Temporal effects of fire and urbanization on plant species turnover at the wildland-urban interface

Mali M. Hubert, Ecology and Evolutionary Biology, The University of Tennessee, Knoxville, TN and Monica Papes, Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN

Background/Question/Methods
In recent decades, anthropogenic pressures have changed fire regimes nationwide thus increasing the size and severity of forest fires. In the urbanizing mesic forests of the southern Appalachian region of the United States, wildfires have been suppressed for the last 80 years, thus landscapes in this region may no longer be resilient to high severity fires that can arise from the accumulation of plant biomass. Due to the expanding fire niche and more frequent wildfires in the southern Appalachian region in recent years, managers need to understand the effects of severe wildfire on plant communities. Here, we investigated understory plant communities at 18 sites affected by the 2016 Chimney Tops 2 fire in Gatlinburg, Tennessee, and in the adjacent Great Smoky Mountains National Park. We studied recovery post wildfire and species turnover of plant communities within the wildland-urban interface. Our findings will contribute new insights into how pulse (fire) and press (urbanization) stressors may potentially interact to impact biodiversity under global change.
Results/Conclusions
Overall, community metrics showed consistent negative change from the 2018 to the 2019 sampling season. Within all fire severities (unburned, low/medium, high), we observed a compositional turnover and loss of species from 2019 compared to 2018. Communities in high burn areas were the least stable (CS = 1.843) among the fire severities. When assessing community stability of natural and exurban areas, natural communities were slightly more stable (CS = 2.583) than exurban ones (CS = 2.528). Differences in species composition across the two sampling years were not statistically significant, indicating that plant communities are homogenous within year, despite location (natural or exurban). Finally, α and β diversity measures revealed that low/medium burn areas had the greatest α diversity compared to the other burn severities in 2018, whereas unburned areas had the greatest α diversity in 2019. When parsing out β diversity, high burn exurban areas in 2018 had greater β-diversity (β = 4.319) compared to natural unburned areas (β = 3.650). Similarly, in 2019, high burn exurban areas still had greater β-diversity (β = 4.045) compared to natural unburned areas (β = 2.764). Beta diversity in high burn exurban areas remained relatively stable and slightly decreased in natural unburned areas. Results from this study can be used to improve predictions of plant species composition at sites that are influenced by fire events and recurring urban development.