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Territories are typically defined as spatially exclusive areas that are defended against conspecifics. Given the spatial nature of territoriality, it is inherently density dependent, but the economics of territoriality also depend on the distribution and abundance of defended resources. Our objectives were to assess the effects of changing population density and food availability on individually based territorial phenotypes.We developed a novel analytical framework that bridges spatially explicit territories with social network analysis to model density‐dependent territorial phenotypes. Using the outputs from our data pipeline, we modelled plasticity in territory size and territory intrusion rates in a long‐term study population of North American red squirrels Tamiasciurus hudsonicus. Red squirrels defend year‐round territories around a central hoard (midden) of white spruce Picea glauca cones. Importantly, white spruce is a masting species that produces large cone crops every 4–7 years (i.e. mast years) in our study area interspersed with non‐mast years when few cones are produced. In the spring following mast years, populations are approximately double in size, but are lower in the spring of non‐mast years.We predicted that territory size and intrusion rates would decrease as resource abundance, and consequently population density, increased. By contrast, as resource abundance decreased via depletion, and therefore density decreased, territories should increase in size and intrusions should also increase.As we expected, individual territory size and territorial intrusions were negatively density dependent, such that increased density after mast years resulted in smaller territories and fewer intrusions. When considering between‐individual variation in plasticity across a density gradient, individuals responded differently to changes in population density within their lifetime.Our results show that territory size and intrusion rates display negative density dependence. When food becomes available in the autumn of a mast year and density in spring of the following year increases, territories shrink in size to effectively a small area around the midden. While our findings for red squirrels are unique compared to other systems, they serve as a reminder that the direction and strength of fundamental ecological relationships can depend on the nature of the system. [ABSTRACT FROM AUTHOR]

Climate change is predicted to increase forest fires in boreal forests, which can threaten the sustainability of forest genetic resources. Wildfires can potentially impact genetic diversity and population structure in forest trees by creating population bottlenecks, and influencing demography, effective population size (Ne) and various evolutionary processes. We have investigated this critical issue in a widely-distributed, transcontinental, ecologically and economically important and fire-intolerant boreal conifer, white spruce (Picea glauca (Moench) Voss). We tested the hypothesis that in a predominantly outcrossing species with long distance gene flow, such as white spruce, located in primary undisturbed forests, normal forest fires do not adversely affect genetic diversity and population structure. We used 10 nuclear genic and genomic microsatellite loci to examine genetic diversity and population structure of post-fire pristine old-growth (PF-OG) and adjacent post-fire naturally regenerated young (PF-YR) stands. The genetic diversity, inbreeding and genetic differentiation levels, Bayesian population structure, Ne and latent genetic potential were statistically similar between the PF-OG and PF-YR populations. None of the microsatellites showed any signature of selection. Our study demonstrates that normal wild forest fires do not adversely affect genetic diversity, differentiation, and population genetic structure in white spruce. The results should have wide significance for sustainable forest management. [ABSTRACT FROM AUTHOR]

Assisted gene flow according to expected climate gradients is considered as a forest management strategy to mitigate impacts of environmental change on forest growth. However, the effects of seed translocation on wood properties and lumber quality remain unknown. This study evaluated the effect of provenance origin on lumber production and quality at rotation age in two white spruce provenance trials established in contrasting environments in eastern Canada. Based on 108 sample trees, which resulted in 943 pieces of lumber, average volume production per tree at the southernmost site was twice that of the production at the northern site. Provenance had a significant influence on growth and lumber strength in the first sawlog but had no effect on lumber stiffness and wood density. Although visual grade yields of No. 2 and better were high in both trials (over 86%), the machine stress rated (MSR) grade potential and percentage of lumber that met the bending stiffness design values of the visual grades were generally low (12%–26%). Hence, plantation-grown lumber should preferably be machine stress rated to ensure its fitness for structural applications in buildings. Management strategies aiming to efficiently sequester carbon should primarily maximize volume productivity in northern sites, as moving seed sources north still reduces provenance productivity, while breeding programs should aim to prevent decrease in lumber stiffness due to augmented productivity and shortened rotation cycles. [ABSTRACT FROM AUTHOR]

An increase in the frequency and magnitude of drought events threatens the health of forests and the economic, ecological, and societal services they provide. It has been widely demonstrated that trees undergoing a succession of stresses may accumulate lesions that in turn lead to a decrease in their vigor and eventually to death. However, recent studies have shown that a nonlethal stress should also initiate a stress memory, which triggers a faster and stronger plant defensive response when a new stress occurs. Although this mechanism is well understood in many herbaceous plants, a better understanding in trees is needed. The aim of our study was to explore the capacity of two forest tree species to develop a stress memory. A greenhouse experiment was conducted to evaluate the tree seedlings' vigor after one or two consecutive droughts separate from a rehydration period during the same growing season. No stress memory pattern was observed for the two tree species as, on the contrary, we even observed a stress accumulation pattern in sugar maple. It remains possible that some individuals in our study developed stress memory, but that we were not able to detect it. The fine‐tuning of experimental parameters and the conducting of longitudinal studies would be helpful to detect individual capacity in stress memory activation. [ABSTRACT FROM AUTHOR]

In recent decades, forest nurseries in eastern Canada have been faced with periods of mild winter weather, delayed snowfall, and low seedling protective snow cover combined with winter rains instead of snowfall. These extreme conditions have resulted in the loss of millions of seedlings, in particular those that overwinter outdoors, probably due to their winter dehardening. The main objective of this study is to simulate different periods of warm weather at the beginning and end of winter and evaluate their effects on the dehardening and growth of Picea mariana and Picea glauca seedlings in response to different freezing temperatures. Three warming treatments were simulated (control, 1 day, and 3 days of warming at 10 °C) followed by three freezing temperatures (−4, −12, and −20 °C). In winter, regardless of the warming treatment, the seedlings of the two species tolerated the different freezing temperatures without any apparent damage. However, at the end of winter and in the absence of snow cover, the seedlings did not show frost tolerance at −20 °C. On the other hand, the seedlings showed normal growth after undergoing frosts at −4 °C and −12 °C, similar to that observed for control seedlings. Different cultural practices and protection strategies are proposed to improve frost tolerance and reduce the winter loss of seedlings. [ABSTRACT FROM AUTHOR]

The demand for exterior wood siding is stagnating in North America due in part to perceptions of low durability and the need for frequent maintenance. One way to address these concerns is to modify the wood to improve its physical properties, while maintaining its appearance. In this study, white spruce was treated with organosilanes and a combination of aluminum treatments followed by a thermal treatment to improve the dimensional stability and the wood durability. Anti-swelling efficiency (ASE), leaching and decay tests were performed on the treated Canadian wood species. The quantity of hydroxyls available after treatment was evaluated by water vapor sorption. The results showed that the treatment improved the dimensional stability up to 50%. Available hydroxyls decreased by as much as 37%. The organosilanes treatment was resistant to leaching, while the aluminum was observed to leach. Organosilanes in combination with aluminum showed brown rot resistance. The addition of aluminum to the organosilanes treatment did not have effect on dimensional stability but it had a great impact on the brown rot resistance. [ABSTRACT FROM AUTHOR]

