White Spruce Research Articles

A comprehensive framework to evaluate the financial impacts of genetic improvement on wood products from planted forests

Increasing the productivity of planted forests may efficiently provide an important part of the world’s growing demand for wood while protecting natural forests. In this study, we developed an integrated modelling framework to evaluate the financial impacts of improving productivity of planted forests by tree breeding. Using this framework, we compared three genetic improvement scenarios of white spruce plantations, a key reforestation species in North America, and evaluated the differences in the derived wood product assortments in terms of quantity, quality, and revenues. Favouring the production of wood volume appears as the best way to enhance financial gains from white spruce plantations in the current market. The scenario that focused on increasing tree height produced a greater volume of wood products and larger lumber pieces, which resulted in the greatest revenues. In comparison, favouring wood stiffness over volume led to poorer results, as the increased product quality was not sufficient to surpass the financial gain associated with greater wood volumes. While we successfully provided an evaluation of the product assortments derived from genetically improved plantations, the proposed framework would benefit from more data input to help maximize financial gains from a range of tree breeding strategies.

Biennial aerial application of Bacillus thuringiensis Berliner var. kurstaki is the most cost-effective approach of protection against spruce budworm (Choristoneura fumiferana [Clemens])

Key messageAerial application of Bacillus thuringiensis Berliner var. kurstaki (Btk) every second year to stands of white spruce (Picea glauca (Moench)Voss.), black spruce (Picea mariana Mill.) and balsam fir (Abies balsamea (L.) Mill.) is the most cost-effective spraying scenario for reducing the impact of spruce budworm (Choristoneura fumiferana Clemens) on wood production, providing a similar level of forest protection, but at lower cost, to the standard scenario currently used in which 50% of current year’s foliage is protected every year.ContextInsect outbreaks can have significant effects on forest productivity and various formulations of Bacillus thuringiensis Berliner var. kurstaki (Btk) are used to reduce their damage. In the Province of Québec, Canada, control programs aim to protect at least 50% of current-year foliage to limit tree mortality, but little information exists on the long-term cost-effectiveness of such programs.AimsOur goal was to evaluate the benefit/cost ratio and the efficacy of different Btk protection scenarios in reducing coniferous tree mortality and growth losses over a 11-year period. We hypothesized that less-intensive protection approaches (Btk applications every 2 or 3 years) may provide similar levels of protection but with higher cost-effectiveness ratios than the standard program currently used in Quebec.MethodsIn 2007, we established nineteen 100-ha experimental units in Quebec’s Côte-Nord region to determine the efficacy and cost-effectiveness of different Btk spraying scenarios for reducing tree mortality and volume losses in coniferous stands dominated by mature balsam fir trees (Abies balsamea (L.) Mill., with white spruce (Picea glauca (Moench) Voss.) and black spruce (P. mariana Mill.) as companion species. Tree mortality was monitored annually in three circular plots of 400 m2 within each experimental unit. Growth losses were evaluated using stem analyses.ResultsMortality was much higher in balsam fir than in black spruce and white spruce (respectively 74.4%, 13.8% and 5.9% in untreated stands) in all protection scenarios. The application of Btk every 2 years reduced balsam fir mortality to a level similar to the standard scenario (10.3% vs 7.15%, respectively) at a much lower cost. Growth losses have also been reduced but not to the same extent as in the standard scenario.ConclusionSpraying Btk every 2 years provides effective protection to balsam fir and is the most cost-effective scenario. A less intensive use of Btk would mitigate impact on non-target lepidoptera and allow protecting other areas, such as habitat of the woodland caribou, a threatened species which avoids disturbed areas.

