Population structure of epiphytic lichens associated with old deciduous trees in boreal forests

Mikko Kuusinen, Tuija Konttinen, Ilkka Hanski, Weidong Gu
University of Helsinki

Old deciduous trees, particularly Populus tremula and , support a characteristic epiphytic lichen flora including many specialist species in the boreal forests of Fennoscandia. As these tree species have only a minor commercial value, they have traditionally been removed from managed forests in Finland. Several species associated with these trees have also disappeared or become rare in the managed forests.

In this study we aim: 1. to describe and analyze the spatial population structure of selected epiphytic lichen species associated with old deciduous trees in a virgin and fragmented boreal forest landscape, and 2. To estimate the critical density of suitable substrate trees at a landscape scale for the long-term survival of the species.

Seven cyanobacterial lichen species, Lobaria pulmonaria, L. scrobiculata, Nephroma bellum, N. laevigatum, N. parile, N. resupinatum and Parmeliella triptophylla, known to specialize on old deciduous trees, have been selected for the study. The occurrence of the species has been studied in two boreal forest landscapes in Finland: (1) Kuhmo, in the middle boreal zone (mosaic of old-growth and young managed forests) and (2) Evo, in the southern boreal zone (managed forest area with a few patches of old-growth).

The study areas have been divided into 100 m x 100 m squares according to the Finnish national coordinate system (Grid 27°E). In each 1 ha grid cell (1) the occurrence and frequency of the lichen species and (2) the number of the most suitable substrates for the lichen species, Sorbus aucuparia and Tilia cordata, were also included in the Evo area. All living trees (Populus DPH³15 cm, other species DPH³10 cm), as well as dead standing trunks and recently fallen logs were included in the survey.

Fig.1. The distribution and abundance (number of trees) of Lobaria pulmonaria in a 4 km x 4 km area of a fragmented southern boreal forest landscape (Evo). The abundance of suitable substrate trees (Populus tremula, Salix caprea, Sorbus aucuparia and Tilia cordata) is also shown. The area is divided into two parts: (1) an old-growth forest patch (59 ha, "virgin area") and (2) the managed forests (1541 ha) surrounding this patch. The results are presented in a 100 m x 100 m grid.