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Spatial heterogeneity of land cover response to climatic change in the Nilgiri highlands (Southern India) since the last glacial maximumUniversité de Poitiers, UMR 6532 HYDRASA, Bâtiment des Sciences Naturelles, 40 Avenue du Recteur Pineau, 86022 Poitiers, France, laurent.caner{at}univ-poitiers.fr
CIRAD, UPR Spatialisation, Maison de la Télédétection, 500 rue Jean-François Breton, TA 40/MTD 34398 Montpellier cedex 5, France
Department of Geography, Université Denis-Diderot Paris 7, CNRS UMR 8591, case courrier 7001, 2 Place Jussieu, 75251 Paris cedex 05, France
French Institute of Pondicherry, 11 Saint Louis Street, P.B. 33, Pondicherry 605 001, India
CIRAD, UPR Recyclage et risque, Avenue Agropolis, Montpellier F 34398, France
Fourteen hillslope soil profiles were sampled under natural vegetation (ie, grassland or forest) and plantations in the Nilgiri highlands, Southern India. Delta 13C ratios were measured at different depths and 14C ages determined for six profiles. In these highland soils where the turnover rate of organic matter is extremely low, the
Key Words: India • soil organic matter • carbon isotope ratios • Asian monsoon • land cover • late glacial maximum • Holocene • spatial heterogeneity • climatic change impacts
The Holocene, Vol. 17, No. 2,
195-205 (2007) |
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13C ratios of entire soil profiles have recorded signatures of past land cover. By correlating the data with results previously obtained from peat bogs and with knowledge concerning the history of human settlement, we distinguish three contrasting trajectories of palaeoenvironmental history and landscape change since the last glacial maximum. In the Central Nilgiris, between 18 and 10 ka BP, forest expansion occurred through the conjunction of a wetter climate (the maximum of southwest monsoon-related humidity occurring at c. 11 ka BP) and higher temperatures; since 10 ka BP, the reversal towards grassland vegetation is attributed to drier conditions. In the Western Nilgiris, where strong southwest monsoon winds permanently restrict forest patches to sheltered valley sites, steady but limited expansion of forest from 18 ka BP to the present is recorded and attributed to rising temperatures. The Southern and Eastern Nilgiris, where the northeast monsoon contributes 20% of the annual rainfall, are the less sensitive to fluctuations in the southwest monsoon. In these areas, rapid and extensive expansion of forest occurred mainly as a consequence of higher temperatures from 18 ka BP to the present. Massive deforestation by Badaga cultivators and Europeans planters followed after the sixteenth century AD.As a result, and in contrast with the Western Nilgiris where the land cover mosaic has remained remarkably stable in the last 18 ka BP, the current landscape differs sharply from the land cover pattern detected by the soil record.