Species diversity and altitudinal preferences of lichens on selected substrata in Ritigala Strict Natural Reserve

The objective of this research was to study corticolous and saxicolous lichen diversity and distribution in Ritigala Strict Natural Reserve (SNR). For this survey, 34 plots, covering different forest types at different elevations: < 300 m, between 300 m and 500 m and > 500 m were established. The plot area was 250 m × 250 m except above 500 m, where it was smaller (10 × 10 m). Trees selected to register lichens were Drypetes sepiaria and Ficus microcarpa at lower elevation (< 300 m), Diospyros affinis and Dimocarpus longana at mid elevation (300–500 m) and Pterospermum suberifolium, Syzygium zeylanicum and Neolitsea cassia at high elevations (< 500 m). Coverage and frequency of lichens were recorded by randomly placing a 250 cm2 quadrate on bole of each tree. Morphology, anatomy, reproductive structures and biochemistry of lichens were examined for their identification. Shannon’s diversity index was used to determine the lichen diversities at different elevations. Data were statistically analysed to reveal the distribution pattern of lichens with change in elevation. Two hundred and eighty-six different lichens collected represented 27 families, 72 genera and 152 species. The distribution pattern of species reflected variability in environmental conditions at different elevations. Higher lichen diversities (1.48 and 1.45) were recorded at higher and lower altitudes than at mid altitudes (1.14). It is envisaged that microclimatic conditions at lower altitudes have encouraged the growth of lichens with trebouxioid photobionts, while shady and cooler niches supported those with cyanobacterial photobionts. Trentepohlioid lichens dominated at mid-elevations. At higher elevations, sunny locations encouraged the growth of trebouxioid folioses while shady and wet places supported cyanobacterial photobionts. Distinct species assemblages at different elevations showing restrictive species distribution signifies the need of protection of Ritigala SNR for lichen conservation.