Spatial pattern in the occurrence of the lichen Lobaria pulmonaria in managed and virgin boreal forests

Two populations of the lichen Lobaria pulmonaria, growing on aspens and goat willows in 12 and 20 km(2) study areas of boreal forest in Finland, were surveyed thoroughly to investigate the factors influencing the spatial distribution of the lichen. In one study area, where forestry has been intensive and old-growth forest is highly fragmented, L. pulmonaria was sparse and grew mostly on willows. In contrast, a large and continuous virgin forest area supported a higher incidence of L. pulmonaria, with the lichen being common on both aspens and willows. In both study areas, the distributions of aspen and willow were clumped over the scales of 100-1000 m. The spatial pattern of L. pulmonaria was more clumped in the managed forest than in the virgin forest. The reduced incidence of the lichen on aspens in the managed area was attributed to a disruption of habitat continuity and small average tree size. There was no comparable reduction in the incidence on willows, probably because the willow had a very aggregated distribution in the managed area, which probably facilitated local colonization of the lichen. Presence of the lichen was significantly related to size-corrected local density of aspen and willow trees as well as to spatial connectivity to neighboring lichen-occupied trees.