SOME STUDIES ON THE DIVERSITY AND DISTRIBUTION OF LICHENS ON RITIGALA MOUNTAIN

Abstract

Studies on lichens at Ritigala Mountain revealed that a marked variation exists inthe distribution and diversity of lichens with change in elevation. Light andmoisture are two main environmental factors that changed the microclimate,which in turn determine the distribution of lichens at different elevations. Most ofthe lichens recorded on the barks of trees and rocks at lower elevation belonged togenera such as Dirinaria, Graphis, Parmelia, Psyxine, Pyremula and Parmotrentaand, Leptogium. At mid elevation (i.e. between 400 - 500m contour line)diversity and distribution found to be much different from those at lowerelevations. Crustoses such as species of Myreotrema, Thelotrema, Porina,Phyllospora, Ocellularia and several sterile ones were found on tree trunks androcks. However, the lichen diversity of the crowns of trees at mid elevation seemsto be somewhat similar to that at lower elevation although tree species aredifferent. At mid elevation, tree trunks get only diffused light while the canopygets more direct light. The difference in distribution and diversity observed onbarks could mainly be due light condition prevailing at mid elevations.

At elevations above 600m, genera observed were very much different to thosefound at lower levations. Commonest genera recorded were Heterodeeermia,Pseudocyphellaria, Sticta, Collema, Leptogium and Parmelia. At higherelevations, it is cool but sunny during the day while nights are cooler and wet dueto mist. Thus. differences observed with respect to lichen diversity could be dueto the difference in microclimate that prevails at higher elevations.

Air quality studies indicated that air pollution due S02 is minimal in this area.Thisresearch reveals that Mount Ritigala supports extremely interesting and diverselichen community which has not yet been explored fully yet. Similar to vascularplants, lichens show a marked zonation in the distribution of various species. Thiscould be mainly due to differences in the microclimate at different attitudes. Aslichens are sensitive to changes in the microclimate (specially with respect to airpollutants) it is important that the prevailing conditions are maintained. Anyactivities that lead to severe atmospheric pollution may cause significant changesin the existing lichen diversity.