Diversidade e estrutura do sub-bosque de florestas ecotonais no Maranhão: relações fitogeográficas e influência do meio urbano

Abstract

The forest fragments of Maranhão are fundamental for the conservation of transition areas. The analysis of the understory is fundamental for the maintenance of biodiversity, when this stratum is understood in terms of distribution and dynamics. The objective was to evaluate the similarity of species composition and density in the understory of two urban and non-urban ecotonal forests in Maranhão in relation to adjacent domains. The study was carried out in two fragments of Ombrophilous Forest located in transition areas on the Island of Maranhão, which are: the Sítio Santa Eulália (2°31'04''S and 44°16'30''W), in São Luís, and the Sítio Aguahy (02°38'47” S 44°09'05” W), in São José de Ribamar. The first forest fragment receives urban influence and has an area of mangroves, has undergone processes of plant suppression over the years and today comprises a vegetated area of approximately 167 ha within the city. The second fragment does not receive urban influence and comprises an area of 400 ha in a rural area that features Manguezal and RestingaFor the phytosociological survey, 30 plots of 25m² were randomly demarcated, 10m apart and 30m from the edge. From the data obtained, the phytosociological parameters and the Shannon index (H') and Pielou index (J') were analyzed. The Mann Witney test, non-metric multidimensional scaling and Hutcheson's t test were performed to assess whether there is a difference in the richness, diversity and density of the floristic composition between the areas. A Bray-Curtis similarity matrix was also generated, and the Jaccard similarity index was calculated for cluster analysis by unweighted averages (UPGMA) from the vegan package in R. The typical species of urban and non-urban areas were identified and for them the Analysis of Indicator Species was used. A total of 103 species, 64 genera and 33 families were identified in the non-urban area (Sítio Aguahy). In the urban area (Sítio Santa Eulália) 58 species, 44 genera and 25 families were identified. After the analysis, it was found that the median of species richness in the non-urban area was significantly higher than in the urban area. The NMDS analysis evidenced the existence of a difference in the floristic composition and in the density of each species occurring in the two areas. In the floristic comparison between the sampled areas and the Amazon and Cerrado regions, there was low similarity, with some isolated locations. Despite the floristic heterogeneity between forest types, the areas of the Maranhão Island were grouped into the Amazonian and transitional areas. In the analysis of indicator species from the indication value, a list with six species for non-urban areas was obtained, highlighting Faramea nitida and Ocotea glomerata. Six more species were considered typical of urban areas, highlighting Rourea induta, Protium heptaphyllum and Randia armata. The diversity and equability indices found in the urban forest are similar to the understory of other urban Amazonian forests. The similarity showed a greater influence of the Amazon biome on the understory of the study areas, even with species from the Cerrado. This factor may be related to the humid tropical climate and the hydrological regime of Maranhão. It is suggested that the areas of the present study have a gradual ecotonal influence, but a greater sampling of the plant community in Maranhão is necessary to determine the areas as ecotones in the state.