Knowledge gaps about mixed forests : What do European forest managers want to know and what answers can science provide?

Research into mixed-forests has increased substantially in the last decades but the extent to which the new knowledge generated meets practitioners' concerns and is adequately transmitted to them is unknown. Here we provide the current state of knowledge and future research directions with regards to 10 questions about mixed-forest functioning and management identified and selected by a range of European forest managers during an extensive participatory process. The set of 10 questions were the highest ranked questions from an online prioritization exercise involving 168 managers from 22 different European countries. In general, the topics of major concern for forest managers coincided with the ones that are at the heart of most research projects. They covered important issues related to the management of mixed forests and the role of mixtures for the stability of forests faced with environmental changes and the provision of ecosystem services to society. Our analysis showed that the current scientific knowledge about these questions was rather variable and particularly low for those related to the management of mixed forests over time and the associated costs. We also found that whereas most research projects have sought to evaluate whether mixed forests are more stable or provide more goods and services than monocultures, there is still little information on the underlying mechanisms and trade-offs behind these effects. Similarly, we identified a lack of knowledge on the spatio-temporal scales at which the effects of mixtures on the resistance and adaptability to environmental changes are operating. Our analysis may help researchers to identify what knowledge needs to be better transferred and to better design future research initiatives meeting practitioner's concerns. This article is based upon work from COST Action FP1206, EuMIXFOR, supported by COST (European Cooperation in Science and Technology). The authors want to specially thank the large number of forest managers that were involved in the participatory process and kindly responded to the surveys. The first author also thanks the Spanish Ministry of Economy and Competitiveness for funding the project AGL2015-70425-R which partly supported his contribution to this study. MM acknowledges support by grant IUT21-4 of the Estonian Ministry of Education and Research and DS support by project III 43007 (2011–2017) from Ministry of Education, Science and Technological Development of Republic of Serbia.