Climate exceeded human management as the dominant control of fire at the regional scale in California’s Sierra Nevada

Abstract

The societal impacts of recent, severe fires in California highlight the need to understand the long-term effectiveness of human fire management. The relative influences of local management and climate at centennial timescales are controversial and poorly understood. This is the case in California’s Sierra Nevada, an actively managed area with a rich history of Native American fire use. We analyzed charcoal preserved in lake sediments from Yosemite National Park and spanning the last 1400 years to reconstruct local and regional area burned. Warm and dry climates promoted burning at both local and regional scales. However, at local scales fire management by Native Americans before 850 and between ca. 1350 and 1600 CE and, subsequently, Yosemite park managers from ca. 1900 to 1970 CE, decoupled fire extent dictated by regional climate scenarios. Climate acts as a top-down, broader scale control of fire, but human management serves a bottom-up, local control. Regional area burned peaked during the Medieval Climate Anomaly and declined during the last millennium, as climate became cooler and wetter and Native American burning declined. This trend was accentuated by 20th century fire suppression policies, which led to a minimum in burned area relative to the last 1400 years. In light of projected anthropogenic greenhouse gas emissions and predicted climate changes in California, our data indicate that although active management can mitigate local fire activity, broader regional burning may become more spatially extensive than has been observed in the last century.