Epiphytic lichen biomass in a boreal Norway spruce forest

Alectorioid and foliose lichens were weighed from full-size branches of Picea abies cut at two canopy heights in 100 trees in an old subalpine forested area in eastern Norway. The mean lichen biomass per branch decreased from 46 to 37 g moving upwards from 2-3 to 5-6 m canopy height. The lichen biomass correlated strongly with branch size variables, branch diameter alone explaining 48% of the variation in lichen biomass per branch (n = 200). The alectorioid/foliose biomass ratio increased from 0.149 at 2-3 m to 0-316 at 5-6 m. Site factors reflecting openness of the canopy were computed for the branch at 2-3 m in all trees. The alectorioid/foliose biomass ratio increased significantly with the indirect site factors, suggesting that light, or factors associated with light, determine the balance between these two growth forms in tree canopies. Within the alectorioid biomass component, genera with usnic acid (Alectoria, Usnea) decreased with height, whereas the genus Bryoria with melanic pigments increased. According to the literature, dark melanic pigments have higher visible light screening efficiency than the yellowish usnic acid. Such patterns suggest a functional role for cortical pigments in the niche differentiation of alectorioid lichens.