A VEGETATION STUDY IN TWO SELECTED SITES OF MEETHIRIGALA FOREST RESERVE

Abstract

Meethirigala Forest Reserve, which is a patch of tropical evergreen rain forest, situated in theGampaha District, bordering the Kegalle District, was studied, to characterise the forest withrespect to vegetation structure. Floristic composition, stratification, species richness, speciesdiversity and basal area of the vegetation were studied during a period of eight monthscommencing from February 2000. Data were collected from a site (A) presumed to be a lessdisturbed and relatively disturbed (B). Site A is situated within the area belongs to a monasteryand hence is of restricted accessibility. Two plots each from the two sites, of the size, 30m*30mwere sampled.

Species richness was higher (42 species) in site B than in A (14). Diversity of species in site Awas 2.08 and in site B it was 3.35. These figures showed a significant difference at 1%confidence level according to t-test. Species richness determined by Margalefs index shows asignificant difference between the plots with site A, 2.0 and site B having 6.1. The evenness insite A (2.08) was lower than in site B (3.35). Endemism was higher in site A with 21.4%endemic species and in site B it was 11.9%. The distribution of individuals in stem diameter(dbh) classes was similar in both the sites with a reversed "J" shaped curve, indicating this forestcommunity being composed mostly of smaller plants. However in site B there were noindividuals representing largest class taken into consideration (i.e. 70-80 em) and it contains themost number of individuals in dbh class 3 (i.e. 20-30 ern) whereas in site A dbh class 2 has themost number of individuals. Basal area figures in site A is greater with a III.24m2 of total basalarea and a stand basal area orO.94m2 In site B the values are 81.71m2 and 0.74 respectively.However both the sites showed a reversed "J" curve with regard to basal area distribution,among individuals. Considering the height class distribution, class I (i.e. <5m) showed aconsiderable increase in the number of individuals in site A than in site B. In site A, especially inplot I the understorey was of relatively low density and the stratification was disturbed. Theaverage slope calculated was 0.38 m per meter in site A. It was 0.46m per meter in site B

Distribution of dbh in the community shows reversed "J" curve, a trend similar to that ofSinharaja rain forest community. This is true for both the sites in Meethirigala. In site A thenumber of individuals in the largest height class considered is similar to that of the Pasoh ForestReserve in Malaysia. Pioneer species like Macaranga peltata and Schumercheria castaneaefoliaare found in site B. Endemism figures are significantly lower in Meethirigala than in Sinharaja.Results of the present study suggest that, the natural structure of both the forest sites have beenaltered by human activity. Selective logging, destroying the forest for other non-timber productsand encroachment of forestland have caused disturbance to the forest vegetation in site B. Site Aappears more disturbed. This may be due to the fact that the two plots selected in sight A arelocated near the steam and they are more easily accessed by the villagers. It appears that bothsites are disturbed more or less to a similar extent.