Forest restoration as a double‐edged sword: the conflict between biodiversity conservation and pest control

Abstract

1. Forestry has markedly changed a large proportion of the world's boreal forests, often with negative effects on biodiversity. As a result, forest restoration is increasingly implemented to counteract the negative effects. However, restoration measures aimed at mimicking natural disturbance regimes could simultaneously increase the risk of unwanted negative effects, such as damage by forest pest species. This study compares the effect of two restoration methods (prescribed burning and gap-cutting), on both biodiversity conservation and pest control, to provide a basis for solutions to this potential conflict. 2. Bark beetles are ideal for studying this conflict, as this group is both species-rich and contains notorious pest species. We conducted a unique, large-scale field experiment in which we compared the effect of two different restoration methods on the abundance, species richness and assemblage composition of bark beetles. In addition, we estimated uncontrolled tree mortality by the number of trees that died post-restoration. 3. Beetles were divided in two groups, primary and secondary, the former with an ability to kill growing trees. Bark beetle diversity did not differ between treatment groups prior to restoration. However, after restoration, assemblage composition and primary bark beetle abundance differed between the treatments. Furthermore, species richness was higher in burned and gap-cut stands compared to reference stands. 4. The number of trees that died post-restoration was highest on burned sites, whereas no difference was found between gap-cut and reference stands. The number of dead trees was correlated with the number of primary beetles. 5. Synthesis and applications. We demonstrate the potential for a conflict between forest restoration for biodiversity conservation and the potential risk for tree mortality caused by forest pests. This is likely to become a problem in many boreal forests; however, our results suggest that this conflict can be moderated by the choice of restoration method. The restoration method gap-cutting had a similar positive impact on bark beetle species richness as compared to the burning method, but did not as burning, increase tree mortality. Thus, in areas where there is an apparent risk for pest outbreaks, our data suggest that gap-cutting should be the chosen method to avoid an unwanted increase in tree mortality at the stand level.

Foraging behavior of the Eurasian Three-toed Woodpecker (Picoides tridactylus) and its implications for ecological restoration and sustainable boreal forest management

“…Fire induces profound changes in stand characteristics, which influence tree substrate availability and quality (Stokland et al 2012, 2018. This may result in changes in both the abundance and assemblage composition of saproxylic insects, the main food source of Threetoed Woodpeckers (Saint-Germain et al 2004a, b, 2008, Hyvärinen et al 2009, Boucher et al 2012, Hekkala et al 2014, Kärvemo et al 2017. It has been suggested that burning homogenizes the quality of tree species in terms of nutrients and structure, making them more equal for saproxylic insects and reduces differences in insect diversity among tree species (Wikars 2002, Toivanen andKotiaho 2010).…”

Experimental evidence on biodiversity impacts of variable retention forestry, prescribed burning, and deadwood manipulation in Fennoscandia

“…In these operations, the amount of post-harvest CWD is important (Joelsson 2017). Gap felling, with gaps 20 m in diameter, benefits cambium consumers, particularly bark beetles (Scolytidae: Scolytinae), but has minor effects on the overall composition of the beetle assemblage (Hjältén et al 2017b;Kärvemo et al 2017). Specifically, xylophages of fresh CWD benefit from felling, apparently due to the rich pulse of slash and stumps, whereas some other species groups may decline, such as mycetophages (Heikkala et al 2016b;Jokela et al 2019; Table 2).…”

“…On the other hand, burning affects some bark beetles negatively (Toivanen and Kotiaho 2010), so prescribed burning may also decrease risks for economic damage (though see, e.g., Kärvemo et al 2017).…”

Dead wood fungi in North America: an insight into research and conservation potential

“…1) (DeFries et al 2004). In addition, logging is a common strategy in forest management to guard against the spread of species targeting decomposing wood (Karvemo et al 2017). For example, bark beetles are natural inhabitants of old-growth trees and their control has started a debate between loggers and environmentalists who disagree on the best way to combat them (Grotta 2013;Stokstad 2017).…”