Phosphogypsum (PG) is a by-product of phosphorus fertilizer production that is stored in large piles (stacks). Typically, PG stack reclamation focuses on topsoil caps vegetated with grass which has limited economic return. Therefore, a study was conducted using the short-rotational tree species (Picea glauca, Populus balsamifera) to determine their potential in PG stack reclamation. Five soil amendments (compost, compost with mycorrhizal fungi, manure pellets, black earth, mycorrhizal fungi) with a control (no amendment on PG) were used in a field experiment to determine whether they would enhance the growth of the planted species. After two years, amendments had little effect on the height, diameter or biomass of either species. P. balsamifera on PG (control) was significantly healthier than in amended soils. The healthiest and most successful trees for both species were found in the control treatment. Organic amendments (compost, manure) had significantly higher nitrate and phosphorus than most of the other treatments. Black earth and mycorrhizal fungi did not affect any soil properties relative to the control. This study suggests short-rotational forestry plantations of Populus balsamifera appear to be meeting reclamation objectives for PG stacks, similar to traditional grass covers; however, the built soil profile could limit tree success in future. [ABSTRACT FROM AUTHOR]

Four Picea glauca (Moench) Voss trees grown at each of four square spacing intensities between trees: 1.2 m, 1.8 m, 4.3 m, and 6.1 m in a plantation established in 1967 in the Petawawa Research Forest, Ontario, Canada (lat. 45.59° N, long. 77.25° W, elev. 168 m) and sampled at four different heights (1.3 m, 4.3 m, 7.3 m, 10.3 m) were used to study the impact of spacing between trees and sampling height on nine wood quality attributes (ring width, ring density, tracheid length, tracheid diameter, latewood proportion, intra-ring density variation, ring area, earlywood width, and latewood width). In the juvenile wood, ring width was wider and ring density higher than in the mature wood. Tracheid length was longer and tracheid diameter wider in the mature wood compared to the juvenile wood. The variation of ring density between the two wood zones was limited, and latewood proportion did not show any difference with wood zone. Sampling height induced variation in more wood quality attributes than did spacing. Except for growth rate, spacing between trees did not significantly impact wood quality attributes. Most of these variations were registered between widely different spacings. [ABSTRACT FROM AUTHOR]

Broadcast motor-manual or manual brushing treatments applied to control aspen (Populus tremuloides Michx.) in young spruce (Picea glauca (Moench) Voss) plantations often result in increases in the number of aspen stems and the amount of aspen competition. In this study data collected at three locations is used to examine the potential effectiveness of spot brushing treatments, applied over radii ranging between 1.0 and 2.5 m around individual spruce, to aspen that are two, four or six years old. Results indicate that spot manual or motor-manual treatments result in reductions in the number and size of aspen stump sprouts compared to the untreated control. However, when aspen size and vigour are reduced due to site or other factors, as observed for blocks at one location, post-treatment aspen densities may still be high (e.g., above 5000 stems ha−1). Spot treatments applied when aspen regeneration was two years old were observed to be less effective than treatments applied at ages 4 or 6. At two study locations where control was effective, spot brushing treatments significantly increased spruce diameters after treatment compared to untreated. Broadcast or spot treatment using basal bark application of triclopyr ester (Release®) herbicide at one of the study sites resulted in similar increases in spruce diameter to those observed for motor-manual treatment. [ABSTRACT FROM AUTHOR]

Climate change is increasing the frequency and intensity of drought events in many boreal forests. Trees are sessile organisms with a long generation time, which makes them vulnerable to fast climate change and hinders fast adaptations. Therefore, it is important to know how forests cope with drought stress and to explore the genetic basis of these reactions. We investigated three natural populations of white spruce (Picea glauca) in Alaska, located at one drought-limited and two cold-limited treelines with a paired plot design of one forest and one treeline plot. We obtained individual increment cores from 458 trees and climate data to assess dendrophenotypes, in particular the growth reaction to drought stress. To explore the genetic basis of these dendrophenotypes, we genotyped the individual trees at 3000 single nucleotide polymorphisms in candidate genes and performed genotype-phenotype association analysis using linear mixed models and Bayesian sparse linear mixed models. Growth reaction to drought stress differed in contrasting treeline populations. Therefore, the populations are likely to be unevenly affected by climate change. We identified 40 genes associated with dendrophenotypic traits that differed among the treeline populations. Most genes were identified in the drought-limited site, indicating comparatively strong selection pressure of drought-tolerant phenotypes. Contrasting patterns of drought-associated genes among sampled sites and in comparison to Canadian populations in a previous study suggest that drought adaptation acts on a local scale. Our results highlight genes that are associated with wood traits which in turn are critical for the establishment and persistence of future forests under climate change. [ABSTRACT FROM AUTHOR]

1. Boreal forest soils contain large stocks of soil carbon (C) that may be sensitive to changes in climate and disturbance. Destablization of boreal forest soil C through changes in C inputs, belowground C pools and/or wildfire could feedback to accelerate rising atmospheric CO2 concentration. Additionally, increasing frequency of severe fires may be changing the dominant forest types and reshaping aboveground C stocks. 2. Although controls on ecosystem C pools have received considerable attention, many studies have been limited to locations near the road system, leading to uncertainty in current and future C stocks across boreal Alaska. Here, we leveraged 545 randomly selected and spatially balanced Forest Inventory and Analysis (FIA) plots across ~13.5 million hectares in interior Alaska to examine the factors governing soil and live tree C pools. 3. Forest type mediated the effects of mean summer air temperature and the probability of near-surface permafrost on soil C. Meanwhile, forest type, stand age and aspect were the primary drivers of live tree C. Overall, plots with a known history of wildfire during the past 70 years did not have significantly different soil C stocks than plots without a known history of fire, likely due to the historical predominance of low severity fires. 4. Where wildfire likely initiated a transition to deciduous trees (19% of plots), live tree and soil C pools were reduced by 16% and 20%, respectively. Ecosystem C likely recovered over time, as maturing deciduous stands rapidly gained C in live trees. Deciduous stands without a known fire had comparatively very large live tree C stocks, suggesting a significant change in the distribution of ecosystem C following severe fire. 5. Synthesis. Our results highlight the nuanced interactions among wildfire, landscape position and forest type that will play important roles in shaping future boreal ecosystem C stocks. [ABSTRACT FROM AUTHOR]

Static bending tests to measure modulus of elasticity (MOEST) or wood stiffness provide an indicator of the structural performance of a finished product. These tests are however, slow and expensive. Tests to measure MOE using non-destructive testing (NDT) provide alternatives to MOEST tests; however, relationships between the different modes of measurement need to be established. Non-destructive testing MOE measured by two methods (SilviScan [MOESS] and time of flight [MOETOF]) have been compared with MOEST for lodgepole pine and white spruce. The relationships between stress wave speed (SWS) and MOEST have also been evaluated. Simple linear regressions of MOESS, MOETOF, and SWS had greater explanatory power (higher coefficients of determination (R2)) than did multiple linear regressions including growth rate or other wood fibre attributes. Simple linear regression from MOETOF and MOESS on MOEST had lower R2 for lodgepole pine than for white spruce; however, the converse was true for SWS. SWS had the highest R2 (89%) and MOESS the lowest R2 (47%) when regressed on MOEST in lodgepole pine. The results were tool and species specific, suggesting that R2 between MOEST and non-destructive testing MOE values must be validated separately for each commercial tree species and for each measurement technique. [ABSTRACT FROM AUTHOR]

