United States

Department of

Agriculture

Forest

Service

General

Technical

Report WO-57

orest Biomass

Resource of the

United States

United States

Department of

Agriculture

Forest Service

General

Technical

The Forest Biomass Resource

e United States

Noel D. Cost, Project Leader, SE1

James 0. Howard, Project Leader, PNW

Bert Mead, Research Forester, PNW

William H, McWilliams, Research Forester, SO

W. Brad Smith, Research Forester, NC

Dwane D. Van Hooser, Project Leader, INT

Eric H. Wharton, Research Forester, NE

‘Forest Service experiment stations are: SE=Southeastern; PNW=Pacific Northwest;

SO=Southern; NC=North Central; INT=lntermountain; NE=Northeastern.

i
Acknowledgements

The authors would like to thank Daniel D. Oswald and Karen Waddell--Pacific Northwest Forest and Range Experiment Station, Portland, OR--for their assistance with the

Resources Planning Act data base and the information retrieval system that supports

it; and James T. Bones--Forest inventory, Economics, and Recreation Research,

Washington, DC--for his contributions to the development of this study.

ii
Highlights

The dry weight of all live trees on timberland is almost 18 billion dry

tons, or 36.9 dry tons per acre.

Tree biomass is evenly divided between the two major species

groups -- softwoods accounting for 48 percent and hardwoods for

52 percent.

0 Most of the softwood biomass--more than 5 billion dry tons, or 61

percent of the softwood tree biomass--is in the West. Approximately 9 billion dry tons, or 93 percent of the hardwood tree

biomass, is in the East.

0 The largest portion of total tree biomass, almost 72 percent, is

found in tree boles. Tree tops account for 17 percent, and cull

trees 11 percent.

0 Most of the total tree biomass is on privately owned land. Ten

billion dry tons, or 55 percent of the total tree biomass, is on lands

owned by individuals and corporations (other than forest industry).

e Almost 3 billion dry tons of total tree biomass, or 8i percent of all

national forest biomass, is on national forests in the West. Two

billion dry tons of biomass on forest industry lands, or 77 percent

of all forest industry biomass, is concentrated in the South and

West.

Information on additional components of total forest biomass

varies by region. These components can contribute significant

amounts of biomass. Hardwood tree biomass in the Lake States,

for example, is 73 percent of the total hardwood forest biomass.

The remainder is stumps, foliage, seedlings, saplings, and shrubs.

ackground

Over the last decade, biomass statistics have

been published for most states. However, the

existing aggregate data are either limited or out

of date. The most recent statistics on biomass

were for 1980 (U.S. Department of Agriculture

1981). The development of such data continues

to lag even though user interest is high. This

study was initiated to provide current biomass

data for the United States and was conducted

by Forest Service research units throughout the

country.

Initially, biomass statistics were used primarily

to determine the amount of logging residue that

might be generated from commercial timber

harvesting. Biomass statistics were reported according to timber-oriented components of the

total forest resource: wood and bark weight,

biomass of the tree bole, biomass on timberland, etc. Many of the conventional definitions of

tree biomass are still slanted toward industrial

wood use.

However, recent policy is being made at the

State, national, and international level on the

optimum allocation of the total forest resource

for a variety of traditional and nontraditional uses. New segments of the research community

have begun to study the global effects of climate change and the effect of manmade pollution on major ecosystems of the world. Current

biomass standards may have little application

for environmental assessments and global resource analyses.

The biomass statistics presented in this report

remain focused on standards related to the timber component of the forest resource, since

most users of forest resource data continue to

think in terms of timber production. For the first

time, though, additional data has been compiled on the total forest resource, which includes all forest land areas regardless of productivity potential. It also includes stumps,

foliage, seedlings, saplings, and shrubs.

The biomass statistics we developed were

based on current data. Under the authority of

the Forest and Rangeland Renewable Resources Planning Act of 1974 and the Forest

and Rangeland Renewable Resources Research Act of 1978, the USDA Forest Service

conducts periodic forest inventories of all

States. We used the most current biomass data

from these forest inventories.

The data was compiled from existing data

bases, Where no data existed, volume data

compiled from the timber chapter of the 1989

Resource Planning Act assessment were used

as a base, applying appropriate conversion factors to estimate bole biomass. Total tree

biomass estimates were developed through

two methods: one from integrated biomass

equations and the other from component estimates that were added to the information from

the data base. Additional components for both

methods were provided as available.

Definition of Terms

Biomass

Forest biomass. The weight of wood, bark, and

foliage in all living woody plants above the

ground, measured in oven-dry tons. Includes

tree biomass; stump and foliage biomass associated with tree biomass; and the biomass of

seedlings, saplings, and shrubs. Does not include the biomass of grasses, forbs, etc.

