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Rare Species
     

 Rain forest are known to contain a great diversity of species with low population densities. Having analysed the general structure of the forest and its species composition it is possible to go a step further and study the actual distribution of species in space, and their population sizes i.e. the number of individuals of each species. such studies have in fact been carried out in the Sinhaaja, and show that there is a high degree of species localization with respect to spatial distribution. Among the woody flora above 30 centimeters  girth, 26% of the species were restricted to a single site. The majority densities. For instance, among the trees, 50% are represented by less than 10 individuals per hectare while 15% had only a single individual per hectare. Similar trends are exhibited by the smaller life forms such as the treelets, shrubs, and herbs ; their localization is even more marked probably because their dependence on micro-habitats is greater. While 15% were represented by only one individual in an area of 1,000 square centimeters, 87% had less than 100 individuals in an equivalent area.    

A rare Fern (Lindsaea repens)

 

A rare orchid (Dendrobium macarthiae)

 

A rare endemic Plant "Binara" (Exacum trinervium)

A rare orchid of medicinal value "Wanaraja" (Anoectochilus setaceus)

The most significant geological feature of the forest is a distinctive zone of basic rocks which are referred to as the "Sinharaja basic zone", and which consist of horneblende, pyriclasts, basic charnokites, pyroxene amphiobolites inter-banded with minor accurrences of quartzites, garnetbiotite gneisses and intermediate chrnokites. The basic chrnokites and pyroxene amphibolites indicate an igneous origin prior to metamorphism, created by a low pressure. It is thought that this basic rock formation has led to the desilication processes in the surrounding areas of Ratnapura and Deniyaya which have gem-fields of cordierite-bearing rocks.

                The basic zone also coincides with an aeromagnetic anomaly stretching from Nawalakande through Pitakele and ending at the Denuwankanda-Beverly Estate area.