Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Species identifications have been historically difficult in the economically important spruce budworm (Choristoneura fumiferana) pest complex. Morphological, ecological, behavioural, and genetic characters have been studied to try to understand the taxonomy of this group, but diagnostic character states differ in frequency rather than being complete replacements between each species. I developed a morphology-based character system that focuses on forewing colour components (Chapter 2), as well as eight simple sequence repeats (SSRs, also referred to as microsatellite markers) (Chapter 3). I tested these along with a 470 bp region of COI mitochondrial DNA (mtDNA) (Chapter 2, 4) to determine their congruence with putative species that were identified by adaptive traits (larval host plant, length of larval diapause, larval and adult morphology, pheromone attraction, distribution). The morphometrics system was effective for identification of the five species tested, with only slight overlap between C. fumiferana and C. biennis. MtDNA distinguished C. fumiferana and C. pinus pinus, but the remaining species shared haplotypes. SSRs distinguished four species (C. fumiferana, C. pinus pinus, C. retiniana, C. lambertiana) but the remaining four species that were included in this survey (Chapter 4) remained mixed within two populations. There was evidence for hybridization between several species pairs. I also conducted a detailed study (Chapter 5) in Cypress Hills, an isolated remnant coniferous forest in western Canada, where identifying individuals from the Choristoneura fumiferana complex has been impossible due to the unusual ecogeographic characteristics of the area. I integrated data on behaviour, ecology, morphology, mtDNA, and SSRs, comparing Cypress Hills populations to those from other regions of North America to determine which species they resembled most. I delimited at least three populations, resembling C. fumiferana, C. occidentalis and C. lambertiana. Adult flight phenology, along with pheromone attraction, were identified as major isolating mechanisms between these populations. My studies highlighted the importance of integrative taxonomy for understanding species boundaries. Their patterns of differentiation suggest that spruce budworm species have recently diverged via natural selection in spite of some gene flow. Overall, this work is intended to contribute to more accurate identification of specimens and a better understanding of the evolutionary processes that drive speciation. / Systematics and Evolution

This dissertation is concerned with effects dispersal and forest structure on forest insect population dynamics, and with identifying generating processes by comparing observed patterns to model predictions. In chapter 2, we investigated effects of changing forest landscape patterns on integro-difference models of host-parasitoid population dynamics. We demonstrated that removing habitat can increase herbivore density when herbivores don't disperse far, and parasitoids disperse further, due to differences in dispersal success between trophic levels. This is a novel potential explanation for why forest fragmentation increases the duration of forest tent caterpillar outbreaks. To better understand spatial model behaviour, we proposed a new local variation of the dispersal success approximation. The approximation successfully predicts effects of habitat loss and fragmentation on realistically complex landscapes, except when outbreak cycle amplitude is very large. Local dispersal success is useful in part because parameters can be estimated from widely available habitat data. In chapter 3, we investigated how well a discretized integro-difference model of mountain pine beetle population dynamics predicted the occurrence of new infestations in British Columbia. We found that a model with a large dispersal kernel, and high emigration from new, low severity infestations yielded the best predictions. However, we do not believe this to be convincing evidence that many beetles disperse from new, low severity infestations. Rather, we argued that differences in habitat quality, detection errors, and Moran effects can all confound dispersal patterns, making it difficult to infer dispersal parameters from observed infestation patterns. Nonetheless, predicting infestation risk is useful, and large kernels improve predictions. In chapter 4, we used generalized linear mixed models to characterize spatial and temporal variation in the propensity of jack pine trees to produce pollen cones, and account for confounding effects on the relationship between pollen cone production and previous defoliation by jack pine budworm. We found effects of stand age, and synchronous variation in pollen cone production among years. Accounting for background patterns in pollen cone production clarified that pollen cone production declines in with previous defoliation, as expected.

