Predicting Differences in Forest Stand Nutrient Uptake and Removal: Potential Effects of Increased Biomass Removals for Energy On Long-Term Site Sustainability.

Increases in fossil fuel prices have generated great interest in the use of forest biomass as a source of energy.  In Maine, where forestry is a large component of the state’s economy, the shift to increased utilization of forest biomass raises questions about the long-term sustainability of forests.  We parameterized the model REMSS for balsam fir to assess whether increases in forest biomass utilization over current levels could reduce long-term productivity.  The REMSS model was parameterized with regional balsam fir data from the primary literature.  Balsam fir monocultures of varying site indices at age 50 were generated and grown forward in the Northeast Variant of the Forest Vegetation Simulator (NE-FVS) to use as input data to REMSS.  REMSS was run for each of four simulated silvicultural regimes:  unmanaged, pre-commercial thinning only, commercial thinning only, and pre-commercial thinning followed by commercial thinning.   Cumulative nutrient removal predicted by REMSS for each of these regimes were compared to empirical data in the literature and found to be similar.  To assess the potential effects of increases in biomass removal to support bioenergy interests, an increase factor of 25% over the pre-commercial thinning/commercial thinning scenario model output was applied.  The project is currently assessing nutrient cycling data for relevant forest types to compare with modeled output in order to determine if there are nutrient limitations of concern.  More research into forest stand dynamics on a case by case basis is necessary to minimize reductions in site sustainability with increased removals of biomass.