The western spruce budworm, Choristoneura occidentalis Freeman (Lepidoptera: Tortricidae), is a serious defoliator of conifers in the western U.S. and western Canada. In 1985 epidemic levels of the budworm caused average tree defoliation in west-central Idaho to increase to 83%, up substantially from the 35% average tree defoliation of 1984. Associated with this increase in defoliation was a change in the relative stand defolation ranking between the two years. found to damage all types and In 1985 the budworm was developmental stages of reproductive structures of Douglas- fir, including: seedcone buds, pollen-cones buds, maturing cones, and seeds. Differential selection of feeding sites was observed, with a significantly higher proportion of larvae found in seedcone buds than in pollen-cone buds. Shortly after larval emergence, 25% of the total number of seed-cones buds were infested. A subsample of 171 branch tips indicated that only 9% of pollen-cones, while less than 2% of the vegetative buds contained larvae. A total of 640 cones from 21 trees were examined. Of these cones, 76% were infested with larvae, however not all of the seeds were destroyed. The average percent of destroyed seeds per tree was found to be exponentially related to the average current defoliation of the tree.

Forest disturbances and the spatial patterns they create affect ecosystem processes through their influence on forest vegetation from individual trees to landscapes. In the boreal and mixed-wood forests of eastern Canada the main agents of disturbance are logging, fire, and defoliation by the spruce budworm (SBW, Choristoneura fumiferana). These disturbances are similar in that they remove forest biomass and influence forest succession but also distinct in that logging creates patterns that are different than those created by natural disturbances. All disturbances are indirectly linked to each other through their mutual effects on forest spatial structure and succession. Through such feedbacks, spatial disturbance legacies can facilitate or constrain further disturbances, including forest management. Surprisingly, the long term spatial consequences of interactions among multiple natural and anthropogenic disturbances remain largely unexplored. This thesis investigates how, and at what spatial scale, legacies in forest composition and age structure influence natural disturbance dynamics, and how natural disturbances constrain forest management. I address four specific questions: (i) For how long do spatial legacies of different forest management strategies persist on the landscape? (ii) How do interactions among logging, fire, SBW, and succession affect timber availability and long term forest patterns in age and composition? (iii) How do these patterns differ from those created by each disturbance individually? And, (iv) How can management be used to reduce the extent and severity of fires and SBW defoliation through the manipulation of forest structure? The key scientific innovations of this thesis are: (i) Characterization of the duration and influence of spatial legacies on forest disturbances and sustainability; (ii) Development of a dynamic spatial forest simulation model that includes distinct successional rules that respond to different types of disturbance and shifts in disturbance regimes; and, (iii) Development and application of a wavelet-based significance testing framework to identify key scales of expression in forest spatial patterns. These innovations provide a scientific basis for landscape level forest management strategies designed to reduce the long term impacts of defoliating insects and to meet multiple objectives.

Thesis (M.S.)--Oregon State University, 1988. / Typescript (photocopy). Includes bibliographical references (leaves 35-41). Also available on the World Wide Web.

Mémoire (M.Ress.Renouv.)--Université du Québec à Chicoutimi, 1995. / Document électronique également accessible en format PDF. CaQCU

Thèse (M.Ress.Renouv.) -- Université du Québec à Chicoutimi, 2003. / Bibliogr.: f. [59]-64. Document électronique également accessible en format PDF. CaQCU

I assessed the relationship between natural disturbances and climate in Douglas-fir forests in western North America. I quantified synchrony within disturbance types, explored the potential for synergism between disturbance types, and analyzed changes in disturbance dynamics that have occurred following Euro-American settlement of western North America. I used new and previously published dendrochronological reconstructions of disturbance histories and climatic variability to explore these complex interactions at multiple spatial scales over the last three centuries. I used dendroentomological methods to reconstruct western spruce budworm outbreaks at thirteen sites along a transect running from central Oregon to western Montana. These forests experienced repeated, often decadal-length western spruce budworm outbreaks over the last three centuries. I compared my records with previously published outbreak reconstructions and found widespread synchrony of outbreaks at stand-level, regional, and sub-continental scales. At ten of my sites, I also reconstructed or obtained previously published reconstructions of fire dates. I compared these disturbance histories with dendroclimatological drought records to quantify the influence of moisture availability on disturbances. I found that fires were more likely to occur during drought years, while western spruce budworm outbreaks were most likely to begin near the end of droughts. After approximately 1890, fires were largely absent from these sites and western spruce budworm outbreaks became longer-lasting, more frequent, and more synchronous, likely due to land-use induced changes in the structure and composition of forests. My results show no discernible impact of defoliation events on subsequent fire risk. Any effect from the addition of fine and coarse fuels during defoliation events was too small to detect given the overriding influence of climatic variability. If there is any relationship between the two disturbances, it is a subtle synergistic relationship wherein each disturbance type dampens the severity but does not alter the probability of occurrence of the other disturbance type over long time scales. This dissertation includes unpublished co-authored material. / 10000-01-01

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

Mémoire (M.Ress.Renouv.)--Université du Québec à Chicoutim, 2000. / Document électronique également accessible en format PDF. CaQCU

Mémoire (M.Ress.Renouv.)--Université du Québec à Chicoutimi, 2001. / Document électronique également accessible en format PDF. CaQCU

Thèse (M.Ress.Renouv..) -- Université du Québec à Chicoutimi, 2006. / Bibliogr.: f. 40-52. Document électronique également accessible en format PDF. CaQCU