Floristic and Structural Heterogeneity in a Neotropical Riparian Wetland: Conservation Implications

Despite the incontrovertible importance of wetland ecosystems, our understanding of the causes underlying the spatial heterogeneity of their attributes is still insufficient. Here, we assess the spatial variation of the floristics (species composition and their relative abundances) and quantitative structure (vegetation cover) of the San Pedro Mártir River riparian herbaceous wetlands (Tabasco, Mexico), and explore potential factors responsible for within- and among community variation. Vegetation was sampled at 10 sites along a 40-km stretch of the river. Per site cover of the recorded morphospecies was assessed with digital photography, and community diversity was analyzed using the Hill numbers framework. Total richness was 76 morphospecies (67 identified to some taxonomic category); the drastic decrease in true diversity with increasing q values indicated that few species dominate the community matrix, while numerous remaining species occupy the small interstices among them. Three Cyperaceae species had the largest importance in the community, with Cladium jamaicense being the most frequent and having the largest cover along the river. Ward’s site classification and NMDS ordination indicated the existence of four floristically and structurally different vegetation groups. Within sites, GLMMs showed a weak inverse relationship between species richness and distance from the river, but no relationship for plant cover. Fluvial geomorphology, and possibly regional geological heterogeneity, are the main factors determining the spatial variation of these herbaceous wetlands. Deep understanding of the relationship of herbaceous riparian wetlands with their environment will improve the prediction of the effects of modifications of fluvial dynamics and support efficient conservation strategies.