Abstract Background Semi-arid shrublands in Mediterranean type ecosystems are increasingly vulnerable to altered fire regimes, with some sites recovering to native shrub dominance while others undergo vegetation type conversion by invasive herbaceous species. Many factors could influence post-fire vegetation recovery in the years immediately following fire, including the identity of initially colonizing species, climate (e.g. drought), and herbivore-induced mortality. The relative importance of these factors, and how they interact to influence vegetation recovery, is unknown. Methods This study investigated coastal sage shrub recovery following a 2021 wildfire; pre-fire the site was dominated by evergreen shrubs, with almost complete loss of vegetation during the fire. The experiment manipulated rainfall (with drought shelters) and mammalian herbivory (with exclosures), in adjacent sites that experienced differing fire severity (severe, moderate, and unburned). Results Plots with high burn severity had higher shrub seedling establishment and survival, lower initial invasive cover, and greater recovery of evergreen shrub cover (70%) after four years than plots that experienced a moderate burn (which achieved 25% evergreen shrub cover after four years). Structural equation modeling found evidence for both direct and indirect effects of fire severity on shrub recovery: moderate fire severity increased post-fire invasive cover which suppressed shrub recruitment. This finding highlights the importance of both burn severity and post-fire competition for determining the trajectory of post-fire vegetation recovery in semi-arid shrubland ecosystems. Mammalian herbivory significantly suppressed seedling recruitment and survival regardless of burn severity. By 2024, survival in moderate burn exclosures was about eight times higher than in open plots and doubled in severe burn plots. Drought treatments did not significantly affect shrub cover, recruitment, or survival, despite significantly reducing soil moisture. Conclusions Altogether, our results suggest that high severity fires can promote faster shrub recovery than moderate fires, but only if seedlings do not experience intense herbivory. Our findings further reveal the importance of integrated management strategies that address prescribed fire, herbivory, and invasive species to enhance vegetation recovery in fire-prone shrublands.
Smith et al. (Thu,) studied this question.