Forests and Water Yield: A Synthesis of Recent Disturbance Effects on Streamflow and Snowpack in Western Coniferous Forests
Location
Logan Golf & Country Club, Logan, UT
Start Date
3-26-2019 5:00 PM
End Date
3-26-2019 7:00 PM
Description
In coniferous western forests, recent widespread tree mortality provided a testbed for the long-held theory that forest cover loss increases water yield. This paper synthesizes studies that quantified hydrologic response to recent disturbances, and reassesses the question: Does water yield increase after forest disturbance? We reviewed 66 studies of hydrologic responses to standing-replacing (severe wildfire and harvest) or non-stand replacing (drought, insects, and low-severity wildfire) disturbances. Hydrologic response to disturbance was highly variable. Various studies detected increases, no change, or even decreases in streamflow or snow accumulation. While loss of the overstory canopy leads to reduced sublimation of intercepted snow and reduced overstory transpiration, in some cases these reductions were offset by increased snowpack sublimation, increased transpiration by surviving vegetation, and increased soil evaporation. Unexpected decreases in snow accumulation or streamflow were observed most often in watersheds with high total and solar radiation and rapid growth of post-disturbance vegetation. Additionally, most studies characterized forest density and disturbance effects qualitatively, which hinders quantitative assessments of the linkage between forest disturbance and water resources. To increase our understanding of process-level responses, which determine the net effect of disturbance on water resources, requires improving our quantitative characterization of forests and disturbance. The response of post-disturbance streamflow and evapotranspiration depends on vegetation structure, climate, and topography, and new hypotheses continue to be formulated and tested in this rapidly evolving discipline.
Forests and Water Yield: A Synthesis of Recent Disturbance Effects on Streamflow and Snowpack in Western Coniferous Forests
Logan Golf & Country Club, Logan, UT
In coniferous western forests, recent widespread tree mortality provided a testbed for the long-held theory that forest cover loss increases water yield. This paper synthesizes studies that quantified hydrologic response to recent disturbances, and reassesses the question: Does water yield increase after forest disturbance? We reviewed 66 studies of hydrologic responses to standing-replacing (severe wildfire and harvest) or non-stand replacing (drought, insects, and low-severity wildfire) disturbances. Hydrologic response to disturbance was highly variable. Various studies detected increases, no change, or even decreases in streamflow or snow accumulation. While loss of the overstory canopy leads to reduced sublimation of intercepted snow and reduced overstory transpiration, in some cases these reductions were offset by increased snowpack sublimation, increased transpiration by surviving vegetation, and increased soil evaporation. Unexpected decreases in snow accumulation or streamflow were observed most often in watersheds with high total and solar radiation and rapid growth of post-disturbance vegetation. Additionally, most studies characterized forest density and disturbance effects qualitatively, which hinders quantitative assessments of the linkage between forest disturbance and water resources. To increase our understanding of process-level responses, which determine the net effect of disturbance on water resources, requires improving our quantitative characterization of forests and disturbance. The response of post-disturbance streamflow and evapotranspiration depends on vegetation structure, climate, and topography, and new hypotheses continue to be formulated and tested in this rapidly evolving discipline.