Relationship of understory development in thinned loblolly pine plantations to overstory structure and site characteristics in the Virginia Piedmont
Understory forage production, species composition, and nutrient concentrations were studied in relation to overstory structure and site characteristics in thinned loblolly pine (Pinus taeda) plantations in the Virginia Piedmont. Stands exhibited a wide range in overstory basal areas (18.8 to 43.5 m²/ha) and site indices (14.2 to 23.8 m at base age 25 years). Understory forage production for the 0 to 2 m stratum averaged 610 kg/ha and ranged from 154 to 1690 kg/ha. Initially, differential models were used to develop prediction equations relating understory production to overstory characteristics, but an empirical prediction equation proved to be somewhat superior. Forage production was most predictable from total overstory basal area, canopy cover, and slope position. Understory species composition was analyzed with respect to overstory structural and site gradients, using vegetation ordination techniques. Species composition was less closely related to these gradients than was production; however, the greatest species diversity appeared to occur during the period following thinning but before crown closure, when successional and mid-tolerant species coexisted. Nutrient concentrations in forage material averaged 4643 cal/g for gross energy, 38.3 percent for invitro dry matter digestibility by white-tailed deer (Odoooiteus virginiana) and 8.4 percent for crude protein. There were no apparent trends of these nutrient concentrations with respect to overstory structural or site characteristics. Forage based carrying capacities for white-tailed deer were computed using values from this study for production and nutrient concentrations, and values from the literature for deer forage preferences and nutrient requirements. Results indicated that the pine habitat could support 0.03 to 0.19 lactating does per ha during the summer season, and that energy and not protein is likely the limiting nutritive parameter. Suggestions are made for future research in pine overstory-understory and wildlife habitat relationships. These include the use of experimental overstory manipulation followed by periodic remeasurements to directly observe changes in understory production and species composition, intensive sampling to determine specific local wildlife forage preferences, and the quantification of wildlife movements and population dynamics.