Relationships between loblolly pine (Pinus taeda L.) yield and woody plant diversity in Virginia Piedmont plantations

Abstract

This study was established to determine the effects of competition control on loblolly pine (<i>Pinus taeda</i> L.), woody plant diversity, and wildlife habitat quality in Virginia Piedmont plantations 12-14 and 24-27 years of age. The responses of loblolly pine and competing woody vegetation in plantations 12-14 years of age were analyzed at 8 levels of competition control: total, 2/3, 1/3, or no woody stem control in combination with either total or no herbaceous vegetation control. As woody stem (plus herbaceous) control increased, pine yield increased, and percent hardwood basal area (PHWD BA) and overstory plant diversity (Shannon index (H’)) decreased. Understory percent woody cover, and woody plant species richness, evenness, and diversity (H’) were not affected at any of the competition control levels. Regression analysis was used to determine relationships between loblolly pine yield, hardwood dominance and overstory plant diversity. Pine yield was negatively correlated to PHWD BA (R²=0.74), while overstory diversity (H’) was proportional to PHWD BA (R²=0.97) and inversely related to pine yield (R²=0.77). The relationship between diversity and PHWD BA was consistent for plantations 12-14 and 24-27 years of age, while relationships of yield to PHWD BA and to diversity were altered in the older plantations.

In plantations 12-14 years, competition control reduced proportions of oak and hickory species and reduced canopy structural heterogeneity, but increased proportions of other fruit bearing plant species, and increased deer browse availability and ground stratum heterogeneity. In plantations 24-27 years, competition control altered plant species composition and increased structural heterogeneity.