Comportamento de 12 espécies arbóreas em recuperação de área degradada pela extração de areia

Abstract

This study was carried out at the municipality ofRibeirão Vermelho, Minas Gerais state, Brazil, in área containg remmants ofseasonal forest and "cerrado"(savanna). Small patches ofriverine forest found on the margins ofthe Rio Grande are higlily degraded at the present mainly by the extraction ofriver bed sand and pebbles. The present study aimed at mitigating the impacts caused by these activities adopting two approaches: testing tree species in the reclamatíon ofa particular degraded área, and assessing the natural regeneration with the purpose ofindicating species wich was used on the reclamatíon ofthose áreas through soil recovery leveis. The experiment was set up at a 3,0 x 1,5 m spacing using 12 species distributed in a quinconx system. Soil fertilization varied in P leveles (100, 200, and 400g P/plant), chosen after soil chemical analyses. The source was simple super-phosphate. The statical design was randon blocks with a 12 x3 design (12 species x3 fertilizer leveis), with a total of36 treatmenth and 3 repetitions. The experiment contained 108 sample units. The interation species-fertilizer was not signifícant using treatment means. Two years after planting the following it coud be concluded: the degraded área is recovering and the species are growing following the secondary succession pioneer, light-demanding climax and shade-tolerant species; preliminary observations indicated as most promissing species Acácia mangium and Schinus terebinthifolius survivorship in the field, Acácia mangium, in terms ofmean diameter at the ground levei; and Schinus terebinthifolius, in terms ofcrown área. These two species are thus recomended for the reclamation of áreas degraded by the extraction of river bed sand. The natural regeneration was assessed in may 2000, through the survey ofali plants with total height >50 cm. The foUowing parameters were obtained: total height (m), diameter at the ground levei (cm), and crown área (m2). The phytosociological parameters were: absolute density, relative density, absolute dominance, relative dominance, absolute frequency, relative frequency, importance value index, and cover value index. The percent soil cover index was determined visually. Ametal frame with 40 x40 cm ofdimensions was used to sample ali individuais with total height < 50 cm. The follwing clonclusions were reached by the study: (a) the vegetation ofthe degraded área is at early stage ofsecondary succession, characterized mainly by the presence ofshrubbbs ofthe genera Baccharis. Leguminosae was the family with the highest contribution to species richness, with 5 species followed by Asteraceae, with 3. Sesbania exasperata was the most abundant species on the natural regeneration. It was also the specie with the highest density, frequency and dominance, with highest potencial to recover áreas degraded by sand extraction. Among the wood species sampled in the expenmental área Sesbania exasperata produced the highest values for both ímportance value index and percent soil cover index. The visual analysis used to assess soil cover leveis was adequate to this study, although its subjective and qualitative aspects. From the toai área of2430 m2, 84% was covered with the natural regeneration.