Productivity, carbon budgets and nutrient cycling in pine-switchgrass systems

Potential markets and policy incentives for bioenergy have stimulated interest in options for producing more biomass in forestry and agroforestry systems. Growing switchgrass between rows of loblolly pine is a promising option for the US South.

NCASI is providing support for measurements of productivity and site characteristics at pine-switchgrass research sites established independently in Louisiana, North Carolina, and Mississippi by scientists from Louisiana State University (LSU), Weyerhaeuser Company, and Mississippi State University (MSU), respectively. In Louisiana, switchgrass was established in juvenile, mid-rotation, and late-rotation loblolly pine, with diverse densities of pine in each age class. In North Carolina, switchgrass and loblolly pine were established in the presence and absence of logging residues. In Mississippi, switchgrass was established within diverse clonal and open-pollinated genotypes of loblolly pine.

Dr. Michael Blazier (LSU) is coordinating measurements across study locations in collaboration with Drs. Zakiya Leggett and Eric Sucre of Weyerhaeuser Company and Dr. Scott Roberts (MSU). Objectives include quantifying plant and soil carbon, soil respiration, potential nitrogen mineralization, pine and switchgrass nutrient uptake efficiency, soil nutrient concentrations, and loblolly pine carbon allocation patterns. Preliminary results show that the presence of pine increased switchgrass coverage across all treatments at the Louisiana site, possibly due to the beneficial effects of shading, but that increasing tree cover reduced switchgrass coverage in the mid-rotation stand. The presence of switchgrass had no effect on initial tree height growth on one site but slightly reduced initial height growth on another site. In addition to soil characteristics and carbon budgets, investigators will assess wildlife habitat characteristics at each site.

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