Does burning history affect drought response in a South African mesic grassland?

Abstract Background and aims Since climate change increases drought frequency and intensity, an understanding of grassland responses to a combination of fire and drought may aid in predicting future changes in plant communities. The study evaluated the response of a mesic grassland plant community, under different long-term prescribed burning regimes, to a drought event. Methods The study was conducted at Ukulinga Research Farm, Pietermaritzburg, South Africa. Following a 2-year drought, where rainfall fell below 600 mm, a long-term (~70 years) experiment comprising three burning frequencies was resurveyed using the same sampling procedure and site selection by Kirkman, et al. (2014) after their initial annual surveys from 2005–2010. Species composition was compared among the unburned, annual and triennial burn treatments. Results The findings showed that the burning regime influenced species composition, but the plant community remained largely unaffected pre and post drought. Annual burn had a higher species diversity and richness, followed by triennial burn while the unburned area presented the lowest. Fire exclusion led to the dominance of forbs, and unpalatable grasses, while annual burning promoted palatable grass abundance, and the three-year burning interval remained with a high forb dominance. Conclusion The grassland plant community exhibited limited compositional change following the short-term drought event, whereas long-term burning regimes had a significant influence on species diversity and composition. Annual burning maintained a species-rich community dominated by palatable grasses, while fire exclusion promoted forb and woody species encroachment. These findings suggest that long-term fire management exerts a stronger influence on mesic grassland composition than the short-term drought evaluated in this study. Hence frequently burned grasslands may be more adapted to withstand the impacts of drought, since frequent fires promote a diverse, species-rich grassland.