Résumé
In the tropical Andes, impacts of both natural and anthropogenic disturbances have been detected over a period exceeding 4000 years. However, the history of the environment remains unknown in most Andean regions. To infer possible interactions between climate and humans, we analysed the pollen content of an 8.5 m deep peat core extracted from a peat bog located near the Nevado Coropuna volcano on the slope of the Western Cordillera in southern Peru (15 degrees 30S, 72 degrees 40W, 6380 m). Results showed that taxa of the upper Puna expanded when cooler and moister climatic conditions prevailed during a time period that includes the early and the mid Holocene (9700-5200 cal. yr BP). An increase in shrub pollen frequencies and a decrease in the Poaceae/Asteraceae ratio are attributed to a drier climate during the late Holocene (5200-3000 cal. yr BP). After 3000 cal. yr BP, the vegetation cover resembled that of today. Both archaeological and pollen data attest to the beginning of agriculture from 2200 cal. yr BP. Around 900 cal. yr BP, the vegetation cover suddenly changed, probably because of a colder and drier climate. Past societies continued their agricultural activities despite this abrupt change. Our results emphasize the specific geographical location of Nevado Coropuna astride the Western Cordillera and the western edge of the Altiplano, which is consequently subject to both Pacific and Atlantic influences.