Stream ecosystems are dependent on organic material from the riparian zone as a major energy source for lotic food web dynamics.  Leaf litter entering streams is processed by a combination of physical and biological mechanisms.  While detrital food web dynamics have been thoroughly investigated in temperate zones, much less is known about tropical ecosystems.  As part of an NSF-sponsored Biocomplexity project in Puerto Rico, we are quantifying the changes in riparian vegetation associated with road corridors.  Where roads cross streams, exotic vegetation comprises as much as 80% of the riparian cover while virtually no exotic species are found near streams away from roads.  The transformation from native riparian vegetation to exotic species have profound effects on the detrital processing and ultimately on nutrient cycling in these tropical streams.