LB 32-270 - Variation in California fern microclimate in forest and chaparral ecosystems post-fire

Climate change is contributing to more severe and more frequent wildfires in California. While previous studies have documented post-fire recovery in redwood forests and chaparral shrublands, it is unknown how ferns are affected by wildfires in these ecosystems. Ferns typically thrive in the shady understory of trees or shrubs. However, fires temporarily reduce or remove the canopy cover of trees and shrubs, potentially increasing the temperature and water deficit experienced by understory ferns. We hypothesized that the post-fire microclimate of redwood and chaparral ferns would differ from the unburned control sites in each ecosystem. We compared fern microclimate at sites burned by the 2020 Dolan Fire (redwood) and the 2018 Woolsey Fire (chaparral) to nearby unburned control sites. In the redwood forest, we also compared burn sites in which the canopy burned fully, partially, or not at all. At each site, we assessed photosynthetically active radiation (PAR), temperature, and relative humidity. For both redwood and chaparral ecosystems, we found significant differences in PAR, air temperature, and relative humidity among sites (one-way ANOVA, p < 0.05). While burned sites typically experienced higher PAR, some variation among sites was not accounted for by burn status. Similarly, while we found differences in air temperature and relative humidity among sites, there were no clear patterns showing consistent differences among burned versus unburned sites. These findings suggest that ferns may be adapted to a greater range of microclimates than previously realized and may be minimally impacted by the post-fire microclimate. Further studies are needed to determine the long-term impact of fern survival and recruitment post-fire, especially with regards to the smaller gametophyte stage.