The Influence of Fire Regimes on the Subtropical grasslands in Bardia National Park, Nepal
Summary
The open grasslands of Bardia National Park in Nepal are critical habitats for several endangered species, yet they are increasingly threatened by the encroachment of woody vegetation. This process reduces forage availability for large herbivores and compromises the prey base for species such as the Greater One-horned Rhinoceros, Asian Elephant, and Royal Bengal Tiger. These grasslands rely on disturbance to remain open, and fire has long served this role, but the effects of repeated burning on grassland structure and biodiversity remain understudied in the region.
This thesis investigates how fire regimes shape vegetation structure and species composition in Bardia’s subtropical grasslands. A Sentinel-2 burn-detection model was developed for the years 2016 to 2025, achieving 92 percent accuracy and a Cohen’s κ of 0.84 for early-season fires. Fifty 10 × 10 metre plots were sampled for vegetation data.
Fire mapping revealed clear spatial patterns. Fires were most frequent in accessible southern floodplain grasslands, where prescribed burns are regularly applied, and in drier northeastern Sal forest terraces, where fires tend to occur naturally later in the season. Moist riverine zones burned rarely. Vegetation structure showed consistent responses across the fire gradient: although canopy height and bulk density tended to decline with fire frequency, only NDVI increased significantly. Dried biomass remained stable, indicating that productivity recovers quickly after burning. Early-successional traits, particularly those of pioneer tall grasses, appeared to drive the increase in greenness. Species composition responded less strongly: Saccharum spontaneum was more common in frequently burned plots, while Narenga porphyrocoma dominated long-unburned areas. Shannon diversity increased linearly with fire frequency and recent burns, offering partial support for the Intermediate Disturbance Hypothesis.
The findings suggest that a fire regime with frequent and well-timed burns helps maintain the open structure of Bardia’s disturbance-climax grasslands. An adaptive approach where small-scale burning, cutting, and managed grazing is combined is likely the best management option for reversing the encroachment of trees and supporting grassland-dependent wildlife. However, these results are impacted by several limitations such as severe under-detection of late-season fires, a single-season sampling window, and limited samples. Nevertheless, the results highlight the importance of research to inform sustainable fire management under increasingly variable climatic conditions.