PS 28-89 - Insect Herbivore Communities and Associated Damage in White Spruce (Picea glauca, Pinaceae) Sylviculture in the Boreal Forest of Québec

Background/Question/Methods

Sylvicultural practices aim to maximize tree growth but are increasingly required to also mimic natural ecosystem processes. Herbivorous insects can cause considerable damage to trees in plantations but are also key players in forest biodiversity. Sylviculture under ecosystem-based management thus must minimize damage by herbivorous insects while preserving diversity of this trophic level. This study aims to examine the herbivore community and associated damage on white spruce (Picea glauca, Pinaceae) in plantations and in natural regeneration in the northern mixed-wood boreal forest of Québec. We selected ten sites in two treatments, forest (F) and plantations (P), sampling ten young trees in each site in late summer 2020 and in both early and late summer 2021. We question whether the rate of arthropod herbivory differs between the two treatments, partition damage between various feeding guilds (sapsuckers, chewers, leaf-miners, and gall-forming insects) and link herbivore damage to environmental factors and plant traits. We also sampled herbivorous and predatory insects in order to compare herbivore communities and estimate predation pressure in the two habitats.

Results/Conclusions

Results suggest insect herbivore abundance and overall damage were higher in plantation than in forest trees. In particular, damage from sapsuckers was much higher in plantations, and was paralleled by the high relative abundance of aphids. Leaf chewers were equally recorded in both habitats. A fungal disease also caused more damage to the young shoots in the plantation than in the forest. Differences in damage were linked to lower canopy cover and higher leaf toughness in the plantation. We conclude that although damage is higher in plantations, this does not pose a significant threat to tree growth and that plantations do support a diverse community of insect herbivores. These findings reflect background endemic herbivory in the absence of pest outbreaks. A spruce budworm (Choristoneura fumiferana) outbreak is beginning in the region, and it remains to be seen whether the patterns observed here will be maintained.