2.1. Study area

The study was carried out in the surroundings of the city of Oulu (65°00"N, 25°30"). The study area totals about 245 km². It is typical coastal lowland with the highest hilltops reaching 100 m a.s.l. with a lot of rivers, small lakes and ponds. About 60 % of the total area is covered by a mosaic of forests and bogs. The proportion of bogs is very high, roughly half of the woodland area. At present, however, about 60 % of the bogs are dry (Kaila 1993). The forests are dominated by pine Pinus silvestris mixed with Norwegian spruce Picea abies and birch Betula sp. Modern forestry with clear-cuts and pine plantations tends to increase the mosaic pattern of the landscape. About 25% of the forests are in a mature stage. The diversity of successional stages is increased by the secondary succession of dried bogs and abandoned fields. Cultivated fields comprise 14 % of the area.