Commercial production of high-quality lumber for Nordic conifers is negatively impacted by long rotation age and adverse negative correlations between growth and wood quality traits. A prospective solution to ensure sufficient fibre quality from future plantations is to identify key wood traits for desired applications and to consider them in tree breeding programs. In this study, we used the widespread and largely reforested white spruce (Picea glauca [Moench] Voss) in Canada to investigate the genetic control of wood flexural properties such as stiffness, i.e. modulus of elasticity (MOE), and strength, i.e. modulus of rupture (MOR). We also looked at their phenotypic and genetic correlations with other wood quality and growth traits to assess the efficiency of indirect methods of selection to improve wood flexural properties in the context of multi-trait selection in tree breeding programs. To achieve this, standardized solid wood samples, growth records and standing tree wood quality traits were collected from 289 trees belonging to 38 white spruce families from a polycross genetic trial established on two different sites in the province of Quebec, Canada. Flexural stiffness and strength, height, diameter at breast height (DBH) and wood density showed moderate to high heritability. Flexural stiffness was also positively correlated at the genetic level with flexural strength, average wood density and acoustic velocity as an indirect measure of dynamic MOE (⁠|${r}_{\mathrm{G}}$|  = 0.99, |${r}_{\mathrm{G}}$|  = 0.78 and |${r}_{\mathrm{G}}$| = 0.78, respectively). When selecting the top 5 per cent of the trees, the expected genetic gains varied from 3.6 per cent for acoustic velocity to 16.5 per cent for MOE. Selection based on wood density and acoustic velocity would result in considerable genetic gains in flexural stiffness. Several multi-trait selection scenarios were tested to investigate the genetic gains obtained from selecting with different combinations of growth and wood quality traits. The results showed that indirect selection for wood flexural properties by means of acoustic velocity and wood density are efficient methods that can be combined in operational white spruce breeding programs to increase simultaneously genetic gains for growth and wood flexural properties. [ABSTRACT FROM AUTHOR]

The forest industry typically uses visual appearance to evaluate the wood quality when salvaging dead standing trees. We investigated whether the visual appearance of white spruce (Picea glauca (Moench) Voss) defoliated by the spruce budworm (Choristoneura fumiferana (Clem.)) accurately reflects wood quality measured using nondestructive techniques. Longitudinal and transverse acoustic velocities were measured on white spruce, representing three condition categories assessed visually, ranging from live trees to dead standing trees with signs of decay. Generalized linear models were used to determine whether there were significant differences in longitudinal and transverse acoustic velocities among the visual categories. Longitudinal velocities significantly differed between the live and poorest visual categories. Transverse velocities did not differ by visual category. We found that tree appearance provides coarse but useful insight into intrinsic wood quality. We recommend that forest managers use acoustic, non-destructive technologies on marginal trees to measure the wood quality of salvaged trees to ensure the wood is utilized for the highest and best use thereby optimizing possible values. [ABSTRACT FROM AUTHOR]

Stand tending using glyphosate to promote coniferous overstory trees has been a common practice in the boreal forests of Alberta. However, there are concerns about the impact of this practice on biodiversity of understory species. This study examined the impact of broadcast glyphosate application during the active reforestation phase, two to several years post-harvest, on forest plant diversity 25 to 40 years post-harvest. Herbicide treatments had the desired effect of shifting tree layer dominance from deciduous to coniferous species, driven by a 25-fold reduction in the density of trembling aspen (3927 vs. 154 stems·ha−1, untreated and treated, respectively). However, understory plant diversity was not significantly different between treated and untreated sites as examined by the Shannon–Wiener (H) and evenness (E) indices. Shared plant species (beta) across sites was high. Of the seven site-indicator species examined, three had significantly lower cover on treated sites: Wild sarsaparilla, low bush-cranberry and oak fern. Total understory plant cover was significantly greater in the treated portion (98.0%) versus untreated (71.4%); however, this difference was not significant when bryophytes were excluded in the analysis. The establishment, maintenance and monitoring of larger long-term trials is strongly recommended. [ABSTRACT FROM AUTHOR]

Site index (SI) is a commonly used measure of forest site productivity and is affected by climate change. Therefore, climate effects on site productivity were analyzed and modeled for jack pine (Pinus banksiana Lamb.), black spruce (Picea mariana (Mill.) B.S.P.), red pine (Pinus resinosa Ait.), and white spruce (Picea glauca (Moench) Voss) plantations using annual/seasonal values of climate variables. Jack pine and black spruce trees were each sampled from 25 plantations (sites), and red pine and white spruce trees were sampled from 30 and 31 plantations, respectively, from across Ontario, Canada. Stem analysis data collected from 201 jack pine, 211 black spruce, 90 red pine, and 93 white spruce trees were used in this study. To analyze and model climatic effects on site productivity, parameters of the stand height models were expressed in terms of climate variables. A nonlinear mixed-effects modelling approach was applied to fit the stand height models. Climate effects on site productivity was evaluated by predicting stand heights in three areas (the central, eastern/southeastern, and western parts of Ontario) for the period 2021 to 2080 under three emissions trajectories (representative concentration pathways (RCP) 2.6, 4.5, and 8.5 watts m−2). Climate effects on site productivity depended on tree species and location. For jack pine, climate effects were positive and pronounced only in western Ontario under all emissions scenarios. The effects were negative and mild after breast height age (BHA) 50 in central Ontario for black spruce. Similarly, the effects were negative and more pronounced at all areas after BHA 35 for red pine. On the other hand, for white spruce the effects were negative and highly pronounced from a young age under all scenarios, mainly in the southeast. For all species except for jack pine, climate effects were more pronounced under RCP 8.5 than the other two scenarios. [ABSTRACT FROM AUTHOR]

Masson pine (Pinus massoniana) is a core industrial tree species that is used for afforestation in southern China. Previous studies have shown that miR172 regulates plant growth and development, and the mechanism by which pma-miR172 affects flower development was explored in our study. In this research, we cloned and identified P. massoniana miR172 and its target gene PmAP2L3. The results showed that the 225 bp miR172 precursor was obtained, and the phylogenetic tree constructed based on the miR172 precursor sequence showed that P. massoniana miR172 has high homology with miR172 from Picea sitchensis and Picea glauca in gymnosperms. The target gene PmAP2L3 encodes a protein of 637 amino acids, and subcellular analysis revealed that the PmAP2L3 protein localised predominantly in the cytoplasm of P. massoniana.Compared with wild-type (WT) Arabidopsis , the miR172-overexpressing transgenic line blossomed more, while the 35 S:: PmAP2L3 and 35 S:: rAP2L3 transgenic lines were shorter. These results suggest that miR172 may promote flower development by inhibiting the target gene PmAP2L3. • In P. massoniana , miR172 and its target gene PmAP2L3 was obtained and their relationship was verified. • miR172 may promote flower development by inhibiting the target gene PmAP2L3. [ABSTRACT FROM AUTHOR]

SUMMARY: Spruces (Picea spp.) are coniferous trees widespread in boreal and mountainous forests of the northern hemisphere, with large economic significance and enormous contributions to global carbon sequestration. Spruces harbor very large genomes with high repetitiveness, hampering their comparative analysis. Here, we present and compare the genomes of four different North American spruces: the genome assemblies for Engelmann spruce (Picea engelmannii) and Sitka spruce (Picea sitchensis) together with improved and more contiguous genome assemblies for white spruce (Picea glauca) and for a naturally occurring introgress of these three species known as interior spruce (P. engelmannii × glauca × sitchensis). The genomes were structurally similar, and a large part of scaffolds could be anchored to a genetic map. The composition of the interior spruce genome indicated asymmetric contributions from the three ancestral genomes. Phylogenetic analysis of the nuclear and organelle genomes revealed a topology indicative of ancient reticulation. Different patterns of expansion of gene families among genomes were observed and related with presumed diversifying ecological adaptations. We identified rapidly evolving genes that harbored high rates of non‐synonymous polymorphisms relative to synonymous ones, indicative of positive selection and its hitchhiking effects. These gene sets were mostly distinct between the genomes of ecologically contrasted species, and signatures of convergent balancing selection were detected. Stress and stimulus response was identified as the most frequent function assigned to expanding gene families and rapidly evolving genes. These two aspects of genomic evolution were complementary in their contribution to divergent evolution of presumed adaptive nature. These more contiguous spruce giga‐genome sequences should strengthen our understanding of conifer genome structure and evolution, as their comparison offers clues into the genetic basis of adaptation and ecology of conifers at the genomic level. They will also provide tools to better monitor natural genetic diversity and improve the management of conifer forests. The genomes of four closely related North American spruces indicate that their high similarity at the morphological level is paralleled by the high conservation of their physical genome structure. Yet, the evidence of divergent evolution is apparent in their rapidly evolving genomes, supported by differential expansion of key gene families and large sets of genes under positive selection, largely in relation to stimulus and environmental stress response. Significance Statement: The genomes of four closely related North American spruces indicate that their high similarity at the morphological level is paralleled by the high conservation of their physical genome structure. Yet, the evidence of divergent evolution is apparent in their rapidly evolving genomes, supported by differential expansion of key gene families and large sets of genes under positive selection, largely in relation to stimulus and environmental stress response. [ABSTRACT FROM AUTHOR]

