Effects of forest edges on the distribution, abundance, and regional persistence of wood-rotting fungi

Designing reserves and management practices to contribute to the persistence of old-forest specialized species in fragmented landscapes requires data on plant and animal species responses to edges. We studied 15 edges between Picea abies [L. Karsten] dominated old-growth forests and young clearcuts (6-23 years), old clearcuts (25-39 years), and natural peatlands in eastern Finland. All fallen spruce logs (10-cm diameter; 10,679 logs) in old-forest fragments (13-85 ha) were located by GPS positioning system. Environmental variables and occurrences of old-forest indicator fungi ( Phlebia centrifuga P. Karsten, Amylocystis lapponica [Romell] Singer, Fomitopsis rosea [Alb. & Schwin.: Fr] P. Kartsen, Phellinus ferrugineofuscus [P. Kartsen] Bourdot); a light-adapted fungus (Gloeophyllum sepiarium [Wulfen: Fr] P. Karsten); and a pathogen and saprophyte fungus ( Fomitopsis pinicola [SW.: Fr] P. Karsten) were investigated. The frequency of G. sepiarium was higher and the frequencies of old-forest indicator fungi and F. pinicola were lower near ( 25 m) young clearcut edges in comparison with interiors. Frequencies of some indicator fungi, however, were highest at intermediate distances (10-25 m) from old clearcut and peatland edges. Indicator fungi preferred thick logs of intermediate decay stages in moist biotopes, and their incidence patterns in old-growth forest stands were aggregated. We applied a geographic information system (GIS)-based edge model to calculate edge-interior area relationships of 2,698 old-forest fragments with three values for depth of edge effect: 25 m, 2 (height of old forest), and 2 (differences between the heights of old and adjacent forests). Interior area was reduced to 55-71% of the original with different depth-of-edge values. Total numbers of separate interior areas increased, although interior areas disappeared from the smallest fragments. The results showed that the edge effect is complex and also that it changes when the edge matures because of interactions among several factors. We suggest that sequential management of forests adjacent to reserves and the formation of larger reserves would increase the capacity of the reserves to maintain edge-sensitive species.