Dinâmica de fragmentos florestais da Mata Atlântica na região do Médio Vale do Paraíba do Sul, Rio de Janeiro

Abstract

Atlantic Forest is one of the most threatened biome in the world. Despite of its richness in terms of biodiversity it occupies only 11-16% of the original area and appears as a mosaic of fragments in the landscape. At Rio de Janeiro State and especially in Middle Valley of Paraíba do Sul River, the forest (and landscape) degradation was favored by several crop cycles and relief, extremely hilly. Today the fragments in the region are immerged mainly in pasture matrix with a low capacity support. The knowledge of biogeochemistry cycles in these important landscape components is scarce and could contribute for a biological conservation programs. In this direction, this study was carried out to characterize the structure of tree fragment in different successional stages (initial - IS, intermediary – INS and advanced stages, AS) and those carbon and nutrient compartments and fluxes. Above and below ground (fine roots: <2 mm) biomass and carbon accumulation were estimated using allometric equations and monolith method, respectively. Natural abundance of 13C was used to evaluate the dynamic of soil organic matter. The contribution of rainfall and forest for nutrient cycling inside the fragment was accessed by a biweekly sampling program. Fifteen pluviometers and ten stemflow collectors were installed at the breast height of selected trees to represent each fragment and compartment. All those compartments were monitored for 1 year, but the sampling frequency was weekly. An addition study was developed using geographic information system to evaluate the expansion of those fragment over a 30 years chronosequence. The AS fragment presents the highest richness (thirty four botanic families), aboveground biomass (one hundred seventy one Mg ha-1) a tendency to stock more carbon and nutrients in this compartments. Fine roots were concentrated in the superficial soil layer (0-10cm) for all fragments and season (3,08 Mg ha-1 dry and 2,51 Mg ha-1 wet), but highest values were detected to AS fragment. Despite of this biomass the CO2 soil efflux was higher to INS fragment (16,0 Mg ha-1) in comparison to AS (13,5 Mg ha-1) and IS ( 15,5 Mg ha-1) fragment. Areas of AS and INS had showed an increase of δ 13C values in the 0-10 cm layer in relation to the layer of 10-20 cm, from (-27.2 ‰ to -26.5 ‰) and in AS -26.5 ‰ to -25.2 ‰ in INS and the values of δ 13C stabilize from 60 cm deep. This is an indication that the progress of regeneration of forest areas are already reflected in soil carbon. Therefore arrive at the conclusion that despite of fragmented landscape of Middle Valley of Paraíba do Sul River, the ecological memory of Atlantic Forest in the region, associated to decline in cattle management contributed to an increase of fragments area.