billion in annual economic activity. Our forests provide boundless 

opportunities for outdoor recreation, from hunting and fishing to camping and 

hiking. What Iowan can resist the brilliance of Iowa’s trees in fall color, the 

fragrance of spring wildflowers in bloom, the shade of a strong maple tree in 

the summer, or the warmth of wood stove burning native oak during an Iowa 

winter day?

To understand how Iowa’s forests are doing, a partnership was established 

between the Forest Inventory and Analysis program of the USDA Forest 

Service and the Forestry Bureau of the Iowa Department of Natural 

Resources. Using a systematic and scientific effort, the 1999-2003 report 

on Iowa’s forests was completed. This report indicates that Iowa is gaining 

forestland, and that our diverse forests of oaks, hickories, maples, and many 

other species are healthy and growing.

But this report also shows that Iowa is losing its valuable oak trees to old age 

and lack of adequate regeneration as shade tolerant species such as sugar 

maple, basswood, and ironwood replace our sun-loving oaks. Iowa’s forests 

also face threats from exotic insects on our borders, such as the emerald ash 

borer and gypsy moth, as well as stiff competition from exotic and invasive 

plants, such as garlic mustard and bush honeysuckle, that now outcompete 

the natural regeneration of our native trees and shrubs. 

The results of this report will be used by the Iowa DNR Forestry Bureau in 

partnership with many governmental and volunteer organizations to expand 

sustainable forest management on private and public lands across our state. 

Current and new private forestland owners hold the key to the future of forests 

in Iowa. Please use this report to learn about Iowa’s forests, to encourage the 

establishment of new forests, and to improve our current forests to sustain the 

many benefits our forests provide.

John Walkowiak, Forestry Bureau Chief
­­­­

Iowa’s Forests

1999-2003 Part A

USDA Forest Service

Forest Inventory and Analysis Program

Northern Research Station, St. Paul, MN

Earl C. Leatherberry, W. Keith Moser, Charles Perry, Christopher Woodall, 

Edward Jepsen, Steve Pennington, and Aron Flickinger
Acknowledgments

The authors thank the individuals who contributed both to the inventory 

and analysis of Iowa’s forest resources. Staff located in St. Paul, Minnesota, 

involved in the 1999-2003 inventory included Dennis May, Program 

Manager, and Bill Burkman, Supervisor Forester. Administration office 

staff Barb Fuller, Tracie Hamilton, and Katrina Edwards. Staff with key 

responsibilities in selecting and establishing inventory plot locations included 

Ronald McRoberts, Mark Nelson, Dale Gormanson, Mark Hatfield, Geoffrey 

Holden, Dan Kaisershot, Dacia Meneguzzo, and Barb Johnson. Staff with key 

responsibilities in collecting the field data included Peter Koehler, Thomas 

Goff, Dave Haugen, Mark Jeranek, Joseph Kernan, Mark Majewsky, Ben 

Nurre, Ron Piva, M. Reichenberg, Gary Stachowicz, Will Smith, and Brian 

Wall. Staff with key responsibilities in editing field data included Barb Knight 

and James Blehm. Staff with key responsibilities for data management, 

processing, and estimation included Gray Brand, Mark Hansen, Pat Miles, 

Kevin Nimerfro, and Jim Solomakos. Ron Hackett and Gerhard Raile provided 

supply logistical services and data recorder support to field staff. Joseph 

Boykin reported on the first (1999) Iowa annual inventory cycle. Cassandra 

Olson contributed substantial time and her field knowledge to nonnative 

species analysis. Ron Piva conducted the timber products output study of 

2000. Brett Butler generated tabular data on family forest owners from the 

National Woodland Owner Survey. Steve Pennington provided information 

about forest health conditions in Iowa. The following provided information 

about Iowa’s forests and contributed constructive comments in manuscript 

review: Cassandra Olson, David Haugen, John Walkowiak, Paul Tauke, Aron 

Flickinger, and Wayne Fuhlbrugge.

Note: A companion (Part B) of this document, available online, contains sample design and estimation procedures, quality of 

estimates analysis, and core tables of forest attributes.
Foreword

In mid-continental North America, the 36 million acres of land that lie 

between the Mississippi River on the east and the Missouri and Big Sioux 

Rivers on the west are considered some of the most productive land in the 

world. Before Euro-American settlement, what is now Iowa was mostly prairie, 

with forests covering about 18 percent of the area. Settlement and agriculture 

transformed the landscape. Today, most land in Iowa is cultivated and forests 

are mostly woodlots or riparian corridors covering only 7 percent of the State. 

Although forest area has declined over the years, woods and wooded river 

bottoms are scattered throughout Iowa, providing an array of services and 

benefits to Iowans and visitors alike. They reduce air pollution, enhance water 

quality, promote plant diversity, provide wildlife habitat, produce timber, are 

used for recreation and relaxation, and increasingly are places where people 

build their homes. The services and benefits derived from Iowa’s forests are 

important to the State’s economy and contribute to the quality of life of the 

State’s residents. 

The demands placed on forest resources will continue to increase, as will 

biological threats from nonnative plants and insects. The challenge is to 

maintain Iowa’s forests in such a way that they are available for use and 

enjoyment today and for future generations. Reporting on trends in the 

condition and status of forest resources is critical in determining whether 

they are being used or maintained in a sustainable way. The USDA Forest 

Service’s Forest Inventory and Analysis program in partnership with the Iowa 

Department of Natural Resources’ Bureau of Forestry inventoried Iowa’s forest 

resources in 1954, 1970, and 1990. Beginning in 1999, annual inventories 

were conducted such that a portion of field plots was inventoried each year; 

a full inventory was completed after 5 years. The first full Iowa inventory was 

completed in 2003 and covers the period 1999 to 2003. Iowa’s forests have 

much to tell us, as was stated eloquently by an author whose name history 

failed to record (van Buren 1938). 
­­­­

The oaks and the pines, and their brethren of the woods, have seen so many 

suns rise and set, so many seasons come and go, and so many generations 

pass into silence, that we may well wonder what “the story of the trees” 

would be to us if they had tongues to tell it, or we ears fine enough to 

understand. 

We do not presume that we can tell the full story of Iowa’s forests. We 

recognize that the State’s history is replete with stories of individual trees or 

groves; for example, the “plow in the oak” in Audubon County or the “lost 

grove” in Webster County. However, it is our hope the information provided 

here will stimulate discussion about the State’s forest resources. 
­­­­

Highlights ....................................................................................................... 7

Forest Features .............................................................................................. 13

Iowa’s Forests and People........................................................................ 14

Woodlots and Bottomland Forests—Where are They?.......................... 17

Forest Tree Diversity ............................................................................... 20

Large Trees are Predominant in Iowa’s Woods....................................... 22

Forest Stand Age..................................................................................... 24

How Dense are the Woods?.................................................................... 26

Biomass: The Whole Tree....................................................................... 29

Forest Growth ......................................................................................... 31

Forest Tree Removals.............................................................................. 33

Forest Tree Mortality .............................................................................. 35

Oaks—A Special Situation .................................................................... 37

Whose Woods are These? Family Forest Owners................................... 39

Whose Woods are These? Public Forests................................................ 43

Forest Health ................................................................................................ 45

Insects and Diseases................................................................................ 46

The Emerald Ash Borer: An Ominous Threat....................................... 48

Forest Invaders: Nonnative Plant Species.............................................. 49

Undesirable Forest Disturbances ............................................................ 51

Down Woody Debris—Is There a Fire Danger?..................................... 53

Ozone Damage ........................................................................................ 57

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

Contents
­­­­

Forest Products.............................................................................................. 67

Growing-Stock Volume .......................................................................... 68

Sawtimber Volume.................................................................................. 71

Timber Products Output......................................................................... 74

Wildlife Habitat...................................................................................... 77

Forest-Based Recreation and Tourism .................................................... 79

Data Sources and Techniques....................................................................... 81

Forest Inventory...................................................................................... 82

National Woodland Owner Survey........................................................ 82

Forest Health Monitoring Program ........................................................ 82

Iowa Woodland Invasive Species Inventory .......................................... 83

Timber Products Output and Use Assessment ....................................... 83

National Survey of Fishing, Hunting, and Wildlife-Associated 

 Recreation, Iowa, 2001..................................................................... 83

References..................................................................................................... 84
­­­­

Highlights

 Since the 1970s, forest area has increased by more than a million acres to 

2.6 million, nearly matching what was present in 1954. 

 Although most forest area is located in the eastern half of Iowa, some 

counties adjacent to the Missouri River in western Iowa and the southern 

tier of counties increased in forest area by as much as 10 percent between 

1990 and 2003. 

 Most of Iowa’s forest stands are fully or moderately stocked, suggesting that 

in the near term, stands are capable of supplying timber for the State’s wood 

products industry. 

 Many oak-dominated stands are at the successional stage where harvest is 

economically advantageous.

 Annual net growth of growing stock has more than doubled since the 1980s.

 The threat of wildfire is low due to the relatively small amount of down 

woody debris in forest stands.

On the Plus Side
­­­­

 Some counties near larger urban areas declined in forest area between 1990 

and 2003. 

 The increasing number of shade-tolerant species could reduce tree species 

diversity in Iowa’s forest stands as shade-intolerant species no longer are 

able to compete in a more shady environment. 

 Forest stands dominated by oak trees contain a greater proportion of area in 

the older age classes.

 The lack of significant disturbances in hardwood stands has not adequately 

opened stands to necessary seedling development.

 Most oaks are at the age at which they are prolific seed producers, benefiting 

mast-eating wildlife. However, as fewer young oak move up in age class, 

mast-dependent wildlife species could decline.

 Absent forest management, nonstocked and poorly stocked woodlots likely 

will fail to reach their physical or economic potential. 

Problem Areas
 The increasing use of bio-based material from agriculture crops to produce 

liquid transportation fuels and biodegradable products could adversely affect 

the amount of forest area.

 Shade-tolerant hardwoods, primarily maples in the midstory level of stands, 

are replacing oaks due to an absence of stand disturbances.

 Forest succession and harvesting are slowing the overall growth of northern 

red oak and white oak, both of which are ecological and economically 

important species.

 The long-term availability of red and white oak is threatened due to oak 

regeneration failures. Absent silvicultural intervention, red oak and white 

oak will have a reduced role in the timber products industry.

 Average annual tree mortality has increased steadily since 1954. This trend 

likely will continue due to the threat posed by nonnative insects. 

 The number of people owning forests in Iowa increased substantively during 

the past decade. This has resulted in the parcelization of forest ownership, 

woodlands removed from timber production, and the threat of reduced 

wildlife habitat. 

Issues to Watch
10
The Features, Health, and Products 

of Iowa’s Forests

13

FEATURES HEALTH PRODUCTS

Forest Features
14

FEATURES HEALTH PRODUCTS

Iowa’s Forests and People

Background:

What This Means:

What We Found:

Iowa is largely a prairie State with forests found in woodlots and along stream and 

river bottoms. Because forests are relatively scarce, assessing change in their status and 

condition is important. 

Throughout Iowa’s history, the area of forests has fluctuated (fig. 1.1), reaching its nadir in 

the 1970s when there were only 1.6 million acres—4 percent of the State’s total land area. 

Between 1974 and 2003, forest area increased by 1.1 million acres to 2.6 million, nearly 

matching the area present in 1954 (fig. 1.1). During the same time, farmland declined by 

2.5 million acres (fig. 1.2). Meanwhile, Iowa’s human population increased modestly from 

2.6 million in 1950 to 2.9 million in 2002. During the 1950s, there was the equivalent of 

one acre of forest for each person living in Iowa. In the 1970s, when many farmers were 

plowing from fencerow to fencerow, the per capita area of forest declined to about a half 

acre, but has since rebounded to nearly an acre (fig. 1.3). 

