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Survival and growth of planted white spruce (Picea glauca (Moench) Voss) were assessed at year 15 in boreal mixedwood stands of northern Alberta, Canada, in stands that were deciduous-dominated prior to logging or were conifer-dominated. Three overstory retention levels (0%, 50%, and 75% retention) and four site preparation treatments (mound, high speed mix, scalp, and no treatment) were evaluated. In deciduous-dominated stands, planted spruce performed best in the 50% retention; here, stem volume was at least double that of any other retention treatment after 15 years. In contrast, spruce had reduced growth in coniferous-dominated stands in both 50% and 75% retention treatments compared with the 0% retention. Survival of planted spruce was unaffected by level of retention, but survival was lower in coniferous-dominated stands than in deciduous-dominated stands; in the coniferous-dominated stands, survival was better with mounding and mixing and lowest with scalp treatments. All height variables tended to be greater in the mix and mound site preparation treatments. Finally, the best estimates of future total growth (regenerated spruce and deciduous combined) in the coniferous-dominated stands were in the clearcut treatment. In terms of regenerated spruce growth, the best estimates occurred in the deciduous-dominated – 50% retention stand planted with soil mixing–mounding treatments, where projected growth of spruce was comparable with that of open-grown and tended stands in Alberta’s boreal forests.

International audience; A greenhouse inoculation experiment and field study were conducted to determine the cause of an outbreak of Septoria musiva cankers on Populus balsamifera in a northern Alberta plantation. Four clones of P. balsamifera, five clones of putatively resistant P. deltoides, and one susceptible hybrid poplar clone, Northwest, were inoculated with seven isolates identified as S. musiva. Four of the isolates were from P. balsamifera in Alberta and the others were from P. deltoides in Quebec. Results indicated that disease severity was similar for Alberta and Quebec isolates (P = 0.243) and that P. balsamifera had the greatest mean disease severity (x-bar = 4.20), P. deltoides had the lowest (x-bar = 2.76), and Northwest was intermediate (x-bar = 3.45). A genetic analysis comparing six polymorphic polymerase chain reaction restriction fragment length polymorphism loci and the mitochondrial small subunit ribosomal DNA sequences of the seven isolates indicated that the Alberta population was made up of at least three distinct genotypes. Canker incidence and age on Northwest and 56 different clones of P. balsamifera in a plantation were recorded. Canker incidence (P = 0.726) and the canker age distributions (P = 0.994) were similar for the two species. In conclusion, contrary to what has been reported in the literature, P. balsamifera appears to be quite susceptible to Septoria canker.

Most artificial inoculations of Populus spp. stems with Septoria musiva have required host wounding to induce canker development; in the absence of wounds, frequencies of cankers have been low. Three greenhouse inoculation experiments were conducted to demonstrate the reliability and repeatability of an inoculation method that did not require wounding. In the first, 16 clones of hybrid poplar were inoculated with three isolates of S. musiva to compare responses following wounding and inoculation with mycelium (wound inoculation) with responses following inoculation of nonwounded trees by spraying with a conidial suspension (spray inoculation). Stem disease severity among clones following spray inoculation was correlated with stem disease severity following wound inoculation. A significant clone–isolate interaction was detected with spray inoculation but not wound inoculation. In the other two greenhouse experiments, 29 clones of hybrid poplar and 69 clones of Populus balsamifera were inoculated with a spore suspension mixture of three isolates. In both cases, the experimental error was similar to that obtained in previous experiments, in which trees were wound inoculated, and was adequately small to permit detection of differences in responses among clones. Ultimately, field studies will be needed to determine the best inoculation method for predicting stem responses to this pathogen under field conditions. However, relative to wound inoculation, spray inoculation of nonwounded trees has the advantage of yielding faster results, permitting inoculation with a mixture of isolates, and not circumventing potential mechanisms for resisting penetration. The ability to infect stems without wounding creates opportunities for numerous types of epidemiological and disease control studies that are difficult to conduct with wound inoculation.

Open range grazing by cattle is common on heterogeneous montane landscapes in western Canada. These areas are often jointly managed for forestry, leading to concerns over forest re-establishment following clear cut harvest and cattle impacts on tree regeneration. A network of 154 field plots were used to examine cattle utilization across five coniferous cut blocks within three large pastures of SW Alberta over a 2 year period. Specific objectives were to: (1) quantify cattle presence across cut blocks under free-choice conditions; (2) identify the environmental factors responsible for observed patterns of cattle presence, including topography, distance to water, forage characteristics and slash properties; and (3) document cattle impact on conifer seedlings. Averaged over 2 years, evidence of cattle was found in 46 % of plots, primarily as herbage removal. Cattle presence across logged areas was associated with plots at lower elevations and closer to water, and to a lesser extent, those areas with greater forage biomass but lower quality. Forest surveys done 3 years after harvest indicated most tree regeneration consisted of planted lodgepole pine (Pinus contorta Loudon) and naturally regenerating Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). While regeneration among plots remained below the provincial requirement of 80 % stocking, ranging from 68 to 77 % among cut blocks, this deficit was not attributed to cattle impact, as only two tree seedlings surveyed had evidence of livestock-induced damage. Finally, cattle visitation to plots was lower with taller slash in select pastures, suggesting slash may deter cattle use of some cut blocks. Overall, the results of this study support the notion that forest management and cattle grazing are compatible uses on Montane landscapes managed for multiple purposes.

