The vertical gradient of bark pH and epiphytic macrolichen biota in relation to alkaline air pollution

Vertical changes in bark pH and epiphytic lichen biota on Norway spruce and Scots pine were studied. Sample plots were situated in Estonia at different distances from alkaline air pollution sources. Bark pH increased vertically in all sample plots, its mean values being higher in polluted plots. Proportion of dust indicators was clearly highest in the most polluted sample plot, increasing significantly with height in the canopy; no dust indicators were found on the first 2 m near the ground in any of the sample plots.