During the second half of the 20th century, forest area increased largely due to changes 

in the agricultural sector. Technological advancements in farming improved yields, 

allowing marginal lands such as that prone to erosion or flooding to be taken out of 

production. A decline in dairy production and an increase in feedlot use reduced the 

pasturing of cattle. Hardwood trees naturally recolonized many old pastures and fields, 

resulting in an increase in forest area. With population growth slowing, the per-capita 

share of forest area increased. Comparison of forest area and population suggests relative 

access to the services and benefits forests provide. The future trajectory of forest area in 

Iowa is difficult to discern, though several scenarios 

are possible. Demand for liquid transportation fuels 

such as ethanol and biodiesel from agriculture crops 

could increase tillage and reduce forest area. The use 

of corn in making biodegradable plastic containers 

could expand, again increasing tillage and using 

land to grow genetically improved, short-rotation 

crops for biomass could reduce forest area. When the 

Conservation Reserve Program ends, lands currently 

with trees may return to agriculture or pasture. 

However, in the coming decades, the demand for 

high-end wood products could increase, leading to 

an increase in oak management, a resurgence in 

Photo courtesy of USDA Natural Resources Conservation Service hardwood plantings, and woodlot management. 
15

FEATURES HEALTH PRODUCTS

Figure 1.1. Total forest area in Iowa, 

1850-2003.

	 1850	 1954	 1974	 1990	 2003

7

6

5

4

3

2

1

0

Year

Millions of acres

40

30

25

20

15

10

5

0

Millions of acres

1974	 1990	 2003

Inventory year

35

Figure 1.2. Changes in farmland 

and forest land in Iowa between 

1974-2002 and 2003 (data on forest 

land were collected in 2003; farmland 

data were collected in 2002).

Farmland	 Forestland
16

FEATURES HEALTH PRODUCTS

Figure 1.3. Per capita forest area in 

Iowa, 1954-2003.

	 1954	 1974	 1990	 2003

1.2

1.0

0.8

0.6

0.4

0.2

0

Inventory year

Per capita acres
17

FEATURES HEALTH PRODUCTS

Woodlots and Bottomland Forests—Where are They?

Background:

What This Means:

What We Found:

In the past, Iowa’s forests existed where environmental conditions—temperature, wind, 

soil, water, and fire—converged to form optimal conditions for tree growth. In the 20th 

century, the actions of farmers largely dictated the location of the State’s forests. 

To describe the relative location of Iowa’s forests, we divided the State into four inventory 

units: Northeastern, Southeastern, Northwestern, and Southwestern. Most of Iowa’s forest 

area is in the Southeastern and Northeastern units (fig 1.4), with forest area accounting 

for approximately 11 percent of the land area in each unit. In the Southwestern unit, 

6 percent of the land is forested versus only 2 percent in the Northwestern unit. The 

eastern units combined have 2.2 million acres of forest, or 83 percent of total forest area in 

the State. Much of Iowa’s forests are concentrated in several counties in the eastern units 

(fig. 1.5), though forest area increased throughout the State between 1990 and 2003 

(fig 1.6). Most notable were increases in forest area along the Missouri River and across 

the southern tier of counties. Several counties in the sphere of the urban areas of 

Waterloo/Cedar Falls (Fayette and Buchanan), Des Moines (Warren, Marion, and Polk), 

and Cedar Rapids and Iowa City (Linn, Jones, and Johnson) experienced a net loss of 

forest area between 1990 and 2003. 

In western Iowa, where precipitation is lower and the weather can be harsh and extreme, 

woodlots are rare and most forests are found along protected sections of stream or river 

bottoms. In eastern Iowa, greater precipitation and less extreme weather are more 

conducive to tree growth. Rivers are larger with more extensive riparian forests, and 

farmers tend to own woodlots as part of their holdings. In the Northeastern unit, forests 

are common on slopes that preclude agricultural activities. Much of the increase in 

forest area in the Southeastern unit resulted from old pastures becoming forest area. In 

former pastures, established trees along with new growth often qualified as forest. In 

some bottomland areas, forests 

became established through 

plantings or natural regeneration. 

In eastern Iowa, some woodlots 

are being converted to housing 

developments. Improved roads 

and interstate highway corridors 

likely will lead to the creation 

of additional home sites from 

woodlands.

Photo courtesy of USDA Natural Resources Conservation Service
18

FEATURES HEALTH PRODUCTS

Figure 1.4. Forest area by forest 

resource unit, Iowa, 2003. 

1,400

1,200

1,000

800

600

400

200

0

918.2

1303.6

99.7

343.7

Northeastern

Unit

Southeastern Northwestern Southwestern

Millions of acres

Northwestern Unit

Northeastern Unit

Southwestern Unit

Southeastern Unit
19

FEATURES HEALTH PRODUCTS

Figure 1.5. Percentage of forest area 

by county, Iowa, 2003.

Figure 1.6. Change in forest area 

as a percentage of total land area in 

Iowa, 1990-2003.

Northwestern Unit
­­­­20

FEATURES HEALTH PRODUCTS

Forest Tree Diversity

Background:

What This Means:

What We Found:

Trees of a particular species tend to grow together because they have similar growth 

characteristics and site requirements. A single species can dominate a stand or a stand 

may comprise a mix of species. Identifying forest species provides information about forest 

succession, wildlife habitat, wood potentially available for products, and the need for 

silvicultural applications (stand improvements). 

Iowa’s forest stands contain just over a billion trees growing among 68 species of forest 

trees. Hardwood or deciduous trees occupy 97 percent of Iowa’s forest area. Oak/hickory 

forests are the most extensive (fig. 1.7) and include mostly white oaks, northern red oaks, 

bur oaks, and a mix of upland hardwoods trees. Softwood or conifer dominant stands cover 

only 1 percent of the forest area in Iowa. However, softwoods, primarily eastern redcedar, 

are mixed with hardwoods in the eastern redcedar/hardwood forest type. Between 1990 

and 2003, the number of forest trees increased by 21 percent. American elm is the most 

abundant tree in Iowa, accounting for 14 percent of total live forest trees (fig. 1.8). 

Maples, including boxelder, are the second most abundant forest tree species in the State. 

Between 1990 and 2003, maples increased by nearly 50 percent, accounting for 11 percent 

of total trees. Eastern hophornbeam, a small, short-lived tree that grows beneath other 

trees, also increased in number and now accounts for 10 percent of total forest trees. 

White and northern red oaks declined by 11 and 18 percent, respectively, while shingle 

and bur oak increased. As a group, oaks remained about the same, accounting for 10 

percent of total trees. 

The oak/hickory forest dominates, but the elm/ash/cottonwood forest type group and the 

maple/beech/birch forest type group have a significant presence. The maple/beech/birch 

group, consisting primarily of shade-tolerant trees, is increasing. Oaks are shade intolerant 

and in some stands, sugar maple and other shade-tolerant species form a dense layer in 

the understory, leaving fewer openings for oak regeneration. This is especially true of red 

and white oak, both of which declined between 1990 and 2003. However, shingle oak, 

found mostly in southeastern Iowa, and bur oak, found throughout the State, increased. 

American elm accounts for 14 percent of forest trees, though the effects of Dutch elm 

disease limit its ability to dominate. The increasing number of shade-tolerant species 

could reduce tree species diversity in Iowa’s forest stands as shade-intolerant species no 

longer can compete in a more shady environment.
­­­­21

FEATURES HEALTH PRODUCTS

Maple/beech/birch

16%

Other hardwoods

2%

Softwoods

1%

Nonstocked

2%

Elm/ash/

cottonwood

26%

Oak/hickory

53%

Figure 1.7. Area of timberland in Iowa 

by forest type group, Iowa, 2003.

Shingle oak

Honeylocust

White ash

Northern red oak

Green ash

Bur oak

White oak

Hackberry

Maples

Hickories

East hophornbeam

American elm

0 20 40 60 80 100 120 140 160

Millions of trees

Species

Figure 1.8. Number of all live trees 

by selected species and groups of 

species, Iowa, 1990-2003.

	 1990	 2003
­­­­22

FEATURES HEALTH PRODUCTS

Large Trees are Predominant in Iowa’s Woods

Background:

What This Means:

What We Found:

Forests generally contain trees of various sizes. Stand size is a measure of the average 

diameter of the dominant trees in a stand, measured at 4.5 feet above ground, commonly 

called diameter at breast height (d.b.h.). There are three stand-size classes: sawtimber—

large trees, softwoods at least 9 inches in d.b.h. and hardwoods at least 11 inches d.b.h.; 

poletimber—medium trees, 5 inches in d.b.h. to sawtimber size; and sapling/seedling—

small trees, 1 to 5 inches in d.b.h. Tracking change in the distribution of stand-size class 

provides information about forest sustainability and succession, wood potentially available 

for products, wildlife habitat, and recreation potential. 

Sawtimber-size stands continue to predominate in Iowa’s forests (fig. 1.9). Since 1954, 

the area of sawtimber has increased by 64 percent and now occupies 1.7 million acres, or 

nearly two-thirds of the forest area. At the same time, the area of poletimber-size stands 

first declined but then increased, currently occupying 603,000 acres, or 23 percent of the 

forest area. The area of sapling-seedling stands has remained fairly stable in recent years, 

occupying 307,000 acres, or 11 percent of the forest area. Three percent of the forest 

area is nonstocked. Forest types with a preponderance of area in the sawtimber size class 

include northern red, bur, and white oaks, silver maple, and American elm (fig. 1.10). 

Conversely, nearly half the area of the eastern redcedar and eastern redcedar/hardwood 

types are in sapling/seedling-size stands.

Over the years, forest trees in Iowa generally have grown larger. The high proportion of 

total area in large-diameter trees indicates a maturing hardwood forest. The expanding 

area of sawtimber stands suggests that timber harvesting or other disturbances are reducing 

few stands to early successional stages. In the past, timber harvesting was by selective 

cutting or high-grading. The lack of significant disturbances in hardwood 

stands has not opened stands to progressive seedling development. Some 

smaller trees are prevented from maturing properly by large overstory 

trees, as suggested by the static nature of sapling-seedling stands since the 

1970s. Between 1990 and 2003, the area of poletimber-size stands in the 

sugarberry/hackberry/elm/green ash, and elm/ash/locust types increased, 

suggesting recruitment of sapling-seedling trees into the larger class. Trees 

associated with those forest types typically are found on bottomland sites, 

pointing to an expanding lowland forest. The relatively high proportion 

of sapling-seedling area in the eastern redcedar and eastern redcedar/hardwood types 

indicates that eastern redcedar typically is the first tree species to become established in 

abandoned fields and old pastures.

Paul Wray, Iowa State University, www.forestryimages.org
­­­­23

FEATURES HEALTH PRODUCTS

Inventory year

1954

Thousands of acres

1,800

1974 1990 2003

1,600

1,400

1,200

1,000

800

600

400

200

0

	 Sawtimber	 Poletimber	 Sapling-seedling	 Nonstocked Figure 1.9. Area of timberland by 

stand-size class, Iowa, 1954-2003.

Figure 1.10. Percentage of select 

forest types by stand size class, Iowa, 

2003.

