A study by UC Berkeley professors demonstrates how natural wildfires in multiple national park basins benefit the surrounding ecology.

The study, which began in 2002, focuses specifically on the Illilouette Creek basin in Yosemite National Park and Sequoia and Kings Canyon National Parks’ Sugarloaf Creek basin. It explores how policies allowing lightning-ignited fires have shaped the landscape in the past half-century, according to campus postdoctoral researcher Zack Steel.

Steel said the goal of these policies is to restore fire regimes — natural burning cycles that prevent catastrophic fires in the long term.

“Historically there were frequent fire systems burning with low severity every 15 years or so, clearing out brush and small trees and leaving larger trees intact,” Steel said. “Before European colonization, there was a lot of fire, and the systems were used to it. One way to think about it is that if you burn these areas at low severity, you avoid catastrophic burns.”

During the managed wildfire period, the basins experienced a significant decrease in forest cover, particularly the Illilouette Creek basin, which saw a 20% reduction, according to the study. Steel said this reduction in forest cover provides room for growth and enriched biodiversity, creating a “mosaic” of habitat types.

Co-author Brandon Collins said that during the investigation, researchers observed large patches of trees being killed. Collins noted that this is not “terribly unnatural,” as the environment has adapted to those conditions and a strong regeneration will come in its wake.

He added that in some areas, flushes of wildflower growth were observed, which invites populations of pollinators.

“A lot of us that grew up in California have gotten used to these forested landscapes,” Steel said. “When folks go into a lot of these places that have seen fire, there are dead trees and logs on the ground. It’s not this contiguous forest we expect to see; there’s an aesthetic we are not used to. It’s really that messiness that is part of how these ecosystems have functioned historically.”

Restoration of fire regimes also increased water and moisture in these watersheds where more openings in forest canopies allowed precipitation to reach soil more efficiently. The basin saw a 30% increase in soil moisture with an increase in the basin’s streamflow, according to the study.

Collins said approaches to reforestation need rethinking because current approaches focus on maximizing density, which diminishes space for shrubs and breaks in canopy cover. He added that while this maximization seems like the “right thing,” it is incorrect from a fire perspective.

“Continued support at the highest levels of government, as well as from the public, would be needed to maintain existing managed wildfire programs and expand them to others forested areas,” the study reads. “Were fire to be removed from managed fire areas, woody cover and water use would again increase, diminishing the positive impacts of these programs.”