What is the effect of prescribed burning in temperate and boreal forest on biodiversity, beyond pyrophilous and saproxylic species? A systematic review
Background
While the effects of prescribed burning on tree regeneration and on pyrophilous and/or saproxylic species are relatively well known, effects on other organisms are less clear. The primary aim of this systematic review was to clarify how biodiversity is affected by prescribed burning in temperate and boreal forests, and whether burning may be useful as a means of conserving or restoring biodiversity, beyond that of pyrophilous and saproxylic species.
Methods
The review examined primary field studies of the effects of prescribed burning on biodiversity in boreal and temperate forests in protected areas or under commercial management. Non-intervention or alternate levels of intervention were comparators. Relevant outcomes were species richness and diversity, excluding that of pyrophilous and saproxylic species. Relevant studies were extracted from a recent systematic map of the evidence on biodiversity impacts of active management in forests set aside for conservation or restoration. Additional searches and a search update were undertaken using a strategy targeted to identify studies focused on prescribed burning interventions. Grey literature and bibliographies of relevant published reviews were also searched for evidence. Studies were assessed for internal and external validity and data were extracted, using validity assessment and data extraction tools specifically designed for this review. Studies were presented in a narrative synthesis and interactive map, and those which were suitable were quantitatively synthesised using meta-analyses, subgroup analysis and meta-regression.
Results
Searches generated a total of 12,971 unique records. After screening for relevance, 244 studies (from 235 articles) were included in this review. Most studied forests were located in the USA (172/244), with the rest located in Canada, Europe and Australia. Eighty-two studies reporting 219 comparisons were included in the quantitative synthesis. Within the meta-analyses for each group of taxa, we identified a small to moderate volume of evidence, and heterogeneity was ubiquitous. Prescribed burning had significant positive effects on vascular plant richness, non-native vascular plant richness, and in broadleaf forests, herbaceous plant richness. Time since the burn, forest type and climate zone were significant moderators predicting the effect of burning on herbaceous plant richness. No other significant relationships were identified.
Conclusions
Knowledge gaps exist for studies outside North America, in mixed forests and for non-plant organism outcomes. We identify a need to apply study designs consistently and appropriately, minimising the impact of confounding factors wherever possible, and to provide extensive detail in study reports. We recommend that researchers build long-term datasets charting the impacts of prescribed burning on succession. The lack of consistent findings was likely due to high inter-study heterogeneity, and low numbers of comparable studies in each quantitative synthesis. We found no consistent effects of moderators, and were unable to test the effect of many potential moderators, due to a lack of reporting. Rather than making any general recommendations on the use of prescribed burning for biodiversity restoration, we provide an evidence atlas of previous studies for researchers and practitioners to use. We observe that outcomes are still difficult to predict, and any restoration project should include a component of monitoring to build a stronger evidence base for recommendations and guidelines on how to best achieve conservation targets. Prescribed burning may have harmful effects on taxa that are conservation-dependent and careful planning is needed.
Keywords
Fire regime, Disturbance, Forest conservation, Controlled burn, Forest set-aside, Forest reserve, Habitat management, Prescribed burn
Background
Forests set aside from productive forestry are often considered best conserved by non-intervention. However, biodiversity is often maintained in natural forests by a background level of disturbance, which, in some forests, takes the form of forest fires. Set-aside forests may therefore benefit from continuation of such disturbances, which, in forests under protection, must be managed anthropogenically. While the effects of prescribed burning on tree regeneration and on pyrophilous and/or saproxylic species in some regions are well known, effects on other organisms are less clear and/or consistent. It would be valuable to broaden the knowledge of how prescribed burning affects forest biodiversity, particularly because this practice is increasingly considered as a conservation management intervention. The primary aim of the proposed systematic review is to clarify how biodiversity is affected by prescribed burning in temperate and boreal forests. The ultimate purpose of the review is to investigate whether and how such prescribed burning may be useful as a means of conserving or restoring biodiversity, beyond that of pyrophilous and saproxylic species, in forest set-asides.
Methods
The review will examine primary field studies of how prescribed burning affects biodiversity in boreal and temperate forests. We will consider studies made in such forests anywhere in the world, and will include forests both in protected areas and under commercial management. Non-intervention will be used as a comparator. Relevant outcomes will include a range of measures of biodiversity, including abundance and diversity, but not of pyrophilous and saproxylic species. Relevant studies will be taken from a recent systematic map of the evidence on biodiversity impacts of active management in forests set aside for conservation or restoration. Additional searches and a search update will be undertaken in a subset of databases from the systematic map, using a search string targeted to identify studies focused on prescribed burning interventions. Searches for additional literature will be made in the bibliographies of existing reviews of forest burning. Traditional academic literature and grey literature in English, French, Swedish and Finnish will be considered. Stakeholders who engage in prescribed burning will be asked to provide relevant grey literature.