Pollen analytical study of late-Holocene sediments from Trans-Yamuna segment of Western Doon valley of Northwest Himalaya
Keywords:Pollen analysis, Palaeofloristics, Late-Holocene, Sirmuri Tal, Western Doon valley
A trench across a Quaternary fault in a berm was dug out at Sirmuri Tal in the Trans- Yamuna segment of Western Doon valley in Himachal Pradesh. Pollen analytical investigation of 4.90 m deep trench profile from Sirmuri Tal has shown that between 2800 to l800 years BP, mixed open vegetation comprising chiefly grasses, sedges, Cheno/Am, Artemisia and Ranunculaceae together with sparsely distributed trees viz., Emblica officinalis, Shorea robusta, Holoptelea, Mallotus, Grewia, Meliaceae, etc. grew in the region under dry climatic regime. The lake did exist, but it was small in dimension as indicated by the meagre presence of aquatic taxa such as Typha and Potamogeton. Subsequently, between 1800 to 400 years BP, mixed deciduous forests were established as reflected by the improvement in Emblica officinalis, Mallows, Grewia, etc. as well as invasion of Terminalia, Adina cordifolia, Acacia and Syzygium in the region. The overall increased diversity in the forest floristics signifies that the moist climatic condition prevailed in the region during this period. Lake became wider in expanse as implied by the improved frequencies of Potamogeton and Typha and first encounter of Dinoflagellate cysts in good number. Since 400 years BP and onwards, the climate deteriorated as evidenced from the decline in the vegetation cover. The lake transformed into a swamp as evidenced by the increase in sedges and Chen/Am and a simultaneous decline in aquatic vegetation. The excessively high frequencies of Pinus pollen denote its transportation by wind and water from nearby subtropical belt where chirpine forests occur luxuriantly.