Litterfall inputs and understory vegetation of riparian and upland areas with different land-use history in a montane wet tropical forest

To determine if riparian zones are characterized by particular vegetation life-forms (such as grass, herb, fern, vine, shrub, palm or tree) and to compare components of litter production (leaves, wood, and reproductive parts) with those of upland areas, we sampled two riparian and two upland areas in the Luquillo Forest Dynamics Plot (LFDP), northeast Puerto Rico.  The LFDP, a tropical wet forest plot where previous land use history is known, was divided into four sites; the previously disturbed north upland and riparian area of Quebrada Toronja, the minimally disturbed south upland and riparian area of Quebrada Prieta.  To determine understory vegetation life-form composition, nine 5 x 5 m plots were sampled in each of the four sites.  All vegetation between 25 cm and 200 cm in height within the plots was identified and species were classified by life-form.  Litter-fall production and its components were estimated by placing 15 collecting baskets in each of the four sites within the LFDP.  Ferns and vines were more abundant in the riparian areas than in the upland area.  Small trees were more abundant in the minimally disturbed south upland.  Leaf-litter production rates were highest in the north upland, and lowest in the minimally disturbed south upland area.  However, when we controlled for previous land use, riparian areas had higher productivity rates as compared to the minimally disturbed upland area.  In this study, we observed that riparian zones had greater amounts of ferns and vines, higher values of tree species richness and higher leaf-litter production rates, as compared to upland areas within this wet forest landscape.