Ecohydrological Implications of Drought for U.S. Forests

Thursday, 17 December 2015
Poster Hall (Moscone South)
James Matthew Vose, USDA Forest Service, Southern Research Station, Center for Integrated Forest Science, Raleigh, NC, United States, Chelcy Miniat, USDA Forest Service, Southern Research Station, Coweeta Hydrologic Laboratory, Otto, NC, United States, Charles Luce, USDA Forest Service, Boise, ID, United States, Heidi Asbjornsen, University of New Hampshire Main Campus, Durham, NH, United States, Peter V Caldwell, US Forest Service, Southern Research Station, Otto, NC, United States, John L Campbell, USDA Forest Service, Northern Research Station, Vallejo, CA, United States, Gordon Grant, Oregon State University, Corvallis, OR, United States, Dan Isaak, Rocky Mountain Research Station, Boise, ID, United States, Ge Sun, USDA Forest Svc, Eastern Forest Environmental Threat Assessment Center, Raleigh, NC, United States and Loheide II Steven, University of Wisconsin-Madison, Civil and Environmental Engineering, Madison, WI, United States
The relationships among drought, surface water flow, and groundwater recharge are not straightforward for most forest ecosystems due to the strong role that vegetation plays in the forest water balance. Hydrologic responses to drought can be either mitigated or exacerbated by forest vegetation depending upon vegetation water use and how drought affects forest population dynamics. Because different species and functional groups vary in their ecophysiological traits that influence water use patterns, changes in species assemblages can alter hydrological processes from the stand to the watershed scales. Recent warming trends and more prolonged and frequent droughts have accelerated the spread and intensity of insect attacks in the western US that kill nearly all of the canopy trees within forest stands, changing the energy balance of the land surface and affecting many hydrologic processes. In contrast, some eastern forest tree species and size classes can tolerate drought better than others, suggesting the potential for drought-mediated shifts in both species composition and structure. Drought-related shifts in species composition may impact streamflow; however, predicting how these changes will impact hydrologic processes at larger spatial scales presents a considerable challenge. The biogeochemical consequences of drought are closely linked to changes in vegetation and hydrology. For example, droughts can have a concentrating effect on solutes in stream water due to the limited volume of water. As with other natural disturbances, droughts are difficult to prepare for because they are unpredictable. However, there are management options that may be implemented to minimize the impacts of drought on water quantity and quality. Examples include reducing leaf area by thinning and regenerating cut forests with species that consume less water.