Fruticose arboreal lichen biomass accumulation in an old-growth balsam fir forest

Abstract

The standing biomass accumulation of lichens from the genera Alectoria, Bryoria, and Usnea was studied along two environmental gradients, altitude and height along the vertical tree axis, in an old-growth balsam fir (Abies balsamea (L.) Mill.) forest. Lichens were sampled from 50 trees in five sampling sites at an altitude of 720-1068 m asl and encompassing three vegetation belts (mountain, subalpine, and alpine). The lichen biomass accumulation rate was studied at branch and tree levels. The Gompertz equation was used to assess the relationship between time since lichen colonization and standing lichen biomass. The relationship between tree lichen biomass and age was not significant. Colonization delay was assumed to correspond to the age of the youngest branch supporting a given lichen taxon, and our results show that it increased from mountain to alpine belts. Variations in lichen accumulation were related to the branch position along the tree height and altitude. Lichen biomass accumulation rates decreased from tree top to base. We speculate that this reduction reflects a response to microclimatic gradients, aging of thalli, fragmentation, competition, succession, and caribou grazing. The accumulation rate was greater in the mountain belt (r = 0.063) than in the alpine belt (r = 0.027). In the subalpine belt, the relationship between lichen biomass and time was not significant (p > 0.05). The decrease in accumulation rate along the altitudinal gradient may be primarily explained by climatic conditions.Key words: arboreal lichens, lichen biomass accumulation, altitude effect, height in tree effect, Alectoria, Bryoria, Usnea.