Fruticose arboreal lichen biomass accumulation in an old-growth balsam firforest

The standing biomass accumulation of Lichens from the genera Alectoria, Bry oria, and Usnea was studied along two environmental gradients, altitude and height along the vertical tree axis, in an old-growth balsam fir (Abies ba lsamea (L.) Mill.) forest. Lichens were sampled from 50 trees in five sampl ing sites at an altitude of 720-1068 m asl and encompassing three vegetatio n 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 stand ing lichen biomass. The relationship between tree lichen biomass and age wa s not significant. Colonization delay was assumed to correspond to the age of the youngest branch supporting a given lichen taxon, and our results sho w that it increased from mountain to alpine belts. Variations in lichen acc umulation were related to the branch position along the tree height and alt itude. Lichen biomass accumulation rates decreased from tree top to base. W e speculate that this reduction reflects a response to microclimatic gradie nts, aging of thalli, fragmentation, competition, succession, and caribou g razing. 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 relationshi p between Lichen biomass and time was not significant (p > 0.05). The decre ase in accumulation rate along the altitudinal gradient may be primarily ex plained by climatic conditions.