Variações espaço-temporais e características funcionais da vegetação de dunas costeiras no Sudeste do Brasil

Abstract

Coastal zones are highly dynamic systems and natural phenomena induce significant modifications in plant communities. Moreover, environmental factors associated with sea distance and soil attributes can have large effects on coastal dune vegetation. The objectives of this study were evaluate changes in species composition and structure of sand dune vegetation, in space and time, related to seasonal precipitation; detect variation species and functional structure in a gradient of distance from seashore; evaluate the spatial variation of soil attributes of sand dune vegetation along the sea distance gradient, and the temporal variation of these attributes as a function of seasonal precipitation; and present an updated list of species of the coastal dune vegetation of the state of Rio de Janeiro. The vegetation was sampled during three years, in the rainy and dry seasons, in three restingas on the coast of the state of Rio de Janeiro (Brazil), throughout the 120 permanent plots of 1 m2 along transects perpendicular to the sea. Ten traits related to dispersal, establishment, and persistence were selected. Ten composite soil samples were collected in each site and during each season at a depth of 0-15 cm, chemical and granulometric analyses were conducted. Furthermore, floristic survey and bibliographic review of the nine restingas regions of this state has been carried out. Results indicate that temporal change of species composition were due to the occurrence of locally rare species, while change of the vegetation structure (cover, frequency, dominance) was related to seasonal precipitation and coastal dynamics. However, distinct temporal patterns of composition and structure were found between the three sites, possibly as a result of ecological filters and environment heterogeneity. Seasonally, during rainy periods there were increases in frequency and total cover of the species, while during dry periods there were reductions. Therefore, the dominant species alternated between seasonal periods influenced by precipitation or by sand accretion/erosion processes. These species have differentiated attributes, and these attributes change along the gradient. Differences in functional structure and diversity in relation to the distance gradient indicate distinct filtering processes in the assembly of these dune systems. Functional diversity was positively associated with the distance from the sea in two sites. The most important functional traits associated with the distance gradient were the leaf length and thickness, clonality, and seed length. Results also showed that some soil attributes varied along the sea distance gradient. The three sites presented differences in soil granulometry and positive correlation between cation exchange capacity and soil organic matter. Only the total exchangeable bases and the effective cation exchange capacity presented negative correlation with precipitation in site 2, sodium (Na) presented negative correlation in site 3, and there was no significant correlation in site 1. Additionally, there were no temporal variations of soil attributes in any of the sites. Ninety-eight species were registered, distributed along 81 genera and 38 families, from which the species richest families are Asteraceae (12 species), Poaceae (12 species), Fabaceae (11 species) and Rubiaceae (6 species). The majority of the species have herbaceous habits, predominantly the camephyte-autochoric species. They present wide geographical distribution or are restricted to some of the Brazilian states, mostly those resembling the Atlantic Forest. These results are important in understanding spatial-temporal dynamics, functional attributes of dune vegetation, soil attributes and conservation of coastal ecosystems