Effects of altitude and tree height on the distribution and biomass of fruticose arboreal lichens in an old growth balsam fir forest

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Abstract
Biomass and distribution of arboreal fruticose lichens were studied along two environmental gradients, height along vertical tree axis and altitude, in an old growth balsam fir (Abies balsamea [L.] Mill.) forest in the McGerrigle Range, Gaspé Provincial Park, Québec. Biomass was estimated by subsampling 53 balsam firs selected from five plots, systematically distributed along an elevational transect. Three vegetation belts (mountain, subalpine, and alpine) located between 720 and 1068 m (above sea level) were sampled. Alectoria sarmentosa, Bryoria spp. and Usnea spp. represented the bulk of epiphytic lichen vegetation. Both gradients influenced lichen biomass and species diversity on balsam fir. The bulk of lichen biomass was found at intermediate heights in trees. In the mountain belt, the number of lichen species was positively correlated with tree height and diameter. Total lichen biomass on trees was predicted by tree diameter and vegetation belt (ln[biomass + 1] = 2.91x + k; R2 = 0.87; k = -2.07, -3.4, or -5.2 in the mountain, subalpine and alpine belts, respectively). In the same order, estimates of total lichen standing crop were 1306 kg/ha, 150 kg/ha and 11 kg/ha. Decrease in lichen biomass in the alpine and subalpine belts may be related to decrease of tree size, harsh environmental conditions and caribou grazing.