Integrating roundwood harvesting with collecting traditionally unmerchantable harvest residue largely depends on the operational and economic viability for harvest contractors. This study compared machine time of motion, harvest volumes, productivity, and profits of two harvesting methods in a shelterwood system in the Canadian Great Lakes-St. Lawrence (GLSL) forest region. Conventional “tree length” (TL) harvesting only harvested merchantable roundwood and “full tree” (FT) harvesting residues and roundwood. FT harvesting required significantly more feller buncher time of motion compared to TL harvesting, but there were no significant differences in time of motion for other machines. FT harvesting yielded greater volumes of residue (34.1 ± 6.9 m 3 ha −1 ), small poles, and medium poles compared to TL. Average profits were 36% higher using FT harvesting ($611 ± 560 CAD ha −1 ), compared to TL ($450 ± 506 CAD ha −1 ), but these differences were not statistically significant. The increased profits at FT blocks were largely from residual management services (such as chipping) versus the sale of residues for bioenergy feedstocks. The results from this study suggest that FT harvesting recovers greater merchantable volumes and can be equally or more profitable at the contractor level than TL harvesting in GLSL shelterwood systems.

In selection-managed northern hardwood forests, tree markers select trees for harvest based on their vigour and quality, which are assessed based on the presence or absence of defects. Recent research has shown that trees that develop crown dieback decline in vigour, but not necessarily in quality, and tree marking simulations indicate that prioritizing the harvest of these high-quality salvage trees increases value recovery by 17–18% compared to existing prescriptions. However, this is likely an overestimate because the tree marking simulations did not account for various operational constraints. We developed an operational tree marking prescription that prioritizes recovery of high-quality salvage trees and conducted a field trial to compare it to two prescriptions commonly used in Ontario. Few high-quality salvage trees were marked under the existing prescriptions, but most were marked under the new prescription, which also retained more high-vigour trees. The new prescription also recovered 15-16% more value, though this difference was not statistically significant. Our results demonstrate that prioritizing high-quality salvage trees increases stand vigour while maintaining or potentially increasing value recovery under operational conditions.

Trees can differ enormously in their crown architectural traits, such as the scaling relationships between tree height, crown width and stem diameter. Yet despite the importance of crown architecture in shaping the structure and function of terrestrial ecosystems, we lack a complete picture of what drives this incredible diversity in crown shapes. Using data from 374,888 globally distributed trees, we explore how climate, disturbance, competition, functional traits, and evolutionary history constrain the height and crown width scaling relationships of 1914 tree species. We find that variation in height-diameter scaling relationships is primarily controlled by water availability and light competition. Conversely, crown width is predominantly shaped by exposure to wind and fire, while also covarying with functional traits related to mechanical stability and photosynthesis. Additionally, we identify several plant lineages with highly distinctive stem and crown forms, such as the exceedingly slender dipterocarps of Southeast Asia, or the extremely wide crowns of legume trees in African savannas. Our study charts the global spectrum of tree crown architecture and pinpoints the processes that shape the 3D structure of woody ecosystems.

Recent studies have highlighted the need to update hardwood tree marking guides by changing the criteria used to assess vigour and quality, and thus the priority for deciding which trees to remove and retain during selection harvests. However, these studies have recommended different criteria, so it remains uncertain which should be included in the classification systems used to assess vigour and quality. We review these studies with the aim of reducing this uncertainty and identifying potential improvements to the provincial tree marking guides for northern hardwood forests in Canada, particularly the Ontario Tree Marking Guide. We review the differences in methodologies and summarize which defects have been shown to affect vigour and/or quality. The defects that should be used to assess vigour are canopy dieback, cankers, and fungi. Decaying wounds, wounds without decay, canopy density, and bark condition could also be used as secondary criteria for borderline cases in which the primary criteria are not decisive. The defects that should be used to assess quality are cankers, fungi, cracks, cavities, and decay (including black bark and wounds with moisture or soft wood). We present a new classification system based on these results and identify potential challenges to its implementation.

