Resilience of an ancient tropical forest landscape to 7500 years of environmental change

There is growing recognition that the fate of the world's terrestrial biodiversity depends on the management of human-dominated tropical forest landscapes. While global environmental change is transforming the ecology of tropical forests, a number of studies have also demonstrated that tropical forests are able to recover following disturbance. But are tropical forests resilient to environmental and anthropogenic disturbances over timescales of centuries or millennia? Here we examine the relationship between vegetation cover and variation in monsoon rainfall, soil erosion, and fire over 7500. years in an ancient tropical landscape in the Western Ghats of India. We collected two overlapping sediment sequences at one study site and analysed them with palaeoecological techniques to reconstruct vegetation cover. Results suggest that climate and land-use changes might have had synergistic effects on this forested landscape, although the relationship between these factors and vegetation cover has varied over time. Results also indicate that the weakening of monsoon around 5750 BP might have caused a threshold event altering this landscape to a low tree-cover state. Although anthropogenic fire has maintained this landscape in low tree cover state from 3500 BP, this degraded tree-grassland mosaic has remained relatively resilient to fluctuations in environmental and anthropogenic factors. Tree taxa present throughout the sequence have lighter seeds than those absent in parts of the sequence, suggesting that dispersal mode might be an important factor in their persistence. Despite maintaining a degraded and fragmented forest mosaic, however, this landscape has supported populations of heavy-seeded trees and a probable refuge to their dispersal agents. We suggest that retaining tree cover on this landscape, even if fragmented, is key to maintaining its ecological resilience to environmental and anthropogenic disturbance.