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This dissertation is concerned with effects dispersal and forest structure on forest insect population dynamics, and with identifying generating processes by comparing observed patterns to model predictions. In chapter 2, we investigated effects of changing forest landscape patterns on integro-difference models of host-parasitoid population dynamics. We demonstrated that removing habitat can increase herbivore density when herbivores don't disperse far, and parasitoids disperse further, due to differences in dispersal success between trophic levels. This is a novel potential explanation for why forest fragmentation increases the duration of forest tent caterpillar outbreaks. To better understand spatial model behaviour, we proposed a new local variation of the dispersal success approximation. The approximation successfully predicts effects of habitat loss and fragmentation on realistically complex landscapes, except when outbreak cycle amplitude is very large. Local dispersal success is useful in part because parameters can be estimated from widely available habitat data. In chapter 3, we investigated how well a discretized integro-difference model of mountain pine beetle population dynamics predicted the occurrence of new infestations in British Columbia. We found that a model with a large dispersal kernel, and high emigration from new, low severity infestations yielded the best predictions. However, we do not believe this to be convincing evidence that many beetles disperse from new, low severity infestations. Rather, we argued that differences in habitat quality, detection errors, and Moran effects can all confound dispersal patterns, making it difficult to infer dispersal parameters from observed infestation patterns. Nonetheless, predicting infestation risk is useful, and large kernels improve predictions. In chapter 4, we used generalized linear mixed models to characterize spatial and temporal variation in the propensity of jack pine trees to produce pollen cones, and account for confounding effects on the relationship between pollen cone production and previous defoliation by jack pine budworm. We found effects of stand age, and synchronous variation in pollen cone production among years. Accounting for background patterns in pollen cone production clarified that pollen cone production declines in with previous defoliation, as expected.

The western spruce budworm (Choristoneura occidentalis Freeman) is the most widespread and destructive defoliator of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests in British Columbia. Over the past two decades, western spruce budworm outbreaks have been sustained and widespread in the interior of British Columbia, leaving the forest industry and many forest-dependent communities increasingly vulnerable to the economic consequences of these outbreaks. While a great deal is known about the impact of western spruce budworm outbreaks on tree growth and form, substantial knowledge gaps remain as to the historic variability of western spruce budworm outbreaks and the consequences of defoliation on fundamental characteristics such as wood structure. This research focused on describing historic and contemporary western spruce budworm outbreaks across multiple spatial and temporal scales in south-central British Columbia using dendrochronology and wood anatomy techniques. Outbreak histories over the past 435 years were reconstructed using a network of tree-ring chronologies from central British Columbia, revealing that 12 western spruce budworm outbreaks have occurred since the early 1600s, with a mean return interval of 30 years. Further, the research illustrates that outbreaks observed over the last 40 years are not unprecedented, which does not support the perception that western spruce budworm is moving northward into central British Columbia. To evaluate the effects of a single western spruce budworm outbreak on the anatomical characteristics of Douglas-fir stemwood, tree ring data was collected from permanent sample plots that sustained both periodic and chronic western spruce budworm feeding. In mature even-aged stands of Douglas-fir, a documented outbreak occurred from 1976 to 1980 in the coastal transition zone of southern British Columbia. Based on microscopic wood anatomical measurements it was shown that the tree rings formed during this outbreak had significantly lower percentages of latewood, reduced mean cell wall thickness and smaller radial cell diameters relative to wood formed during periods without budworm feeding. Western spruce budworm defoliation temporarily modified cellular characteristics, which has implications for wood quality. In uneven-aged stands of mature Douglas-fir, located in the xeric southern interior of British Columbia, there has been a sustained western spruce budworm outbreak since 1997. Tree rings formed during this outbreak had progressively larger earlywood lumen area and radial cell