Demonstration forests have been established across the northern hardwoods of the United States to assess the economic and environmental implications of partial harvest systems, such as single tree selection and diameter limit cutting. Single tree selection has been studied at several sites in the northern hardwoods of Canada, but there has not been a structured comparison of partial harvest systems within one site. We assessed the initial harvest results at the Blue Heron Demonstration Forest, in which four partial harvest systems – single tree selection (STS), financial maturity selection (FMS), diameter limit cutting (DLC), and crop tree release (CROP) – and a control treatment were implemented with multiple replicates within a typical northern hardwood forest in central Ontario. DLC harvested the most volume as well as basal area, followed closely by FMS. STS harvested the least basal area and volume and generated the lowest product values as well as the lowest stumpage revenue. However, STS did not harvest significantly more low vigour trees, nor did it significantly increase the proportion of basal area that is high vigour, suggesting that alternative partial harvest systems like FMS may achieve silvicultural objectives while yielding superior financial results over multiple cutting cycles.

In northern hardwood forests, tree markers select the trees to be harvested during logging operations using classification systems that assign harvest priorities based on the presence of a wide range of individual defects. According to the most recent advances in our understanding of the impact of defects on both tree vigour (the risk of mortality or decline in growth) and quality (the potential for recovering valuable sawlogs), tree markers should adopt a simpler classification system that considers fewer defects than the current operational practice, and they should prioritize the removal of trees with crown dieback. Since the probability of developing defects and dying increases substantially with tree diameter, tree markers should also favour the removal of larger trees that have maintained their quality. However, these recommendations were developed based on tree-level analyses. To provide further validation at the stand scale, we compared stand improvement and value recovery under three tree marking regimes: a new, simplified regime based on the recommendations above, and two regimes used in the province of Quebec, Canada. To do so, we conducted tree marking simulations and value recovery assessments in 14 managed stands distributed across the northern hardwood range of Quebec. Our results confirmed that the simplified tree marking regime not only facilitated stand improvement by removing a greater proportion of low-vigour trees, but also recovered significantly more value (17% on average) at the stand scale. By prioritizing the removal of trees with crown dieback, the simplified regime was superior at salvaging the current value of low-vigour trees before they die or decline in quality. Based on our results, we propose simplified and empirically-validated tree marking guidelines for northern hardwood forests.

In northern hardwood forests, selection silviculture aims to remove low-vigor trees that are likely to die or grow slowly to increase the growth of the remaining high-vigor trees, particularly those afforded more exposure to direct light. However, few studies have quantified the relative importance of crown position and vigor in determining growth and mortality. In this article, we did so for the most common species, sugar maple (Acer saccharum Marsh.), and we quantified the difference in growth and mortality between each of four crown classes to determine whether fewer classes can be used to describe competition-related variation in growth. Our results show that mortality is primarily determined by vigor, competition reduces growth more than the defects used to assess vigor, and there is only a modest difference in growth between dominant and co-dominant trees, indicating that these two classes can be merged because they are effectively released, unlike trees that are surrounded by competitors. Based on these results, we conclude that stand improvement should not be prioritized over crown spacing, and that tree markers should release surrounded trees to whatever extent possible, including as many trees as possible and low-vigor trees where necessary. We identified three ways to balance stand improvement and crown spacing in selection-managed northern hardwood forests. First, tree markers should not only release high-vigor trees, but also low-vigor trees that will be retained. Second, tree markers should focus on releasing trees surrounded by competitors rather than dominant and co-dominant trees. Third, rather than maximizing lateral light exposure for a few select trees, tree markers should release trees to whatever extent possible, including as many trees as possible and low-vigor trees where necessary. Finally, we provide a heuristic method for classifying crown position and implementing our spacing recommendations.

