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Riparian zones are areas of transition between aquatic and terrestrial ecosystems, and their vegetation provides many important ecosystem services that are becoming of greater importance due to the changing climate. To understand riparian conditions along headwater tropical streams in terms of species composition and structure, we surveyed riparian tree communities and physical conditions in adjacent streams in the Luquillo Experimental Forest. We determined riparian substrate condition visually by estimating ground and vegetation attributes and measuring slope and elevation in a series of riparian plots at three stream sites. We determined riparian forest composition by identifying stem species and recording their height and diameter in plots. Our results demonstrated that elevation and slope were the main differences among sites, while all sites had similar ground and vegetation conditions. Species composition in all sites was characterized by hydrophytic species. However, although the most abundant species were generalists, we also found many species that were only observed once or twice per site. Overall, our results indicate that although recent and major hurricanes influence structure and composition at this site, riparian areas still maintain a large proportion of hydrophytic and rare tree species. 

Within a forest, differences in landform spatial variation (i.e., geomorphic settings: valley, slope, and ridge) could affect the species richness and distribution present at a particular site. Previous studies have confirmed that plant species richness and biomass changes after a hurricane and such values can vary among geomorphic settings. Understory vegetation, including ferns, herbs, climbers, graminoids, and shrubs, accounts for more than two thirds of flora in tropical ecosystems, but there is limited information of the effect of hurricanes on these communities. We evaluated the structure and composition of understory vegetation in a post-hurricane forest in relation to geomorphic settings. This study was conducted in El Verde Research Area in the Luquillo Experimental Forest, Puerto Rico. We established 1-m2 plots within three geomorphic settings: riparian valley, slope, and ridge. Within each plot we identified species, estimated percent of cover, and collected biomass samples. Additionally, we estimated species accumulation curves and analyzed species composition among geomorphic settings using multivariate ordination. The relative species abundance of vegetation life-forms was similar among geomorphic settings, but graminoids and climbers exhibited differences in species composition. Higher forest understory biomass and percent vegetation cover was observed at this immediate post-hurricane period than what was reported pre-hurricane. The understory of valley areas had a more distinct species composition than what was observed among ridge and slope areas. The understory vegetation patterns observed would need to be followed through time and among the landforms to confirm the hurricane disturbances effects at these understory scale.