Drakensberg, Cathedral Peak, Brotherton Experimental Warming

Fire is a key driver of biodiversity and ecosystem functioning in montane grasslands. However, rising temperatures linked to climate change present an escalating threat to these high-elevation systems. Despite the central role of fire, the extent to which it interacts with warming to shape biodiversity and ecosystem functioning remains poorly understood. To address this gap, we implemented an in-situ full-factorial warming experiment using open-top chambers (OTCs), nested within the long-term Brotherton fire-manipulation experiment in the Maloti-Drakensberg mountains of South Africa. Across these warming and fire treatments, we measured microclimate, plant biomass and species composition. Consistent with expectations of enhanced plant growth under elevated temperatures, we observed increased plant biomass in the warming treatments. In total, we recorded 35 grass and forb species in the experiment. Dissimilarity in composition was better explained by fire frequency than by warming. While OTC- based experimental warming significantly increased average macroclimatic air temperature by 0.6°C (± 0.07°C SE; p < 0.001), soil and surface temperature as well as soil moisture varied across combinations of fire frequency and warming treatments. We found diverse microclimatic (soil and surface temperature and soil moisture) responses to the interaction of fire and warming, showing that vegetation can act as a mediator between macro and microclimatic conditions. By contributing to a better understanding of how pyrodiversity influences microclimate, we offer initial insights to inform future fire management policy under a warming climate. While plant communities seem resistant to change from warming, there is an associated increase in phytomass with implications for fire severity. We suggest applying intermediate fire frequencies by fire managers as this could mitigate both soil moisture loss and extreme temperatures.