Local distribution patterns of lichen epiphytes in a western Norwegian deciduous forest : relationship to available substrate

Environmental variables and epiphytic lichen flora of 279 deciduous rich bark trees of a boreonemoral rainforest in the oceanic region of Western Norway were studied. The lichen flora from base to breast height of the tree trunks was investigated for epiphytic macrolichens with cyanobacterial photobiont, 41 species were studied. Descriptive spatial patterns were summarised for each species based upon presence/absence data in two ways: by (1) point pattern analysis and (2) semivariance analysis, e.g. using the geoR package of the R software. Patterns of distribution of trees and their properties were summarised in the same ways (point pattern analysis applicable to geo-referenced tree occurrences only; not to their characteristics). Modelling of species presence (binary response variable) as function of the entire set of predictors was performed primarily using R software. The study revealed a main gradient from trees with great dimensions at low elevation in the north to trees with small dimensions at higher elevation in the south. Fourteen of the investigated lichen species were strongly affiliated with the north end of the gradient, nine species with the south end and only one was spread out evenly. Tree dimension and elevation were found to be the two most important environmental factors. Of the lichen species investigated 16 were oceanic, 24 indicators of long old forest continuity with high and stable humidity, 26 indicators of old deciduous forest continuity and 8 red-listed species. A total of 2/3 of trees investigated was pollarded and these trees had greater dimensions of the stem and higher species richness than the unpollarded 1/3. The old pollarding practice has almost ceased and the remaining pollards in the woodland are relicts (‘living deads’) with a limited lifespan, making the hot spot habitat in need of conservation and recruitment of new host trees.