Paleoenvironmental changes dating back to 30,000 yr B.P. documented in a pollen record from central Brazil (lat. 19°S) permit the reconstruction of climatic changes related to shifts of the Antarctic polar fronts. The paleoclimatic inferences were obtained by a study of modern vegetation and pollen distribution, taking into account present-day climatic parameters. At 30,000 yr B.P. the climate must have been warmer and moister than today judging from the high amount of tree pollen taxa characteristic of floodplain forest. From 17,000 to 14,000 yr B.P. the climate was drier although tree pollen percentages were relatively high. After 12,000 yr B.P.Araucariaforest elements increased, suggesting a moister and cooler climate. TheAraucariaforest disappeared during a short interval between 11,000 and 10,000 yr B.P. This could be related to the Younger Dryas event. At the beginning of the Holocene the climate became cool and moist again, as indicated by the reexpansion of theAraucariaforest. The latter was progressively replaced by a mesophytic semideciduous forest indicating warmer and drier climate after 8500 yr B.P. At 5000 yr B.P. an arid interval was followed by the expansion of mesophytic semideciduous forest elements.

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Aim The aim was to examine the links between past biome stability, vegetation dynamics and biodiversity patterns. Location South America. Time period Last 30,000 years. Major taxa studied Plants. Methods We classified South America into major biomes according to their dominant plant functional groups (grasses, trees and shrubs) and ran a random forest (RF) classification with data on current climate. We then fitted the algorithm to predict biome distributions for every 1,000 years back to 21,000 yr BP and estimated biome stability by counting how many times a change in climate was predicted to shift a grid cell from one biome to another. We compared our model‐based stability map with empirical estimates from selected pollen records covering the past 30 kyr in terms of vegetation shifts, changes in species composition and time‐lag of vegetation responses. Results We found a strong correlation between our habitat stability map and regional vegetation dynamics. Four scenarios emerged according to the way forest distribution shifted during a climate change. Each scenario related to specific regional features of biome stability and diversity, allowing us to formulate specific predictions on how taxonomic, genetic and functional components of biodiversity might be impacted by modern climate change. Main conclusions Our validated map of biome stability provides important baseline information for studying the impacts of past climate on biodiversity in South America. By focusing exclusively on climatic changes of manifested relevance (i.e., those resulting in significant habitat changes), it provides a novel perspective that complements previous datasets and allows scientists to explore new questions and hypotheses at the local, regional and continental scales.

A long terrestrial record, Colônia CO-3, from the Atlantic rainforest region in Brazil (23°52′S, 46°42′20 ʺW, 900 m a.s.l.) registrates variations in the forest expansion during the last 100,000 yr. The 780-cm depth core was analyzed at 2-cm intervals and arboreal pollen frequencies were compared to nearby speleothem stable isotope records and neighboring marine records from the tropical Atlantic. To evaluate regional versus global climate forcing, our record was compared with Greenland and Antarctic ice-core records. These comparisons suggest that changes in temperature seen in polar latitudes relate to moisture changes: e.g., to changes in the length of the dry season, in tropical and subtropical latitudes during glacial as well as interglacial times. These climatic changes result from changes in the frequency of polar air incursions to these latitudes inducing a permanent cloud cover and precipitation. This is an important result that should help define paleoclimatic features in the Southern Hemisphere for the last glaciation.