A Floresta Atlântica do litoral norte do Paraná, Brasil
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With recent questions raised showing the problems caused by global warming, mainly due to the increase in greenhouse gas emissions (especially CO2, used by plants during photosynthesis), there has been a growing interest in defining the quantities of biomass contained in natural forests, considered important carbon sinks in the earth fs ecosystems. With this purpose in mind, in the year 2000 a long-term project was started in Antonina, on the coast of Parana, in the Rio Cachoeira Natural Reserve, a 8,600 ha protected area. This study provides information regarding the floristic and phytosociological survey and the estimate of the stock and increase in biomass of the tree sinusia of the reserve. The data was obtained by setting up circular plots, each one consisting of three concentric sample units: in the 4 m radius sample unit, all individuals with a diameter at breast high (DBH) between 5 and 20 cm were measured; in the 14 m radius, elements with 20.DBH<35 cm; and in the 20 m radius sample, trees with DBH.35cm. All of the 188 plots set up were used in the floristic and biomass inventory, totaling 23.6 ha of sampling, considering the different vegetation features in the various classes of soil found in the area. For the phytosociological survey 77 plots colonized in Cambisols were selected. Within each formation of the Dense Ombrophilous Forest found in the area (Alluvial, Lowlands and Submontane), four successional tree stages were identified: very young (established between five and 15 years after disturbance); young (between 15 and 30 years); advanced (30-40 years) and mature forest (areas not disturbed for over 50 years or altered original areas). In the floristic survey, 335 native species and 20 exotic species were recorded. Myrtaceae, Fabaceae, Rubiaceae and Lauraceae were confirmed as the richest families in the Atlantic Forest. 24 species (7%) fall into the category of endangered species, a greater value than found in the majority of studies carried out in this same biome (around 2%). Of the general structural parameters of the community, a gradual increase in the basal area and the richness of species throughout the successional process was observed. The individuals of shade-intolerant species were more abundant in the very young forest, decreasing significantly in the subsequent phases of succession. As for dispersion, the zoochoric plants were abundant in all of the successional phases, and contrary to the references found for tropical forests, there was no predominance of anemochoric individuals in the initial phases. The development of the vegetation structure depends a good deal on the initial colonization after a disturbance. The preservation of original formations amid the vegetation mosaic that makes up the Atlantic Forest is essential to the conservation of the diversity of this biome: despite the structural similarity between the advanced stage and the mature forest, the presence of 25% of exclusive species in the latter demonstrates its importance as a stronghold of richness for the formation. The biomass varied between 169 Mg.ha-1 for the initial secondary vegetation to 513 Mg.ha-1 in the mature forests, values that correspond to the general estimates of stocks for tropical forests. The presence of trees remaining from the original cover interfered in defining the procedure for accumulated biomass in the initial stage, since large-sized trees would not occur naturally in this late phase. As a result of this situation, the values of biomass above the soil (that represent at least 78% of the total biomass in these formations) were not significantly different in the first two seral stages. However, it was found that the storage of biomass increases during the successional process, with no variation resulting from the edaphic component. The increase of aboveground biomass did not differ significantly between the sample categories analyzed, but was greater in the initial phases, with no record of a gradual tendency to decrease in value during the successional process. The loss of biomass through decomposition and the rate of mortality do not show any ordering related to the successional process. The accumulation of biomass remained at expressive rates throughout the successional process, which includes sections of the mature forest, indicating the importance of these formations as a source for accumulating organic matter in tropical zones.
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