For example, a forest floor strewn with lupine and violets—typically found in places like Northern California and Canada—may be replaced with flowers and shrubs more often seen in drier southern climates, such as manzanita and monkey flower.
“The plants we’re finding underneath our forests are becoming more like those seen in Mexico and Southern California,” said lead author Jens Stevens, a postdoctoral scholar with the John Muir Institute of the Environment at the University of California–Davis.
“Under climate change, we’re seeing species from drier, warmer areas increasingly taking over. It’s a long process, but forest disturbance, be it thinning or wildfire, has the potential to hasten those shifts.”
Open and Closed Canopies
Pockets of cooler microclimates remain in forests that were thinned before a wildfire occurred. These forests burned less hot and therefore left some tree canopy, allowing for both northern and southern plant species to coexist.
“A balance of open, intermediate, and closed canopy across the landscape is good,” Stevens said. “If you can increase microclimates, you can increase diversity.”
The study, published in the Journal of Ecology, 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 the Angora Fire in 2007 and the American River Complex fires that burned northeast of Sacramento in 2008.
Study co-authors include Andrew Latimer of the plant sciences department and Susan Harrison of the environmental science and policy department, both at University of California–Davis, and and Hugh Safford of the USDA Forest Service Pacific Southwest Region.
The USDA Forest Service Pacific Southwest Region, California Energy Commission, and the USDA National Institute of Food and Agriculture funded the work.