Climate change and its impact on tropical montane ecosystems in southern India

The montane regions (>2000 m MSL) of the Western Ghats in southern India feature stunted evergreen forests (C3 plant type) interspersed with extensive grasslands (C3 or C4 plant types). We have studied the vegetational history of this ecosystem in relation to climate change during the late Quaternary through stable-carbon isotope analysis of peat deposits as indicators of C3 or C4 plant types. Grasslands (of C4 type) were predominant during the last glacial maximum (20-18 kyr sp) and again during 6-3.5 kyr sp, while forest and possibly C3 grassland expanded during the deglaciation, attaining their peak distribution at 10 kyr sp. The shift in C3 and C4 plant types seems related to changes in moisture and atmospheric CO2, with lower moisture and CO2 levels favouring the latter plant types. The oscillating climate and vegetation has influenced the structure and composition of the montane ecosystem. Plant diversity of the near-pristine montane forests is relatively lower than other comparable sites in the neotropics. The implications of global change on the tropical montane ecosystem, in particular the composition of the angiosperm and vertebrate communities, are discussed. In particular, an expansion of montane forest and replacement of C4 with C3 grassland can be expected. Human impact on the natural vegetation, such as conversion of grasslands to monoculture plantations of wattle and eucalypts may, however, interfere with natural succession caused by global climate change. Endemic mammals such as the Nilgiri tahr would face increased risk of extinction.