Under climate change circumstances, increasing studies have reported the temporal instability of tree growth responses to climate, which poses a major challenge to linearly extrapolating past climate and future growth dynamics using tree‐ring data. Space‐for‐time substitution (SFTS) is a potential solution to this problem that is widely used in the dendrochronology field to project past or future temporal growth response trajectories from contemporary spatial patterns. However, the projected accuracy of the SFTS in the climate effects on tree growth remains uncertain. Here, we empirically test the SFTS method by comparing the effect of spatial and temporal climate variations on climate responses of white spruce (Picea glauca), which has a transcontinental range in North America. We first applied a response surface regression model to capture the variations in growth responses along the spatial climate gradients. The results showed that the relationships between growth and June temperature varied along spatial climate gradients in a predictable way. And their relationships varied mainly along with local temperate condition. Then, the projected correlation coefficients between growth and climate using SFTS were compared against the observed. We found that the growth response changes caused by spatial versus temporal climate variations showed opposite trends. Moreover, the projected correlation coefficients using the SFTS were significantly lower than the observed. This finding suggests that applying the SFTS to project the growth response of white spruce might lead to an overestimation of the degree of tree maladaptation in future climate scenarios. And the overestimation is likely to get weaker from Alaska and Yukon Territory in the west to Quebec in the east. Although this is only a case study of the SFTS method for projecting tree growth response, our findings suggest that direct application of the SFTS method may not be applicable to all regions and all tree species. [ABSTRACT FROM AUTHOR]

Recent climate warming is expected to increase tree growth and productivity, substantially altering ecological function and boundaries in northern ecosystems. Although climate largely determines the range and growth of trees in any biome, variations in microsite conditions can influence growth on a finer scale. Red foxes (Vulpes vulpes) are found in most terrestrial ecosystems and are considered ecosystem engineers through their denning activities. Added soil nutrients from prey remains, feces, and urine could benefit tree growth on dens in subarctic regions by alleviating soil nutrient limitations. We examined growth in white spruce (Picea glauca) trees growing on eight red fox dens and paired control sites at the Arctic treeline. Radial growth was 55% higher for trees on dens than on control sites between 1897 and 2017, despite similarities in tree ages and densities. This enhanced growth was more pronounced in younger trees, consistent with the decrease in growth with age among all trees. By promoting tree growth near the treeline, red foxes may act as hotspots for tree reproduction. Although the impacts on tree growth largely depend on the spatial distribution of dens, predators can create distinct microhabitats across the landscape, leading to increased vegetation productivity, persisting over many decades. [ABSTRACT FROM AUTHOR]

The carbon sequestration potential of exotics might be considered as one of the several alternatives for forest adaptation to climate change. The results presented here demonstrate that exotic larches' (Larix spp.) growth rates for both carbon accumulation and traditional forest products exceed those of both natural regeneration and other planted species when planted on a good site in Maine. Recent re-measurement of a species-site trial established in 1988 represents the 34th growing season. Species included Black Spruce (BS) (Picea mariana Mill.), European larch (EL) (Larix decidua Mill.), hybrid larch (HL) (L. x marschelensi), Japanese larch (JL) (L. kaempferi (Lam.) Carrière), Jack pine (JP) (Pinus banksiana Lamb.), Red pine (RP) (Pinus resinosa Ait.), Tamarack (TL) (L. larcinia (Du Roi) K. Koch), and White spruce (WS)(Picea glauca (Moench) Voss). All three of the exotic larches outgrew the other species. Hybrid larch had over nearly twice the merchantable volume (m3 ha−1) and over three times the sawlog volume (green tonnes ha−1) than Red pine. Hybrid larch had the highest growth rate at age 34, over 20 m3 per hectare per year (nearly 3.3 cords ac−1 year−1 or 6.8 tons−1 acre−1 year−1). The other two exotic larches are growing at over 19 m3 ha−1 year−1 (3 cords acre−1 year−1 or 6.4 tons acre−1 year−1). Converting these growth rates to accumulation of CO2eq over the 34-year period produces stunning contrasts compared to native species. Over the 34-year period, larch hybrids sequestered 2.4 times as much CO2eq as the untreated plots (444 vs. 186 tonnes−1 ha−1). We discuss practical implications for forest management and carbon policies. [ABSTRACT FROM AUTHOR]

Global warming is predicted to extend the growing season of trees and plants, and advance spring phenology. However, intensification of extreme climate events in midlatitude forests, from weakening of the jet stream and atmospheric blockings, may expose trees to increased risk associated with more frequent late-spring frosts. Still, little is known regarding the intraspecific variation in frost tolerance and how it may be shaped by local adaptation to the climate of seed origin. As part of an assisted migration trial located in different bioclimatic zones in the province of Quebec, Canada, and following an extensive late-spring frost that occurred at the end of May 2021, we evaluated the frost damages on various white spruce (Picea glauca) seed sources tested on three sites (south, central, and north). The severity of frost damages was assessed on 5,376 trees after the cold spell and an early spring warming which advanced bud flush by approximately 10 days on average. The frost damage rate was similar among sites and seed sources and averaged 99.8%. Frost damage severity was unrelated to the latitude of seed origin but was variable among sites. The proportion of severely damaged trees was higher in the northern site, followed by central and southern sites. The proportion of severely damaged trees was linearly and inversely related to tree height before the frost event. Apical growth cancelation was not significantly different among seed sources including local ones, and averaged 74, 46, and 22%, respectively, in central, northern, and southern plantation sites. This study provides recommendations to limit the loss of plantation productivity associated with such a succession of spring climate anomalies. Implications for seed transfer models in the context of climate change and productivity of spruce plantations are discussed in the light of lack of local adaptation to such pronounced climate instability and ensuing large-scale maladaptation [ABSTRACT FROM AUTHOR]

White spruce (Picea glauca) spans a massive range, yet the variability in respiratory physiology and related implications for tree carbon balance at the extremes of this distribution remain as enigmas. Working at both the most northern and southern extents of the distribution range more than 5000 km apart, we measured the short‐term temperature response of dark respiration (R/T) at upper and lower canopy positions. R/T curves were fit to both polynomial and thermodynamic models so that model parameters could be compared among locations, canopy positions, and with previously published data. Respiration measured at 25°C (R25) was 68% lower at the southern location than at the northern location, resulting in a significantly lower intercept in R/T response in temperate trees. Only at the southern location did upper canopy leaves have a steeper temperature response than lower canopy leaves, likely reflecting canopy gradients in light. At the northern range limit respiration is nearly twice that of the average R25 reported in a global leaf respiration database. We predict that without significant thermal acclimation, respiration will increase with projected end‐of‐the‐century warming and will likely constrain the future range limits of this important boreal species. Summary Statement: White spruce (Picea glauca) needle respiration at the northern limit of the species range is three times higher than at the southern range limit (when measured at 25°C). This high carbon cost likely challenges tree survival and contributes to the location of the northern treeline. [ABSTRACT FROM AUTHOR]

