Using relative diameter to improve density measures in Allegheny hardwood stands

Relative measurements of density in even-aged stands of mixed hardwoods have proven more useful for assessing crowding than absolute measures. Species composition and average tree size often result in large differences in absolute measures of density such as numbers of trees per acre or basal area per acre. The measure currently used for Allegheny hardwood stands assesses relative density by summing the growing space of all trees as a function of their species and diameter. The relative density calculated by this measure is well correlated with net basal-area growth in unthinned stands and stands that have been silviculturally thinned, predominantly from below. But in stands that have been thinned to alter stand structure, the correlation with net basal-area growth in poor. We tested several measures of relative density that included a term for relative diameter. Equations of this type give measures of density that are as highly correlated with net stand growth as the current measure in stands that have been silviculturally thinned. But in stands that have been thinned in ways that alter stand structure, the new measures are more highly correlated with net stand growth. The new model requires knowledge of the average stand diameter before thinning.