Vegetation, climate and fire dynamics of Upper Montane Forest and Campos de Altitude during the Holocene in southeastern Brazil

Abstract

The Atlantic Forest biome is well known as one of the mostly biodiversity regions on earth, hosting high species endemism and species/area ratio. It stretches around 1,300,000 km2 along the Brazilian coast between latitudes 3º and 33º S and longitudes 35º and 57º E. Due to the increase of human impact through the intensification of land-use and consequent broad landscape replacement along the centuries, only 10-15% of the Atlantic Forest biome remains in a natural or semi-natural state, being considered one of the most priority areas for conservation. It encompasses a wide variation of climates and geomorphologies, resulting in a complex mosaic of different ecosystems. Among them, the Araucaria forest, upper montane Atlantic rain forest (cloud forest) and the campos de altitude (high elevation grassland) occur on the Brazilian coastal highlands, which extends for about 1000 km parallel to the coastline from southern to southeastern Brazil. The Araucaria forest distribution is related to humid and relative cold climatic conditions, between 400 and 1400 m a.s.l. in southern Brazil and in smaller fragments at altitudes between 1400 and 1800 m a.s.l. in southeastern Brazil. Currently, it has been reduced to c. 7% of its original distribution. The upper montane Atlantic rain forest spread in the upper slopes of the Brazilian coastal highlands of southern and southeastern Brazil, normally above around 1100 m a.s.l. in the south and above around 1500 m a.s.l. in the southeast, mainly occupying the concavities and protected sites. The campos de altitude is a typical open vegetation, restricted to small areas on the summits of the higher peaks and plateaux. Palaeoecological studies demonstrated that, although the mosaic of these ecosystems has prevailed along the Holocene, the perpetuation of campos de altitude is very fragile. The grassland vegetation expands under colder and dry climate conditions and seems to be fire adapted suggesting that the current area of campos de altitude is larger than the modern climate alone would dictate, especially in warmer, lower elevation sites. Moreover, climate changes studies suggest a warmer and wetter climate during the 21st century which it is likely to intensify the upward movement of the Atlantic Forest at the expense of open ecosystems like the campos de altitude. In this research, the past and present relationship of the mosaic of campos de altitude and upper montane forests (Araucaria forest and upper montane Atlantic rain forest) are explored through palynological analyses. Foremost, the currently correlation between vegetation cover and pollen production was investigated. It was observed that arboreal taxa are over-represented in campos the altitude assemblage and that the campos de altitude pollen assemblage represents a much larger source area than the forest pollen assemblage, which is comprised of more local taxa. Afterwards, a record of the last almost 10,000 years was analysed. This study showed that, although upper montane forest taxa have been in the broader region of the study site throughout the Holocene, the forest vegetation has spread mostly in Late Holocene. Until around 1350 cal yr BP campos de altitude vegetation was much more widespread. Overall, the results demonstrated that increase in temperature and precipitation throughout the Holocene favoured the upward expansion of the forest. Furthermore, the research indicated that fire was presented before human arrival in southeastern Brazil, implying an adaptation of open vegetation to frequent fire. Latter, the dynamics of the vegetation on the last seven centuries was investigated. The outcomes revealed that anthropogenic disturbances such as fire, livestock grazing and logging have played a clear role in driving grassland-forest relationships in southeastern Brazilian highlands. Based on the outcomes of this research, the maintenance of the mosaic of forest-grassland in the current and projected climate trends depends on an active disturbance management and a changed in conservation focus from forest to non-forest habitats.