Authors: William Stewart,Robert F. Powers,Kathryn McGown, Lindsay Chiono, Teresa Chuang
The implementation of California’s Renewable Portfolio Standard may drive an increase in the use of woody biomass for renewable energy generation. This will likely have both positive and negative environmental impacts. This report reviews the published literature relevant to the potential environmental impacts of increased woody biomass use for energy generation in California and identifies information gaps that exist in understanding the potential impacts.
The major environmental benefit will be the utilization of woody biomass residues for energy from biomass that would have decomposed or burned anyway. Other potential environmental benefits associated with increased biomass utilization include potential reduced losses of forest carbon storage to wildfires, insect disease infestations, and severe weather events such as icestorms and droughts. Based on historic use patterns, most of the increased biomass utilized for bioenergy used by Californians will be a by-product of timber production in western states and Canadian provinces as well as from forest thinning and hazardous fuels treatment projects in California. The major environmental concerns associated with additional biomass harvesting addressed in the literature and in recent guidelines are 1) protecting long term soil productivity, 2) minimizing harvest related erosion and water quality impairment, 3) and maintaining important wildlife habitat and biodiversity elements across the larger landscape.
Much of the published literature and guidelines to limit the negative environmental impacts of pulpwood or biomass for energy harvests are based on experiences in the Eastern United States and Europe that have very different soils, tree species, and wildfire regimes than California. Long-term experiments in California’s mixed conifer forests show no loss of long term (~20 year) productivity from biomass harvesting, but there are few results for other forest types, woodlands, or shrublands. Alternative residue management, site preparation, and transportation design and maintenance techniques could mitigate or negate the forest floor and forest soil carbon losses associated with harvesting. The potential loss of certain size classes of live trees, snags, and downed wood from wildfires, other disturbances, or biomass harvests could have negative effects on wildlife habitats and biodiversity. Current predictive tools have limited capability in measuring the impacts of operations other than commercial harvests. Fires, both natural and planned, are also a major source of potentially avoidable carbon dioxide and methane emissions but field based results are limited. Key information gaps could be reduced by implementing and evaluating long-term experimental wildlife habitat and forest productivity projects across a greater range of forest types - especially where treatments and wildfires interact.