United States

Department of

Agriculture

Forest Service

Northeastern

Research Station

Research Paper NE-716

M. B. Adams

D. R. Owens

Specific Gravity of Coarse

Woody Debris For Some

Central Appalachian

Hardwood Forest Species
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Abstract

Although coarse woody debris (CWD) may play an important role in nutrient cycling

in eastern hardwood forests, it rarely is included in nutrient budgets for most

ecosystems. Meaningful nutrient budgets require reliable estimates of biomass and

nutrient concentrations. The CWD of 21 tree species was sampled in a central

Appalachian forest within the Fernow Experimental Forest in West Virginia. The

specific gravity of CWD was determined for three decay classes. Mean values

ranged from 0.360 to 0.729 g cm-3 for decay class 1 (least decayed wood; coefficient

of variation = 22.2 percent), 0.286 to 0.560 g cm-3 for class 2 (CV = 22.7 percent),

and 0.215 to 0.442 g cm-3 for class 3 (CV = 26.8 percent). Black locust and several

oaks had the highest specific gravity; fire cherry, yellow-poplar, and basswood had

the lowest densities across all decay classes. Specific gravity decreased by nearly

50 percent from class 1 to 3.

The Authors

M. B. ADAMS and D. R. OWENS are, respectively, supervisory soil scientist and

Project Leader and hydrologic technician with the Northeastern Research Station’s

Timber and Watershed Laboratory at Parsons, West Virginia.

Manuscript received for publication 12 January 2001
1

Introduction

Coarse woody debris (CWD) may play an important role in

nutrient cycling in forested ecosystems (Boddy 1983;

Harmon et al. 1986), but it is rarely included in nutrient

budgets for most ecosystems. Meaningful nutrient budgets

require reliable estimates of biomass and nutrient

concentrations. For CWD, these estimates often are not

based on species-specific measurements of specific gravity

at various stages of decay but on fresh, solid wood, or on

values averaged across species and thus may not accurately

represent CWD. There are few specific gravity values for

hardwood tree species by decay class (Idol et al. 1999), and

they are lacking for many of the tree species found in

Appalachian hardwood forests.

We sampled CWD of 21 tree species commonly found in

Appalachian hardwood forests (Table 1). Our objective was

to obtain estimates of specific gravity for three wood-decay

classes for these species, so that survey data (volume or

amount of wood) can be more accurately converted to

biomass in constructing nutrient budgets for entire

ecosystems. This research was part of a larger study

evaluating the productivity and nutrient cycling in

Appalachian hardwood forests (Adams 1999).

Methods

Samples of dead wood (> 10 cm diameter) were collected

from 21 tree species from each of the three decay classes.

Part of a larger system for describing CWD of species on the

Fernow Experimental Forest (L. Thomasma, unpublished),

the classes are:

1. Wood is uniformly firm along the bole length; bark is

mostly intact.

2. Wood is soft in some places but not uniformly so; bark is

loose and may be absent.

3. Wood is soft throughout and can be crushed or broken

easily; little or no bark remains.

Downed wood on untreated areas of the Fernow was

identified as to species and decay class for sampling. A

single crew was used to collect and assess samples. Disks

were removed from 20 pieces of CWD for each species and

decay class. These samples were returned to the lab where

they were subsampled. We used only wood for which the

species could be determined positively. Dead wood that is so

decayed that the species cannot be recognized is

comparable to Class IV and V wood in other systems, and

was not included in this study (Maser et al. 1988).

Each sample was weighed immediately after being brought

into the lab. The green volume of the CWD sample was

determined by water displacement. Samples were then dried

in a forced-air oven at 65o

C, until constant weight was

achieved (about 5 days) and then reweighed. A lower oven

temperature was used to reduce potential nitrogen losses so

that future nutrient analyses would not be compromised.

However, to assure comparability with standard procedures,

a subset of CWD samples were dried at 65o

C and then at

102o

C for another 3 to 5 days and the difference in mass

determined. At the higher temperature, oven-dry mass

changed less than 1 percent (generally less than 0.5

percent), so we believe that our mass estimates are accurate

and comparable. Specific gravity was calculated as dry

weight (in grams) divided by the green volume (in mL or

cm3

).

Unbalanced, one-way analysis of variance was used to

evaluate the effect of species on specific gravity for the three

decay classes; Duncan’s multiple range was used to

compare species means within decay classes. A paired t-test

was used to test the hypothesis that specific gravity values

for freshly dead wood (class 1) did not differ from published

values (U.S. Dep. Agric. 1974). All comparisons were

evaluated for statistical significance at p=0.05 unless

otherwise indicated.

