Research Opportunities in Hydrology and Biology in Future Watershed Studies

Abstract

The effects of timber harvesting practices on water resources are mostly known from paired watershed studies. The first paired watershed study in the United States was in Colorado and designed to assess the effects of timber harvesting on water yield (Bates and Henry 1928). Many of these studies were designed to have demonstrable effects on water resources, specifically the timber harvesting was large in comparison to the watershed area (up to 100%), streamside vegetation buffers were not used, all timber including non-merchantable materials were removed, or the forest regeneration was suppressed by herbicide applications. Although these experiments helped identify the hydrologic processes affected by timber harvesting, they do not necessarily represent the effects of normal forest operations. The scope of watershed studies was soon expanded beyond water quantity and the processes of the hydrologic cycle to include water quality. Measurements of inputs and outputs, as precipitation and streamflow, were used for chemical budgets. In the 1960s, 150 forested experimental watersheds were being studied; only 12 of these remain relatively active and half of those are long term ecological research sites (Ziemer and Ryan 2000). Many of the active research watersheds tend to focus on ecological processes in the watershed, rather than focus on hydrological processes as related to ecology. Nonetheless, several lessons learned from Alsea and other watershed studies (Stednick et al. 2004) are worth repeating. The original AlseaWatershed Study and the ongoing research have provided some very useful lessons in forest hydrology and the effects of timber harvesting on hydrological responses. Timber harvesting of a large area in a watershed (Needle Branch) resulted in increased annual water yield. These water yield increases are higher in wetter years and lower in wetter years. As vegetation grows and the hydrological processes of interception, transpiration, and storage