3. Threats to Sandy Shore Habitats in Sri Lanka from Invasive Vegetation

Sandy shore vegetation is under threat due to invasions from non-native or invasive species resulting from human interventions. As previous studies have shown, the natural zoning in Sri Lanka is so disturbed that it is possible to record only a few native species. This study was conducted at three representative study sites in the Western Province of Sri Lanka. We recorded twenty one families, 53 genera and 63 species in the sandy shore vegetation. Of these, approximately 14.28% (or 9 species) were found to be native species with Ipomea pes-capre and Spinifex littoreus as the most abundant native species at the study site. About 9.52% (or 6 species), namely, Chromolaena odorata, Cuscuta campestris, Lantana camara, Mikania micrantha, Opuntia stricta and Sphagneticola trilobata were found to be on the national list of invasive species in Sri Lanka. The study shows that a variation in plant diversity is to be found across the gradient of the shore with native species not as abundant and gradually decreasing landward while non-native weeds are more abundant and increasing landward from the sea. The Shannon Diversity Index shows that the diversity of species increases landward due to invasion. The Simpson diversity indices demonstrate that the vegetation is mainly dominated by non-native or invasive species. Thus, the study shows that the typical zoning nature and species composition found in sandy shore vegetation have been disturbed by the spread of invasive species, the main cause of which is ongoing human intervention. Under the existing policy directions, the available legislation therefore has to be enforced in order to restrict the spread of invasive species on sandy shores in Sri Lanka.