	 Sawtimber	 Poletimber	 Sapling-seedling

Northern red oak

Bur oak

White oak

Silver maple/American elm

Black walnut

Hard maple/basswood

Cottonwood

Sugarberry/hackberry/elm/g.ash

White oak/red oak/hickory

Elm/ash/locust

Eastern redcedar

Eastern redcedar/hardwood

100

90

80

70

60

50

40

30

20

10

0

Forest type

Percent
­­­­24

FEATURES HEALTH PRODUCTS

Forest Stand Age

Background:

What This Means:

What We Found:

Iowa’s forest stands vary in age. Age is estimated based on core samples from dominant 

or codominant trees from the overstory of a stand. Estimating age is important because 

it provides information about successional development of forest stands and, in turn, its 

capacity for delivering ecosystem services and wood products. For instance, a forest equally 

divided between age classes likely will yield an even flow of timber for wood products. A 

forest with trees of various ages also is important in maintaining diversity in forest wildlife 

populations and for esthetic enjoyment. 

Forest stands in Iowa can be grouped into three broad age categories: 1 to 40 years old, 41 

to 80 years old, and 81+ years old. Since 1974, the area of timberland in stands between 

age 41 and 80 has been expanding and currently accounts for 55 percent of timberland 

area, up from 38 percent of total in 1974, or more than a half million additional acres 

(fig. 1.11). Between 1990 and 2003, stands dominated by trees older than 80 years 

declined in area by 11 percent, or more than 120,000 acres. As a proportion of forest area, 

younger stands remained fairly stable, increasing by 220,000 acres between 1990 and 2003. 

Stand age varies by species. In 2003, stands dominated by oak trees contained a greater 

proportion of area in the oldest age class (fig. 1.12). Non-oak hardwood stands generally 

are younger. Because of its commercial value, black walnut seldom grows into the older 

age class. Stands with a significant number of eastern redcedar account for only 3 percent 

of forest area, but most of them are young.

Most of the stands in Iowa’s forests are more than 40 years old; oak stands generally are 

older. Most oak stands came into existence and were maintained by disturbances such as 

fire and timber harvesting, both of which promote regeneration by allowing sunlight to 

reach oak seedlings on the forest floor. In the absence of stand disturbances, shade-tolerant 

hardwoods (e.g., maples) in the midstory are replacing oaks. The age distribution of oaks 

has important implications for Iowa’s timber products industry and woodlot owners’ 

personal income from harvesting. With fewer large, high-quality oaks likely to come from 

Iowa’s woodlots, income and value-added economic activity will decrease. Further, certain 

wildlife species would be adversely affected by fewer oaks. Generally, older oaks are prolific 

seed producers, benefiting mast-eating wildlife. However, as fewer young oaks move up in 

age, these wildlife species could decline.
­­­­25

FEATURES HEALTH PRODUCTS

Northern red oak

100

90

80

70

60

50

40

30

20

10

0

Forest type

Timberland (percent)

	 1-40 years	 41-80 years	 81+ years

Timberland (percent)

90

80

70

60

50

40

30

20

10

0

100

1974	 1990	 2003

Inventory year

Bur oak

Silver maple/American elm

White oak/red oak/hickory

Black walnut

Hard maple/basswood

Elm/ash/locust

Sugarberry/hackberry/elm/g.ash

Cottonwood

Eastern redcedar

Eastern redcedar/hardwood

	 1-40 years	 41-80 years	 81+ years

Figure 1.11. Distribution of timberland 

by stand age class, Iowa, 1974-2003.

Figure 1.12. Distribution of 

proportion of area for selected forest 

types by age class, Iowa, 2003.
­­­­26

FEATURES HEALTH PRODUCTS

How Dense are the Woods?

Background:

What This Means:

What We Found:

The extent to which trees occupy 

woodlots and river corridors indicates 

the stage of stand development and 

suggests the potential array of benefits 

that might be derived. For instance, 

stand density can be an indicator of 

the need for harvesting trees or other 

activities that promote growth in 

stands.

We used three features of stands to derive measures of density: number of growing-stock 

trees per acre of timberland, growing-stock volume per acre of timberland, and percentage 

of timberland by stocking class. The average number of growing-stock trees per acre of 

timberland increased between 1954 and 1990, but decreased between 1990 and 2003 

(fig. 1.13). Meanwhile, the average volume of growing stock per acre of timberland 

increased each inventory year, more than doubling between 1954 and 2003 (fig. 1.14). 

Stocking, a relative measure of tree density, is used to describe how fully trees occupy 

stands. Most of the timberland is in the fully stocked (22 percent of all timberland) or 

moderately stocked (33 percent) categories (fig. 1.15). A stand is considered fully stocked 

when trees occupy the amount of space in a stand that creates conditions for the best 

growth and form. About one-third of Iowa’s timberland area is poorly stocked. Such 

stands contain insufficient good growing trees per acre to fully utilize the site. Nonstocked 

timberland, 11 percent of the State’s timberland area, represents stands in which stocking 

of live trees is less than 10 percent.

The decrease in the average number of growing-stock trees per acre and the corresponding 

increase in average volume per acre point to a mature forest with trees that are fairly 

well spaced and that have good growth characteristics. In a mature forest, the decline in 

number of growing-stock trees per acre suggests optimal site occupancy. On the better 

sites, more favorable growing conditions allowed certain trees to gain early dominance, 

thus reducing the number of competing trees. The remaining trees grow more vigorously 

than those on poor sites and add additional volume over the same period. Paradoxically, 

many woodlots are nonstocked or poorly stocked. This can be explained by several 

concurrent activities that affect stand development in Iowa’s woodlots: (1) agricultural 

lands reverting to forests—stocking densities in those woodlots usually are low, (2) 

livestock grazing reduces stocking, and (3) overcutting. Most of Iowa’s woodlots are 

Photo courtesy of USDA Forest Service, Northeastern Area, State and Private Forestry
­­­­27

FEATURES HEALTH PRODUCTS

fully or moderately stocked, suggesting that for the near term, stands are capable of 

supplying timber for the State’s wood products industry. Many oak-dominated stands are 

successional and at the stage where harvesting is economically advantageous. However, 

to meet timber demands over the longer term, forest management should focus on 

encouraging forest owners to improve stocking in the poorly stocked and nonstocked 

woodlots. Absent forest management, nonstocked and poorly stocked woodlots likely will 

fail to reach their physical or economic potential. Average number of growing-stock trees per acre

350

1954	 1974	 1990	 2003

Inventory year

300

250

200

150

100

50

0

Figure 1.13. Average number of 

growing-stock trees per acre of 

timberland, Iowa, 1954-2003.
­­­­28

FEATURES HEALTH PRODUCTS Average growing-stock volume per acre in cubic feet

1200

1954	 1974	 1990	 2003

Inventory year

Figure 1.14. Average volume of 

growing stock per acre of timberland, 

Iowa, 1954-2003. 1000

800

600

400

200

0

Timberland area (percent)

35

Nonstocked

Stocking class

Figure 1.15. Percentage of 

timberland by stocking class, Iowa, 

1999-2003. 30

25

20

15

10

5

0

Poorly

stocked

Moderately

stocked

Fully

stocked

Overstocked
­­­­29

FEATURES HEALTH PRODUCTS

Biomass: The Whole Tree

Background:

What This Means:

What We Found:

Tree biomass is the total dry weight of all live aboveground components of forest trees. 

These include boles, stumps, tops, and limbs. In commercial timber harvesting, the 

bole usually is the primary product because it contains wood used as lumber or veneer. 

Biomass estimates are increasing in importance for analyses of carbon sequestration, 

fiber availability for fuel, and fuel loads in stands. As new industries emerge around the 

production of bio-based products (e.g., biocomposites and biofuels), residual biomass 

from forest thinning and timber harvest take on added environmental and economic 

importance. 

Live aboveground tree biomass exceeds 106.6 million dry tons, an average of about 40 

dry tons/acre of forest area. Total aboveground tree biomass increased by 27.3 million 

dry tons between 1990 and 2003. The bole—the trunk or main stem of trees—accounts 

for nearly 7 of every 10 dry tons of forest-tree biomass. Stumps, tops, and limbs account 

for one-fourth of biomass followed by small trees (1 to 5 inches) at 6 percent of all live 

aboveground tree biomass (fig. 1.16). Eighty-seven percent of total aboveground biomass 

is on privately owned woodlots (fig 1.17), though on a per-acre basis, biomass tends to be 

greater on public than on private forests (fig. 1.18).

In Iowa, the average acre of forest has about 40 dry tons of aboveground live-tree biomass. 

How much is 40 dry tons of tree biomass? On average, corn stover—corn harvest residues 

consisting of dried stalks, leaves, husk, and cobs—range from 3 to 4.5 dry tons/acre in 

fields producing 100 to 150 bushels of corn/acre. The typical forest acre in Iowa has 

roughly 10 times as much dry biomass as an acre of corn following harvest. The difference 

is that tree biomass is live while corn harvest residue is not. The increase in tree biomass is 

attributable to the increase in forest area and growth on trees. On private woodlots, where 

biomass per acre is about 18 percent lower than on public forests, increases in biomass 

could be an important income producer as carbon trading emerges as a major vehicle for 

mitigating greenhouse gases.
­­­­30

FEATURES HEALTH PRODUCTS

Figure 1.16. Distribution of 

components of live-tree biomass, 

Iowa, 1999-2003.

Figure 1.18. Per-acre aboveground 

dry weight of all live-tree biomass by 

owner group, Iowa, 1999-2003.

1.16 1.17

Stumps, tops,

limbs

25%

All live trees

1 to 5 inches

6%

Boles

69%

Federal

4%

County/

local

1%

Private

87%

State

8%

Figure 1.17. Ownership of forest 

biomass (dry tons) for growing-stock 

and non-growing-stock trees on 

timberland, Iowa, 1999-2003.

Tons per acre

48

Federal

Owner group

State County/

local

Private

46

44

42

40

38

36

34
­­­­31

FEATURES HEALTH PRODUCTS

Forest Growth

Background:

What This Means:

What We Found:

The capacity of woodlots to grow wood volume is an indicator of health, vigor, and 

development stage of trees in stands. Forest growth is expressed as average annual net 

growth. Net growth is gross growth minus mortality. Averaged annual net growth is based 

on the average growth rate between 1990 and 1999 to 2003, the years between the two 

most recent inventories. 

Average net annual growth of growing stock has increased substantially since 1990 and 

now is 117.5 million cubic feet (ft3

) per year (fig. 1.19). Between 1990 and 2003, an 

average of 46 ft3 of wood was added to each acre of timberland each year, predominantly 

in mature trees. As a result, average growing-stock volume per acre of timberland had 

more than doubled since 1954, increasing from 532 to 1,112 ft3 in 1999-2003. Hardwood 

growth accounts for 98 percent of the total average annual growth of growing stock. 

Between 1991 and 1999-2003, eight species led by silver maple and bur oak experienced 

growth that combined accounts for two-thirds of net annual growth (fig. 1.20). Silver 

maples produced the largest portion of growth (13 percent of total growth) followed by 

bur oak (12 percent), and black walnut and eastern cottonwood (8 percent each). 

Iowa’s forest stands currently are growing wood at increased rates. The rate for silver 

maple, a prolific seed producer that grows rapidly, exceeds all other species. Second is bur 

oak, a hardy species that can endure weather extremes and many of the maladies that 

affect other oak. Established cottonwoods continue to put on substantial annual growth 

and black walnut, a high-value wood, is managed for growth. However, growth rates for 

northern red and white oak are slowing. Both species are economically important so this 

slowing has implications for their future role in the State’s timber products industry. To 

ensure that red and white oak are available for commercial wood products, owners should 

be encouraged to manage these species for regeneration and growth.
­­­­32

FEATURES HEALTH PRODUCTS Million cubic feet

140

1954

Inventory period

1954 to 1973 1973 to 1990 1990 to

1999-2003

120

100

80

60

40

20

0

Species

Northern red oak

2

Million cubic feet per year

White oak

Hackberry

American elm

Eastern cottonwood

Black walnut

Bur oak

Silver maple

0 4 6 8 10 12 14 16 18

Figure 1.19. Average annual net 

growth of growing stock per inventory 

reporting period, Iowa, 1954 to 

1999-2003.

