Mid-Holocene vegetation and climatic changes in southwestern Garo Hills,Meghalaya,northeast India based on pollen records

摘要

This paper presents a palynological observation on 180 cm deep sedimentary soil profile procured from the Kathali wetland of southwestern Garo Hills to reconstruct the palaeovegetation and climatic changes in the region. Three climatic phases have been recognized based on the major arboreal pollen taxa. In the first phase (4,620 to 1,030 cal yr BP), the tropical mixed deciduous forest was flourishing composed of Shorea robusta, Schima, Duabanga and Bombax under warm and humid climatic conditions. The presence of evergreen taxa, Elaeocarpus and Mesua, along with Nepenthes and Impatiens pollen, is strongly indicative of the high monsoonal activity in the region. The second phase (1,030 to 560 cal yr BP) was observed to be similar as the first phase with comparatively low values of arboreal taxa under relatively less warm and humid climatic condition. The debut of cereal pollen, along with the other cultural pollen taxa especially Brassica and Solanaceae, signals anthropogenic activities in this region. Lastly, in the third phase, around 560 cal yr BP to present, low values of arboreal taxa was noticed. The absence of Mesua and Nepenthes pollen in relation to the increased values of cereal and other cultural pollen in this phase suggests the deterioration of forest in relation to the expansion of anthropogenic activities in the region. The increased values of marshy taxa and decline in the frequencies of aquatic taxa were also observed, which indicates the comparatively poor water logged conditions in and around the study region.