Diversidade funcional de comunidades vegetais ao longo de gradientes estuarinos
Tibério, Fernanda Cristina dos Santos
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The estuarine regions are distributed along the coasts worldwide and show gradients of environmental conditions. Flooding and salinity are often considered the most important factors to influence plant species distribution in estuarine communities. Nevertheless, other factors such as geographic localization, geomorphological formation and variations of the flooding cycles may influence plant community s organization. Some studies also indicate expressive differences in species distribution patterns between temperate and tropical estuaries. Functional diversity may support the understanding of diversity patterns through the distribution and composition of functional traits in plant communities and help us understand the differences among distinct estuaries. Functional traits may be directly measured from plant individuals or determined as categories for each species (or group of species) and must be related to relevant processes in the community. Using the information of functional traits and species composition (or abundance) in each community, we may calculate functional diversity indices and then evaluate its variation patterns along the estuarine gradients. In chapter 1 of this thesis, we investigated the variations of plant functional diversity in three salt marshes of the west coast of England. In salt marshes, soil redox potential water content and the relative tide height are important factors to determine the colonization and species diversity of plant communities. Our results showed that plant functional diversity increased along the flooding gradient and that soil redox potential and relative tide height were the main factors to influence the variation of functional diversity. In chapter 2, we investigated plant functional diversity of two estuaries with distinct flooding cycles (open and closed) in the coast of São Paulo State. We observed that functional diversity varied mainly along the flooding gradient, increasing at higher elevations at both estuaries. Salinity was also important to functional diversity in the open estuary. We also observed functional diversity indices showed higher values at closed estuary. This result might be related to the longer and less predictable flooding cycle in the closed estuary, which generates a less sharp pattern of species distribution, so traits combination and functional diversity are higher. The factor considered important filters for species distribution are also major determinants of plant functional diversity in estuarine communities. Nevertheless, the investigation of functional diversity patterns helps us identify and discuss how the effect of different flooding cycles on estuarine communities.