No abstract

The European conquest of the New World produced major socio-environmental reorganization in the Americas, but for many specific regions and ecosystems, we still do not understand how these changes occurred within a broader temporal framework. In this paper, we reconstruct the long-term environmental and vegetation changes experienced by high-altitude wetlands of the southcentral Andes over the last two millennia. Pollen and charcoal analyses of a 5.5-m-long core recovered from the semi-arid puna of northern Chile indicate that while climatic drivers influenced vegetation turnaround, human land use and management strategies significantly affected long-term changes. Our results indicate that the puna vegetation mostly dominated by grasslands and some peatland taxa stabilized during the late Holocene, xerophytic shrubs expanded during extremely dry events, and peatland vegetation persisted in relation to landscape-scale management strategies by Andean pastoralist societies. Environmental changes produced during the post-conquest period included the introduction of exotic taxa, such as clovers, associated with the translocation of exotic herding animals (sheep, cattle, and donkeys) and a deterioration in the management of highland wetlands.

Changes in climate conditions during the Holocene are documented in different parts of South America, showing contrasting responses to global changes. This study was conducted in the wet puna at an elevation of 4040 m a.s.l. on the eastern side of the Cordillera Real in Bolivia near Lake Titicaca. Pollen, charcoal, and stable isotopes in a sediment core collected in the peatland of Escalerani were analyzed. Results revealed environmental changes during the past 7500 yr BP, with an increase in wet climate conditions from 5900 to 4700 cal. yr BP and 3500 to 1300 cal. yr BP, and two dry periods between 4700 and 3500 cal. yr BP and 1300 to 560 cal. yr BP. Changes in hydrological conditions ranged from local changes because of glacier melting to regional changes in annual rainfall variability, related to South American monsoon activity. Moreover, our results highlight the importance of cloud convective activity from the Amazon basin along the adiabatic gradient, which maintained moist conditions at high elevations even during the mid-Holocene dry phase. The last 70 years have been characterized by the degradation of the peatland because of human activity.

Our study is located in northern Beni and aims to improve knowledge on regional landscape changes from the last 8600 years, based on pollen and charcoal analyses from a lacustrine sediment core from Lake Ginebra. Our results showed that gallery forest and lacustrine sediment were observed from 8645 until 3360 cal yr BP. After a change from a lacustrine to a swamp environment at 1700 cal yr BP, the Cerrados and the Mauritia swamp became installed 1000 years ago on our study site. The environmental changes we observed over the last 8600 years in the Ginebra record reinforce the evidence of a west–east climatic gradient with the persistence of rain forest throughout the Holocene on the western side and the presence of the Cerrados until the late Holocene on the eastern side. Moreover, the persistence of a wet forest in the early to mid-Holocene in southwestern Amazonia highlighted some local responses to the global trend that could be related to the distance from the Andes; while in the late Holocene, both an increase in insolation and strengthening of the South American summer monsoon system enabled the installation of a seasonal flooded savanna in northern Beni and of the rain forest in eastern Beni.