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Climate change is expected to increase winter temperatures in boreal climates. White spruce ( Picea glauca (Moench) Voss) is vulnerable to spring frost damage due to its habit of early budbreak, which may be exacerbated or lessened with increasingly warm winters at its southern range edge. We tested the effects of episodic warming during the quiescent stage on budbreak time and growth of seven seed sources grown in a common garden setting in Minnesota, USA. Treatment plots were warmed with infrared lamps for 4 days each in February, March, or February and March to simulate a midwinter thaw. Control plots for each treatment and an overall control were included for comparison. Trees warmed in February experienced a slight delay in spring budbreak, but differences in budbreak time were generally not significant. Terminal growth was significantly and negatively correlated with time of budbreak but not with time to growth cessation. Our results suggest that white spruce is relatively resilient to the effects of intermittent warming but that warming early in the season may delay budbreak time, which is expected to reduce terminal growth. [ABSTRACT FROM AUTHOR]

Mixed-species stands present a number of opportunities for and challenges to forest managers. Boreal mixedwood stands in eastern Canada are often characterized by a dominant canopy of shade-intolerant aspen ( Populus tremuloides Michx.) with more shade-tolerant conifers in the mid- to sub-canopy layers. Because the aspen and conifer components often attain optimal merchantable sizes at different moments in stand development, there is an interest in developing silvicultural practices that allow partial or total removal of aspen and favour accelerated growth of residual conifers. We tested four partial harvesting treatments in mixed aspen - white spruce ( Picea glauca (Moench.) Voss) stands in which different proportions of aspen (0%, 50%, 65%, and 100% basal area) were removed. Ten years after treatments, 72 spruce stems representing dominant, co-dominant, and suppressed social classes were destructively sampled for stem analysis. Using linear mixed effect models, we analyzed growth as a function of treatment intensity, time since treatment, social status, pretreatment growth rate, and neighbourhood competition. Relative to control stands, radial and volume growth responses were detected only in the extreme treatment of 100% aspen removal. In relative terms, suppressed trees showed the greatest magnitude of cumulative growth increase. Compared with control trees, average annual radial and volume increments were, respectively, 23.5% and 7.1% higher for dominant trees, 67.7% and 24.1% higher for co-dominant trees, and 115.8% and 65.6% higher for suppressed trees over the 10 years after treatment. Growth response was proportional to pretreatment growth rate, and among neighbouring trees, only coniferous neighbours had a negative effect on white spruce growth. Our results suggest that in similar mixed-stand conditions, relatively heavy removal of overstory aspen accompanied by thinning of crowded conifers would result in greatest growth response of residual spruce stems. [ABSTRACT FROM AUTHOR]

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Exponential fertilization has been shown to be a useful technique for improving seedling quality during nursery production. In this study, we evaluated ( i) the impact of exponential vs. conventional fertilization on trembling aspen ( Populus tremuloides Michx.) and white spruce ( Picea glauca (Moench) Voss) seedlings during nursery production and ( ii) the growth performance and nitrogen (N) utilization of those seedlings in response to foxtail barley ( Hordeum jubatum L.) competition after the transplantation of seedlings in a greenhouse experiment. Exponential fertilization with an application rate higher than the conventional fertilization increased the internal N reserve in trembling aspen and white spruce seedlings during nursery production and also increased new leaf, new stem, and old stem biomass and N retranslocation rates in trembling aspen seedlings but not in white spruce seedlings after transplantation. Foxtail barley competition decreased N concentrations in seedlings and soil N uptake by the seedlings; however, increased N retranslocation rates with foxtail barley competition were observed in white spruce seedlings but not in trembling aspen seedlings. Our results suggest that the growth performance of seedlings was improved by N loading, whereas the impact of vegetation management was species specific. [ABSTRACT FROM AUTHOR]

