Background & Rational
White spruce and adaptation strategy to climate change
The white spruce (Picea glauca) is a long-living tree species found throughout Canada. It contributes significantly to the economy by generating substantial revenue through various products, including timber, pulp, and paper. White spruce is also ecologically important, as it is an important component of Canada's boreal coniferous forests and provides food and shelter for many birds and small mammals (Bérubé-Deschênes et al., 2016 & Petrinovic et al., 2009).
Figure 1: Appearance, needles, trunks and cones of white spruce (Picea glauca) (Government of Ontario, 2023).
Climate warming stands as a paramount concern in the conservation efforts aimed at preserving white spruce populations. The habitat suitable for these populations has shifted 207 km northward from 1961 to 1999, with the trend expected to persist in the future (Gray & Hamann, 2013). White spruce populations situated in northern Canada face a higher risk of drought stress induced by elevated summer temperatures resulting from climate warming, as these northern populations show lower resistance to heat and drought (Chhin et al., 2004). Given the broad spectrum of temperatures and precipitation white spruce spans across Canada, distinct populations exhibit considerable phenotypic plasticity, the assisted migration of white spruce, incorporating genotypes adapted to future climatic scenarios, emerges as a potent conservation strategy.
Previous studies have identified the populations originating from Southern Ontario, near the southern edge of the species' range, as more resilient to drought stress and better suited for northwest habitat (especially Alberta) than the local population in the future (Sinclair, 2019). However, climate warming also amplifies stress from insects, fungi, and pathogens on plants. However, there is a noticeable research gap concerning the adaptation of southeast white spruce populations to pests and diseases in northwest environments.
Previous studies have identified the populations originating from Southern Ontario, near the southern edge of the species' range, as more resilient to drought stress and better suited for northwest habitat (especially Alberta) than the local population in the future (Sinclair, 2019). However, climate warming also amplifies stress from insects, fungi, and pathogens on plants. However, there is a noticeable research gap concerning the adaptation of southeast white spruce populations to pests and diseases in northwest environments.
Eastern spruce budworm and management
Eastern spruce budworm is considered as one of the significant pests to white spruce populations in northern Canada. The eastern spruce budworm (Choristoneura fumiferana) is a native North American species and is recognized as one of the most significant threats to coniferous forests in the region. Outbreaks of eastern spruce budworm occur periodically, roughly every 30-40 years, and exhibit distinct characteristics. During these outbreaks, the Eastern Spruce Budworm can cause several years of defoliation in extensive conifer stands, resulting in a significant number of tree deaths (Government of Canada, 2022).
Figure 2 & 3: Eastern spruce budworm (C. fumiferana) adult and larvae, defoliation caused by C. fumiferana, and its lifecycle, C. fumiferana outbreak often takes place in Mays, during larva feeds (right), the distribution of white spruce (green) and eastern spruce budworm, (yellow) in Canada (Government of Canada, 2022; Marshall. & Roe., 2021).
It is estimated that a single outbreak of spruce caterpillars could lead to the loss of an additional 96 million cubic meters of timber supply over the next 30 years. This loss is equivalent to approximately 66 million tons of carbon dioxide emission. Therefore, it is imperative to take proactive measures to prevent and manage eastern spruce budworm outbreaks in order to safeguard our forests and minimize their environmental impact (MacLean., 2019).
The main methods to manage eastern spruce budworm outbreaks include removing the most susceptible stand, using insecticides, and reducing future susceptibility by planting or thinning and enhancing forest resilience. The use of pesticides is mainly targeted at eastern spruce budworm outbreaks that have been detected. Pesticide use also has the problem of being costly and causing cumulative ecological consequences (Hartz. et al., 2023). In order to develop a fitted migration plan and make forest management more sustainable, studies on the performance of southeast populations to eastern spruce budworm in northern environment is necessary.
The main methods to manage eastern spruce budworm outbreaks include removing the most susceptible stand, using insecticides, and reducing future susceptibility by planting or thinning and enhancing forest resilience. The use of pesticides is mainly targeted at eastern spruce budworm outbreaks that have been detected. Pesticide use also has the problem of being costly and causing cumulative ecological consequences (Hartz. et al., 2023). In order to develop a fitted migration plan and make forest management more sustainable, studies on the performance of southeast populations to eastern spruce budworm in northern environment is necessary.
Chemical defense of trees and terpenoid
The strategies that plants use to protect against leaf-eating insects rely heavily on secondary or defense metabolites, and these compounds can vary both between and within different plant species (Wittstock & Gershenzon, 2002; Mumm & Hiker, 2006; Moore et al., 2014; Moreira et al., 2014). White spruce possesses of different types of terpenes, specifically monoterpenes and sesquiterpenes, which are classes of hydrocarbon compounds found in the essential oils of various plants. Monoterpenes have a molecular structure composed of two isoprene units, while sesquiterpenes consist of three isoprene units, making them larger and more complex than monoterpenes. They can influence the tree's resistance to insect herbivores (Carmona et al., 2011; Kolosova & Bohlmann, 2012; Ulah, 2023). Although there is a lack of precise information on the composition and levels of these terpenes in white spruce foliage, it is anticipated that they may vary across the species' range due to interactions with pest species, fungal endophytes (which are plant symbionts), and environmental factors (Daoust et al. 2010; Fuentealba & Bauce, 2012; Ennis et al., 2017). Hence, investigating needle terpenoid concentration levels of white spruce populations from diverse origins in northern environments can serve as an effective means to anticipate the resistance of this genotype to the eastern spruce budworm in the future. This knowledge, in turn, will aid in the strategic selection of genotypes for afotrstation purposes and the formulation of a more judicious migration plan.
Research hypothesis and objectives
The hypotheses of this study are that the white spruce from southeast population have less foliar terpenoid content and needles with higher terpenoid concentration can cause more weight loss and higher mortality rate of eastern spruce budworm larvae than needles with lower terpenoid concentration.
The main objectives of this research are:
1. investigating whether white spruce populations from the southeast exhibit lower foliar terpenoid content. Additionally, the study aims to explore the correlation between needle terpenoid concentration.
2. To explore the impact on weight loss and mortality rates of eastern spruce budworm larvae.