A nutrient budget for a selection harvest: implications for long-term sustainability.

摘要

Declining concentrations of Ca and other base cations in soils and surface waters in eastern North America have led to concerns that forests may become nutrient limited, particularly in regions that are harvested. We constructed a nutrient budget for a selection harvest in central Ontario that is typical of eastern North America. Atmospheric deposition (5-year average) and mineral weathering (PROFILE) were considered as the sole inputs to the forest, while exports included nutrient losses in streams and removed in stems. Sugar maple (Acer saccharum Marsh.) was the only tree species removed in the study (~30% of basal area) and harvesting had no strong impact on stream chemistry. Mass balance calculations were performed on average values, but with estimates of uncertainty associated with each input parameter. A Monte Carlo simulation was run (10000 runs) for Ca, Mg, K, Na, P, N, and S. In the absence of harvesting, average mass balance estimates are positive for all nutrients except S. When harvesting is considered, average mass balances remain positive for all nutrients except Ca, K, and S. Monte Carlo simulations demonstrate that mass balances for Na are always positive, while mass balances for Mg, K, N, P, and S range from slightly positive to slightly negative. In contrast, mass balance simulations for Ca are always negative and average net losses represent 1% of the current exchangeable soil Ca pool.