Biodiversity and ecological forest-cover domains in boreal landscapes

Studies of spatial forest patterns have traditionally focused on habitat remnants within a landscape, but few have explicitly accounted for natural habitat patterns inherent to those landscapes. At broader scales, all cover types are to some degree subdivided. In boreal forest landscapes, forests, peat lands and water bodies form a variety of different spatial structures depending on their proportions and arrangement. To assess the spatial arrangement of forest patches relevant to organisms and ecological processes, we systematically sampled and analysed 57 boreal forest landscapes (10,000 ha in size) in central Finland. Our results show that even though forest is spatially very subdivided into discrete patches in boreal landscapes it becomes generally well-connected if narrow non-forested gaps are ignored. The proportion of forest cover varied from 17.8 to 75.3% and the number of discrete forest patches from 37 to 213. The average percolation threshold for forest cover was 46.8%. If ≤100 m wide non-forested gaps were ignored and forest patches were joined, the percolation threshold dropped to 33.3%. There were on average 13 discrete clusters of forest patches if forest patches within 200 m distance were combined. These results suggest that if a boreal forest species is able to cross even relatively narrow non-forested gaps, it is likely to perceive these boreal forest landscapes as continuous. Even though our present analysis was based on static forest cover patterns, it is important to consider landscape pattern domains when assessing habitat fragmentation and its consequences to populations of organisms.