Modelling Inter- and Intra-specific Competition in Loblolly Pine (Pinus taeda L.) Plantations on Cutover, Site-prepared Lands

Abstract

The presence of volunteer hardwood species in loblolly pine plantations demands studies on both intra- and inter-specific competition in order to build growth and yield models and to guide vegetation management for these stands. This paper, based on analyses of data collected from a thinning study, reports an investigation of responses of loblolly pine and hardwood species towards intra- and inter-specific competition. Under high levels of overall competition, hardwood species were more competitive, both intra- and inter-specifically. Intra-specific competition was more effective in reducing hardwood basal area growth than inter-specific competition under high levels of overall competition. However, under low levels of overall competition, intra- and inter-specific competition were quantitatively similar toward loblolly pine basal area growth. The basal area growth of hardwoods was significantly related to levels of inter-specific competition, but not with intra-specific effects under low levels of overall competition. More than half of the variability in loblolly pine basal area growth under unthinned control and light thin treatments could be accounted for by competition effects. However, only one third of the variability could be explained for loblolly pine under heavy thin treatment. For hardwood species, the percentage of growth variation accounted for by competition was about 45%, and did not change among the thinning treatments. Different resource demands between the two categories of tree species and a certain amount of thinning shock were suggested by the modelling results.