TEMPERATURES ARE RISING and forest fires, already larger and more frequent than the historical norm, are projected to increase dramatically with anthropogenic warming.

That’s the general consensus among scientists studying the relationship between fire activity and climate change in the Sierra Nevada. But a study released last week found an influence on past fire activity even greater than climate: human beings.

Since 1600, the way humans have used land in the Sierra has had more effect on fire behavior than climate change, said Valerie Trouet, associate professor of dendrochronology at the University of Arizona and lead coauthor of the study, published November 14 by the Proceedings of the National Academy of Sciences.

This conclusion has profound implications for the future, when higher temperatures are predicted to intensify fire activity in California. Average annual temperatures in the western United States have already risen by 1.9F (1.1C) since 1970. With every increase of 1.8F (1C), the area burned annually in the Sierra Nevada is projected to increase by as much as 300 percent, according to research by the Union of Concerned Scientists.

The study about humans and fire, coauthored by Alan H. Taylor of Penn State, suggests that land managers and owners can affect fire behavior through activities that make forests more resilient.

“By changing land use, we can at least buffer some of the effects of climate change,” Trouet said.

The most useful tool to do that is fire itself, said Craig Thomas, conservation director for Sierra Forest Legacy, a coalition focused on Sierra Nevada national forest issues. Using controlled fires to burn ground litter and small trees breaks the fuel continuity from the surface to the crowns of trees, where fire is more difficult to control.

“If we take the advice of this paper, we are going to build a real fire program with crews dedicated to lighting managed fires across many different land ownerships,” said Thomas, cochair of a statewide multiparty partnership dedicated to increasing the use of fire to benefit natural resources.

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