The resilience of northern ecosystems is being tested as the temporal and spatial distribution of wildfires change. Wildfires at treeline are predicted to facilitate a northward advance of boreal tree species, as the tundra is in close proximity to fire-adapted species climatically primed for range expansion. To study the effects of wildfire at treeline, we asked (1) how does wildfire change the environmental characteristics of treeline microsites, and (2) in the absence of viable seed limitation, do burned treelines increase the likelihood of tree seedling emergence? We measured numerous biotic and abiotic factors at three treelines in Yukon, Canada, each consisting of a burned and unburned treatment. Our observational study was paired with a manipulative seeding experiment of black spruce (Picea mariana (Mill) B.S.P.) and white spruce (Picea glauca (Moench) Voss) to determine what environmental characteristics facilitated seedling emergence potential across site treatments. When comparing site treatments, results indicated that within the first two decades after wildfire, soil temperatures (GDD) were more extreme at burned treelines during the summer and winter. An examination of plot data in ordination space showed clear differences in organic layer depth and vegetation cover between treatments. While some of these changes would seem to benefit germination potential, spruce seedling emergence was extremely limited over the study period. Model results indicated little association between seedling emergence and recent fire; however, seedling emergence was positively associated with moss substrate found across treatments and reduced cover of tall multi-stemmed shrubs. We conclude that wildfire can create seedbed conditions that benefit seedling emergence, but low-severity wildfires create a variety of microsite conditions that limit overall availability of these seedbeds. Furthermore, emerging seedlings may experience new barriers to establishment, as burned treelines exhibited changes in soil temperature extremes and snow depth. [ABSTRACT FROM AUTHOR]

Forest protection against eastern spruce budworm, Choristoneura fumiferana (Clemens), relies on aerial applications of Bacillus thuringiensis (Btk). However, Btk prescriptions have been developed for balsam fir (Abies balsamea (L.) Mill.) stands, generating uncertainty as to the relevance of this protection approach on white spruce (Picea glauca (Moench) Voss). The main goal of this study was to evaluate the efficacy of three Btk application treatments (early application, late application, and double application) for protecting white spruce and balsam fir in mixed stands. Our results show that all Btk treatments tested kept defoliation under the 50% threshold on balsam fir (27.7 to 38.1% less defoliation than in controls). In contrast, differences in defoliation among treatments were not significant for white spruce. Larval mortality was significantly lower on white spruce than on balsam fir. The low efficacy of Btk treatments on white spruce may be explained by its shoot phenology (most bud caps were still present during the early application), and its foliar chemistry, which could decrease Btk efficacy. Consequently, many larvae may survive simply because Btk spores do not reach them, or because they may consume sublethal doses. We recommend maintaining the current strategy in mixed stands, as it provides a good protection for balsam fir. Further research is needed to determine the causes of the low efficacy of Btk treatments on white spruce.

The relative proportions of different chemical components in wood tissues is one of the underlying factors that control wood properties. These proportions vary within and between woody tissues, and an accurate description of these variations is critical for parameterizing forest biogeochemical budgets and models. White spruce (Picea glauca (Moench) Voss) spacing intensities trials in the Petawawa Research Forest, Ontario, Canada, were sampled to evaluate variations in carbon (C), nitrogen (N), and hydrogen (H) concentrations between different tissue types, i.e., bark, cambium, knots, earlywood, latewood, and wood. Samples were freeze-dried and oven-dried to test the impact of the drying methods on these chemical elements. Freeze-dried C (51.14) and H (6.18) concentrations were significantly higher than those of oven-dried C (50.55) and H (6.06). Freeze-dried N (0.18) did not differ from oven-dried N (0.17). The spacing intensities impacted C, H, and N, with C content being higher in wider square spacings (4.3 m and 6.1 m), while the reverse was true for N and H, which exhibited higher content in smaller square spacings (1.2 m and 1.8 m). The results of this study also suggested that when it comes to the content of chemical elements, bark and knots should be treated as separate fuel types, whereas other woody tissues can be aggregated.

Purpose: The objective of this study was to compare the accumulation over time of organic carbon (C) in soil and vegetation of abandoned agricultural lands left to natural vegetation succession or afforested with planted white spruce (Picea glauca (Moench) Voss) in Abitibi (Canada). The agricultural areas of this region originated from the clearing of forested lands in the late 19th -early 20th centuries. The aim was to determine whether afforestation of such lands is a relevant tool for C sequestration and climate change mitigation. Methods: Field and laboratory measures for tree, shrub and herbaceous strata, woody debris and soil down to a 50 cm depth were carried out on abandoned agricultural lands that were either left to natural succession or planted, to determine total C stocks. The experimental design was a chronosequence covering 50 years, with sites representing various stages following agriculture abandonment and plantation. Results: There was no significant difference in the amount of C stored by lands that were either planted or left to natural succession over a 50-year time period. Both types of lands were found to be net C sinks. Abandoned lands left to natural succession stored 1.3 times more C in the soil compared with afforested lands, while the latter stored twice as much C in aboveground biomass. Conclusions: These results put into perspective the use of afforestation to increase land C sinks and suggest that natural succession might also play a role in land management practices in the context of climate change mitigation. [ABSTRACT FROM AUTHOR]

Diameter at Breast Height (DBH) plays an important role in forest management. New technologies such as airborne and terrestrial Light Detection and Ranging (LiDAR) are expensive and time-consuming. We explored the iPad LiDAR sensor to measure DBH considering affordability and availability. The study was carried out at a research forest plantation near Thunder Bay, Ontario, Canada. Five plots were selected for differences in stem spacing, average DBH and species, and made 360° scans separately. A manual circle fitting method was used to produce circular features for the estimation of DBH. The coefficient of determination (R2) between estimated DBH and field measurements was 0.52, indicating a moderate accuracy. The Root Mean Square Error (RMSE) of DBH estimation ranged from 2.82 cm to 8.24 cm. The accuracy of smaller red pine trees was found to be relatively higher than that of larger red pine and white spruce trees. These accuracies did not change with the distance from the scanning location to trees. Therefore, results showed the potential use of an iPad LiDAR Scanner for DBH estimation. We recommend developing an application combining the iPad's location and LiDAR sensors and incorporating a precise positioning method for fieldwork, and further broad field testing. [ABSTRACT FROM AUTHOR]

An agreement between the provincial government of Québec, Canada and the forest industry executing forest management activities on public lands has been established regarding non-utilized woody material (NUWM) left on the cutting area. Problems linked to this agreement are compounded by labor shortages, which have an impact on the precision of the mandatory inventories. The objectives of this study were to: (1) reconstruct and estimate the merchantable NUWM volume beyond the last processed log of balsam fir and white spruce with the use of harvester on-board computer (OBC) data, (2) design a software tool to estimate and spatialize merchantable NUWM, and (3) perform an explorative comparison between the OBC method and conventional field inventory. In total, five sites were harvested to develop the volume algorithms. Each site was harvested by a single-grip harvester operating a different OBC system (OPTI4G, Log Mate 500, and Log Mate 510). Results suggest that, with Varjo's model and linear regression, estimation of NUWM volume using OBC data is possible. The spatialization tool positioned NUWM within the harvest area for StanForD and StanForD 2010. The explorative comparison highlighted a possible cost reduction of approx. 36.8 $/ha and an increase of precision for the OBC method. [ABSTRACT FROM AUTHOR]

