Fire suppression in many dry forest types has left a legacy of dense stands, closed canopies, and homogeneous landscapes. These landscapes have high water demands and fuel loads, and when burned can result in catastrophically large fires - undesirable characteristics considering the warming and drying trends projected for the Western US. Alternative forest and fire treatments based on managed wildfire - a regime in which fires are allowed to burn naturally, and only suppressed under defined management conditions - offer a potential strategy to ameliorate the effects of fire suppression. Understanding the long-term effects of this strategy on vegetation, water and forest resilience is increasingly important as the use of managed wildfire becomes more widely accepted. The Illilouette Creek Basin in Yosemite National Park has experienced 40 years of managed wildfire, reducing forest cover by 22%, and increasing meadow areas by 200% and shrublands by 24%. Upscaling of over 3000 soil moisture observations made since 2013 suggests that large increases in wetness occurred in sites where fire caused transitions from forests to dense meadows. The runoff ratio (ratio of annual runoff to precipitation) from the basin appears to be increasing or stable since 1973, compared to declines in runoff ratio for nearby, unburned watersheds. Hydrologic processes associated with snow deposition and melt, and summer water losses through evaporation, appear to be significantly different within closely located vegetation types. Managed wildfire appears to increase landscape and hydrologic heterogeneity, and likely improves resilience to disturbances such as fire and drought, although more detailed analysis of fire effects on basin-scale hydrology is needed.
Professor Sally Thompson is Assistant Professor of Surface Hydrology at UC Berkeley. Her undergraduate training was in Chemistry and in Environmental Engineering, at the University of Western Australia, in Perth Australia. Following completion of her bachelor degree, Sally worked for several years as an environmental engineering consultant in Western Australia. She was awarded a General Sir John Monash Award, Australia's equivalent to a Rhodes or Fulbright scholarship, which supported her PhD research in ecohydrology at the Nicholas School of the Environment at Duke University. Following postdoctoral research split between Princeton, Purdue and at Duke, she took up her current position at UC Berkeley. Sally has won the American Geophysical Union's Hydrology Early Career Award, the NSF CAREER award, and the Jim Dooge Award from the European Geophysical Union. Her research tackles the interface of life with the hydrologic cycle, aiming to understand the implications of biological functioning on hydrological processes spanning the scales of leaf stomata to regional land use change.