Development of a qPCR Assay for the Detection and Quantification of the Fungal Pathogen Calonectria canadiana on Conifers

ABSTRACTA real‐time PCR TaqMan assay was developed for the detection of Calonectria canadiana, a fungal pathogen responsible for damping off, root rot and seedling blight in conifer forest nurseries in central and eastern North America. While highly significant in Quebec Forest nurseries, coniferous seedling mortality decreased significantly when nurseries transitioned from bare root to container seedling production. However, over the past few years, this pathogen has re‐emerged as a threat and millions of container white spruce seedlings were culled in two nurseries in eastern Quebec. A sensitive detection and quantification assay for C. canadiana was essential to investigate the biological and environmental factors driving this new epidemic. We designed primers and a TaqMan probe targeting the internal transcribed spacer (ITS) of C. canadiana. The resulting Ccan TaqMan assay successfully differentiated C. canadiana from other soil‐borne pathogens of the Nectriaceae encountered in Quebec Forest nurseries. The limit of detection of the assay was established at eight copies of C. canadiana ITS. The Ccan TaqMan assay quickly identified the presence of the pathogen in both symptomatic and asymptomatic white spruce (Picea glauca) seedlings. Furthermore, we demonstrated that the pathogen was more easily detected when DNA was extracted from necrotic needles at the base of the stem rather than from necrotic roots. This molecular tool will greatly aid in understanding the biology and epidemiology of C. canadiana.

Differential response by seedlings of three sub-boreal conifer species to high- and low-carbon wood ash amendment

In Canada, there is a need to implement value-added uses for wood ash (hereafter ash) generated from bioenergy facilities as most ash is landfilled. Ash application to forests can provide benefit via nutrient supply, amelioration of soil acidity and, sometimes, increased tree growth. However, information is limited on the response of conifer species to different wood ash types applied to fine-textured soil typical of north-central B.C. We conducted a 16-month seedling pot trial that examined the response of Douglas-fir ( Pseudotsuga menziesii), lodgepole pine ( Pinus contorta var. latifolia), and hybrid white spruce ( Picea glauca × engelmannii) to high- (HCA) and low-carbon ashes (LCA) applied (up to 10 Mg mineral matter ha−1 equiv.), with and without fertilizer N (200 kg N ha−1 equiv.), to fine-textured forest soil. Pine and spruce exhibited a 1.6- and 1.4-fold increase in shoot biomass at the high rate of HCA with fertilizer N. At study end, the high rate of LCA had the greatest soil pH, EC and total K in the upper forest floor, but the HCA had greater total B, P and Zn. LCA elicited increased foliar B in pine, but HCA increased foliar Ca in spruce when co-applied with fertilizer N. In general, Douglas-fir growth did not respond to ash treatments, and seedling mortality was observed in some LCA treatments. Ash treatments helped offset some nutrient deficiencies induced by N fertilization. Ash type influenced soil chemical as well as seedling growth and nutrition responses.

White spruce presence increases leaf miner effects on aspen growth in interior Alaska

Alaska’s boreal forests are experiencing rapid changes in climate that may favor deciduous-dominated systems, with important implications for global biogeochemical and energy cycles. However, aspen (Populus tremuloides Michx.) has experienced substantial defoliation from the aspen leaf miner (Phyllocnistis populiella Cham., hereafter ALM) in Alaska, resulting in significant growth reductions. We conducted a tree-ring and Δ13C study to test the hypothesis that moisture limitation may have predisposed aspen to leaf miner damage. Contrary to our hypothesis, differences in climate-growth correlations between relatively severely and lightly affected trees were negligible during the pre-outbreak decades. Stands with greater summer precipitation had more limited ALM impact, however differences among models were small and multiple climate variables were suitable predictors of ALM impact. The strong negative relationship we detected between tree-ring Δ13C and basal area increment (BAI) suggested that interannual variation in Δ13C was driven primarily by variation in photosynthesis, limiting the utility of Δ13C as a tool to detect stomatal responses to moisture-limitation. Instead, we found that larger, faster-growing individuals on gentler slopes showed a stronger absolute reduction in BAI (pre-ALM BAI−post-ALM BAI), but were similar in relative BAI reduction (pre-ALM BAI/post-ALM BAI), with smaller, slower growing trees. Older trees and stands with greater relative abundance of white spruce [Picea glauca (Moench) Voss] had greater relative ALM impact whereas slower growing trees on steeper slopes were less affected. The significant effect of white spruce abundance on ALM impact was likely due to favorable leaf miner overwintering habitat provided beneath white spruce trees, which can lead to increased leaf miner survival and thus greater reductions in aspen growth. Our results illustrate the subtle but complex biotic interaction between microclimate and pest physiology in determining ALM-induced aspen growth reductions, adding important nuance to a hypothesized increase in deciduous tree cover in Alaska’s boreal forest.