Results and Discussion

Mean specific gravity ranged from 0.360 to 0.729 g cm-3 for

decay class 1, (coefficient of variation = 22.2 percent), 0.286

to 0.560 g cm-3 (CV = 22.7 percent) for class 2, and 0.215 to

0.442 g cm-3 (CV = 26.8 percent) for class 3 (Table 1). Across

all species, mean specific gravity decreased by nearly 50

percent from class 1 to 3 (Fig. 1, Table 1).

Mean specific gravity differed significantly among species

within decay classes (p=.0001). For the least decayed wood

(class 1), chestnut oak and black locust had significantly

higher specific gravity than other species (Fig. 2). The

specific gravity of black locust also was significantly higher

than all other species in class 2. We could not locate black

locust that fit the definition of decay class 3, probably

because of the even age of the forest (approximately 90

years) and the strong decay resistance of black locust wood.

Additionally, there were no white oak in class 3 and only one
2

value for this species in class 2, i.e., it is difficult to

distinguish between white oak and other oaks at later stages

of decay. Except for scarlet oak, all class 3 values for specific

gravity ranged from 0.215 to 0.368 g cm-3 (Table 1, Fig. 2).

Fire cherry, basswood, and yellow-poplar consistently had

the lowest specific gravity for all decay classes. Generally,

species of CWD with the highest class 1 values showed the

greatest change from class 1 to 3 (Fig. 2).

Of the tree species found in mixed hardwood forests, those

rated as the most decay resistant are black cherry, American

chestnut, chestnut oak, white oak, and sassafras. Black

locust showed exceptionally high decay resistance (U.S.

Dep. Agric. 1974). It is important to note that all of the

chestnut CWD that we sampled had been dead for

approximately 60 years, which attests to its decay

resistance. There was relatively little salvage of chestnut

killed by blight in these control areas, so the wood available

for sampling was large in diameter. The wood in decay class

1 was sampled from the outer portion of these large stems.

Thus, while the wood met our requirements for class 1, it

cannot be considered as “freshly dead.”

Table 1.—Mean specific gravity (g cm-3) of dead wood of 21 tree species on the Fernow Experimental Forest,

by species and decay class (standard deviation in parentheses; N = 20 unless indicated otherwise)

Decay class

Species Scientific name 1 2 3

Red maple Acer rubrum 0.602 (.045) 0.441 (.067) 0.317 (.037)

Sugar maple A. saccharum 0.679 (.040) 0.392 (.086) 0.276 (.058)

Sweet birch Betula. lenta 0.635 (.069) 0.420 (.099) 0.283 (.085)

Yellow birch B. lutea 0.636 (.043) 0.385 (.058) 0.234 (.045)

American chestnut Castanea dentata 0.360 (.046) 0.348 (.038) 0.255 (.056)

Bitternut hickory Carya cordiformis 0.610 (.074) 0.367 (.074) 0.249 (.050)

Shagbark hickory C. ovata 0.551 (.071) 0.479 (.087) 0.308 (.065)

American beech Fagus grandifolia 0.598 (.070) 0.372 (.042) 0.245 (.042)

White ash Fraxinus americana 0.475 (.070) 0.286 (.070) 0.317 (.048)

Yellow-poplar Liriodendron tulipifera 0.458 (.046) 0.353 (.055) 0.215 (.024)

Cucumbertree Magnolia acuminata 0.425 (.028) 0.399 (.084) 0.250 (.059)

Sourwood Oxydendrum arboreum 0.524 (.103) 0.406 (.034) 0.337 (.057)

Fire cherry Prunus pensylvanica 0.401 (.029) 0.337 (.026) 0.216 (.026)

Black cherry P. serotina 0.577 (.072) 0.499 (.049) 0.346 (.097)

White oak Quercus alba 0.644 (.036) 0.508 (n=1) (n=0)

Scarlet oak Q. coccinea 0.571 (.053) 0.502 (.041) 0.442 (.033)

Chestnut oak Q. prinus 0.729 (.078) 0.489 (.093) 0.294 (.042)

Northern red oak Q. rubra 0.650 (.057) 0.495 (.121) 0.368 (.098)

Black locust Robinia pseudoacacia 0.725 (.031) 0.560 (.053) (n=0)

Sassafras Sassafras albidum 0.432 (.028) 0.388 (.042) 0.338 (.025)

American basswood Tilia Americana 0.406 (.024) 0.333 (.032) 0.256 (.019)

Our study did not directly address decay rates or resistance.

Many factors contribute to decay rates of wood (Harmon et

al. 1986). Decomposition rates may reflect qualitative

differences among log substrates rather than simple

quantitative relationships (Showalter 1992). The rate and

progression of decay also are important in understanding the

roles of deadwood in nutrient cycling, as wildlife habitat and

food sources, and in carbon sequestration and release. For

example, American chestnut decays from the inside

(heartwood) out, resulting in valuable habitat for wildlife but

has different nutrient release rates than a species like fire

cherry, which decays quickly and uniformly.

