DIVERSllY OF UNDERSTOREY VEGETATION IN THREE LOWLAND RAIN FORESTS IN SOUTHWEST OF SRI LANKA

Abstract

The study examined the diversity and composition of understorey vegetation in SinharajaMan & Biosphere forest reserve, Kanneliya forest reserve, and Oliyagankele forestreserve. The understorey vegetation was sampled in 54, 27, and 27 plots in Sinharaja FR,Kanneliya FR, and Oliyagankele FR respectively each 5 m x 5 m. Ecological indices andimportant value index. which is the expression of the dominance of particular species indifferent habitats, were calculated

The diversity index (Shannon's) calculated for understorey species found in each plotenumerated at Sinharaja FR, Kanneliya FR. and Oliyagankele FR showed that that thereis no significant difference in diversity among reserves except for slightly higherdiversity observed in Kanneliya forest reserve. A total of 68, 77, and 63 understoreyspecies were found from Sinharaja, Kanneliya, and Oliyagankele FR respectively. Therewere 40 endemic understorey species in Sinharaja FR and in Kanneliya each, and 36 inOliyagankele FR. There were ill, 17, and 14 understorey species found only fromSinharaja, Kanneliya and Oliyagankele FR respectively. The most common family inSinharaja FR and Oliyagankele FR was the Euphorbiaceac, and Fabaceae was inKanneliya FR. There were slight differences in species composition within each forestreserve from valley to ridge.

Results of this study shows that although the difference in diversity is not significant,there are differences in the composition of the understorey as the elevation and meanannual rainfall decreases from Sinharaja FR to Oliyagankele FR. This study also foundthat that are higher percentage of endemic in the understorey of all three study sites.