Pollen evidence of vegetation succession, climatic changes and human impact in southern Madhya Pradesh during last ca 6,700 years

Abstract

Pollen records of a 2.0 m deep sediment profile from Barehata Tal portray the vegetation scenarios and contemporaneous climatic events of southern Madhya Pradesh prior to Mid–Holocene. Between 6,700 and 6,015 cal yr BP, the region supported open mixed tropical deciduous forests comprising sparingly distributed trees, viz. Moringa oleifera, Acacia, Trewia nudiflora, Madhuca indica, Terminalia and Aegle marmelos under a warm and less–humid climate than today. The record of Cerealia pollen from the beginning of the pollen sequence denotes the cereal–based arable crop economy in the region. The lake did exist, but it was of small expanse as depicted by the deficient aquatic element, Potamogeton. Around 6,015 to 4,848 cal yr BP, the enhancement in Acacia, Moringa oleifera, Trewia nudiflora, Madhuca indica coupled with moderate increase in Terminalia, Aegle marmelos, Holoptelea, etc. suggest the proliferation of mixed deciduous forests with the arrival of a warm very humid climate attributed to active SW monsoon. The agrarian activities also intensified with the initiation of favourable climatic condition as testified by the increase in Cerealia and cropland weeds. The lake turned bigger in stretch as documented by the improvement in Potamogeton and Typha along with sporadic appearance of Zygnema. The abrupt decline in the number as well as frequencies of the trees existing earlier implies that the forest became sparse around 4,848 to 3,671 cal yr BP with the onset of a warm and dry climate, most likely due to weak SW monsoon. Between 3,671 and 2,450 cal yr BP, the expansion forests took place with the substantial rise of Acacia, Madhuca indica and Holoptelea and re–incursion of Tectona grandis, Buchanania lanzan, Schleichera oleosa, Schrebera, Aegle marmelos, Grewia, etc. This diversification of the forests signifies the advent of a warm and moderately–humid climate. There was augmentation in the agricultural practice and other human activities as evidenced from the consistent encounter of Cerealia and culture pollen. The lake attained a wider spread as a result of increased monsoon precipitation. Around 2,450 to 1,230 cal yr BP, the forests declined, which is manifested by the depletion in the prominent ingredients, excepting Grewia, Schleichera oleosa, Tectona grandis and Aegle marmelos. This change in the vegetation scenario reflects the prevalence of a warm and less–humid climate again. However, from 1,230 cal yr BP onwards, the enrichment of forests elucidates that a warm and humid climate prevailed in response to increased monsoon precipitation.