Variáveis ambientais e a distribuição de espécies arbóreas em um remanescente de floresta estacional semidecídua montana no campus da Universidade Federal de Lavras, MG

Espírito-Santo, Fernando Del Bon and Oliveira-Fillho, Ary Teixeira de and Machado, Evandro Luiz Mendonça and Souza, Josival Santos and Fontes, Marco Aurélio Leite and Melo Marques, João José Granate de Sá (2002) Variáveis ambientais e a distribuição de espécies arbóreas em um remanescente de floresta estacional semidecídua montana no campus da Universidade Federal de Lavras, MG. Acta Botânica Brasílica, 16 (3). pp. 331-356.

Abstract

Environmental variables and the distribution of tree species within a remnant of tropical montane semideciduous forest in Lavras, southeastern Brazil). The purpose of the present contribution was to seek patterns of spatial distribution of the tree community in a remnant of tropical semideciduous forest and their correlation with environmental variables, stressing both catenary variations of soil properties and edge effects. The forest fragment, known as Mata da Subestação, covers an area of 8.75ha and is located on the campus of the Federal University of Lavras (UFLA), southeastern Brazil (21º13’17’’S and 44º57’47’’W), with altitudes ranging from 910 to 940m. The sampling was carried out using two transects, A and B, 80m apart, containing 21 and 31 adjacent 20 x 20m quadrats, respectively. Both transects followed the direction of the main slope, linking opposite forest edges. In each quadrat all individuals with diameter at breast height (dbh) = 5cm were identified to the species level and measured (dbh and height). A detailed topographical survey was carried out on the sampled area. Samples of the top 20cm of soil were collected at the centre of each quadrat for chemical and textural analyses. The soils of each quadrat were classified and two soil catenas were identified: transect A contained Nitosols (lower slope) and Oxysols (upper slope) while transect B contained Nitosols (slope base), Cambisols (lower slope) and Oxysols (upper slope). The floristic survey performed in the sample transects and in the whole fragment totalled 238 species belonging to 143 genera and 57 families. The 3120 individuals recorded in the plots belonged to 175 species, 115 genera and 49 families. The Shannon diversity index H’ = 4,19 nats.individual-1 and evenness J’ = 0,81 were high when compared to similar surveys in the same region. The high index of rare species (relative density <1 of 84,5% suggests that genetic isolation due to fragmentation may jeopardize the biological conservation of many species with time. The Oxysols of both transects were more acidic, poorer in exchangeable bases and richer in aluminium than Nitosols and Cambisols. The composition and structure of the tree community differed among the soil groups. Canonical correspondence analysis indicated that the abundance distribution of the species was significantly correlated with topographic and soil variables; there was no clear correlation with the forest edges. The most strongly correlated variables were the mean elevation, the saturation of bases and the proportions of sand, silt and clay. Therefore, the distribution of tree species in the fragment is apparently influenced primarily by soils nutritional status and ground water regime. The heterogeneity of both soils and topography may have contributed to make undetectable by the methods used any edge effect on the composition and structure of the tree community.