Comparison of Deep and Machine Learning Approaches for Quebec Tree Species Classification Using a Combination of Multispectral and LiDAR Data

Accessing tree species information is required for making appropriate decisions in forest management. 3D photo-interpretation using high spatial resolution aerial imagery is used to provide information on tree species in the province of Quebec. However, the shortage of qualified interpreters and the increasing costs of 3D photo-interpretation have affected the production of the forest inventory. In this study, we employed deep and machine learning models to classify nine tree species (i.e., paper birch, yellow birch, red maple, poplar, black spruce, white spruce, tamarack, jack pine, and balsam fir). We used a combination of spectral and vertical structural information extracted from 30-cm aerial imagery and airborne light detection and ranging (LiDAR) data in a 9 , 100 km 2 forested area in Quebec, Canada. The results indicated that Dense Convolution Network (DenseNet) achieved the best overall accuracy of 78%, outperforming machine learning methods by 5%. In addition, the models’ performance was independently assessed using permanent and temporary ground sample plots, acknowledging the superiority of DenseNet in terms of overall accuracy (73%) in predicting the dominant species. Our results suggest that the combination of aerial imagery and airborne LiDAR data, using deep learning approaches, can be applied to accurately map tree species.

Modelling Diameter at Breast Height Distribution for Eight Commercial Species in Natural-Origin Mixed Forests of Ontario, Canada

Diameter at breast height (DBH) is a unique attribute used to characterize forest growth and development for forest management planning and to understand forest ecology. Forest managers require an array of DBHs of forest stands, which can be reconstructed using selected probability distribution functions (PDFs). However, there is a lack of practices that fit PDFs of sub-dominating species grown in natural mixed forests. This study aimed to fit PDFs and develop predictive models for PDF parameters, so that the predicted distribution would represent dynamic forest structures and compositions in mixed forest stands. We fitted three of the simplest forms of PDFs, log-normal, gamma, and Weibull, for the DBH of eight tree species, namely balsam fir (Abies balsamea [L.] Mill.), eastern white pine (Pinus strobus L.), paper birch (Betula papyrifera Marshall), red maple (Acer rubrum L.), red pine (Pinus resinosa Aiton), trembling aspen (Populus tremuloides Michx), and white spruce (Picea glauca [Moench] Voss), all grown in natural-origin mixed forests in Ontario province, Canada. We estimated the parameters of the PDFs as a function of DBH mean and standard deviation for these species. Our results showed that log-normal fit the best among the three PDFs. We demonstrated that the predictive model could estimate the recovered parameters unbiasedly for all species, which can be used to reconstruct the DBH distributions of these tree species. In addition to prediction, the cross-validated R2 for the DBH mean ranged between 0.76 for red maple and 0.92 for red pine. However, the R2 for the regression of the standard deviation ranged between 0.00 for red pine and 0.69 for sugar maple, although it produced unbiased predictions and a small mean absolute bias. As these mean and standard deviations are regressed with dynamic covariates (such as stem density and stand basal area), in addition to climate and static geographic variables, the predicted DBH distribution can reflect change over time in response to management or any type of disturbance in the regime of the given geography. The predictive model-based DBH distributions can be applied to the design of appropriate silviculture systems for forest management planning.

