Global changes in climate and land use are altering fire regimes worldwide, causing dramatic shifts in fire frequency. The effect of changes in fire frequencies on ecosystem carbon and nutrient cycling is controversial, however, because resilience varies across ecosystems. Here, we seek to characterize the variability in resilience by focusing on the responses of both plants and soils, which are intrinsically linked. We test the hypothesis that the resilience of both ecosystem components is coupled, such that greater losses of plant biomass lead to greater losses of soil carbon, and that higher soil nutrient availability can buffer against fire-driven losses of biomass. We will present data from several long-term fire frequency manipulation experiments where both the plant communities and soils were sampled to evaluate mechanisms conferring resilience.
Results/Conclusions
We found surprisingly high resilience in woody plant biomass at several sites, where the turnover in tree species composition buffered against fire-driven biomass losses. Furthermore, losses of soil carbon were variable, and in some cases accompanied by compensatory responses such as the physicochemical and biological stabilization of organic matter. Finally, variability in underlying soil nitrogen across sites was not always a good predictor of cross-site changes in tree biomass, potentially because of the colonization of tree species with conservative nutrient use strategies in frequently burned plots that were able to maintain growth despite low nitrogen conditions. We will discuss other factors such as climate and phylogeny as contributors to cross-site variability in the resilience of ecosystems to changing fire frequencies.