Climate change alters wildfire severity and return intervals. In the southeastern US, climate change coupled with urbanization is leading to increased occurrences of wildfires at the wildland-urban interface. Plant communities and associated soil microbiomes may be differentially sensitive to disturbances like fire and the degree of sensitivity may be moderated by their history with urbanization. We took advantage of a recent wildfire in the Great Smoky Mountains National Park (GSMNP) and surrounding urban area (Gatlinburg, TN) to examine how a pulse of fire disturbance interacted with a press of urbanization disturbance to affect plant and microbial communities and ecosystem processes. We measured plant and soil communities and soil biogeochemistry along a gradient of fire intensity in urban (Gatlinburg, TN) and natural (GSMNP) environments. We hypothesized that the diversity and composition of the herbaceous plant community, soil and root hyphal abundance, soil microbial community composition and activity, and microbial biomass would be more sensitive to fire in GSMNP compared to the urban environment because on-going urbanization disturbance would filter for disturbance-tolerant taxa. We expected the differential sensitivity to fire of the plant and microbial communities would have implications for soil carbon and nutrient pools.
Results/Conclusions
Two years after the fire, plant abundance (F = 1.38, P = 0.40) and richness (F = 0.26, P = 0.65) were similar in burned sites and unburned sites in urban and park environments, but composition varied with burn severity (R2 = 0.12, P < 0.001). Soil microbial communities experienced legacy effects of fire and these responses were buffered by their history with urbanization. Soil microbial biomass decreased with burn severity more in urban sites than park sites (F = 4.21, P = 0.02). Saprotrophic fungi were most abundant in moderately burned sites in urban and park settings (F = 4.63, P = 0.02). Root-symbiotic fungi had similar abundances in burned and unburned sites in park and urban settings (F = 1.41, P = 0.27). Root colonization of symbiotic fungi was highest in unburned park sites (F = 5.20, P = 0.02). Ecosystem parameters were not tightly linked to biological responses to fire. Soil dissolved organic carbon (DOC) was highest in urban moderately burned sites (F = 3.39, P = 0.04). In sum, biodiversity hotspots in the southeastern US are sensitive to multiple simultaneous disturbances that leave a legacy on plants, soil microorganisms, and entire ecosystems.