Large Variation in Stand-Scale Sustainability of Forest Biomass Harvesting in Central New Hampshire

Matthew A. Vadeboncoeur, Steven P. Hamburg, Ruth D. Yanai, Joel D. Blum, Erik A. Hobbie

Forest management in the northeastern US might intensify over the next few decades due to increased demand for bioenergy. If forests are to continue regenerating, the large amounts of N, P, Ca, Mg, and K removed from the ecosystem by whole-tree harvesting must be replaced by atmospheric inputs, the depletion of plant-available nutrients stocks in the rooting zone, weathering of primary minerals, or fertilizer inputs. We conducted an analysis to determine the number of harvest rotations required to exhaust the available soil stocks of N, P, Ca, Mg, and K in the soil across the region under various harvesting and nutrient availability scenarios. We based our analysis on quantitative soil pit data from 14 northern hardwood stands across the White Mountain region of New Hampshire. At current levels of N deposition, all modeled rotations (30-year whole-tree harvest, and 100-year stem-only and whole-tree harvests) would be sustainable in terms of N. Calcium limitation was encountered after 1-4 rotations under the 100-year whole-tree harvest scenario, and after 2-10 rotations in the 100-year stem-only scenario. However, the ability of ectomycorrhizal fungi to weather the primary mineral apatite may offer an escape from Ca and P limitation. Regenerating forests in the region already show some signs of P limitation and increased apatite weathering rates. All stands were located on granitic till, but variations soil depth and in parent material mineralogy drive a fivefold difference in available Ca, and a tenfold difference in weatherable Ca.

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