A comparison of techniques for measuring density and concentrations of carbon and nitrogen in coarse woody debris at different stages of decay

Abstract

This research considered the relationship between the stage of decay and the concentration of nitrogen (N, %) and the ratio of carbon to N (C/N) in coarse woody debris. Density (g/cm3) was used as an indicator of the stage of decay. In samples collected from the red spruce – Fraser fir (Picea rubens Sarg. – Abies fraseri (Pursh) Poir.) forest of the southern Appalachians, density explained up to 60% of the variation in N and C/N in coarse woody debris. The technique used to estimate density was important. Laboratory-based methods (including displacement and mensuration density) explained the greatest degree of the variation, with coefficients of determination (r2) ranging from 0.39 to 0.59 (p < 0.001) for N and from 0.39 to 0.58 for C/N (p < 0.001). Field-based methods (including penetrometer and resisto graph readings) explained a smaller but still significant degree of the variation, with r2ranging from 0.17 to 0.25 (p < 0.01) for N and from 0.14 to 0.26 for C/N (p < 0.05). Consideration of within-bole heterogeneity in density improved the explanation of variation in N and C/N for a single bole. Density provides a continuous indicator of stage of decay that is not bound by the artificiality of discrete decay classification systems. Furthermore, statistical models relating density to N and C/N provide a means of hind casting and (or) forecasting changes in N and C/N in coarse woody debris at different stages of decay.