Forest Soil Calcium Dynamics and Water Quality: Implications for Forest Management Planning

Forest management planning is increasingly focused at the landscape scale. The resulting increase in planning unit size has fueled debate about forest sustainability, particularly at local scales. In boreal and temperate regions, Ca depletion in forest and aquatic ecosystems is a recently debated issue. Planning decisions that sustain forest soil and surface water Ca require identification of sites sensitive to Ca loss and application of silvicultural prescriptions that maintain background Ca pools and fluxes. Therefore, I synthesized data on forest Ca cycling and export and long-term (>10 yr) soil exchangeable Ca pools and changes in surface water quality. Findings indicated that hardwood forest soils contained over three-times more (P < 0.05), their catchments exported three-times more (P < 0.05), and through leaf-litter fall they recycled twice (p < 0.01) as much Ca as conifer-mixedwood forests. Nonetheless, over similar timeframes, forest floor in mature hardwood stands lost more (P < 0.05) Ca than did conifer-mixedwood soils, which was consistent with net stream and lake Ca losses (P < 0.01). However, surface water acid neutralizing capacity increased (P < 0.01), possibly due to greater sulfate declines relative to Ca. On average, based on soil concentrations and contents, forestry practices did not significantly deplete Ca in either cover type. Study results indicate that stand-and catchment-scale forest Ca pools and fluxes can be used to identify areas potentially sensitive to Ca depletion and water quality degradation. However, considerable variation exists in Ca and acidification responses to external stressors, limiting spatial and temporal projections.