Late Pleistocene palaeoclimate based on vegetation of the Eastern Himalayan foothills in the Indo-Burma Range, India

The Eastern Himalayan foothills constitute an important part of the Indo-Burma hotspot due to their richness in biodiversity and representative nature for the region. This contribution enhances the data bank on the variation in rich floral diversity from northeast India. Here, we present the first palynological report for the region on palaeovegetation and past climate variations as reflected in the Subankhata swamp of Assam. This is an attempt to show the affinity of the vegetation records of this swamp with Indo-Burma flora based on the remarkable similarity in the trend of vegetation changes over a time period of about 27,000 yrs. The studied palynoassemblage reflects six different vegetational and climatic phases (S-I to S-VI) since the Late Pleistocene. The first phase (S-I) comprises compact organic clay with a little silt. During this phase, a vast lowland savanna forest existed in a cool and dry climate regime similar to what was observed during the Ice Age. Later, during the S-II phase, the forest initially continued with little alteration in tree taxa under a relatively less cool and dry climate. Thereafter, the establishment of forest occurred under the influence of moderate monsoons that led to the onset of a warm and humid climate during the S-III phase which mainly comprises organic clay with silt. During the span of the S-IV phase, vegetation consisting of Dipterocarpaceae, Mesua ferrea, Elaeocarpus and Syzygium are found, indicating warm and humid climatic conditions with high rainfall. The clearance of forest by humans has also been noted in this period. Subsequently, during the S-V zone, the beginning of a gradual decline in arboreals suggests an acceleration in forest clearance, possibly due to human activities as the climate turned warm and less humid. Entering the S-VI zone (probably Late Holocene), a drastic decline occurred in major tree elements, implying relatively dry climatic conditions indicating weakened monsoonal activity. The trend in our findings shows a clear affinity of these variations in the region with the whole Indo-Burma range since the Late Pleistocene.