Aerially applied verbenone-releasing laminated flakes protect Pinus contorta stands from attack by Dendroctonus ponderosae in California and Idaho
Nancy E. GilletteNadir ErbilginJeffrey N. WebsterLee PedersonSylvia R. MoriJohn D. SteinDonald R. OwenK.M. BischelDavid L. Wood
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Dendroctonus
Mountain pine beetle
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.
Mountain pine beetle
Dendroctonus
Picea engelmannii
Abies lasiocarpa
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Abstract Recent large and severe outbreaks of native bark beetles have raised concern among the general public and land managers about potential for amplified fire activity in western North America. To date, the majority of studies examining bark beetle outbreaks and subsequent fire severity in the U.S. Rocky Mountains have focused on outbreaks of mountain pine beetle ( MPB ; Dendroctonus ponderosae ) in lodgepole pine ( Pinus contorta ) forests, but few studies, particularly field studies, have addressed the effects of the severity of spruce beetle ( Dendroctonus rufipennis Kirby) infestation on subsequent fire severity in subalpine Engelmann spruce ( Picea engelmannii ) and subalpine fir ( Abies lasiocarpa ) forests. In Colorado, the annual area infested by spruce beetle outbreaks is rapidly rising, while MPB outbreaks are subsiding; therefore understanding this relationship is of growing importance. We collected extensive field data in subalpine forests in the eastern San Juan Mountains, southwestern Colorado, USA, to investigate whether a gray‐stage (<5 yr from outbreak to time of fire) spruce beetle infestation affected fire severity. Contrary to the expectation that bark beetle infestation alters subsequent fire severity, correlation and multivariate generalized linear regression analysis revealed no influence of pre‐fire spruce beetle severity on nearly all field or remotely sensed measurements of fire severity. Findings were consistent across moderate and extreme burning conditions. In comparison to severity of the pre‐fire beetle outbreak, we found that topography, pre‐outbreak basal area, and weather conditions exerted a stronger effect on fire severity. Our finding that beetle infestation did not alter fire severity is consistent with previous retrospective studies examining fire activity following other bark beetle outbreaks and reiterates the overriding influence of climate that creates conditions conducive to large, high‐severity fires in the subalpine zone of Colorado. Both bark beetle outbreaks and wildfires have increased autonomously due to recent climate variability, but this study does not support the expectation that post‐beetle outbreak forests will alter fire severity, a result that has important implications for management and policy decisions.
Mountain pine beetle
Abies lasiocarpa
Dendroctonus
Picea engelmannii
Salvage logging
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Dendroctonus
Mountain pine beetle
Ophiostoma
Abies lasiocarpa
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The objective of our project has been to determine the effects of fire on bark beetle populations in the Greater Yellowstone Ecosystem. Our general hypothesis has been that fire damaged trees provide refugia for mountain pine beetles (D. ponderosae) that allow populations to persist during non-outbreak periods. Our work combines field testing of bark beetle populations within a range of forests from burned to unburned, as well as spatial analyses (remote sensing) to determine whether the forest more proximal to fires have greater incidences of beetle mass attack. New efforts have focused on determining whether lodgepole pine (P. contorta) and whitebark pine (P. albicaulis) have differing chemical defensive capacities to beetle attack.
Mountain pine beetle
Dendroctonus
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The European spruce bark beetle (Ips typographus) and the North American mountain pine beetle (Dendroctonus ponderosae) may kill millions of trees during outbreak periods. Both species have also experienced large outbreaks in recent years. But the magnitude of the outbreaks of D. ponderosae is much larger. In this review we compare the outbreak history of I. typographus in Sweden with D. ponderosae in British Columbia in Canada. We also discuss some possible explanations for the difference in outbreak magnitude between the two species. During the last fifty years (1960-2009), three outbreaks of I. typographus have occurred in Sweden which resulted in a volume of about 9 million m3 of killed Norway spruces (Picea abies). During the same period D. ponderosae has killed about 600 million m3 of lodgepole pine (Pinus contorta) in British Columbia. Based on a literature review we suggest two factors that may contribute to the much more severe outbreaks caused by D. ponderosae: (1) a lower colonisation density needed by D. ponderosae to overcome tree defences and (2) a higher reproductive success of D. ponderosae in killed trees. In addition, the proportion of old stands, susceptible to bark beetle attacks, is much higher in British Columbia than in Sweden.