Background: Picea species are distributed and planted world-wide due to their great ecological and economic values. It has been reported that Picea species vary widely in growth traits in a given environment, which reflects genetic and phenotypic differences among species. However, key physiological processes underlying tree growth and the influencing factors on them are still unknown. Results: Here, we examined needle structures, needle chemical components, physiological characteristics and growth traits across five Picea species in a common garden in Tianshui, Gansu province in China: Picea glauca, P. mariana, P. likiangensis, P. koraiensis, and P. crassifolia, among which P. glauca and P. mariana were introduced from North America, P. likiangensis was from Lijiang, Yunan province in China, P. koraiensis was from Yichun, Heilongjiang province in China, and P. crassifolia was native to the experimental site. It was found that nearly all traits varied significantly among species. Tissue-level anatomical characteristics and leaf mass per area (LMA) were affected by needle size, but the variations of them were not associated with the variations in photosynthetic and biochemical capacity among species. Variations in area-based maximum photosynthesis (Pnmax) were affected by stomatal conductance (gs), mesophyll conductance (gm) and biochemical parameters including maximum carboxylation rate (Vcmax), and maximum electron transport rate (Jmax). The fraction of N allocated to different photosynthetic apparatus displayed contrasting values among species, which contributed to the species variations in photosynthetic nitrogen use efficiency (PNUE) and Pnmax. Additionally, all growth traits were positively correlated with Pnmax and PNUE. Conclusion: Needle structures are less important than needle biochemical parameters in determining the variations in photosynthetic capacity across the five Picea species. Pnmax and PNUE are closedly associated with the fraction of N allocated to photosynthetic apparatus (Pphoto) compared with leaf N content per area (Narea). The tremendous growth differences among the five Picea species were substantially related to the interspecies variation in Pnmax and PNUE. [ABSTRACT FROM AUTHOR]

As northern latitudes experience rapid winter warming, there is an urgent need to assess the effect of varying winter conditions on tree growth and forest carbon sequestration potential. We examined tree growth responses to variability in cold-season (November–- April) frequency of freeze days (FFD) over 1951 to 2018 using tree-ring data from 35,217 trees and 57 species at 4,375 sites distributed across Canada. We found that annual radial growth responses to FFD varied by species, with some commonalities across genera and clades. The growth of gymnosperms with late spring leaf-out strategies was negatively related to FFD; years with high FFD were most detrimental to the annual growth of Pinus banksiana, Pinus contorta, Larix lyalli, Abies amabilis, and Abies lasiocarpa. In contrast, the growth of angiosperms with early leaf-out strategies, namely, Populus tremuloides and Betula papyrifera, was better in the coldest years, and gymnosperms with intermediate leaf-out timing, such as widespread Picea mariana and Picea glauca, had no consistent relationship to FFD. Tree growth responses to FFD were further modulated by tree size, tree age, regional climate (i.e., mean cold-season temperature), and local site conditions. Overall, our results suggest that moderately warming winters may temporarily improve the growth of widespread pines and some high-elevation conifers in western Canada, whereas warming winters may be detrimental to the growth of widespread boreal angiosperms. Our findings also highlight the value of using species-specific climate-growth relationships to refine predictions of forest carbon dynamics. [ABSTRACT FROM AUTHOR]

Past research has shown that remotely sensed spectral information can be used to predict tree health and vitality. Recent developments in unmanned aerial vehicles (UAVs) have now made it possible to derive such information at the tree and stand scale from high-resolution imagery. We used visible and multispectral bands from UAV imagery to calculate a set of spectral indices for 52,845 individual tree crowns within 38 forest stands in western Canada. We then used those indices to predict the mortality of these canopy trees over the following year. We evaluated whether including multispectral indices leads to more accurate predictions than indices derived from visible wavelengths alone and how the performance varies among three different tree species (Picea glauca, Pinus contorta, Populus tremuloides). Our results show that spectral information can be effectively used to predict tree mortality, with a random forest model producing a mean area under the receiver operating characteristic curve (AUC) of 89.8% and a balanced accuracy of 83.3%. The exclusion of multispectral indices worsened the model performance, but only slightly (AUC = 87.9%, balanced accuracy = 81.8%). We found variation in model performance among species, with higher accuracy for the broadleaf species (balanced accuracy = 85.2%) than the two conifer species (balanced accuracy = 73.3% and 77.8%). However, all models overpredicted tree mortality by a major degree, which limits the use for tree mortality predictions on an individual level. Further improvements such as long-term monitoring, the use of hyperspectral data and cost-sensitive learning algorithms, and training the model with a larger and more balanced data set are necessary. Nevertheless, our results demonstrate that imagery from UAVs has strong potential for predicting annual mortality for individual canopy trees. [ABSTRACT FROM AUTHOR]

Precise delineation of individual tree crowns is critical for accurate forest biophysical parameter estimation, species classification, and ecosystem modelling. Multispectral optical remote sensors mounted on low-flying unmanned aerial vehicles (UAVs) can rapidly collect very-high-resolution (VHR) photogrammetric optical data that contain the spectral, spatial, and structural information of trees. State-of-the-art tree crown delineation approaches rely mostly on spectral information and underexploit the spatial-contextual and structural information in VHR photogrammetric multispectral data, resulting in crown delineation errors. Here, we propose the spectral, spatial-contextual, and structural information-based individual tree crown delineation (S3-ITD) method, which accurately delineates individual spruce crowns by minimizing the undesirable effects due to intracrown spectral variance and nonuniform illumination/shadowing in VHR multispectral data. We evaluate the performance of the S3-ITD crown delineation method over a white spruce forest in Quebec, Canada. The highest mean intersection over union (IoU) index of 0.83, and the lowest mean crown-area difference (CAD) of 0.14 m 2 , proves the superior crown delineation performance of the S3-ITD method over state-of-the-art methods. The reduction in error by 2.4 cm and 1.0 cm for the allometrically derived diameter at breast height (DBH) estimates compared with those from the WS-ITD and the BF-ITD approaches, respectively, demonstrates the effectiveness of the S3-ITD method to accurately estimate biophysical parameters. [ABSTRACT FROM AUTHOR]

While deployment of white spruce (Picea glauca (Moench) Voss) from seed orchards is increasing in Alberta, genetic gain is only considered in pure spruce stands due to uncertainties in measuring yields in mixedwood stands. To better understand the performance of improved spruce in mixedwood stands, we compared the effects of interspecific competition on growth of improved (1.9% height gain at a 100-year rotation) and unimproved spruce in northeastern Alberta. By age 8 years the improved spruce showed no advantage over the unimproved spruce in either height (1.36 ± 0.36 m vs. 1.42 ± 0.38 m) or diameter (23.68 ± 7.33 mm vs. 25.65 ± 6.85 mm), and the largest diameter trees were found in a nutrient-poor subxeric site. A distance-independent Lorimer's index including tree size ratio, combined with a power function, accounted for most of the growth variation in diameter and height from 2016 to 2017. The unimproved and improved spruce had different growth-competition curves across ecosites, and their height growth was less sensitive to competition than diameter growth. These results highlight several considerations for managing improved spruce, including (i) deploying higher genetic worth seedlots, (ii) developing realized gain trials with a good statistical design, and (iii) developing growth and yield functions for improved spruce in mixedwood stands. [ABSTRACT FROM AUTHOR]