Figure 1.20. Average annual net 

growth of growing stock on timberland 

for selected species, Iowa, 1990 to 

1999-2003. 
­­­­33

FEATURES HEALTH PRODUCTS

Forest Tree Removals

Background:

What This Means:

What We Found:

The amount of wood volume removed annually from woodlots is an indicator of wood 

consumption and forest resource sustainability. Wood volume is removed from stands 

through timber harvesting, cultural operations (e.g., timber-stand improvement), land 

clearings, and changes in land use. 

Tree removals volume averaged 50.3 million ft3 between 1954 and 1973 (fig. 1.21). From 

the early 1970s into the late 1980s, annual average removals declined to 22 million ft3 and 

then rose to 25.5 million ft3

 from 1999 to 2003. Between 1955 and 1974, tree removals 

exceeded net annual growth. As a percentage of total tree volume, the removal rate has 

dropped steadily since the 1950s (from 4.8 percent to 0.9 percent today).

The percentage change in annual average removal rates among species over the two 

most recent inventory periods has been highly variable, e.g., black walnut (439 percent), 

northern red oak (124 percent), silver maple (-20 percent), white oak (-42 percent), 

and eastern cottonwood (-58 percent). From 1991 to 2003, virtually all removals were 

hardwoods. Softwood removals totaled 250,000 ft3/year, or about 1 percent of the total. 

Virtually all removals (24.5 million ft3/year) were from privately owned forests. Northern 

red oaks had the largest average annual removals at 6.2 million ft3/year, nearly one-fourth 

of total removals (fig. 1.22).

Land clearings and changes in land use always have been a significant component of 

removals. During the 1950s and 1960s, most removals resulted from woodlots being 

cleared or opened to grazing, and river bottom stands being cleared for row-crop 

agriculture. Since the mid-1970s, the agriculture land base has stabilized with a slight 

decline while the volume of wood removals has declined to less than 1 percent of total 

tree volume. Black walnut experienced a substantial increase in removals to meet the 

market demands for its wood. White oak removals continued to decline while northern 

red oak removals more than doubled (about one-fourth of all removals). The latter 

removals are relatively large because red oak is valued and much of the resource is at 

economic maturity. However, the relatively large volume of this species being removed is 

cause for concern about the long-term availability of red and white oak due to the lack of 

small trees and regeneration failures. Red and white oak are the life blood of Iowa’s timber 

products industry and a shortage of quality oaks would adversely affect the industry. 
­­­­34

FEATURES HEALTH PRODUCTS Removals (million cubic feet)

Inventory period

1954 to 1973 1973 to 1990 1990 to

1999-2003

50

40

30

20

10

0

Species

Black oak

1

Million cubic feet per year

Eastern cottonwood

White oak

Bur oak

Silver maple

American basswood

Black walnut

Northern red oak

0 2 3 4 5 6 7

Figure 1.21. Average annual 

removals of growing-stock volume, 

Iowa, 1954 to 1999-2003. Values 

represent average annual removals 

for the period since the previous 

inventory.

Figure 1.22. Average annual 

removals of growing stock on 

timberland for selected species, Iowa, 

1990 to 1999-2003.
­­­­35

FEATURES HEALTH PRODUCTS

Forest Tree Mortality

Background:

What This Means:

What We Found:

Tree mortality is caused by factors such as disease, insect attack, physical damage, weather, 

climatic change, and old age—often in combination. Mortality volume is the volume 

of wood in trees that died from natural causes. It does not include volume removed by 

human action, e.g., from harvesting. 

The average annual mortality increased steadily between 1955 and 2003, reaching 24.5 

million ft3, nearly a threefold increase (fig. 1.23). Between 1990 and 1999 to 2003, 

American elm had the largest average annual mortality at 2.9 million ft3

, followed closely 

by silver maple and eastern cottonwood (fig. 1.24). Those species combined accounted for 

more than one-third of total average mortality between 1990 and 1999-2003. Mortality in 

northern red oak and white oak is fairly low, though black oak mortality exceeds 2 million 

ft3/year. The average annual mortality for black walnut is nearly 2.5 million ft3/year. 

The amount of mortality associated with American elm is the result of Dutch elm disease, 

which has expanded throughout the State. Black oak mortality is primarily the result of 

oak wilt and oak decline. The widespread flooding of 1993 was especially damaging. Trees 

submerged in water for weeks were stressed and weakened, rendering them susceptible 

to disease and insect attacks. Mortality rates likely will increase in the near term because 

Iowa’s woodlots contain many older trees, and could be accelerated by non-native insects 

or pathogens, including gypsy moth and emerald ash borer.
­­­­36

FEATURES HEALTH PRODUCTS Mortality (million cubic feet)

Inventory period

1954 to 1973 1973 to 1990 1990 to

1999-2003

30

Species

Northern red oak

Million cubic feet per year

0

Figure 1.23. Average annual 

mortality, Iowa, 1954 to 1999-2003.

Figure 1.24. Average annual 

mortality of selected species, Iowa, 

1999-2003.

25

20

15

10

5

0

0.5 1.0 1.5 2.0 2.5 3.0 3.5

White oak

Black oak

Black walnut

Eastern cottonwood

Silver maple

American elm
­­­­37

FEATURES HEALTH PRODUCTS

Oaks—A Special Situation

Background:

What This Means:

What We Found:

Oaks are special to Iowans—the oak (no specific species) is designated as the State tree. 

Northern red and white oaks are the premier species in the State’s wood products industry. 

Oaks provide mast and habitat for numerous bird and mammal species, and are revered 

for their stately presence. However, as we have chronicled here, over the last century 

the cumulative impacts of human actions have changed Iowa’s forests. Once dominated 

by oaks, these forests are in transition as the number of northern red and white oak trees 

has declined. Stands of oaks have an inordinate amount of area in larger trees—more 

than 95 percent of the stands where red and white oak are a plurality are composed of 

large-diameter trees. Many of these stands contain trees that are more than 80 years old. 

Northern red oak is being removed at a rate that far exceeds that of other species. Indeed 

northern red and white oaks are at a juncture where their continued strong presence on 

the landscape is in question.

To gauge the future status of oaks in Iowa, we compared the number of oak saplings—live 

trees that are 1 to 5 inches in d.b.h.—with other common forest species. Iowa’s woodlots 

contain substantially fewer oak saplings than saplings of other species (fig. 1.25). On a per 

acre basis, oaks also have far fewer saplings than other forest species (fig. 1.26). 

The low rate of oak regeneration as expressed by the number of saplings is perplexing to 

forest managers because there is no single cause of poor regeneration, which is the result of 

the cumulative impact of human actions and the biological consequences of those actions. 

For instance, recurrent fire is important for oak regeneration because it eliminates many of 

the oak’s competitors. However, fire suppression has resulted in non-oaks taking over oak 

stands. Over the years, it has proven difficult to convince family forest owners of the value 

of cultivating and managing for oak. If oaks are to remain a viable component of Iowa’s 

forests, active woodlot management to promote oak regeneration must be increased.
­­­­38

FEATURES HEALTH PRODUCTS Millions of saplings

Figure 1.25. Number of saplings by 

selected species, Iowa, 1999-2003.

Figure 1.26. Average number of 

saplings per acre of forest land, by 

selected species, Iowa, 1999-2003.

Species

Northern red oak

120

110

100

90

80

70

60

50

40

30

20

10

0

White oak

Bur oak

Shingle oak

Honeylocust

Green ash

White ash

Hackberry

Hickories

Maples

E. hophornbeam

American elm

Saplings/acre of forest (number)

Species

Northern red oak

45

White oak

Bur oak

Shingle oak

Honeylocust

Green ash

White ash

Hackberry

Hickories

Maples

E. hophornbeam

American elm

40

35

30

25

20

15

10

5

0
­­­­39

FEATURES HEALTH PRODUCTS

Whose Woods Are These? Family Forest Owners

Background:

What This Means:

What We Found:

Iowa’s family forest land owners are stewards of an important resource that provides both 

personal and societal benefits. As stewards, landowners maintain their woodlots to protect 

and enhance their personal interest while providing environmental and other benefits to 

the public. An owner’s relationship with forests has important implications for resource 

sustainability, including the sustainable production of timber and the continued flow of 

goods and services.

We used data from the National Woodland Owners 

Survey to describe Iowa’s family forest owners (Butler 

and Leatherberry 2004, 2005). An estimated 138,000 

family forest owners in Iowa hold nearly 82 percent 

of the forest area in the State (fig. 1.27). The number 

of family forest owners increased dramatically over 

the last decade as nearly half acquired land during 

that time (fig. 1.28). As the number of owners 

increased, the average size of forest holdings decreased from 31 acres in 1993 

(Birch 1996) to 12 acres in 2003 (fig. 1.29). Family forest owners tend to be older than 

the general population: 65 percent are age 55 or older and 6 percent are age 75 or older 

(fig. 1.30). People own forests primarily for privacy and aesthetic enjoyment (fig. 1.31). 

Many family forests owners are concerned that others may infringe on their land—

trespassing and illegal dumping are paramount concerns. They also tend to be concerned 

about possible future harm that insects, disease, and nonnative plants could cause. Despite 

these concerns, only 1 percent of owners have a written forestry management plan and 

these people hold only 5 percent (87,000 acres) of family forest land. Twenty-nine percent 

of family forest owners have harvested timber from their woodlots, but only 8 percent 

have harvested saw logs. Most owners that harvested wood used it as firewood. 

The increase in owners, many seeking the privacy and aesthetic enjoyment afforded by 

trees, has led to forests being broken into ever smaller tracts. In the coming years, more 

woodlots likely will be sold or change owners because more than one-third of family 

forest owners are 65 years old or older and they own 43 percent of family forests. Current 

ownership trends point to most new owners being “hobby” farmers or absentee owners. 

Harvesting timber from woodlots likely will decline because timber production is not an 

important reason for owning forests. Also closing family-owned forests to public use likely 

will increase, shutting off traditional uses such as hunting.

Photo courtesy of USDA Natural Resources Conservation Service
40

FEATURES HEALTH PRODUCTS

Business

6%

State

7%

Local

2%

Federal

3%

Family

82%

Figure 1.27. Distribution of forest 

area by type of owner, Iowa, 2003.

Figure 1.28. Distribution of family 

forest owner and acres tenure, Iowa, 

2003.

Percent

Family forest owner tenure

60

< 10 years

50

40

30

20

10

0

10 - 24 years 25+ years No answer

	 Owners	 Acres
41

FEATURES HEALTH PRODUCTS

	 Owners	 Acres

	 1993	 2003

Thousands of acres

Size of holding (acres)

800

1 - 9

700

600

500

400

300

200

100

0

10 - 49 50 - 99 100 - 499 500+

Figure 1.29. Distribution of family 

forest owners by size of holding, Iowa, 

1993 and 2003.

Figure 1.30. Distribution of family 

forest by owner and acreage by age, 

Iowa, 2003.

Percent

Age (years)

<35

35

30

25

20

15

10

5

0

35 - 44 45 - 54 55 - 64 65 - 74 75+ No answer
42

FEATURES HEALTH PRODUCTS

Figure 1.31. Distribution of family 

forest owners and acreage by 

reasons for owning forests, Iowa, 

2003.

