Vegetation vis-a-vis climate and glacial fluctuations of the Gangotri Glacier since the last 2000 years

摘要

Pollen analysis of a 1.25 m sediment profile from an outwash plain at Bhujbas (3800 m asl) near Gangotri Glacier has revealed the vegetational changes in relation to climatic and glacial fluctuations in the area during the past 2000 years. Around 2000 years BP, open Juniperus-Betula forest occupied the area vacated by the glacier, revealing comparatively cooler and moist climate than the one prevailing at present. Subsequent increase of local arboreal taxa (Juniperus, Betula, Salix) and extra local elements (mainly Pinus) around 1700 years BP, indicates further amelioration of climate, i.e. increase of both precipitation and temperature in this region. Around 850 years BP there is a shift in the vegetational pattern, with sharp increase in Ephedra and other steppe elements notably Artemisia and Asteraceae. This reflects a trend towards drier climatic conditions, which is also evidenced by a decrease in Ferns and Potamogeton. At the upper part of the diagram, i.e. during recent times, climate again reverted to warm and moist, and due to increase in temperature, resulting in the retreat of snout to higher elevations.