Population-specific climate sensitive top height curves and their applications to assisted migration

Growth and yield (G&Y) of forest plantations can be significantly impacted by maladaptation resulting from climate change, and assisted migration has been proposed to mitigate these impacts by restoring populations to their historic climates. However, genecology models currently used for guiding assisted migration do not account for impacts of climate change on cumulative growth and assume that responses of forest population to climate do not change with age. Using provenance trial data for interior lodgepole pine (Pinus contorta subsp. latifolia Douglas) and white spruce (Picea glauca (Moench) Voss) in western Canada, we integrated Universal Response Functions, representing the relationship of population performance with their provenance and site climates, into top height curves in a G&Y model (Growth and Yield Projection System, GYPSY) to develop population-specific climate sensitive top height curves for both species. These new models can estimate the impact of climate change on top height of local populations and populations from a range of provenances to help guide assisted migration. Our findings reveal that climate change is expected to have varying effects on forest productivity across the landscape, with some areas projected to experience a slight increase in productivity by the 2050s, while the remainder are projected to face a significant decline in productivity for both species. Adoption of assisted migration, however, with the optimal populations selected was projected to maintain and even improve productivity at the provincial scale. The findings of this study provide a novel approach to incorporating assisted migration approaches into forest management to mitigate the negative impacts of climate change.

Mixing trembling aspen and white spruce increases the understory vegetation cover and improves soil properties but effects vary with broadleaf density

Despite the importance of species mixtures to ecosystem-based forest management, density effect of broadleaf trees in the mixture on understory vegetation and soil properties are poorly understood. In this study, we examine the effects of trembling aspen [aspen] (Populus tremuloides Michx.) -white spruce [ spruce] (Picea glauca (Moench) Vos) mixtures that vary in the proportion of aspen on understory vegetation cover, soil nutrient supply rates, and soil properties. Data were collected from an established study located in Alberta, Canada at age 20 and included the following treatments: 1. Natural regeneration of pure aspen; 2. Retaining only 1600 planted spruce ha−1 by controlling aspen and understory vegetation; 3. Retaining only 1600 planted spruce ha−1 by controlling understory vegetation; 4–7. Retaining only 400 planted spruce ha−1 along with unthinned aspen, 2000, 1200, and 800 aspen ha−1. In mixed stands, competition control around the spruce was done for its establishment, and subsequent thinning was done to control the density of aspen. The findings of our analysis showed that mixed stands had higher total vascular plant cover, potential soil N supply rates, soil pH, and lowered C: N ratio compared to monocultures of spruce or aspen. The treatment (mixed stands) with unthinned aspen along with spruce increased the above-mentioned variables most compared to other mixtures. Moreover, total forb cover was higher in the mixture with the highest density of aspen, but grass cover was higher in the lowest density of aspen. Our findings hint that the effect of mixing tree species on understory vegetation cover may be influenced by the density of broadleaf tree in the mixture. Further studies need to be conducted to reach a concrete conclusion. Regardless, this result might be useful for forest managers to take a decision for ecosystem-based forest management.

Tree improvement increases the growth of white spruce (Picea glauca): Evidence from 15-year-old operational plantations in Alberta