The representation of snow processes in forest growth models is necessary to accurately predict the hydrological cycle in boreal ecosystems and the isotopic signature of soil water extracted by trees, photosynthates and tree-ring cellulose. Yet, most process-based models do not include a snow module; consequently, their simulations may be biased in cold environments. Here, we modified the MAIDENiso model to incorporate a new snow module that simulates snow accumulation, melting and sublimation, as well as thermal exchanges driving freezing and thawing of the snow and the soil. We tested these implementations in two sites in eastern and western Canada for black spruce (Picea mariana (Mill.) B.S.P.) and white spruce (Picea glauca (Moench) Voss) forests, respectively. The new snow module improves the skills of the model to predict components of the hydrological cycle. The MAIDENiso model is now able to reproduce the spring discharge peak and to simulate stable oxygen isotopes in tree-ring cellulose more realistically than in the original snow-free version of the model. The new implementation also results in simulations with a higher contribution from the source water on the oxygen isotopic composition of the simulated cellulose, leading to more accurate estimates of cellulose isotopic composition. Future work may include the development of inverse modelling with this new version of MAIDENiso to produce robust reconstructions of the hydrological cycle and isotope processes in cold environments. [ABSTRACT FROM AUTHOR]

Mechanistically predicting the evolutionary response of tree species to climate change requires an understanding of genetic variation in relevant traits. Here we compared the phenotypic and genetic variation in the Leaf Economics Spectrum (LES) traits and the response of gas exchange to vapour pressure deficit (VPD) in lodgepole pine (Pico) and white spruce (Pigl), an early and a late successional species dominating the boreal forests of western Canada.We measured gas exchange, foliar nitrogen and lamina mass to area ratio in 697 c. 30‐year‐old trees in two field progeny trials. We analysed the response of gas exchange rates to VPD using a novel quantitative genetic model, the function‐valued trait approach.Pico showed greater phenotypic variation in the LES traits and greater genetic variation in photosynthetic rate than Pigl, but the species showed no significant difference in their phenotypic correlations between the LES traits. Pico showed a less sensitive stomatal response to VPD than Pigl and no significant genetic variation in stomatal sensitivity. In contrast, Pigl showed a positive correlation between the genetic values of stomatal sensitivity to VPD and stomatal conductance under low VPD.Our study region is projected to see an increase in VPD with climate change; the less sensitive and genetically diverse stomatal response to VPD in Pico could make this species more vulnerable to climate‐change‐induced droughts. A free Plain Language Summary can be found within the Supporting Information of this article. [ABSTRACT FROM AUTHOR]

White spruce (Picea glauca) emits monoterpenes that function as defensive signals and weapons after herbivore attack. We assessed the effects of drought and methyl jasmonate (MeJA) treatment, used as a proxy for herbivory, on monoterpenes and other isoprenoids in P. glauca. The emission of monoterpenes was significantly increased after MeJA treatment compared to the control, but drought suppressed the MeJA-induced increase. The composition of the emitted blend was altered strongly by stress, with drought increasing the proportion of oxygenated compounds and MeJA increasing the proportion of induced compounds such as linalool and (E)-β-ocimene. In contrast, no treatment had any significant effect on the levels of stored monoterpenes and diterpenes. Among other MEP pathway-derived isoprenoids, MeJA treatment decreased chlorophyll levels by 40%, but had no effect on carotenoids, while drought stress had no impact on either of these pigment classes. Of the three described spruce genes encoding 1-deoxy-D-xylulose-5-phosphate synthase (DXS) catalyzing the first step of the MEP pathway, the expression of only one, DXS2B, was affected by our treatments, being increased by MeJA and decreased by drought. These findings show the sensitivity of monoterpene emission to biotic and abiotic stress regimes, and the mediation of the response by DXS genes. [ABSTRACT FROM AUTHOR]

MYB transcription factors play important roles in plant growth and development,metabolism,responses to biotic and abiotic stresses. In order to explore the structure and function of R2R3-MYB genes in Pinus massoniana, we identified 17 R2R3-MYB genes based on the transcriptome dataset of P. massoniana, and then investigated their physical and chemical properties, phylogenetic relations, gene tissue specificity with qRT-PCR, and expression patterns of these genes in the development process of flower organs and under different abiotic stresses. The results were as follows:(1)Seventeen PmMYBs subcellular were predicted to locate in cell nucleus, without transmembrane structure. They all contained Motif1 and Motif2 conserved motifs. These 17 PmMYBs genes could be divided into nine subgroups according to phylogenetic analysis, which were closely related to gymnosperms such as Pinus taeda and Picea glauca.(2)The expression patterns of PmMYBs genes in different tissues and under salt stress, drought stress, lead stress and low temperature stress were validated by qRT-PCR. As a result, a total of 17 genes were constitutive expressed, but the expression levels were different in different tissues. All genes appeared to be involved in flower development. Seven MYB genes seemed to be involved in the transformation of male and female traits as they were differently expressed in different stages of flower development. Moreover, those genes may also be involved in abiotic stress responses, as most of the genes were up-regulated under abiotic stress. Their unique expression patterns may suggest that they function at different stages of stress. A few genes were down-regulated under stress, especially PmMYB11 gene. This study systematically analyze the characteristics, evolutionary and expression patterns of R2R3-MYB genes in Pinus massoniana during flower development and abiotic stress, and provides a reference for further study on the function and stress response mechanism of R2R3-MYB gene in P. massoniana. [ABSTRACT FROM AUTHOR]

If the modern climate trend continues for an additional 20–40 years, forests along the southern border of Canadian taiga may shift into new ranges of annual temperature and precipitation that are similar to the modern climate of central New York State, United States. Here we investigate the possible future response of white spruce (Picea glauca (Moench) Voss) to a warmer climate by studying trees planted 90 years ago near the southern limit of their climate tolerance in central New York, 300 km south of the boreal forest where this species is prevalent. We employed high-frequency recording dendrometers to determine radial growth phenology of six mature white spruce trees during 2013–2017. The results demonstrate significant reductions in the length of radial growth periods inversely proportional to the number of hot days with air temperature exceeding 30 °C. During years with very hot summers, the start of radial growth began about 3 days earlier than the 2013–2017 average. However, in those same years, the end of radial growth was also about 17 days earlier resulting in a shorter (70 days versus 100 days) radial growth season. Abundant (350–500 mm) summer precipitation, which resulted in soil moisture values of 20%–30%, allowed us to dismiss drought as a factor. Instead, a likely cause of reduced radial growth was mean temperature that exceeded optimal growth ranges, exacerbated by temperature extremes in ranges that lead to photoinhibition. The latter case was evident in the two warmest growing seasons (2013 and 2017), marked by extended periods of high daytime temperature (>30 °C) followed by early cessation of radial growth independent of seasonal precipitation. [ABSTRACT FROM AUTHOR]

Conifer breeding programmes are increasingly selecting for wood quality in addition to growth so to ensure a sufficient flow of high-quality fibre from future forest plantations. As wood density is one of the most frequently used indicators of wood quality, there is a growing interest to consider this trait in selection, and thus enhance the properties of end-use products from planted trees. However, wood density varies at different scales within trees, with pith-to-bark patterns and year-to-year fluctuations representing two important sources of variation. From both physiological and end-use points of view, it is desirable to produce stems with limited pith-to-bark and year-to-year wood density variation. In the present study, we assessed patterns of pith-to-bark and year-to-year variation in 2196 wood density patterns and evaluated the genetic control of traits characterizing this variation. The experimental data came from a 15-year-old white spruce genetic trial representing 93 full-sib families replicated in two contrasting environments in Quebec, Canada. To separate pith-to-bark from year-to-year variation, non-linear models were developed to describe pith-to-bark patterns of variation in the mean ring density (MRD) of individual trees as well as for latewood density (LWD) and latewood proportion. We observed that pith-to-bark variation was more under genetic control than year-to-year variation, for which only LWD and proportion of latewood width to overall ring width reached moderate genetic control. Little genotype-by-environment interaction was observed although wood density patterns differed significantly between sites. The present approach could help identify trees or families that tend to have limited pith-to-bark and year-to-year variation in wood density as part of tree genetic improvement programmes to provide future trees with more uniform and desirable wood attributes. [ABSTRACT FROM AUTHOR]