Northern hardwoods are susceptible to a wide range of defects that can reduce the amount of sound wood with desirable qualities, such as the clear sapwood of sugar maple trees. Yet, the rate at which trees decline in quality due to the development of such defects has never been quantified in northern hardwood forests due to a dearth of repeat inventories that record the appearance of defects over time. As a result, it remains uncertain whether, and how, selection management reduces the probability of decline in quality. In this study, we quantify the rate at which trees decline in quality due to the development of defects, and we test several hypotheses regarding the influence of selection management on quality. Our results show that (1) the probability of decline in quality increases as trees grow larger; (2) crown dieback also increases the probability of decline in quality; (3) the probability of decline in quality is slightly lower in managed stands than in unmanaged stands, and (4) the probability of decline in quality increases with the mean annual temperature of the site. Finally, we combined our estimates of the probability of decline in quality with previous estimates of the probability of mortality to assess the overall risk associated with retaining trees of different species, sizes, and vigour profiles. The resulting metric can inform efforts to improve the management of northern hardwood forests by providing an integrated estimate of the risk that the value of a tree will be reduced, or eliminated, due to mortality or decline in quality.

Northern hardwood forests include many degraded stands dominated by trees of low vigour due to past management. To facilitate the implementation of stand improvement, several classification systems have been developed to help tree markers visually assess tree vigour at time of harvest based on the presence of in-dividual defects. Because very few studies have tried to empirically validate such systems, it remains uncertain whether many of these defects should be used to guide the tree marking process. In this study, we assess tree vigour using repeated measurements collected as part of long-term silvicultural trials conducted in 615 permanent plots throughout the northern hardwood forest of Quebec, Canada. We aimed to determine whether the defects that are commonly used for classification have a significant effect on both growth and survival over three decades, using 9,338 sugar maple and 1,316 yellow birch trees. We also conducted a retrospective analysis to quantify the rate at which vigorous trees develop defects. Our results confirmed that crown dieback is by far the best indicator of vigour for both sugar maple and yellow birch trees. Conversely, our results revealed that stem defects did not contribute much to explaining the variation in vigour, except for the presence of cankers and fungi, which had modest effects. Consequently, stem defects should not be used as the main indicators of tree vigour, and existing classification systems should be simplified by reducing the number of stem defects under consideration for this purpose. Lastly, our results showed that the rate that vigorous trees develop defects increased with increasing diameter, more so than the probability of surviving. Thus, assessing the risk of retaining large trees should not only be based on survival, but also on the risk of developing defects that reduce the growth and value of trees.

Boreal forests are experiencing severe climatic changes that vary widely across the broad geographic distribution of the biome. The changes are greatest near the subarctic treeline where trees often exhibit high climatic sensitivity because climatic conditions approach the limits of their physiological tolerance. Despite the importance of subarctic boreal forests, the lack of field-acquired growth data remains a critical issue that limits the generalization of forest productivity models across the entire boreal biome. Using tree-ring chronologies from remote stands distributed along three latitudinal gradients ranging from 65 to 102°W, we investigated recent trends in black spruce growth and their relationships with recent climate warming near the subarctic treeline in eastern Canada. Our results show a generally positive effect of temperature and a negative effect of precipitation, both indicating that black spruce growth is temperature-limited near its northern range limit. However, we observed a strong gradient in temperature-growth coupling within a small latitudinal gradient (about one degree of latitude), where strong temperature constraints appear limited to the northernmost, coldest stands. Moreover, the positive growth response to temperature decreased from wetter to dryer sites and climate-growth coupling declined over the study period in the driest sites. These results suggest that the growth increase associated with warmer temperature may be limited by reduced precipitation and potential moisture limitation. Lastly, our results suggest that acute climatic events have the potential to induce abrupt shifts in tree climate-growth relationships. Such results indicate that the expected beneficial effect of warming on high latitude tree growth may be less generalized and more complex than previously thought in northeastern Canada, perhaps due to factors other than temperature, which might confound the climate-growth coupling southwards. Thus, our results highlight the need for a better understanding of additional growth drivers in these poorly studied regions and for physiologically informed definitions of acute climatic events, in order to refine broad-scale forest productivity modeling.

