California tree carnage: A decade of drought and fire killed a third of Sierra Nevada forests

Admirers of California’s Sierra Nevada mountains are familiar with the swaths of blackened trees flanking its sprawling green forest ranges. A new University of California, Berkeley study quantifies that devastation, finding nearly a third of southern Sierra conifer forests have died in the last decade.

California has seen devastating bouts of drought and record-breaking wildfire events in the last several years. From 2011-2020, a combination of fire, drought and drought-related bark beetle infestations killed 30% of forests in the Sierra Nevada mountain range between Lake Tahoe and Kern County, according to the analysis.

“It’s kind of a wake up call, even to those of us that are kind of steeped in this field,” said Zackary Steel, lead author of the study. “We’re moving from knowing this is a problem to quantifying the problem.”

On top of the overall decline in total conifer forest in the region, half of mature forest habitat and 85% of high-density mature forests were either wiped out entirely or became low-density forests.

The study also found areas protected as habitat for the California spotted owl, an endangered bird at the center of a historic battle between environmental activists and the timber industry, saw worse declines in tree canopy than non-protected areas.

That finding led the study’s authors to call for a rejection of traditional conservation methods that preserve forests as-is, before the loss of all mature forests in the Sierras. Using fire as a tool for landscape regeneration and removing low-lying vegetation can keep fires from becoming as devastating.

The research led by Steel analyzed a variety of Forest Service data on forest canopy, tree height and wildfire perimeters, and compared spotted owl protected area data gathered over nine years.

The Sierra Nevada region of California covers almost 27 million acres that provide habitat for thousands of wildlife species and is home to dozens of conifer species. Native redwoods are the world’s tallest trees, giant sequoias are the world’s widest, and the Great Basin bristlecone pine is the world’s longest-living tree.