Tree biomass. The weight of wood and bark in

all living trees 5.0 inches in diameter at breast

height and larger above a l-foot stump height,

measured in oven-dry tons. Includes the

biomass of live sound trees and the biomass of

live cull trees.

Forest Components

Commercial tree species. Softwood and hardwood tree species suitable for industrial wood

products. Excludes tree species of typically

small size, poor form, or inferior quality.

Foliage. The leaves and fruits of live sound and

live cull trees, 5.0 inches in diameter at breast

height and larger.

Hardwoods. Dicotyledonous trees, usually

broad-leaved and deciduous.

1
Live sound trees. Live trees of commercial

species 5.0 inches in diameter at breast height

and larger, above a l-foot stump height, and

meeting regional specifications for freedom

from defect. Includes tree boles and tree tops.

Live cuN trees. Live trees 5.0 inches in diameter

at breast height and larger, above a l-foot

stump height, not meeting regional specifications for freedom from defect. This includes live

trees of commercial tree species that have such

poor form that they do not contain a sawlog,

that are not commercial tree species, and in

which 50 percent of the cull is rotten.

Saplings. Live trees between 1.0 inch and 4.9

inches in diameter at breast height.

Seedlings. Live trees less than 1 .O inch in diameter at breast height that are free to grow,

Shrubs. Plants that have persistent, woody

stems and relatively low growth habits, and that

generally produce several basal shoots instead

of a single bole. They differ from trees by their

low stature and nonarborescent form (Society

of Range Management 1974).

Softwoods. Coniferous trees, usually evergreen

and having needles or scalelike leaves.

Stumps. The central stem of live sound and live

cull trees, 5.0 inches in diameter at breast

height and larger, between the ground and a

1 -foot height.

Tree boles. The central stem of live trees, 5.0

inches in diameter at breast height and larger,

between a 1 -foot stump height and a 4-inch top

diameter outside the bark, or until the stem

breaks into branches before it reaches this minimum diameter.

Tree tops. The branches of live sound and live

cull trees, 5.0 inches in diameter at breast

height and larger, outside of the minimum top

diameter for tree boles. Includes the upper

stem, limbs, twigs, etc.

Forest industry lands. Lands owned by companies or individuals that operate primary woodusing facilities.

Forest /and. Land areas 1 acre in size at least

1 O-percent stocked with trees of any size. Does

not include productive-reserved land.

National forest lands. Federal lands legally designated as national forests or purchase units.

Other forest /and. Forest land not producing or

capable of producing at least 20 cubic feet of

annual crops of commercial timber. Does not

include productive-reserved land.

Other private lands. All privately owned lands

except forest industry lands.

Other public lands. Lands other than national

forests that are administered by Federal, State,

county, or local municipalities.

Productive-Reserved /and. Forest land withdrawn from timber utilization because of administrative designation, such as park land.

Timberland. Forest land producing or capable

of producing at least 20 cubic feet of annual

crops of commercial timber. Does not include

productive-reserved land.

Literature Cited

Society for Range Management, Range Term

Committee, M.M. Kothmann, Chair. 1974. A

Glossary of Terms Used in Range Management.

Denver, CO: Sot. for Range Management: 25.

U.S. Department of Agriculture. 1981. Tree

Biomass--a state-of-the art compilation. Gen.

Tech. Rep. WO-33; Washington, DC: U.S. Department of Agriculture, Forest Service. 34 p.

2
Index to Tables

The data are presented in tables of tree

biomass by class of timber and ownership; forest biomass by class of material--including

stumps, foliage, seedlings, saplings, and

shrubs; and tree biomass per acre on forest

land. Because most of the data were developed

from the timber assessment volume data in the

1989 Resources Planning Act, the only species

information is major species group (softwoods

and hardwoods).

Table Page

The statistics are reported in dry weight.

Biomass is often reported in green weight, a unit

desirable to the timber-using industry since it

reflects the economic cost of removing wood

from the forest. Dry weight is a more common

base. It yields an easier solution to environmental questions, such as the carbon content of the

world’s standing timber, and is more consistent

over time, avoiding seasonal variations that occur when measuring in green weight.

Table Page

1 Softwood tree biomass on

timberland in the United

States, by State and section,

and class of timber, 1987

2 Hardwood tree biomass on

timberland in the United

States, by State and section,

and class of timber, 1987

3 Total tree biomass on

timberland in the United

States, by State and section,

and class of timber. 1987

4 Softwood tree biomass on

timberland in the United

States, by State and section,

and ownership class, 1987

4

6

8

10

Hardwood tree biomass on

timberland in the United

States, by State and section,

and ownership class, 1987

12

Total tree biomass on

timberland in the United

States, by State and section,

and ownership class, 1987

14

Total forest biomass on

timberland in the United

States, by major species

group, section, region, and

class of material, 1987

16

Total tree biomass per acre

on forest land in the United

States, by major species

group, section, region, and

land class, 1987

19

ay not add due to rounding.