Commercial thinning represents one of the treatments used in intensive management to increase the growth of the residual stems. Therefore, commercial thinning would decrease the wood mechanical properties, but the negative effects are temporary according to some authors. To our knowledge, no studies have focused on the effects of commercial thinning on wood mechanical properties according to tree social classes. The objective of this study is to verify, at the stem level, ( i) the effect of different commercial thinning intensities on the stem volume increment according to social classes (dominant, codominant, intermediate, and oppressed) and ( ii) the effect of commercial thinning on wood mechanical properties of white spruce ( Picea glauca (Moench) Voss), and ( iii) to determine if these effects on wood mechanical properties varied between social classes. The measurements were made from samples collected in a 32-year-old white spruce plantation that was thinned in 1989. We used stem analysis to measure volume increments, while the mechanical properties were measured on small pieces of wood (10 mm × 10 mm × 150 mm) without defects at dbh. Thinning has a significant positive effect on the stem volume increment for the dominant and codominant trees and no negative effect on the wood density, the modulus of elasticity and modulus of rupture for all thinning intensities and all social classes combined. After thinning (1989-2000), the modulus of elasticity increased by 50% in the dominant and by 70% in the codominant trees. This study allows us to consider the commercial thinning as a silvicultural tool to increase the productivity of white spruce plantations without affecting negatively the wood mechanical properties. Considering our results, we recommend that the intensity of the first commercial thinning should remove 35% of the basal area. [ABSTRACT FROM AUTHOR]

Vertical and horizontal patterns of light within gaps and expansion of trees into gaps were examined in young stands dominated by trembling aspen (Populus tremuloides Michx.) in northeastern British Columbia and northwestern Alberta. Lateral growth of branches of aspen edge trees averaged 15.2 cm/year and was similar to crown expansion rates reported for edge trees in eastern North America. Branches growing into gaps were significantly longer than those growing away from gaps and are likely to lead to gap shrinkage and reductions in light within gaps. However, height growth of edge trees was not significantly different from that of trees within the surrounding stands. Models describing relationships between diffuse transmittance and locations within gaps and surrounding stand height were developed in this paper. Sky view angle (SVA) was found to be effective for predicting transmittance to different locations within gaps. When SVA values exceed 1.2 (at the B.C. sites), white spruce (Picea glauca (Moench) Voss) will receive <40% of full sunlight, which is less than optimal for spruce height growth. [ABSTRACT FROM AUTHOR]

CO2–light interactions can influence the competition among boreal plants, but are poorly understood. We investigated the effect of such interactions on the growth and biomass of 1-year-old black spruce (Sb) (Picea mariana (Mill.) BSP) and white spruce (Sw) (Picea glauca (Moench) Voss) grown with CO2 concentrations ([CO2]) of 360 and 720 µmol·mol–1 under 30%, 50%, and 100% light, in greenhouses. There were significant two-way and three-way interactions. Root collar diameter (RCD) of Sw decreased with decreasing light, while in Sb, there was no significant difference in RCD for plants grown under 50% or 30% light. Height was greater for plants grown under 100% light than if the plants were shaded. Elevated [CO2] increased RCD by 33% and enhanced stem volume by 67%, 98%, and 84% under 100%, 50%, and 30% light, respectively. The CO2 enhancement of total biomass was relatively higher under lower light, and greater for Sb than Sw. Elevated [CO2] decreased specific leaf area under 50% light only. Root mass was generally higher under 100% light than when shaded. Elevated [CO2] increased the root mass of Sb under 100% light, but decreased it under 30% light. Elevated [CO2] decreased the shoot/root ratio under 100% light, but increased it under 30% light. Our data suggest that raising [CO2] will likely increase species competitiveness under low light conditions, and that the increase will be greater in species that are relatively shade tolerant. [ABSTRACT FROM AUTHOR]

