Quantitative pollen-based reconstruction of the vegetation diversity in response to the late-Holocene climate change near Karwar, south-west coast of India

In low latitude regions, due to impact of abrupt climate change/human interference, significant changes in vegetation, particularly the destruction of the highly fragile mangrove ecosystem has been noticed in different tropical areas of the world. In this study, a sediment core collected from the Kali Estuary has been used to determine the vegetation distribution of the Western Ghats since the late Holocene. Pollen and magnetic susceptibility data have been used as proxies to achieve objectives of the study. There has been a dramatic decrease in mangroves, evergreen (tree taxa) and deciduous forest pollens and the abundance of herbaceous/savanna type grassland pollen over the past 3.5 ka. This is supported by the significant decrease of the low-frequency magnetic susceptibility (χlf) of the core reflecting the decrease in the summer monsoon rainfall. Therefore, the post-3.5 ka time period marks the beginning of the recolonization of vegetation. Rarefied diversity pattern plots were used to evaluate abundance and evenness in the pollen data as a result of the late-Holocene climate change. A significant increase in the diversity of herbaceous/savanna grassland taxa in the post-3.5 ka sequence of the core indicates the regional expansion of the agriculture in the Kali River basin. In contrast, the reduction in the taxonomic diversity of mangroves and arboreal taxa implies less-conducive environmental conditions for their growth, with further reduction due to anthropogenic interference. The magnetic susceptibility of the core measured at one cm interval indicates the general decrease in the intensity of the summer monsoon rainfall.