Late Quaternary vegetation, climate and fire history of the Araucaria forest and campos region from Serra Campos Gerais, ParanáState (South Brazil)

Abstract

New palynological and charcoal data from a bog (24°40′S, 50°13′W, 1200 m asl) of Serra Campos Gerais, northeastern ParanáState, allow a complete and detailed reconstruction of the late Quaternary vegetation and climate history of the South Brazilian highlands. The late-glacial period, which starts at 12,500 14C yr BP, indicates the predominance of a diverse grassland vegetation (campos) with scattered stands of Araucaria forest and Atlantic rain forest, probably growing in valley bottoms. This suggests 3 to 5°C colder and drier climates than at present. Judging from the absence of charcoal, fires must here been rare during late-glacial times. The early and mid-Holocene (until 2850 14C yr BP) is marked by a predominance of campos vegetation on the highlands and expansion of tropical rain forest trees in the valleys, indicating warm climates and perhaps an increase in annual precipitation compared to the late-glacial. A migration of Araucaria forest from the valleys onto the highlands did probably not occur. Seasonal drought is probably the major factor explaining the absence of an expansion of Araucaria forests on the southern Brazilian highlands in the early and mid-Holocene. Palaeofires were more frequent at the beginning of the Holocene, probably ignited by Amerindians at that time. First expansion in the valleys or an initial migration of Araucaria angustifolia from valleys into the Serra Campos Gerais highland occurred during the late Holocene (2850-1530 14C yr BP), indicating a wetter climate with a shorter dry season. Fires during this period had the highest frequency and may have influenced the migration of Araucaria into the campos areas. A marked expansion of Araucaria forest, forming a mosaic of grassland and Araucaria forest patches on the highlands, took place only in the last 1500 years. This suggests onset of a high precipitation climate without a strong annual dry season. Fires were also less frequent. Logging of Araucaria forests occurred during the last centuries.