Early height growth of eastern white spruce (Picea glauca (Moench) Voss) rooted cuttings was compared with that of seedlings using annual measurements collected over 5 years in a farm field test replicated on three sites. The experiment included 148 full-sib families obtained from controlled crossings of superior trees selected for a white spruce breeding population in Quebec. Fifteen additional seedlots were used as controls. The average growth rate of seedlings (37.3 cm·year–1) was slightly larger than that of rooted cuttings (36.2 cm·year–1). The yearly growth rate increased over the test period, and it did so at a somewhat higher rate for the seedlings. The relative size of the estimated variance components and the moderate rank correlations of full-sib family height growth features between the two propagule types suggest that tree breeders should favour seedlings over rooted cuttings to rank families for selection purposes, but vegetative propagation would prove useful for bulking up scarce valuable genotypes. [ABSTRACT FROM AUTHOR]

Formation of the shoot apical meristem (SAM) has been extensively investigated in zygotic embryos of flowering plants, where it follows a prolonged and dynamic developmental pattern underlined by precise temporal and spatial changes in gene expression. Studies conducted on the plant model system Arabidopsis have revealed that SAM formation is controlled by a genetic network and involves the participation of several regulatory genes expressed at different stages of development. As a general rule apical meristem development in vivo occurs very early; at the globular stage of development in flowering plants and in club-stage embryos of conifers. Once formed, meristems of zygotic embryos are stable structures that become reactivated at the onset of germination. Shoot apical meristem formation during in vitro embryogenesis is demarked by structural events similar to those described for zygotic embryos, although differences can be observed during the late phases of development, where cellular differentiation and formation of intercellular spaces disrupt the architecture of SAMs produced in culture. These events, which denote the “unstable” nature of SAMs of somatic embryos, often result in poor conversion frequency and reduced plant regeneration. By using Picea glauca (Moench) Voss (white spruce) somatic embryos and microspore-derived embryos of Brassica napus L. (canola) as model systems, this review provides methods for improving SAM formation through manipulations of the culture medium which alter the cellular redox status. Meristem marker genes from Arabidopsis, such as WUSCHEL (which is required for the acquisition of stem fate identity), represent a valuable tool for estimating the quality of SAM produced by microspore-derived embryos of canola. In spruce, the identification of two novel meristem marker genes, HBK1 and PgAGO, will allow similar studies in conifers. [ABSTRACT FROM AUTHOR]

The effects of six mechanical site preparation treatments, two stock-type treatments, and early chemical release on survival and growth of planted white spruce (Picea glauca (Moench) Voss) were studied in the BWBSmw1 biogeoclimatic zone of northeastern British Columbia. After 20 years, spruce height and diameter were larger in all mounding treatments than in the control. Early results suggested better spruce performance on large than small mounds, but after 20 years, growth was equally good on small mounds as on mounds with 20 cm mineral capping. Spruce planted on hinge positions in the Bräcke patch and blade scarification treatments did not survive or grow well. Early chemical release improved spruce growth equally as well as the mounding treatments. Twenty year spruce survival averaged 71% in the 14 and 20 cm mound treatments, 60% in the early chemical release treatment, and ≤35% in the Bräcke patch and blade scarification treatments. A large stock type was also planted in untreated ground and, after 20 years, had similar survival and growth as the standard stock type. Differences in survival had a large effect on basal area at age 20 years. Trend analysis showed that treatments diverged into two distinct groups with regard to spruce size during the 20 year span of the study. [ABSTRACT FROM AUTHOR]

