Pine In British Columbia Research Articles

Climate-induced outbreaks in high-elevation pines are driven primarily by immigration of bark beetles from historical hosts.

Warming temperatures are allowing native insect herbivores to expand into regions that previously exceeded their thermal tolerance, encounter new host species, and pose significant threats to native communities. However, the dynamics of these expansions remain poorly understood, particularly in the extent to which outbreaks remain reliant on emigration from historical hosts or are driven by local reproduction within novel hosts in the expanded range. We tested these non-mutually exclusive hypotheses using spatially explicit data on mountain pine beetle (Dendroctonus ponderosae), which historically undergoes intermittent outbreaks in low-elevation lodgepole pine (Pinus contorta), but is now causing severe mortality in a high-elevation endangered species, whitebark pine (Pinus albicaulis). We compiled data from 2000 to 2019 across British Columbia, Canada, at 1-km2 resolution, and analyzed spatiotemporal patterns of beetle infestations, lodgepole pine distributions, expansion into habitats dominated by whitebark pine, and the likelihood of future outbreaks in all pine communities under simulated conditions. Overall, we found strong support for the hypothesis of emigration from the historical host species continuing to be a major driver of outbreaks in the more recently accessed host. First, beetle population pressure was consistently the best predictor of infestation severity in both lodgepole and whitebark pine, and appeared to be mostly unidirectional from lodgepole to whitebark pine. Second, infestations in lodgepole pine were of a longer duration than those in whitebark pine, which appeared too brief to sustain transitions from endemic to eruptive dynamics. Furthermore, resource depletion appears to drive emigration from lodgepole pine, whereas in whitebark pine drought appears to favor establishment of immigrants although bioclimatic factors and stand structure preclude self-sustaining outbreaks. Finally, we project that most pine in British Columbia will be at risk in the event of a new major outbreak. We describe implications for conserving and protecting whitebark pine and to other climate-driven range expansions.

Signatures of Post-Glacial Genetic Isolation and Human-Driven Migration in the Dothistroma Needle Blight Pathogen in Western Canada.

Many current tree improvement programs are incorporating assisted gene flow strategies to match reforestation efforts with future climates. This is the case for the lodgepole pine (Pinus contorta var. latifolia), the most extensively planted tree in western Canada. Knowledge of the structure and origin of pathogen populations associated with this tree would help improve the breeding effort. Recent outbreaks of the Dothistroma needle blight (DNB) pathogen Dothistroma septosporum on lodgepole pine in British Columbia and its discovery in Alberta plantations raised questions about the diversity and population structure of this pathogen in western Canada. Using genotyping-by-sequencing on 119 D. septosporum isolates from 16 natural pine populations and plantations from this area, we identified four genetic lineages, all distinct from the other DNB lineages from outside of North America. Modeling of the population history indicated that these lineages diverged between 31.4 and 7.2 thousand years ago, coinciding with the last glacial maximum and the postglacial recolonization of lodgepole pine in western North America. The lineage found in the Kispiox Valley from British Columbia, where an unprecedented DNB epidemic occurred in the 1990s, was close to demographic equilibrium and displayed a high level of haplotypic diversity. Two lineages found in Alberta and Prince George (British Columbia) showed departure from random mating and contemporary gene flow, likely resulting from pine breeding activities and material exchanges in these areas. The increased movement of planting material could have some major consequences by facilitating secondary contact between genetically isolated DNB lineages, possibly resulting in new epidemics.

Using excess greenness and green chromatic coordinate colour indices from aerial images to assess lodgepole pine vigour, mortality and disease occurrence

Here, we test the feasibility of using two colour indices to assess differences in stand-health metrics in 54 plots of lodgepole pine in British Columbia, Canada. Colour indices of excess greenness (EG) and green chromatic coordinate (GCC) were calculated over two spatial scales from colour images captured from a Cessna T210 flying at 600m above ground level. EG and GCC were then compared to five ground-based metrics of stand health: vigour, mortality, foliar disease occurrence, western gall rust occurrence, and root disease symptoms. Colour indices, calculated at both tree and plot scales, significantly related to the ground-based metrics of stand health, except western gall rust occurrence. These relationships were influenced by canopy closure, but were unaffected by foliar nitrogen concentration. Using linear regression models, ground-based stand-health metrics accounted for 36.5–60.9% of the variability in colour indices. Within research projects, EG and GCC values could be used to set thresholds below which ground-checks of stand health would be warranted.

