Seed rain and seed bank dynamics area critical component for the establishment, development and regeneration of native plant communities. On Mona Island, Puerto Rico, the invasive African grass, Megathyrsus maximus (Figure 1) has invaded many areas. Grasses often become invasive and may have direct and indirect negative effects on native biodiversity and ecosystems (D’Antonioetal.1998). To better understand the ecological role of M.maximus on Mona Island, we are collecting and documenting information on the native seeds that reach the soil. With this information, our goal is to determine the effects of M.maximus on the distribution patterns and availability of Cactaceae seeds in the soil. We hypothesize that M.maximus interferes with seed rain deposition and we predict there will be a reduction in diversity and abundance of Cactaceae seeds in areas where the grass has invaded.National Science Foundation HRD #07348226 Institute for Tropical Ecosystem Studies (ITES)and University of Puerto Rico, Río Piedras Campus