Logging strategy influences colonization of common chlorolichens on branches of Picea abies

Increased knowledge about how lichen colonization responds to logging is a prerequisite for developing guidelines in forest management aimed to maintain biodiversity. Within an experimentally logged boreal spruce forest we studied effects of different logging strategies and distance to the forest edges on colonization of epiphytic chlorolichens. Within a fine-grained (23 clearcuts, 0.2 ha each) and a coarse-grained area (3 clearcuts, 2.25 ha each) we sampled 90 branches. In addition 20 branches were sampled in an untouched control area. The 15 youngest annual shoots along the main axes on each branch were analyzed. Establishment of the dispersed diaspores, most of them Hypogymnia, was mainly limited to shoot ages 4-6 where the needles also were present. Independent of logging strategy the occurrence of small lobules increased with increasing distance from the edges, indicating unfavorable conditions for establishment at the edges or a lower supply of diaspores. A distinct decrease in the number of thalli of Cavernularia hultenii was observed in the two logged areas compared to the control branches. The colonization of Hypogymnia spp. and Platismatia spp. was successful in the fine-grained area, while a coarse-grained pattern of logging caused a significant decrease in the number of thalli, from shoot age 5 for Hypogymnia and shoot age 9 for Platismatia. An early drop of needles in the coarse-grained area, especially at the forest edges, supports the assumption that the occurrence of needles is important for a successful colonization. A higher rate of growth of these species in the coarse-grained area, compared to the other two areas, illustrates that logging does not necessarily cause unfavorable conditions for growth of already established thalli. In conclusion, establishment of the diaspores is less successful in logged areas. Thus, a fragmented logging pattern influences the colonization negatively, even for common chlorolichens. Moreover, the response to logging strategy is species-specific. Development of management guidelines should be based on wide scientific knowledge about the species life-history characteristics.