Cyanobacterial macrolichens on Populus tremula as indicators of forest continuity in Finland

The frequency of cyanobacterial or cephalodial macrolichens on old standing Populus trees in southern and middle boreal Finland was surveyed on 22 sample plots containing 22-41 trunks. The sample plots were divided into four main groups according to location and human impact: (A) middle boreal +/- old-growth, (B) southern boreal old-growth, (C) southern boreal slightly managed and (D) southern boreal strongly managed plots. The number of cyanobacterial lichen species per tree was mainly 0-2 and only rarely exceeded 5 on some large old-growth trees. All cyanobacterial species occurred exclusively or more frequently on the old-growth plots. Thus the occurrence of cyanobacterial lichens proved to be a potential simple indicator of the continuity of the forest stand. The best indicator species were Lobaria pulmonaria, Nephroma spp., Pannaria pezizoides and Parmeliella triptophylla.