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Despite the mounting imperative for managers to help forests adapt to the rapidly shifting climate and related stressors, significant gaps remain between recommendations for adaptive forest management and its actual implementation across the globe. The research presented here offers a novel qualitative analysis regarding the current nature, extent, and drivers of adaptive management in the northeastern United States. Based on 32 in-depth semi-structured interviews with rural (n = 17) and urban foresters (n = 15) across New England and New York, we share a summary of (1) important environmental drivers of adaptation across the region, (2) commonly employed adaptive strategies, (3) significant barriers to adaptation, and (4) approaches to working through named barriers. We categorize adaptive practices of foresters as options of resistance, resilience, or transition, highlighting opportunities to increase the use of all three options across the landscape.

Forester and logger responses to the invasive emerald ash borer (EAB) could substantially affect regions across the United States. We analyzed forester and logger responses to EAB in Massachusetts and Vermont, exploring characteristics associated with purposeful targeting of substantial ash properties; managing forests differently because of EAB; and regeneration goals. One-third of respondents increased timber sales on ash properties, motivated by ecological, not economic, impacts of EAB. Nearly 60% said EAB changed their management activity in stands with ash; changes influenced by the ecological impact of EAB and not economic factors. Those influenced by EAB’s ecological impact to choose properties with substantial ash were more likely to have increased harvest area size, sawtimber removal, and harvest intensity. Loggers were more likely than foresters to remove small-diameter ash and low-grade trees. Both rated regenerating economically valuable species well adapted to the site as their highest essential priority. Study Implications: There is a finite window to address emerald ash borer (EAB) to sustain ash and its cultural, ecological, and economic benefits. Given the time constraint and limited resources available to address EAB, finding strategic approaches to mitigate EAB impact is critical. This survey sought to understand forester and logger response to EAB; given their impact on the landscape, informing their management strategies is one critical approach to the conservation of ash. Understanding the ecological impact of current management approaches could help optimize silvicultural strategies. Silvicultural strategies mitigating EAB ecological impacts would likely be of greatest interest to foresters and loggers.

Spatial arrangement of trees is determined by a complex suite of factors including disturbance history, competition, and resource availability. These spatial patterns drive adaptive capacity by influencing arrangement of growing space, neighborhood competitive relationships, and disturbance response, with irregular patterns supporting higher adaptive capacity. While spatial structure in relation to disturbance and climate change resilience has been studied in dry conifer forests and old-growth temperate forests, it has never been explored in the context of climate adaptive management in mesic, second-growth forests. To address this gap, we analyzed tree spatial patterns in second-growth northern hardwood forests under four different climate adaptation management approaches: no action; resistance or resilience to impacts of climate change; and transition to future-adapted forest types. We used spatial point statistics approaches to describe how patterns differed among the four treatments. We found that the treatments focused on future adaptation led to patterns with variable tree spacing and clumping, while those focused on perpetuating current conditions resulted in less pattern variation. This indicates that adaptation strategies that include uneven-aged regeneration methods that restore and maintain tree spatial patterns historically generated by gap dynamics can be successful in altering resource availability patterns and adaptation space in forest stands.

Black ash ( Fraxinus nigra Marsh.) forests of north-central North America are currently threatened by the non-native emerald ash borer ( Agrilus planipennis, EAB). Despite the wide distribution of F. nigra ecosystems, and the concern over EAB impact, little is known about their structure and natural stand dynamics. We sampled six old-growth F. nigra stands to assess structure, composition, tree recruitment, and past disturbance. Dendrochronological results revealed that disturbance rates fluctuated markedly over the past 200 years or more, but remained relatively low, suggesting small- to moderate-scale disturbances. Recruitment age structures revealed that ( i) F. nigra is able to maintain long-term dominance through extended longevity as a canopy tree, and ( ii) these systems have fairly continuous recruitment over time, with most sites showing F. nigra recruitment in every decade in the chronology. We speculate that recruitment is coupled with water table fluctuations, in addition to canopy disturbance, as these stands are subject to both frequent flooding and effective soil drought (given the shallow root systems). The low rates of past canopy disturbance and associated gap-phase replacement by F. nigra highlight the potential for dramatic shifts in these systems following emerald ash borer invasion and subsequent canopy tree mortality.

