PRELIMINARY SURVEY OF SERPENTINE VEGETATION IN UDA WALAWE AREA

Abstract

Serpentine, bearing the general formula: Mg.,Si205(OH)4 denotes a group ofhydrous, magnesium silicate minerals. Sri Lanka too, serpentine bodies occurroughly on the boundary of Vijayan and Highland series of rocks. The threeprincipal serpentine areas of Sri Lanka are 'Ginigal-pelessa' and 'Indikola-pelessa'both close to Uda Walawe and, 'Ussangoda' near Nonagama Junction.

Within broad climatic zones, soils developed on serpentine mineral substratesharbor unique vegetation communities. Such communities are referred to aslithobiomes and have attracted scientific attention. Other examples of lithobiomesare vegetation on limestone and saline soils etc., which are interspersed withinzonal soils.

Ginigal-pelessa and Indikola-pelessa serpentine bodies are located about threekilometers apart. The area receives a rainfall of about 1325mmlyr and the averagenumber of rainy days per year is 94. The maximum amount of rain comesbet ween October and December.

The objective of the present study was to initiate a survey of vegetation in thesetwo unique areas. The study was initially begun in September 1998 in Ginigalpelessaand was extended to Indikola-pelessa in 1999. It included reconnaissanceof the two areas followed by a survey of plant species and soil. Woody plantspecies were studied in 10 x 10m quadrats whereas, grasses and herbaceous plantswere examined in 1 x 1m quadrats. Density of the grass vegetation and theabundance of woody plants along with girth were recorded. Slope of the areaswas measured with an Abney level. Also examined in each area was a shallowsoil pit and soil depth was measured in selected points, by means of an auger.Soil color was determined with the aid of a color chart, yet no soil chemicalanalyses were done.

In Ginigal-pelessa the maximum slope is 15% and it is 12% in Indikola-pelessa.The substrate in both places is an undifferentiated soil developed from serpentineminerals. It is shallow «45cm in Ginigal-pelessa and <42cm in Indikola-pelessa)and overlies partly weathered serpentinite rocks. The color varies from 7.5 3/2YR-wet. It is friable (dry) and very friable (wet). It is a silty loam, which isslightly sticky, and slightly plastic when wet. Reddish Brown Earth (RBE)Surrounds the two areas, where the terrain is slightly undulating. The aggregateextent of the two areas is more than four km2. Yet, only a few hectares of theassociated vegetation remain fairly inact in Ginigal-pelessa whereas, almost theentire serpentine vegetation has been drastically changed in Indikola-pelessa,

The vegetation in both places has a savanna-like physiognomy though the woodyplants are somewhat stunted. Dominant non-woody species is the tussock agrassCymbopogon flexuosus Wats. This grass (max. Height 1.2m) along with otherherbaceous and low woody plants provide a dense cover. The woody species arescattered apart.

In Ginigal-pelessa 15 plant species belonging to 12 families were identified in thesampling quadrats. Based on life form their distribution is as follows:herbs/grasses 03, creepers 02, low shrub spp. 02, shrub spp. 05 and tree spp. 03.Among all woody species Morinda tinctoria Roxb, is the most abundant. Spatialattributes are; mean distance 1.8m. max. distance 25.6 m and min. Distance 3.2m.Dinsity of trees is 18 II OOOm",Max. tree height is 4m.

In lndikola-pelessa, a place of archaeological importance, 23 species belonging to16 families were found. Their life form distribution is as follows: herbs/grasses01, creepers 04, low shrub spp. 03, shrub spp. 03 and tree spp. 12. Thedominance of Morinda tinctoria is not seen in this locality. Spartial atrtributesare; mean distance 4.465m. max distance 9.30m and min. Distance 1.9m. Dinsityof trees is 39/l000m2. Max. tree height is 3.5m whereas most of the tree speciesare in shrub form.

Absence of succulent xerophytes in both areas is striking. This suggests thatmicrohabitat aridity is not a factor. Yet, the stunted nature of the plants may bedue to other edaphic factors (e.g. shallow soil profile, mineralogical conditions).In both places periodic burning as in patanas, is an arresting factor.

In relatively undisturbed sites, near-normal growth of such wood species asAzadirachta indica A Juss. (neern), Teminalia catappa L. (Kottamba),Anarardium occidentale L. (cashew) and leucaena leucocephala Lam, (ipil-ipil)indicates that deep-rooted perennials can do well in these serpentine areas.Therefore, the area seems sustable for conservation forestry and wood-fuel lots.