Diversidade e padrões estruturais da vegetação halófila-psamófila das restingas do Rio de Janeiro

Abstract

The restingas of the State of Rio de Janeiro are predominantly quaternary sedimentation areas, geographically discontinued, formed on the basis of palaeoclimatic changes, sea level fluctuations and longitudinal sediment transport. The diversity and structure of halophyte-psammophyte present in these restingas are the main focus of this study, which analyzes the floristic, life form and dispersal syndrome, as well as the pattern richness and diversity, the distribution of species, and vegetation cover, leaf litter, bare soil, and salinity of sea water. Nine areas of restinga were sampled, Praia do Sul, Marambaia, Grumari, Marapendi, Maricá, Massambaba, Barra de São João, Jurubatiba and São João da Barra. 90 species were found which were distributed in 33 families, 68 genera, being the largest specific richness families: Asteraceae (10), Poaceae (9 species), Fabaceae (9) and Rubiaceae (6). Was recorded a low species richness in areas evaluated, ranging from 25 to 48. Only 11 species occurred in all areas (Alternanthera maritima, Blutaparon portulacoides, Canavalia rosea, Cereus fernambucensis, Euphorbia hyssopifolia, Ipomoea imperati, Ipomoea pes-caprae, Panicum racemosum, Remirea maritima, Sporobolus virginicus, Stenotaphrum secundatum), and 12 are dominant, in one or more areas (Allagoptera arenaria, Alternanthera maritima, Blutaparon portulacoides, Canavalia rosea, Ipomoea imperati, Ipomoea pes-caprae, Mollugo verticillata, Panicum racemosum, Remirea maritima, Spermacoce capitata, Sporobolus virginicus, Stenotaphrum secundatum) and there are a large number of rare species. The Shannon diversity index ranged from 1,49 to 2,40, and the Pielou equability went from 0,82 to 0,60. The cluster formed two major groups, the first consisting of Barra de São João, Praia do Sul, Marambaia, Grumari and Marapendi, and the second by Jurubatiba, São João da Barra, Maricá and Massambaba. The most similar floristically areas were Maricá and Massambaba (58%), Grumari and Marapendi (56%), and Barra de São João and Praia do Sul (50%). The vegetation presents a characteristic flora, with difference in composition between the areas, and similarity between geographically closer areas. One third species identified are camefitos (34,56%), followed by phanerophytes (20,98%), geophytes (16,04%), hemicryptophytes (12,34%), therophytes (13,58%) and two lianas. In the dispersion predominates autocory (41,97%), followed by anemochory (33,33%) and zoochory (24,69%). The size of the areas perpendicularly to the sea is not related to increased richness, nor has the standard increased with the distance from the sea. There are differences of richness and diversity among the areas, there isn t homogeneity along the coast. There is a zonation, with species distributed near the sea (Allagoptera arenaria, Alternanthera maritima, Blutaparon portulacoides, Canavalia rosea, Cassytha filiformis, Cereus fernambucensis, Hydrocotyle bonariensis, Ipomoea pes-caprae, Schinus terebinthifolia, Sophora tomentosa, Stenotaphrum secundatum, Cyrtocymura scorpioides), and along the gradient perpendicular to the sea (Chamaecrista flexuosa, Euphorbia hyssopifolia, Ipomoea imperati, Mollugo verticillata, Panicum racemosum, Paspalum maritimum, Remirea maritima, Sporobolus virginicus). The logarithmic series model is what best represents the vegetation, regardless of the diversity or richness. The vegetal coverage ranged between areas. The bare soil and leaf litter are closely related to vegetation covering, with variation among areas.