The review team conducted a scoping exercise to assess alternative search terms, testing them against a set of about 20 articles known to be relevant. A preliminary search string was later modified and amended based on suggestions received during the public review. This resulted in the following final selection of search terms:
Subject: forest*, woodland*, “wood* pasture*”, “wood* meadow*”
Forest type: boreal, boreonemoral, hemiboreal, nemoral, temperate, conifer*, deciduous, broadlea*, “mixed forest”, spruce, “Scots pine”, birch, aspen, beech, “Quercus robur”, Swed*
Intervention: conserv*, restor*, rehabilitat*, “active management”, (prescribed OR control* OR experiment*) AND (burn* OR fire*), thinn*, (partial OR selecti* OR gap OR retention) AND (felling OR cutting OR harvest*), “green-tree retention”, *introduc*, remov*, graz*, girdl*, ditch*, flood*, fenc*, exclos*, pollard*, coppic*
Outcomes: *diversity, species AND (richness OR focal OR target OR keystone OR umbrella OR red-list* OR threatened OR endangered OR rare), “species density”, “number of species”, indicator*, abundance, “dead wood”, “woody debris”, “woody material”, “forest structure”, habitat*
The terms within each of the categories ‘subject’, ‘forest type’, ‘intervention’ and ‘outcomes’ will be combined using the Boolean operator ‘OR’. The four categories will then be combined using the Boolean operator ‘AND’. An asterisk (*) is a ‘wildcard’ that represents any group of characters, including no character.
The search terms within the ‘forest type’ category have been chosen to optimise the likelihood of finding relevant studies in Sweden or in forests elsewhere that are dominated by tree species commonly occurring in Sweden. However, the terms should also be capable of identifying a satisfactory share of relevant studies carried out in other boreal and temperate forest types throughout the world.
The selection of search terms above translates to the following search string:
English: forest* OR woodland* OR “wood* pasture*” OR “wood* meadow*”
AND (boreal OR boreonemoral OR hemiboreal OR nemoral OR temperate OR conifer* OR deciduous OR broadlea* OR “mixed forest” OR spruce OR “Scots pine” OR birch OR aspen OR beech OR “Quercus robur” OR Swed*)
AND (conserv* OR restor* OR rehabilitat* OR “active management” OR ((prescribed OR control* OR experiment*) AND (burn* OR fire*)) OR thinn* OR ((partial OR selecti* OR gap OR retention) AND (felling OR cutting OR harvest*)) OR “green-tree retention” OR *introduc* OR remov* OR graz* OR girdl* OR ditch* OR flood* OR fenc* OR exclos* OR pollard* OR coppic*)
AND (*diversity OR (species AND (richness OR focal OR target OR keystone OR umbrella OR red-list* OR threatened OR endangered OR rare)) OR “species density” OR “number of species” OR indicator* OR abundance OR “dead wood” OR “woody debris” OR “woody material” OR “forest structure” OR habitat*)
Searches will also be made using the following French and German counterparts to the English search string (although they in some cases will have to be simplified):
French: forêt* OR forestièr* OR “pâturag* bois*” OR “bois prés” OR “prairie boisée”
AND (boréale OR boréonémorale OR hémiboréale OR némorale OR tempéré* OR conifère OR résineus* OR feuillu* OR “forêts mixtes” OR épinette OR “pin sylvestre” OR bouleau OR peuplier OR hêtre OR “Quercus robur” OR Suèd*)
AND (conserv* OR restaur* OR réhabilit* OR ((dirigé* OR expériment*) AND (brûlag* OR incend* OR feu)) OR éclairci* OR CPRS OR ((partiell OR jardinag* OR retention OR troué*) AND (coupe OR récolte* OR exploit*)) OR *introduit* OR éliminat* OR enlève* OR pâtur* OR annel* OR drain* OR canalis* OR inond* OR clôtur* OR exclos* OR têtard OR taillis)
AND (*diversité OR ((espèce OR taxon) AND (richesse OR vises OR cibles OR clé OR disparition OR menacé* OR rare)) OR “densité des espèce” OR “nombre des espèce” OR indicatrice* OR abondance OR “bois mort” OR “debris ligneux” OR “matériel ligneux” OR “structure de la forêt” OR habitat*)
