Análise da estrutura e do estoque de fitomassa de uma floresta secundária da região de Manaus AM, dez anos após corte raso seguido de fogo

In Amazonia, fire is widely used for soil preparation in the agriculture and cattle ranching, either by small or big farmers. The combination of low fertility of the soil and low price of the land usually leads to typical shift cultivation as soon as the natural sources of nutrients are exhausted, when new primary forests are felled and burned. Due to that, secondary forests originated from abandoned agriculture or pasture activity projects cover huge areas in the Brazilian Amazonia. This study was carried out in the Tropical Forestry Experimental Station (EEST/INPA), around 50 kilometers north of Manaus, the capital of Amazonas State. A secondary forest ("capoeira"), 10 years old, was selected for this study; its land use history includes clear cutting followed by fire. Two different samples of primary forests were included as control plots for the "capoeira". All individuals with diameter at breast height (DBH) greater than 5 cm were measured and recorded in a single area of 0,4 ha for each treatment. Ten years after burning, the secondary forest is still very different in comparison with primary forest, in terms of important parameters of the vegetation structure, such as floristic composition, abundance, frequency, dominance, index of value of importance (IVI) and the diameter distribution. In "capoeira" studied the dominant species are mainly of the following botanical families: Annonaceae, Arecaceae, Burseraceae, Cecropiaceae, Euphorbiaceae, Fabaceae, Lecythidaceae, Melastomataceae, Mimosaceae, Sapindaceae and Sterculiaceae. The estimates of dry biomass were 56.2 t. ha-1 ± 12 (CI 95%) and 339.7 t.ha-1 ± 66.7 (CI 95%) for "capoeira" and primary forest, respectively.