Abstract
Exploitation over the last 50 years has altered the Fennoscandian boreal forest landscapes quite considerably. The situation in our two study areas in Lierne (Berglia and Raudberga) in central Norway in three periods, the 1950s, the 1970s and 1999, exemplifies this development. The ecological consequences of the landscape alterations identified during this period are illustrated by tracing the trend of the bird guild associated with old-growth forest. We have used existing and estimated density data for this guild, theories on landscape ecology and Geographical Information System (GIS) analyses. At Berglia, the area covered with old-growth forest was reduced by a further 19 % in 1999 compared with the "pristine" situation where 65 % of the landscape was forested. At Raudberga there has been a further 36 % reduction from the original 72 % coverage, leaving just 36 % of this area covered by old growth. Given our assumptions (e.g. a 100-metre edge effect), the old-growth bird guild has been declining at ratios of 1.23 - 1.49 at Raudberga and 1.60 - 1.93 at Berglia relative to the reduction in the proportion of areas covered by old-growth forest stands, a significantly higher rate of decline than the one-to-one relationship expected if the loss of habitat areas had been the only effect. The difference in the spatial habitat configuration between these two areas can explain some of the variation as Raudberga shows a more coarse-grained fragmentation pattern. If the current trends, according to ourbest-fit models, are allowed to continue until 2050, only 30 - 44 % of the population sizes at the “pristine” state will survive at Berglia and 22 - 32 % at Raudberga. For some of the species involved, this certainly implies that the critical threshold value for maintaining viable population sizes will be exceeded, not least because the long-established practice of clear-felling will lead to a lack of important habitat features such as dead wood and large trees in the landscape. The boreal forest is, however, a natural, dynamic system whose resilience should be quite good and, as shown by our best possible scenario, a significantly improved situation can be achieved by 2050. However, this presupposes that the current alarming trends aretaken seriously by the management authorities, and that the multi-professional knowledge available is applied in future planning processes for our rural areas.
