Tropical forest understorey riparian and upland composition, structure, and function in areas with different past land use

Questions Although past land-use effects on composition and structure are described for many forest types, forested riparian areas have been overlooked. Riparian areas may contain unique species and high species richness, as well as contribute basal leaf-litter resources for aquatic fauna. We asked: (a) does past land use alter composition in riparian vs upland areas in wet tropical forest; (b) which vegetation life forms characterize riparian zones; and (c) what is the composition and quantity of leaf litter in riparian zones compared to uplands? Location Riparian and upland locations in tropical wet forest, Luquillo Forest Dynamics Plot (LFDP), Luquillo Experimental Forest, Puerto Rico. Methods Stratified random sampling was conducted in riparian and upland areas of LFDP with high and low past land use. Understorey vegetation life form composition and cover were sampled in plots. Leaf-litter species composition and components were estimated with collecting baskets placed throughout riparian zones and uplands. Results Ferns and lianas were more abundant in riparian areas than uplands. Ordination of species composition groups was distinct for riparian and upland areas with different past land use when based on leaf litter, but this ordination pattern was not as clear in plot vegetation. Conclusion Characterized by greater presence of ferns and lianas, riparian zones had higher species richness values and greater leaf litter biomass. Distinct leaf-litter species composition within riparian and upland areas may result from a combination of different land-use histories, various plant types, and environmental conditions. Although riparian areas are proportionally a small component of the forested landscape, they are significant contributors to ecosystem process, terrestrial and aquatic linkages, and plant community composition.