Dominância de uma espécie arbórea como estruturadora de matas savânicas africanas

Abstract

In african savannas, the dominance of certain tree species and their greatest contribution to the structure is common. This study evaluated the floristic and structural patterns among african savannah woodlands dominated by a tree species or genus, as well as the spatial pattern in species composition between woodlands and the influence of extractivism on the structure. Data were collected in thirteen woodlands grouped into four savannah formations: Mopane, Acacia, Mecrusse and Guibourtia in southern Mozambique. The DBH ≥ 10 cm was measured for all trees in the 0.2 ha plots, the trees height was also estimated and the coordinates of each plot were recorded. In each woodland, observations were made about the degree of resource extraction and herbivore frequency and categorical predictor variables were generated about the influence of extractivism and herbivores on the structure. NMDS and hierarchical cluster analysis were used to assess floristic differentiation and grouping. The Simpson, Pielou and Jaccard index were analyzed. The Mantel test was used to analyze spatial dependence in species composition. Parametric and non-parametric tests were used to compare the structure between woodlands and GLM to evaluate the influence of extractivism and herbivore frequency on the structure. The results indicate a floristic differentiation between four savannah formations and the same types of woodlands show similarity in the composition of tree species. Higher diversity of tree species were found in Acacia woodlands. Species turnover between the same type of woodlands was moderate and nestedness was low. There is no correlation between spatial distance and species abundance and a weak positive correlation in relation to the presence and absence of species. The dominance of one tree specie was found in Mecrusse, Mopane and Guibourtia woodlands and single genus dominance in Acacia woodlands. There is a difference in the structure of four savannah woodlands formations. There is no difference in structure between Mecrusse woodlands and between Acacia woodlands and there is a difference between Mopane woodlands and Guibourtia woodlands. Charcoal extraction and the frequency of elephants and buffaloes in woodlands influence the reduction in tree density and differences in structure between woodlands dominated by the same tree species.