Differential impact of fire on tree diversity, composition, structure and carbon stock in tropical savanna

Tropical savannas are characterized as a stable and fire-dependent biome, in which recurrent fire is a prominent feature. Fire frequency stands out as one of the most influential parameters in the savanna fire regime. In Asia, savannas are often misclassified as derived or degraded forests, India is no exception. Due to its patchy distribution, longstanding confusion over the vegetation type, little scientific attention was paid to the ecological and compositional aspects of savanna concerning fire frequency. Understanding the tree community dynamics concerning fire frequency has immense potential, particularly in the Indian context. This study was conducted in the savanna ecosystem of Sathyamangalam Tiger Reserve (STR), Western Ghats, to understand the long-term response of trees to fire frequency. A fire frequency map of the savanna spanning 33 years (from 1990 to 2022) was generated from Landsat satellite imagery. As per fire frequency, the composite map was stratified into fifteen different fire frequency classes (F0-F14). Furthermore, stratified random sampling was done to examine tree parameters. Parameters such as tree density, diversity, species richness, and basal area exhibited significant differences across fire frequency groups. Conversely, tree above-ground biomass and carbon stock showed non-significant changes concerning fire frequency. Species composition, visualized through non-metric multidimensional scaling, revealed two distinct clusters between unburned and high-fire frequency groups. Additionally, fire frequency significantly impacted the regeneration process, with the highest proportion of species in the moderate fire frequency group exhibiting good and fair regeneration, compared to the lowest proportion in the unburned group. The exhibited structural and compositional changes in tree communities in the savanna ecosystem of STR underscored the impacts of fire frequency on biodiversity conservation and call for holistic management of forest fires.