Growth-Density Relationships in Loblolly Pine Plantations

Abstract

An understanding of relationships between stand volume growth and stand density is important for making informed management decisions. Contradictions concerning these relationships have been attributed to differences in definitions of volume growth and stand density, among other pitfalls. Models were developed to test growth-density relationships using past-growth data from three thinning studies in 11- to 41-year-old loblolly pine (Pinus taeda L.) plantations. Relationships between gross growth and stand density measures of basal area per hectare, stand density index, volume per hectare, and relative spacing were compared. Relative growth-density relationships were also compared by relating the growth and density of thinned plots to unthinned plots. Analyses indicated that gross volume growth increases with increasing stand density when accounting for age, quadratic mean diameter, and site quality. Results from relative growth-density relationships suggested that thinned stands can exhibit increased growth at relatively lower densities compared to that of an unthinned stand on a similar site. The fitted models, across all four density measures, indicated ever-increasing gross volume growth with increasing stand density within the range of observed data for loblolly pine plantations.