	 Acres	 Owners

Reasons for owning forests

Owners (percent)

Privacy

0

Aesthetics

For heirs

Part of farm, home

Hunt and fish

Investment

Timber

10 20 30 40 50 60 70
43

FEATURES HEALTH PRODUCTS

Whose Woods Are These? Public Forests

Background:

What This Means:

What We Found:

Public forests are a critical part of Iowa’s natural resource wealth. They provide access to 

outdoor education and recreational opportunities, managed wildlife habitat, and protect 

special and unique areas. Public forests under special access rules are an indicator of Iowa’s 

awareness of and commitment to the value of forests to future generations. 

About 12 percent (309,000 acres) of forests in Iowa are publicly owned and scattered 

throughout the State. State government, principally the Iowa Department of Natural 

Resources, owns 6 of every 10 acres that are publicly held, followed by the Federal 

Government (3 of every 10 acres), and county and municipal governments holding nearly 

1 of every 10 acres (fig. 1.32). Nearly 40,000 acres of public forests are reserved.

Most public forests are in state forests and parks. Stephens State Forest in the 

Southeastern unit is the largest with nearly 14,000 acres in seven units. The newest state 

forest, the 11,000-acre Loess Hills Forest in the Southwestern unit, is unique because of 

the windblown loess soils and varied plant life. These and other state forests—Shimek, 

Yellow River, and several smaller units—preserve larger blocks of forests and educate 

people about their value and uses. Many of Iowa’s 83 state parks and recreation areas 

are places where people go to enjoy nature and an outdoor experience. Among federally 

owned forests, the USDI Fish and Wildlife Service and the U.S. Army Corps of Engineers 

are principal owners, overseeing wildlife refuges and flood control and navigational 

systems with accompanying recreation areas. Most of the reserved forests (28,000 acres) 

are owned by State agencies. These are areas where natural processes occur without 

interference from humans.
44

FEATURES HEALTH PRODUCTS

Figure 1.32. Distribution of public 

forest ownership, Iowa, 2003.

Fish and

Wildlife Service

8% Departments of

Defense or Energy

4%

Local

13%

Other Federal

17%

State

58%
45

FEATURES HEALTH PRODUCTS

Forest Health
46

FEATURES HEALTH PRODUCTS

Insects and Diseases

Background:

What This Means:

What We Found:

Insects and diseases often cause damage when forests are affected by stressors such 

as drought and storm damage. Forest trees growing on poorer sites are particularly 

vulnerable. Monitoring of and responding to insect and disease outbreaks are important in 

maintaining healthy and vigorous forests.

Several forest insects and diseases have been 

identified that adversely affect the health of Iowa’s 

forests. Among these are Dutch elm disease, 

white oak decline, and general tree decline 

and dieback. Dutch elm disease, caused by the 

fungus Ophiostoma umli/novo-umli, occurs in every 

county. The gypsy moth (Lymantria dispar), which 

defoliates trees and is approaching from the East, 

is being monitored. In 2003, more than 3,500 field traps yielded 159 moths, an insufficient 

number to be considered a viable breeding population. White oak decline, a complex of 

insects and diseases that kills mature trees, is concentrated in northeastern Iowa (fig. 2.1). 

Oak wilt infection also damages trees, particularly in southeastern Iowa (fig 2.2). Caused 

by the fungus Ceratocystis fagacearum, oak wilt invades the water-conducting tissues 

(xylem) of oak trees. The foliage then wilts and dies. This disease is spread via root grafts 

and sap-feeding nitidulid beetles. General tree decline or dieback damages certain forest 

stands. Scattered dieback/decline occurs in native white and green ash in about one-third 

of Iowa’s counties, mostly in central and eastern Iowa. The cause of ash dieback/decline is 

unknown. In 2003, drought conditions over much of the State affected trees, particularly 

in southwestern Iowa where extensive areas of oak are stressed. Forty-seven percent of 

Iowa’s family forest owners consider insects or diseases an important threat to the overall 

health of forests.

Damage from insects and diseases remains largely localized, though the supply of oak for 

commercial use and wildlife habitat could decline. Forest management practices—control 

and containment—have been effective in combating insects and diseases. For example, 

early detection and eradication have prevented the establishment of viable breeding 

populations of the gypsy moth.

Joseph O’Brien, USDA Forest Service, www.forestryimages.org
47

FEATURES HEALTH PRODUCTS

Figure 2.1. Shaded area indicates 

occurrence of white oak decline in 

Iowa, 2003. (Source: USDA Forest 

Service, Forest Health Highlights, 

2003. Available online: http://fhm.

fs.fed.us/fhh/fhh-03/ia/ia_03)

Figure 2.2. Shaded area indicates 

occurrence of oak wilt in Iowa in 2002. 

(Source: USDA Forest Service, Forest 

Health Highlights, 2002. Available 

online: http://fhm.fs.fed.us/fhh/fhh02/ia/ia_02)
48

FEATURES HEALTH PRODUCTS

The Emerald Ash Borer: An Ominous Threat

Background:

What This Means:

What We Found:

The emerald ash borer (Agrilis planipennis), native to East 

Asia, is a bark-burrowing insect that kills ash trees. In 

Iowa, white, green, and black ash trees are susceptible, as 

are several horticultural varieties. The adult beetles nibble 

on ash foliage but cause little damage. The larvae feed on 

the inner bark of ash trees, disrupting a tree’s ability to 

transport water and nutrients. The emerald ash borer was first identified in the United 

States in the Detroit, Michigan, area and has spread to Ohio and Indiana. Although the 

borer is not known to be in Iowa, forest managers are concerned about the potential loss 

of ash from borer attacks.

The 60.9 million ash trees in Iowa’s woodlots and along its streams and rivers account 

for an estimated 6 percent of forest trees in the State. Ash trees are found (at least one 

tree per acre of timberland) on 35 percent of the timberland area in Iowa. Ash is seldom 

dominant in most woodlots, but this species, particularly green ash, is common along 

rivers and streams in the western half of the State. Ash accounts for an estimated 

3 percent of all live-tree volume and its use in the timber products industry is relatively 

limited. Ash contributes less than 3 percent of total statewide roundwood and saw log 

production. Between 1994 and 2000, ash saw log production in Iowa fell by 294,000 board 

feet1, or nearly 12 percent. 

If the emerald ash borer enters Iowa, about one-third of the State’s forests would be 

affected. Ash mortality would be widespread and would severely affect lowland forests 

as it accounts for a large portion of lowland trees. In woodlots, mortality would be 

less noticeable because tree species other than ash dominate most of Iowa’s woodlots. 

Mortality in urban areas would be more obvious and result in adverse economic impacts 

because ash is used widely as a shade and landscaping tree. The impact of the emerald 

ash borer on the State’s timber products industry would be modest. Ash trees have not 

been used extensively by the industry and ash saw log production has declined in recent 

years. Although ash trees account for only 6 percent of forest trees, they occupy a unique 

ecological niche in Iowa’s forests. The loss of ash trees would have a profound effect on 

forest ecosystem integrity, and possibly an irrevocable effect on forest species diversity. 

To monitor the threat of an emerald ash borer invasion, the Iowa Department of Natural 

Resources, Forestry Bureau, and several Federal and State agencies have implemented 

early detection programs.

1

A board foot is 1 foot long, 1 foot wide, and 1 inch thick.

David Cappaert, www.forestryimages.org
49

FEATURES HEALTH PRODUCTS

Forest Invaders: Nonnative Plant Species

Background:

What This Means:

What We Found:

Nonnative plants can overtake native woodland plants, threatening ecological diversity 

and increasing forest management costs through their impact on forest tree regeneration 

and growth. The Iowa Department of Natural Resources has identified four species—

buckthorn, honeysuckle, garlic mustard, and multiflora rose—as nonnative plants that are 

adversely affecting the State’s forests.

In 2002, we began collecting data on 

nonnative woodland plant species from 

26 ground vegetation plots, a subset of 

forest inventory plots. The most prevalent 

nonnative species was multiflora rose 

(Rosa multiflora), which was found on 

more than one-third of sample plots 

(fig. 2.3). Common burdock (Arctium 

minus), was the second most common 

nonnative species. Several nonnative tree species were introduced by early settlers to 

make life easier on the prairie. The most common of these in Iowa, Siberian elm and 

Russian olive, were planted as shade trees in yards and around buildings. They also were 

used extensively for windbreaks, shelterbelts, and livestock protection, and to control 

soil erosion. There are an estimated 2.4 million Siberian elm and 173,000 Russian olive 

trees in forest stands in Iowa. An estimated 46 percent of family forest owners, holding 

46 percent of family-owned forests in Iowa, consider “undesirable plants” as an important 

forest health concern. 

Nonnative plant species are an emerging forest health concern in Iowa because they 

compete with native plant species for resources and threaten ecological diversity by 

altering natural plant communities. Nonnative plants pose an economic threat by 

lowering land values for agriculture, forestry, and recreation. In western and central 

Iowa, Siberian elm and Russian olive are problematical because they are moving from 

windbreaks, shelterbelts, and other protective plantings and invading formerly cultivated 

areas or forest edges. Both species are fast growing, hardy, and adaptable to most sites, 

often forming a dense shrub layer that displaces native species.

Paul Wray, Iowa State University, www.forestryimages.org
50

FEATURES HEALTH PRODUCTS

Figure 2.3. Occurrence of invasive 

plant species on vegetative diversity 

plots (n = 26), Iowa, 2001-2003.

Nonnative species

Number of sample plots

Autumn olive

0

Common buckthorn

Amur honeysuckle

Garlic mustard

Bush honeysuckles

Reed canary grass

Common burdock

Multiflora rose

2 4 6 8 10
51

FEATURES HEALTH PRODUCTS

Undesirable Forest Disturbances

Background:

What This Means:

What We Found:

Undesirable disturbances in forest stands can alter or degrade forest health. We recognize 

an area as disturbed when at least 1 acre of forest is affected by any type of naturally 

occurring event or human activity that occurred within the last 5 years and observable 

damage occurred to 25 percent of the individual trees in the stand. Observable damages 

do not include silvicultural activities or other intended changes to forests.

The 1999-2003 inventory revealed three primary causes of disturbances: livestock, 

weather, and wild animals. Disturbance caused by livestock occurred on an estimated 

390,300 acres, or 15 percent of total forest area. Weather-caused damages occurred on 

an estimated 197,100 acres (7 percent). Although severe weather such as ice storms, wet 

heavy snow, and strong winds are common occurrences, major regional-scale weather 

events such as the widespread floods of 1993 can severely affect Iowa’s forests (fig. 2.4). 

Ninety-four percent of weather-induced damage was from flooding. Floods increase stress 

on trees, particularly root systems, eventually killing them.

Most disturbances in Iowa’s forests and woodlots are caused by livestock, primarily 

through grazing. The State’s farmers have a long history of pasturing livestock in woodlots. 

Trampling and soil compaction slows tree growth, exposes tree roots, and impedes 

regeneration of native tree species. Overbrowsing by wildlife, particularly white-tailed 

deer, induces stress in trees. Much of the weather-caused disturbances occurred in the 

elm/ash/cottonwood forest type group, which consists of species such as cottonwood, 

hackberry, willow, and green ash that grow best in moist, low-lying areas, e.g., floodplains. 

Trees in these areas were in water for an extended period during the floods of 1993. Many 

trees that were stressed became increasingly susceptible to secondary insect and disease 

attacks.
52

FEATURES HEALTH PRODUCTS

Figure 2.4. Shaded areas represent 

counties severely impacted by the 

floods of 1993. (Source: USDA Forest 

Service, Forest Health Highlights, 

1995. Available online: http://fhm.

fs.fed.us/fhh/fhh-95/ia_95)
53

FEATURES HEALTH PRODUCTS

Down Woody Debris—Is There A Fire Danger?