Spruce–fir (Picea–Abies) forests of the North American Acadian Forest Region are at risk of disappearing from the northeastern United States and Canada due to climate change. Species distribution models (SDMs) have been used to predict changes in this critical transitional ecosystem in the past, but none have addressed how seasonal patterns of temperature and precipitation interact to influence tree species abundance. Inferences have also been limited by contemporary inventory data that could not fully characterize species ranges because they either, (1) only sampled species occurrence after large‐scale human disturbance and settlement, or (2) did not span critical geopolitical boundaries (e.g., the US–Canadian border) that intersect the focal species' range(s). Here, we built new SDM models to better assess the bioclimatic distribution of four spruce–fir species and to test the importance of seasonal climate interactions. We compiled an extensive database of tree occurrence and abundance from recent (~1955–2012) and historical time periods (1623–1869) to model current species distributions and to predict how these might change under future climate. We found that including historical tree data in our SDMs revealed previously unrecognized suitable habitat along the southern edge of species' contemporary ranges. Random forest models predicted occurrence with high accuracy (area under receiver operator curve >0.98), and the seasonal climate variables that emerged as most important for these cold‐adapted species all included interactions that reflected sensitivity to colder temperatures, and preferences for wet weather concentrated in the winter months. Under moderate climate warming (representative concentration pathway 6.0), the northeastern United States retained additional suitable habitat when historical data were included through 2060 for three of the four species: red spruce (Picea rubens), black spruce (Picea mariana), and balsam fir (Abies balsamea), while white spruce (Picea glauca) habitat contracted into Canada. In contrast, future predictions from models that used contemporary data alone forecast extirpation for all four species from the northeastern United States. Overall, these findings highlight that prediction of species ranges in transitional ecosystems that span geopolitical boundaries and gradients of intense land use are improved when historical data and seasonal climate interactions of both temperature and precipitation variables are incorporated. [ABSTRACT FROM AUTHOR]

Simple Summary: We measured the foliage area, weight and number of buds on young and mature balsam fir and white spruce trees. With these measurements, total amounts of foliage per tree and per unit area of forest land can be calculated. These estimates can be used to determine the absolute numbers of insects feeding on these trees, numbers that are important in understanding patterns and fluctuations of population abundance. We also discovered that spruce budworm larvae occur preferentially in buds arranged in clusters. We describe the distribution and amount of foliage, expressed as foliated branch surface area, weight, or number of buds in the live crown of healthy open-grown and closed-canopy balsam fir and white spruce trees. Balsam fir and white spruce have very similar total foliage surface area and weight. The live crown of white spruce trees contains fewer buds than balsam fir of similar dimensions. Thus, bud density per unit foliage weight or surface area is higher in balsam fir than in white spruce. We also observed that buds tend to grow in clusters more often on balsam fir than on white spruce, and that larvae of the spruce budworm preferentially attack buds that grow in clusters. Equations were developed to predict the total surface area and weight of foliage as well as number of buds in the live crown for estimation of absolute population density of spruce budworm. These equations use diameter at breast height (DBH) and the number of nodes in the live crown as predictors. When data on the number of live nodes are unavailable, it can be estimated from tree height. Equations were also developed from which to estimate foliage area, weight or bud numbers from DBH only. [ABSTRACT FROM AUTHOR]

Understory protection harvesting is a form of partial cutting that can be used in aspen (Populus tremuloides Michx.)-dominated stands that have understories of white spruce (Picea glauca (Moench) Voss). This practice involves removing 75% to 85% of the merchantable aspen while minimizing damage to the advance spruce regeneration, in addition to leaving 15% to 25% of the aspen standing to reduce potential windthrow of the spruce understory. In this paper, we summarize results from 18 stands measured 10 to 12 years after understory protection harvest. Diameter growth of spruce increased during the first five years after harvest while height growth increased during the second five-year period (5 to 10 or 7 to 12 years after release). Consistent with other studies, mortality rates of aspen trees ≥7.1 cm DBH (diameter breast height, 1.3 m) averaged 45.0% over the 10–12 year period following harvesting. Spruce mortality averaged 27.5% over the same 10–12 year period. Substantial aspen regeneration was evident across most harvested blocks, with aspen sapling densities 10–12 years from harvest being higher in removal (14,637 stems⋅ha−1) than in buffer areas (6686 stems⋅ha−1) and in extraction trails (7654 stems⋅ha−1). Spruce sapling (>1.3 m height and <4 cm DBH) densities averaged 1140 stems⋅ha−1 in removal areas at ages 10–12, with these trees likely being present as seedlings at the time of harvest. Mixedwood Growth Model projections indicate merchantable volumes averaging 168 m3⋅ha−1 (conifer) and 106 m3⋅ha−1 (deciduous) 70 years from harvest, resulting in MAI (mean annual increment) for this period averaging 2.0 m3⋅ha−1⋅y−1 with MAI for a full 150-year rotation of approximately 2.5 m3⋅ha−1⋅y−1. [ABSTRACT FROM AUTHOR]

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. • Total understory vegetation cover was higher in the mixture than in monoculture. • The mixture increased the potential nitrogen supply rates compared to monoculture. • Soil properties were improved in the mixture compared to monoculture. • The mixture effect was dependent on the density of broadleaf in the treatments. [ABSTRACT FROM AUTHOR]

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. • Impact of tree improvement on white spruce was assessed operationally. • 17% greater growth in DBH and height was observed in improved white spruce. • Site index of improved white spruce was increased by 2 m. • Improved and unimproved stands were similarly affected by competition. [ABSTRACT FROM AUTHOR]

• May minimum temperature is the primary driver of budburst in boreal conifers. • P. mariana showed the highest response to warmer springs and P. glauca the lowest. • Precipitation's effect on budburst is limited when compared to temperature. • Changes in bud phenology may disrupt host-insect interactions. • Budburst timing correlates with latitude and ecological provinces. Budburst is a pivotal event in plant life, representing a crucial response to seasonal meteorological shifts. Boreal tree species exhibit species-specific phenologies, and the rate of phenological changes under warming conditions may differ among these species. In this study we aim to investigate the timing of budburst in three coniferous species [Balsam fir (Abies balsamea), black spruce (Picea mariana) and white spruce (Picea glauca) (Pinaceae)]; identify the main drivers of budburst, its rate of advance and the spatiotemporal patterns of budburst in relation to climate across Canada using a time period of 1980–2021. The timing of budburst was observed at 2839 locations stretching from Alberta to Newfoundland. We developed response functions between budburst and climate (air temperature, precipitation and solar radiation) and used the strongest correlations to test their effect on budburst using species, time and the ecoclimatic framework of Canadian ecoprovinces. We applied spatially constrained multivariate clustering and identified natural budburst clustering across Canada. We found a baseline difference of 17 days in the budburst of black spruce relative to that of balsam fir and white spruce. Mean minimum temperature of May was negatively correlated with budburst date. Black spruce advanced budburst at a rate of change per degree of temperature (−3.33 days °C−1), twice that of balsam fir and white spruce (−1.53 and −1.27 days °C−1, respectively). Cluster distribution of budburst timing matched well with the distribution of Canadian ecoprovinces. Budburst within the clusters followed clinal patterns in temperature across Canada. Mean minimum temperature in May is the main factor driving budburst in northern tree species. Under a warmer spring, we project an earlier budburst, with black spruce being the species expected to show the greatest rate of change. The identified clustering patterns did not vary with precipitation, which represents the primary longitudinal gradient across Canada. [ABSTRACT FROM AUTHOR]