Citation:Pillai AAS, Anoop A, Sankaran M, Sanyal P, Jha DK and Ratnam J (2017) AbstractTropical grasslands and savannas are globally extensive, and are of significant environmental, economic, and ecological importance. These ecosystems are anticipated to be particularly sensitive to future changes in climate, and understanding how these systems have responded to climatic changes in the past can provide us with insights into their potential responses to future global change. In this study, the temporal dynamics of C3-C4 vegetation changes in response to changes in moisture availability, local fire events and changing levels of herbivory in a summer-rainfall region of Western India are reconstructed for the past ~4600 cal yr BP. Paleodata such as stable carbon isotope of bulk organic matter ( 13 Corg), oxygen isotope from carbonate shells ( 18 Oshell), macro-charcoal and herbivore dung fungal spores are reported from the retrieved cores of two wetland sites located in the Banni grasslands of Western India. Results show that vegetation in the Banni was composed mostly of C3 vegetation from ~4600 to ~2500 cal yr BP, after which there was a decline in C3vegetation. From the late-Holocene to the present, there was a mix of both C3 and C4 vegetation, with C4 grasses being more abundant in the ecosystem. These shifts were coincident with rainfall changes from more mesic conditions during ~4600 to ~2500 cal yr BP to more arid conditions towards the present as indicated by 18 Oshell isotope data. The period of increase in C4 vegetation also coincides with a period of increased biotic disturbances in the ecosystem, particularly fire. Given the current scenarios of global warming, recurrent drought events and increased anthropogenic use of similar ecosystems, such studies can provide us insights into potential future trajectories of these ecosystems.3

Tropical semi-arid grasslands are a widespread and ecologically and economically important terrestrial biome. Here, we use paleoecology to understand woodland-grassland transitions across the mid-to-late Holocene period in the Banni grassland, western India. Multi proxy analyses involving palynology, phytoliths and elemental geochemistry were carried out on two sediment cores retrieved from wetlands (Chachi and Luna), to understand temporal fluctuations in vegetation, moisture availability and other environmental parameters. Based on the results, the Chachi core was divided in to two major climatic phases. Phase 1 (4600-2500 cal yr BP) was characterized by high precipitation and abundance of pollen types and phytolith morphotypes that indicate the presence of woody savanna, and mesic herbaceous taxa. Phase 2 (2500 cal yr BP to the present) was characterized by lower precipitation, lower abundance of mesic taxa and an increase in grass phytolith abundance. However, the period from ~1000 cal yr BP to the present was characterised by the increased abundance of leguminous taxa, dryland herbs/shrubs and a decline in grass phytolith abundance. The Luna core (~1000 cal yr BP to the present) also showed results matching with the Chachi core for this latter period. Overall, moisture availability in the ecosystem appears to have declined since 4600 cal yr BP, and the vegetation has responded to this. Although the balance between tree, shrub and grass elements has fluctuated, overall, the region has remained as an open 'grass and shrub savanna' with sparse woody vegetation throughout this period. Our study 3 provides insights into the vegetation dynamics and environmental settings in a poorly understood tropical arid-grassland ecosystem from Asia during the mid-late Holocene.