Background:

What This Means:

What We Found:

Down woody debris in the form of fallen trees, branches, litter fall, and duff plays a critical 

role in Iowa’s forests. Such debris largely determines forest fire behavior, provides valuable 

wildlife habitat, and is an important carbon stock.

The fuel loadings of down woody materials (fuel-hour classes) are not exceedingly high 

in Iowa (fig. 2.5). Compared with neighboring Missouri and Illinois, Iowa’s loadings of 

100- and 1,000+-hr fuels are not significantly different, but the loadings of the smallest 

fuels (1 and 10 hr) are significantly greater than in Illinois and Missouri. The small sample 

size (n = 21) should be noted for the down woody inventory in Iowa (hence the large 

standard errors). There was an apparent trend in total down woody fuel loadings (fine and 

coarse woody debris) among classes of live-tree density in the State (fig. 2.6). The sizeclass distribution of coarse woody debris is heavily skewed (88 percent) toward pieces less 

than 8 inches in diameter (fig. 2.7a). The decay-class distribution of coarse woody debris is 

dominated by moderate stages of decay across the State (fig. 2.7b). The spatial distribution 

of coarse woody debris volumes indicates that coarse woody debris volumes are highest in 

the Northeastern unit (fig. 2.8).

The fuel loadings in Iowa’s forests are not a sizeable fire hazard except in local areas when 

fuel moistures are extremely low. Given the highly fragmented nature of Iowa’s forests, 

coarse woody volumes are not substantially high in a contiguous pattern across the State. 

Iowa’s coarse woody debris resource is dominated by small pieces. Overall, down woody 

materials do not pose a sizeable fire danger, and there is sufficient coarse woody debris to 

provide wildlife habitat for smaller fauna. 
54

FEATURES HEALTH PRODUCTS

Figure 2.5. Estimates of mean fuel 

loadings (tons/acre) and associated 

standard errors by fuel-hour class for 

Illinois, Iowa, and Missouri.

	 Illinois	 Iowa	 Missouri

Tons/acre

Fuel-hour classes

6

1-hr

5

4

3

2

1

0

10-hr 100-hr 1000+-hr

Down woody fuels (tons/acre

Basal area (sq.ft./acre)

14

0.0 - 30.0

12

10

8

6

4

2

0

30.1 - 60.0 60.1 - 90.0 90.1 - 120.0 120.1+

Figure 2.6. Estimates of mean down 

woody fuels (tons/acre, fine and 

coarse woody debris) and associated 

standard errors by stand density 

(basal area/acre), Iowa, 2001-2003.
55

FEATURES HEALTH PRODUCTS

9%

2% 1%

88%

15%

36%

23%

22%

4%

Decay class

1

2

3

4

5

2.7a

2.7b

Figure 2.7a,b. Mean distribution 

of coarse woody debris (pieces per 

acre) by size class and decay class 

(1=least decayed...5=most decayed), 

Iowa, 2001-2003.

3.0 - 7.9

8.0 - 12.9

13.0 - 17.9

18.0+

Coarse woody

diameter (inches)
56

FEATURES HEALTH PRODUCTS

Figure 2.8. Interpolated map 

(inverse-distance weighting) of 

coarse woody debris volumes, Iowa, 

2001-2003.
57

FEATURES HEALTH PRODUCTS

Ozone Damage

Background:

What This Means:

What We Found:

Bioindicator species in eastern Iowa and downwind of major urban areas are at moderate 

risk of ozone injury while forests in most of western and central Iowa are at low risk. 

Ozone exposures occasionally reached sufficient hourly concentrations and seasonal 

cumulative values to cause foliar injury on the more sensitive bioindicator species. 

However, it is difficult to assess these subtle effects because of other critical growth and 

health variables, e.g., drought, insects, diseases, competition, and invasive species. 

Ozone bioindicator data were first collected in 2000 and the national ozone grid consisting 

of seven permanent biosites in Iowa was established in 2002. Species used most commonly 

were common milkweed, black cherry, blackberry, and white ash. Foliar injury was limited 

on bioindicator species from 2000 to 2002: 

Parameter 2000 2001 2002

Number of biosites 8 8 7

Biosites with injury (%) 0 0 15

Number of plants evaluated 312 379 673

Number of plants with injury 0 0 1

Average number of species/biosite 1.9 2 3.5

Ground-level ozone exposures in Iowa are among the lowest of the North-central 

States and are modest compared to the serious pollution in the Chicago and St. Louis 

metropolitan areas (fig. 2.9). Seasonal cumulative exposures calculated from ozone 

monitoring stations indicate that significant portions of the State fall below critical 

exposure thresholds, resulting in significant foliar injury, growth loss, or other adverse 

long-term consequences. 

Iowa’s forests are exposed to peak hourly concentrations of ozone and seasonal cumulative 

concentrations above preindustrial levels. However, these exposures generally are not 

sufficient to result in observable or measurable adverse impacts. Consequently, the risk 

from ozone is considered low over most of the State. Ozone-sensitive species in eastern 

Iowa and downwind of major urban areas are at modest risk during summers with aboveaverage ozone concentrations. 
58

FEATURES HEALTH PRODUCTS

Figure 2.9. Average national ozone 

exposure, 1999-2003.
59

FEATURES HEALTH PRODUCTS

Rich soils are the foundation of productive forests. Inventory and assessment of the forest 

soil resource provides critical baseline information on forest health and productivity, 

particularly in light of continued natural and human disturbance.

The forests of Iowa are largely underlain by mollisols and alfilsols; entisols and vertisols 

also are present (fig. 2.10). Mollisols are identified by the presence of a mollic (dark and 

humus rich) surface horizon and high base saturation. Mollisols developed under Iowa’s 

prairie landscape and now are some of the most productive croplands in the Nation. 

Alfisols are fertile soils generally possessing an illuvial clay horizon and a medium to high 

base saturation. Most alfisols developed under deciduous forest. Entisols are identified 

by the absence of pedogenic horizons; this may be the result of insufficient time for soil 

development or resistant parent material. In Iowa, these soils are most common along 

drainages. Vertisols are clay-rich soils that undergo dramatic shrink and swell cycles that 

churn the soil over time. They are identified by the layer greater than 25 cm (10 inches) 

thick that includes a slickenslides—polished and grooved surfaces and generally have 

dimensions exceeding 2 inches—within 40 inches of the surface clay content exceeding 

30 percent, and cracks that open and close periodically. The forest floors under the elm/

ash/cottonwood forest type group are thinner than those under other groups (fig. 2.11).

 At the same time, the elm/ash/cottonwood group occurs on soils with a higher coarse 

fragment content (fig. 2.12) and exchangeable sodium (fig. 2.13). The elm/ash/cottonwood group also has higher sulfur concentrations than the oak/hickory group (fig. 2.14). 

Soils under the maple/beech/birch group have higher phosphorus concentrations than 

those under the elm/ash/cottonwood group (fig. 2.15). Other chemical properties are 

similar across all forest-type groups. A soil quality index (SQI), which combines distinct 

physical and chemical soil properties, revealed that SQI values generally increase from 

east to west (fig. 2.16). Greater amounts of carbon are stored in soils that are 0 to 4 inches 

thick, while carbon averages generally increase from southeast to northwest (fig. 2.17). 

The Des Moines lobe soils have the highest averages for both SQI and soil carbon.

Trees associated with the elm/ash/cottonwood forest type group deposit litter that breaks 

down more quickly than that of many trees in other groups, and they do not accumulate 

the same amount of forest floor over time. The high coarse fragment content under the 

elm/ash/cottonwood group might result from stands primarily in riparian zones. Most of 

the phosphorus available to trees is from decomposing organic material. The thin forest 

floor and low phosphorus content of elm/ash/cottonwood forest soils indicate a potential 

nutrient deficiency. The potential for a phosphorus deficiency would have to be tested 

Soils

Background:

What This Means:

What We Found:
60

FEATURES HEALTH PRODUCTS

against phosphorus requirements by the species in question. The causes and implications 

of the observed sodium and sulfur patterns require additional investigation. 

Figure 2.10. Southern limits of last 

glacial and present soil orders, Iowa.
61

FEATURES HEALTH PRODUCTS

Figure 2.11. Forest-floor thickness 

for selected forest type groups, Iowa, 

2003 (data from 2001-2003; error 

bars represent 1 standard error).

Figure 2.12. Coarse fragment 

content by selected forest type 

groups, Iowa, 2001-2003 (error bars 

represent 1 standard error; similar 

results were observed in the 10-20 

cm samples).

Forest-floor thickness (cm)

Forest type group

5

Elm/ash/cottonwood

4

3

2

1

0

Maple/beech/birch Oak/hickory

Forest type group

Elm/ash/cottonwood Maple/beech/birch Oak/hickory

Coarse fragment content (%)

30

25

20

15

10

5

0
62

FEATURES HEALTH PRODUCTS

Figure 2.13. Exchangeable sodium 

for selected forest type groups, Iowa, 

2001-2003 (data from 2001-2003; 

error bars represent 1 standard error).

Figure 2.14. Exchangeable sulfur 

for select forest type groups, Iowa 

2001-2003 (error bars represent 1 

standard error).

Exchangeable Na (cmol(+)/kg)

Forest type group

35

Elm/ash/cottonwood Maple/beech/birch Oak/hickory

Forest type group

Elm/ash/cottonwood Maple/beech/birch Oak/hickory

Exchangeable S (mg/kg)

30

25

20

15

10

5

0

25

20

15

10

5

0
63

FEATURES HEALTH PRODUCTS

Figure 2.15. Phosphorus 

concentration for selected forest type 

groups, Iowa, 2001-2003 (error bars 

represent 1 standard error).

Phosphorus concentration, Olsen method (mg/kg)

Forest type group

90

Elm/ash/cottonwood Maple/beech/birch Oak/hickory

80

70

60

50

40

30

20

10

0
64

FEATURES HEALTH PRODUCTS

Figure 2.16. Soil quality index values 

for plots and averaged across Major 

Land Resource areas, Iowa, 

2001-2003.
65

FEATURES HEALTH PRODUCTS

Figure 2.17. Soil carbon 

sequestration observed on plots 

and averaged across Major Land 

Resource areas, Iowa, 2001-2003.

67

FEATURES HEALTH PRODUCTS

Forest Products
68

FEATURES HEALTH PRODUCTS

Growing-Stock Volume

Background:

What This Means:

What We Found:

Growing-stock volume is a measure that has been used to estimate the amount of wood 

suitable for manufacturing products. Growing stock is wood volume in standing trees 

that are healthy, sound, reasonably straight, and more than 5 inches in d.b.h. Estimating 

live wood that is potentially available for manufacturing wood products is important 

in economic planning and development and is an essential consideration in evaluating 

sustainable forest management.

Growing-stock volume has increased steadily since 1974 and currently totals an estimated 

2.9 billion ft3 (fig. 3.1). Ten species account for 75 percent of all growing-stock volume in 

Iowa (fig. 3.2). Between 1990 and 2003, several of the 10 species increased substantially 

in growing-stock volume (fig. 3.2). Noteworthy was the increase in black walnut (198 

percent), hackberry (137 percent), bur oak (118 percent), and eastern cottonwood (115 

percent). Growing-stock volume currently averages 1,122 ft3/acre of timberland, nearly 

twice the amount in 1954 (fig. 3.3). Increases in volume were substantial in all but the 

smallest diameter classes (fig. 3.4). 