A Site Index Model for Lodgepole Pine in British Columbia

A height growth and site index model was developed combining permanent sample plot (PSP) and stem analysis (SA) data from the Sub-Boreal Spruce biogeoclimatic zone of British Columbia, Canada. SA data were screened for indications of early suppression, virtually eliminating that source of bias. Estimation was based on a stochastic di erential equation form of the Bertalan y-Richards growth curve, including environmental and measurement/sampling variation. Methods involve the inclusion of mixed e ects, and obtaining simultaneous maximum likelihood estimates for all the parameters. Di erences in error structure between PSP and SA data were taken into account. The model fits the data well, and compares favorably to existing alternatives.

Comparison of lodgepole and jack pine resin chemistry: implications for range expansion by the mountain pine beetle,Dendroctonus ponderosae(Coleoptera: Curculionidae)

The mountain pine beetle, Dendroctonus ponderosae, is a significant pest of lodgepole pine in British Columbia (BC), where it has recently reached an unprecedented outbreak level. Although it is native to western North America, the beetle can now be viewed as a native invasive because for the first time in recorded history it has begun to reproduce in native jack pine stands within the North American boreal forest. The ability of jack pine trees to defend themselves against mass attack and their suitability for brood success will play a major role in the success of this insect in a putatively new geographic range and host. Lodgepole and jack pine were sampled along a transect extending from the beetle’s historic range (central BC) to the newly invaded area east of the Rocky Mountains in north-central Alberta (AB) in Canada for constitutive phloem resin terpene levels. In addition, two populations of lodgepole pine (BC) and one population of jack pine (AB) were sampled for levels of induced phloem terpenes. Phloem resin terpenes were identified and quantified using gas chromatography. Significant differences were found in constitutive levels of terpenes between the two species of pine. Constitutive α-pinene levels – a precursor in the biosynthesis of components of the aggregation and antiaggregation pheromones of mountain pine beetle – were significantly higher in jack pine. However, lower constitutive levels of compounds known to be toxic to bark beetles, e.g., 3-carene, in jack pine suggests that this species could be poorly defended. Differences in wounding-induced responses for phloem accumulation of five major terpenes were found between the two populations of lodgepole pine and between lodgepole and jack pine. The mountain pine beetle will face a different constitutive and induced phloem resin terpene environment when locating and colonizing jack pine in its new geographic range, and this may play a significant role in the ability of the insect to persist in this new host.

A Provincial and Regional Assessment of the Mountain Pine Beetle Epidemic in British Columbia: 1999-2008

Western Canada is currently experiencing an epidemic infestation of mountain pine beetle (Dendroctonus ponderosae Hopkins). In British Columbia, the infestation extends over more than 13 million ha and has resulted in a wide-range of social, economic, and ecological impacts. In this study, we compile the known environmental drivers of the infestation and assess these drivers against the actual outcomes of the infestation to date. To support our investigation, we defined the population at risk to mountain pine beetle attack as the spatial extent of pine in British Columbia (approximately 525,329 km^2 ) and used a range of driver variables known to influence the location and success of beetle infestations (i.e., proportion of pine, climatic factors, and l atitude adjusted elevation) as inputs to a two-step clustering algorithm. We generated 15 cl usters representing unique combinations of these driver variables. Variables that represent resulting conditions or infestation outcomes (i.e., cumulative amount of pine killed, proportion of pine remaining, distance to nearest infestation, or stand susceptibility) were then used to characterize these clusters and to identify areas of the province with similar drivers, but with different infestation conditions and outcomes. When the entire study area is considered, our findings indicate that th e most susceptible areas of pine in British Columbia were attacked by the beetle fi rst and that heretofore uninfested areas with similar conditions were likely sp ared from infestations initially due to their abundance of im mature pine. However, infestations in less optimal areas increased ma rkedly in 2007 and 2008, as the competition for hosts increased. A regional assessment of the clusters (for areas in the north, cen tral, and southern regions of British Columbia) further indicated that the beetles may have opportunities to expand in northern and central areas-depending on short-term climatic conditions. By relating our current understanding of infestation drivers to the 2008 infestation, we were able to identify those areas of the province that are most vulnerable to continued infestation. Our results confirm that mountain pine beetle will likely continue to be the dominant forest health concern in British Columbia for many years to come.

