Plaza-Muñiz, Wilmarie

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    Spatial distribution and seed dynamics of invasive Mimosa pigra in Laguna Cartagena National Wildlife Refuge, Puerto Rico
    (2014) Plaza-Muñiz, Wilmarie; Chinea-Rivera, Jesús D.; College of Arts and Sciences - Sciences; Kolterman, Duane A.; Hulshof, Catherine M.; Thaxton, Jarrod M.; Department of Biology; Robles, Wilfredo
    The Laguna Cartagena National Wildlife Refuge (LCNWR) in southwest Puerto Rico contains one of the most important freshwater wetlands on the island. Mimosa pigra is rapidly invading the site, information on how environmental variables (flooding and shade from grasses) affect seed dynamics may have management implications. For this study I mapped the spatial distribution of the species in the lagoon. Two large populations of M. pigra were found in LCNWR in two different areas of the refuge, one on the north side and the largest one on the southwest side, in which 162 clumps were recorded. The southwest side population is presumed to be the older one. Also, since the species was found near waterways and near refuge borders, I conducted a seed burial experiment in the greenhouse to determine the effects of water depth and shade on seed survival and germination. Seeds were collected from LCNWR in November 2012 and equal numbers of scarified and un-scarified seeds were sown into replicate trays. Each tray received one of three water treatments (moist soil, minimal flooding, and complete flooding). Shade treatments (shade from grass litter vs. no shade) were applied to half of each tray. A total of 2,400 seeds were sown and germination was measured every week for sixteen weeks. Overall 18% of seeds germinated in the study. Experimental results demonstrate that both shade and flooding reduced total seed germination over the course of the study. Seed germination under grass shade was nearly two times lower than unshaded (62% vs. 38%) while flooded conditions (either minimal or complete flooding) reduced germination by more than 50% when compared to un-flooded moist soil. In addition, I estimated Mimosa pigra seed bank composition in the field. Ten random transects of 20 m were constructed in areas of the southwest side of the lagoon where M. pigra shrubs were present and three soil cores were taken in each transect. Seed germination from the soil cores was quantified and seedlings identified to species. From the soil cores only two mimosa plants germinated. This indicates a low frequency of viable M. pigra seed in the soil, contrary to expectations. This may be due to changes in water flow of the lagoon or seed predation. The relative elevation and the flood duration of the lagoon may contribute to the distribution of the invasive species M. pigra in this area. A decrease in seed germination will be expected if the water levels of the lagoon are maintained high. Efforts to reduce M. pigra regeneration should potentially target areas that experience extended periods of moist soil without inundation and where shading is minimal.