Concepts about forests and water

Abstract

Six concepts concerning forests, forestry, and water resources are discussed: (1) the role of the forest canopy in erosion control; (2) the impact of disturbance on soils; (3) the variability of natural water quality; (4) the impact of harvesting on water quality; (5) the role of extreme experiments; and (6) the effectiveness of forestry best management practices (BMP). The literature shows that the forest floor, not the canopy, protects soils from erosion. Harvesting can be conducted in ways that limit compaction and essentially confine overland flow to areas of exposed mineral soil on roads, trails, and log landings. Overland flow from these areas can be controlled and converted to subsurface flow before it reaches streams and lakes. Thus, effects to watershed hydrology are small. Undisturbed watersheds tend to have better quality water than highly disturbed watersheds, but the undisturbed character of a catchment does not assure high-quality water. Undisturbed forests vary greatly in sediment and chemical exports that are controlled by variables such as streamflow, soils, geology, air pollution, and land use history. Conversely, timber harvesting does not necessarily have measurable or biologically meaningful negative effects on water quality. Forestry BMP have proven effective in controlling adverse changes to in-stream sediment and water chemistry. Many studies that have reported large changes in water quality often represent extreme treatments not associated with typical forest operations, or they have not employed BMP. Properly and adequately used forestry BMP protect watershed resources while allowing the removal of wood products. Copyright © 2006 by the Society of American Foresters.