Elevational gradients of terricolous lichen species richness in the Western Himalaya

Elevation confers limitations on distribution of organisms through correlated variations in temperature, moisture, radiations and precipitation. The elevation gradients of terricolous lichen species richness in Garhwal, western Himalaya were assessed using generalized additive models, in order to compare distribution patterns of different growth-forms, photobiont types, and dominant families. A total of 148 terricolous lichen species belonging to 42 genera and 19 families were recorded. The total species richness showed unimodal relationship with elevation, where the highest species richness was observed at mid elevations (3,200 m). The species richness of lichens with green algae (chlorolichens) and of lichens with cyanobacteria (cyanolichens) also exhibited significant unimodal elevational patterns with cyanolichens peaked at somewhat lower (2,800-2,900 m) elevation than chlorolichens (3,200 m). Growth forms showed statistically significant relationship of species richness to elevation, with crustose and squamulose lichens reaching their maxima at higher elevation than foliose, fruticose and dimorphic terricolous lichens. Unimodal pattern of species richness was also followed by six dominant families, with these families reaching maximum richness at different elevations. Elevational variation in topography, climate, and competition from vascular plant communities, together with the tolerance of specific growth forms to zoo-anthropogenic pressures, shape the distribution of terricolous lichens in the Garhwal Himalaya.