Population Dynamics and Conservation Significance of Native and Non-native Grass and Sedge Species on the Sand Flats of Guana Island, British Virgin Islands

A systematic survey was conducted in 2013 to identify the plant species composition of the sand flats of Guana Island, British Virgin Islands. A total of eight species were enumerated on the sand flat: broadleaf panicum (Brachiaria adspersa (Trin.) Parodi), Indian bluegrass (Bothriochloa pertusa (L.) A.Camus), thin paspalum (Paspalum setaceum Michx.), goosegrass (Eleusine indica (L.) Gaertn.), common bermudagrass (Cynodon dactylon (L.) Pers.), southern sandbur (Cenchrus echinatus L.), crowfootgrass (Dactyloctenium aegyptium (L.) Beauv.), and tropical fimbry (Fimbristylis cymosa R.Br.). The greatest Species Relative Density (RD) was observed for Bothriochloa pertusa (76%) and Fimbristylis cymosa (10%), while the RD of all remaining species was <= 5%. The Shannon Diversity Index of the sand flat was 0.93, while the Shannon Equitability Index was 0.45, indicating moderate species diversity present within the sand flat. Although all eight species identified were previously reported on the island, characterization of their presence on the sand flat may provide further insights into their conservation significance, potential invasiveness, impacts on the ecosystem, and possible need for management/control. Continued monitoring of Cenchrus echinatus may be highly warranted due to previous documentation as an invasive species capable of displacing native vegetation in tropical regions.