The timber producing forest land-base in Alberta, Canada, is decreasing due to the increase in allocation of land to other uses such as agriculture, infrastructure, energy development and conservation areas, while the demand for forest products continues to increase. Tree improvement, first implemented in Alberta in 1975, is one strategy used for increasing forest productivity to meet an increasing demand for fibre and forest products. To quantify the operational impact of tree improvement on white spruce productivity, we collected data from 15-year-old white spruce stands in Alberta: 11 stands planted with seedlings from improved (seed orchard) seedlots and seven stands planted with seedlings from wild (unimproved) seedlots. Eight plots (100 m2 circular plots) within each stand were randomly established for measurement (18 × 8 = 144 plots). Diameter at breast height (DBH), tree height, crown width, and branch diameter for each tree inside the plots were measured. Mixed effects models, with site and plot considered random, were used to evaluate the effect of tree improvement on the growth of white spruce. Basal area per ha of competitor species was used to develop a non-spatial competition index, and to compare the growth of improved and unimproved white spruce response to competition. Individual trees from improved stands showed 17% greater DBH and height compared to individual trees from unimproved stands. Individual trees of improved stands also had a greater height and smaller branch diameter for a given DBH than the trees grown in unimproved stands. Overall, tree improvement increased the site index of white spruce by 2 m while both improved and unimproved stands were similarly, and negatively, affected by competition. The application of tree improvement in white spruce resulted in an increase in growth rate, site index, and quality of timber, which will help offset the increasing demand for forest products.

Limited Differences in Insect Herbivory on Young White Spruce Growing in Small Open Plantations and under Natural Canopies in Boreal Mixed Forests.

In managed boreal forests, both plantations and natural regeneration are used to re-establish a cohort of conifer trees following harvest or disturbance. Young trees in open plantations generally grow more rapidly than under forest canopies, but more rapid growth could be compromised by greater insect damage. We compared insect damage on white spruce (Picea glauca (Moench) Voss, Pinaceae) growing in plantations with naturally regenerated trees under mature forest canopies in boreal forests (Québec, Canada). We selected ten sites in the naturally regenerated forest and in small, multispecies plantations and sampled ten young trees of 2.5-3 m (per site) in late summer 2020 and again in early and late summer 2021. We compared overall rates of herbivory, galls (adelgids), damage by the spruce budworm (Choristoneura fumiferana, Clemens), and defoliation from sawflies. Overall, insect herbivory damage remained at similarly low levels in both habitats; an average of 9.3% of expanding shoots were damaged on forest trees and 7.7% in plantation trees. Spruce budworm damage increased from 2020 to 2021 and remained higher in under-canopy trees, but damage rates were negligible at this early stage of the outbreak (1.5% in forest vs. 0.78% of buds damaged on plantation trees). While damage due to galls was higher in plantations, the overall low level of damage likely does not pose a significant impact on the growth or mortality of young trees.

Seedling recruitment in response to stand composition, interannual climate variability, and soil disturbance in the boreal mixed woods of Canada

AbstractAimSeedling recruitment is a vital process for forest regeneration and is influenced by various factors such as stand composition, climate, and soil disturbance. We conducted a long‐term field experiment (18 years) to study the effects of these factors and their interactions on seedling recruitment.LocationOur study focused on five main species in boreal mixed woods of eastern Canada: trembling aspen (Populus tremuloides), paper birch (Betula papyrifera), white spruce (Picea glauca), balsam fir (Abies balsamea), and white cedar (Thuja occidentalis).MethodsSixteen 1‐m2 seedling monitoring subplots were set up in each of seven stands originating from different wildfires (fire years ranging from 1760 to 1944), with a soil scarification treatment applied to every other subplot. Annual new seedling counts were related to growing‐season climate (mean temperature, growing degree days and drought code), scarification, and stand effects via a Bayesian generalized linear mixed model.ResultsSoil scarification had a large positive effect on seedling recruitment for three species (aspen, birch and spruce). As expected, high mean temperatures during the seed production period (two years prior to seedling emergence) increased seedling recruitment for all species but aspen. Contrary to other studies, we did not find a positive effect of dry conditions during the seed production period. Furthermore, high values of growing degree days suppressed conifer seedling recruitment. Except for white cedar, basal area was weakly correlated with seedling abundance, suggesting a small number of reproductive individuals is sufficient to saturate seedling recruitment.ConclusionOur findings underscore the importance of considering multiple factors, such as soil disturbance, climate, and stand composition, as well as their effects on different life stages when developing effective forest management strategies to promote regeneration in boreal mixed‐wood ecosystems.

