What is the impact of active management on biodiversity in boreal and temperate forests set aside for conservation or restoration? (systematic map)
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.
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.
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.
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.
Biodiversity, Boreal forest, Temperate forest, Disturbance legacy, Forest conservation, Forest restoration, Forest set-aside, Forest reserve, Habitat management, Partial harvesting, Prescribed burning, Thinning, Grazing, Browsing, Dead wood
The traditional approach to limiting impacts of forestry on biodiversity is to set aside forest areas of particular conservation interest, either as formally protected reserves or on a voluntary basis. Many set-asides are left more or less untouched, but some of them have a history of disturbances such as wildfires, forest grazing, coppicing or small-scale felling. Such areas may gradually lose the qualities that were to be safeguarded unless the disturbances are re-introduced (e.g. by burning) or replaced with alternatives (e.g. gap-felling). Active management of forest set-asides may be particularly relevant in areas where the biota has been impoverished by intensive and large-scale harvesting. Here, biodiversity may not be able to recover adequately without restoration measures such as gap-felling or creation of dead wood.
In recent years, interest in active management of forest set-asides has increased, but opinions differ among conservationists on how such management should be balanced against non-intervention. The topic of the proposed systematic review has therefore met approval among stakeholders in Sweden, where it is currently an issue of high concern.
The review will examine primary field studies of how various forms of active management have affected biodiversity in boreal or temperate forests set aside for conservation or restoration. The primary focus will be on forest types represented in Sweden. In some cases, useful insights about management options may also be provided by studies of interventions in commercially managed forests. Non-intervention or alternative forms of active management will be used as comparators. Relevant outcomes include assemblage diversity (species richness, diversity indices), abundance of different functional or taxonomic groups of organisms, population viability of target species, and indicators of forest biodiversity such as forest structure and amounts of dead wood.
The relevant scientific literature may turn out to be very heterogeneous, however. Numerous combinations of management forms and biodiversity outcomes can be conceived, and it remains to be seen whether any such combination is covered by sufficiently many studies to allow a meaningful meta-analysis. Nonetheless, it should be feasible to achieve a useful narrative synthesis of the available evidence.