Mid-Holocene vegetation shifts and climate change in the temperate belt of Garhwal Himalaya

Abstract

Pollen analysis of 3.06 m deep sediment core from the temperate lake-Nachiketa Tal, has brought out the vegetation shifts and climatic oscillations in the temperate region of Garhwal Himalaya since Mid-Holocene. The pollen sequence depicts that between 5,304 and 3,912 yr BP the mixed conifer forests dominated by Pinus cf. wallichiana together with Cedrus and Abies occupied most of the landscape under a regime of a cold and dry climate. The record of pollen of aquatic element, Potomogeton and freshwater alga-Botryococcus implies the existence of the lake. The broad-leaved forests mainly constituted of oak (Quercus cf. semecarpifolia) occurred sparsely in the moist and shady situations. Between 3,912 and 2,975 yr BP the mixed conifer forests got transformed into mixed oak-broad-leaved forests as evidenced from the much expansion of Quercus and improvement of its close allies Alnus, Betula, Carpinus, Juglans, Salix, etc. This change in the vegetation pattern suggests that a warm and humid climate prevailed in the region. Around 2,975 to 1,872 yr BP the abrupt decline in Quercus and its broad-leaved associates and a corresponding spurt in Pinus cf. wallichiana reflect the re-establishment of pine dominated conifer forests with reversal of cool and dry climate. Subsequent expansion of Quercus and broad-leaved taxa around 1,872 to 767 yr BP and declining trend of conifers took place with the prevalence of warm and moderately humid climate. The sporadic encounter of Cerealia pollen during this phase indicates that the area was under cereal-based agricultural practice. Since 767 yr BP onwards a warm and less humid climate prevailed than before and consequently relatively less-diversified mixed broad-leaved oak forests continued to thrive in the region, with relatively reduced frequencies of Quercus and other thermophillous broad-leaved elements.