Much of the increase in growing-stock volume since the 1970s 

is due to the growth of larger trees, riparian forest restoration, 

and the reversion of pasture to timberland. Currently, Iowa’s 

woodlots supply much of the wood for the State’s timber 

products industry. However, the industry could be adversely 

affected by increasing mortality and changing species 

composition. Much of the oak volume is near maturity and 

at risk from age-induced mortality. The species composition 

of woodlots and riparian forests is changing; for example, 

the growth rate of silver maple exceeds that of commercially 

important species such as red and white oak. Bill Cook, Michigan State University,

www.forestryimages.org
69

FEATURES HEALTH PRODUCTS

Figure 3.1. Total volume of growing 

stock on Iowa’s timberland, 1954 

through 1999-2003.

Volume (billion cubic feet)

Inventory year

3.5

1954

3.0

2.5

2.0

1.5

1.0

0.5

0.0

1974 1990 1999 - 2003

Figure 3.2. Net volume of selected 

hardwoods in Iowa for the 1990 and 

1999-2003 inventories.

Species

Million cubic feet

0

Hackberry

50 100 150 200 250 300 350

American basswood

Shagbark hickory

American elm

Black walnut

Northern red oak

Bur oak

Silver maple

White oak

Eastern cottonwood

	 1990	 2003
70

FEATURES HEALTH PRODUCTS Growing-stock volume per acre (cubic feet)

Inventory year

1,200

1954

1,000

800

600

400

200

0

1974 1990 1999 - 2003

Figure 3.3. Average growing-stock 

volume per acre of timberland in Iowa, 

1954 through 1999-2003.

Figure 3.4. Distribution of growingstock volume by diameter class in 

Iowa for the 1990 and 1999-2003 

inventories.

Million cubic feet

Diameter class (inches)

500

6

450

400

350

300

250

200

150

100

50

0

8 10 12 14 16 18 20 22-28 29+

1990	 2003
71

FEATURES HEALTH PRODUCTS

Sawtimber Volume

Background:

What This Means:

What We Found:

Sawtimber is the wood in the saw log portion of a tree (the section of a tree’s bole 

between the stump and the saw-log top, measured in board feet). Live sawtimber volume 

is used to determine the monetary value of wood volume in a tree or how much usable 

product might be manufactured from that volume. When saw logs are sawn into pieces by 

sawmills, the pieces are converted to products such as lumber, veneer, and furniture stock.

Sawtimber volume declined between the 1954 and 1974 inventories but then rebounded 

in the 1980s and increased steadily to 10.5 billion board feet in 2003 (fig. 3.5). Between 

1990 and 2003, average sawtimber volume per acre of timberland increased substantially, 

from 2,979 to 4,072 board feet. Virtually all sawtimber volume is in hardwoods (fig. 3.6). 

Since the 1990 inventory, most commercial species increased in total sawtimber volume, 

with black walnut, bur oak, and eastern cottonwood increasing by more than 100 percent 

(fig. 3.7). As a percentage of total sawtimber volume, black walnut volume increased from 

4 percent in 1990 to 7 percent in 2003.

Sawtimber volume increased substantially between 1990 and 2003, with black walnut 

showing the largest percent change in volume. This reflects the commercial importance 

of this species. Many woodland owners actively manage black walnut to maximize its 

stumpage value. In northern red oak and white oak, sawtimber volume increased modestly 

compared to most other species. This reflects both high demand for oak saw logs and oak 

regeneration failures.
72

FEATURES HEALTH PRODUCTS Sawtimber volume (million board feet)

Inventory year

12.0

1954

10.0

8.0

6.0

4.0

2.0

0

1974 1990 1990 - 2003

Figure 3.5. Total sawtimber volume 

on Iowa’s timberland,1954 through 

1999-2003.

Figure 3.6. Percentage of total 

sawtimber volume on timberland in 

Iowa for selected species, 1999-2003.

Eastern cottonwood

14%

White oak

11%

Silver maple

10%

Northern red oak

10%

Bur oak

9%

Black walnut

7%

American elm

4%

Black cherry

1%

Other hardwoods

32%

Softwoods

1%
73

FEATURES HEALTH PRODUCTS

Selected species

Percent change 1990 - 2003

Black walnut

0

Bur oak

Eastern cottonwood

Silver maple

White oak

Sugar maple

Northern red oak

Black cherry

50 100 150 200 250

Figure 3.7. Percent change in total 

sawtimber volume on Iowa timberland 

for selected species, 1990 to 2003.
74

FEATURES HEALTH PRODUCTS

Timber Products Output

Background:

What We Found:

Through the process of converting harvested trees into 

products such as lumber, veneer, or pulp, Iowa’s forest 

resource provides income to both woodland owners 

and wood-processing mills. To better understand the 

effects of the primary wood use and manufacturing 

sector on the economy and its impacts on forests, it is 

important to monitor timber products outputs.

We survey Iowa’s wood-processing mills periodically to estimate the amount of wood 

volume that is processed into products. The two most recent surveys were conducted 

in 1994 (Piva 1997) and 2000 (Piva and Michel 2003). In 2000, there were 59 primary 

wood-processing mills in Iowa—57 sawmills, 1 pulp mill, and 1 veneer mill (fig. 3.8). 

Sawmills declined by 12 between 1994 and 2000, while the number of veneer and pulp 

mills remained unchanged. In 2000, primary mills in Iowa processed 19.9 million ft3 of 

industrial roundwood, an increase of nearly 7 percent over 1994. Less than 1 percent of 

the industrial roundwood processed was softwood. Nearly three-fourths (14.2 million 

ft3) of the industrial roundwood processed was cut from Iowa’s woodlots and forests. The 

remaining 28 percent (5.7 million ft3) was imported, mostly from surrounding states. 

Saw logs accounted for 88 percent of the total industrial roundwood produced in 2000, 

followed by pulpwood at 8 percent and veneer logs at 4 percent (fig. 3.9). Iowa’s forests 

provided 88.6 million board feet of saw logs to sawmills in Iowa and adjacent states. Mills 

in adjacent states processed 14.6 million board feet of saw logs from Iowa. Overall, saw 

log production fell by 118,000 board feet, or less than 1 percent, between 1994 and 2000. 

Increases in saw log production among black walnut, red oak, white oak, and soft maples 

were offset by losses in production from cottonwood and basswood (fig. 3.10). Veneer log 

production increased from 2.8 million board feet in 1994 to 3.6 million board feet in 2000, 

a 27-percent increase. Black walnut and white oak accounted for 70 percent of the veneer 

log production in 2000. However, veneer production declined for both white and red oak. 

Pulpwood production increased by 63 percent, from 10,000 cords in 1994 to 17,000 cords 

in 2000. Cottonwood accounted for 44 percent of the volume harvested for pulpwood 

in 2000.
75

FEATURES HEALTH PRODUCTS

What This Means: Nearly all the wood-processing facilities in Iowa are sawmills processing State-grown saw 

logs. These mills provide woodland owners with 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 greater demand on the hardwood resource. An important consideration for the 

future of Iowa’s primary wood-products industry is its ability to procure high quality wood 

and deliver products that will lead to value-added production in the State. Currently, 

some saw logs are shipped to out-of-state mills for processing, providing less benefit 

to Iowa’s economy. And the continued availability of high-quality red and white oak 

saw logs is problematical because sawtimber volume for those species is showing only 

modest increases while saw log production remains relatively high. Absent sufficient oak 

regeneration, timber products output from those species could decline.

Figure 3.8. Location of primary 

wood-processing mills by region, 

Iowa, 2000.
76

FEATURES HEALTH PRODUCTS

Figure 3.9. Industrial roundwood 

production by product produced, 

Iowa, 2000.

Figure 3.10. Saw log production by 

species group, Iowa, 1994 and 2000.

Veneer logs

4%

Pulpwood

8%

Saw logs

88%

Million board feet

Species group

25

Red oak

	 1994	 2000

Cottonwood

White oak

Soft maple

Black walnut

Other species

Hard maple

Basswood

20

15

10

5

0
77

FEATURES HEALTH PRODUCTS

Wildlife Habitat

Background:

What This Means:

What We Found:

Iowa’s woodlots and river bottom forests are important habitat for wildlife. The 

combination of forest features form the environment in which wildlife species find suitable 

conditions for reproducing, feeding, and resting. The State’s oak/hickory forests have high 

wildlife values because acorns are a dietary staple of many animals and birds.

Iowa’s forests, which provide habitats for more than 300 species of wildlife, comprise 

mature stands with distinct vertical layers—ground and shrub layers, and canopy. Each 

layer provides food, cover, nesting, and resting sites for different species of wildlife, and 

within each vertical layer are trees of various forms. The typical wooded acre has 391 live 

trees, 109 rough trees, 10 standing dead trees, 4 rotten trees, and various types of down 

woody debris. The larger live trees produce copious annual crops of mast and seeds, and 

each tree form along with woody debris provide microhabitats that are used by wildlife. 

The habitat requirements of many wildlife species include being at a distance from human 

populations to reproduce. Although Iowa’s forests are in small tracts, more than half of 

the area is more than 1,000 feet from the nearest road (fig. 3.11). Woodland owners, both 

private and public, manage some forests for wildlife. The National Woodland Owner 

Survey (Butler and Leatherberry 2005) revealed that Iowa’s family forest owners are active 

in wildlife-related activities. In the last 5 years, wildlife or fisheries improvement projects 

have been initiated on 17 percent (283,000 acres) of woodland held by family forest 

owners. For these owners, hunting and fishing are primary reasons for owning forest lands. 

The Iowa Department of Natural Resources manages 340 wildlife areas totaling more than 

270,000 acres. This acreage contains diverse habitat types, including wetland, grassland, 

forest land, and agricultural crops. The Upper Mississippi River National Wildlife and Fish 

Refuge is an important publicly owned wildlife habitat resource.

Their composition and structure make Iowa’s mature forests suitable as habitat for a 

variety of wildlife species. Oak-hickory woodlots and wooded stream bottoms amid 

croplands and pastures attract species that prefer forest edges. For instance, the whitetailed deer has flourished to the point that some Iowans are concerned about their 

population. The nature of trees in a stand influences the mix of wildlife. For instance, 

rotten and standing dead trees are essential for cavity-nesting birds and are used as a perch 

by raptors. Large blocks of forests are rare in Iowa. Continued forest fragmentation, where 

these blocks are carved into ever smaller pieces, likely will reduce habitat for some species 

but also lead to an increase in deer and other species attracted to forest edges.
78

FEATURES HEALTH PRODUCTS

Figure 3.11. Percentage of forest 

area by distance to road, Iowa, 

1999-2003.

Distance to road

Percent of forestland

100 to

500 ft

0

501 to

1,000 ft

1,001 ft

to 0.5 mile

0.5 mile

to 3 miles

5 10 15 20 25 30 35 40 45
79

FEATURES HEALTH PRODUCTS

Forest-Based Recreation and Tourism

Background:

What This Means:

What We Found:

Forests provide economic and social benefits throughout the State by improving the 

quality of life through recreation opportunities resulting from a diverse landscape. Forestbased recreation and tourism create economic activity and are important for attracting 

and retaining employees and retired people.

The 2001 National Survey of Fishing, 

Hunting, and Wildlife-Associated Recreation 

(USDI Fish and Wildlife Service, and U.S. 

Department of Commerce, Bureau of the 

Census 2001) provides insight into the 

importance of forest-based recreation and 

tourism to Iowa’s economy. In 2001, more 

than 1 million individuals at least 16 years old 

participated in wildlife-watching activities, 

including observing, feeding, and photographing wildlife. Forests often were the setting 

for these activities. Nine of every 10 individuals who engaged in wildlife-watching live in 

the State. Wildlife watchers spent $188.4 million on this activity in 2001 (fig. 3.12a), an 

average of $184 per participant. Between 1991 and 2001, the number of wildlife-watching 

participants increased. In 2001, about 243,000 people hunted in Iowa for an average of 

16 days. Hunters spent $167 million on equipment and trip-related expenses (fig. 3.12b). 