Logging of aspen (Populus tremuloides Michx.) forests on public grazing land in west central Alberta creates a mosaic of habitat types that may alter cattle (Bos taurus) use of these landscapes. We used an extensive network of field plots and global positioning system (GPS) collars deployed on cattle within four experimental pastures, each containing a mix of uncut forest, clear cut forest, partially harvested areas, and in-block haul roads, to examine habitat preferences during mid-summer grazing in 2008 and 2009. We also examined the effect of two cattle stocking rates the first year. Although cattle removed similar amounts of forage in all habitats, GPS data indicated cattle spent more time in uncut forests, and avoided clear cuts and in-block haul roads during both years, patterns that remained consistent under either livestock stocking rate tested. Observed patterns of habitat use were attributed to conservative cattle stocking rates consistent with or greater than those allocated on publicly grazed forest land in Alberta, combined with specific habitat attributes. Preferred use of uncut forest was attributed in part to favorable forage quality, which was positively associated with cattle utilization (standardized β = +0.13) among plots. Although forage use by cattle of plots also increased with forage biomass (β = +0.33), sharp increases in biomass following clear cut logging appeared to be offset by reductions in forage use associated with increased slash cover (β = −0.12) and sapling density (β = −0.11), both of which may have impeded cattle access. As a result, forage removal remained similar among habitats. Finally, cattle use of forage decreased with increasing distance from water (β = −0.22), highlighting the importance of ensuring reliable access to water across forested pastures to prevent localized overuse. Overall, the reduced time cattle spent in clear cut habitats coupled with similar forage removal suggests that under low cattle stocking rates, grazing can be compatible with deciduous forest management in the region.

The integration of multiple uses on public rangeland requires reliable information on patterns of livestock use. We used GPS data and field plot utilization indices to examine cattle selection at the landscape and patch levels, respectively, within a heterogeneous Montane environment of SW Alberta, Canada. We also evaluated factors associated with patterns of summer cattle use, including topographic features, distance to water and roads, as well as forage quantity and quality. Cattle preferred lowland and upland grasslands, while avoiding conifer forests and clear cuts. Selection patterns differed markedly between the landscape and plot scales. At the landscape scale, forage use was related to abiotic factors, primarily slope ( β = −0.70) but also distance to water (−0.34) and distance from roads (+0.21). The negative impact of slope was greater than that observed in previous studies, and has implications for identifying primary ranges and deriving sustainable carrying capacities in Montane landscapes. At the plot (feeding patch) scale, forage use was additionally related to biomass availability ( β = +0.58), and to a lesser extent crude protein concentration (+0.16), highlighting the importance of forage characteristics in regulating cattle use. Lowland grasslands had the highest biomass and received the greatest forage use (43% utilization). Low visitation (44% of plots) and associated forage use (3% herbage utilization) by cattle within cut blocks, combined with conservative forage use across all habitats (3–43%), indicate grazing by cattle is consistent with maintaining other uses within this area, including riparian function, native grassland conservation and forest management.

Summary To test the hypothesis that galls resulting from infection by western gall rust [Endocronartium harknessii (J. P. Moore) Y. Hiratsuka] on lodgepole pine [Pinus contorta Dougl. ex Loud.] create hydraulic constrictions that reduce tree growth, the hydraulic conductivity (Kψ; m2 s−1 Pa−1), leaf area (AL) and sapwood area (AS) were measured on 6- to 15-year-old trees having galls encircling 0–100% of the stem. Increases in gall encirclement were accompanied by decreases in Kψ, foliar nitrogen concentration, AL and AS, although the AL:AS ratio remained constant. Dye flow patterns through galled stem sections indicated that water moved primarily through the non-galled portions of the stem. In a second field study, xylem and phloem wounds were applied to 13-year-old galled and non-galled trees on either the galled or non-galled side of the tree. Although both galls and xylem wounds reduced Kψ, radial and height growth were unaffected. In aggregate the two experiments showed that although trees are quite tolerant to small galls and short term reductions in Kψ, the disruption of water movement by larger galls may be sufficient to initiate a chain of events leading to tree death, especially in very dense stands with high levels of intraspecific competition.

Fourteen clones of hybrid poplar were inoculated with 19 isolates of Septoria musiva Peck under greenhouse conditions to determine the magnitude of the clone, isolate, and clone × isolate interaction effects. Septoria musiva isolates were collected from five geographic areas, two symptoms (canker and leaf spot), and two host types (native species and hybrid poplar). The hybrid poplar clones were classified by parent type ( Populus deltoides Bartr. ex Marsh., Populus laurifolia Lebed. × Populus nigra L., and P. deltoides × (P. laurifolia × P. nigra)). There were no significant differences among geographic areas (p = 0.443), symptoms (p = 0.842), or hosts (p = 0.304) of origin for the 19 isolates nor significant differences among the three parent types (p = 0.089). Clone, isolate, and clone × isolate interaction effects were all significant, accounting for 65%, 15%, and 18%, respectively, of the explained variation. These results indicate that clones rather than parent types should be the focus of resistance screening programs and that the pathosystem should be stable given the relatively small clone × isolate interaction. These results also indicate that a single isolate should be sufficient for preliminary screening of disease resistance in hybrid poplars.

In recent years boreal forests have been harvested to retain a portion of the original canopy, thereby providing forest structure, mostly for biodiversity reasons. Boreal mixedwood cutovers were surveyed at one and five years after harvesting with approximately 10% structural retention, to quantify the mean annual mortality rates of the residual trembling aspen, balsam poplar, paper birch and white spruce trees. For comparison, "natural" mortality rates by species were estimated from permanent sample plots in stands of similar composition. Species ranking of the annual mortality rates of residuals in areas harvested with structural retention were: poplar (10.2%) > birch (8.7%) > aspen (6.1%) > spruce (2.9%). Annual mortality rates were 2.5 to 4 times greater than in the reference stands. The majority of broadleaved species died as snags (~70%–90%), while most spruce died due to windthrow (80%). Mortality rates increased with slenderness coefficient for codominant and understory poplar and for understory birch. For aspen, codominants were most likely to die, while in spruce, dominant trees and trees with the greatest damage to the bole from harvesting operations had the highest mortality. Key words: Alberta, Betula papyrifera, dieback, harvesting damage, mixedwood forests, variable retention, Picea glauca, Populus balsamifera, Populus tremuloides, structural retention, sustainable forest management

