Integrating nature conservation effectively in forests managed for timber production implies reconciling a trade-off between ecological and economic objectives. In continuous cover forest management, this culminates in decisions about tree harvesting (or retention) determining both the prevalence of tree-related microhabitats in the forest and the economic viability of timber management. Applying an innovative mixed methods approach, we compare conservationists and foresters performing a tree selection exercise. We assess the outcomes of their forest management decisions quantitatively and explore their strategies and the underlying reasoning based on qualitative data. Our findings show that particularly the habitat trees differ greatly between the two groups: while conservationists retained almost exclusively large oaks at often high opportunity costs, foresters retained a notable number of smaller-diameter hornbeams. These differences are related to a different perception of opportunity costs of retention by both groups, as well as because they do not agree about how to value current tree-related microhabitats and their projection into the future. Such diverging patterns of reasoning imply incompatible interpretations of what constitutes a habitat tree. Our results indicate that it is important to apply benchmarks for evaluating ecological goals as well as to increase foresters’ and conservationists’ understanding about the motivations and restrictions of the respective counterpart. Our study points out a significant potential for (mutual) learning, and illustrates the complementarity of quantitative and qualitative research methods to examine tree selection behaviour.

The implementation of biodiversity conservation measures in forests managed for timber production usually implies trade-offs between ecological and economic objectives. In continuous cover forestry these trade-offs emerge at the scale of selecting individual trees for timber harvesting or habitat retention. Tree selection determines both the economic viability of timber management and the prevalence of treerelated microhabitats, considered a multi-taxon indicator of forest biodiversity. Recent studies find that tree selection is influenced by several factors, such as individual management preferences and goals, professional education and institutional context. To gain a deeper understanding of tree-selection practices in the context of retention forestry, we analyse four tree-selection exercises on silvicultural training sites (Marteloscopes) performed by groups with different professional backgrounds: conservationists, foresters, and students of each. Based on qualitative data from participant observations and group discussions, we explore their decision-making strategies, reasoning, and practices. Our analysis provides novel insights into decision-making processes when implementing conservation measures, especially with regard to dealing with trade-offs and uncertainties. Our findings indicate that tree-selection decisions are not merely the result of cognitive and rational weighing processes. They can be understood as practices requiring experience, professional routine, and intuition. These practices differ across professional cultures. Despite these differences, the participants of the analysed Marteloscope exercises developed an understanding of the other stakeholders' motivations and restrictions. The setting stimulated a change of perspective that built awareness in many of the participants of their own routines and biases. This may facilitate professional cooperation, crossdisciplinary learning, and the implementation of biodiversity conservation.

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