Vegetation and fire history in Araucaria forest and Grasslands, Southern Brazil

Abstract

Southern Brazil offers a great opportunity to analyse woodland and grassland mosaics, their pollen-vegetation relationships and its long-term vegetation and fire history. This research was carried out in two stages; first an analysis of the relationship between pollen and vegetation percentages which provide insights into the general understanding of the landscape, the representativeness and the pollen productivity of selected taxa. Second, we study the long-term changes in the vegetation and fire from a sediment record recovered among this vegetation mosaic. The relationships between pollen and vegetation indicated that the open vegetation taxon Poaceae, was the highest pollen producer in this forest-grassland mosaic. However, grasses were considered in here a poor reference taxon as they appeared in all vegetation types and obscured the results in shrublands and woodland scenarios. On the other hand, we documented the under-representation of Araucaria angustifolia despite the nature of its pollination mode (wind-pollinated). We believe that this result was perhaps hampered for its dioecious reproduction and for the mixed dispersion types involved in the mosaic of woodlands-grasslands which indirectly affect the dispersal models computed. Long-term palaeoecological results from Lagoa Dourada, a Holocene sediment record from Vila Velha state park in Paraná state, showed that Araucaria forest, after its initial establishment at ~7000 cal yr BP, experienced a stepwise expansion first at ~5700 and second at ~3080 cal yr BP, thus periods were characterized by different climatic conditions, coming from a warm and dry Early Holocene, to a wet and cool Mid-Holocene and to a humid Late Holocene. We documented that fire activity also contributed to changes in the vegetation through the observation and analyses of pre and post-fire events in the region. Human activity has been detected in here during particularly some fire peaks episodes; at 1600 cal yr BP and at 1380 cal yr BP, which are concurrent with the agricultural practices of the Taquara/Itararé groups as already documented for southern Brazil. Another anthropogenic signal was detected in here for the last ~220 cal yr BP, this one related to the arrival of the Europeans between 1703 to 1800, we evidenced a complete reorganization of natural ecosystems in which particularly Araucaria was affected due to timber production and plantation of Pinus and Eucalyptus started.