Septoria musiva , the causal agent of Septoria canker, has caused widespread damage to plantations of hybrid poplar across North America. A greenhouse experiment was conducted to evaluate the size of interactions between the genotype factors of (i) clone, (ii) isolate, and (iii) the clone–isolate interaction and the environmental factor of water stress. Four clones of hybrid poplar were inoculated with four isolates of S. musiva and subsequently exposed to two levels of water stress (stressed and unstressed). Tree height, root collar diameter (RCD), and disease severity were measured 56 d after inoculation. Water stress reduced height and RCD growth by approximately 30% but did not affect disease severity (P = 0.258). Of the explained variability, 97.5% was attributable to genotype effects (89% from clone, 0% from isolate, and 8.5% from clone–isolate interaction). The remaining 2.5% of the variation was accounted for by the genotype – water stress interaction. These results suggest that clonal effects will be more important determinants of disease severity under greenhouse conditions than genotype – water stress interactions.

One of the challenges of managing spruce-aspen mixedwoods in the boreal forest is the difficulty in determining site index for spruce in those stands in which it occurs primarily in the understory. A study was conducted to determine if growth increment of understory spruce, adjusted for available light, could predict spruce site index. In each of nine stands, spruce site index was determined for three dominant trees. Available light (measured as proportion transmitted) and growth increment (estimated by the growth intercept method) were recorded for three to eight understory spruce per stand. Growth increment adjusted for available light predicted spruce site index better (R2 = 0.56 or 0.63, depending on the model used) than unadjusted growth increment (R2 = 0.10), thus indicating the potential for using light-adjusted growth increment to predict site index.

Seasonal changes in aspen (Populus tremuloides Michx.) resistance to shearing force were described to determine their apparent contribution to seasonal changes in cattle utilization. Shearing resistance of current-year, 1-year-old, and 2-year-old stem-age classes were measured from late spring to early fall. For all stem-age classes, resistance to shearing force increased with time, partially due to increasing stem diameter. Depending on stem-age class, resistance to shearing force increased by 200%-2000% between the first and last measurements of a given year. Increased resistance of aspen stems to shearing force in late summer may reduce their selection by cattle. Grazing management that defers cattle entry until midsummer could reduce damage to re-generating aspen associated with cattle foraging in cut blocks.

It is difficult to maintain, in trembling aspen (Populus tremuloides), controlled levels of aspen shoot blight (ASB) caused by Pollaccia americana, under field conditions. Thus, simulating the disease by mechanical wounding may be useful in crop-loss assessment. Three treatments were compared to evaluate the suitability of decapitation as a surrogate for ASB: (1) artificial inoculation with P. americana causing ASB and (2) cutting of the shoot between the fifth and sixth expanded leaves (decapitation), both these treatments being later referred to as injury treatments, and (3) no injury (control). The three treatments were applied to trees from four different seed lots, which subsequently grew under field conditions, and to two different clones held in a growth chamber at soil temperatures of 6, 12, or 20 °C. Leader length, frequency of axillary-shoot development, and lateral- and axillary-shoot lengths were evaluated. Trees infected with ASB and trees that were decapitated responded very similarly and ha...

The survival and impact on canola of Leptosphaeria maculans, the causal agent of blackleg, might be reduced by agents that decompose canola stubble. Fifty-six fungal isolates from wood or canola were evaluated for their ability to overcome several biological and (or) physical constraints to their effectiveness in decomposing and (or) eliminating L. maculans from canola stubble. Relative to fungi from canola, wood decay fungi were more tolerant of reduced water potential but somewhat less tolerant of lower temperature. Wood decay fungi were no better than those isolated from canola at decomposing sterile canola stubble and less able than Coprinus spp. and Cyathus olla in colonizing and surviving in nonsterile stubble. None of the isolates were effective in eliminating L. maculans from stubble pieces or causing significant decomposition of nonsterile stubble either under laboratory conditions or in the field. These results suggest that considerable effort would be required to find isolates effective in mana...

Infection of lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) by western gall rust has been shown to decrease with tree height and age, but the effects of those two factors have not been separated. Five replicate artificial inoculations were done on a total of 327 trees of different ages in two height classes. Temperature and percentage of spore germination at the height of inoculation, shoot development (stem elongation at the time of inoculation as a proportion of final shoot elongation), main stem leader length at the time of inoculation, tree height, and tree age were measured. Modeled percentages of infected trees and the number of galls per 10 cm of shoot length decreased by 85% and 88%, respectively, as tree age increased between 2 and 10 years, indicating the undesirability of early, aggressive precommercial thinning of lodgepole pine stands in areas where western gall rust is common. By controlling and (or) statistically accounting for inoculum, microclimate, and phenological factors, it was possible to demonstrate that changes in susceptibility with tree age are sufficient to account for the reduction in infection with tree height.

Intensive hog production is expanding into semi-arid regions of Alberta, where perennial forage lands are increasingly targeted for manure applicati on despite limited guidelines for its efficient use. Herbage yield and crude protein were assessed over two consecutive years within two native rangelands and two tame pastures, following different rates (10, 20, 40, 80 and 160 kg ha-1 NH4-N), methods (surface banding vs. subsurface injection) and seasons (fall vs. spring) of one-time liquid hog manure (LHM) application. Increasing manure rates improved grass yield across all sites the first growing season after treatment, from 1626 to 3576 kg ha-1. Although absolute increases in production were greatest on tame pasture, relative yield increases were similar among sites. Average crude protein (CP) concentration also increased from 69 to 91 g kg-1 in the first year. Despite low rainfall and the absence of a yield response in the second year, grass CP and crude protein yield (CPY) were maximized with increased manure application, highlighting the positive effects of manure on forage production, even with drought. Forb yields demonstrated variable effects among sites, with increasing manure decreasing alfalfa and increasing native forbs. Overall, both semi-arid tame pastures and native rangelands responded positively to LHM application, highlighting the complementary nature of hog and forage production under these conditions. Key words: Crude protein yield, forage, hog manure, injection, native rangeland, precipitation