German: (Wald OR Wälder)
AND (boreal* OR boreonemoral* OR hemiboreal* OR nemoral* OR temperat* OR gemäßigt* OR Schwed*) OR Nadelwald OR Laubwald OR Mischwald OR Fichte* OR Waldkiefer OR Birke* OR Aspe* OR Buche* OR “Quercus robur”)
AND (Naturschutz* OR Renaturierung* OR ((kontrolliert* OR Experiment*) AND Feuer) OR Durchforstung* OR Femelschlag OR Femelhieb OR Femelnutzung OR Einzelstammnutzung OR Einzelbaumnutzung OR Einzelbaumernte OR Lochhieb OR Einführung* OR Entnahme* OR Beweidung OR Ringeln* OR Entwässerung* OR Zaun* OR *zäunung OR Ausschluss*)
AND (Diversität OR Biodiversität OR Artenvielfalt OR (Art* AND (gefährdet OR bedrohte OR seltene OR “Rote* Liste”)) OR Artenzahl OR Zielart* OR Schlüsselart* OR Schirmart* OR Artendichte OR Indikatorart* OR Abundanz OR Totholz OR Waldstruktur* OR Habitat)
No time, language or document type restrictions will be applied.
At some of the websites mentioned below, searches will also be made for relevant literature in Finnish, Russian and Swedish. The search terms will have to be customised to each of these websites, since few of them accept long and complex search strings. Final search strings used for each search will be recorded in an Appendix, together with search dates.
The search aims to include the following online databases:
Academic Search Premier
GeoBase + GeoRef
Nauchnaya elektronnaya biblioteka
Web of Science
Wiley Online Library
Internet searches will be performed using the following search engines:
Google Scholar (http://scholar.google.com)
In each case, the first 200 hits (based on relevance) will be examined for appropriate data.
Websites of the specialist organisations listed below will be searched for links or references to relevant publications and data, including grey literature.
Ancient Tree Forum (http://www.ancient-tree-forum.org.uk)
Bureau of Land Management, US Dept. of the Interior (http://www.blm.gov)
Environment Canada (http://www.ec.gc.ca)
European Commission Joint Research Centre (http://ec.europa.eu/dgs/jrc)
European Environment Agency (http://www.eea.europa.eu)
Food and Agriculture Organization of the United Nations (http://www.fao.org)
Finland’s environmental administration (http://www.ymparisto.fi)
International Union for Conservation of Nature (http://www.iucn.org)
Natural Resources Canada (http://www.nrcan.gc.ca)
Nordic Council of Ministers (http://www.norden.org)
Norwegian Environment Agency (http://www.miljødirektoratet.no)
Norwegian Forest and Landscape Institute (http://www.skogoglandskap.no)
Norwegian Institute for Nature Research (http://www.nina.no)
Parks Canada (http://www.pc.gc.ca)
Society for Ecological Restoration (http://www.ser.org)
Swedish County Administrative Boards (http://www.lansstyrelsen.se)
Swedish Environmental Protection Agency (http://www.naturvardsverket.se)
Swedish Forest Agency (http://www.skogsstyrelsen.se)
Swedish University of Agricultural Sciences (http://www.slu.se)
UK Environment Agency (http://www.environment-agency.gov.uk)
United Nations Environment Programme (http://www.unep.org)
United States Environmental Protection Agency (http://www.epa.gov)
US Forest Service (http://www.fs.fed.us)
Other literature searches
As a check of the comprehensiveness of our searches, relevant articles and reports will also be searched for in bibliographies of literature reviews. Moreover, each member of the review team will use national and international contacts to get information on current research related to the topic of the review, and also to find non-peer-reviewed literature, including reports published in e.g. Swedish, Finnish, Estonian or Russian. In addition, unpublished data (e.g. records of prescribed fires and other interventions) may be available from forest owners, consultants or local authorities involved in the management of forest set-asides. Stakeholders will be asked to suggest suitable contacts.
