High species richness of tropical riparian trees influences the diversity of organic detritus entering streams, creating temporal variability in litter quantity and quality. We examined the influence of species of riparian plants and macroinvertebrate exclusion on leaf-litter breakdown in a headwater stream in the Luquillo Mountains of Puerto Rico. Leaf litter of <span name="style_italic">Dacryodes excelsa</span> (Burseraceae), <span name="style_italic">Guarea guidonia</span> (Meliaceae), <span name="style_italic">Cecropia scheberiana</span> (Moraceae), <span name="style_italic">Manilkara bidentata</span> (Sapotaceae), and <span name="style_italic">Prestoea acuminata</span> (Palmae) were incubated in litter bags in a pool of Quebrada Prieta. Fine mesh bags were used to exclude macroinvertebrates during leaf breakdown, and coarse mesh bags allowed access to decapod crustaceans (juvenile shrimps and crabs) and aquatic insects (mainly mayflies, chironomids, and caddisflies). <span name="style_italic">D. excelsa</span> and <span name="style_italic">G. guidonia</span> (in coarse- and fine-mesh bags) had significantly higher breakdown rates than <span name="style_italic">C. scheberiana, M. bidentata</span>, and <span name="style_italic">P. acuminata</span>. Breakdown rates were significantly faster in coarse-mesh bag treatments for all leaf types, thus indicating a positive contribution of macroinvertebrates in leaf litter breakdown in this headwater stream. After 42 days of incubation, densities of total invertebrates, mayflies and caddisflies, were higher in bags with <span name="style_italic">D. excelsa</span> and <span name="style_italic">G. guidonia</span>, and lower in <span name="style_italic">P. acuminata, C. scheberiana</span> y <span name="style_italic">M. bidentata</span>. Decay rates were positively correlated to insect densities. Our study highlights the importance of leaf identity and macroinvertebrate exclusion on the process of leaf litter breakdown in tropical headwater streams. Rev. Biol. Trop. 62 (Suppl. 2): 143-154. Epub 2014 April 01.. Decay rates were positively correlated to insect densities. Our study highlights the importance of leaf identity and macroinvertebrate exclusion on the process of leaf litter breakdown in tropical headwater streams. Rev. Biol. Trop. 62 (Suppl. 2): 143-154. Epub 2014 April 01.

descomposición de hojarasca; insectos acuáticos; arroyo tropical; macroconsumidores; detritívoros; Puerto Rico; bosque lluvioso tropical.