Assessment of tsunami damage on the .coastal vegetation in five selected districts in the coastal zone of Sri Lanka, after one and half years of tsunami

Abstract

Tsunami, the ki lIer wave swept nearly two thirds of the coast of Sri Lanka on 26lh of December, 2004.About 40,000 people died and around 500,000 people were displaced, more than 119,000 housesdamaged either fully or partially. About 13 coastal districts were directly affected, the north and eastsuffered the brunt of the blow accounting for about 2/3 of deaths and 60% of displacements. In termsof ecological aspects, with the exception of few species, most of the vegetation suffered total orpartial death, lagoons, estuaries, coral reefs, sea grass beds, salt marshes and mangroves experiencedthe damage at varying levels. Th is study was conducted with the patronage of the Food and AgriculturalOrganisation of the UN to scientifically assess the response of the coastal ecosystems with specialreference to coastal forests to the Tsunami, almost one and half years of the incident.

The study focused on 5 tsunami affected districts namely, Kalutara, Galle, Matara, Hambantota andArnpara. In each district, approximately 6 sampling locations selected based on the topography mapsand ground information. In each sampling location, a transect which was 10m wide and upto 250minland was taken. The transect was divided into 50m blocks, the first one laid at the start of vegetationline of the beach. In each 50m section of the transect, all the plant species were enumerated. For theground vegetation, percentage ground cover was taken. Using an index, the level of damage wasevaluated for each plant. Composite soil samples were taken at each 50m segment and analysed forElectrical Conductivity, Soil Organic Carbon and major nutrients. Water samples were taken fromexisting wells located close by.

Although most of the vegetation, except for few exceptions, suffered badly at the time of Tsunami,there was extensive regeneration on the coast at the time of our study. The species which sufferedthe tsunami damage most were Palmyrah palm (Borassus flab ellifer), Del (Artocarplls nobilis),Araliya tBorassus flabellifer), Puwak (Areca catechu), Banana (Musa sppv; Kitul (Caryota urens),Guava (Psidium guajava), Avacardo pears (Persea gratissimai, trees of Citrus family ie Oranges,Lemon, Lime (Citrus spp.) Alstonia, Teak (Tectona grandis) etc. Of these, most of the species hadregenerated to varying degrees, the most difficult ones being Araliya, Palmyrah, plants of citrus family,Kitul, Guava.

With a view to find out the species which are more robust in the regeneration, percentage groundcover (in ground vegetation) and relative abundance (in tree/shrub vegetation) were taken in each 50m segment of a plot. The districts did not vary significantly in the biodiversity. However, the speciesabundance showed a significant variation especially between the districts ofthe western coast (Kalutara,Galle, Matara) with that of south and eastern coasts (Hambantota and Ampara). While Mudu bimthamburu (Ipomea pescaprae) was the most prominent ground cover in the western districts, Maharavana ravul (Spinifex spp.) was more prominent in both south and eastern districts. With regard tothe abundance of trees/shrubs, Wetakeiyya (Pandanus spi, Coconuts (Cocos nuciferai, Gam suriya(Thespesia spp.y, Mudilla (Barringtonia spp.i, Domba were most abundant. In the South and Easterndistricts, Maliththan (Woodfordiafruitocosa), Andara (Prosopisjuliflora), Palmyrah palm, Cashwnut (Anacardium occidentale) and Neem iAzadirachta indica), Indi, (Phoenix spp) Korakaha/Kayan (Memecylon angustifoliumi were prominent. In the South and South-eastern districts, Aththana(Datura mete/), Wal kochchi had spread into invasive levels while the regeneration of Ranawara(Cassia auriculata) also had increased.

With regard to the physical parameters, soil carbon content showed a decrease with the increase indistance from the beach. The Electrical Conductivity (EC) also showed a decreasing trend with theincreasing distance from the beach in all the districts studied. In general, all the nutrients (Total N,Available P, Available K, Ca, Mg and Na) showed an increase upto about 50m compared to that ofnon tsunami levels and then decreased. The pH of the water samples taken in all the districts werebetween 7-8 indicating a neutral level while the EC values were higher than the standard of 4 milsemens.

With regard to the establishment of Green Belt, the coastal area could be broadly categorised intonatural, rural and urban landscapes. For the natural landscapes like mangroves, sand dunes and coastalforests, facilitation/restoration of the natural vegetation is recommended. Selection of species shouldbe in line with the naturally occurring ones in the ecosystem. In total locations, planting a strip ofnatural littoral woodland and strand plants seaward of agricultural crops is suitable. For urban locations,patches of natural vegetation could be integrated as far as possible with the most suitable concept forthe area. There could be open grassed/sandy/paved parks or playgrounds or sports grounds of varioussizes, provided there is a substantial belt of trees on the seaward side, and in cyclone prone areas,wind shelter belts on all sides. In cyclone prone areas, wind shelter belts should be planted aroundcrops and settlements: the trees and shrubs used could be introduced species as well as indigenous/native (found naturally in Sri Lanka) and endemic (found naturally only in Sri Lanka) species.

The design of the Green belt should inc lude both ground vegetation, shrubs and then trees. Based onthe study results, composition of the vegetation for both ground vegetation, shrub layer and the treelayer has been proposed for all the 5 districts. In the tree layer, there were two distinctions, one for thebioshield which is located at close proximity to the sea and then the trees outside the bioshield comprisingof more multipurpose ones serving both protection and production purposes. Further, general designswere recommended for the west coast and southeast and eastern coasts. Guidelines were also proposedfor rehabilitation of the mangrove areas and sand dunes.