Contrasting physiological strategies explain heterogeneous responses to severe drought conditions within local populations of a widespread conifer

Understanding how trees prioritize carbon gain at the cost of drought vulnerability under severe drought conditions is crucial for predicting which genetic groups and individuals will be resilient to future climate conditions. In this study, we investigated variations in growth, tree-ring anatomy as well as carbon and oxygen isotope ratios to assess the sensitivity and the xylem formation process in response to an episode of severe drought in 29 mature white spruce (Picea glauca [Moench] Voss) families grown in a common garden trial. During the drought episode, the majority of families displayed decreased growth and exhibited either sustained or increased intrinsic water-use efficiency (iWUE), which was largely influenced by reduced stomatal conductance as revealed by the dual carbon‑oxygen isotope approach. Different water-use strategies were detected within white spruce populations in response to drought conditions. Our results revealed intraspecific variation in the prevailing physiological mechanisms underlying drought response within and among populations of Picea glauca. The presence of different genetic groups reflecting diverse water-use strategies within this largely-distributed conifer is likely to lessen the negative effects of drought and decrease the overall forest ecosystems' sensitivity to it.

Are operational plantations meeting expectations? A large-scale assessment of realized versus anticipated yield in eastern Canada

Forest plantations play an increasingly important role in meeting global demand for wood. They usually have higher yield than naturally regenerated forests. Thus, plantations can support economically viable wood production, enable forest conservation elsewere, help mitigate climate change by contributing to carbon sequestration and increase forest resilience and resistance to biotic and abiotic stressors. If yield of plantations is not as high as anticipated, then their use could generate important sustainability issues. There are still major gaps in our understanding of the factors that influence yield, even with respect to black spruce, white spruce, and jack pine, three of the most commonly planted tree species in northeastern North America. Our objective was to evaluate the yield of forest plantations of these species over a 416 000 km2 region that was representative of northeastern North American forests. Contrary to our prediction, realized yield of operational plantations was consistently lower than anticipated. Site index and competition both played a significant role in determining the yield of plantations. In the context of uncertain realized yield of operational plantations, we emphasize the necessity of relying on adaptive management to determine harvest levels that are compatible with sustainable management objectives.

Evaluation of branch sampling, ocular assessments, and aerial surveys for estimating spruce budworm defoliation

We compared three methods for estimating current-year spruce budworm ( Choristoneura fumiferana (Clem.)) defoliation from 2014 to 2021 using a network of 99 permanent sample plots in central Gaspé Peninsula, Québec. Percent current-year defoliation was measured by assessing shoots from mid-crown branches, ocular ratings of all individual trees using binoculars, and provincial government aerial surveys. Ocular survey defoliation differed from branch sample defoliation in 5–6 out of 7 years, consistently underestimating defoliation, across the full range of defoliation severity observed. Nested mixed-effect models for fir–spruce combined, balsam fir, white spruce, and black spruce ocular survey defoliation bias resulted in marginal R2 of 0.40, 0.47, 0.82, and 0.86, respectively. Current defoliation severity and its interaction with previous year defoliation and weather conditions significantly affected ocular survey bias. Correspondence of aerial survey estimates and mean plot defoliation occurred in only 43% of all plot-years and ranged from 14%–58% in individual years. Differences between aerial survey defoliation and plot values mainly resulted from assigning an adjacent class (e.g., light <30% assigned as moderate 31%–70% defoliation) or misplaced defoliation polygon boundaries, suggesting that assignment of aerial survey defoliation to plots or specific ground areas needs ground truth sampling.

