Herbivory and fire influence soil and plant nutrient dynamics in Chitwan National Park, Nepal

Abstract

In the context of global biodiversity loss and climate change, understanding how herbivores and fire shape plant-soil nutrient dynamics across vegetation types has become a global priority. In tropical Asia, the combined effects of herbivore assemblages, fire regimes, and plant community diversity on nutrients remain poorly understood. We investigated how herbivory and fire influence soil nutrients (nitrogen (N), phosphorus (P), potassium (K), and cation exchange capacity (CEC)) and plant nutrients (N, P, K), across five vegetation types - two forests (riverine, Shorea) and three grasslands (tall, short, grazing lawn) in Chitwan National Park, Nepal. Across 50 plots (400 m² each), we quantified mammalian herbivory pressure using dung counts, fire frequency using satellite data, and analyzed 150 soil and 187 plant samples for nutrient concentrations. Herbivore dung and fire frequency varied markedly across habitats: herbivores were largely absent from tall grasslands while present in all other vegetation types, whereas fires were rare in short grassland and grazing lawns but frequent in tall grassland and forests. Overall, forests had higher soil and plant nutrient concentrations than grasslands. Soil N, K, and CEC increased with increasing dung counts across vegetation types, whereas plant K decreased with increasing dung counts only in Shorea forests and grazing lawns. Soil P and CEC increased, while plant N, P and K decreased with increasing fire frequency across vegetation types. For the two forest types, interactions between dung and fire counts decreased soil P, plant N and plant P in riverine forest but had no effect in Shorea forest. These findings highlight the additive and interactive impacts of herbivory and fire on nutrient cycling, emphasizing the need to manage disturbance regimes to sustain soil fertility, habitat quality, and biodiversity resilience in tropical landscapes.