Department of Geography, University of Peradeniya
Serpentine, bearing the general formula: Mg3Si,OS(OH)a denotes a group of hydrous, magnesium silicate minerals. Sri Lanka too, serpentine bodies occur roughly on the boundary of Vijayan and Highland series of rocks. The three principal 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 substrates harbor unique vegetation communities. Such communities are referred to as lithobiomes and have attracted scientific attention. Other examples of lithobiomes are vegetation on limestone and saline soils etc., which are interspersed within zonal soils.
Ginigal-pelessa and Indikola-pelessa serpentine bodies are located about three kilometers apart. The area receives a rainfall of about 1325mm/yr and the average number of rainy days per year is 94. The maximum amount of rain comes between October and December.
The objective of the present study was to initiate a survey of vegetation in these two unique areas. The study was initially begun in September 1998 in Ginigal-pelessa and was extended to Indikola-pelessa in 1999. It included reconnaissance of the two areas followed by a survey of plant species and soil. Woody plant species were studied in 10 x lOm quadrats whereas, grasses and herbaceous plants were examined in 1 x lm quadrats. Density of the grass vegetation and the abundance of woody plants along with girth were recorded. Slope of the areas was measured with an Abney level. Also examined in each area was a shallow soil 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 chemical analyses 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 serpentine minerals. It is shallow (<45cm in Ginigal-pelessa and <42cm in Indikola-pelessa) and overlies partly weathered serpentinite rocks. The color varies from 7.5 3/2 YR-wet. It is friable (dry) and very friable (wet). It is a silty loam, which is slightly sticky, and slightly plastic when wet. Reddish Brown Earth (RBE) Surrounds the two areas, where the terrain is slightly undulating. The aggregate extent of the two areas is more than four kmZ. Yet, only a few hectares of the associated vegetation remain fairly inact in Ginigal-pelessa whereas, almost the entire serpentine vegetation has been drastically changed in Indikola-pelessa.
The vegetation in both places has a savanna-like physiognomy though the woody plants are somewhat stunted. Dominant non-woody species is the tussock agrass, Cytnbopogon flezuosus Wats. This grass (max. Height 1.2m) along with other herbaceous and low woody plants provide a dense cover. The woody species are scattered apart.
In Ginigal-Pelessa 15 plant species belonging to 12 families were identified in the sampling quadrats.Based onlife form their distribution is as follow:herbs /grasses 03,creepers 02,low shrub spp. 02 shrub spp.05 and tree spp. 03.Among all woody specie Morinda tinctoria Roxb, is the most abundant.Spacial attributes are; mean distance 1.8m max. distance 25.6 m and min.distance 3.2m. Density of trees is 18 /1000m;, Max. tree height is 4m.
In Indikola-pelessa, a place of archaeological importance, 23 species belonging to 16 families were found. Their life form distribution is as follows: herbs/grasses 01, creepers 04, low shrub spp. 03, shrub spp. 03 and tree spp. 12. The dominance of Morinda tinctoria is not seen in this locality. Spartial atrtributes are; mean distance 4.465m. max distance 9.30m and min. Distance 1.9m. Dinsity of trees is 39/1000m2. Max. tree height is 3.5m whereas most of the tree species are in shrub form.
Absence of succulent xerophytes in both areas is striking. This suggests that microhabitat aridity is not a factor. Yet, the stunted nature of the plants may be due 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 as Azadirachta indica A Juss. (neem), Teminalia catappa L. (Kottamba), Anatardium 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.