Relationships between loblolly pine yield and woody plant diversity in Virginia Piedmont plantations

This study was established to determine the effects of competition control on loblolly pine (Pinus taeda L.) yield and woody plant diversity in Virgin ia Piedmont plantations 12-14 years of age. In a factorial experiment, lobl olly pine and competing woody vegetation were analyzed at eight levels of c ompetition control: total, two-thirds, one-third, or no woody stem control in combination with either total or no herbaceous vegetation control. Pine yield increased linearly with increasing levels of woody control intensity. As woody control increased, noncrop woody plant basal area and woody plant diversity (Shannon index (H')) in the canopy decreased. Woody plant specie s richness in the canopy was reduced by herbaceous control and by total woo dy control. Percent woody cover, H', and species richness in the understory were not affected at any level of competition control. Regression analysis was used to examine relationships between loblolly pine yield, noncrop woo dy dominance and canopy plant diversity (H'). Pine yield was negatively cor related (R-2 = 0.74) with the percentage of noncrop woody basal area (PNCW BA) in the canopy, while canopy diversity was proportional to PNCW BA (R-2 = 0.97). Canopy diversity was inversely related to pine yield (R-2 = 0.77), with a high trade-off in diversity at low yield levels, but with decreasin g sensitivity as pine yield increased.