Influence of prior growth suppression and soil on red spruce site index

Abstract

Dominant trees of shade tolerant species are often unsuitable for estimating site index because episodes of growth suppression can mask inuences of site. A large-scale study in eastern Maine, based on 698 red spruce (Picea rubensj trees sampled with increment cores, and 92 trees sampled by stem analysis, addressed Mo objectives: (1) Can spruce trees with histories of suppression be used to estimate site index if suppressed periods are converted to free-growth equivalents? and (2) Do important differences in soil physical properties based on drainage and profile characteristics correspond to meaningful differences in site index? Forty-two percent of the cored trees experienced some form of radial growth suppression. Several methods of adjusting for suppression history, using only periods of stand development when trees grew freely, produced site index estimates that did not differ statistically from those of trees on the same soil class that showed no prior suppression. Statistically significant, but practically small, differences in site index were found behveen good and poor soils; however, high variability in site index within soils suggests that accurate productivity classification requires stand-specific site index estimates.