Epiphytic lichens in old-growth forest fragments in Finland

Laura Kivistö & Mikko Kuusinen
Department of Ecology and Systematics, P.O. Box 47, FIN-00014 University of Helsinki, Finland

Introduction

Diverse and rich epiphytic lichen flora is a distinctive part of old-growth boreal forest environment. Especially old, shady and moist spruce-dominated forests preserve a rich epiphyte flora. During the last decade our forest landscape has dramatically changed from large old-growth forests to the mosaic composed of clear-cuts and mainly planted, younger forest stands. This study examines the effect of old-growth forest fragmentation on epiphytic lichens. It is part of the project "Biodiversity in boreal forests" (lead by Prof. Ilkka Hanski), which studies ecology and dynamics of species in complex landscapes.

Methods

The study was made in two areas: Kuhmo in middle-eastern Finland is an area where the old-growth forests are not yet totally fragmented and forest patches are quite recently isolated, whereas Häme, southern Finland, has a longer history in forest utilization. In Kuhmo 5 small spruce-dominated old-growth forest fragments were selected in three isolation time classes:

  1. under 7 years,
  2. 12-20 years and
  3. over 25 years in isolation from larger (>100 ha) old-growth forests. Two sets of control areas were also selected: 9 ha sample plots within large (>100 ha) old-growth forest areas and small forest islands surrounded by large open wetlands. In Häme 18 old-growth forest areas were selected. The occurrence and abundance of 30 old-growth forest indicator lichen species was mapped in each fragment. These species are most abundant in old-growth spruce-dominated forest stands and are dependent on typical structural elements of old-growth forests, such as old trees, snags and decaying stumps.

Results

The indicator species numbers were lower in southern Finland (Häme) than in middle-eastern Finland (Kuhmo, Fig. 1). The average indicator species number in Häme was 11 and in Kuhmo 15. The effect of old-growth forest fragmentation may be more pronounced in the southern areas, were the utilization of the forests has been more efficient and has lasted for a longer time. The variation in indicator species numbers between the study areas proves to be mainly in species growing on deciduous trees (Fig. 3). Especially old aspens (Populus tremula) and goat willows (Salix caprea) support a rich epiphyte flora with many cyanobacterial lichen species, which are sensitive to the changes in forest structure and require long habitat continuity. These tree species are rare in managed forests, and epiphytes along with many other organisms confined to these trees are becoming threatened.




Fig. 1. Number of indicator species in old-growth forest fragments. The first five columns represent the study areas in Kuhmo in middle-eastern Finland, where the old-growth forest patches are quite recently isolated. The study areas are grouped according to their time interval since isolation. The sixth column on the right represents the study areas in Häme in southern Finland, where old-growth forests are very fragmented and have been isolated for a longer time.




Fig. 2. Pannaria pezizoides is one of the old-growth forest indicator lichen species in Finland. It grows especially on the bases of old deciduous trees and junipers (Juniperus communis).




Fig. 3. Proportions of different substrates for indicator lichens. The first 15 columns represent the study areas in Kuhmo in middle-eastern Finland. The study areas are grouped according to their time interval since isolation. The three columns on the right represent the study areas in Häme in southern Finland