Abstract
AbstractThe long‐term greenhouse gas emissions implications of wood biomass (‘bioenergy’) harvests are highly uncertain yet of great significance for climate change mitigation and renewable energy policies. Particularly uncertain are the net carbon (C) effects of multiple harvests staggered spatially and temporally across landscapes where bioenergy is only one of many products. We used field data to formulate bioenergy harvest scenarios, applied them to 362 sites from the Forest Inventory and Analysis database, and projected growth and harvests over 160 years using the Forest Vegetation Simulator. We compared the net cumulative C fluxes, relative to a non‐bioenergy baseline, between scenarios when various proportions of the landscape are harvested for bioenergy: 0% (non‐bioenergy); 25% (BIO25); 50% (BIO50); or 100% (BIO100), with three levels of intensification. We accounted for C stored in aboveground forest pools and wood products, direct and indirect emissions from wood products and bioenergy, and avoided direct and indirect emissions from fossil fuels. At the end of the simulation period, although 82% of stands were projected to maintain net positive C benefit, net flux remained negative (i.e., net emissions) compared to non‐bioenergy harvests for the entire 160‐year simulation period. BIO25, BIO50, and BIO100 scenarios resulted in average annual emissions of 2.47, 5.02, and 9.83 Mg C ha−1, respectively. Using bioenergy for heating decreased the emissions relative to electricity generation as did removing additional slash from thinnings between regeneration harvests. However, all bioenergy scenarios resulted in increased net emissions compared to the non‐bioenergy harvests. Stands with high initial aboveground live biomass may have higher net emissions from bioenergy harvest. Silvicultural practices such as increasing rotation length and structural retention may result in lower C fluxes from bioenergy harvests. Finally, since passive management resulted in the greatest net C storage, we recommend designation of unharvested reserves to offset emissions from harvested stands.
Highlights
The temporal impacts of burning wood biomass for generating energy (‘bioenergy’) on long-term greenhouse gas emissions are uncertain (McKechnie et al, 2011), yet demand for wood bioenergy continues to increase in the United States and abroad (Buchholz et al, 2009)
The carbon (C) emitted from wood bioenergy may eventually be re-sequestered through regeneration and increased growth rates in residual trees, (Eriksson et al, 2007; Malmsheimer et al, 2008; Nunery & Keeton, 2010), there is uncertainty about the length of that recovery period and the potential for a C ‘dividend’ in the longterm with fossil fuel offsets
We sought to understand the effects of staggering bioenergy harvests, both spatially and temporally, on the net landscape C flux in the northeastern United States
Summary
The temporal impacts of burning wood biomass for generating energy (‘bioenergy’) on long-term greenhouse gas emissions are uncertain (McKechnie et al, 2011), yet demand for wood bioenergy continues to increase in the United States and abroad (Buchholz et al, 2009). We sought to understand the effects of staggering bioenergy harvests, both spatially and temporally, on the net landscape C flux in the northeastern United States. We define a ‘landscape’ as a collection of stands that are harvested using different silvicultural prescriptions and scheduled independently. This landscape is not spatially explicit, it serves as a. Amount of carbon intact in the forest stand (aboveground live tree, aboveground dead tree, coarse woody debris) and in wood products. These carbon stocks can be called pools. Carbon taken up by live trees through photosynthesis minus loss from respiration (Net Primary Productivity)
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