Relative frequency distribution of observed annual mortality expressed in aboveground (AG) carbon (C) (Mg CO

The invasive shrub Scotch broom (Cytisus scoparius (L.) Link) is a pervasive threat to regenerating Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) stands in the Pacific Northwest, USA. Field observations indicate that the susceptibility of areas to Scotch broom invasion and dominance can vary by site. We selected 10 sites throughout the western Pacific Northwest that spanned a gradient of soil textures and other factors to test the site-specific susceptibility of Douglas-fir to overtopping by Scotch broom. We expected to find that the ability of Scotch broom to dominate a site was mediated by site-level factors, particularly those influencing soil water - the most limiting factor to growth in the region. We found Scotch broom and Douglas-fir were inversely affected by site-level factors. In general, Douglas-fir absolute height growth rates were more competitive with those of Scotch broom on fine-textured soils than on more coarsely textured soils. We also found Douglas-fir to have a more dramatic response to increasing down woody material than Scotch broom. Scotch broom height growth approached an asymptote at 3 m. Sites with fast-growing Douglas-fir were able to surpass this height 6-7 years after planting and appear likely to avoid suppression by Scotch broom. USDA National Institute for Food and Agriculture [GRANT11325729] Published version We thank the Washington Department of Natural Resources, Green Diamond Resource Company, Port Blakely Tree Farms, the National Fish and Wildlife Foundation, and Olympic Resource Management for providing the sites needed for this study. We also thank Dave Peter and James Dollins for their help setting up and maintaining this study, as well as, taking field measurements. Janet Prevey and Matthew Russell helped with model construction. Funding for this project was provided by the USDA National Institute for Food and Agriculture (Grants gov. No. GRANT11325729). Public domain – authored by a U.S. government employee

Epigeous fungal fruiting has important impacts on fungal reproduction and ecosystem function. Forest disturbances, such as timber harvest, impact moisture, host availability, and substrate availability, which in turn may drive changes in fungal fruiting patterns and community structure. We surveyed mushrooms in 0.4 ha patch cuts (18 months post-harvest) and adjacent intact hardwood forest in northern New Hampshire, USA, to document the effects of timber harvest on summer fruiting richness, biomass, diversity, and community structure of ectomycorrhizal, parasitic, and saprobic mushroom taxa. Fungal fruiting richness, diversity, and community heterogeneity were greater in intact forests than patch cuts. Among functional groups, ectomycorrhizal fruiting richness, diversity, and biomass were greater in unharvested areas than in the patch cuts, but parasitic and saprobic fruiting did not differ statistically between the two forest conditions. Our findings suggest that timber harvest simplifies fungal fruiting communities shortly after harvest, in particular triggering declines in ectomycorrhizal taxa which are important symbionts facilitating tree establishment and regeneration. Multi-aged silvicultural practices that maintain mature forest conditions adjacent to and throughout harvested areas through deliberate retention of overstory trees and downed woody material may promote fungal fruiting diversity in regenerating stands.

Several aspects of the forest carbon cycle have not been examined in detail, including sources of variation in carbon dioxide (CO2) emissions from coarse woody material (CWM). To address this knowledge gap, we examined CO2 emissions from Acer saccharum Marshall logs within four harvesting treatments, using closed chambers fitted to the logs. We found that CO2 emissions were highest for logs in small (31.8 ± 20.4 µmol·CO2·m−3·s−1) and large gaps (29.6 ± 24.4 µmol·CO2·m−3·s−1) compared to those in control (13.9 ± 8.3 µmol·CO2·m−3·s−1) and thinned matrix (13.6 ± 8.0 µmol·CO2·m−3·s−1) treatments. CO2 flux rates did not differ between gap sizes, but they increased with temperature, which was higher in the small gap treatment. In addition, two individual logs fitted with multiple closed chambers revealed significant within-log variability in CO2 emissions. On a subset of logs repeatedly sampled throughout the day, we found that log surface temperature generally peaked at midday and was positively correlated with CO2 emissions, although this relationship was weak in one log. This study provides insight into sources of variation in CO2 emissions from CWM while improving our understanding of the forest carbon cycle.

Uncertainty surrounding global change impacts on future forest conditions has motivated the development of silviculture strategies and frameworks focused on enhancing potential adaptation to changing climate and disturbance regimes. This includes applying current silvicultural practices, such as thinning and mixed-species and multicohort systems, and novel experimental approaches, including the deployment of future-adapted species and genotypes, to make forests more resilient to future changes. In this chapter, we summarize the general paradigms and approaches associated with adaptation silviculture along a gradient of strategies ranging from resistance to transition. We describe how these concepts have been operationalized and present potential landscape-scale frameworks for allocating different adaptation intensities as part of functionally complex networks in the face of climate change.

