Padrões de regeneração arbórea em mosaicos agrícolas do sudeste do Pará

Abstract

This study aims to describe and analyze patterns of tree regeneration in three different agricultural mosaics of the eastern Amazon, in order to check the influence of the types of land use on regeneration. The following questions were raised: Are the floristic structure and composition of regenerating trees affected by the various land-use types applied in the agricultural mosaics? Can the effect of land-use types on tree-regeneration vary according to the used scale? Is there a relationship between soil characteristics and tree-regeneration? Do tree-regeneration patterns respond similarly to distinct agricultural mosaics? The study was conducted in three areas of small family farmers in the settlements of Maçaranduba , Travessão 338-S and Palmares II, located in the southeast of Pará State, region of the arc of deforestation. The regeneration was inventoried at 45 sampling points in each farm, totaling 135 sampling points. Plots of 1 x 1m 0 x 50 m (500 m²) were distributed regularly in each sampling point to inventory tree seedlings with 10 cm < height < 200 cm. In each sampling point soil samples were also collected to analyze fourteen soil variables. Agricultural mosaics showed good ability to conserve biodiversity of trees, primarily evidenced by the high diversity of species found between the types of use. In most types of land use, forest species showed a higher number of species, including the cultivated areas, a fact that shows a significant capacity for the conservation of forest species in such open environments. The burned forest of Palmares II had the highest number of pioneer seedlings between the forests. The principal component analysis (PCA) showed that the types of land use had influence on the soil characteristics and on the structure and floristic composition of tree regeneration in the mosaics of Maçaranduba and Palmares II, however this effect was not seen in the Travessão 338-S. This result demonstrates that the influence of the type of use for tree regeneration depends of a mesoscale, where the composition of each mosaic, established from different management approaches, will interfere in the patterns of regeneration. The response obtained in Traverse 338-S, where the structure and floristic composition, in addition to soil characteristics, did not respond to the types of land use, was due to increased coverage of forest areas in the mosaic, which occupied 51% of the total area inventoried. This percentage decreased to 24 and 33% in Maçaranduba and Palmares II, respectively. These different levels of forest cover can assist us in defining the size of areas of forest protection necessary for the maintenance of the potential of tree regeneration in agricultural mosaics. The Travessão 338-S also had the highest number of species among the mosaics, associated with the greater diversity of types of uses and the presence of cacao cultivation, which had a regenerating density similar to the forests. In Maçaranduba and Palmares II, there were differences between forest and cultivated environments, evidenced by differences in the number of species and individuals between the types of use. There was further distinction between forests, associated with the different disturbs suffered in each area. The preparation of the area for cultive with fire was probably decisive for differences in soil between the type of land use, mainly in the agricultural mosaics of Maçaranduba and Palmares II, which were influenced by the types of land use and affected indirectly the regeneration.