Conflicts may arise between cattle and aspen fibre production if both occur on the same landbase. The effect of cattle on aspen regeneration was evaluated by determining the effect of four treatments (No grazing, June-only grazing, July-only grazing and continuous June-July grazing on five variables (aspen height and density, percentage of aspen trampled, foraged and dead). Continuous June-July grazing impeded aspen regeneration relative to the control. The effect of cattle on aspen mortality was likely indirect, rather than a consequence of foraging and trampling. Reducing stocking levels or delaying cattle grazing may be necessary to reduce the adverse effect of cattle grazing on aspen regeneration. Key words: grazing, cattle, aspen, regeneration, browsing, trampling

Fungal colonization of aspen (Populus tremuloides Michx.) roots was examined in boreal mixedwood sites that were mechanically site prepared 8–10 years earlier for white spruce (Picea glauca (Moench) Voss) regeneration using disc trenchers or ripper plows. A survey of root wounds determined that Armillaria sinapina Bérubé & Dessureault and Armillaria ostoyae (Romagn.) Herink were both wound pathogens of aspen; however, A. sinapina was more frequently associated with wounds than was A. ostoyae. Armillaria ostoyae was more common on unwounded root tissues. Sixty percent of wounds infected by A. sinapina were not compartmentalized and the likelihood of an A. sinapina infection did not increase with increasing wound size. Pathogenic fungi other than Armillaria were rarely associated with root wounds. Sever wounds were associated with furrows; scrape wounds were located both along and between furrows irrespective of the site-preparation technique (ripper plow vs. disk trencher).

The impacts of partial cut systems on nutrient availability and understory vegetation are poorly understood. To examine these responses, white spruce dominated stands in the boreal mixedwood of Alberta were clear-cut or partial-cut and the forest floor treated by slash burning, mixing, mounding, or scalping in a split-plot design. Soil nutrient availability (ion exchange resin), net N mineralization (in situ incubations), and vegetation (density and cover) responses were assessed. With the exception of higher Mg availability in the clearcuts, differences in nutrient availability were driven by forest floor disturbance and not harvest method. Relative to controls, burning increased availability of NH4+, NO3–, and P, and scalping increased Ca and Mg but diminished K. Controls had low levels of NO3–. The mixing treatment substantially reduced net N mineralization. In terms of vegetation, partial cuts reduced root suckering by Populus spp. (Populus tremuloides Michx., Populus balsamifera L.) relative to clearcuts. Burning and mounding stimulated fireweed (Epilobium angustifolium L.) cover, while scalping increased Populus spp. sucker density. In contrast, mixing largely reduced vegetation establishment, likely because of the destruction of roots and rhizomes and reduced N supply. Nutrient availability and vegetation establishment were more strongly controlled by forest floor disturbance than by partial canopy retention.

Scytalidium uredinicola Kuhlman et al. is considered an important mycoparasite of western gall rust caused by Endocronartium harknessii (J.P. Moore) Y. Hiratsuka (= Peridermium harknessii J.P. Moore). The temporal occurrence of S. uredinicola and its impact on the ability of western gall rust spores to germinate were determined. Scytalidium uredinicola was not isolated from either external or internal tissues of 3- to 5-year-old galls at any time of the year. However, it was isolated from the external, but not internal, tissues of 6- to 9-year-old galls in most months and from both external and internal tissues of 10+-year-old galls in all months. On galls older than 10 years, S. uredinicola overwintered beneath the periderm and colonized developing rust sori prior to peridial rupture in April. Spore viability of western gall rust was consistently reduced by 85% throughout the period of sporulation over two sporulating seasons. Because S. uredinicola requires considerable time to become persistent and per...

Moltzan, B. D., Blenis, P. V., and Hiratsuka, Y. 2001. Effects of spore availability, spore germinability, and shoot susceptibility on gall rust infection of pine. Plant Dis. 85:1193-1199. Temporal changes in three factors (shoot susceptibility, spore availability, and spore germinability) were evaluated to estimate their effects on the infection of lodgepole pine (Pinus contorta var. latifolia) by Endocronartium harknessii. Germinability of rust spores from sori free of hyperparasites remained above 80% during the growing season and thus would not have significantly limited infection. In contrast, there was a slight, but statistically insignificant, increase in estimated susceptibility as infection increased from 94% of maximum at 45% shoot elongation to maximum susceptibility at 90% shoot elongation. This was followed by a precipitous decline in estimated susceptibility to 57% of maximum when shoots were 95% elongated. Spore availability was 24% of maximum when shoots were 45% elongated, and thus may have been limiting at the beginning of the growing season. At the end of the growing season, spore availability declined prior to, or simultaneous with, the decline in susceptibility. The combined effect of both factors drastically reduced the number of infections estimated to occur once shoots are more than 95% elongated. As shoots elongated, relatively more infections formed higher on the shoot, supporting the hypothesis that periderm is important in limiting infection.

Disease resistance may represent the best approach for controlling shoot blight, caused by Pollaccia americana Ondrej, in aspen (Populus tremuloides Michx.) plantations. Experiments were conducted to develop methods for screening for resistance under greenhouse conditions. Chickpea agar supported abundant inoculum production. An inoculum concentration of 5 × 104 spores/mL and a seedling age of 5-9 weeks were appropriate for evaluating infection. Infection severity was not correlated with tree height or leaf number. Differences in infection among clones varied with fungal isolate. The number of isolates and replicates needed to detect resistance differences among clones was calculated using estimated values of experimental error and clone × isolate interactions.

