Grazing and Fire Effects on Community and Ecosystem Processes in a Tall-Grass Mesic Savanna Ecosystem in Southern India

Abstract

Grazing and fire are processes that are integral to savannas and grasslands worldwide. However, very few studies have evaluated the effects of fire and grazing on community and ecosystem processes in savannas and grasslands in the Indian context. Here, I report results from an experimental study that investigated the individual and interactive effects of grazing and fire on community and ecosystem level processes in mesic tall-grass savannas of the southern Western Ghats, India. Burning had no effect on species richness or composition of herbaceous plant communities in these grasslands, and within 2 years following burning vegetative cover in burnt plots was indistinguishable from unburned plots. Grazing treatments, on the other hand, significantly reduced the relative abundance of the dominant tall-grass species Cymbopogon flexuosus in plots, resulting in a concomitant increase in herbaceous plant species richness relative to unburned plots. At the ecosystem level, grazers did not enhance soil N availability and N turnover rates in this mesic tall-grass savanna, which is most likely a consequence of the low herbivore densities in the study area. Burning, on the other hand, resulted in greater soil N availability in plots at the start of the growing season, but such effects were short-lived and did not persist. Interestingly, greater soil N availability in burnt plots appeared to be a consequence of lowered N uptake by plants, associated with lower plant biomass in burned plots, rather than an increase in N mineralization rates in soils. Results from this study suggest that tall-grass communities dominated by C. flexuosus are quite stable with respect to perturbations by fire. However, grazers, when coupled with fire, have the potential to significantly enhance species richness and induce plant compositional shiftsCompostional shiftsin this mesic tall-grass savanna, particularly when grazing intensity is high.