Holocene vegetation, climate and human habitation in the Central Ganga Plain, based on pollen records from the lake deposits

摘要

The paper encompasses the Quaternary vegetation and climatic inferences drawn through the investigations onthree lakes, viz. Lahuradewa, Sant Kabir Nagar District; Basaha, Unnao District and Misa Tal, Lucknow District, alllocated close to settlements in the Central Ganga Plain. The pollen sequence from Lahuradcwa Lake has revealed thatbetween 10600 and 9250 yr BP, open vegetation largely comprising grasses, Cheno/Am, Artemisia, etc. together withscanty trees of Acgle marmelos, Holoptelea, Tenninalia,etc. grew in the region under a cool and dry climate. The recordof aquatic taxa indicates the existence of lake. Between 9250 and 6400 yr BP, with the amelioration of climate a few moretrees, viz. Bombax, Emblica officinalis, Syzygium, Lagerstrocmia, etc. also invaded the region. The increase in aquatictaxa implies that the lake turned wider owing to improved monsoon rain. The appearance of Cerealia pollen around 7000yr BP depicts the initiation of agricultural practices. During 6400 to 4050 yr BP, the much expansion of Bombax,Madhuca indica, Holoptelea, etc. suggests the establishment of forest groves with the further increase in monsoonprecipitation. The expansion of agricultural practices is reflected by steady presence of Cerealia and other culture pollen.Between 4050 and 1300 yr BP, the enrichment of forest groves denotes the further enhancement in monsoon rainfall.The more frequent record of culture pollen portrays the acceleration in agriculture. Since 1300 yr BP onwards, the climateturned dry as indicated by sparse presence of trees in the forest groves. However, the agricultural practices continued withsame intensity as before. The studies on two other lakes, viz. Basaha Jheel and Misa Tal in the region of Unnao and Lucknow, respectivelyhave deciphered the short-term climatic variability and vegetation in the much later phases during 3300 yr BP to present.At Basaha Jhecl, open vegetation dominated by grasses with sprinkled trees of Bauhinia, Ho/optcica, Sapotaccae, etc.occupied the region under a semi-humid climate around 3300 yr BP. The record of Cerealia and other culture pollen isindicative of moderate agricultural practices. During 3200 to 2800 yr BP, the climate changed to humid as inferred by theimprovement in the arboreals. Between 2800 and 2200 yr BP the decline in trees and culture pollen taxa suggests the onsetof dry climate and depletion in agricultural practices. From 2200 yr BP onwards, the further decline in trees and lack ofCerealia pollen imply the reduced precipitation and desertion of settlement by the inhabitants. Pollen data from Misa Tal has deduced the scanty vegetation indicative of low rainfall and the occupancy ofagriculture during 2000 to 1850 yr BP. This time is marked by the ruling of Kushanas. The rulings of Gupta, Turkic andMughal dynasties spanning from 1850 to 300 yr BP, are manifested by the climatic improvement and prosperity inagriculture as reflected by the rise of trees and aquatics as well as better representation of Cerealia and other culture pollentaxa. The British Period faced the decline in rainfall and agricultural prosperity.