Composition and structure of tree species in two forest fragments in southern amazon region

The level of human-induced disturbance and forest fragment size affect the distribution and composition of tree species in Amazonian forest fragments. The severity of disturbance can be better understood by analyzing floristic and phytosociological parameters of tree communities in forest fragments. We seek to find what are the differences between floristic, distribution and the successional stages of the trees in two forest fragments at the Amazonian Arc of deforestation. Two forest fragments were selected, one altered (area I) and one preserved (area II), where the number of individuals and of species, diversity index, similarity, importance value index, mean diameter and successional stage of trees were evaluated. The number of individuals and number of species and the diversity index were higher in the preserved fragment than in the altered one, due to the lower alterations such as clearings in the first. In area I, a total of 106 species were found, and in area II 126, with 69 species common to both ones. Fabaceae had the highest number of species, and the Protium altissimum (Aubl.) Marchand the highest importance value in both areas. The total number of late secondary species in the areas I and II was 26 and 34, respectively. One threatened species was found in the preserved area. The diversity index, number of species, the number of individuals and the number of secondary species of the tree communities were higher in the area II.