Balancing risks of disturbance from mountain pine beetle and western spruce budworm

Abstract

The effect of removing lodgepole pine (Pinus contorta Dougl. ex Loud.) and retaining Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) to reduce the risk of disturbance from mountain pine beetle (Dendroctonus ponderosae Hopk.) in mixed conifer stands in southern British Columbia, Canada, on population processes influencing outbreaks of western spruce budworm (Choristoneura occidentalis Free.) was evaluated in 10 paired (open vs. closed) field plots. Overall feeding damage to Douglas-fir was significantly, but only slightly, lower in open stands compared with closed stands. Although open plots tended to recruit more budworms, the losses resulting from the dispersal of spring-emerging budworms in search of feeding sites were significantly greater in open plots. The forest management benefits of these early season losses were mitigated, however, by more mortality of budworms from natural enemies, particularly diseases, in the closed plots during the budworm feeding period. These results are discussed in terms of compensating population processes and balancing objectives in forest pest management. In this case, selective harvesting of lodgepole pine as a mitigation strategy for the mountain pine beetle conserved the midterm timber supply potential represented by associated Douglas-fir even in the presence of an outbreak of the western spruce budworm.Résumé : Dans les peuplements mélangés de conifères du sud de la Colombie-Britannique, au Canada, on élimine le pin tordu (Pinus contorta Dougl. ex Loud.) en conservant le douglas de Menzies (Pseudotsuga menziesii (Mirb.) Franco) pour réduire les risques de perturbation par le dendroctone du pin ponderosa (Dendroctonus ponderosae Hopk.). L'effet de cette pratique sur les processus démographiques qui influencent les épidémies de tordeuse occidentale de l'épinette (Choristoneura occidentalis Free.) a été évalué dans 10 paires (peuplements ouverts vs peuplements fermés) de parcelles sur le terrain. Globalement, les dommages subis par le douglas de Menzies à cause du broutement étaient, quoique légèrement, significativement plus faibles dans les peuplements ouverts que dans les peuplements fermés. Bien que les peuplements ouverts aient eu tendance à recruter plus de tordeuses, les pertes dues à la dispersion des tordeuses qui émergent au printemps à la recherche d'endroits pour se nourrir étaient plus élevées dans les peuplements ouverts. À la suite de ces pertes en début de saison, les bénéfices de l'aménagement forestier ont cependant été atténués par une plus forte mortalité des tordeuses causée par ses ennemis naturels, particulièrement les maladies, dans les peuplements fermés pendant la période de broutement de la tordeuse. La discussion porte sur la compensation des processus démographiques et l'équilibre entre les objectifs en lien avec le contrôle des ravageurs forestiers. Dans ce cas, la stratégie qui préconise la récolte sélective du pin tordu pour atténuer l'impact du dendroctone du pin ponderosa a permis de maintenir le potentiel d'approvisionnement en bois à mi...

Comparative Genome Sequence Analysis of Choristoneura occidentalis Freeman and C. rosaceana Harris (Lepidoptera: Tortricidae) Alphabaculoviruses

“…Although few patent baculovirus infections were identified in these SBW, it has recently been reported that field-collected and laboratory-reared SBW had high prevalence of single and mixed covert infections of CfMNPV, CfDEFNPV and a GV [27]. In contrast to the low prevalence of baculoviruses in SBW populations in New Brunswick [26], diagnosis of field-collected wSBW larvae from British Columbia showed high levels of mortality (up to 70%) due to ChocNPV and other entomopathogens [18]. To date, only the wSBW betabaculovirus (ChocGV) genome has been sequenced [28].…”

“…The wild-type ChocNPV was isolated from wSBW larvae collected from the field in British Columbia, Canada in 2007 [18] (ChocNPV_BC1, GenBank accession number KC961303). ChroNPV was isolated from OBL larvae collected near Saint-Quentin, New Brunswick, Canada in 1992 [26], [30] (ChroNPV_NB1, GenBank accession number KC961304).…”

“…In North America, the spruce budworm (SBW), C. fumiferana , is the major defoliating insect pest of coniferous forests, especially in eastern Canada [13], where it exhibits prolonged, cyclical, population outbreaks [14], [15]. The western SBW (wSBW), C. occidentalis , occurs west of the Rocky Mountains from central British Columbia to New Mexico [16], [17] and is a major defoliator of Douglas fir ( Pseudotsuga menziesii ) and other conifers in western North America [18]. The specific epithet for C. occidentalis has recently been challenged and C. freemani suggested as a replacement [19].…”

Tree regeneration and future stand development after bark beetle infestation and harvesting in Colorado lodgepole pine stands

“…Based on these conditions, our stand simulations predict a large change in overstory composition across the majority of the landscape in the two centuries after the outbreak. However, because of the susceptibility of subalpine fir to a number of insects and disease agents (Alexander et al, 1990;Nealis et al, 2009) a patchy overstory structure and uneven-age distribution may develop in untreated beetle-killed forests. It is uncertain to what extent the increase in downed wood and the regeneration of ladder and canopy fuels will alter fire risk in recovering beetle-killed forests (Jenkins et al, 2008), but wildfire is likely to regenerate lodgepole pine dominance on a portion of the landscape.…”

Disturbance–climate relationships between wildfire and western spruce budworm in interior British Columbia

“…, Nealis et al. ). Reduced twentieth‐century fire activity within this region has resulted in forest infilling and the encroachment of woody vegetation into grasslands historically maintained by low‐ and mixed‐severity fire regimes (Klenner et al.…”