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2009 Harvard Forest REU Student Symposium Abstracts

Author:
Dunbar Carpenter - Smithsonian Conservation Biology Institute at the National Zoo

Title:
Biomass Energy and a Changing Forest Landscape: Modeling the Effects of Intensified Harvesting of Massachusetts' Forests for Biomass Energy Production

Abstract:

Climate change, residential development, and timber harvesting are likely to be the primary disturbance agents affecting the forests of Massachusetts in the coming decades. One source of uncertainty is the potential rise of a forest biomass energy industry and the ensuing increases in harvesting to meet demand for feedstock. Under Massachusetts’ Renewable Portfolio Standard, potential future demand for biomass electricity could be around 165 MW, which would require up to 2 million Mg of woody biomass annually. The purpose of this study is to assess the effect of such increased demand for wood on the forest landscape of western Massachusetts. A spatially explicit forest landscape simulation model (LANDIS-II) was used, incorporating individual species-age cohorts, biomass accumulation and decomposition, disturbances, and other ecosystem process. Three scenarios were developed: a baseline scenario projecting current trends in development and harvesting into the future, and two biomass energy scenarios in which harvesting increases stepwise in intensity and extent. The scenarios were run for 50 years and the species composition, aboveground living biomass, and harvested biomass of the resulting forest landscapes were compared.



Changes in species composition were slight, but present, under the biomass energy scenarios, with white pine and red oak increasing relative to the baseline scenario, and black birch, beech, and hemlock decreasing. Living aboveground biomass increased by 2.0%, from 225 to 229 Mg/ha under the baseline scenario, while decreasing to 207 Mg/ha (-7.9%) and 201 Mg/ha (-10.7%) in the two biomass scenarios. In all three scenarios, most of the change in biomass occurred in the first 20 years and then leveled off. The difference in standing biomass translates to a net carbon sequestration of 1.9Tg over 50 years under current trends, compared to a 7.3 and 9.9Tg of net emissions in the biomass energy scenarios. In spite of this, the amount of biomass feedstock harvested in the biomass future scenarios was only enough to generate 90 and 100 MW of power, well short of potential future demand. These results indicate that demand for biomass energy is likely to greatly increase the importance of harvesting as a disturbance on the forest landscape. Furthermore, pursuing a renewable energy policy that relies heavily on biomass power is likely to come at the cost of a diminished forest carbon sink.


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