Vegetation dynamics in response to climate change from the wetlands of Western Himalaya, India: Holocene Indian summer monsoon variability

摘要

India's agricultural output, economy and societal well-being are strappingly dependent on the stability of the southwest summer monsoon precipitation, its variability and extremes. Deviations in the Indian summer monsoon (ISM) precipitation may profoundly impact the agricultural productivity and gross domestic product (GDP) of the country. Understanding the spatiotemporal dynamics of the ISM precipitation during the Holocene is significant in many respects, particularly in terms of human development and establishment of centres of civilisations. Here, pollen records of the variability in ISM precipitation and their interpretation in terms of vegetation and climate change from two wetlands (Gharana and Nanga; Ramsar sites) of the Western Himalaya (India) is presented. The results suggest that between similar to 8536 and 5296 cal yr BP, mixed conifer/broad-leaved forests occurred in the Jammu region (Gharana Wetland sediment profile) under a cool and dry climate, probably indicating decreased monsoon precipitation. Subsequently, they were succeeded by mixed broad-leaved/conifer forests between similar to 5296 and 2776 cal yr BP under a warm and humid climate with increased monsoon precipitation, partly corresponding to the Holocene Climate Optimum (HCO). Between similar to 2776 and 1376 cal yr BP, with more expansion of broad-leaved forest elements in response to a warm and more humid climate the dense mixed broad-leaved/conifer forests came into existence in the region, indicating a further increase in monsoon precipitation. From similar to 1376 cal yr BP to present, the climate deteriorated, as manifested by the replacement of dense mixed broad-leaved/conifer forests by mixed conifer/broad-leaved forests in the region. The palaeoclimatic inferences drawn from the Nanga Wetland sediment profile of Samba District match with the Gharana Wetland sediment profile of Jammu District for the late-Holocene. This study provides insights into the vegetation dynamics, associated climate change and the ISM variability from the poorly understood wetland ecosystems of Southeast Asia during the Holocene.