Evaluating environmental effects of managing loblolly pine (Pinus taeda L.) plantations intercropped with switchgrass (Panicum virgatum L.) for biofuel production

Background/Question/Methods

Intensively managed loblolly pine (Pinus taeda L.) plantations have the potential to provide many ecosystems services.  Management regimes designed for sawtimber management often consist of wide rows providing opportunities to explore intercropping of dedicated energy crops for biofuel production.  Switchgrass (Panicum virgatum L.) serves as a model energy crop that can be harvested annually and utilized as a feedstock for biofuel production, while simultaneously managing loblolly pine for high quality wood products. This novel conceptual framework could be applied to any number of feedstocks. Prior to establishing an intensive management system such as intercropping across the forested landscape, it is critical to understand if these systems are environmentally sustainable.   Specifically, how this management strategy affects long-term soil productivity, water quantity and quality and biodiversity. As a result of this gap in scientific knowledge, several research studies have been established in loblolly pine (Pinus taeda L.) plantations throughout the Southeastern U.S. that investigate environmental effects of intercropping and/or biomass management.  These studies are comparing the following treatments: 1) traditional loblolly pine plantation, 2) loblolly pine with switchgrass (intercropped) between the trees and 3) switchgrass planted on land previously managed as a loblolly pine plantation.

Results/Conclusions

Initial results show no treatment effects on soil carbon, nitrogen, or phosphorus. However, soil compaction was higher in the treatments with switchgrass as compared to the traditional pine treatments. Total organic carbon and total Kjeldahl nitrogen from groundwater samples resulted in no difference between treatments. Additionally, the soil water depth did not vary between treatments during the growing season. Preliminary results revealed that there were no treatment effects on relative abundance or richness for herpetile captures for the first two years of monitoring.

The research efforts and most recent results that will be discussed will vary from the plot level/scale to the watershed scale.  In some cases, we will use these data to make inferences at the landscape scale. These efforts are being conducted in collaboration with numerous universities and government agencies with the results being communicated to the scientific community through publications and presentations. The ultimate goal of these studies is to inform reasonable policy relative to sustainability of biomass production in these systems and to provide direction for developing guidelines and sustainable management practices for biomass