The Use of Average number of Neighbours for Predicting Lichen Sensitivity: a Case Study

Abstract

The sensitivity of lichen species to air pollution was assessed by examining aspects of their rate of disappearance over a 5 year period in an area with rising SO₂ concentration. These rates of disappearance were compared with the ecological index of species proposed by LeBlanc & DeSloover in 1970, i.e. the index of average number of neighbours for a given species. Linear correlation showed that this ecological index is a reasonably accurate indicator of species sensitivity. When the selection of species was performed according to criteria other than SO₂ sensitivity, viz. according to the predilection of lichens for eutrophicated bark, the ecological index proved reliable only when trees whose conditions were non-optimal for this group were excluded. When applied to the group of species that avoids eutrophicated bark the ecological index proved most reliable, although the group of ‘ nitrophilous ’ species may also be used in air pollution indicator studies.