Wildfires in Sierra Nevada, Becoming Larger and More Severe

Recent Research Concludes That Forest Wildfires in Sierra Nevada and Southern Cascades are Becoming Larger and More Severe

VALLEJO, Calif., Oct. 27, 2008—Recent research published in October 2008 in the journal Ecosystems, “Quantitative evidence for increasing forest fire severity in the Sierra Nevada and southern Cascade Mountains, California and Nevada, USA,” has concluded that forest wildfires in a large area of California and western Nevada are not only getting larger and more frequent, but they are burning more severely.

A team led by U.S. Forest Service Regional Ecologist Hugh Safford and Remote Sensing Specialist Jay Miller found that low–and–middle–elevations forests in an approximately 50,000 km² area of California and western Nevada experienced a notable increase in the area of wildfire burning at “high severity” (i.e., at an intensity that leads to complete or nearly complete mortality of forest stands) between 1984 and 2006. The average size of high severity patches also increased by almost 100 percent over the same time period. Furthermore, mean and maximum fire size, and area burned annually have all risen substantially since the beginning of the 1980s, and are now at or above values from the decades preceding the 1940s, when fire suppression became national policy. All of these trends are occurring in concert with a regional rise in temperature and annual precipitation, but also in the face of massive and increasingly more expensive efforts to control wildfires. A close examination of the climate–fire relationship suggests that escalating fire size, burned area and severity are linked to changing climate, but another major factor appears to be increases in forest fuels, due to long-term fire suppression.

Before the arrival of Euroamericans, most low–and–middle–elevation forests in the Sierra Nevada were characterized by frequent, low to moderate severity fire. Although the number of acres that burn today are much less than during presettlement times due to fire suppression, fire behavior is becoming more extreme and ecosystem impacts are inevitable. Through their growing tendency to kill larger patches of canopy trees, contemporary fires are contributing to increasing levels of forest fragmentation. With continuing increases in the percentage of high severity fire and high severity patch size, post-fire erosion, stream sedimentation, nutrient cycling, carbon sequestration and natural forest regeneration processes will also be increasingly impacted, and human safety is also a rising concern.

For interviews with either Dr. Safford or Mr. Miller, please contact John Heil at (707) 562-9004.