Data capturing multiple axes of tree size and shape, such as a tree's stem diameter, height and crown size, underpin a wide range of ecological research-from developing and testing theory on forest structure and dynamics, to estimating forest carbon stocks and their uncertainties, and integrating remote sensing imagery into forest monitoring programmes. However, these data can be surprisingly hard to come by, particularly for certain regions of the world and for specific taxonomic groups, posing a real barrier to progress in these fields. To overcome this challenge, we developed the Tallo database, a collection of 498,838 georeferenced and taxonomically standardized records of individual trees for which stem diameter, height and/or crown radius have been measured. These data were collected at 61,856 globally distributed sites, spanning all major forested and non-forested biomes. The majority of trees in the database are identified to species (88%), and collectively Tallo includes data for 5163 species distributed across 1453 genera and 187 plant families. The database is publicly archived under a CC-BY 4.0 licence and can be access from: https://doi.org/10.5281/zenodo.6637599. To demonstrate its value, here we present three case studies that highlight how the Tallo database can be used to address a range of theoretical and applied questions in ecology-from testing the predictions of metabolic scaling theory, to exploring the limits of tree allometric plasticity along environmental gradients and modelling global variation in maximum attainable tree height. In doing so, we provide a key resource for field ecologists, remote sensing researchers and the modelling community working together to better understand the role that trees play in regulating the terrestrial carbon cycle.

Tree stems have been identified as globally significant methane (CH 4 ) sources; however, little information exists on emissions from tree wounds and branches. CH 4 emissions can occur from the decomposition of anaerobic heartwood, which is also associated with wounds; CH 4 may also be transported through the transpiration stream and emitted from branches. We compared CH 4 emissions between tree stems and branches and assessed whether trees with major wounds emit more than those without. CH 4 fluxes were measured from stems, branches, and wounds (classified as major or minor) of two dominant tree species in an upland temperate forest, and from the soil, and scaled up to the stand level. Branches and stems of both species emitted CH 4 , and the per unit area emission rates from branches were similar to (or in some cases greater than) stems. Trees with major wounds had greater CH 4 emission rates than those without, from unblemished sections of their stems and from the wounds. At the stand scale, branches, stems, and wounds accounted for 83%, 9%, and 8% of net CH 4 emissions from trees, respectively, and collectively offset 63% of the soil CH 4 sink. These results indicate that tree branches and wounds can be important CH 4 sources in forests.

We reviewed recent literature to identify the positive and negative effects of thinning on both stand- and tree-level resistance and resilience to four stressors that are expected to increase in frequency and/or severity due to global change: (1) drought, (2) fire, (3) insects and pathogens, and (4) wind. There is strong evidence that thinning, particularly heavy thinning, reduces the impact of drought and also the risk and severity of fire when harvest slash is burned or removed. Thinning also increases the growth and vigor of residual trees, making them less susceptible to eruptive insects and pathogens, while targeted removal of host species, susceptible individuals and infected trees can slow the spread of outbreaks. However, the evidence that thinning has consistent positive effects is limited to a few insects and pathogens, and negative effects on root rot infection severity were also reported. At this point, our review reveals insufficient evidence from rigorous experiments to draw general conclusions. Although thinning initially increases the risk of windthrow, there is good evidence that thinning young stands reduces the long-term risk by promoting the development of structural roots and favouring the acclimation of trees to high wind loads. While our review suggests that thinning should not be promoted as a tool that will universally increase the resistance and resilience of forests, current evidence suggests that thinning could still be an effective tool to reduce forest vulnerability to several stressors, creating a window of opportunity to implement longer term adaptive management strategies such as assisted migration. We highlight knowledge gaps that should be targeted by future research to assess the potential contribution of thinning to adaptive forest management. One of these gaps is that studies from boreal and tropical regions are drastically underrepresented, with almost no studies conducted in Asia and the southern hemisphere. Empirical evidence from these regions is urgently needed to allow broader-scale conclusions.

