Integrating Biodiversity Metrics in Life-Cycle Analysis of Intensive Biomass Production in North American Forests: Challenges and Considerations

Energy policy in the United States and Canada has increasingly promoted developing plant-based biofuels to complement, and potentially provide alternatives to, fossil fuels.  This has resulted in more interest in intensive biomass production to meet anticipated growth in demand.  Native grasses, woody species, and forestry residues currently show promise as a local energy source for wood products facilities and for producing marketable biofuels.  Large scale adoption of intensive biomass production in forests, however, has potential to alter management, species composition, physical structure, and landscape configuration of forests in some regions of North America.  Because forest lands support a large proportion of biodiversity in many regions, it is important to understand how biodiversity may respond to practices associated with biomass production systems and what additional information is needed by forest managers and policymakers.  Additionally, it has been argued by many that it is necessary to examine the full life cycle of biomass-derived fuels to understand implications of their production and use using a comprehensive set of environmental indicators, including land use and biodiversity.  Existing Life Cycle Analysis (LCA) studies, however, often focus only on greenhouse gasses and energy. 

We use results of a review of documented relationships between intensive production of forest biomass and forest biodiversity in North America to highlight challenges and applications of biodiversity as an indicator for biomass harvesting systems within Life Cycle Impact Assessment (LCIA), one of the phases of LCA.  We searched the literature for papers that characterized biodiversity responses to at least one of four treatments related to biomass harvesting: removal of forest harvest residues (coarse woody debris [CWD] manipulations), thinning, intercropping and short-rotation woody crops.  Three levels of biodiversity (ecosystem, species, and genetic diversity) have been considered in LCIA approaches, but only information on species diversity offers enough depth or rigor to provide inference.  Biodiversity responses from reviewed literature included species richness, diversity, abundance of taxa or groups of species (guilds) and abundance of individual species for birds, mammals, reptiles, amphibians, and invertebrates.  We used meta-analyses to summarize biodiversity response to the four biomass harvest treatments.

We found a wealth of literature reporting effect on birds, small mammals and invertebrates. Few studies were found investigating response of amphibians and reptiles to biomass removal. We found that removal of snags and CWD may have more significance for birds than for other taxa.  A decrease in abundance of invertebrates in CWD or snag removal plots is a possible mechanistic explanation for the reported lower bird abundance and diversity.  Forest thinning treatments had generally positive effects on diversity and abundance across all taxa.  We found biodiversity response to biomass harvest at least somewhat dependent on harvest intensity.  More research is needed to determine effects of short rotation woody crops, intercropping, fine woody debris removal and geographic variability.  Our review highlights the need for manipulative experiments designed to test biomass removal hypotheses.

Existing literature confirms that biodiversity response to biomass production is complex, influenced by site-specific factors temporal and spatial scale of analyses, taxa being considered, and other factors.  Challenges for biodiversity assessment within the LCA framework for biomass harvesting include those inherent to the multi-dimensional complexity of biodiversity itself and several complications related to the non-linear responses of biodiversity to biomass harvesting.  Thus, generic LCAs that do not account for complexities such as these likely offer limited insight into actual implication of biomass production for biodiversity.