In northeastern Alberta, the current biomass and periodic annual biomass increment (PAI) was measured in 29 stands of maturing aspen (Populus tremuloides)-white spruce (Picea glauca), aged 48 to 105 years. Plots in pure aspen were paired with nearby plots of aspen growing on a similar landform but with a spruce understory. Biomass was estimated by diameter at breast height and allometric equations. Totalled over both species, there was 10.5 % greater PAI and 10.0 % greater biomass in the mixed plots than in the pure aspen plots. Pure aspen plots, however, had 12.9% greater aspen biomass and 25.2% greater aspen PAI than the aspen component of mixed plots. The apparent decline in productivity of aspen in the mixed stands, however, could not be related to the variation in spruce abundance in these mixed stands. Key words: mixed wood management, understory, spruce boreal mixed wood

To evaluate the threat of armillaria root disease in precommercially thinned lodgepole pine (Pinus contorta var. latifolia), a total of 66 15 × 15-m plots were established in dense lodgepole pine regeneration, 18 to 21 years after harvest, on three infested sites near Hinton, Alberta. Three treatments (2.5-m spacing, 1.5-m spacing and an unspaced control) were randomly applied to plots having similar densities and levels of mortality. After 11 years there was no significant difference among the treatments in cumulative percent mortality. Based on observed levels of mortality, it would appear that spacing need not be avoided in infested stands, although it likely would be prudent to space more closely than 2.5 m in younger stands and in parts of stands having more than 5–10% mortality. Key words: precommercial thinning, spacing, armillaria root disease, Armillaria ostoyae

Buried canola straw underwent 1.6 to 2 times as much decomposition as straw on the soil surface. Decomposition of Brassica napus L. was slightly less than that of B. rapa L. and cultivar effects were small in one year and insignificant in the other. Because treatment effects varied between stems and roots, plant portion likely should be considered in decomposition studies. Key words: canola, straw decomposition, burial, cultivars

First-summer establishment and overwinter survival of planted and seeded white spruce (Picea glauca (Moench) Voss) germinants were assessed in five microsites in the understory of trembling aspen (Populus tremuloidesMichx.) dominated boreal mixedwood stands. Mineral soil mounds, rotten logs, large exposed patches of mineral soil, normal LFH forest floor, and small screefed patches of mineral soil were examined. The mounds and rotten logs had the highest soil temperature, lowest soil strength, and accumulated the least amount of deciduous leaf litter whereas the small screefs were at the other extreme. First-summer establishment of planted seedlings was greatest on the rotten logs, mounds, and large exposed patches; the large exposed patches had the highest establishment of seeded trees. Over 85% of the planted seedlings that were in good condition in September survived the winter. Overwinter survival of seeded trees was least on small screefed patches, but survival of these trees was increased by covering them with small plastic cups. Low soil temperature, high seedbed strength, and high vegetation cover were associated with reduced seedling establishment whereas high litter accumulation was associated with reduced overwinter survival. Resume : L'etablissement au cours de la premiere saison estivale et la survie apres une saison hivernale de semis d'epinette blanche (Picea glauca (Moench) Voss), plantes ou ensemences, ont ete evalues dans cinq microsites en sous-etage de peuplements melanges domines par le peuplier faux-tremble (Populus tremuloidesMichx.) et situes en foret boreale. Des buttes de sol mineral, des billes en decomposition, de larges plaques de sol mineral expose, le parterre forestier normalement recouvert de litiere et de petites plaques de sol mineral denude ont ete examines. Les buttes et les billes en decomposition etaient les microsites ou la temperature du sol etait la plus elevee et la cohesion du sol la moins elevee. Ces microsites accumulaient la plus faible quantite de litiere de feuilles de feuillus tandis que les petites plaques denudees se situaient a l'autre extreme. L'etablissement des semis plantes au cours de la premiere saison estivale etait le plus eleve sur les billes en decomposition, sur les buttes et les grandes plaques de sol mineral expose. Dans le cas des semis ensemences, l'etablissement etait le plus eleve sur les grandes plaques de sol mineral expose. Plus de 85% des semis plantes qui etaient en bon etat en septembre ont survecu pendant l'hiver. La survie des semis ensemences apres une saison hivernale etait la plus faible sur les petites plaques denudees mais la survie de ces abres a ete amelioree en les recouvrant de petits verres en plastique. Une temperature du sol basse, la cohesion elevee du lit de germination et une couverture de vegetation haute etaient les facteurs associes a un plus faible etablissement des semis tandis qu'une forte accumulation de litiere etait associee a une survie hivernale reduite. (Traduit par la Redaction)

Vingt-quatre peuplements de pin de Murray (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.), âges de 26 a 32 ans et eclaircis entre l'âge de 15 et 23 ans, ont ete examines dans le centre-ouest de l'Alberta. L'âge du peuplement au moment de l'eclaircie etait le meilleur predicteur individuel de la formation de galles sur les arbres qui en etaient exempts lors de l'eclaircie (infection posterieure a l'eclaircie). La hauteur du peuplement etait aussi un bon predicteur de l'infection posterieure a l'eclaircie apres un ajustement pour les effets de la localisation du peuplement et les annees d'infection severe. Le nombre de galles par arbre au moment de l'eclaircie etait le meilleur predicteur de l'incidence des galles sur tous les arbres, incluant ceux qui avaient des galles au tronc au moment de l'eclaircie (infection totale). Les infections au tronc diminuaient avec l'âge et la hauteur des arbres. Pres de 60% des galles au tronc couvraient 40% ou moins de la circonference du tronc. Il n'y avait pas de relation entre le degre d'encerclement et la hauteur ou l'âge des galles. Dans les endroits ou la rouille-tumeur est commune, les amenagistes devraient considerer la possibilite de retarder l'eclaircie.