Previous attempts to quantify methane (CH4) fluxes from tree foliage have yielded ambiguous results, and very few studies have measured in situ foliar CH4 fluxes, particularly in upland sites. Here we quantify CH4 fluxes from tree foliage in upland and lowland temperate forests in central Ontario, Canada. Foliar CH4, carbon dioxide, and water vapor fluxes were measured in direct sunlight and imposed darkness using an off-axis-integrated cavity output spectroscopy system, and results were scaled to the stand level using estimates of sunlit and shaded leaf area index. We show that foliage in the upland site was consistently a CH4 sink during the day (− 0.54 nmol m−2 s−1 ± 0.06 SE in direct sunlight), representing about 38

Changing climates are altering the structural and functional components of forest ecosystems at an unprecedented rate. Simultaneously, we are seeing a diversification of public expectations on the broader sustainable use of forest resources beyond timber production. As a result, the science and art of silviculture needs to adapt to these changing realities. In this piece, we argue that silviculturists are gradually shifting from the application of empirically derived silvicultural scenarios to new sets of approaches, methods and practices, a process that calls for broadening our conception of silviculture as a scientific discipline. We propose a holistic view of silviculture revolving around three key themes: observe, anticipate and adapt. In observe, we present how recent advances in remote sensing now enable silviculturists to observe forest structural, compositional and functional attributes in near-real-time, which in turn facilitates the deployment of efficient, targeted silvicultural measures in practice that are adapted to rapidly changing constraints. In anticipate, we highlight the importance of developing state-of-the-art models designed to take into account the effects of changing environmental conditions on forest growth and dynamics. In adapt, we discuss the need to provide spatially explicit guidance for the implementation of adaptive silvicultural actions that are efficient, cost-effective and socially acceptable. We conclude by presenting key steps towards the development of new tools and practical knowledge that will ensure meeting societal demands in rapidly changing environmental conditions. We classify these actions into three main categories: re-examining existing silvicultural trials to identify key stand attributes associated with the resistance and resilience of forests to multiple stressors, developing technological workflows and infrastructures to allow for continuous forest inventory updating frameworks, and implementing bold, innovative silvicultural trials in consultation with the relevant communities where a range of adaptive silvicultural strategies are tested. In this holistic perspective, silviculture can be defined as the science of observing forest condition and anticipating its development to apply tending and regeneration treatments adapted to a multiplicity of desired outcomes in rapidly changing realities.

The Canadian forest sector requires detailed information regarding the amount and characteristics of the forest resource. To address these needs, inventory systems that spatially quantify timber and other forest related ecosystem services are required, that are accurate, comprehensive and timely. The Assessment of Wood properties using Remote Sensing (AWARE) was a five-year project involving collaboration between seven Canadian universities, and seven forest companies with support provided by provincial and federal forestry agencies and other non-for-profit forestry focused organisations. AWARE provided methods and tools to enhance the characterization of forests at national, landscape and individual tree scales. The project supported 24 post-doctoral fellows, PhD and MSc students that examined the roles that advanced three-dimensional remote sensing technologies can play in the development of accurate forest inventory systems across Canada. In this review we examine the AWARE research project, review research highlights, key outcomes, future research needs, and provide an assessment of successes and challenges the project faced over its five-year lifetime.

Le secteur forestier canadien a besoin d’information détaillée au sujet de la quantité et des caractéristiques des ressources forestières. Pour répondre à de tels besoins, des systèmes d’inventaire exacts, complets et opportuns qui quantifient spatialement le bois d’œuvre et les autres services écosystémiques liés aux forêts sont nécessaires. Le projet quinquennal AWARE (Assessment of Wood Attributes using Remote sEnsing [évaluation des attributs du bois à l’aide de la télédétection]) était une collaboration entre sept universités canadiennes et sept entreprises forestières soutenue par des organismes forestiers provinciaux et fédéraux et d’autres organismes sans but lucratif-axés sur la foresterie. AWARE a fourni des méthodes et des outils pour améliorer la caractérisation des forêts à une échelle nationale, du paysage et de l’arbre individuel. Vingt-quatre boursiers de recherches postdoctorales et étudiants au doctorat et à la maîtrise se sont associés au projet et ont examiné les rôles que les technologies de télédétection tridimensionnelle (3D) de pointe peuvent jouer dans la conception de systèmes d’inventaire forestier précis partout au Canada. Dans le présent article de revue, nous nous penchons sur le projet de recherche AWARE, les points saillants de la recherche, les résultats clés et les besoins futurs en recherche et présentons une évaluation des réussites et des défis auxquels le projet a été confronté au cours de ses cinq ans.

