Abstract
Floristic surveys allow us to make a momentary assessment of the structure and degree of conservation of the vegetation, supporting future actions for the sustainable use of forest resources. The aim of this work was to study the floristic and structural composition of fragments of floodplain forest in the Cajari River Extractive Reserve, Amapá state, Brazil. Systematic sampling was applied with the allocation of 27 plots of dimensions 10 m x 100 m each, with inclusion level of individuals greater than or equal to 10 cm in diameter at chest height. The floristic diversity of species was determined by the Shannon Diversity Indexes and Pielou Equability. The characterization of the horizontal structure was determined by the parameters: density, frequency and relative and absolute dominance, values of ecological importance and the diametrical distribution. The families Fabaceae and Euphorbiaceae were the ones that obtained the highest richness of species and number of individuals. The species Virola surinamensis Warb., Hevea brasiliensis (HBK) Muell. Arg., Pentaclethra macroloba (Willd.) Kuntze and Mora paraensis (Ducke) Ducke, were the most abundant. The várzea forest fragments presented high diversity and high ecological dominance of species. The J-inverted diametric distribution, characteristic of natural forests, indicates that it is a mature forest component with an expressive group of dominating (hyperdominant) species, such as the species V. surinamensis and M. paraensis. Most species presented aggregate distribution. It is hoped that these results may serve the environmental control and control bodies as strategies for the use of forest resources and in the design of the management plan of Resex.
Highlights
Humid tropical forests are the major ecosystems in terms of the diversity of plant species in the world
A significant sample intensity is important for a good sampling of the species richness in a given area, being a relation of the increment of the area sampled as a function of the number of species accumulated
The cumulative curve of species by area has often been used in phytosociological surveys to test sample adequacy (Hack et al, 2005)
Summary
Humid tropical forests are the major ecosystems in terms of the diversity of plant species in the world. Floodplain forests are the second most abundant type of vegetation in the Amazon, covering 75.880.8 km, representing 1.6% of the Amazon biome, constituting the second largest forest environment in the region in terms of structure, diversity and spatial representativeness (Queiroz & Machado, 2008), as a result of the hydrogeomorphological dynamics of Amazonian river systems (Wittmann et al, 2010). In the last decades, large areas of these forests have been suppressed conventionally, without forest management (Miranda et al, 2018a). In this sense, protecting and at the same time utilizing this range of forest resources requires knowledge about the ecology of these ecosystems and species (Wittmann et al, 2013, Costa et al, 2018). Conservation initiatives, forest management, and forest fragments restoration require detailed studies on forest inventories and ecology of tree communities
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