SUMMARY
In recent years there has been growing interest in the study on lichen diversity with relation to altitudinal gradient and anthropogenic disturbances , as changes in lichen community composition may indicate air quality and microclimatic changes. The altitudinal data of species diversity and its subsequent changes with respect to time and space may provide vital information regarding impact of air pollution and/or climate change at regional or global scales. Chopta-Tungnath and adjoining areas of Garhwal Himalaya provide habitat and ecological variation with range of altitude lying between 300 to 3000 m. Out of the 116 species of lichens known from the studied area, the highest species diversity was observed between altitudes 1800 to 2100 m. Lichen communities occurring between 600–1800 m were dominated by members of Physciaceae, while Parmeliaceae were most common above 1800 m. Altitude beyond 2100 m experiences high precipitation, varying temperature conditions and increased incident UV radiation, which are responsible for controlling the variability in lichen diversity to a great extent in the region. The diversity of secondary metabolites in lichen species and consequent changes in species composition at various altitudes indicate the association of secondary chemicals in conferring the lichens resistance to biotic and abiotic stresses. The correlations of lichen diversity, secondary metabolites and the altitudes at which the lichens are growing, present suggestive role of secondary metabolites in determining species composition and sustainability in different environmental conditions.