Tradeoffs between timber and wildlife habitat quality increase with density in longleaf pine (Pinus palustris) plantations

Longleaf pine (Pinus palustris), a historically abundant tree species in the southeastern United States, is often planted to restore the ecologically and culturally important longleaf pine ecosystem that once covered vast acreages in the southeastern United States. Government cost-share programs that support establishment of these plantations place restrictions on planting rates to promote wildlife habitat, as greater tree planting density may reduce canopy openness and herbaceous plant cover that are critical components of habitat for priority species, including gopher tortoise (Gopherus polyphemus) and Bachman's sparrow (Peucaea aestivalis). However, there is expressed concern among some forest managers that more open grown trees in the plantations will be of inferior timber quality with more and larger horizontal branches and associated knots. We examined how density affects dynamics and tradeoffs among understory vegetation structure and composition, longleaf pine stem form (branch density and straightness), and longleaf pine survival by sampling 73 plantations of various ages (5-25 years) and planting rates (653-2445 trees per hectare (TPH)/264-990 trees per acre (TPA)) throughout the southeastern United States. We documented a relationship between planting rate and longleaf pine stand density at time of sampling (r = 0.69, p = 0.0001) and relationships between stand density and habitat and timber quality metrics. Greater stand density resulted in lower tree diameters but greater stand basal area than lower stand density. Higher planting rates led to lower branch density and lower straightness grades than lower planting rates. Canopy openness decreased with greater stand density, and bare ground cover and herbaceous cover decreased as density and stand age at time of sampling increased. Based on our results, we suggest that lower maximum planting rates are appropriate when wildlife habitat is a program objective because lower rates result in fewer tradeoffs, as reducing planting rates slows degradation of wildlife habitat when compared with higher maximum planting rates that have only mixed benefits on timber quality.

Automated summary

Planting rates and density affect the ecological and timber quality aspects of longleaf pine plantations. Higher planting density results in smaller tree diameters and larger stand basal area, while higher planting rates lead to lower branch density and lower straightness grades. Increasing stand density reduces canopy openness and ground cover, decreasing herbaceous plant cover.