Managed Wildfire Effects on Forest Resilience and Water in the Sierra Nevada
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Fire suppression in many dry forest types has left a legacy of dense, homogeneous forests. Such landscapes have high water demands and fuel loads, and when burned can result in catastrophically large fires. These characteristics are undesirable in the face of projected warming and drying in 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%. Statistical upscaling of 3300 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. Managed wildfire appears to increase landscape 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.
Keywordsforest structure montane hydrology mixed conifer meadow wildfire resilience soil moisture fire ecology wildland fire use
The authors specially thank Kate Wilkin for her field expertise, and all of this project’s field crew members and volunteers: Miguel Naranjo, Andy Wong, Perth Silvers, Jeremy Balch, Seth Bergeson, Amanda Atkinson, Tom Bruton, Diane Taylor, Madeleine Jensen, Isabel Schroeter, Katy Abbott, Bryce King, Zubair Dar, Katherine Eve, Sally McConchie, Karen Klonsky, and Yves Boisramé. The vegetation maps were created by GIS technicians Julia Cavalli, Miguel Naranjo, and Melissa Ferriter, with guidance from Professor Maggi Kelly. We thank Jan van Wagtendonk and John Battles for discussions related to this project. Thanks to financial support from Joint Fire Science Grant # 14-1-06-22, Sigma Xi Grants in Aid of Research, the UC Berkeley SMART program, Hellman Fellows Program, and the UC Berkeley Philomathia Graduate Fellowship in Environmental Sciences. The authors thank Yosemite National Park for permitting us to conduct research in wilderness areas.
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