Abstract
Floristic studies provide valuable information on species richness in a region, and are particularly important if these areas belong to less studied environments, such as rocky outcrops, that may increase our knowledge. An important aspect for species colonization includes the mechanisms of diaspores dispersal in each community; these are essential to understand its structure, dynamics, and the regeneration process, and constitute an important tool for conservation. We developed a floristic survey on a granite-gneiss outcrop with the objective to increase the knowledge on plant diversity, through a floristic similarity analysis and detection of dispersal syndromes of sampled species, in a semi-arid region of Brazil. The fieldwork included collection and observation of the botanical material in loco during a period of 12 months. A total of 161 species belonging to 127 genera and 50 families of angiosperms were recorded. Fabaceae, Asteraceae and Convolvulaceae were the most representative families in number of species. Allophylus quercifolius (Mart.) Radlk. (Capparaceae) and Lafoensia pacari A. St.-Hil. (Lythraceae) represented new records for the State of Paraiba. The autochoric syndrome was the most representative, with 51.5 % of the recorded species; the anemochory was the second most representative syndrome with 26.7 % of the species; and finally the zoochory, representing 22.3 % of the species. The floristic similarity dendrogram showed the formation of three well-defined groups, whose area with the highest value (J = 33.2) is located in a Caatinga region called Cariri Paraibano, while the lowest value observed (J = 5.2), occurred in a settled area in two geomorphological units, a crystalline complex and a plateau region. These results may be due to the varying topographic conditions and edaphic heterogeneity arising from the specific geological formation of the region. These results yet demonstrate that, in rocky outcrops, abiotic syndromes represent an effective dispersion of its diaspores, favoring plant specie's colonization dynamics.
Highlights
With a wide distribution in tropical areas, inselbergs feature a range of sizes and degrees of isolation associated with major biomes of the world, allowing experimental work, as well as being excellent elements to address different topics related to biodiversity and conservation (Porembski & Barthlott, 2000; Romer, 2005)
Due to its own characteristics, inselbergs form centers of diversity for certain functional groups of plants that are well adapted to extreme environmental conditions, and where the occurrence of seeds adapted to these conditions, becomes greater in these formations than in the adjacent matrix (Hunter, 2003; Porembski, 2007)
According to Araújo, Oliveira & Lima-Verde (2008), the vegetation that is established on rocky outcrops in the semi-arid region has a high species richness, demonstrating the relevance of studies related to the biology and ecology of these species, and the conservation actions for these areas (Scarano, 2007)
Summary
Due to the little substrate available and extreme microclimate conditions, the vegetation that is established in these environments is very different from its surroundings, favoring even the development of ephemeral vegetation (Sarthou & Villiers, 1998). Environmental conditions inherent to these formations are capable of providing niches to different taxa, depending on the surrounding vegetation and environmental pressure. In such harsh environments, the presence of effective dispersive mechanisms is of paramount importance for the development and establishment of seedlings (Willson & Traveset, 2000)
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