What are the effects of even-aged and uneven-aged forest management on boreal forest biodiversity in Fennoscandia and European Russia? A systematic review

Abstract

Background Forest harvesting changes forest habitat and impacts forest dependent species. Uneven-aged management is often considered better for biodiversity than even-aged management, but there is an ongoing discourse over the benefits and disadvantages of different silvicultural systems. This systematic review contributes to the public discussion and provides evidence for policy making by synthesising current evidence on impacts of even-aged and uneven-aged forest management on biodiversity in boreal forests of Fennoscandia and European Russia. In this review even-aged and uneven-aged forest management are compared directly to each other as well as to natural forest to provide a broad basis for public discussion. Methods Both peer-reviewed and grey literature were searched in bibliographical databases, organizational webpages and internet search engines in English, Finnish, Swedish and Russian. Articles were screened for relevance by their title/abstract and again by full text. The inclusion of studies was assessed against pre-defined criteria published in an a priori protocol. A narrative synthesis and meta-analysis were conducted to describe the evidence base and to compare species richness and abundance between differently managed forests. The influence of habitat specialism, taxon, years since harvesting, deadwood availability and harvesting intensity on species richness and abundance were also tested. Review findings Searching identified 43,621 articles of which 137 articles with 854 studies had independent data and were included in the narrative synthesis. Of those, 547 studies were included in the meta-analysis. The most studied taxa were arthropods, vascular plants, bryophytes, fungi, and lichens. Results showed that forests with less disturbance (uneven-aged and mature even-aged) host more forest dependent species than young even-aged forests (< 80 years old) although the difference was only marginally significant for mature even-aged forests (> 80 years old). Uneven-aged forest had similar number of species and individuals than natural forest whereas even-aged forest had less species than natural forest. Open habitat species and their individuals were more numerous in young even-aged forests and forests undergone retention harvest. Effect sizes found were mostly large indicating strong and uniform impact of forest management based on species’ habitat preferences. In addition to habitat specialism, years since harvest explained some of the differences found in species richness and abundance due to increase of open habitat species in the early successional stages and forest dependent species in late successional stages. Taxon had limited explanatory power. Conclusions Habitat preferences determine species’ response to different harvesting methods and the magnitude of effect is large. Less disturbance from harvesting is better for forest dependent species whereas opposite is true for open habitat species. Uneven-aged and mature even-aged forests (> 80 years old) are important to maintain biodiversity in boreal forests. However, the results also highlight that natural forests are needed to ensure the future of forest dependent species in Fennoscandia and European Russia. Given that a broader set of biodiversity aspects are to be protected, best overall biodiversity impacts for a variety of species at landscape level can be achieved by ensuring that there is a mosaic of different forests within landscapes.

Nordic forest management towards climate change mitigation: time dynamic temperature change impacts of wood product systems including substitution effects

“…Still, more climate-smart Nordic forest landscapes require mosaics of varying forests including even-, uneven-aged, and natural forests comprising multi-layered mixed stands (Savilaakso et al 2021;Eyvindson et al 2021;Soimakallio et al 2021). Change across all of Europe is urgent given projected climate change and connected economic losses of forests at the end of the century, in the absence of effective counteraction (Hanewinkel et al 2013).…”

Critical appraisal in ecology: What tools are available, and what is being used in systematic reviews?

“…These results indicate that 4.0% of reviews labelled as systematic reviews in this field conducted critical appraisal, and that while the number of reviews labelled as systematic reviews has increased over time (Figure 1), there has been little change in the proportion of these reviews that conducted critical appraisal. Of the 27 included reviews, 20 (74%) investigated topics related to applied ecology, 12,[45][46][47][48][49][50][51][52][53][54][55][56][57][58][59][60][61][62][63] while 10 (37%) investigated other topics in ecology. 11,45,48,62,[64][65][66][67][68][69] Three of the reviews investigated topics related to both applied ecology and other topics in ecology 45,48,62 (see the Supplementary Material for details).…”

“…Two of the CATs 57,60 were very similar indicating one was likely based on the other, however this was not acknowledged. Similarly, Häkkilä et al 52 and Savilaakso et al 59 reported using the same CAT but provided no references to the other review nor to an existing CAT. There were items across all CATs classified as bias at the study-and outcome-levels, generalisaility, precision, and reporting quality, as well as items that were classified as mixed or 'other' (see Table 1 for a summary, and Supplementary Material for details of the items).…”

Widespread Unquantified Conversion of Old Boreal Forests to Plantations

“…One key prerequisite to meeting this challenge is distinguishing natural forests and forests established through planting or seeding following harvest, that often exhibit profound differences in ecological and biogeochemical functions (Savilaakso et al., 2021; Vilà et al., 2013). Older, uncut boreal forests store more carbon (Fredeen et al., 2005; Jonsson et al., 2020) and harbor larger numbers of species than planted forests do (Bradshaw et al., 2009; Jonsson et al., 2020; Patry et al., 2017; Savilaakso et al., 2021), in part linked to larger amounts of old and large dead trees (Fridman, 2000; Martin et al., 2021; Nordén et al., 2013; Santaniello et al., 2017). In an increasingly fragmented landscape, strict protection of these old forests may greatly increase habitat connectivity (Mikusiński et al., 2021), which is also culturally and economically important, for recreation and for reindeer herding because lichens found mainly in older forests are important winter food (Sandström et al., 2016).…”