Parameterization of the 3-PG model for Pinus elliottii stands using alternative methods to estimate fertility rating, biomass partitioning and canopy closure

The forest simulation model, 3-PG, has been widely applied as a useful tool for predicting growth of forest species in many countries. The model has the capability to estimate the effects of management, climate and site characteristics on many stand attributes using easily available data. Currently, there is an increasing interest in estimating biomass and assessing the potential impact of climate change for slash pine (Pinus elliottii Engelm. var. elliottii), a commercially important tree species of the southeastern U.S. The 3-PG model had not been previously parameterized for this species. Using data from the literature and long-term productivity studies, we parameterized 3-PG for slash pine stands, developing new functions for estimating biomass pools at variable starting ages, canopy cover dynamics, allocation dynamics, density-independent tree mortality and the fertility rating. The model was tested against data from measurement plots covering a wide range of stand characteristics (age, productivity and management), distributed within and beyond the natural range of the species, including stands in Uruguay, South America. Across all tested sites, estimations of survival, basal area, height, volume and above-ground biomass agreed well with measured values. The bias was small and generally less than 7%. This paper reports the first set of 3-PG parameter estimates for slash pine, showing new methodologies to determine important estimates. The model can be applied to stands growing over a large geographical area and across a wide range of ages and stand characteristics.