We do not know when most of this deadwood originated, so

we could not calculate decay rates. Such information would

be useful in determining nutrient loss rates over time and the

longevity of dead woody debris. We are currently analyzing

the nutrient content of the samples of dead wood collected in

this study for a future publication. In addition, a study to

evaluate decay rates has begun on the Fernow Experimental

Forest, where we have tagged CWD originating from two

windstorms in 1993 and 1998. Logs will be resampled over

time to estimate rates of mass and nutrient loss.
3

Figure 1.—Mean CWD specific gravity by decay class; vertical bars are standard errors.

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

1 2 3

Decay class

Specific gravity (g/cm3)

Figure 2.—Mean CWD specific gravity for 21 tree species for three decay classes.

0

0.2

0.4

0.6

0.8

Chestnut oak

Black locust

Sugar maple

N. Red oak

White oak

Yellow birch

Sweet birch

Bitternut hickory

Red maple

American beech

Black cherry

Scarlet oak

Shagbark hickory

Sourwood

White ash

Yellow-poplar

Sassafras

Cucumbertree

American basswood

Fire cherry

American chestnut

Species

Specific gravity (g/cm3)

Decay Class 1

Decay Class 2

Decay Class 3
4

Literature Cited

Adams, M. B. 1999. Acidic deposition and sustainable

forest management in the central Appalachians, USA.

Forest Ecology and Management. 122:17-28.

Boddy, L. 1983. Carbon dioxide release from

decomposing wood: effect of water content and

temperature. Soil Biology and Biochemistry. 15: 501-510.

Harmon, M. E.; Franklin, J. F.; Swanson, F. J.; Sollins, P.;

Gregory, S. V.; Lattin, J. D.; Anderson, N. H.; Cline, S. P.;

Aumen, N. G.; Sedell, J. R.; Lienkaemper, G. W.;

Cromack, K., Jr.; Cummins, K. W. 1986. Ecology of

coarse woody debris in temperate ecosystems.

Advances in Ecological Research. 15: 133-302.

Idol, T. W.; Pope, P. E.; Figler, R. A.; Ponder, F., Jr. 1999.

Characterization of coarse woody debris across a

100-year chronosequence of upland-oak-hickory

forests. In: Stringer, J. W.; Loftis, D. L., eds. Proceedings,

12th central hardwood forest conference; 1999 February

28-March 1-2; Lexington, KY. Gen. Tech. Rep. SRS-24.

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

Service, Southern Research Station: 60-67.

Maser, C.; Tarrant, R. F.; Trappe, J. M.; Franklin, J. F. 1988.

From the forest to the sea: a story of fallen trees. Gen.

Tech. Rep. PNW-GTR-229. Portland, OR: U.S.

Department of Agriculture, Forest Service, Pacific

Northwest Research Station.

Showalter, T. D. 1992. Heterogeneity of decomposition

and nutrient dynamics of oak (Quercus) logs during

the first 2 years of decomposition. Canadian Journal of

Forest Research. 22: 161-166.

U.S. Department of Agriculture, 1974. Wood handbook.

Agric. Handb. 72. Washington, DC: U.S. Department of

Agriculture.
Printed on Recycled Paper

Adams, M.B.; Owens, D.R. 2001. Specific gravity of coarse woody debris for

some central Appalachian hardwood forest species. Res. Pap. NE-716.

Newtown Square, PA: U.S. Department of Agriculture, Forest Service,

Northeastern Research Station. 4 p.

Although coarse woody debris (CWD) may play an important role in nutrient cycling

in eastern hardwood forests, it rarely is included in nutrient budgets for most

ecosystems. Meaningful nutrient budgets require reliable estimates of biomass and

nutrient concentrations. The CWD of 21 tree species was sampled in a central

Appalachian forest within the Fernow Experimental Forest in West Virginia. The

specific gravity of CWD was determined for three decay classes. Mean values

ranged from 0.360 to 0.729 g cm-3 for decay class 1 (least decayed wood), 0.286 to

0.560 g cm-3 for class 2, and 0.215 to 0.442 g cm-3 for class 3. Black locust and

several oaks had the highest specific gravity; fire cherry, yellow-poplar, and

basswood had the lowest densities across all decay classes.

Keywords: down dead wood, decay class, wood density
Headquarters of the Northeastern Research Station is in Newtown Square,

Pennsylvania. Field laboratories are maintained at:

Amherst, Massachusetts, in cooperation with the University of Massachusetts

Burlington, Vermont, in cooperation with the University of Vermont

Delaware, Ohio

Durham, New Hampshire, in cooperation with the University of New Hampshire

Hamden, Connecticut, in cooperation with Yale University

Morgantown, West Virginia, in cooperation with West Virginia University

Parsons, West Virginia

Princeton, West Virginia

Syracuse, New York, in cooperation with the State University of New York,

College of Environmental Sciences and Forestry at Syracuse University

Warren, Pennsylvania

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