Impacts of forest biomass removal on water yield across the United States
Water is essential to all forms of life on earth and is a powerful, integrated indicator of environmental health and ecosystem sustainability (Asbjornsen et al. 2015). In some areas of the United States, water availability and water quality are declining as a result of urbanization, climate change, and increased water demand for agricul- tural irrigation, power generation, and domestic water use (Sun et al. 2008). Forest hydrological studies across the United States and around the world in the past century (Vose et al. 2011) show that forests greatly influence water quantity and quality. Forests play an important role in regulating the quantity, quality, and timing of water yield from watersheds—and, thus, in maintaining the ecosystems that depend on water (Edwards, Williard, and Schoonover 2015). It is estimated that over half of the water supply from the United States is provided by domestic forestlands (Brown, Hobbins, and Ramirez 2008; Sun, Caldwell, and McNulty 2015); therefore, forest management—such as reforestation/afforestation, tree harvesting, stand thinning, and other forest management practices—can influence watershed water yield (i.e., outflow from a drainage basin) by altering the terrestrial hydrological cycle. This cycle involves precipitation, evapotranspiration (ET), infiltration, soil moisture dynamics, and streamflow (Sun, Caldwell, and McNulty 2015; Stednick 1996; Christopher, Schoenholtz, and Nettles 2015). For example, deforestation generally elevates total streamflow and peak flow rates due to the reduction of ET caused by the removal of forest canopies (Brown et al. 2013), decrease in soil infiltration capacity as a result of soil compaction (Bruijnzeel 2004), and forest road construction (Edwards and Williard 2010). In contrast, afforestation or reforestation generally decreases watershed water yield because ET increases as a result of in- crease in water use by trees that have greater biomass both above- and belowground than vegetation in previous land uses (Sun et al. 2010; Brown et al. 2005).
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