Interchangeable sets of complementary habitat variables allow for flexible, site-adapted wildlife habitat management in forest ecosystems

摘要

Integrating biodiversity conservation into forest management is a major goal in sustainable forestry. Hence, target values for forest structural and compositional stand characteristics are required to ensure wildlife habitats of sufficient extent and quality. Yet, the possibility to meet these targets depends on the patch conditions, notably their initial state and future trajectory. Shaped by succession, site conditions and management regime, not all forest stands can be readily converted into a particular state, which calls for flexible management prescriptions. Using the example of two forest grouse species, capercaillie and hazel grouse, we sought complementary variable combinations - with quantitative thresholds for any given crucial habitat feature - which would likewise offer suitable habitat. Habitat variables were mapped in sampling plots within occupied and non-occupied 1 km(2) grid cells distributed across three Swiss mountain regions. Generalized linear mixed models (GLMM) were combined with conditional inference trees (CIT) to identify species-relevant variable combinations and variable thresholds. Important features for both species were the proportion of bilberry (Vaccinium myrtillus) and the number of basal-branched trees, as well as a low proportion of beech (Fagus sylvatica) in the canopy layer. Hazel grouse additionally favoured rowans (Sorbus aucuparia) as feeding trees and a high percentage of herbs in the ground layer, while the presence of inner forest edges was additionally important for capercaillie. Thresholds were not clear-cut: different values applied for a particular variable depending on other, functionally similar habitat variables present at the site. By delivering information about relevance, interactions and the required amount of crucial variables, we provide alternative options for flexible species habitat management which allows accounting for the prevailing stand conditions.