title: Socioecological transitions trigger fire regime shifts and modulate fire-climate interactions in the Sierra Nevada, USA, 1600-2015 CE.
abstract: Large wildfires in California cause significant socioecological impacts, and half of the federal funds for fire suppression are spent each year in California. Future fire activity is projected to increase with climate change, but predictions are uncertain because humans can modulate or even override climatic effects on fire activity. Here we test the hypothesis that changes in socioecological systems from the Native American to the current period drove shifts in fire activity and modulated fire-climate relationships in the Sierra Nevada. We developed a 415-y record (1600-2015 CE) of fire activity by merging a tree-ring-based record of Sierra Nevada fire history with a 20th-century record based on annual area burned. Large shifts in the fire record corresponded with socioecological change, and not climate change, and socioecological conditions amplified and buffered fire response to climate. Fire activity was highest and fire-climate relationships were strongest after Native American depopulation-following mission establishment (ca. 1775 CE)-reduced the self-limiting effect of Native American burns on fire spread. With the Gold Rush and Euro-American settlement (ca. 1865 CE), fire activity declined, and the strong multidecadal relationship between temperature and fire decayed and then disappeared after implementation of fire suppression (ca. 1904 CE). The amplification and buffering of fire-climate relationships by humans underscores the need for parameterizing thresholds of human- vs. climate-driven fire activity to improve the skill and value of fire-climate models for addressing the increasing fire risk in California.
authors.affiliation: Department of Geography and Earth and Environmental Systems Institute, The Pennsylvania State University, University Park, PA 16802; aht1@psu.edu trouet@email.arizona.edu.
authors.forename: Alan H
authors.initials: AH
authors.lastname: Taylor
authors.affiliation: Laboratory of Tree-Ring Research, University of Arizona, Tucson AZ 85721; aht1@psu.edu trouet@email.arizona.edu.
authors.forename: Valerie
authors.initials: V
authors.lastname: Trouet
authors.affiliation: Pacific Southwest Research Station, United States Department of Agriculture Forest Service, Redding, CA 96002.
authors.forename: Carl N
authors.initials: CN
authors.lastname: Skinner
authors.affiliation: Department of Environmental Science, Policy, and Management, University of California, Berkeley, CA 94720.
authors.forename: Scott
authors.initials: S
authors.lastname: Stephens
keywords: anthropogenic landscapes; climate variability; fire ecology; land use; regime shifts