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Abstract:The mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera, Curculionidae), a native insect of North America, periodically reaches population sizes that cause serious economic impact to the forest industry in western North America. The most recent outbreak in British Columbia (BC), Canada, which began in the late 1990s, is only now (2015) abating, after causing unprecedented tree mortality in lodgepole pine (Pinus contorta Douglas ex. Loudon) forests. In this paper, we make use of permanent research plots to report on the condition of lodgepole pine forests in the Chilcotin Plateau of central BC, which underwent two fully documented mountain pine beetle outbreaks. In this region, the first outbreak started in the late 1970s and lasted until the mid-1980s; the second outbreak began in the early 2000s and ended in 2010. We measured the impacts of these outbreaks in terms of tree mortality and describe the characteristics of the legacies that remain following these outbreaks, including survivors in various canopy layers and levels of existing and new regeneration. We provide evidence in support of the existence of postdisturbance legacies that classify into five distinct stand structure types. Abundant regeneration and surviving intermediate canopy layers in most stands indicate that management actions to restock pine stands in this area will not likely be necessary. The information provided by this study is important for estimating future forest development and timber supply and for forest planning and management.Key words: mountain pine beetle, forest disturbance, forest dynamics.Résumé : L'explosion périodique des populations de dendroctone du pin ponderosa, Dendroctonus ponderosae Hopkins (Coléoptères, Curculionidées), un insecte indigène de l'Amérique du Nord, a de sérieux impacts économiques sur l'industrie forestière dans l'ouest de l'Amérique du Nord. L'épidémie la plus récente en Colombie-Britannique (C.-B.), qui a débuté à la fin des années 1990, commence seulement maintenant (2015) à régresser après avoir causé une mortalité sans précédent dans les forêts de pin tordu (Pinus contorta Douglas ex Loudon). Dans cet article, nous avons utilisé des placettes permanentes de recherche pour produire un rapport sur l'état des forêts de pin tordu sur le plateau Chilcotin dans le centre de la C.-B. qui ont subi deux épidémies bien documentées de dendroctone du pin ponderosa. Dans cette région, la première épidémie a débuté à la fin des années 1970 et s'est poursuivie jusqu'au milieu des années 1980; la seconde épidémie a débuté au début des années 2000 pour se terminer en 2010. Nous avons mesuré les impacts de ces épidémies en termes de mortalité des arbres et nous décrivons les caractéristiques des répercussions qui persistent à la suite de ces épidémies, incluant les survivants dans différentes strates du couvert forestier ainsi que les niveaux de régénération, nouvelle et existante. Nous apportons des preuves à l'appui de l'existence de répercussions des perturbations qui auraient engendré ci...

The mountain pine beetle (MPB; Dendroctonus ponderosae Hopkins) is a native bark beetle and a major disturbance agent in western North American forests. In the 1970s and 1980s, a MPB outbreak occurred in Waterton Lakes National Park (WLNP) in southwestern Alberta. The MPB outbreak resulted in variable levels of mortality of mature lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Watson), reducing density, volume, and basal area of overstory trees. By 2010, lodgepole pine was proportionally no longer the dominant overstory species, with increases in non-pine conifer and broadleaf species. The MPB susceptibility index decreased in most stands over time, especially in stands with the highest MPB-caused mortality. Downed woody material was characterized by fine and coarse fuel mass and volume, which both increased from 2002 to 2010, and the abundance of coarse fuels was highest in 2010, nearly 30 years after peak MPB activity. Density of understory saplings and small regeneration increased from 2002 to 2010 and was dominated by non-pine conifer and broadleaf species; lodgepole pine was nearly absent. Hierarchical clustering using 2010 MPB susceptibility and composition data characterized biological legacies remaining after the MPB outbreak. These legacies suggest multiple successional trajectories in WLNP dominated by species other than lodgepole pine. The MPB outbreak resulted in greater heterogeneity in composition and structure and suggests that stands have been resilient to this disturbance.

Natural enemies play an important role in the regulation of many forest insect populations. The hypothesis that these organisms also reduce invasion potential is one element of a concept known as biotic resistance. While many studies have shown that the abundances of natural enemies are affected by landscape structure and diversity, seasonality, and host tree species, this study tests the hypothesis that these factors affect the biotic resistance of forest communities to invasion by a non‐native tussock moth. At 20 sites on Vancouver Island, Canada, spanning a range of natural to urban forests, small populations of the rusty tussock moth, Orgyia antiqua, an exotic polyphagous tussock moth, were introduced. Introductions were repeated at three different periods in the year, on coniferous and deciduous host trees, and included both late‐instar larvae and pupae. The survival of these small populations was monitored in relation to four landscape variables measured around each site. Spring introductions had significantly lower mortality rates than either early or mid‐summer introductions. There was little difference in predation rates between coniferous and deciduous host trees. The amount and type of forest cover in the landscape had important, but seasonally dependent, effects on survival that likely reflect changes in the habitat requirements of a shifting community of generalist predators. Based on the results, this study concludes that landscapes with intermediate forest cover are the least resistant to invasion by early feeding species such as the rusty tussock moth.