History of western white pine and blister rust in British Columbia

Blister rust (Cronartium ribicola) entered Europe about 300 years after eastern white pine (Pinus strobus) was first planted in Europe. North America imported millions of infected seedlings after blister rust was firmly established throughout Europe. Blister rust probably entered into western North America on multiple occasions and spread throughout British Columbia (BC) by about 1930. Two large saw mills solely cutting western white pine (P. monticola) started in the 1920s with the main production for matches. Blister rust surveys in the 1940s painted a poor picture for the future of western white pine in BC, so it was discriminated against in forest management plans. Harvest volumes declined and the 2 mills ceased production about 1960. Selection of resistant clones from mature parents occurred between 1948 and 1960, but when it was evident that mature tree resistance was not likely to be in their seedlings the program was terminated. A program based on screening seedlings was started in 1983. The selected seedlings are hypothesized to possess age-related resistance that is being expressed at an early age. These and the better parents are incorporated into orchards. Key words: Cronartium, white pine, surveys, match blocks, rust resistance, PR proteins

Variation in pathogenicity of a mountain pine beetle–associated blue-stain fungus, Grosmannia clavigera, on young lodgepole pine in British Columbia

Grosmannia clavigera is the most pathogenic blue-staining fungal associate of the mountain pine beetle (Dendroctonus ponderosae). In contrast to its importance as a primary invader of lodgepole pine (Pinus contorta) sapwood, intraspecific variability in pathogenicity of G. clavigera on lodgepole pine, the predominant host of mountain pine beetles in British Columbia, has not been investigated in detail. The present work reports on pathogenicity indicators induced by five G. clavigera isolates inoculated into lodgepole pines and growth characteristics of the isolates on artificial media. Fungi were inoculated at 200 inoculations/m2 into young lodgepole pine trees. Phloem lesion length, sapwood occlusion area, and sapwood moisture content were measured after 7 or 48 weeks. Three isolates produced long lesions, occluded larger areas, and reduced more the moisture content after 48 weeks compared with the remaining two isolates. Isolate ATCC 18086 induced the strongest pathogenic symptoms after 7 weeks and grew the fastest up to 22.5 °C but grew the slowest at 27.5 °C. In a low-oxygen environment, most isolates grew faster than under ambient conditions. Significant intraspecific variation was observed among G. clavigera isolates for all parameters tested. Key words: Grosmannia clavigera, Ophiostoma clavigerum, mountain pine beetle, blue-stain fungus, intraspecific variation, pathogenicity. Grosmannia clavigera est le plus pathogénique des champignons du bleuissement associés au dendroctone du pin ponderosa (Dendroctonus ponderosae). Contrairement à son importance en tant qu’envahisseur primaire de l’aubier du pin tordu latifolié (Pinus contorta), la variabilité intraspécifique de la pathogénicité de G. clavigera envers ce dernier, hôte principal du dendroctone du pin ponderosa en Colombie-Britannique, n’a pas été étudiée en détail. Les présents travaux font état d’indicateurs de pathogénicité produits par cinq isolats de G. clavigera appliqués sur des pins tordus latifoliés ainsi que des caractéristiques de croissance de ces isolats cultivés en milieu artificiel. De jeunes pins tordus latifoliés ont été inoculés avec le champignon à raison de 200 inoculations/m2. Au bout de 7 ou 48 semaines, la longueur des lésions subies par le phloème, la surface d’occlusion de l’aubier ainsi que son degré d’humidité ont été mesurés. Au bout de 48 semaines, comparativement aux deux autres, trois des cinq isolats avaient produit de longues lésions, occlus de plus larges surfaces et avaient davantage réduit le degré d’humidité. Au bout de 7 semaines, l’isolat ATCC 18086 avait provoqué les symptômes pathogènes les plus aigus. Son taux de croissance avait également été le plus rapide, et ce, jusqu’à 22,5 °C, pour devenir le plus lent à 27,5 °C. La plupart des isolats ont crû plus rapidement dans un environnement faible en oxygène que dans les conditions de milieu ambiant. Une variation intraspécifique significative a été observée chez les isolats de G. clavigera, et ce, relativement à tous les paramètres analysés. Mots-clés : Grosmannia clavigera, Ophiostoma clavigerum, dendroctone du pin ponderosa, champignon du bleuissement, variation intraspécifique, pathogénicité.