Endocronartiumharknessii (J.P. Moore) Hirat. populations never approach the level where all susceptible Pinuscontorta Dougl. ex Loud. var. latifolia Engelm. tissue is infected, even in years when environmental conditions are favourable for infection. A simple simulation model was developed to determine whether a hyperparasite could regulate the rust population and maintain it at an equilibrium level far below host saturation. The model assumed that galls begin sporulating and first become susceptible to parasitism 2 years after formation and requires specification of infection rates for the rust and the hyperparasite, mortality rates for normal and parasitized galls, and the degree to which aeciospore production is reduced following hyperparasite infection. Analysis of the model showed that the hyperparasite could regulate the rust population, producing a stable equilibrium, but only if the various rates were such that healthy galls, in their lifetime, produced enough aeciospores to give rise to more than one new gall, while galls that were parasitized during the first year of aeciospore production produced, in their lifetime, fewer than one new gall. The model of hyperparasite regulation provides one possible explanation of the dynamics of the gall rust pathosystem. It shows that control measures such as sanitation and breeding for resistance may reduce the effectiveness of the hyperparasite in regulating the system and, thus, may fail to achieve the anticipated goals.

Large black stem galls occur sporadically on trembling aspen (Populus tremuloides) in western Canada. Although little is known about their cause or structure, trees having these galls are less likely than surrounding aspen to have advanced decay caused by the fungus Phellinus tremulae. The anatomy and histochemistry of black galls and associated branch galls were studied and compared with normal wood and bark. Light microscopy showed that the cambium of black galls produces greater numbers of cells per growth ring and that growth rings are two to three times wider than normal. Vessel elements and fibers are unusually small and misshapen. Gall xylem has characteristics associated with wounding or infection: ray cells filled with phenolic deposits, and vessel elements occluded by tyloses and granular material. Frequent radial strands of undifferentiated callus tissue surrounded by necrophylactic periderms indicate sites of cambial damage of unknown cause. White areas within dark-colored gall xylem of some samples were free of most of these abnormalities, suggesting that a persistent agent is required for continuing tumor growth. Thickened outer bark harbored a variety of saprophytic fungi, especially hyphomycetes. Surface and internal morphology of black galls was also compared with similar stem galls caused by poplar budgall mites (Aceria parapopuli) and was found to be different. Bacteria, fungi, or mites were not obvious within living tissue, and further studies are necessary to determine the etiology of black galls. Key words: Populus tremuloides, poplar, black gall, wood anatomy.

Efficient use of trembling aspen (Populustremuloides Michx.) is often limited by the presence of extensive decay and stain. Aspen trees with black stem galls of unknown cause reportedly have less advanced decay caused by the fungus Phellinustremulae (Bond.) Bond. & Boriss. than do adjacent trees without galls. Nine field sites having large numbers of galled aspen were surveyed for the presence of P. tremulae conks. Logistic regression showed that the odds of a gall tree having at least one conk was 44% of that for trees without galls, and that the occurrence of conks varied among sites and increased with increasing tree diameter. Inclusion of black galls in models used to predict decay might result in greater accuracy on sites where these galls are prevalent. Black galls may also be potential sources of biological control agents against decay-causing organisms in aspen.

To determine whether spore dispersal gradients of Endocronartiumharknessii (J.P. Moore) Y. Hiratsuka were present adjacent to heavily infected pine stands, spore samplers were placed 0.5 m above ground, at five distances, 2–80 m from the edge of an 18-year-old stand and were operated for a total of 33 days over 2 years. Six weather parameters were recorded inside the stand, and multiple regression was used to determine the relationship between weather and parameters of spore dispersal. To determine whether gradients of lodgepole pine (Pinuscontorta Dougl. var. latifolia Engelm.) seedlings infected by gall rust were present adjacent to heavily infected pine stands, seedling infection was determined in 75-m2 plots centered 2.5–120 m from the stand edge, in five such plots in the center of that stand, and in transects of two-tree plots through a second stand. Spore concentration decreased with increasing distance from the stand edge in accordance with the power law model. Spore concentrations and the slopes of spore dispersal gradients were significantly affected by wind values, although there was considerable unexplained variation. There was little evidence for the existence of disease gradients.

Lodgepole pine (Pinuscontorta var. latifolia Engelm.) seedlings from 23 open-pollinated pine families from five stands in west-central Alberta were inoculated with western gall rust (Endocronartiumharknessii (J.P. Moore) Y. Hiratsuka) spores from four locations within 69 km of those stands. Six weeks after inoculation and at 3-week intervals for 21 weeks thereafter, seedlings were examined for symptoms of infection and galls. Eighteen months after inoculation, most trees in a sample of 1321 had either fully developed galls or no galls; partial gall formation was uncommon. Frequency of gall formation was highly correlated with the area under the disease progress curve (AUDPC) of symptom appearance and the AUDPC of gall appearance. It was also correlated, although less strongly, with the frequency of seedlings that had initially shown symptoms of infection but had no galls 21 weeks after inoculation. Regardless of whether AUDPC of gall appearance, frequency of gall formation, or failure to develop galls following infection was used as the criterion of resistance, the results were similar. Family effects were greater than stand effects, and rust-source effects were smaller than family effects and not always significant. There was no interaction between rust-source effects and either stand or family effects.

Two glasshouse experiments were conducted to determine the potential for Armillaria species to infect fireweed and subsequently use it as a food base for attacking lodgepole pine. Aspen segments colonized by A. mellea and A. ostoyae were used to inoculate fireweed roots. Both species caused infection, although the former was more pathogenic, attacking 28 of 42 inoculated fireweed roots as opposed to 8 of 60 in the case of the latter species. None of the nine pines inoculated with segments of fireweed roots colonized by A. ostoyae became infected, even though the isolates were pathogenic on pine when aspen segments were used as the food base. In contrast, 8 of 29 pine seedlings inoculated with fireweed colonized by A. mellea were killed, thus suggesting that fireweed could play some role in the epidemiology of this disease.

Small patches of dead trees were common among 7- to 15-year-old Pinns contorta var. latifolia in Alberta, Canada. The sizes of clones of Armillaria ostoyae, determined by pairing diploid isolates, was larger than these patches. Pairing diploid isolates on strips of Betula papyrifera provided a clear indication of clonal relationships.

