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Palaeoclimate, palaeoecological and palaeoshoreline studies were carried out for a 2.5 in deep sediment core deposited since, similar to 3700 yrs BP in the central part of Pichavaram mangrove wetland, Cauvery river delta. Presently, the study area is dominated by Avicennia officinalis, A. marina and Suaeda sp. with fringes of Rhizophora sp. along the backwater channel. Based on sedimentology, palynological and thecamoebian analysis, it is inferred that since 2100 yrs BP the climate amelioration took place from warm and humid with strengthened monsoon to a dry and arid climate coupled with weakened monsoon condition inducing changes in ecology vulnerable for mangroves. Consequently, the vegetation too evolved from moist deciduous/evergreen forest to mixed deciduous forest and a reduction in mangrove diversity. The qualitative and quantitative study show a decline in the mangroves since the last millennium which may be attributed to the increased salinity along with enhanced anthropogenic activities in Pichavaram estuary. This is reflected by the dominance of salt tolerant mangrove associates since the last millennium.