Maîtrise (M.Ress.Renouv.)--Université du Québec à Chicoutimi, 1999. / Document électronique également accessible en format PDF. CaQCU

Future climate changes will alter disturbance regimes worldwide with important implications for many ecological and social systems. In west central British Columbia, Canada, fire and insect disturbances have shaped the historic character of Douglas-fir (Pseudotsuga menziesii var. glauca Beissn. Franco) dominated forests. However, since AD 1900 fire suppression and other forest management practices have led to denser forests and conifer encroachment into grasslands. Considering climate changes in interior British Columbia are expected to result in warmer and drier conditions, understanding the influence of climate on forest disturbances is crucial for land managers tasked with both mitigating the effects of disturbance and promoting resilience in forest ecosystems. This research focused on developing multi-century, annually-resolved records of fire and western spruce budworm outbreaks to evaluate: the historic climate conditions related to these disturbances; the influence of grassland proximity on disturbance-climate relationships; and, whether western spruce budworm outbreaks were related to fire activity. At the landscape scale, a detailed study in the Churn Creek Protected Area revealed spatially variable stand structure and fire-climate relationships at a low elevation forest-grassland ecotone over the interval AD 1600 to 1900. This finding suggests the site was characterized by fires of mixed-severity dominated by frequent, low-severity, fires related to positive antecedent moisture conditions punctuated by widespread fires of moderate to high severity related to intervals of persistent drought. At the regional scale, the influence of interannual climate variability and large-scale patterns of climate variability (e.g. El Nino Southern Oscillation) was evaluated using new and existing records of fire history and multiple climate pattern reconstructions. Regional fire activity was shown to be significantly related to interannual climate variability, and no consistent patterns between regional fire years and the individual phases or phase combinations of large-scale patterns of climate variability were detected. The findings suggest that the spatial expression of large-scale climate patterns translates into weak and undetectable terrestrial effects related to fire activity in this region. The influence of grassland proximity on disturbance history was investigated using site-level and regional tree-ring reconstructions of western spruce budworm outbreaks and fire activity based on four sites adjacent to grasslands and four sites not adjacent to grasslands between AD 1600 and 1900 (fire) and AD 1600 and 2009 (western spruce budworm). Fires affecting grassland proximal sites were more frequent than fires occurring in forests not adjacent to grasslands, and the character of western spruce budworm outbreaks was generally consistent among all sites. Fire activity was related to both warm, dry and cool, wet conditions in the fire year and/or year(s) preceding the fire depending on proximity to grasslands, suggesting climate conditions associated with both fine fuel growth and drying are key determinants for fire activity. The initiation of western spruce budworm outbreaks was significantly related to drought and this relationship was enhanced at sites adjacent to grasslands. At the site-level and regional scale, no consistent association was found between the initiation of western spruce budworm outbreaks and fire years indicating the historic interaction between these disturbances is weak or non-existent. / Graduate

Western spruce budworm (Choristoneura occidentalis (Freeman)) is a native defoliator of the Interior Douglas-fir (Pseudotsuga menziesii var. glauca (Mirb.) Franco) forests of British Columbia, Canada. This thesis used dendrochronology and the software program OUTBREAK to reconstruct a defoliation history of Douglas-fir for nineteen forest sites near Kamloops in central British Columbia. By comparing the radial growth response of non-host ponderosa pine trees to Douglas-fir trees growing in nearby but separate stands, seven western spruce budworm outbreaks were distinguished over the past 300 years. Although there is considerable variation in the timing and duration of these western spruce budworm events at the stand level, synchronous outbreaks have occurred at approximately 43-year intervals. Climate variation appears to have been important to budworm outbreaks in the 20th century. Notable outbreaks tended to occur during years of early springs with average air temperature, following winters with lower than average precipitation. Based on this finding, it is proposed that with high overwintering survival, increased population growth rates, and a longer growing season, the extent of future outbreaks will shift northward and may increase in size.

Western spruce budworm (Choristoneura occidentalis (Freeman)) is a native defoliator of the Interior Douglas-fir (Pseudotsuga menziesii var. glauca (Mirb.) Franco) forests of British Columbia, Canada. This thesis used dendrochronology and the software program OUTBREAK to reconstruct a defoliation history of Douglas-fir for nineteen forest sites near Kamloops in central British Columbia. By comparing the radial growth response of non-host ponderosa pine trees to Douglas-fir trees growing in nearby but separate stands, seven western spruce budworm outbreaks were distinguished over the past 300 years. Although there is considerable variation in the timing and duration of these western spruce budworm events at the stand level, synchronous outbreaks have occurred at approximately 43-year intervals. Climate variation appears to have been important to budworm outbreaks in the 20th century. Notable outbreaks tended to occur during years of early springs with average air temperature, following winters with lower than average precipitation. Based on this finding, it is proposed that with high overwintering survival, increased population growth rates, and a longer growing season, the extent of future outbreaks will shift northward and may increase in size.

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

No description available.

