HERBÁCEAS EM ÁREAS DE DUNAS DA ILHA DO MARANHÃO: DIVERSIDADE, RIQUEZA E CONSERVAÇÃO.

Abstract

The Brazilian coastline is approximately 9,200 km long, showing a variety of geomorphological formations, with complex and highly fragile environments and ecosystems. The coastal environments of Brazil are highly impacted and exploited due to real estate expansion, burning, among others; actions that have caused strong pressure on vegetation. In this context, the herbaceous composition is fundamental importance for the dunes, because it helps the containment of the soil and it can be considered indicator of altered environments, because the species are sensitive to abrupt changes in the microclimate and its soil. In the Northeastern, studies on the herbaceous stratum for areas of restingas and dunes are still scarce, despite Maranhão having the second largest coast of the country. The objective of this work was to identify the dominant species in the dune areas, to record the herbaceous composition in the entropized and conserved dunes, in addition to verify the diversity, richness and degradation of the vegetation. The present study was developed in the anthropized and preserved dunes of the Island of Maranhão. The collections occurred between May 2015 and May 2016. The herbaceous stratum was sampled through the plots method, distributed in transects of 100m, parallel to each other and perpendicular to the sea, totaling 50 plots of 1x1m in each area. It was recorded data as richness, diversity and herbaceous vegetation cover of both areas. In order to evaluate the difference in composition and in the degree of anthropization in the areas, the following tests were used: W of Shapiro-Wilk (distribution of data), t Student's (Species richness) and t Hutcheson (Comparing diversity). The results showed, through non-metric multidimensional scaling (NMDS) and similarity analysis (ANOSIM), that there is a difference in the taxonomic composition between the anthropized and conserved areas. The species richness was significantly higher (T = 3.7394; p = 0.0001) in the anthropized dunes (4.9 ± 2.8) than in the preserved dunes (3.9 ± 1.8). The diversity and equability were higher in the conserved areas (H’ = 3,464 nats/ind.; J’ = 1,940) than in the anthropized areas (H’ = 3,374 nats / ind.; J' = 1.799). In total, 3,643 individuals were enrolled in 91 species, 59 genera and 27 families. A total of 2,075 individuals were sampled in the anthropized dunes, 77 species in 24 families. While in the conserved dunes, there were 1,568 individuals, 60 species in 25 families. The five species that presented higher VI for the six areas were: Paspalum maritimum, Paspalum ligulare, Cassytha filiformis, Chamaecrista hispidula and Ipomoea imperati. These results suggest that the degradation contributes to the loss of the diversity of the coastal flora, mainly on the herbaceous composition. Therefore, additional studies are necessary in order to expand and understand the factors that may affect the herbaceous composition of dunes.