Stand structure interacts with previous defoliation to influence herbivore fitness

Population studies of tree-defoliating insects in Canada: a century in review

“…Broadly speaking, we would highlight several practical advancements arising from Canadian population research for outbreak defoliators. Much of the research to date draws attention to the predominance of natural enemies in regulating populations, although recent work has reintroduced the potential importance of host quality as an indirect factor influencing population decline (e.g., Régnière and Nealis 2007;Moreau and Quiring 2011). This insight has contributed to several striking examples of successful biological control for invasive species (e.g., winter moth and European spruce sawfly) and to some extent native pests (e.g., larch sawfly and balsam fir sawfly).…”

“…Although the duration of the outbreak peak to collapse was similar between thinned and unthinned stands (i.e., two to four years), the amplitude of population fluctuations and associated defoliation was higher in thinned stands, owing at least in part to higher larval survival (Moreau 2004;Moreau et al 2006a;Ostaff et al 2006). Complementary experiments showed that precommercial thinning altered the relative and overall impact of bottom-up (host plant quality) versus top-down (natural enemies) forces on larval survival (Moreau et al 2006b) and reduced the negative influence of previous defoliation on foliage nutritional quality and associated larval performance (Moreau and Quiring 2011). Overall, these studies drew attention to the potentially negative influence of commercial forestry practices on defoliator outbreaks, but also provided the basis for developing a useful biological control agent (the virus) that has since become part of the integrated pest management programme for balsam fir sawfly (Moreau et al 2005).…”

Short-term response of coleopteran assemblages to thinning-induced differences in dead wood volumes

“…Commercial thinning creates sun-exposed understory conditions and can increase biomass, diversity, and cover of understory plants (Thomas et al, 1999), thus increasing the abundance of plant feeders and their predators (Maleque et al, 2007). Moreover, thinning-induced changes in trees and thinning-induced changes in other biotic and abiotic conditions can also increase the performance and densities of non-beetle invertebrates that can be used as prey by beetles (Moreau et al, 2006;Moreau and Quiring, 2011;Fuentealba and Bauce, 2012). Commercial thinning therefore appears as a good compromise between forest management and wildlife conservation; the input of fresh woody debris and the effect of canopy openness on the development of understory vegetation favor both plant and insect diversity.…”

Tree insects and pathogens display opposite tendencies to attack native vs. non-native pines

“…2a). It has been reported that thinning can work against forest health for the case of defoliators, because changes in stand structure due to thinning can increase survival and reproductive performance of defoliators (Mason et al, 1992;Bauce, 1996;Moreau and Quiring, 2011), perhaps because it increases foliar growth, which tends to be correlated with increased foliar nitrogen and decreased foliar defences (Bauce, 1996;Carlyle, 1998;Feeney et al, 1998;Wallin et al, 2004;Moreau and Quiring, 2011). Our study did not reveal any (potentially undesirable) tendencies for thinning to increase the nutritional value of foliage, but we did record a strong pattern of higher foliar N, higher phloem N, and greater phloem thickness on sites that were most favourable for tree growth (good sites vs. bad sites in Fig.…”