Dose-Dependent Pheromone Responses of Mountain Pine Beetle in Stands of Lodgepole Pine

We conducted seven behavioral choice tests with Lindgren multiple-funnel traps in stands of mature lodgepole pine in British Columbia, from 1988 to 1994, to determine the dose-dependent responses of the mountain pine beetle, Dendroctonus ponderosae Hopkins, to its pheromones. A multifunctional dose-dependent response was exhibited by D. ponderosae to the pheromones cis- and trans-verbenol in areas with low population numbers. In an area with a high population level of D. ponderosae, the response was directly proportional to release rates. No dose-dependent response was exhibited by D. ponderosae to exo-brevicomin at low release rates. At rates of release >0.5 mg/d, exo-brevicomin interrupted the attraction of D. ponderosae in a dose-dependent fashion. The bark beetle predators, Enoclerus sphegeus (F.) and Thanasimus undatulus (Say), showed dose-dependent responses to only a few pheromones, with trap catches directly proportional to release rates. The multi-functional response of D. ponderosae to verbenols is consistent with an optimal attack density hypothesis.

Dose-Dependent Pheromone Responses ofIps pini,Orthotomicus latidens(Coleoptera: Scolytidae), and Associates in Stands of Lodgepole Pine

We conducted four behavioral choice tests in stands of mature lodgepole pine in British Columbia, from 1988 to 1991, to determine the dose-dependent responses of Orthotomicus latidens (LeConte) and Ips pini (Say) to their respective pheromones. Dose-dependent responses were exhibited by I. pini to (±)-ipsdienol and lanierone, with trap catches directly proportional to pheromone release rates. We found differences in sex ratio of I. pini in their responses to ipsdienol but not lanierone. There was no dose-dependent response exhibited by O. latidens to its pheromone, (±)-ipsenol, with or without the presence of the host kairomone, (−)-&bgr;-phellandrene. The bark beetle predator, Enoclerus lecontei (Wolcott), showed a dose-dependent response to lanierone. Thanasimus undatulus (Say) was attracted to ipsenol in a dose-dependent fashion only when traps were also baited with &bgr;-phellandrene. Neither T. undatulus nor E. sphegeus (F.) exhibited dose-dependent responses to ipsdienol.

Environmental and inoculum-source effects on resistance of Idaho F2 western white pine in British Columbia

An Idaho orchard seed source (RTB F2) of western white pine (Pinus monticola) was confirmed as having fewer blister rust cankers (average 18%) caused by Cronartium ribicola than native stock (average 62%) in plantations in the interior of British Columbia, Canada, but not at low, coastal elevations (average 59%). Placing RTB F2 seedlings at different sites after five separate inoculation tests confirmed that more cankers developed at the coast than in the interior of British Columbia. This suggested that differences between coast and interior results were due to environmental effects, not to inoculum sources, as coastal and interior inoculum caused the same effects. Putative resistance traits in RTB F2 are needle shed and fungicidal short shoot. However, needle shed occurred only at one site, and it was associated with poor growing conditions, not genetic traits. Most seedlings classified as fungicidal short shoot 2 years after inoculation eventually developed cankers. However, after 3 or 4 years, some seedlings shed their infected needles naturally without developing cankers (a spots-only response), and others developed resistant cankers called slow canker growth. Based on published data, only 35% of the inoculated seedlings were expected to be cankered, but because needle shed did not occur, and because fungicidal-short-shoot seedlings were observed longer than in the previous study, 98% (mean value) were cankered when planted at the coast, and 74% (mean value) were cankered when planted in the interior. As an alternative to a needle-shed trait to account for the good field resistance (few cankers) of Idaho F2 stock in the British Columbia interior, it is hypothesized that good field resistance is the result of both a short growing season and natural infection at a later age, which enhances resistance responses

Distribution and severity of white pine blister rust and mountain pine beetle on whitebark pine in British Columbia

A major decline in the abundance of whitebark pine (Pinus albicaulis Engelm.) has recently occurred in the United States, primarily as a result of white pine blister rust (Cronartium ribicola J.C. Fisch. ex Raben.). However, no information on the status of whitebark pine in British Columbia, Canada, was available. We sampled 54 subalpine stands in British Columbia, examining all whitebark pine trees within plots for evidence of blister rust and mountain pine beetle (Dendroctonus ponderosae Hopk.) damage. About 21% of all whitebark pine stems were dead, and blister rust was the most important agent of mortality. Of all living trees sampled, 27% had obvious blister rust infection (cankers), but actual incidence was suspected of being as high as 44% (using all evidence of blister rust). Blister rust incidence and whitebark pine mortality were significantly related to differences in stand structure and the presence of Ribes spp., but relationships with local climate and site variables were absent or weak. The lack of strong relationships with climate suggests favourable conditions for the spread of the disease throughout most of British Columbia. Very little evidence of mountain pine beetle was found. Overall, the prospects for whitebark pine in British Columbia do not appear good; a large reduction in population levels seems imminent.

