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Using multi-scale trembling aspen tree-ring width data from Alberta, we show that scaling has a profound influence on dendroecological inferencing. At all scales of sampling, there is a significant climatological signal whose strength is nevertheless superseded by the pervasive effect of insect herbivory. At the smallest spatial scale, 20 km * 20 km, we demonstrate a quasi-periodic pattern of sharp growth reductions and the existence of negative spatial correlations among successive outbreaks. At the intermediate spatial scale of 20 km * 80 km, we show that the period 1930-1963 was marked by extremely low correlations in aspen ring widths, with much higher correlations occurring both before and after, despite high variance in precipitation that might have caused ring widths to correlate under moisture limitation. At the largest spatial scale of the entire province, aspen ring widths in the boreal forest became decorrelated abruptly in 1916, after cycling synchronously for the previous 80 years. This occurred despite a warming climate that heightened moisture limitation. Something in the environment prevents some outbreak cycles from rising to maximum intensity and from spreading to maximum extent. This appears to be the key to better predictability and management of forest insects and forests at short and long time-scales. Key words: forest tent caterpillar, insect dendroecology, outbreak periodicity, synchronization, trembling aspen, Introduction Resources, such as food and shelter, are distributed patchily in space, affecting the dynamics of both animal population growth and movement (Wiens 1976; Baker 1978; Hanski 1999). In the [...]

We use simulation models of the winter biology of two forest insects--emerald ash borer (Agrilus planipennis Fairmaire, 1888) and mountain pine beetle (Dendroctonus ponderosae Hopkins, 1902)--to illustrate the anticipated effect of the polar vortex of the winter of 2019 on overwintering survival. Cold spells in late January and early and mid-February were cool enough that relatively high levels of mortality of both species may be expected in many parts of northern Canada. However, the high mortality response is not ubiquitous, and neither is it particularly severe compared with winter weather patterns from earlier decades. Forest insect pest managers will be required to carry on their usual work of population assessment and response. As Earth's climate continues to warm, overwintering survival should, on average, increase in both species. However, the common occurrence of a split polar vortex associated with increasingly meridional jet stream flows should bring the odd winter of heavy mortality. Key words: insect ecophysiology, cold tolerance, winter mortality, predictive modeling. Nous avons utilise des modeles de simulation de la biologie hivernale de deux insectes forestiers--l'agrile du frene (Agrilus planipennis Fairmaire, 1888) et le dendroctone du pin ponderosa (Dendroctonus ponderosae Hopkins, 1902)--pour illustrer les effets anticipes du vortex polaire de 2019 sur la survie hiemale. Les vagues de froid qui sont survenues a la fin janvier ainsi qu'au debut et a la mi-fevrier ont ete suffisamment intenses pour qu'on puisse s'attendre a des taux de mortalite relativement eleves chez les deux especes dans plusieurs regions du nord du Canada. Cependant, la mortalite elevee n'est pas une reponse generalisee ni particulierement severe comparativement a l'allure du climat hivernal des decennies precedentes. Les gestionnaires des insectes forestiers nuisibles devront poursuivre leur travail habituel concernant l'evaluation et la reaction des populations. La survie hiemale devrait en moyenne augmenter chez les deux especes a mesure que le climat de la terre continue de se rechauffer. Cependant, l'occurrence frequente d'un vortex polaire divise associe a une circulation de plus en plus meridionale du courant jet devrait produire des hivers inhabituels accompagnes d'une forte mortalite. [Traduit par la Redaction] Mots-cles: ecophysiologie des insectes, tolerance au froid, mortalite hivernale, modelisation predictive., Introduction One of the most important factors that has historically limited the spread and impact of terrestrial invasive species in Canada has been the country's relatively cold climate. This climate [...]

Thinning, the selective removal of some trees from a forest, is one way forest managers can reduce the probability that a forest will be susceptible to attack by bark beetles. Although this method has been shown to be effective, it is not clear whether the effect arises when pre-outbreak populations are small or during the epidemic phase when outbreaks are growing. We adopted a population dynamics approach to determine if the effect of limit or basal area thinning could be observed in the form of differential beetle recruitment using lodgepole pine (Pinus contorta Dougl. ex Loud.) and ponderosa pine (Pinus ponderosa Dougl. ex P. & C. Laws.) mortality data from previously published studies as a proxy measure of mountain pine beetle (Dendroctonus ponderosae Hopkins) population size. We found that mountain pine beetle populations exhibit density-dependent population dynamics that are influenced by the silvicultural history of their host's stand. Thinning did not change the epidemic equilibrium but instead caused a shift in dynamics from linear to nonlinear. In a validation test, the models developed for thinned and unthinned stands predicted reproductive rates in independent locations. These data also suggest the epidemic dynamics of mountain pine beetle may be sensitive to perturbations and to systematic trends associated with climate variability and climate change. L'eclaircie, c'est-a-dire l'elimination selective de certains arbres dans une foret, est un des moyens qu'utilisent les amenagistes forestiers pour reduire la probabilite qu'une foret soit susceptible aux attaques des scolytes. Meme si cette methode s'est averee efficace, on ne sait pas si l'effet survient lorsque les populations qui precedent une epidemie sont faibles ou durant la phase epidemique lorsque les epidemies progressent. Nous avons adopte une approche de dynamique de population pour determiner si l'effet de l'eclaircie basee sur un diametre limite ou sur la surface terriere pouvait etre observe sous la forme d'une difference de recrutement de scolytes a l'aide de donnees de mortalite du pin tordu latifolie (Pinus contorta Dougl. ex Loud.) et du pin ponderosa (Pinus ponderosa Dougl. ex P. & C. Laws.). Ces donnees viennent d'etudes deja publiees et ont ete utilisees comme mesure indirecte de la taille des populations du dendroctone du pin ponderosa (Dendroctonus ponderosae Hopkins). Nous avons decouvert que les populations de dendroctone du pin ponderosa ont une dynamique de population dependante de la densite qui est influencee par le passe sylvicole de leurs peuplements hotes. L'eclaircie n'a pas modifie l'equilibre epidemique mais a plutot change la dynamique, de lineaire a non lineaire. Dans un test de validation, les modeles developpes pour les peuplements eclaircis et non eclaircis predisaient le taux de reproduction pour des endroits independants. Ces donnees indiquent egalement que la dynamique des epidemies du dendroctone du pin ponderosa pourrait etre sensible aux perturbations et aux tendances systematiques associees a la variabilite du climat et au changement climatique., Introduction Bark beetles (Coleoptera: Scolytinae) are one of the most significant natural disturbance agents of coniferous forests in North America. Since the mid-1990s, large areas of forest have been damaged [...]

Abstract: We investigated the long-term effects of drought and defoliation by forest tent caterpillars on trembling aspen radial growth in the province of Ontario using a dendroecological approach. Drought, as [...]