The last 50.000 years in the neotropics (Southern Brazil) : evolution of vegetation and climate

In the "Lagoa Campestre" (lake) of Salitre (19°S, 46°46'W, 970 m elev.), there are plant taxa belonging to many ecological groups that are encountered nowhere else at this latitude. Frequent incursions of polar advections causing cooling and humidity, a cool and foggy climate in the middle of the depression and warmer temperatures on the surrounding slopes help to maintain all these groups within a fairly restricted area. Late Pleistocene-Holocene climatic change has had a considerable impact on the flora and vegetation of Salitre. The pollen record of the 6 m deep core LC3 shows how cold forest trees such as #Araucaria angustifolia$ and #Drimys brasiliensis$, semi-deciduous forest, halophytic plants and peat bog started to develop on this site. The initial period, between c. 50,000 and 40,000 yr B.P., was an arid phase not recorded in any other neotropical lowland site. It was followed by a period of high moisture levels (40,000 to 27,000 yr B.P.) with a maximum estimated at c. 35,000 yr B.P. The Late Glacial maximum is missing because of a gap in sedimentation. Humidity gradually increased during the Late Pleistocene, between 16,000 and 11,000 yr B.P. The early Holocene, 9500 to 5000 yr B.P., is characterized by a more marked seasonal pattern and higher temperatures, reaching a maximum c. 5000 yr B.P. The spread of semi-deciduous forest between 4000 and 3000 yr B.P. attests to a return of humidity. Comparison with the Serra Negra section (19°S, 46°45'-46'W, 1170 m elev.) not far from Salitre confirms the high moisture rates recorded at c. 35-40,000 yr B.P. (although temperatures were cooler at the altitude of Serra Negra, as is attested by the presence of #Araucaria$ forest) and also confirms the strong impact of polar advections on the climate of Southeastern Brazil. (Résumé d'auteur