SREL Reprint #3548

Environmental effects of short-rotation woody crops for bioenergy: What is and isn't known

Natalie A. Griffiths1, Benjamin M. Rau2, Kellie B. Vaché3, Gregory Starr4, Menberu M. Bitew5,
Doug P. Aubrey6,7, James A. Martin6,7, Elizabeth Benton7, and C. Rhett Jackson7

1Climate Change Science Institute and Environmental Sciences Division,
Oak Ridge National Laboratory, Oak Ridge, Tennessee
2USDA Forest Service, Savannah River Forestry Sciences Lab, Aiken, South Carolina
3Department of Biological and Ecological Engineering, Oregon State University, Corvallis, Oregon
4Department of Biological Sciences, University of Alabama, Tuscaloosa, Alabama
5USDA ARS, Southwest Watershed Research Center, Tucson, Arizona
6Savannah River Ecology Laboratory, University of Georgia, Aiken, South Carolina
7Warnell School of Forestry and Natural Resources, University of Georgia, Athens, Georgia

Abstract: Logging and mill residues are currently the largest sources of woody biomass for bioenergy in the United States, but short-rotation woody crops (SRWCs) are expected to become a larger contributor to biomass production, primarily on lands marginal for food production. However, there are very few studies on the environmental effects of SRWCs, and most have been conducted at stand rather than at watershed scales. In this manuscript, we review the potential environmental effects of SRWCs relative to current forestry or agricultural practices and best management practices (BMPs) in the southeast United States and identify priorities and constraints for monitoring and modeling these effects. Plot-scale field studies and a watershed-scale modeling study found improved water quality with SRWCs compared to agricultural crops. Further, a recent watershed-scale experiment suggests that conventional forestry BMPs are sufficient to protect water quality from SRWC silvicultural activities, but the duration of these studies is short with respect to travel times of groundwater transporting nitrate to streams. While the effects of SRWC production on carbon (C) and water budgets depend on both soil properties and previous land management, woody crops will typically sequester more C when compared with agricultural crops. The overall C offset by SRWCs will depend on a variety of management practices, the number of rotations, and climate. Effects of SRWCs on biodiversity, especially aquatic organisms, are not well studied, but a meta-analysis found that bird and mammal biodiversity is lower in SRWC stands than unmanaged forests. Long-term (i.e., over multiple rotations) water quality, water use, C dynamics, and soil quality studies are needed, as are larger-scale (i.e., landscape scale) biodiversity studies, to evaluate the potential effects of SRWC production. Such research should couple field measurement and modeling approaches due to the temporal (i.e., multiple rotations) and spatial (i.e., heterogeneous landscape) scaling issues involved with SRWC production.

Keywords: aquatic macroinvertebrates, best management practices, bioenergy, carbon/water tradeoffs, hydrologic modeling, soil organic carbon, southeastern United States, terrestrial biodiversity, water quality, woody feedstocks

SREL Reprint #3548

Griffiths, N. A., B. M. Rau, K. B. Vache, G. Starr, M. M. Bitew, D. P. Aubrey, J. A. Martin, E. Benton, and C. R. Jackson. 2019. Environmental effects of short-rotation woody crops for bioenergy: What is and isn't known. Global Change Biology Bioenergy 11(4): 554-572.

This information was provided by the University of Georgia's Savannah River Ecology Laboratory (srel.uga.edu).