Restauração ecológica de mata ciliar dominada por pastagem no nordeste do Pará, Brasil

Abstract

Among the forest typologies affected by deforestation are the riparian forests. The misuse and conversion of these forests into areas of agricultural crops and pastures has led to the degradation of these ecosystems, so beyond the legal need for recomposition it is necessary to create conditions for the ecosystem to restore its ecological integrity, its biodiversity and achieve long term stability. In this way, this dissertation aimed to analyze the benefits of forest restoration methods, with different leveis of intervention, in the initial process of restoration of riparian forest converted to pasture and dominated by exotic grass. The experiment was carried out in a pasture established in the 1990s, in the municipality of Terra Alta, Northeast of the state of Pará. Four treatments were tested: control (without intervention); stimulus to the soil seed bank (initial grass control and soil rotation); introduction of tree species by seed (sowing in pits) and introduction of tree species by planting (planting in rows). The period studied was 22 months after the isolation of the pasture and implantation of the treatments. The stimulus to the soil seed bank decreased the soil cover dominance with Brachiaria grasses and accelerated the process of natural regeneration of the native species, initially with high density of individuais and herbaceous species, but with a gradual increase of the establishment of shrub-arboreal species. At 22 months, individuais density and richness were low and similar among the four treatments, demonstrating that exotic grasses act as an ecological filter making it difficult to establish species. Acacia mangium, Cecropia palmata and Vismia guianensis are pioneer regenerating species capable of competing with the grasses and structure the riparian forest, requiring the management of the exotic species A. mangium. The species introduced by seeds presented germination above 85% in five of eight species. Survival was high for Hymenea courharil (100%) and Carapa guianensis (87.5%). Schizolohium parahyha var. amazonicum showed higher growth in height (175.5 cm) and four species have height less than 100 cm. The majority of species introduced by seedlings presented high survival (above 85%). The mean height was higher in the species Inga edulis (153.9 cm) and Virola surinamensis (107.7 cm), the others presented height less than 100 cm. In the introduction of seedlings by seeds and seedlings there was no difference between the diameter values of the species within the treatments. The predominance of weed and liana species and the parameters evaluated for woody vegetation (shrubs and trees) indicate that the riparian forest under different leveis of intervention is in the initial stage of the secondary succession, characterized by different heliophilous living habits, low wealth of woody species and little expressive forest structure recovery. The entrance and recruitment of regenerating tree species in the restoration methods, evidences the resilience of the riparian forest dominated by exotic grass.