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The relationship between forest stand composition in southern interior British Columbia and fluorescent pseudomonad bacteria populations was investigated using seedling bioassays. The objectives of this study were to (i) compare the relative population sizes of fluorescent pseudomonads baited from soils in pure paper birch (Betula papyrifera Marsh.), pure Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), and mixed stands of the two species and (ii) determine if fluorescent pseudomonads from these soils have inhibitory effects against the root pathogen Armillaria ostoyae (Romagn.) Herink in vitro. Soil from birch stands supported four times more pseudomonads on seedling baits than soil from Douglas-fir stands, with the mixed stands intermediate. Soil from young stands yielded twice as many rhizosphere pseudomonads as soil from mature stands. Pseudomonad population size was positively correlated with percent cover and density of birch, and negatively correlated with basal area of Douglas-fir, percent cover of Douglas-fir, and carbon/nitrogen ratio of the soil. Greater than 50% of the fluorescent isolates reduced radial growth of A. ostoyae by more than 20% and greater than 90% reduced biomass of the fungus in dual culture tests. Cell-free bacterial culture filtrates added to the growth medium also reduced growth of A. ostoyae. This study provides evidence that paper birch provides a more favorable environment for fluorescent pseudomonads than Douglas-fir and suggests a mechanism by which paper birch can positively influence the susceptibility of managed forest stands to Armillaria root disease. [ABSTRACT FROM AUTHOR]

Reports on the measured rates of decomposition at three sites representing the major mixedwood forest types of British Columbia: (i) boreal forests of white spruce (Picea glauca (Moench) Voss) and trembling aspen (Populus tremuloides Michx.), (ii) coastal forests of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and red alder (Alnus rubra Bong.), and (iii) a wet interior forest of Douglas-fir, paper birch (Betula papyrifera Marsh.), and lodgepole pine (Pinus contorta Doug. ex Loud.). Mass loss of litter of each species (both pure and in combination with the other species) that was measured in forests of each species to determine (i) if broadleaf litter decomposed faster than needle litter, (ii) if litter decomposed faster in broadleaf or mixedwood forests than in coniferous forests, and (iii) if mixing with broadleaf hastened decomposition of needle litter; Broadleaf litters that decomposed faster than needles during the first year but, thereafter, decomposed more slowly; Litter that tended to decompose faster in the broadleaf forests than in the coniferous forests; No evidence to indicate that the addition of broadleaf litter hastened decomposition of needle litter; Results that indicate that the mixing of needle litter with broadleaf litter is unlikely to hasten decomposition in mixedwood forests of British Columbia.

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. 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-terme que constitue le douglas de Menzies associé au pin tordu, même en présence d’une épidémie de tordeuse occidentale de l’épinette. [ABSTRACT FROM AUTHOR]