Climate change, wildfires in Tahoe forest impacting plant diversity, study reports | SierraSun.com

Climate change, wildfires in Tahoe forest impacting plant diversity, study reports

Josh Staab
jstaab@sierrasun.com
Researchers are finding that plants commonly found in drier, southwestern climates are replacing vegetation burned in Lake Tahoe-area wildfires.
Courtesy NASA Earth Observatory |

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TRUCKEE, Calif. — Researchers are finding further changes in Lake Tahoe’s forests, another result, they believe, of climate change.

As wildfires continue to burn in California, clearing brush and tree canopies in their wake, researchers are finding the plants replacing the burned vegetation have more in common with flora found in southern areas of the West.

The findings came as part of a study by the University of California, Davis, published in a June Journal of Ecology report.

Jens Stevens, lead author of the report and a postdoctoral scholar with the UC Davis John Muir Institute of Environment, said the plants being discovered in area forests are also part of the ecosystems in places like Mexico and Southern California.

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READ MORE: High-elevation fires are prompting change in Sierra Nevada forest management, a new study reports.

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In a process termed “thermophilization,” climate change is likely shifting plant communities toward species from warmer regions, Stevens said.

Canopy disturbances such as fire may hasten this process by increasing temperature and moisture stress on forest floors, yet little is known about the mechanisms that might drive such shifts, or the consequences of these processes for plant diversity.

The findings may not necessarily be a bad thing, Stevens said. It may just depend on one’s view of the role wildfires play in promoting biodiversity in areas long impacted by human footprints.

“Under climate change, we’re seeing species from drier, warmer areas increasingly taking over,” Stevens said. “It’s a long process, but forest disturbance, be it thinning or wildfire, has the potential to hasten those shifts.”

The findings report a forest floor that may have been home to lupine and violets — typically found in places like Northern California and Canada — may be replaced with flowers and shrubs like manzanita and monkey flower, often associated with southern, warmer climates.

You want diversity of forest structure, Stevens said, meaning regardless of how humans view a forest, a more diverse forest, by its natural order, begets more diversity.

“The consensus is certain forests in the Tahoe area would still be consistently getting fires before we started putting them out,” Stevens said.

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READ MORE: 36,000 Lake Tahoe-area trees are dead or dying as California’s drought persists.

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However, Stevens notes pockets of cooler microclimates remain in Tahoe’s forests that were thinned before a wildfire occurred.

These microclimates burned less hot, and therefore left some tree canopy, allowing for both northern and southern plant species to coexist.

It’s a tricky balance, Stevens said, but one that can promote biodiversity while continuing to keep forests thinned and free of unneeded fire fuels.

“In this case, it may be possible to have our cake and eat it too,” Stevens said. “You retain diversity in what you’re interested in across the landscape.”

The study examined 12 different mixed-conifer sites in California, stretching from Modoc to San Bernardino counties and encompassing several sites in the Sierra, including forests burned by South Lake Tahoe’s Angora Fire in 2007 and the American River Complex fires that burned northeast of Sacramento in 2008.

Stevens believes these types of wildfires can be used as a tool if, “we could get more comfortable with fires in April when the forests are less dry.”

“If we’re thinking about species moving on their own as climate changes, we can affect how that move changes,” Stevens said. “If you manage for a mixture of changes today, you can keep more species around for tomorrow.”