Until recently it has been assumed that the main site of methane exchange between the terrestrial biosphere and the atmosphere is soils. However, recent research has shown that tree stems can contribute substantial methane flux; moreover, the few studies that have examined foliar methane flux in situ have found non-negligible fluxes. Foliar methane uptake appears to be mediated by methanotrophic endophytes and is appreciable in upland forests where soils also show net methane oxidation. In contrast, foliar release of methane can occur in lowland forests in which soils show net methane release as a result of transport of dissolved methane through the xylem stream. There is evidence that both foliar methane uptake (and release) are mediated by stomatal conductance, suggesting that the capacity for foliar methane fluxes may be closely related to other gas-exchange-related functional traits of leaves that covary along the fast-slow leaf economics spectrum. Here we compile data on reported rates of foliar methane uptake in upland forests to test this idea. Data from three northern forest sites in Canada and Sweden indicate that: (1) methane uptake capacity is generally higher in broadleaf angiosperms than in conifers; and (2) methane uptake capacity is positively correlated with leaf nitrogen content, but shows a saturating pattern with a maximum rate of ~0.6-0.7 nmol m-2 s-1. We contend that foliar methane uptake has been under-appreciated as an important process in the global carbon cycle, but that patterns suggest a close linkage to other plant traits that will permit integration of this process into existing carbon cycle models.

Coarse woody debris (CWD) is a dynamic source of nutrients in managed forests of eastern North America. The temporal patterns of nutrient export from CWD are challenging to study, and efficient methods are lacking. We made empirical measurements of CWD density, volume, and nutrient concentrations in 5 stages of decay, and paired them with a decay class transition model to project the long-term nutrient dynamics of CWD in a managed northern hardwood forest. The model was used to describe stand-level changes in CWD nutrient pools over 40 years following a selection harvest, and to compare CWD nutrient pools in managed and unmanaged stands. The C content of CWD decreased throughout decay, and mirrored density losses. N, P, and Ca content increased throughout decay, Mg content remained relatively constant, and K was rapidly lost. At the stand level, despite a rapid loss of mass and density, the model projected an initial gain in total N, P and Ca stored in CWD during the first 4–8 years after harvest, whereas net C, Mg, and K began to decrease immediately. The average volume, mass, C and K stocks of CWD in managed stands were approximately 10% lower than unmanaged stands, and N, P, Ca, and Mg were up to 16% lower. This is the first study to use a decay class transition model to study the dynamics of nutrients other than C, and the model serves as a template upon which other models of CWD decay can be built.

Climate strongly limits the physiological processes of trees near their range limits, leading to increased growth sensitivity. Northeastern North America is experiencing considerable warming, so the growth of trees near the northern treeline represents a key indicator of forest responses to climate change. However, tree-ring series and corresponding climatic data are scarce across the forest-tundra ecotone when compared to southern boreal regions, resulting in fewer studies on growth-climate relationships focused on this ecotone. Using daily climatic data, we identified trends in growing season heat accumulation and the intensity of acute climatic events over the last several decades in the southern and the northern parts of the forest-tundra ecotone in northeastern North America, and investigated their influence on black spruce radial growth. We found that black spruce trees responded positively to the increase in growing season temperatures and heat wave intensity, suggesting that growth is currently limited by suboptimal temperatures. While tree growth in the southern region generally benefited from warm spring temperatures, vulnerability to late spring frosts reduced tree growth in the northern region and increased probability of abrupt growth decline. In this region, late spring frosts offset approximately half of the additional growth that would otherwise occur over the course of a warm growing season. This vulnerability of northern trees may result from local adaptations to short growing seasons, which initiate biological activities at colder temperatures in the spring. Overall, our results highlight the need to explicitly incorporate acute climatic events into modeling efforts in order to refine our understanding of the impact of climate change on forest dynamics.