Long-insert sequence capture detects high copy numbers in a defence-related beta-glucosidase gene βglu-1 with large variations in white spruce but not Norway spruce

Conifers are long-lived and slow-evolving, thus requiring effective defences against their fast-evolving insect natural enemies. The copy number variation (CNV) of two key acetophenone biosynthesis genes Ugt5/Ugt5b and βglu-1 may provide a plausible mechanism underlying the constitutively variable defence in white spruce (Picea glauca) against its primary defoliator, spruce budworm. This study develops a long-insert sequence capture probe set (Picea_hung_p1.0) for quantifying copy number of βglu-1-like, Ugt5-like genes and single-copy genes on 38 Norway spruce (Picea abies) and 40 P. glauca individuals from eight and nine provenances across Europe and North America respectively. We developed local assemblies (Piabi_c1.0 and Pigla_c.1.0), full-length transcriptomes (PIAB_v1 and PIGL_v1), and gene models to characterise the diversity of βglu-1 and Ugt5 genes. We observed very large copy numbers of βglu-1, with up to 381 copies in a single P. glauca individual. We observed among-provenance CNV of βglu-1 in P. glauca but not P. abies. Ugt5b was predominantly single-copy in both species. This study generates critical hypotheses for testing the emergence and mechanism of extreme CNV, the dosage effect on phenotype, and the varying copy number of genes with the same pathway. We demonstrate new approaches to overcome experimental challenges in genomic research in conifer defences.

Aspen and Spruce Densities Affect Tree Size, Future Stand Volume, and Aboveground Carbon Following Precommercial Thinning

Data collected over a 30-year period from an experiment replicated across 21 locations in western Canada are used to explore the effects of precommercial thinning of trembling aspen to a range of densities in combination with three initial white spruce densities on tree growth and stand dynamics. Increasing differentiation amongst the 15 treatments was observed with age after thinning for both spruce and aspen responses. Spruce height and diameter declined with increasing aspen density. At age 10 spruce diameter with no aspen was 1.5× that of spruce in unthinned while it was 2.6× that of spruce in unthinned at age 28. Following thinning aspen DBH and crown width declined with increasing density of retained aspen while slenderness and height to crown base of aspen increased. Thinning to 1500 aspen·ha−1 resulted in aspen DBH that was 22% larger relative to the unthinned at age 28. Spruce volume and stemwood biomass at age 90, estimated using the Mixedwood Growth Model (MGM21), declined with increasing initial aspen density, with the complete removal of aspen resulting in nearly double the spruce volume of unthinned plots. However, total stand volume, total stand biomass, and stemwood carbon at age 90 are predicted to be largest in mixed stands with aspen densities of 1500 stems·ha−1 or higher.

The phenotypic and genetic effects of drought-induced stress on wood specific conductivity and anatomical properties in white spruce seedlings, and relationships with growth and wood density.

Drought frequency and intensity are projected to increase with climate change, thus amplifying stress on forest trees. Resilience to drought implicates physiological traits such as xylem conductivity and wood anatomical traits, which are related to growth and wood density. Integrating drought-stress response traits at the juvenile stage into breeding criteria could help promote the survival of planted seedlings under current and future climate and thus, improve plantation success. We assessed in greenhouse the influence of drought-induced stress on 600 two-year-old white spruce (Picea glauca) seedlings from 25 clonal lines after two consecutive growing seasons. Three levels of drought-induced stress were applied: control, moderate and severe. Seedlings were also planted at a 45° angle to clearly separate compression from normal wood. We looked at the phenotypic and genetic effects of drought stress on xylem specific hydraulic conductivity, lumen diameter, tracheid diameter and length, and the number of pits per tracheid in the normal wood. We detected no significant effects of drought stress except for tracheid length, which decreased with increasing drought stress. We found low to high estimates of trait heritability, which generally decreased with increasing drought stress. Genetic correlations were higher than phenotypic correlations for all treatments. Specific conductivity was genetically highly correlated positively with lumen diameter and tracheid length under all treatments. Tracheid length and diameter were always negatively correlated genetically, indicating a trade-off in resource allocation. Moderate to high genetic correlations sometimes in opposite direction were observed between physico-anatomical and productivity traits, also indicating trade-offs. A large variation was observed among clones for all physico-anatomical traits, but clonal ranks were generally stable between control and drought-induced treatments. Our results indicate the possibility of early screening of genetic material for desirable wood anatomical attributes under normal growing conditions, thus allowing to improve the drought resilience of young trees.

