Soil productivity index: predictions of site quality for white spruce plantations

One of the few site-quality models that has incorporated the biological effects of multiple soil properties on optimum root growth is the soil productivity index (PI) model. This study aimed to determine if the PI model could be used to estimate site quality for Picea glauca plantations. The PI model includes an estimate of optimum vertical root distributions that is used to weight the relative effects of mineral-soil characteristics on aboveground biomass. Relative topographic and climatic information are also used. Site index and PI were not significantly correlated, but PI was more highly correlated with aboveground stand biomass and mean annual biomass increment than was site index. Site index was more highly correlated with biomass estimates in older plantations (35-43 yr), whereas PI was more highly correlated to biomass estimates in younger ones (19-34 yr). -from Authors