Juvenile lodgepole pine (Pinuscontorta Dougl. var. latifolia Engelm.) were excavated at three sites near Hinton, Alberta. In all cases in which Armillariaostoyae (Romagn.) Herink had become established in the root collar or taproot, it was also able to colonize lateral roots. In cases in which only lateral roots were infected, subsequent colonization generally was primarily distal to the point of infection. Rhizomorphs were associated with 89% of 21 infected roots, whereas only 19% of 70 roots with no associated rhizomorphs were infected. Stumps, roots, and debris from the previous generation of trees were the inoculum sources for 78% of 36 infected juvenile trees, and infected regeneration served as the inoculum source for the remaining trees. Rhizomorphs occasionally were attached to the roots or rhizomes of plants other than pine, especially fireweed (Epilobiumangustifolium L.). There was no spatial relationship between stumps and symptomatic trees. Nearest neighbor analysis indicated that the likelihood of an individual tree developing symptoms was dependent on whether trees within 0.15 m were dead or dying but independent of the apparent health of trees at greater distances.

Resistance to the western gall rust fungus, Endocronartium harknessii, was observed in 3-, 10-, 20-, and 33-month-old greenhouse-grown seedlings of lodgepole pine (Pinus contorta var. latifolia). Three sites of resistance were identified: epidermal, cortical, and cambial. In cases of epidermal resistance, penetration of the epidermis occurred, but infection was prevented by an apparent hypersensitive response. Cortical resistance occurred where infected cells in the cortex were successfully isolated by necrophylactic periderm and the infected tissue was exfoliated with the rhytidome. In cambial resistance, infections progressed to the vascular cambium where infected cells and cambial initials were inactivated. This resulted in abnormal secondary xylem development, characterized by a zone of pathological tissue extending from the pith to the epidermis. In a number of infected seedlings, cambial function was restored and infected lesions were overgrown. Live mycelium was often maintained in cortical lesions and in some cases reinvaded healthy cortical cells. These latent-type infections resulted in the initiation of gall formation up to 1 year after initial resistance to infection occurred. Key words: tree improvement, western gall rust, pine stem rust.

Six-week-old Pinus contorta seedlings were inoculated with spores of the western gall rust fungus Endocronartium harknessii. Of 660 seedlings inoculated, 174 showed early symptoms and were sampled for histological observation in the 7 weeks following inoculation. Pigmentation of epidermal cells was the first externally visible response to infection, generally occurring 14–28 days after inoculation. Developing symptoms were extremely variable, ranging from little or no visible response to severe necrosis. The appearance of external symptoms was largely due to changes occurring in underlying infected cortical cells such as the production of phenolic compounds, necrophylactic periderm, or necrotic tissue. Intercellular lignin deposition was observed in infected tissue and was thought to be associated with necrophylactic periderm formation. Suppression of normal exophylactic periderm development was evident in virtually all infected tissue zones. Infection of the vascular cambium occurred as early as 21 days after inoculation and resulted in the subsequent formation of distorted xylem tracheids typical of gall tissue.

Hybrid genotypes that arise between plant species frequently have increased susceptibility to arthropod pests and fungal pathogens. This pattern has been attributed to the breakdown of plant defenses ('Hybrid susceptibility' hypothesis) and (or) to extended periods of susceptibility attributed to plant phenologies in zones of species overlap and (or) hybridization ('phenological sink' hypothesis). We examined these hypotheses by assessing the susceptibility of parental and hybrid Populus host genotypes to a leaf spot disease caused by the fungal pathogen Septoria musiva. For this purpose, 214 genotypes were obtained from morphologically pure zones of P. balsamifera and P. deltoides, and from an intervening zone of overlap and hybridization on the drainage of the Red Deer River, Alberta, Canada. Genotypes were identified as P. balsamifera, P. deltoides, or hybrid using a suite of 27 species-specific SNP markers. Initially the genetic structure of the hybrid zone was characterized with 27.7% of trees classified as admixed individuals. To test the hybrid susceptibility hypothesis, a subset of 52 genotypes was inoculated with four isolates of S. musiva. Levels of susceptibility were P. balsamifera > F1 hybrid > P. deltoides. A further 53 genotypes were grown in a common garden to assess the effect of genotype on variation in leaf phenology. Leaf phenology was more variable within the category of hybrid genotypes than within categories of either parental species. Leaf phenology was also more variable for the category of trees originating in the hybrid (P. balsamifera - P. deltoides [hybrid and parental genotypes combined]) zone than in adjacent pure zones of the parental species. The results from the inoculation experiment support the hybrid intermediacy hypothesis. The results from the common garden experiment support the 'phenological sink' hypothesis. These findings have greatly increased our understanding of the epidemiology and ecology of fungal pathogens in plant hybrid zones.

Two experiments were conducted to test the hypothesis that white spruce (Piceaglauca (Moench) Voss) is less liable than lodgepole pine (Pinuscontorta Dougl. var. latifolia Engelm.) to be attacked by Alberta isolates of Armillaria. In the first experiment, 27 two-year-old containerized pine and spruce were inoculated with each of 19 different isolates representing North American biological species (NABS) I and V, the Foothills variant of NABS I, and A. mellea s.str. In the second experiment, 10 containerized seedlings of both species were inoculated with eight different isolates of NABS I and transferred to 2-L pots 2 months later. Inoculum survived better in association with spruce seedlings than with pine. In both experiments, spruce seedlings were more frequently infected than pine seedlings, and more likely to die when infected, although this difference was significant only in the first experiment. Favoring or planting spruce on sites with Armillaria root rot, therefore, cannot be recommended in Alberta.

