Does the type of silvicultural practice influence spruce budworm defoliation of seedlings?

Abstract

Spruce budworm (Choristoneura fumiferana (Clem)) is the main defoliator in the boreal forest of North America, and its outbreaks have major ecological and economic consequences and represent a challenge for forest management. Numerous studies have addressed the effects of this defoliator on mature trees, whereas the effects of spruce budworm on regeneration remain elusive. Furthermore, intensive exploitation practices during the last decades have left a large area of the Canadian boreal forest in an early development stage. In this context, it becomes vital to understand those factors affecting the severity of spruce budworm-related defoliation on regeneration. Here, we determine the defoliation severity of black spruce and balsam fir seedlings in both mature pure black spruce and black spruce-balsam fir stands subjected to two different silvicultural treatments (clear-cutting and partial cutting). Defoliation intensity varied between stand types, silvicultural treatments, species, and height classes. Seedlings in black sprucebalsam fir stands experienced twice the defoliation of those in pure black spruce stands (black spruce seedlings 10% vs. 23%; balsam fir seedlings 29% vs. 47%, respectively). Harvesting methods also influenced seedling defoliation. Under clear-cutting, black spruce seedlings (24%) were three times as defoliated as black spruce seedlings in partial cutting stands (8%), whereas balsam fir seedlings in clear-cutting plots experienced twice the defoliation (42%) of balsam fir seedlings in partial cutting plots (20%). The level of defoliation also increased with seedling height. This study will help silvicultural strategies adapt to the effects of natural disturbance regimes. As the intensity and severity of defoliator outbreaks are expected to increase under climate change, these results will help guide forest management strategies to select harvesting methods that will limit the effects of defoliation on conifer regeneration.

Evaluating the impact of climate change on the black spruce defoliation by spruce budworm

“…The mixed stands of black-spruce-balsam fir having taller seedlings were less vulnerable to be affected by the SBW in comparison to pure stands of balsam fir (Girona et al, 2018a;Houndode et al, 2021;Lavoie et al, 2021). In the similar sprucefir stands, the mortality of fir decreased with an increasing proportion of black spruce (Pothier et al, 2012).…”

“…Damage occurs when the larvae of the budworm feed repeatedly upon the annual shoots, foliage, needles, leaf tissue, pollen, and sometimes seeds and cones of a seedling or tree (Blais, 1983;Cooke et al, 2007;Lavoie et al, 2021). Such consumption resulting in the loss of the tree foliage is referred as defoliation (Figure 1.3).…”

“…The economic and ecological consequences of SBW disturbances have placed these events among the priority topics of Canadian forestry research. Decades of continuous research by various organizations and agencies have improved our understanding of the epidemic cycle (Boulanger & Arseneault, 2004;Girona et al, 2018b;Navarro et al, 2018;Ryerson et al, 2003), SBW effects on forest succession (Bergeron et al, 1995;Lavoie et al, 2021;MacLean, 1980MacLean, , 2016Martin et al, 2020), the synchrony of outbreaks over large areas (Bouchard et al, 2018;Sturtevant et al, 2015), and SBW population dynamics (Pureswaran et al, 2016;Régnière et al, 2019a;Royama, 1984).…”

A review of climate change effects on the regeneration dynamics of balsam fir

“…Balsam fir, largely deemed to be economically insignificant before the 20 th century, experienced an increase in abundance throughout the past century (Forbes et al 1998). In addition, the propensity of balsam fir to produce a large amount of advance regeneration, coupled with its shade tolerance, has allowed it to thrive after partial harvest but also when commercial harvesting operations have clear-cut large stands of forest, particularly when harvesting practices preserve advance regeneration, followed by subsequent precommercial thinning to maximize softwood growth and yield by removing shade-intolerant hardwood species (Belle-Isle and Kneeshaw 2007; Lavoie et al 2021).…”

Editorial: Using Landscape Simulation Models to Help Balance Conflicting Goals in Changing Forests

“…Forest ecosystems have long been affected by forestry practices and climate change will have additional affects (Soja et al, 2007;Boulanger et al, 2017;Montoro Girona et al, 2018) on the distribution of tree species (Iverson and Prasad, 1998) and on natural disturbance regimes (Boulanger et al, 2014;Seidl et al, 2017;Navarro et al, 2018). As these effects will have strong economic and ecological implications, there are strong incentives to adapt forestry practices to mitigate anticipated negative effects of climate change, through for instance increasing uptake of carbon by vegetation (Lal, 2004), tree species diversification (Hof et al, 2017), and minimizing tree damage by natural disturbances (Noss, 2001;Montoro Girona et al, 2019;Lavoie et al, 2021). Such adaptations may have uncertain effects on other ecosystem services provided by forests (Noss, 2001;.…”