Fitossociologia e regeneração natural de uma área de deposição de rejeito do refino de bauxita revegetada com leguminosas arbóreas em São Luís, Maranhão

Abstract

The objective of this work was to evaluate the development of a reforesting activity made in 1997 in order to recover a deposition area 1 of bauxite refining reject (ADRB#1) of Maranhão Aluminum Consortium (ALUMAR), located at the geographic coordinates 2 0 43’29,88” S and 44 018’41,3”W. In this study the floristic composition, the structure of the tree stratum and the structure of the natural regeneration were analyzed. Nine plots with 300 m2 (30 m x 10 m) were systematically distributed. All trees with DBH > 5 cm were sampled and identified. The natural regeneration was evaluated in 2 height strata: stratum 1- plants with 10 cm to 1m high and stratum 2- plants over 1m high and DBH < 5 cm. The stratum 1 was evaluated in 81 plots measuring 2 m x 2 m and the stratum 2 in 9 transects of the 30 m x 2 m. The main parameters analyzed were horizontal structure, vertical structure and community diversity. For the arboreal stratum 289 individuals were sampled summing up 419 trunks (389 alive and 30 dead). These were distributed in 7 families, 19 genus and 22 species. The three most representative families were Leguminosae (14 species, 11 genus and IVI=54,65 %), Bignoniaceae (1 species and IVI=24,5%) and Urticaceae (1 species and IVI=10,1 %). These three families represented 89,1 % of the total IVI. Tabebuia impetiginosa (IVI=14,65 %), Acacia mangium (IVI=12,9 %) and Cecropia cf. pachystachya (IVI=7,6 %) were the three most important species. Cecropia cf. pachystachya was the only spontaneous species in this stratum. Shannon-Weaver Diversity Index (H’) was 2,56 and Evenness (J) was 0,82 for the 10 years-old and 7 months stage. Comparing the indexes to the original natural region forest, these values were comparable to others found in low and mixed reforesting areas studies. 1472 plants, distribute in 12 families, 19 genus and 20 species were identified in stratum 1. The density of plants found was 4,5 individuals/m2. Summing up only the tree seedlings, a density rate of 0,75 individuals/m2 was found .The density of tree seedlings native to the region was 0,0121 individual/m2 or 1 individual/84 m2. The three most important families were Poaceae, Rubiaceae and Bignoniaceae. The richest family was Leguminosae with 7 species. The three most representative species were Panicum maximum, Borreria sp. and Tabebuia impetiginosa. For stratum 2, 104 individuals were sampled, distributed in 9 families, 17 genus and 18 species. The most important families were Leguminosae, Bignoniaceae and Sapindaceae. The most representative species were Mimosa caesalpiniifolia, Tabebuia impetiginosa and Caesalpinia ferrea. In stratum 2 only 2 native species were found. The density observed for all tree species seedling was 0,92 individuals/m2 in stratum 1 and 2 of natural regeneration. These were low values when compared with natural forests. However, they are compatible with the values found in mixed reforestation areas in the state of São Paulo. Analyzing the results, the presence of limiting factors in the areas of natural regeneration was observed which indicates the necessity of adopting management actions to stimulate the regeneration and future sustainability of the forest implemented.