Regeneração natural e banco de sementes em floresta ombrófila densa montana pós-incêndio

Abstract

Fires are a major cause of habitat loss and biodiversity. Faced with this scenario, the affected areas find it more difficult to resume their functionality. Therefore, it is extremely important to know the mechanisms that will support restoration, as well as changes in the post-fire composition. Thus, the present study aimed to investigate the patterns of floristic composition and structure of the adult community, the natural regeneration and the soil seed bank and its association with environmental variables, in a fragment of in montane rainforest after fire, in Serra do Valentim, municipality of Iúna, ES. Woody individuals from the adult stratum and natural regeneration were measured in 30 5x10m plots (2 reference areas and 1 burned area, with 10 plots each). Adult individuals were considered all those with diameter at breast height (DBH) over 2.5 cm. Below 2.5 cm and with a minimum height of 60 cm were considered regenerating.. In the regenerating stratum it was evaluated whether the individual originated from regrowth, which was classified as stem, base and root regrowth. For the seed bank sampling, three soil samples (25cmx25cmx8cm) were taken per plot and homogenized, resulting in only one, totalizing 30 soil seed bank samples per area and season (dry and rainy). The samples were placed in plastic trays and kept in a shade house to induce germination. To analyze the environmental variables, were collected information on canopy opening, soil moisture and density and samples of topsoil (20 cm deep) for routine analysis (chemical and physical). A total of 735 individuals were sampled for the adult community, distributed in 45 families and 165 species, with emphasis to reference 1 with 47% of the individuals. For the natural regeneration, we counted 2172 individuals, 42 botanical families and 220 species. Highlight for the burned area with 119 species, which also presented a greater number of regrowth individuals, 54% of the total. For the seed bank, 1642 individuals were counted, distributed in 31 families and 174 species. The burned area had a greater number of species and the rainy season had a greater density of species 654.4 m². Shannon's diversity index and Pielou's equability for the burnt area were H'= 2.99 nats.ind-1 and J' = 0.82 for the adult community, H'= 3.86 nats.ind-1 and J'= 0.80 for natural regeneration and H' = 2.90 nats.ind-1 and J'= 0.66 for the seed bank. The extended correspondence analysis (DCA) demonstrated the formation of distinct groups between the areas, mainly in the adult community and in the regenerating stratum, whereas for the soil seed bank, only the portions of the reference ecosystems formed groups, while the post-fire area demonstrated high heterogeneity in the distribution of plots. Canonical correspondence analysis (CCA) for the regenerating and adult strata indicated that the burned area is more correlated with the variables canopy opening, pH, phosphorus and potassium, while sodium, moisture, CTC and clay, are more correlated with reference ecosystems. For the seed bank, the axes followed the same trend, however, with the most heterogeneous plots in the diagram. The burnt area is in an advanced process of succession, due to the abundance of zoochoric species and a high contribution of pioneer, early and late secondary species. It is believed that the seed bank can guarantee the resilience of the place. However, the burned area tends to form a new habitat, distinct from the other reference ecosystems evaluated.