Climate-Sensitive Diameter Growth Models for White Spruce and White Pine Plantations

Global change in the climate is affecting tree/forest growth. There have been many studies that analyzed climate effects on tree growth. Results presented in these studies showed that the climate had both positive and negative effects on tree growth. The nature (positive/negative) and magnitude of the effects and the climate variables affecting growth depended on tree species. Climate-sensitive diameter growth models are not available for white pine (Pinus strobus L.) and white spruce (Picea glauca (Moench) Voss) plantations. These models are needed to project forest growth and yield and develop forest management plans. Therefore, diameter growth models were developed for white pine and white spruce plantations by incorporating climate variables. Four hundred white pine and white spruce trees (200 per species) were sampled from 80 (40 per species) even-aged monospecific plantations (five trees per plantation) across Ontario, Canada. Diameter–age pairs were obtained from these trees using stem analysis. A nonlinear mixed-effects modeling approach was used to develop diameter growth models. To make the models climate sensitive, model parameters were expressed in term of climate variables. Inclusion of climate variables significantly improved model fit statistics and predictive accuracy. For evaluation, diameters (inside bark) at breast height were estimated for three geographic locations (east, west, and south) across Ontario for an 80-year growth period (2021–2100) under three climate change (emissions) scenarios (representative concentration pathway or RCP 2.6, 4.5, and 8.5 watts m−2). For both species, the overall climate effects were negative. For white spruce, the maximum pronounced difference in projected diameters after the 80-year growth period was in the west. At this location, compared to the no climate change scenario, projected spruce diameters under RCPs 2.6 and 8.5 were thinner by 4.64 (15.99%) and 3.72 (12.80%) cm, respectively. For white pine, the maximum difference was in the south. Compared to the no climate change scenario, projected pine diameters at age 80 under RCPs 2.6 and 8.5 at this location were narrower by 4.54 (13.99%) and 7.60 (23.43%) cm, respectively. For both species, climate effects on diameter growth were less evident at other locations. If the values of climate variables are unavailable, models fitted without climate variables can be used to estimate these diameters for both species.

Using Ground Penetrating Radar (GPR) to Predict Log Moisture Content of Commercially Important Canadian Softwoods

The non-destructive testing of wood fibre properties is crucial for informing forest management decisions and achieving optimal resource utilization. Moisture content (MC) is an important indicator of wood freshness and may reveal the presence of wood degradation. However, efficient methods are still needed to better monitor this property along the forest–wood value chain. The objective of the study was to develop prediction models to evaluate log MC based on the propagation of ground penetrating radar (GPR) signals. A total of 165 trees representing four species (black spruce (Picea mariana (Mill.) B.S.P.), white spruce (Picea glauca (Moench) Voss), red spruce (Picea rubens Sarg.), and balsam fir (Abies balsamea (L.) Mill.)) were harvested in two regions of the province of Quebec. GPR signals were acquired in the green (fresh) state and at three subsequent drying stages. Partial least squares regression (PLSR) and locally weighted PLSR (LWPLSR) were employed to establish relationships between GPR signals (antenna frequency: 1.6 GHz) and log properties. The models were fitted on three calibration sets containing four drying stages and different species mixes. The LWPLSR models performed better than the PLSR models for predicting log MC, with a lower root mean square error (RMSEp range: 10.8%–20.2% vs. 13.0%–20.5%) and a higher R2p (0.63–0.87 vs. 0.62–0.82). Spruce-only models performed considerably better than fir-only models while multi-species models were in-between. Despite the complex anisotropy of wood and the physics of wave propagation, the GPR technology can be successfully used to estimate log moisture content, but the GPR-based MC models should be calibrated for each specific type of wood material.