Indian Climate and Vegetation

An unresolved issue in the vegetation ecology of the Indian subcontinent is whether its savannas, characterized by relatively open formations of deciduous trees in C 4-grass dominated understories, are natural or anthropogenic. Historically, these ecosystems have widely been regarded as anthropogenic-derived, degraded descendants of deciduous forests. Despite recent work showing that modern savannas in the subcontinent fall within established bioclimatic envelopes of extant savannas elsewhere, the debate persists, at least in part because the regions where savannas occur also have a long history of human presence and habitat modification. Here we show for the first time, using multiple proxies for vegetation, climate and disturbances from high-resolution, well-dated lake sediments from Lonar Crater in peninsular India, that neither anthropogenic impact nor fire regime shifts, but monsoon weakening during the past ~ 6.0 kyr cal. BP, drove the expansion of savanna at the expense of forests in peninsular India. Our results provide unambiguous evidence for a climate-induced origin and spread of the modern savannas of peninsular India at around the mid-Holocene. We further propose that this savannization preceded and drove the introduction of agriculture and development of sedentism in this region, rather than vice-versa as has often been assumed. The savannas of peninsular India: natural or anthropogenic? Large tracts of peninsular India are characterized by savanna vegetation, with a continuous ground-layer, predominantly of C 4-grasses and a woody layer of broadleaf or fine-leafed deciduous C 3-trees 1,2. Although evidence for C 4-vegetation in India, possibly grasslands, dates back to the late Miocene 3 , two lines of evidence suggest that the today existing savannas of the subcontinent may be much younger: first, the savannas of India feature only very few tree species solely restricted to the savannas as may be expected for very old ecosystems; second, many tree species of the moist and wet forests show a clearly disjunct distribution between the moist Western Ghats of southern India and the Himalayas of North and East India, separated by extensive tracts of dry savanna vegetation 4,5. At present even though recent work establishes that modern savannas in India fall within the climatic envelopes for natural savannas elsewhere in the world 6 , it remains unresolved if the modern savannas of peninsular India are man-made, anthropogenic derivates of deciduous forests. Further, the relative extent to which their evolution has been influenced by Holocene climate fluctuations versus the emergence of agro-pastoralism and fire activity in this region remains debated. This debate has culminated in two contrasting hypotheses about the origin of these OPEN

An unresolved issue in the vegetation ecology of the Indian subcontinent is whether its savannas, characterized by relatively open formations of deciduous trees in C 4-grass dominated understories, are natural or anthropogenic. Historically, these ecosystems have widely been regarded as anthropogenic-derived, degraded descendants of deciduous forests. Despite recent work showing that modern savannas in the subcontinent fall within established bioclimatic envelopes of extant savannas elsewhere, the debate persists, at least in part because the regions where savannas occur also have a long history of human presence and habitat modification. Here we show for the first time, using multiple proxies for vegetation, climate and disturbances from high-resolution, well-dated lake sediments from Lonar Crater in peninsular India, that neither anthropogenic impact nor fire regime shifts, but monsoon weakening during the past ~ 6.0 kyr cal. BP, drove the expansion of savanna at the expense of fo...