Mountain pine beetle
Dendroctonus
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Abstract We examined bark beetle responses to fire and fire surrogate treatments 2 and 4 years after the application of prescribed fire in a mixed-conifer forest in northern California. Treatments included an untreated control (C), thinning from below (T), and applications of prescribed fire (B) and T + B replicated three times in 10-ha experimental units. A total of 1,822 pine and fir trees (5.1% of all trees) were killed by bark beetles. Mountain pine beetle (Dendroctonus ponderosae Hopkins) was found infesting ponderosa pine (Pinus ponderosa Dougl. ex Laws.), sugar pine (Pinus lambertiana Dougl.), and lodgepole pine (Pinus contorta Dougl. ex Loud.); western pine beetle (Dendroctonus brevicomis LeConte) was found infesting ponderosa pine; and fir engraver (Scolytus ventralis LeConte) was found infesting white fir (Abies concolor [Gord. & Glend.] Lindl. ex Hildebr.). Significantly higher rates of bark beetle-caused tree mortality occurred on B (9.2%) than on C (3.2%), T (<1%), or T + B (3.3%) cumulatively during the 4-year period. A total of 723 pines (4.4% of all pines) were killed by bark beetles, primarily mountain pine beetle. Attacks resulted in significantly more pine mortality on B (5%) than on C, T, or T + B (all <1%) 2 years after the application of prescribed fire. No significant treatment effects were found during the second sample period or cumulatively during the 4-year period. A total of 1,098 white fir trees (5.8% of all white fir) were killed by the fir engraver. Attacks resulted in significantly higher rates of fir mortality on T + B than on T during both sample periods but not cumulatively during the 4-year period. Overall, bark beetle-caused tree mortality was concentrated in the smaller diameter classes. The implications of these and other results to forest management are discussed.
Mountain pine beetle
Dendroctonus
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Dendroctonus
Mountain pine beetle
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Summary The causes of bark beetle outbreaks – particularly the role of disturbances – are poorly understood. Stand‐scale disturbances, like fires, can suddenly improve local host susceptibility and may attract beetles; however, whether such increases can lead to outbreaks in post‐disturbance stands is unclear. Using low‐density Dendroctonus ponderosae mountain pine beetle populations in Pinus contorta lodgepole pine forests in western Canada, we investigated whether prescribed fires promote outbreaks or provide only short‐term resources. Proportionally more burned than non‐burned trees were attacked. At one site, beetle attacks increased in response to a resource pulse, but the proportions of attacked trees and numbers of attacks per tree declined over four years after fire. Elsewhere, beetle attacks remained very low. As the resource (phloem) quality of burned trees remained high three years after fire, we propose that post‐fire mortality, resulting in fewer available host trees, can at least partially explain why D. ponderosae did not build up populations in burned stands. Synthesis and applications . Our study emphasizes the importance of examining long‐term trends in fire–bark beetle interactions, and of understanding low‐density beetle populations. Because fire does not seem to promote mountain pine beetle outbreaks, we recommend the continued use of prescribed fire for the general management of P. contorta forests with low‐density beetle populations.
Mountain pine beetle
Dendroctonus
Prescribed burn
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Abstract 1 Although mountain pine beetle Dendroctonus ponderosae Hopkins are able to utilize most available Pinus spp. as hosts, successful colonization and reproduction in other hosts within the Pinaceae is rare. 2 We observed successful reproduction of mountain pine beetle and emergence of new generation adults from interior hybrid spruce Picea engelmannii × glauca and compared a number of parameters related to colonization and reproductive success in spruce with nearby lodgepole pine Pinus contorta infested by mountain pine beetle. 3 The results obtained indicate that reduced competition in spruce allowed mountain pine beetle parents that survived the colonization process to produce more offspring per pair than in more heavily‐infested nearby pine. 4 We also conducted an experiment in which 20 spruce and 20 lodgepole pines were baited with the aggregation pheromone of mountain pine beetle. Nineteen pines (95%) and eight spruce (40%) were attacked by mountain pine beetle, with eight (40%) and three (15%) mass‐attacked, respectively. 5 Successful attacks on nonhost trees during extreme epidemics may be one mechanism by which host shifts and subsequent speciation events have occurred in Dendroctonus spp. bark beetles.
Dendroctonus
Mountain pine beetle
Picea engelmannii
Abies lasiocarpa
Pinaceae
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The mountain pine beetle, Dendroctonus ponderosae Hopkins, is a member of a group of beetles known as bark beetles: Except when adults emerge and attack new trees, the mountain pine beetle completes its life cycle under the bark. The beetle attacks and kills lodgepole, ponderosa, sugar, and western white pines. Outbreaks frequently develop in lodgepole pine stands that contain well-distributed, large-diameter trees or in dense stands of pole-sized ponderosa pine. When out-breaks are extensive, millions of trees may be killed each year. Periodic losses of high-value, mature sugar and western white pines are less wide-spread but also serious.
Mountain pine beetle
Dendroctonus
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