Influência do tipo de entorno na intensidade do efeito de borda : diversidade, respostas funcionais e regeneração da vegetação lenhosa de fragmentos protegidos de floresta atlântica

Abstract

The type of predominant land-use in the surrounding of forests remnants can induce abiotic and biotic alterations, mainly at the edges of these remnants, occasioning changes in diversity, functions and regeneration of plant communities. Each of land use types have different dynamics and can influence the strength of edge effects in distinct ways. This thesis aimed at understanding which type of land use adjacent to Atlantic Tropical Forests induces the strongest edge effects. Remnants in an urban-rural gradient located at metropolitan area of Recife had their surroundings mapped to the quantification of urban and rural areas and definition of the study areas: remnants with urban, suburban and rural surroundings. In these areas richness, diversity, functional responses, and regeneration of arboreal and woody understory plants were evaluated along the edge and in the interior of the Forest remnants. Aiming at having a complete structural profile of the vertical occupation of the each remnant selected, plants were sampled for three inclusion criteria:(i) plants with circumference at breast height ≥ 15 cm; (ii) plants with circumference at breast height < 15 cm and circumference at ground level ≥ 3 cm; and (iii) plants with circumference at ground level < 3 cm and height ≥ 10 cm. The high degree of urbanization induced greater heterogeneity between the edge and interior, negatively affecting the richness and diversity of species, particularly in the arboreal component. The richness and diversity of understory species also were greatly affected but in the remnant with low degree of urbanization in the surroundings, dominated by sugar cane plantations. From a functional point of view, the remnant with the most urbanized surrounding was more threatened by the edge effects than the others remnants, and the species with small seed size, lowers maximum heights, abiotic dispersion mode and shade intolerance presented higher proportions of species and individuals at the edges of this remnant. The high understory species, those that do not reach until the canopy, but exceeding 4 m of height, had their regeneration strongly compromised by the increase of the surrounding urbanization. The remnant with an intermediate level of urbanization degree presented in various situations, edge-interior relationship more homogeneous for diversity, functional responses and regeneration. It’s important to know that these remnants have rural activities of low intensities in their surroundings. In this way, in an urban-rural gradient, more urbanized areas surrounding the forest induce more intense edge effect both from a structural point of view as a functional, affecting the edge of the remnant: the richness and diversity of species, especially as to how individuals are organized spatially; the frequency of certain species; the proportion of functional plants traits that tend to increased survival; and the regeneration of the high understory species. Areas with an intermediate level of urbanization and predominance of low intensity rural activities tend to induce softer edge effect that rural areas with intense activity. So, this scenario indicates that: specific management actions should be adopted in the forest edges in order to mitigate the edge effects on vegetation, especially those in contact with more urbanized areas; both the definition of these mitigation measures as planning areas for conservation should consider the structure and dynamics of the type of land use in the forest surroundings; the responses of species should be assessed by vertical occupation category, especially if considered the effectiveness of the responses of species that occupy the middle portion in the vertical stratification of the forest.