Height Growth Models for High-Elevation Subalpine Fir, Engelmann Spruce, and Lodgepole Pine in British Columbia

Abstract To estimate potential productivity of the high-elevation Engelmann Spruce and Subalpine Fir (ESSF) zone of British Columbia forests, the height growth models developed from low-elevation forests are currently used to estimate site indices of subalpine fir (Abies lasiocarpa), Engelmann spruce (Picea engelmannii), and lodgepole pine (Pinus contorta). Whether these models are adequate to describe height growth of high-elevation forests is of concern. We sampled a total of 319 naturally established, even-aged, and undamaged stands with breast height age ≥50 yr (165 for subalpine fir, 87 for Engelmann spruce, and 67 for lodgepole pine) ranging widely in climate and available soil moisture and nutrients. In each sampled stand, three dominant trees were destructively sampled for stem analysis. Height growth models developed from fitting data to a conditioned logistic function explained > 97% variation in height for all three study species. Examined by residual analysis, no models showed lack of fit. These models provided more accurate estimates of site index than the currently used models developed from low-elevation stands or different species. It is recommended that the models developed in this study be applied to estimate site index of the three species in the ESSF zone in British Columbia. West. J. Appl. For. 15(2):62-69.

Distribution and severity of white pine blister rust and mountain pine beetle on whitebark pine in British Columbia

A major decline in the abundance of whitebark pine (Pinus albicaulis Engelm.) has recently occurred in the United States, primarily as a result of white pine blister rust (Cronartium ribicola J.C. Fisch. ex Raben.). However, no information on the status of whitebark pine in British Columbia, Canada, was available. We sampled 54 subalpine stands in British Columbia, examining all whitebark pine trees within plots for evidence of blister rust and mountain pine beetle (Dendroctonus ponderosae Hopk.) damage. About 21% of all whitebark pine stems were dead, and blister rust was the most important agent of mortality. Of all living trees sampled, 27% had obvious blister rust infection (cankers), but actual incidence was suspected of being as high as 44% (using all evidence of blister rust). Blister rust incidence and whitebark pine mortality were significantly related to differences in stand structure and the presence of Ribes spp., but relationships with local climate and site variables were absent or weak. The lack of strong relationships with climate suggests favourable conditions for the spread of the disease throughout most of British Columbia. Very little evidence of mountain pine beetle was found. Overall, the prospects for whitebark pine in British Columbia do not appear good; a large reduction in population levels seems imminent.

Pruning Western White Pine in British Columbia to Reduce White Pine Blister Rust Losses: 10-Year Results

Abstract Survey lines were located in areas that had been pruned to control blister rust (Cronartium ribicola) 10 yr previously and adjacent control (unpruned) areas in 10 stands of western white pine. Stands were classified as densely stocked, moderately stocked, or open. Cankers were tallied and their position noted. The success of pruning varied from stand to stand. Since the stands had not been pruned at an early age, there was only a 4 and 5% reduction in threatening cankers and stem cankers respectively, as few new cankers were initiated. Stands with the greatest increase in cankering had Ribes spp., were open grown, or possessed a high component of small white pine. Repruning these specific stands may be worthwhile, but in general, entering stands again to do either pruning or scribing would produce few additional healthy trees. Doing both treatments, however, may significantly enhance the number of healthy stems. To optimize the benefits of pruning, stands should be entered early and pruning should continue until a sufficient number of stems are pruned to a height of 3 m to ensure full stocking. Other species may be impediments to spore movement within stands, and thus they should not be pruned. Dense stands initially had less rust than open stands and could be entered later, but once spaced, they also need to be pruned to 3 m to minimize rust infection. West. J. Appl. For: 13(2):60-63.