Study inclusion/exclusion criteria
Articles found by searches in databases will be evaluated for inclusion at three successive levels. First they will be assessed by title by a single reviewer. In cases of uncertainty, the reviewer will tend towards inclusion. As a check of consistency, a subset of 100 titles will be assessed by all members of the review team. If the main reviewers’ assessments tend to differ from those of the other team members, the team will discuss and agree on how the inclusion criteria should be interpreted.
Next, each article found to be potentially relevant on the basis of title will be judged for inclusion on the basis of abstract. The reviewer will tend towards inclusion in cases of uncertainty. A subset consisting of at least 100 of the articles will be assessed by at least two reviewers. A kappa statistic  relating to the assessments will be calculated. If this statistic indicates that the reviewers are inconsistent in their assessment (κ < 0.6), discrepancies will be discussed and the inclusion criteria will be clarified or modified.
Finally, each article found to be potentially relevant on the basis of abstract will be judged for inclusion by a reviewer studying the full text. Again, reviewers will tend towards inclusion in cases of uncertainty. Final decisions on whether to include doubtful cases will be taken by the review team as a whole.
Studies or datasets found by other means than database searches will be entered at the last stage of this screening process.
A list of studies rejected on the basis of full-text assessment will be provided in an appendix together with the reasons for exclusion.
Each study must pass each of the following criteria in order to be included.
Relevant subjects: Forests in the boreal or temperate vegetation zones. Any ecosystem with a tree layer will be regarded as forest, which means that studies of e.g. wooded meadows and urban woodlands may be included.
Studies of forests subject to large-scale commercial forestry may also be included, although this review deals with the management of forests set aside from forestry of that kind. The reason is that certain practices commonly applied in commercial forestry (e.g. thinning) may be useful as management options for set-asides too.
Relevant types of intervention: Active management which is used or can be used to conserve or restore forest biodiversity. Relevant management types include but are not restricted to prescribed burning, thinning, livestock grazing, blocking of drainage ditches, introduction or removal of species, and creation of dead wood e.g. through girdling of trees.
Although stakeholders suggested that studies of wildfires should be included, the review team decided not to do so. Wildfire is in most cases not a management option, although it may be possible to choose whether to suppress a fire or not, and while there is an extensive literature on the effects of unplanned and uncontrolled fires (e.g. [22, 23]), their consequences for biodiversity cannot be assumed to be identical to those of prescribed burning. Studies have been made of prescribed burning too, and we judge that they will be sufficient for the needs of this review.
We will also exclude studies of restrictions of public access and creation of artificial habitats such as provisioning of artificial nest sites for vertebrates (the latter management option has already been extensively reviewed, e.g. by Newton ).
Relevant type of comparator: Non-intervention or alternative types of intervention.
Relevant types of outcome: Measures or indicators of biodiversity in the terrestrial environment. Relevant measures of biodiversity include e.g. species richness, diversity indices and abundance of different taxonomic or functional groups of organisms, and also the population viability of target species. Forest structure and amounts of dead wood are two examples of relevant indirect biodiversity indicators.
Relevant type of study: Primary field studies. This criterion excludes e.g. modeling studies and review papers.
Language: Full text written in English, French, German, Danish, Norwegian, Swedish, Finnish, Estonian or Russian.
