Distribution of Biomass in an Indiana Old-Growth Forest from 1926 to 1992
Spetich, Martin A., Parker, George R., The American Midland Naturalist
ABSTRACT.-We examined the structural and spatial distribution of woody biomass in relationship to disturbance in an Indiana old-growth deciduous forest over a 66-yr period. Analysis was done on the core 7.92 ha of a 20.6-ha forest in which every tree 10 cm dbh and over has been tagged and mapped since 1926. Five years are compared-1926, 1976, 1981, 1986 and 1992. Dry weight of living biomass for the 7.92-ha area for these 5 yr was 154 Mg/ha, 207 Mg/ha, 220 Mg/ha, 216 Mg/ha and 211 Mg/ha, respectively. Biomass of dead trees was 1 Mg ha^ sup -1^ yr^ sup --1^ from 1977 through 1981; 4 Mg ha^ sup -1^ yr^ sup --1^ from 1982 through 1986; and 3 Mg ha^ sup -1^ yr^ sup --1^ from 1987 through 1992. Biomass of trees that died between 1976 and 1992 was greatest for midseral species. Living biomass of dominant early to midseral species is declining while that of late seral species is increasing. In 1926 biomass of trees 10 to 25 cm diam consisted of 14% Quercus spp. and 12% Acer saccharum. By 1992 biomass in this diameter range consisted of 1% Quercus spp. and 43% A. saccharum.
Equilibrium patch size was estimated for biomass at each of the five inventory dates to determine if there was a change. Equilibrium patch size for biomass was estimated to be 0.64 ha during all five inventory dates based on the coefficient of variation (CV) of biomass for 16 different grid cell sizes. Grid cell size refers to the size of adjacent cells in a grid that covered the entire study area. The grid with the smallest cells had cells of 0.01 ha. This grid of 0.01-ha cells was aggregated to 15 additional grid cell sizes, where the largest grid cell size was 1.98 ha. CV for all grid cell sizes was highest in 1926 due to effects of prior grazing.
These data indicate an increase in deadwood biomass, a shift in stand composition, recovery from grazing by an increase in small diameter trees and no change in equilibrium patch size over the five inventory dates.
While numerous studies have been published on the structure and composition of deciduous old-growth woodlands in midwestern U.S. (Cain, 1935; Schmelz and Lindsey, 1965; Jackson and Allen, 1968; Williamson, 1975; Runkle, 1982; Parker et al., 1985; MacMillan, 1988; McCune et al, 1988; Runkle, 1990, 1991) relatively few papers on biomass for such woodlands have been published (MacMillan, 1981; Morz et al., 1985; MacMillan, 1988). Most studies of deciduous old-growth forests for the midwest have been confined to short time periods and none have examined spatial pattern of biomass over long time periods. These studies often used importance values, basal area and/or density to estimate the influence of trees in these communities (Wuenscher and Valiunas, 1967; Jackson, 1968;Jackson and Allen, 1968; Schmelz and Hodde, 1971; Schmelz and Lindsey, 1970; Johnson et al., 1973; Jackson and Barnes, 1975; McCarthy et al., 1987). Equations to calculate biomass were not available when many of these studies were implemented. Biomass gives a different perspective on species importance in these forests because biomass can be a more descriptive measure of a tree's ability to compete for and store resources. Biomass estimates take into account differences in wood density, upper stem dimensions and crown morphology (Bell et al., 1984) that importance values and basal area do not. For example, 20 Acer saccharum and 20 Populus deltoides trees that are all 30 cm at dbh have the same basal area estimate. However, these same 20 A. saccharum and 20 P deltoides trees would have biomass estimates of 45 Mg and 86 Mg, respectively.
The spatial scale at which the variability of biomass per unit area becomes stable has not been studied for midwestern forests. But, this measure is important to researchers designing studies to observe biomass dynamics through time and for a better understanding of the scale of effects of disturbance. It has been suggested that the scale at which equilibrium occurs is about 50 times the size of the average disturbance patch (Shugart, 1984). …