Trade‐offs in berry production and biodiversity under prescribed burning and retention regimes in boreal forests

Abstract

Abstract Green tree retention and prescribed burning are the practices used to mitigate negative effects of boreal forestry. Beside their effects on biodiversity, these practices should also promote non‐timber forest products (NTFPs). We assessed: (1) how prescribed burning and tree retention influence NTFPs by examining the production of bilberry, Vaccinium myrtillus and cowberry, Vaccinium vitis‐idaea; (2) if there are synergies or trade‐offs in the delivery of these NTFPs in relation to the delivery of species richness, focusing on five groups of forest‐dwelling species. We used a long‐term experiment located in eastern Finland, with three different harvesting treatments: clear‐cut logging, logging with retention patches and unlogged, which were combined with or without prescribed burning. Eleven years after the treatment application, we scored plant cover and berry production in different microhabitats within these treatments, while species richness data for five species groups (ground layer lichens and bryophytes, vascular plants, saproxylic beetles, pollinators—here bees and hoverflies) were collected at the stand level. Logging favoured cowberry production, particularly for plants growing in the vicinity of stumps. Logging was detrimental for cover and berry production of bilberry. Retention mitigated these negative effects slightly, but cover and berry production were still substantially lower compared to unlogged forests. Prescribed burning increased the cowberry production in retention patches and in unlogged forest. Bilberry production decreased with burning, except in unlogged forest where the effect was neutral. No single management treatment simultaneously favoured all values—NTFPs and richness—and trade‐offs among values were common. Only bilberry production and beetle diversity were higher under retention forestry, or in unlogged stands, compared to logged stands. Prescribed burning favoured many values when performed in combination with retention forestry, or in unlogged stands, but different treatment combinations favoured different species groups. Synthesis and applications. Our results demonstrate that widely applied conservation practices in managed boreal forests are unlikely to benefit all ecosystem values everywhere. If high multifunctionality is desired, managing at a landscape scale, countering the local trade‐offs among values, may be more appropriate than the stand‐scale conservation practices commonly practiced today.