What is the impact of active management on biodiversity in boreal and temperate forests set aside for conservation or restoration? A systematic map

Abstract Background The biodiversity of forests set aside from forestry is often considered best preserved by non-intervention. In many protected forests, however, remaining biodiversity values are legacies of past disturbances, e.g. recurring fires, grazing or small-scale felling. These forests may need active management to keep the characteristics that were the reason for setting them aside. Such management can be particularly relevant where lost ecological values need to be restored. In this review, we identified studies on a variety of interventions that could be useful for conserving or restoring any aspect of forest biodiversity in boreal and temperate regions. Since the review is based on Swedish initiatives, we have focused on forest types that are represented in Sweden, but such forests exist in many parts of the world. The wide scope of the review means that the set of studies is quite heterogeneous. As a first step towards a more complete synthesis, therefore, we have compiled a systematic map. Such a map gives an overview of the evidence base by providing a database with descriptions of relevant studies, but it does not synthesise reported results. Methods Searches for literature were made using online publication databases, search engines, specialist websites and literature reviews. Search terms were developed in English, Finnish, French, German, Russian and Swedish. We searched not only for studies of interventions in actual forest set-asides, but also for appropriate evidence from commercially managed forests, since some practices applied there may be useful for conservation or restoration purposes too. Identified articles were screened for relevance using criteria set out in an a priori protocol. Descriptions of included studies are available in an Excel file, and also in an interactive GIS application that can be accessed at an external website. Results Our searches identified nearly 17,000 articles. The 798 articles that remained after screening for relevance described 812 individual studies. Almost two-thirds of the included studies were conducted in North America, whereas most of the rest were performed in Europe. Of the European studies, 58 % were conducted in Finland or Sweden. The interventions most commonly studied were partial harvesting, prescribed burning, thinning, and grazing or exclusion from grazing. The outcomes most frequently reported were effects of interventions on trees, other vascular plants, dead wood, vertical stand structure and birds. Outcome metrics included e.g. abundance, richness of species (or genera), diversity indices, and community composition based on ordinations. Conclusions This systematic map identifies a wealth of evidence on the impact of active management practices that could be utilised to conserve or restore biodiversity in forest set-asides. As such it should be of value to e.g. conservation managers, researchers and policymakers. Moreover, since the map also highlights important knowledge gaps, it could inspire new primary research on topics that have so far not been well covered. Finally, it provides a foundation for systematic reviews on specific subtopics. Based on our map of the evidence, we identified four subtopics that are sufficiently covered by existing studies to allow full systematic reviewing, potentially including meta-analysis.

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