THE STRUTURE AND COMPOSITION OF NATURAL VEGETATION TYPES IN LOWER WALAWE BASIN IRRIGATION EXTENTION AREA

Sri Lanka has experienced a tremendous boost in large-scale irrigation development. TheUdawalawe irrigation extension project of the Mahawelli Authority will result in theconstruction of a left bank main canal from the Walawe River and the establishment of anirrigation system spanning an area of approximately 15.000 ha. A systematic study onbiodiversity was carried out in the Lower Walawe Irrigation extension area, from February toAugust 2001. This paper summarizes the structure and composition of natural vegetation typesin the study area, during the pre-development stage. A total of 45 transects (each 50mx5m) weredemarcated within 16 sites along the dry to arid zone climatic gradient in the study area. Eachtransect was divided into 10IILx5m sub plots to facilitate sampling and individual plants overlOcm in girth were recorded. The data was analysed using ecological indices (Shannon-Wienerindex and Simpson's Index) and multivariate analyses using the PCORD4 softwareThe area consists of 3 major natural vegetation types; dry thorny scrubland (DTF), rock outcropforests (ROF).and degrade dry zone forest (DDF). A total of 151 plant species, belonging to 52families were recorded from the above vegetation types. The most diverse families wereFabaceae [Relative Diversity (RD)=l1.3], Poaceae (RD=9.3) and Euphobiaceae (RD=8). Interms of density, the most abundant species in the study area were Flueggea leucopyrus(Euphobiaceae) (23.3%) and Phyllanthus polyphyllus (Euphobiaceae) (8.6%)Comparisons of the diversity among vegetation types showed that the degraded dry zone forest"vas high in diversity (Simpson's diversity index; D=17.6, Shannon-Wiener diversity indexH'=3.6) than rock outcrop forests (D=10.7,H=3.1) and scrubland (D=9.9,H=304). Consideringthe species composition and density of flora, a Detrended Correspondence Analysis (DCA)showed the DDF as a distinct cluster, while the ROF exhibited an overlap with the DTS. ATWINSPAN cluster analysis showed that the DTS and DDF separate into two distinct clusters,which correspond to the dry and arid climatic zones. However, the ROF remained as a singlemajor cluster.

Altitudinal Variation of the Floristic Communities in Monaragala, an Isolated Hill in Eastern Sri Lanka

Compared to wet zonehills of Sri Lanka, the floristic communities of hills in drier regions ofits first peniplane has been poorly studied. This study investigatedthe floristic communitiesalong the altitudinal gradient in Monaragala, an isolated hill in the intermediate zone of theisland, by sampling trees and lianas >10 cm g bh, in 99 randomly located 10 m x10 m plots infour transects laid on different aspects of the hill.In the 9,900 m2 sampled in the study, 1,322 individuals were enumerated. They represented44 families, 103 genera and 149 species, among which 45 were endemic to Sri Lanka. Frommultivariate analysis of the plot data, one grassland / savanna and five forest communitiesseparated in relation to their variations in elevation and topography, disturbance level andphysiognomy of the vegetation. These communities were: two disturbed tall forests, onerestricted to low-elevation 210-780 m (LDT) and the other widespread at 540 – 620 m / 920 –950 m (WDT); three undisturbed tall forests, one at mid-elevation 600-880 m (MUT) and theother two on ridge slopes of Sirigala (RUT) and Maragala (IUT) at 880 -1100 m, and the lasta high-elevation disturbed grassland/savanna at 720 – 870 m (HDG).The five leading families in each of the six communities collectively represented 31 of the 44families identified in the study, reflecting familial diversity among the communities. Thedominant families were Sterculiaceae and Rutaceae in the lower elevation, while Lauraceae,Dipterocarpaceae, Myrtaceae, Bombacaceae and Apocynaceae were in mid - and upperelevations. Euphorbiaceae was common to all altitudinal ranges.Most species were restricted to a particular elevation range. At the lower range, Diospyrosebenum, Pterospermum suberifolium, Miliusa indica, Acronychia pedunculata, Alphonseasclerocarpa, Chlorocarpa pentaschista and Drypetes sepiaria. The mid- and higher rangeharboured endemic species and those common to wet zone rainforests, eg. Actinodaphneelegans, A. ambigua, Cullenia ceylanica, Cryptocarya wightiana, Hunteria zeylanica,Calophyllum tomentosum, Dipterocarpus zeylanicus.This study emphasizes that isolated hill forests located outside the wet zone, like Moneragala,harbour diverse and unique floral assemblages which need urgent conservation in a rapidlydeveloping era.

BIODIVERSITY OF THE MADUGANGA MANGROVE WETLAND

The Maduganga estuary and mangrove islets are a complex coastal wetland ecosystem situatedwithin the two Divisional Secretariats of Balapaitiya and Karandeniya in the Galle District ofSouthern Sri Lanka, The total area of the estuary is 915 ha, of which 770 ha consist of openwater, while islands account for 145 ha. With the view of safeguarding the ecological functions,resources and values of the Maduganga estuary fer conservation and future sustenance ofbiodiversity, meN Sri Lanka carried out a systematic assessment of biodiversity in Maduganga.A six-month field survey was conducted from May to October 2000. Field sampling was carriedout at fortnightly intervals' each sampling session spanning over six continuous days. TheMaduganga ecosystem was divided into six major Si rata based on the occurrence of differentvegetation types, human activities and a hypothetical salinity gradient. These strata weresampled for fauna and flora in a systematic manner, using standard techniques. The threats tobiodiversity were also assessedThe survey revealed that the Maduganga wetland consists of 10 major wetland vegetation types.These vegetation types harboured a total of 303 species of plants belonging to 95 families. Thetotal plant species included 19 endemics, 8 nationally threatened species and 9 invasive alienspecies. Based on the extent of occurrence (ha), mangroves and mangrove mixed swamps werethe dominant wetland vegetation types in Maduganga, In addition to these wetland vegetationtypes, three major terrestrial vegetation types are also found in the islands and the surroundingmainland area of the Maduganga estuary. Perennial crops (mainly cinnamon) dominated theterrestrial vegetation types. A total of 98 plant species were recorded from the multi-specieshome gardens. When considering the species richness of flora in different wetland vegetationtypes, mangroves harboured the highest number of species, closely followedby mangrove mixedswamps. Maduganga estuary harbours a small population of a very rare, threatened mangrovespecies Lunmitzera littorea. A total of 248 species of vertebrate fauna, belonging to 121 familieswere recorded from Maduganga. These included 20 species (8%) of endemics, while 30 species(12%) are considered as nationally threatened. The native vertebrate fauna of Madugangarepresents 30% of Sri Lanka's native inland vertebrate species.Maduganga, perhaps one of the last remaining tracts of pristine mangrove forest in Sri Lankawith a rich biodiversity, now appears to be threaten,~c:.with the same predicament that many ofthe island's mangroves now find themselves in, owing to increasing human activity. At present,this wetland is not a protected area under any government department. Therefore, it is envisagedthat the findings of this survey will contribute to the .x'nservation of this unique coastal wetland.

Impact of irrigation on water quality, fish and avifauna of three coastal lagoons in Southern Sri Lanka. [Abstract only].

In Ali, A.; Rawi, C. S. M.; Mansor, M.; Nakamura, R.;Ramakrishna, S.; Mundkur, T. (Eds.), The Asian wetlands: Bringing partnerships into good wetlands practices. Proceedings of the Asian Wetland Symposium, Penang, Malaysia, 27-30 August 200