History of Vegetation Fire Climate Human Impact AND iTS iMplication For cOnservation

Here we demonstrate that palaeoecological and palaeoenvironmental background information from the southern Brazilian highland provide important implications for conservation and management regarding dynamics of vegetation, fire, and human impact including land use. Several pollen records document that the highly diverse patches of grassland are natural, remnants of a large glacial and early-mid Holocene area, and not former forest areas. This suggests that Campos should be protected and not be subject of reforestation as it is at the moment the case, where huge areas of original grassland are being replaced by exotic pine forests.

Pollen data show that Campos area became markedly reduced by the expansion of Araucaria forest, especially during the last about 1100 years caused by a change to wetter conditions. The natural expansion of Araucaria forest, which is nowadays in general not possible due to human activities, would contract the area of Campos. Recent studies show that by excluding grazing and fire present-day Araucaria forest tends to expand over grassland (Oliveira and Pillar 2004, Duarte and Pillar 2006).

The charcoal records indicate that natural fires ignited by lightning were rare in the grasslands of southern Brazil. The increase of fire frequency at the beginning of the Holocene is likely due to the occupation of the southern highland by first Amerindians or later after 7400 cal yr BP as in the Cambará do Sul area. For grassland management and conservation it has to be considered that anthropogenic fires played an important role during the Holocene and has certainly changed the floristic composition. Some plants and present-day plant communities may have adapted to fire (Overbeck et al. 2005). Further, the increase in charcoal coincided with a reduction in diversity in the Campos (Behling and Pillar 2007), but whether this could be seen as a causal relationship is not clear; climate change and mammal extinctions are important factors that may have affected diversity. The record shows that the later expansion of Araucaria forest was possible (or may have be facilitated) despite the high fire frequency and that fire in the surrounding of the study site Cambará do Sul became absent due to the expansion of the forest. Records from other sites, where a mosaic of grassland and forest is found, show still the occurrence of frequent fires.

Consequences of fire and grazing suppression at present in conservation areas with mosaics of forest and grassland in the south Brazilian highland should be carefully considered. The results show that with suppression of fire and grazing an active process of forest expansion, which had been halted by human disturbances, is re-established. If this management is maintained, in a few decades grassland in conservation areas will shrink and eventually disappear by forest expansion. We think that grasslands deserve conservation, and it is not because these ecosystems do not belong to present-day climate, and depend on human disturbances, that they should be condemned to extinction. Furthermore, fire and grazing suppression produce large accumulation of flammable biomass, increasing the risk of catastrophic, uncontrolled fires with unpredictable consequences on biodiversity. Grassland fire, by legislation, is prohibited in farms for management purposes; but in this case grazing by cattle maintains the grassland. The use of a limited number cattle for Campos management might be a good alternative rather than the use of frequent fire with its negative effects such as soil degradation, air pollution and the impact of uncontrolled fires. Large mammals which have lived in the grasslands of southern Brazil until the beginning of the Holocene might be an important factor to maintain the high diversity of the Campos similar to present-day cattle.

This example form southern Brazil shows that management for conservation of the mosaics of grassland and forest should take into account the history of vegetation and fire dynamics in southern Brazil during the late Quaternary. If management for conservation continues to include fire suppression, the present grassland patches will tend to disappear, as forest expansion will not be impeded, with losses to plant and habitat diversity. Grasslands have high biodiversity but are currently subject to severe land-use changes and thus reductions in area due to expansion of agricultural production and silvicultural plantations by exotic forest species, especially Pinus and Eucalyptus. In the few areas that are being protected (less than 0.5% of the biome; MMA 2000), management currently aims at excluding all human influence, including grazing and fire. This means that grassland areas within conservation units will disappear as a consequence of shrub encroachment and forest expansion. In these areas, fire could be used as a management tool to preserve grasslands or forest-grassland mosaics. A decision not to suppress fire, however, would require changes in conservation policies and legislation, since the state legislation prohibits the use of fire as management tool. Maintaining or reintroducing cattle grazing in conservation areas could be an alternative to fire, likewise impeding forest expansion over grasslands.

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