Diversity and richness of the herbaceous plants on urbanized and non-urbanized dunes on the Brazilian Amazonian coast

Urbanization directly affects the structure of vegetation, which makes essential studies focused on understanding and conserving the biodiversity along urban environments. This study aimed to describe the structure of the vegetation and identify the predominant herbaceous species in non-urbanized and urbanized sand dune areas, analyzing their diversity and richness in Maranhão Island. The study was conducted in six dunes area, in which were allocated where 150 plots were allocated in three urbanized area, and 150 plots in three non-urbanized area. We counted all the herbs in each plot (1 m²), recording data on richness, diversity and vegetation cover. To evaluate the difference in the composition of the areas, the following tests were used: Shapiro-Wilk W test (data distribution), Student t test (species richness) and Hutcheson t test (diversity comparison). We recorded 3,643 individuals: of this total, 2,075 individuals in urbanized dunes and 1,568 individuals in non-urbanized dunes; we found 91 species, 59 genera and 27 families. Richness was higher in urbanized areas; however, non-urbanized areas showed greater diversity and uniformity. The floristic composition of the areas differed, according to the species indicator, showing 19 typical urbanized dune species and 9 non-urbanized dune species. NMDS showed that the urbanized and non-urbanized dunes presented distinct species compositions and densities; the ANOSIM revealed a significant correlation between the type of dune and the degree of taxonomic similarity between plots. The diversity of the herbaceous vegetation provides important data that can be used to guide research on conservation and management of dune areas.