Wind direction dominates the transport and deposition of fire proxies in tropical dry forest landscapes of the Western Ghats

Abstract

Few studies have looked at transportation and deposition of fire proxies in an active wildfire in tropical forests. We opportunistically sampled surface sediments from two wetlands a week after a wildfire in the contiguous dry tropical forests of Bandipur and Mudumalai National Parks, Western Ghats, southern India. The wetlands sampled were roughly located between the largest and the second-largest burnt areas. We looked at common fire proxies – macrocharcoal, microcharcoal, microcharcoal/pollen (C/P) ratio and the abundance and distribution of Polycyclic Aromatic Hydrocarbons (PAHs). Macrocharcoal counts per gram of dry sample were low (mean ∼5), while the C/P ratio was ∼1. PAHs were found in both sites with significantly different compositions, one site was dominated by Low Molecular Weight (LMW) PAHs and the other by HMW PAHs. Watershed and climatology analysis were done to constrain potential rework of legacy proxies. Analysis of wind speed and direction and HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model trajectories show that some of the smoke plume from the smaller burnt area passed through our sampling locations and left behind modest traces of the fire. We conclude that wind direction and wet deposition are essential factors determining the transport and deposition of fire proxies in this environment. Hence, multi-site data must be used for an accurate reconstruction of fire histories to account for false absences of peaks in fire proxies.