CLIMATE-CHANGE AND ITS IMPACT ON TROPICAL MONTANE ECOSYSTEMS IN SOUTHERN INDIA

The montane regions (>2000 m MSL) of the Western Ghats in southern Ind ia feature stunted evergreen forests (C3 plant type) interspersed with extensive grasslands (C3 or C4 plant types). We have studied the vege tational history of this ecosystem in relation to climate change durin g the late Quaternary through stable-carbon isotope analysis of peat d eposits as indicators of C3 or C4 plant types. Grasslands (of C4 type) were predominant during the last glacial maximum (20-18 kyr sp) and a gain during 6-3.5 kyr sp, while forest and possibly C3 grassland expan ded during the deglaciation, attaining their peak distribution at 10 k yr sp. The shift in C3 and C4 plant types seems related to changes in moisture and atmospheric CO2, with lower moisture and CO2 levels favou ring the latter plant types. The oscillating climate and vegetation ha s influenced the structure and composition of the montane ecosystem. P lant diversity of the near-pristine montane forests is relatively lowe r than other comparable sites in the neotropics. The implications of g lobal change on the tropical montane ecosystem, in particular the comp osition of the angiosperm and vertebrate communities, are discussed. I n particular, an expansion of montane forest and replacement of C4 wit h C3 grassland can be expected. Human impact on the natural vegetation , such as conversion of grasslands to monoculture plantations of wattl e and eucalypts may, however, interfere with natural succession caused by global climate change. Endemic mammals such as the Nilgiri tahr wo uld face increased risk of extinction.