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

Depuis 1985, plus de 10 millions d’hectares de forêt ont été traités au Canada contre la tordeuse des bourgeons de l’épinette (TBE) avec l’insecticide biologique Btk. Toutefois, aucune étude ne s’est penchée sur les effets de ces traitements sur les sous-bois, bien qu’ils contiennent la majorité de la diversité végétale des forêts boréales et représentent une source importante de nourriture pour plusieurs animaux, dont le caribou forestier, une espèce menacée. Ainsi, il semble impératif de déterminer quelle fréquence de traitements de Btk serait idéale pour réduire les perturbations aux communautés végétales de sous-bois. À l’aide d’un dispositif expérimental où les populations de TBE sont contrôlées, nous avons évalué l’influence de différentes modalités d’épandage de Btk sur la défoliation des peuplements et sur les sous-bois. Nos résultats montrent qu’une diminution de la fréquence des traitements influence positivement la lumière disponible aux sous-bois, la richesse, la présence d’espèces intolérantes à l’ombre et la production de petits fruits, particulièrement dans les stations non traitées, où la défoliation était maximale. Or, un sous-bois diversifié comprenant des espèces intolérantes à l’ombre et de nombreux petits fruits est un habitat idéal pour l’orignal et ses prédateurs communs avec ceux du caribou, l’ours et le loup. Une diminution du contrôle des épidémies de TBE affecterait donc négativement le caribou forestier en augmentant potentiellement le risque de prédation, ce qui est un des principaux facteurs limitant ces populations. Des traitements bisannuels de Btk pourraient donc aider à la protection de l’habitat des populations résiduelles de caribou forestier. / Since 1985, more than 10 million hectares of Canadian forests were treated against spruce budworm (SBW) epidemics using the Btk biological insecticide, but no study has evaluated the effects of these interventions on understory vegetation. Since the forest floor host most of plant diversity in boreal forests and provides critical wildlife habitat for, amongst others, woodland caribou, it is crucial to determine the best Btk treatment frequency to reduce wood losses, application costs, and disturbances to understory communities. In an experimental design, we tested the influence of different spraying frequencies for SBW control on tree defoliation and understory vegetation. We found positive relationships between a decrease in treatment frequency and light availability in the understory, richness, shade-intolerant species cover, and fruit production, particularly in control plots, where defoliation was maximal. An increase in shade-intolerant species and fruit production could provide high-quality forage for moose and its predators, wolves and bears, which can increase predation pressure on caribou. A decrease in SBW control may thus negatively affect woodland caribou by increasing predation risks, the main factor limiting caribou populations in managed forests. Consequently, we suggest that SBW control could help maintain woodland caribou habitat during a SBW epidemic and recommend Btk applications every 2 years to prevent both wood loss and further degradation of woodland caribou habitat. Key

No description available.

Final Report / Contract on 43-8371-4-628 / For: USDA, Forest Service, Southwestern Region / Regional outbreaks of western spruce budworms (Choristoneura occidentalis Freeman) have recurred at least three times in northern New Mexico since the early 1920's when the U. S. Forest Service first began systematic forest-pest surveys and documentation (Lessard 1975, U. S. Forest Service documents). The current outbreak was first noticed in a small area on the Taos Indian Reservation in 1974, and since then the defoliated areas have increased in New Mexico and Arizona to more than 370,000 acres of Federal, Indian, State and private lands (Linnane 1984). Losses in timber values can generally be ascribed to radial growth loss, height growth loss, topkilling, reduced regeneration, and mortality (Carlson et al. 1983, Fellin et al. 1983). A damage assessment project was initiated in 1978 and was aimed at obtaining measurements of some of these losses in budworm infested stands on the Carson National Forest, New Mexico (Holland and Lessard 1979). A large data base has subsequently been developed, including yearly measurements on topkilling, mortality, defoliation, and insect population changes (Stein 1980, 1981, Stein and McDonnell 1982, Rogers 1984). A growth assessment study was undertaken in 1982 to determine the feasibility of using dendrochronological methods to identify the timing of past outbreaks and to quantify radial growth losses associated with budworm defoliation (Swetnam 1984). Results of this work showed that three major outbreaks during the twentieth century were clearly visible in the tree-ring samples obtained from currently infested trees. The radial growth of host trees was corrected for age, climate and other non-budworm environmental effects, and then growth losses were computed as a percentage of expected growth (Swetnam 1984). Additional collections were obtained in 1984 in order to expand the scope of the radial growth study. The objectives included 1) assessment of a larger number of tree -ring samples, 2) comparison of radial growth losses between the two primary host species - Douglas-fir (Pseudotsuga menziesii) and white fir (Abies concolor), 3) comparison of radial growth losses between age classes, and 4) analysis of the relationship between yearly measurements of defoliation, insect populations and radial growth. This report summarizes the findings of the above analyses. Increment core samples from the 1982 collections are included here, therefore this report supersedes the earlier report (Swetnam 1984). Information is also presented on observations derived from the dated tree-ring series on the timing of occurrence of known and inferred spruce budworm outbreaks for the past 284 years (1700- 1983). This is the longest record of spruce budworm occurrence yet developed for western North America.