Introduction

Subtropical grassland ecosystems in southern Brazil present very high levels of biodiversity and have been the predominant land cover type in parts of the region. Despite the strong alteration of the landscapes by deforestation, agriculture and silviculture, in some less disturbed regions a mosaic of Campos (grassland) and forests is found, which have still a somewhat natural aspect. The existence of these mosaics in southern Brazil has puzzled naturalists and ecologists for a long time, because the modern wet climatic conditions would implicate a landscape covered by forest. Early researchers such as Lindman, traveling across the region in late 19th century, observed that forests should be able to expand over these grasslands, and attributed their presence to the transitional situation between tropical forests to the north and temperate grasslands to the south (Lindman 1906). Based primarily on plant geographical evidence, Rambo (1956a, 1956b) and Klein (1975) put forward that the grasslands were the older vegetation type with forest expansion, being a more recent process after changes to more humid climate conditions. Also Hueck (1966) questioned how the southern Brazilian grassland could exist under present humid forest climatic conditions.

Understanding the origin of the grasslands is of prime importance to their conservation and management. In case the mosaics of grasslands and forest are a consequence of human induced deforestation, vegetation management would likely be focused on reestablishment of complete forest vegetation. If grasslands are original and have prevailed in the past due to different climatic regimes, it could be reasonable to conserve these 'natural' relicts and their high biodiversity.

Sustainable management and conservation of modern mosaics of Campos and forest could be assisted by the knowledge of pre-historical and historical reference conditions for past human impact, fire magnitude and frequency of burning, and the applied use of this information in developing long-term management and monitoring plans.

Results from several palaeoecological investigations based on fossil pollen and microfossil charcoal of sediment cores from peat bogs provide important background information on past vegetation and fire dynamics (Figure 1). Most of the sites were sampled on the southern Brazilian highlands were a mosaic of grassland and Araucaria forest is found (e.g., Behling et al. 2004, Behling and Pillar 2007) and a few on the lowland campos region (Behling et al. 2005, 2007). Key questions to be addressed include: How was the formation of the diverse mosaic of forest and grassland vegetation in southern Brazil? Was its development caused by pre-Columbian slash and burn activity and deforestation of the post-Columbian settlers, or rather a natural process of climate driven forest expansion constrained by grassland fires? Are fires natural or of anthropogenic origin? What is the effect of climate change, fire and human impact on the overall biodiversity of the region through the time? How should we management and conserve the modern species rich forest and grassland ecosystems?

With examples from the southern Brazil, we want to demonstrate how essential it is to have knowledge on past vegetation and environment dynamics to understand the modern grassland ecosystem in a holistic way and that this background information has to be considered in developing conservation, restoration and management strategies for grassland ecosystems.

Figure 1. Map showing the distribution of Araucaria forest and Campos in southern Brazil (adapted after Hueck 1953, 1966) and the location of the sites mentioned in the text: (1) Cambará do Sul, (2) Aparados da Serra, (3) Morro Santana, (4) Sao Francisco de Paula (5) Serra do Rio Rastro, (6) Morro da Igreja, (7) Serra da Boa Vista, (8) Serra Campos Gerais and (9) Sao Francisco de Assis.

Figure 1. Map showing the distribution of Araucaria forest and Campos in southern Brazil (adapted after Hueck 1953, 1966) and the location of the sites mentioned in the text: (1) Cambará do Sul, (2) Aparados da Serra, (3) Morro Santana, (4) Sao Francisco de Paula (5) Serra do Rio Rastro, (6) Morro da Igreja, (7) Serra da Boa Vista, (8) Serra Campos Gerais and (9) Sao Francisco de Assis.

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