To investigate the feasibility of a spatially explicit, radiation-based regeneration model for the boreal forest, we tested the predictions of a three-dimensional simulator of photosynthetically active radiation transmission (%PAR), MIXLIGHT, and the growth response of understory Abies balsamea (L.) Mill. (balsam fir) and Picea glauca (Moench) Voss (white spruce) to %PAR in two large (>1 ha) mixed-species forest sites, one in eastern Canada at Lac Duparquet, Quebec, and one in western Canada at Calling Lake, Alberta. Overstory tree locations and dimensions were obtained from aerial photographs or ground measurements and allometric relationships. Seasonal %PAR calculated by MIXLIGHT for the Calling Lake site was very similar to seasonal %PAR measured by quantum sensors (n = 5, %PAR range = 15%–33%, r = 0.93). Daily measurements of %PAR were also predicted well by simulations at both sites (n = 34–36, %PAR range = 1%–45%, r ≥ 0.76). Functional relationships, designed to saturate at the maximum height growth potential of these sites, were developed to predict sapling height growth from simulated seasonal %PAR and initial height (R2 ≥ 0.74). These results demonstrate the potential of the MIXLIGHT simulator for estimating PAR at microsites within heterogeneous forests and for modeling understory tree growth. [ABSTRACT FROM AUTHOR]

We examined the growth of white spruce planted underneath a 33-year-old stand of trembling aspen following thinning and fertilization. Thinning the stand to 2000 stems·ha–1 resulted in increased light reaching spruce seedlings and significant increases in height and diameter growth of seedlings over that observed in either the unspaced or 3000 stems·ha–1 treatments. Fertilization (applied 3 years prior to planting) stimulated development of understory vegetation and did not benefit the planted spruce. While growth was improved by thinning, the benefits of the thinning treatment to establishment of white spruce appeared to be small, and amounted to increasing seedling height from 62 cm (unthinned) to 73 cm (thinned to 1000 or 2000 stems·ha–1) at the end of 5 years. Results indicated that when stands are thinned for the purpose of accelerating growth rates of underplanted spruce, residual basal areas above 25 m2·ha–1 should be retained to suppress growth of understory vegetation. Comparison of height at age 5 for seedlings planted under untended stands at Fort Nelson with three sites near Dawson Creek indicated no differences between locations, when height at the time of planting was included as a covariate. [ABSTRACT FROM AUTHOR]

This study investigated the genetic variation in veneer quality of white spruce (Picea glauca (Moench) Voss) and its correlation with tree growth and wood density. A total of 270 sample trees from 35 families were harvested from 36-year-old provenance-progeny trials at two sites through a thinning operation. A 36-cm long bolt was collected from each sample tree at an 8-foot (or 2.45 m) height for this veneer quality study. The results indicate that conversion of fast-grown white spruce into veneer and plywood may present some problems. Low wood density, numerous knots, and possibly a high proportion of juvenile wood appear to be major factors contributing to low veneer stress grading, resulting in a production of low-quality veneer. This study also showed that the environmental factors at the two sites played an important role in determining veneer quality and tree radial growth. The narrow-sense heritability for veneer density, veneer modulus of elasticity, and veneer roughness were 0.62, 0.13, and 0.14, respectively. The results revealed considerable phenotypic variation and relatively high additive genetic variation in the veneer modulus of elasticity. The phenotypic and genetic correlations between ring width and veneer density or veneer modulus of elasticity were negative. A positive phenotypic and genetic correlation was found between veneer density and veneer modulus of elasticity. This suggests that selection for tree volume growth in white spruce would lead to a decrease in wood density and veneer stiffness. [ABSTRACT FROM AUTHOR]

Multifactor experiments were used to study the effects of (1) shade,moisture, and nutrients on above- and below-ground biomass production of red raspberry (Rubus idaeus L.) and (2) intra- versus inter-specific competition for light, nitrogen, and space in interplantings of raspberry and white spruce (Picea glauca (Moench) Voss) seedlings. Interactive effects among the manipulated resources on seedling growth were common. Raspberry biomass increased with increasing moisture andnutrients or with added nitrogen when nitrogen was the only nutrientmanipulated. Seventy-three percent shade reduced raspberry biomass production, while production under full sun and 30% shade was similar.Raspberry shoot/root ratio increased with increasing nutrients and shade but decreased with age. In mixed plantings with spruce, when nitrogen was added, raspberry biomass and shoot/root ratio increased at the expense of spruce, while the shoot/root ratio decreased with shade in low-nitrogen plots. Spruce height growth was not affected by light level, nitrogen addition, or competition type; however, spruce diameter and biomass production decreased with competition from both raspberry and spruce and increased with increasing growing space and in low-nitrogen shaded plots where raspberry was less common. [ABSTRACT FROM AUTHOR]

