Forest grouse response to forestry practices across four decades

Abstract

Fennoscandivian boreal forests have been logged for centuries, yet only since the second world war has management shifted from selective logging to clear-cutting. In general, this shift equates to fewer stands of uneven age and higher vertical complexity and more stands of even age and lower complexity. Ecological responses to this shift in forestry practice are expected and could be especially significant for umbrella species, those species whose protection affords a sort of trickle-down protection for a host of other species. Two putative umbrella species are the Black Grouse (Lyrurus tetrix) and Western Capercaillie (Tetrao urogallus), large galliform birds of forested habitats of northern Eurasia. We used a 45-year dataset from southeastern Norway to assess how closely each of these species tracked changes in forest cutting class, age, stand density, and in the proportion of deciduous trees. We found that occupancy was hierarchical. The Black Grouse tended to occupy primarily younger (<40 y) forests and secondarily forests with higher cover of deciduous trees (>48%) and, at the understorey level, a dominance of bilberry (Vaccinium myrtilus), whereas the capercaillie tended to occupy primarily forest that had not been logged in many years (cutting class IV or V) and secondarily an understorey layer of bilberry and lower stand density. In general, the Black Grouse tracked change in stand density more closely, whereas the capercaillie restricted occupancy to older forest (>100 y) dominated by conifers. Both species were detected most often when stand density was intermediate, with the densest forest typically avoided. In sum, the Western Capercaillie is likely to be a good umbrella species for old-growth boreal forest, particularly coniferous forest, but the Black Grouse, with its more malleable response to forestry practices, would not, as it occurs in mixed forests that are neither too old nor too young. We conclude that management for healthy Black Grouse populations may require little change from current practice as long as sufficient deciduous cover is retained. By contrast, protection of old-growth or mature forests ultimately will be crucial to persistence of Western Capercaillie populations—the species will occupy cut forest, but it is found in such forests much less often. Such protection may necessitate a shift away from clear-cutting as well as a broader perspective to ensure sufficient old growth is retained across the landscape.