The average hunter spent $680 during the year. Pheasants are highly prized game birds in 

Iowa and pheasant hunters contribute a large share of the money generated from hunting. 

More than 500,000 people fished Iowa’s waters that often are associated with forested 

areas. Anglers averaged 14 days of fishing in 2001 while spending over $336 million on 

trip-related expenditures for equipment, boat fuel, and licenses (fig. 3.12c). The average 

angler spent $438 during the year. Forest-based tourism is important to local communities 

throughout Iowa, particularly those along the Great River Road and the Loess Hills 

Scenic Byway. Both roads, nationally designated, attract visitors interested in viewing tree 

fall foliage and spring blooming of wildflowers.

There are indicators that point to a decline in the number of people who hunt in Iowa. 

Broad demographic changes related to increased urbanization, an aging population, 

and limited access to privately owned hunting lands could further reduce the number 

of hunters, resulting in reduced economic activity from that activity. However, wildlife 

viewing and other nonconsumptive forest-based recreation activities are increasing 

in Iowa.

Photo courtesy of USDA Natural Resources Conservation Service
80

FEATURES HEALTH PRODUCTS

Figure 3.12a. Wildlife-watching 

expenditures in Iowa, 2001.

Trip-related

12%

Other

12%

Equipment

76%

Trip-related

30%

Other

17%

Equipment

47%

Trip-related

31%

Other

3%

Equipment

65%

(Total $188 million)

(Total $167 million)

(Total $336 million)

Source: U.S. Department of Interior, Fish and Wildlife Service, and U.S. Department of Commerce, U.S.

Census Bureau, 2001.

Figure 3.12b. Hunting expenditures 

in Iowa, 2001.

Figure 3.12c. Fishing expenditures 

in Iowa, 2001.
81

Data Sources and Techniques
82

Data Sources and Techniques

Forest Inventory Information on the condition and status of forests in Iowa was obtained from the North 

Central Research Station’s Forest Inventory and Analysis (NCFIA) program. NCFIA 

began fieldwork for the fourth forest inventory of Iowa’s forest resources in 1999. This 

inventory launched the new annual inventory system by which one-fifth of the field plots 

(considered one panel) are measured each year. In 2003, NCFIA completed measurement 

of the fifth and final panel of inventory plots in Iowa. Now that all panels have been 

measured, each will be remeasured approximately every 5 years. Previous inventories of 

Iowa’s forest resource were completed in 1954, 1974, and 1990.

Information about family forest owners was obtained from the National Woodland Owner 

Survey (NWOS) sponsored by the USDA Forest Service’s Forest Inventory and Analysis 

(FIA) program. Initiated in 2002, NWOS is designed to increase our understanding 

of private forest land owners in the United States and enable policymakers, resource 

managers, and others interested in the Nation’s forest resources to better understand 

the social context of forests and formulate more informed opinions and decisions. The 

people identified by the FIA forest inventory as private forest land owners formed the 

sample for the NWOS. Every year, a different set of approximately 6,500 owners from 

across the country are invited to participate in the NWOS. Data are gathered via a mailed 

questionnaire and divided into the following categories: (1) forest land characteristics, 

(2) ownership objectives, (3) forest use, (4) forest management, (5) sources of 

information, (6) concerns and issues, and (7) demographics. For details about the methods 

used to design, implement, and process the data for the NWOS visit: www.fs.fed.us/

woodlandowners. Summary findings from the NWOS also are available at this Web site.

Information about insects and disease was obtained from the Forest Health Monitoring 

program (FHM); which determines the status, changes, and trends in indicators of 

forest condition on an annual basis. The FHM program uses data from ground plots and 

surveys, aerial surveys, and other biotic and abiotic data sources and develops analytical 

approaches for addressing forest health issues that affect the sustainability of forest 

ecosystems. FHM covers all forested lands through a partnership that includes the USDA 

Forest Service, State Foresters, and other State and Federal agencies and academic groups. 

Major FHM activities include detection, evaluation, and intensive site monitoring, 

research on monitoring techniques, and analysis and reporting. For details about the FHM 

program and forest health highlights visit: http://fhm.fs.fed.us/.

National Woodland 

Owner Survey

Forest Health 

Monitoring Program
83

National Survey of 

Fishing, Hunting, and 

Wildlife-Associated 

Recreation, Iowa, 

2001

Iowa Woodland 

Invasive Species 

Inventory

Timber Products 

Output and Use 

Assessment

Some of the information about invasive plant species in Iowa was obtained from the 

Iowa Woodland Invasive Species Inventory, a component of the North Central Plan 

for Documentation and Awareness of Invasive Plants Impacting Forests. The Plan was 

initiated in 2002 by the USDA Forest Service’s Northeastern Area, State and Private 

Forestry. The inventory, managed by the Iowa Department of Natural Resources and 

Iowa State University, is designed to document the current locations and severity of 

key invasive woodland species in the State. The goals of the program are to map the 

distribution and severity of the four major invasive plants found in forests within the 

North Central Region and increase public awareness about invasive species. Volunteers 

are used to collect and report the data needed to develop a strategy for managing invasive 

species. This monitoring project is a cooperative effort among Iowa Department of 

Natural Resources Division of Forests and Prairies, Iowa State University’s Department 

of Forestry and Forestry Extension and Department of Animal Ecology, the Iowa 

NatureMapping Program, and the Northeastern Area, State and Private Forestry. For 

additional information about the Iowa Woodland Invasive Species Inventory visit: http://

www.nrem.iastate.edu/Invasive_Species/Invasives.html or contact the Iowa Department of 

Natural Resources.

Information about timber products output and use was obtained from the 2000 Iowa 

Timber Product Output and Use Assessment study, a cooperative effort among the NCFIA 

and the Iowa Department of Natural Resources, Bureau of Forestry. Using a questionnaire 

designed to determine the size and composition of Iowa’s forest products industry, its 

use of roundwood (round sections cut from trees), and its generation and disposition of 

wood residues, Bureau of Forestry personnel visited all primary wood-using mills within 

the State. Completed questionnaires were sent to NCFIA 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. Timber removals by source of material and harvest residues generated during 

logging were estimated from logging utilization studies previously conducted by NCFIA.

Information on forest-based recreation and tourism was obtained primarily from the 

National Survey of Fishing, Hunting, and Wildlife-Associated Recreation Survey which 

has been conducted since 1955 to gather data on the number of anglers, hunters, and 

wildlife-watching participants in the United States. Information is also collected on how 

often these recreationists participate and how much they spend on their activities. For 

more information about the survey or to receive a copy of the Iowa report, visit: http://

www.census.gov/prod/www/abs/fishing.html.
84

References

Birch, Thomas W. 1996. Private forest-land owners of the northern United States, 1994. Resour. Bull. NE-136. 

Radnor, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 293 p.

Butler, Brett J.; Leatherberry, Earl C. 2004. America’s family forest owners. Journal of Forestry. 102(7): 

4-14.

Butler, Brett J; Leatherberry, Earl C. 2005. Design, implementation and analysis methods for the 

National Woodland Owner Survey. Gen. Tech. Rep. NE-336. Newtown Square, PA: U.S. Department of Agriculture, Forest 

Service, Northeastern Research Station. 43 p.

Piva, Ronald J. 1996. Iowa timber industry—an assessment of timber product output and use, 1994. Resour. Bull. 

NC-182. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 38 p. 

Piva, Ronald, J; Michel, Dennis D. 2003. Iowa timber industry—an assessment of timber product output 

and use, 2000. Resour. Bull. NC-215. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Research 

Station. 49 p.

U.S. Fish and Wildlife Service: U.S. Census Bureau. 2001. National survey of fishing, hunting, 

and wildlife associated recreation. Iowa. (Rev. March 2003) 46 p. + Appendix.

van Buren, Maud. 1938. Quotations for special occasions. New York, NY: The H.W. Wilson Company. 
The U.S. Department of Agriculture (USDA) prohibits

discrimination in all its programs and activities on the

basis of race, color, national origin, gender, religion,

age, disability, political beliefs, sexual orientation, and

marital or family status. (Not all prohibited bases apply

to all programs.) Persons with disabilities who require

alternative means for communication of program

information (Braille, large print, audiotape, etc.) should

contact USDA’s TARGET Center at (202) 720-2600

(voice and TDD).

To file a complaint of discrimination, write USDA,

Director, Office of Civil Rights, Room 326-W, Whitten

Building, 14th and Independence Avenue SW,

Washington, DC 20250-9410, or call (202) 720-5964

(voice or TDD). USDA is an equal opportunity provider

and employer.

Published by:

North Central Research Station

Forest Service

U.S. Department of Agriculture

1992 Folwell Avenue

St. Paul, MN 55108

2006

Web site: www.ncrs.fs.fed.us

About the Authors:

Earl C. Leatherberry (retired) was 

a Resource Analyst with the Forest 

Inventory and Analysis work unit, North 

Central Research Station, St. Paul, 

Minnesota.

W. Keith Moser is a Research Forester 

with the Forest Inventory and Analysis 

work unit, North Central Research Station, 

St. Paul, Minnesota.

Charles H. (Hobie) Perry is a Research 

Soils Scientist with the Forest Inventory 

and Analysis work unit, North Central 

Research Station, St. Paul, Minnesota. 

Christopher Woodall is a Research 

Forester with the Forest Inventory 

and Analysis work unit, North Central 

Research Station, St. Paul, Minnesota.

Edward Jepsen is a Plant Pest and 

Disease Specialist with the Wisconsin 

Department of Natural Resources, 

Madison, Wisconsin.

Steve Pennington (retired) was the Forest 

Health Forester for the Iowa Department 

of Natural Resources – Forestry Bureau 

stationed in Ames.

Aron Flickinger is the Forest Health 

Forester for the Iowa Department of 

Natural Resources – Forestry Bureau 

stationed in Ames.

Leatherberry, Earl C.; Moser, W. Keith; Perry, Charles; Woodall, Christopher; 

Jepsen, Edward; Pennington, Steve; Flickinger, Aron. 2006. Iowa’s forests 1999-

2003 (Part A). Resour. Bull. NC-266A. St. Paul, MN: U.S. Department of 

Agriculture, Forest Service, North Central Research Station. 84 p.

The first completed annual inventory of Iowa’s forests reports more 

than 2.6 million acres, nearly matching what was present in 1954. Most of 

Iowa’s forest stands are fully or moderately stocked, suggesting that for the 

near term stands are capable of supplying timber for the State’s wood products 

industry. The increasing number of shade-tolerant species may lead to less 

tree species diversity in Iowa’s forest stands in the future, as shade-intolerant 

species are no longer able to compete in a more shady environment. Many oakdominated stands are at the successional stage where harvest is economically 

advantageous, yet they contain a greater proportion of area in the older age 

classes. Annual net growth of growing stock has more than doubled since 

the 1980s. The lack of significant disturbances in hardwood stands has not 

adequately opened stands to necessary seedling development. As fewer young 

oak move up in age, mast-dependent wildlife species may decline.

KEY WORDS: forest inventory, forest health, Iowa.
MISSION STATEMENT

We believe the good life has its roots in clean air, sparkling water, rich soil, healthy economies and 

a diverse living landscape. Maintaining the good life for generations to come begins with everyday 

choices about natural resources. The North Central Research Station provides the knowledge and 

the tools to help people make informed choices. That’s how the science we do enhances the 

quality of people’s lives.

For further information contact:

Or visit our web site:

www.nrs.fs.fed.us

North Central Research Station

USDA Forest Service

1992 Folwell Ave., St. Paul, MN 55108