Seed rain and seed bank dynamics are a critical component for the establishment, development and regeneration of native plant communities. On Mona Island, Puerto Rico, the invasive African grass, Megathyrsus maximus, has occupied many areas. When grasses become invasive they may have direct and indirect negative effects on native biodiversity and ecosystems. To better understand the ecological role of this invasive grass on the island, we are collecting information on seed availability and distribution patterns of native and Cactaceae species seeds in the soil. We hypothesized that this introduced grass may interfere with seed rain deposition and predicted that there will be a reduction in diversity and abundance of native and Cactaceae species seeds in areas where the grass has invaded.To address this premise, soil samples were collected from six sites using a 5 x 5 cm and 5 x 7.5 cm soil core samplers, during a dry period on April 2009 and a rainy period on June 2009. Soil samples were sifted for large seeds and processed using a seed flotation method modified from Buhler and Maxwell.
Preliminary results suggest that soils from invaded sites have different seed compositions relative to soils from non-invaded sites with grass seeds dominating the seed composition of invaded sites. Although Cactaceae seeds were detected, no differences in seed abundance between vegetation communities have been detected so far with respect to this taxon.