South and southeast Brazilian grasslands during Late Quaternary times: a synthesis

Abstract

Fourteen pollen records from the south (S) and the southeast (SE) Brazilian regions have been synthesised. Late Glacial records from S Brazilian highlands document the predominance of grassland (campos) where today Araucaria forests occur. Records from SE Brazil show that during pre- and full-glacial times modern tropical semideciduous forest and cerrado (savanna to dry forest) were mostly replaced by grassland and some subtropical gallery forest. Modern montane Araucaria forests and cloud forests in SE Brazil were mostly replaced by grassland during pre- and full-glacial times. There is evidence that the modern tropical Atlantic rainforest in S Brazil was significantly reduced and replaced by cold-adapted forest taxa or grassland during glacial, especially during full-glacial times. The synthesis indicates that grasslands dominated the S and SE Brazilian landscape during the Late Pleistocene where today different forest ecosystems exist. Grassland extended over 750 km from S to SE Brazil from latitudes of about 28°/27° S to at least 20° S. These results indicate that climates in the region were markedly drier and 5–7°C cooler during glacial times. Antarctic cold fronts must have been much stronger and more frequent than today. Studies from S Brazil show that huge areas of Late Pleistocene campos vegetation were still found on the S Brazilian highlands during early and mid Holocene times, reflecting dry climatic conditions with an annual dry period of probably 3 months. Modern wet climatic conditions with no or only short dry periods were not established until the Late Holocene period when Araucaria forests replaced large areas of grassland vegetation after about 3000 ¹⁴C yr B.P. and especially after 1500/1000 ¹⁴C yr B.P.

Introduction

The history of grassland ecosystems in South America, including Late Quaternary grassland distribution, its composition and biodiversity, and the role of fire and human impact has, to date, received little attention. Yet, spatial and temporal variations of subtropical and tropical grassland biomes, shifts of grassland/forest boundaries and changes in the composition of grassland vegetation are an important tool for reconstructing past climate changes. Knowledge of palaeograssland distribution may help to improve models of past vegetation and climate in subtropical and tropical regions.

A review of the Late Quaternary history of tropical South American savannas north and south of the Amazon is published in Behling and Hooghiemstra (2001). The results show that during the full-glacial period, savannas both north and south of the equator expanded, reflecting markedly drier conditions. The Amazon rainforest area must have been reduced. In both hemispheres, climate started to become wetter during the Late Glacial period. During the early Holocene period (until ca. 6000–5000 ¹⁴C yr B.P.) the distribution of savanna was much larger than during Late Holocene periods, documenting drier climatic conditions than during the Late Glacial and Late Holocene periods. The general synchrony of vegetational and climatic changes since the full-glacial, from savanna sites north and south of the equator, suggest that changes in the latitudinal migration of the inter-tropical convergence zone may have played an important role.

This paper provides a continued synthesis of the history of South American grasslands by reviewing the available pollen analytical studies from south (S) and southeast (SE) Brazil.