Floristic dissimilarity and indicator species of Araucaria Forest and ecotones.

A busca do conhecimento sobre a expansão das florestas em relação aos ecossistemas associados (campestre e banhado) aborda a presença de fatores ambientais como o fogo e o pastejo, frequentemente descritos como determinantes dos processos ecológicos favoráveis à dinâmica sucessional. Dessa forma, objetivou-se verificar se existem diferenças na composição florística do interior de fragmentos florestais e entre setores de transição floresta-campo e floresta-banhado, bem como identificar espécies indicadoras para cada um desses ambientes. O estudo foi realizado em fragmentos florestais situados nos municípios de Bom Jardim da Serra e Lages (Coxilha Rica), onde foram instaladas duas parcelas permanentes de 50x50 m, subdivididas em setores de 10x10 m, categorizados em três setores: Floresta Ombrófila Mista, transição floresta x campo e transição floresta x banhado. Há dissimilaridade florística entre os fragmentos florestais dos locais e, também, entre os setores de transição (ecótonos). As espécies indicadoras dos ecótonos estão vinculadas ao estágio inicial da sucessão florestal, apresentando potencial para colonização do campo, podendo atuar no início do processo de expansão da fronteira florestal.AbstractFloristic dissimilarity and indicator species of Araucaria Forest and ecotones. The search for knowledge about the expansion of forests in relation to associated ecosystems (native grassland and wetland) addresses the presence of environmental factors such as fire and grazing, often described as determinants of ecological processes in favor of succession dynamics. The objective here was to verify if there are differences among the floristic composition of the interior of forest fragments and transition sectors of forest-native grassland and forest-wetland, as well as to identify indicator species for each of these environments. The research was conducted in forest fragments located in the municipalities of Bom Jardim da Serra and Lages (Coxilha Rica), SC, where we installed two permanent plots of 50x50 m, subdivided into sectors of 10x10 m categorized into three sectors: Araucaria Forest, forest transition x native grassland and forest x wetland transition. There is floristic dissimilarity between the local forest fragments and also between the transition areas (ecotones). The indicator species of ecotones are linked to early stages of forest succession, with potential for colonization of the field, they can operate in the start of the expansion of the forest boundary process.Keywords: Araucaria Forest; native grassland; wetland; succession.

Wetland succession in a permafrost collapse: interactions between fire and thermokarst

To determine the influence of fire and thermokarst in a boreal landscape, we investigated peat cores within and adjacent to a permafrost collapse feature on the Tanana River Floodplain of Interior Alaska. Radioisotope dating, diatom assemblages, plant macrofossils, charcoal fragments, and carbon and nitrogen content of the peat profile indicate ~600 years of vegetation succession with a transition from a terrestrial forest to a sedge-dominated wetland over 100 years ago, and to a Sphagnum-dominated peatland in approximately 1970. The shift from sedge to Sphagnum, and a decrease in the detrended tree-ring width index of black spruce trees adjacent to the collapse coincided with an increase in the growing season temperature record from Fairbanks. This concurrent wetland succession and reduced growth of black spruce trees indicates a step-wise ecosystem-level response to a change in regional climate. In 2001, fire was observed coincident with permafrost collapse and resulted in lateral expansion of the peatland. These observations and the peat profile suggest that future warming and/or increased fire disturbance could promote permafrost degradation, peatland expansion, and increase carbon storage across this landscape; however, the development of drought conditions could reduce the success of both black spruce and Sphagnum, and potentially decrease the long-term ecosystem carbon storage.

Wetland succession in a permafrost collapse: interactions between fire and thermokarst

To determine the influence of fire and thermokarst in a boreal landscape, we investigated ~600 years of vegetation succession from peat cores within and adjacent to a permafrost collapse feature on the Tanana River Floodplain of Interior Alaska. Radioisotope dating, diatom assemblages, plant macrofossils, charcoal fragments, and carbon and nitrogen content of the peat profile indicate that succession proceeded from a terrestrial forest to a sedge-dominated wetland over 100 years ago and to a Sphagnum-dominated bog in approximately 1970. The shift from sedge to Sphagnum, and a decrease in the detrended tree-ring width index of black spruce trees adjacent to the collapse coincided with an increase in the growing season temperature record from Fairbanks. The concurrent wetland succession and reduced growth of black spruce trees indicates a non-linear ecosystem-level response to a change in regional climate. In 2001, fire was observed coincident with permafrost collapse and resulted in lateral expansion of the bog. These observations and the peat profile suggest that future warming and/or increased fire disturbance could promote permafrost degradation and bog expansion, and increase carbon storage in the collapse; however, the development of drought conditions could reduce the success of black spruce and Sphagnum, decreasing long-term ecosystem carbon storage in the adjacent landscape.