Changes in stand structure in uneven-aged lodgepole pine stands impacted by mountain pine beetle epidemics and fires in central British Columbia
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Abstract:
We examined the development of lodgepole pine (Pinus contorta Dougl.) in uneven-aged stands in the Interior Douglasfir (IDF) biogeoclimatic zone of central of British Columbia (B.C.), which are currently undergoing a massive outbreak of the mountain pine beetle (Dendroctonus ponderosae Hopkins; MPB). Using historical ecological approaches, dendrochronology, and stand measurement data, we determined the roles MPB and fire disturbances have played in the ecological processes of lodgepole pine in an Interior Douglas-fir zone. We found that multiple mixed-severity fires created patchy uneven-aged stands dominated by lodgepole pine. Since fire suppression in the 20 th century, multiple MPB disturbances have maintained the structural complexity of the stands and favoured regeneration of lodgepole pine in the understory despite the absence of fire, resulting in self-perpetuating multi-age lodgepole pine stands. Analysis of the stand structures remaining after multiple MPB outbreaks showed that, even with high overstory mortality, the sample stands contained several MPB-initiated cohorts, consisting of younger and smaller-diameter lodgepole pine. These surviving lodgepole pine layers, which are less susceptible to beetle, will provide important ecological legacies, and could play an important role in the mid-term timber supply chain. We concluded that, in the absence of fire, the MPB plays a more frequent role in directing stand dynamics and structure in uneven-aged lodgepole pine stands resulting in selfperpetuating complex stands in the central interior. We compared and contrasted these findings with those obtained in “even-aged” lodgepole pine stands, also in the Interior Douglas-fir zone in the southern interior, which were investigated in an earlier study. Key words: lodgepole pine, mountain pine beetle, dendroecology, complex stands, mixed-severity fire regimeKeywords:
Mountain pine beetle
Fire history
Dendroctonus
Understory
Bark beetles and their associated fungi are among the greatest natural threats to conifers worldwide, but the degree to which host stored resources influence tree-beetle-fungal interactions has not been investigated. In western North America, the range of the mountain pine beetle (Dendroctonus ponderosae) has expanded from lower elevation Pinus contorta (lodgepole pine) forests into high elevation Pinus albicaulis (whitebark pine), a presumed superior host. I investigated whether stored resources in tree sapwood change after D. ponderosae attack, and whether this change relates to fungal colonization and beetle performance. I also studied how phloem and sapwood resources vary with elevation and tree diameter and examined the effect of tree species and diameter on D. ponderosae host selection. Following beetle attack and fungal colonization, sapwood non-structural carbohydrates (NSC), lipids, and phosphorus declined in attacked trees relative to un-attacked trees. Resource declines were related to the degree of fungal colonization, suggesting a direct benefit to fungi in both host species. In P. contorta, beetle performance was also positively related to stored resources. The concentration of stored resources was generally higher in P. albicaulis than in P. contorta and increased with elevation and tree diameter, suggesting a potential increase in host quality for D. ponderosae and/or fungi. Beetles preferred larger diameter hosts, and although stored resources did not affect beetle performance in P. albicaulis, beetles were more likely to attack P. albicaulis even when larger P. contorta were available. In a parallel system in Norway, phloem NSC and sapwood lipids also declined in Picea abies trees inoculated with the fungus Ceratocystis polonica relative to trees attacked by the bark beetle Ips typographus (which vectors C. polonica) or control trees, again indicating that stored resources enhance fungal colonization. Overall, my results suggest that host stored resources influence the interaction between bark beetles, fungi, and conifers primarily by enhancing fungal growth. Fungal access to stored resources may also benefit beetles in some host tree species. A better understanding of the trophic interactions between beetles, fungi, and conifers may improve our ability to predict bark beetle dynamics and range expansion.
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Dendroctonus
Picea engelmannii
Abies lasiocarpa
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Dendroctonus
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Large infestations of the mountain pine beetle, Dendroctonus ponderosae Hopkins (Coleoptera: Scolytidae), reportedly arise from small, spot infestations that expand, multiply, and eventually coalesce (Safranyik et al. 1974). If these spot infestations can be located and eradicated, the development of outbreaks may be delayed, or even precluded. The principal means of eradication of such spots in forests of lodgepole pine, Pinus contorta var. latifolia Engelmann, in British Columbia is single tree disposal (B.C. Ministry of Forests 1987). This may be accomplished by treating with an arsenical herbicide within 3–4 weeks after attack, cutting, bucking, piling, and burning trees before brood emergence, or extraction and processing of brood trees before emergence.
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Dendroctonus
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Mountain pine beetle
Ophiostoma
Abies lasiocarpa
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Dendroctonus jeffreyi Hopkins and its sibling species, D. ponderosae Hopkins, are bark beetles associated with symbiotic fungi disseminated in maxillary mycangia. Although both D. jeffreyi and D. ponderosae are associated with the fungus Ophiostoma clavigerum (Robinson-Jeffrey & Davidson), D. ponderosae is also associated with a 2nd fungus, Ophiostoma montium (Rumbold von Arx). Adult D. jeffreyi and D. ponderosae that carried O. clavigerum (isolated from D. jeffreyi ), O. clavigerum (isolated from D. ponderosae ), O. montium , or were fungus-free, were reared in the laboratory and introduced into bolts of Pinus contorta Douglas ex Louden and Pinus jeffreyi Greville & Balfour, hosts of D. ponderosae and D. jeffreyi , respectively, to test for effects of the fungi on progeny survival and ability to use different host tree species. Dendroctonus ponderosae associated with O. clavigerum (isolated from D. jeffreyi ) and D. ponderosae associated with O. montium produced brood in both P. contorta and P. jeffreyi . The average weight of female progeny was not significantly affected by fungal or tree species. However, the production of progeny adults was significantly higher, and emergence significantly earlier, for D. ponderosae associated with O. clavigerum (isolated from D. jeffreyi ) and developing in P. contorta than for D. ponderosae developing with O. montium in P. contorta . No brood was produced by D. jeffreyi or by fungus-free D. ponderosae . Larval galleries were shortest in the O. clavigerum / P. contorta treatment, whereas the longest larval galleries were produced in the O. montium / P. jeffreyi treatment. Both host tree species and fungus have an effect on the ability of progeny to successfully develop.
Dendroctonus
Mountain pine beetle
Ophiostoma
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