Potential effect modifiers and reasons for heterogeneity
To the extent that data are available, the following potential effect modifiers will be considered and recorded:
Climate (and climate change)
Mean age of forest stand
Dominant tree species
Type and areal extent of forest set-aside
Type, areal extent, duration and intensity of management activities
Time elapsed from management activities to final data sampling
Landscape aspects (such as degree of isolation)
History of land use and protection
When assessing the outcomes of conservation efforts in set-aside forest areas, the land-use legacy must never be overlooked. It will also be necessary to consider conditions in the surroundings of such areas. Many reserves lie like scattered islands in a ‘sea’ of efficiently managed but species-poor timber production forest. This fragmentation of less exploited, species-rich natural forest can make it difficult to maintain biodiversity within the ‘islands’ set aside from forestry.
A final list of modifiers and causes of heterogeneity to be recorded will be established as the review proceeds.
Study quality assessment
Studies that have passed the relevance criteria described above will be subject to critical appraisal. Based on assessments of their validity, they will be categorised as having high, medium or low susceptibility to bias (e.g. due to presence or absence of replication or data on variance and potential effect modifiers). Studies with high susceptibility to bias will be excluded from the review.
The exact criteria to be applied when assessing study quality will be developed as the review proceeds, but factors such as methodological description, duration between intervention and data sampling, accounting for potential effect modifiers, replication and statistical treatment are likely to feature prominently among them.
Comparison of how different kinds of management affect biodiversity can in principle be made both temporally and spatially. Studies with a ‘BA’ (Before/After) design compare data collected at the same site prior to and following an intervention. Other studies may be based on comparison of different parts of a forest, some that have been subject to a certain kind of active management and some that have not. These may be termed as ‘CI’ (Comparator/Intervention) studies, or ‘BACI’ (Before/After/Comparator/Intervention) if they present data collected both before and after the intervention.
In practice, studies with a CI or BACI design are likely to be more useful than BA studies in the context of this review. This is because of the long time-scale of forest ecosystem changes, which means that a forest set-aside that has been subject to some kind of active management may also be affected by other influences (e.g. climate change, nitrogen deposition, or ecological succession following earlier land-use changes) before management effects have had time to develop fully. Such influences can be controlled for in CI and BACI studies, but not in BA studies.
Detailed reasoning concerning critical appraisal will be recorded in a transparent manner. In general, the quality of a study will be assessed by one reviewer, but final decisions on how to judge doubtful cases will be taken by the review team as a whole.
A list of studies rejected on the basis of quality assessment will be provided in an appendix together with the reasons for exclusion.
Data extraction strategy
Outcome means and measures of variation (standard deviation, standard error, confidence intervals) will be extracted from tables and graphs, using image analysis software when necessary. As a rule, we will extract data on major functional or taxonomic groups, but not on individual species or genera. Where time-series of data are available, we will only extract the most recent results (plus pre-intervention data from BA and BACI studies). Data on interventions and other potential effect modifiers will also be extracted from the included articles, but climatic data will be downloaded from the WorldClim database .
It may in some cases be useful to ask authors of relevant articles to supply data in digital format. This will primarily be done where useful data have been published in graphs from which they are difficult to extract accurately enough, or when it is known or assumed that considerable amounts of relevant but unpublished data may be available in addition to the published results. If raw data are provided, summary statistics will be calculated by us.
Data synthesis and presentation
A narrative synthesis of data from all studies included in the review will describe the quality of the results along with the study findings. Tables will be produced to summarise these results. Where studies report similar outcomes, meta-analysis may be possible. In these cases effect sizes will be standardised and weighted appropriately. Details of the quantitative analysis will only be known when full texts have been assessed for their contents and quality.
If meta-analysis of effect sizes is possible, it will take the form of random-effects models, and meta-regression will be performed where effect modifiers cause significant heterogeneity between studies. Subgroup analysis of categories of studies will also be performed where sufficient studies report common sources of heterogeneity. Publication-bias and sensitivity analysis will be carried out where possible. Overall management effects will be presented visually in plots of mean effect sizes and variance.
As an alternative to a full systematic review (or in addition to such a review), we may compile a systematic map of the evidence base. Such a map would be produced in an easily searchable format and provide basic data on the studies that we have found to be relevant, including study locations, forest types, types of intervention and types of reported outcomes.