Fire suppression caused large changes in forests and a decline in biodiversity. We sought to understand past understory communities and their drivers in an arid mixed conifer forests with long restored fire regimes. This expansive and long-term study utilized natural experiments which were part of Wildland Fire Use program, including the Illilouette Basin in Yosemite National Park and Sugarloaf Valley in Kings Canyon National Park. The Wildland Fire Use areas began in the 1970s when the National Parks allowed lighting strike fires to burn and thus restoring fire regimes. These fires reduced fuels and performed other ecosystem restoration functions such as opening canopies which fostered the re-development of diverse forest understories. We tested how plant communities were influenced by a combination of environmental, plot-scale fire experience, and regional-scale fire experiences.
Results/Conclusions
Plant cover, Simpson diversity, and evenness were strongly influenced by canopy cover, an indirect measurement of mixed severity frequent fire. Plant cover was also influenced burn severity and number of times burnt, although to a lesser degree. Richness was increased by moisture, soil texture, and a diversity of regional-scale fire also called pyrodiversity - the diversity of fire size, severity, season, and frequency. Based on our study, we recommend an overall reduction of canopy cover to restore diverse understories and fine-scale forest structure difference created by the reintroduction of mixed severity fires.