Growth response and recovery of 15N-fertilizer one and eight growing seasons after application to lodgepole pine in British Columbia

This paper reports plant and soil distribution of 15N 1 and 8 years after fertilizer application near Spillimacheen in the British Columbia interior. The experiment was originally established to test the efficacy of fertilization on snow; 15N-urea, 15NH 4NO 3 and NH 4 15NO 3 were applied at 100 kg N ha −1 to 11-year-old lodgepole pine ( Pinus contorta Dougl. var. latifolia Engelm.) in January 1981. After one growing season (October 1981), eight of the 16 plots were destructively sampled. Total recovery of 15N in plot trees was low, from 1.9 to 10.1%. Recovery in understorey was comparable (2.4–3.4%), and 30.6–73.2% of 15N was retained in the soil in organic form. The remaining eight plots were sampled in August 1988. There was a significant growth response to fertilization, amounting to a 34% increase in stem volume for fertilized (ammonium nitrate or urea) versus control trees after eight growing seasons. Approximately two-thirds of the 15N recovered in 1981 could still be accounted for in plant biomass and soil. There had been little additional 15N uptake by plot trees, but more continuing uptake by understorey. About one-fifth of 15N recovered in 1988 was found outside the plot boundaries. The results are consistent with the hypotheses that (i) tree response to fertilization is largely the result of the increase in photosynthetic capacity generated by the first year of uptake, (ii) fertilizer N, once immobilized in the soil, has low availability to crop trees, and (iii) the N mineralized is subject to losses, presumably by leaching and denitrification. Strategies are needed for maximizing the uptake of N in the first growing season. Further research is recommended to determine what factors limit the uptake of available N by trees, and to quantify natural levels of leakage of mineral N from the ecosystem due to denitrification and leaching.

Ipsenol: an aggregation pheromone forIps latidens (Leconte) (Coleoptera: Scolytidae)

Ipsenol was identified from the frass of male, but not female,Ips latidens from British Columbia, feeding in phloem tissue of lodgepole pine,Pinus contorta var.latifolia. The responses ofJ. latidens to sources of ips-enol andcis-verbenol were determined with multiple-funnel traps in stands of lodgepole pine in British Columbia. Ipsenol attracted both male and femaleI. latidens, verifying that it is a pheromone for this species. MaleI. latidens showed a slight preference for (S)-(-)-ipsenol.cis-Verbenol was not produced by beetles of either sex and, in contrast to an earlier report, both enantiomers inhibited attraction to ipsenol-baited traps. The predators,Enoclerus sphegeus andThanasimus undatulus (Cleridae), were attracted to traps baited withcis-verbenol and ipsenol.

Blister rust in inoculated and plantation-tested western white pine in British Columbia

Blister rust in inoculated and plantation-tested western white pine in British Columbia

THE USE OF MONOTERPENES AS KAIROMONES BY IPS LATIDENS (LECONTE) (COLEOPTERA: SCOLYTIDAE)

AbstractThe responses of Ips latidens (LeConte) to multiple-funnel traps baited with various monoterpenes were determined in stands of lodgepole pine in British Columbia. β-Phellandrene was attractive to I. latidens in the absence of the pheromone ipsenol. β-Phellandrene increased the attraction of I. latidens to ipsenol-baited traps while α-pinene, 3-carene, terpinolene, and myrcene reduced trap catches. Differential responses by males and females to sources of ipsenol with or without β-phellandrene suggest that the information conveyed to males differs from that conveyed to females. Species-specific responses to monoterpenes by I. latidens and three sympatric species of scolytids suggest that unique combinations of kairomones could be important in facilitating matings with conspecifics. Pheromones need not be the sole constituent of species-specific chemical messages.

Black-stain root disease on lodgepole pine in British Columbia

Surveys were made for incidence and damage by black-stain root disease (Ceratocystiswageneri) on Pinuscontorta in British Columbia. Incidence surveys indicated the hard pine pathotype to be largely restricted to the west Kootenays, northern Okanagan, and southern Cariboo. Damage surveys of 177 ha in 12 stands revealed severe damage in pure, dense stands, 80 years and older, at elevations above 1000 m. In one-half of the stands, C. wageneri was associated with Armillariaobscura; in one-third, some trees in C. wageneri centres were currently infested with Dendroctonusponderosae. Most disease centres were small, but sometimes there were many per stand, so that up to 46% of a stand was affected. The pattern of disease centres suggested that unknown vectors were responsible for initiating disease centres. Isolations from excavated stumps indicated little survival of C. wageneri after 1 year and none after2 years. Infested stands can be clear-cut and regenerated to P. contorta without risk of infection from the previous stand.