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Research article2022Peer reviewedOpen access

Short-term experimental support for bird diversity retention measures during thinning in European boreal forests

Klein, Julian; Low, Matthew; Sjogren, Jorgen; Eggers, Sonke


Current levels of forestry expansion in boreal forests threaten to radically reduce biodiversity. For many forest dwelling species the threat is not simply because the forest is used for biomass production, but rather how it is used. Retention forestry practices aim to limit impacts on biodiversity during the final felling stage of a forestry cycle. However, the efficiency of such methods in retaining biodiversity have rarely been studied for intermediate forestry stages (e.g., forest thinning) with experimental approaches entirely absent from boreal forests. Therefore, we conducted a before-after control-impact experiment in Sweden to investigate the short-term response in occurrence of individual bird species, guilds, and population trend groups (positive, stable, or negative population trend), as well as the response in nest box occupancy and in the reproductive success of Parus major to three different thinning treatments. The three treatments were i) conventional thinning at the plot and stand scale, (ii) understory retention thinning, where at least 250 spruces with live branches below 2 m above ground are retained per hectare, and (iii) complete retention plots, where the forest was not thinned on-1 ha plots within conventionally thinned forest stands. We found that conventional forest thinning was likely the cause for observed declines in bird occurrence, with-20% of the species showing clear negative responses. Our results indicate that understory retention thinning with double the retention level as previously suggested and combining conventional thinning with complete retention plots, could largely alleviate the short term negative effects of conventional thinning. This was the case for all guilds, population trend groups and individual bird species, except for Poecile montanus, which responded negatively to complete retention. Among the birds occupying the nest boxes, only Cyanistes caeruleus responded to any of the treatments, with higher nest box occupancy upon understory retention thinning. No thinning treatment affected reproductive success in P. major. Our results clearly show that thinning practices that retain the diversity of forest-dwelling birds are possible. Hence, this study provides a crucial puzzle piece towards more sustainable forestry practices in the boreal region.


Bird; BACI; Sweden; Coniferous; Bayesian; Nest box; Reproductive success; Parus major; Poecile montanus; MSOM; Willow tit

Published in

Forest Ecology and Management
2022, Volume: 509, article number: 120084
Publisher: ELSEVIER