diameter, reduced latewood cell wall thickness, latewood radial cell diameters, and lower percent latewood. Mixed-effects models revealed that climatic variables, defoliation severity, defoliation duration, and in limited cases canopy class were the best predictors of xylem features. The severity and duration of western spruce budworm defoliation, as well as site factors that influence moisture conditions effect the degree and direction of anatomical changes in the stemwood of Douglas-fir. This research fills a number of knowledge gaps by providing insights into the temporal and spatial dynamics of western spruce budworm outbreaks in central British Columbia over multiple centuries, and the plasticity of anatomical features in the stemwood of Douglas-fir during discrete western spruce budworm outbreaks. These research findings suggest that Douglas-fir forests are resilient to western spruce budworm outbreaks over space and time. / Graduate

Le changement climatique continue d'affecter la dynamique des paysages forestiers à grande échelle. Cependant, il demeure incertain comment ces changements affecteront les forêts futures et en particulier les épidémies des insectes ravageurs forestiers. Le changement climatique affecte l’émergence des insectes, en perturbant notamment la synchronisation phénologique entre les insectes herbivores et leurs arbres hôtes. De telles perturbations peuvent avoir des conséquences importantes sur le moment de l’émergence, l'étendue et la gravité de l'épidémie. Cette étude vise à comprendre comment le changement climatique pourrait affecter la synchronie phénologique entre la tordeuse des bourgeons de l'épinette (Choristoneura fumiferana), un défoliateur indigène, et ses espèces hôtes (Abies balsamea et Picea mariana) et comment cela pourrait affecter l'étendue des épidémies de la tordeuse des bourgeons de l'épinette dans la région de la Côte-Nord au Québec, Canada. Nous avons exploré les effets de deux facteurs expérimentaux sur l'étendue des épidémies à l'aide d'un modèle de simulation stochastique spatialement explicite à base d’agents (MBA): (1) la température quotidienne représentée selon deux niveaux d'augmentation (+2°C et +4°C) relative à une base de référence 2016 et (2) la variation de la phénologie des arbres hôtes correspondant aux différents niveaux d'incertitude (SD) concernant le moment du débourrement des bourgeons. Nous avons évalué comment ces facteurs ont affecté la variation de l'étendue des épidémies de la tordeuse des bourgeons de l'épinette et la complexité spatiale du patch épidémique sur un horizon de simulation de 20 ans. Nos résultats de simulation indiquent que la synchronisation phénologique arbres hôtes-insectes est fortement affectée par les changements de température, mais de manière non linéaire. Une augmentation de 2°C a permis de réduire l'étendue de l'épidémie en raison de la faible survie des larves, tandis qu'une augmentation de 4°C a entraîné une survie plus élevée des insectes et des épidémies plus importantes. Notre modèle peut aider à prévoir la dynamique future des forêts et faciliter l'élaboration de meilleures stratégies de gestion pour réduire l'effet des épidémies sur les paysages forestiers. / Climate change continues to affect forest landscape dynamics at a global scale. However, it remains uncertain how these changes will affect future forests and in particular outbreaks of forest insect pests. Climate change can affect outbreaking insects by disrupting phenological synchrony between herbivorous insects and their host trees. Such disruptions can have important consequences for outbreak timing, extent, and severity. This study aims to understand how climate change could affect the phenological synchrony between the spruce budworm (Choristoneura fumiferana), a native outbreaking defoliator, and its host trees (Abies balsamea and Picea mariana), and how this might affect the extent of spruce budworm outbreaks in the Côte-Nord region in Quebec, Canada. We explored the effects of two experimental factors on outbreak extent using a spatially explicit stochastic agent-based simulation model (ABM): (1) daily temperature represented as two levels of increase (+2°C and +4 °C) relative to a 2016 baseline, and (2) variation in host phenology represented as four different levels of uncertainty (SD) around the timing of budburst. We assessed how these factors affected variation in spruce budworm outbreak extent and outbreak patch spatial complexity over a 20-year simulation horizon. Our simulation results indicate that host trees-insect phenological synchrony is strongly affected by temperature changes, but in a non-linear way. An increase of 2°C was found to reduce outbreak extent due to poor larval survival, while an increase of 4°C resulted in higher insect survival and larger outbreaks. Our model can help to forecast future forest dynamics and facilitate the development of better management strategies to reduce the effect of outbreaks on forest landscapes.