Hourly measurements of spore release by Endocronartium harknessii (J. P. Moore) Y. Hiratsuka on Pinus contorta Doug. var. latifolia Engelm. were obtained during 2 years. Two spore traps were placed beside both of two sporulating galls and electronic data loggers were used to record environmental data. On rainless days, most spores were trapped between 0900 and 2200, when vapor pressure deficit, temperature, light intensity, and wind velocity were high. A similar pattern of spore release occurred under simulated daytime and nighttime conditions in a growth chamber. On rainy days, most spores were released, on average, over a longer time interval than on dry days. Within 9 h of being placed in a dew chamber, the previously intact peridia on a single gall had ruptured, presumably from pressure caused by spore production. Further evidence that spore production is stimulated by low vapor pressure deficit was obtained by moving 11 galls alternatively between humid and dry conditions. Thus, it is proposed that the diurnal periodicity of spore release on dry days results from the production of spores during the night and the subsequent passive release of those spores during the next day.

Hypocotyls of Pinus densiflora, a species known to be resistant to western gall rust, were inoculated with Endocronartium harknessii and examined by light and electron microscopy. Host cells, when initially infected, were apparently unaffected, as were the haustoria within them. Seedlings were observed to respond to infection in two ways. In the first type of response, infected cells showed signs of necrosis by 9 days after inoculation, although infecting haustoria appeared normal. By 18 days, most cortical cells in the centre of the infected region were necrotic, as were the haustoria within them. Infected cells at the colony margin still appeared healthy, indicating that host cell necrosis lagged behind infection and only occurred after the haustorium was established. Four weeks after inoculation, a ring of suberized and lignified endodermal cells separated the infected cortex from the uninfected vascular tissue and appeared to prevent further inward growth of the fungus. The second response type involved production of encapsulations around haustoria. Encapsulations appeared to have formed after haustoria senescence and were eventually followed by host cell death.

Gremmeniella abietina infects shoots of red and Scots pines through stomata on bracts that subtend short shoots. The germ tube penetrates between guard cells and sparsely colonizes bract tissue by late summer or fall. Only after about late January or early February of the following year does the fungus extend from the bract and begin colonization of the short shoot and surrounding cortical tissue.

Vegetative incompatibility among diploid isolates of Armillaria root rot pathogens (Armillaria spp.) was studied using isolates of North American biological species I (Armillaria ostoyae (Romagn.) Herink) and V (Armillaria sinapina Bérubé & Dessureault). Interspecific, intraspecific, and self crosses were made on dialysis membrane over malt agar media and on wood strips and wood blocks. Hyphal interactions were studied using light microscopy and scanning and transmission electron microscopy. On dialysis membrane, hyphae in the contact zone between the two species, the so-called "black line," were melanized and failed to fluoresce with fluorescein diacetate but stained with 3,3′-diaminobenzidine and L-β-3,4-dihydroxy-phenylalanine, indicating peroxidase and polyphenoloxidase activity in the contact zone. Hyphae adjacent to the contact zone fluoresced and did not show any significant reaction to the other stains. The hyphae of the contact zone in intraspecific crosses and self crosses were not melanized, fluoresced, and did not react with the other stains. No black lines were formed in the interspecific crosses made on or in wood. In both interspecific and intraspecific crosses, pseudosclerotial plates formed between the opposing mycelia. No pseudosclerotial plates were formed in the wood between opposing mycelia of self crosses. Results indicated that the interspecific and intraspecific reactions differ significantly and should be considered as separate and distinct phenomena.

A total of 768 two-year-old lodgepole pine (Pinuscontorta var. latifolia Engelm.) seedlings were transplanted into four different soils, having different capabilities for supporting lodgepole pine growth. Thirty days later, they were inoculated with either of two isolates of North American Biological Species I (Armillariaostoyae (Romag.) Herink) of Armillaria. Log–linear analysis indicated that soil type had a significant effect on inoculum viability, rhizomorph production, frequency of seedling infection, and the likelihood of tree death following infection.

(1988). Axenic Culture of Endocronartium Harknessii. Mycologia: Vol. 80, No. 1, pp. 120-123.

Incidence of western gall rust infection in each of 10 replicated forest openings having diameter height ratios of 2:1, 4:1, and 6:1 was determined along two perpendicular 1-m wide transects. Infection frequencies were not significantly different among the different-sized openings. No pine regeneration was present in openings with diameter:height ratios of 0.5:1 or 1:1, thus precluding direct comparison of our results with those obtained from three other tree host–parasite studies in which disease incidence was greatest in small openings.

The zone of antagonism, known as the "black line," that occurred between the confronting margins of diploid isolates of different Armillaria mellea complex species was enhanced by incubation in L-β-3,4-dihydroxyphenylalanine (L-DOPA). Intraspecific crosses and crosses of genetically identical isolates did not produce a black line after similar treatment with L-DOPA.

Conidial production by Gremmeniella abietina was enhanced by growing the fungus in 8-oz. jars containing V-8 agar and a red pine twig. Survival of G. abietina at temperatures of 12 to 34C was closely related to average temperature and duration of exposure. The fungus survived 27 months in vivo without causing extensive necrosis of the host. Symptom development was more frequent among trees placed outdoors than among trees placed in a coldroom or greenhouse.

Uptake and translocation of maltol into 6-week-old Pinusconforta (Engelm.) var. latifolia seedlings was followed by means of gas chromatography. Maltol concentrations of 6.0–7.3 mg/g seedling dry weight (46–55 μg/seedling) were observed over the first 3 days following a single application of 50 mg maltol/seedling. A split-plot design was used to determine if maltol could reduce seedling infection by Endocronartiumharknessii. Whole plots consisted of two inoculum levels (7 or 30 mg of spores per tray of seedlings) and subplots consisted of four levels of maltol (0, 2, 10, or 40 mg/mL) applied 2 days before inoculation to one-half tray of seedlings at the rate of 5 mL/cavity. The highest concentration consistently and significantly reduced seedling infection relative to the untreated control, although it also caused some phytotoxicity.