Intensive Utilization of Harvest Residues in Southern Pine Plantations: Quantities Available and Implications for Nutrient Budgets and Sustainable Site Productivity

Abstract

The rising costs and social concerns over fossil fuels have resulted in increased interest in and opportunities for biofuels. Biomass in the form of coarse woody residues remaining after traditional timber harvest in the southeastern USA is a potentially significant source of biomass for bioenergy. Questions remain regarding whether the removal of this material would constitute a sustainable silvicultural practice given the potential impact on soil nutrient cycling and other ecosystem functions. Our objective is to review existing studies to estimate quantities of residual materials on southern pine forests that may be available, potential nutrient removals, and potential replacement with fertilizer. Regionally, it is estimated that 32 million Mg year−1 of dry harvest residues may be available as a feedstock. At the stand level, between 50 and 85 Mg ha−1 of material is left on site after typical stem-only harvests, of which half could be removed using chippers at the landing. Based on these estimates, increase in midrotation fertilization rates of 45% to 60% may be needed on some sites to fully replace the nutrients from harvesting residues removed for bioenergy. Field experiments suggest that residue removals do not degrade forest productivity in many cases, but more data are needed to assess the effects of frequent removals (i.e., from short-rotation systems) over longer periods and identify sites that may be particularly sensitive to the practice. A benefit of developing markets for previously nonmerchantable materials may create incentives for improved forest management by landowners.