Reconstructing human-fire-vegetation inter-relationships in a protected dry tropical forest, Mudumalai National Park, southern India

Tropical dry forests are recognized globally as the first frontier of human land-use change, due to multiple factors that make them amenable to human occupation, especially with the use of fire. However, in southern India, biodiversity ‘hotspots’ with human habitation are not uncommon with a long-term co-existence of humans in pristine environments. This points to the need for more accurate evidence-based (using charcoal, pollen, phytoliths) understanding of if, when and how land use and land cover changes impact regional vegetation-fire relationships. We reconstruct the environmental history for Mudumalai National Park, a fire-prone dry forest with >30% of the park subject to annual fires and a west-to-east rainfall-vegetation gradient. We examined a 150 cm sediment profile from an excavation in a seasonal wetland in the wettest part. The record spans 1200 years in time (bracketing radiocarbon dates) with very low macrocharcoal counts (mean - 4), with highest numbers in the surface and near-surface layers. Molecular fire proxies Polycyclic Aromatic Hydrocarbons (PAHs) were also found present - Phenanthrene (Phe), Anthracene (Ant), Fluoranthene (Fl), Pyrene (Py), Benzo[ghi]fluoranthene (Bghi), Benz[a]anthracene (BaA), Chrysene (Chr), Benzo(b)fluoranthene (BbF), Benzo(k)fluoranthene (BkF), Benzo[e]pyrene (BeP), Benzo[a]pyrene (BaP), and Perylene (Pry). Notably, Fl, Py, Bghi, BbF, BaA,and BeP constituted 90% of the total concentrations. Diagnostic ratios of PAHs for source determination pointed at a pyrogenic source consistently across all samples. Paleovegetation proxies n-alkanes (C14-C33) were analyzed and the average chain length (ACL) showed a transition towards higher chain lengths towards the surface indicating a change towards grass sources (C31, C33) in addition to woody biomass-derived compounds (C27, C29). Further analysis to characterize the human-fire-vegetation relationships is underway and to our knowledge, as the first report from a protected forest in India, our study offers critical insights for forest fire management in forested landscapes.