Overstory manipulation and vegetation control treatments were applied at three experimental locations in northern Ontario, Canada, to examine shelter and competition effects on planted white spruce (Picea glauca (Moench) Voss). Overstories were nearly pure trembling aspen (Populus tremuloides Michx.) or aspen-conifer mixedwoods. Overstory treatments included clear-cutting, uniform shelterwood (40% canopy removal), strip shelterwood (widths from 0.5 to 1.0H, where H is the height of dominants), patch shelterwood (diameter about 1.0H), narrow strips (width 0.25H), and intact overstory. Vegetation-control treatmentsincluded herbicide and no-herbicide treatments. Second-year seedlinggrowth was poorest under intact overstories and in 0.25H strips, andvegetation control had little effect on growth in this situation. Vegetation control in clearcuts increased seedling diameter but not height growth. In shelterwood treatments, however, vegetation control often increased both diameter and height growth. Greatest diameter tended to occur in clearcuts with vegetation control, whereas greatest height growth tended to occur in shelterwoods with vegetation control. These differing responses likely occur because diameter growth is influenced primarily by light availability, but height growth is additionally affected by other environmental factors. Combining early vegetation control along with shelterwood treatments appears to provide theoptimum environment for establishing white spruce. [ABSTRACT FROM AUTHOR]

Fall-lifted white spruce (Picea glauca (Moench) Voss) bareroot seedlings were winter stored at -2, -4, and -6 deg. C. The electrolyte leakage and carbohydrate content were periodically measured in roots andshoots during storage. Water relations, gas exchange, bud flushing, and root growth potentials were measured after 4 and (or) 7 months offrozen storage. Shoots and roots of seedlings stored at -6 deg. C had higher electrolyte leakage compared with those stored at -2 and -4 deg. C. Sugar levels increased as a result of frozen storage and werehigher in seedlings stored at -4 and -6 deg. C compared with those at -2 deg. C. Root total nonstructural carbohydrate (TNC) contents declined with storage duration in all storage temperatures. However, seedlings stored at -4 and -6 deg. C maintained slightly higher root TNCthan those stored at -2 deg. C. Needle TNC in seedlings stored at -4and -6 deg. C did not change; however, it declined in seedlings stored at -2 deg. C. Storage temperatures of -4 and -6 deg. C also altered seedling water relations with seedlings stored at these temperatures having lower osmotic potentials at turgor loss point and at full hydration and less elastic cell walls compared with seedlings stored at-2 deg. C. Lower storage temperatures decreased root growth potentials and delayed bud flushing following planting. [ABSTRACT FROM AUTHOR]

Shoot water relations, gas exchange, and carbohydrate content and composition were studied from March 30 to May 11, 1995, in white spruce(Picea glauca (Moench) Voss) seedlings growing in nursery beds. The seedlings exhibited reduced shoot osmotic potentials at turgor loss point and at full hydration from March 30 to April 27 followed by an increase until May 11. Shoot relative water contents also showed a marked increase after April 27. Bulk modulus of elasticity of shoots gradually increased from early to late April indicating a decrease in cell wall elasticity. Net photosynthesis of seedlings recovered rapidlyin mid-April. Both net photosynthesis and stomatal conductance showed a significant linear relationship with minimum air and soil temperatures, and there was a significant linear relationship between net photosynthesis and stomatal conductance. Needle starch content increased, but total sugar content was relatively constant. The composition of soluble carbohydrates changed in early spring with an increase in sucrose accompanied by a decrease in raffinose and other soluble carbohydrates. The results suggest that white spruce seedlings develop characteristics associated with the optimum drought stress resistance inearly spring. [ABSTRACT FROM AUTHOR]