Floristic Survey in Kekanadura Forest Reserve in Matara District of Southern Province of Sri Lanka

Abstract

Kekanadura Forest reserve, with an extent of 333 hectares is situated in Matara District of thesouthern region of Sri Lanka. This national Man and Biosphere forest reserve represents thelowland dipterocarp rain forest type. Being situated closer to the boundary of intermediatezone, it has unique edaphic conditions. Considering vegetation characteristics someresearchers argue that this forest should be categorized under intermediate zone-low countryforest. This area receives 1700 mm mean annual rain fall, and the mean temperature is 31°C.

The main purpose of conducting this baseline survey was get correct idea on existing florawhich are threatened by the Southern Highway project, as its next stage up to Kataragama hasbeen designed to run across one section of the forest reserve and presence of the plants whichare subjected to high commercial exploitation like Gyrinops walla. Due to the reason ofcloser proximity to the University of Ruhuna, this type of baseline survey will be beneficialfor the future academic works too.

The present analysis is based on data collected from 24 plots across 6 line transects. Heighand DBH and Height of all the plants above 5 cm DBH found within the plots were counted.Over all 182 plant species are recorded within this forest reserve. Most of them are commonto other rain forests but some of the rare species like Exacum trinervium are also recordedfrom marginal areas where anthropogenic pressure is high. This forest surrounds a waterreservoir and therefore it will be important to retain the forest cover as it is to prevent soilerosion and to minimize siltation of the tank. The forest area includes 62 ha of Pinusplantation which area is currently undergoing natural regeneration with native species.

The Shannon index of diversity is 1.61 in the natural forest area, while it is 1.35 for the Pinusplantation. Evenness of 0.77 is attributed to plants within the natural forest and 0.76 for treesfound in the Pinus plantation area. The dominance of natural forest and Pinus plantations are0.22 and 0.23 respectively. Highest Important Value Index (IVI) is marked for Dipterocarpuszeylanicus, while the dominant family found in the canopy layer is Euphorbiaceae, whichrepresents 14 species of plants. Threatened species like Gyrinops walla and Artocarpusgomezianus were recorded lower number of individuals.

The natural forest area recorded 1,962 plants per hectare for the plants above 5 cm DBH,which belongs to 92 genera and 43 families. According to the analysis of diameter at breastheight (DBH) and population density of the trees in general, it is recorded that all specieswith typically very large trees have few individuals. The average DBH is 11.6 cm. Smallersized species have a large numerical representation. Dichapetalum zeylanicum, Humboldtialaurifolia, Memecylon sp., and Dracaena thwaitesii are the dominant undergrowth plants. In natural forest area 9.35% of the plants were above 25 cm DBH while it was 19.2 for Pinusplantation. It was also revealed that 53% of the plants in Pinus plantation are found 10 cmdbh. That means the gradual replacement of Pinus plantation by native species, becausejuveniles of the Pinus plantation are not being found in below the sub canopy level.

Shape of this land area tended to apply a more edge effect on the forest reserve, while it alsocaused increased anthropogenic pressure. This is especially true regarding the fauna.However, the hermitage and influence of the Buddhist monks have helped to mitigate suchharmful influences and has helped to protect the nature