Post-tsunami natural regeneration of coastal vegetation in the Hambantota district in south-eastern Sri Lanka

Abstract

A qualitative rapid survey was conducted in 45 plots distributed in the gentle seashore vegetation andsand dunes (n = 13), coastal scrublands (n = 19), and mangroves (n = 13) along the coastline ofHambantota District, affected by the Indian Ocean tsunami. The objective of the survey was toinvestigate the natural regeneration of coastal vegetation 20 months after the tsunami disturbance21 plant species belonging to 19 families were recorded as the prominent plants regenerating inaffected mangroves, while 16 species in 15 families and 32 species in 23 families were observed asprom inent plants to regenerate in affected areas of the gentle sea-shore vegetation and coastalscrublands respectively.In tsunami affected mangrove stands Acanthus iltctfolius (in 50% of study plots), Achrosticumaureum (40%) and Lumnitzera racemosa (17%) were the dominant species establishing in openmuddy substrates, while Clerodendrum inerme (57%), Lumnitzera racemosa and Excoecariaaga//ocha (29% each) were regenerating in sand deposited in the mangrove patches.Ipomoea pes-caprae (85%), Scaevola taccada and Calotropis gigantea (23% each) were observedas the dominant species re-establishing in the gentle seashore vegetation, while Spinifex littoreusshows a slow rate of regeneration. Most of the destroyed Pandanus odoratissimus bushes facingthe beach are not regenerating. Instead a new row of Pandanus was observed regenerating immediatelybacking the original stands. Prominent species regenerating in coastal scrublands are Crotonbonplandianus and Gymnema sylvestre (37% each), Clerodendrum inerme (16%), Calotropisgigantea (10%) and Crateva adansonii (10%) and saplings of Azadirachta indica and Limoniaacidissitna .Invasive alien plants, mainly Opuntia dillennii have established well and spreading vigorously inaffected coastal scrublands (58%), some study plots of gentle seashore vegetation (31 %) as wellas on sand depositions in the affected mangroves (15%). This species was observed replacing thespaces occupied by destroyed Pandanus odoratissimus bushes and Spinifex littoreus beds.Invasive alien plants such as Prosopis juliflora and Lantana camara were also spreading intsunami disturbed coastal scrublands.