Temperate mixedwoods (hardwood–softwood mixtures) in central and eastern United States and Canada can be classified into two overarching categories: those with shade-tolerant softwoods maintained by light to moderate disturbances and those with shade-intolerant to mid-tolerant softwoods maintained by moderate to severe disturbances. The former includes red spruce (Picea rubens Sarg.), balsam fir (Abies balsamea (L.) Mill.), or eastern hemlock (Tsuga canadensis (L.) Carr.) in mixture with northern hardwood species; the latter includes pine (Pinus) – oak (Quercus) mixtures. Such forests have desirable socio-economic values, wildlife habitat potential, and (or) adaptive capacity, but management is challenging because one or more softwood species in each can be limited by depleted seed sources, narrow regeneration requirements, or poor competitive ability. Appropriate silvicultural systems vary among mixedwood compositions depending on shade tolerance and severity of disturbance associated with the limiting softwoods, site quality, and level of herbivory. Sustainability of mixedwood composition requires that stand structure and composition be managed at each entry to maintain vigorous trees of species with different growth rates and longevities and to encourage development of advance reproduction or seed-producing trees of desired species. Regardless of silvicultural system, maintaining seed sources of limiting softwoods, providing suitable germination substrates, and controlling competition are critical. Here, we describe commonalities among temperate mixedwoods in central and eastern North America and present a framework for managing them.

As interest in managing and maintaining mixedwood forests in the northern United States (US) grows, so does the importance of understanding their abundance and distribution. We analyzed Forest Inventory and Analysis data for insights into mixedwood forests spanning 24 northern US states from Maine south to Maryland and westward to Kansas and North Dakota. Mixedwoods, i.e., forests with both hardwoods and softwoods present but neither exceeding 75%–80% of composition, comprise more than 19 million hectares and more than one-quarter of the northern US forest. They are most common in the Adirondack – New England, Laurentian, and Northeast ecological provinces but also occur elsewhere in hardwood-dominated ecological provinces. These mixtures are common even within forest types nominally categorized as either hardwood or softwood. The most common hardwoods within those mixtures were species of Quercus and Acer, and the most common softwoods were species of Pinus, Tsuga, and Juniperus. Although mixedwoods exhibited stability in total area during our analysis period, hardwood saplings were prominent, suggesting widespread potential for eventual shifts to hardwood dominance in the absence of disturbances that favor regeneration of the softwood component. Our analyses suggest that while most mixedwood plots remained mixedwoods, harvesting commonly shifts mixedwoods to either hardwood- or softwood-dominated cover types, but more specific information is needed to understand the causes of these shifts.

Alterations in global climate via extreme precipitation will have broadscale implications on ecosystem functioning. The increased frequency for drought coupled with heavy, episodic rainfall will likely generate impacts to biotic and abiotic processes across aquatic and terrestrial ecosystems. Despite demonstrated shifts in global precipitation, less is known about how extreme precipitation interacts with biophysical factors at controlling future demographic processes, especially those sensitive to climate extremes such as organismal recruitment and survival. We utilized a field-based precipitation manipulation experiment in 0.1 ha forest canopy openings to test future climate scenarios characterized by extreme precipitation on temperate tree seedling survival. The effect of planting seedbed (undisturbed leaf litter/organic material versus scarified, exposed mineral soils), seedling ontogeny, species, and functional traits were examined against four statistically defined precipitation scenarios. Results indicate seedlings grown within precipitation treatments characterized by heavy, episodic rainfall preceded by prolonged drying responding similarly to drought treatments lacking episodic inputs. Moreover, among all treatment conditions tested, scarified seedbeds most strongly affected seedling survivorship (odds ratio 6.9). Compared to any precipitation treatment, the effect size (predicted probabilities) of seedbed was over twice as important at controlling seedling survivorship. Yet, the interaction between precipitation and seedbed resulted in a 27.9% improvement in survivorship for moisture sensitive species. Seedling sensitivity to moisture was variable among species, most closely linked to functional traits like seed mass. For instance, under dry moisture regimes, survivorship increased linearly with seed mass (log transformed; adjusted R

Sustaining the structure, function, and services provided by forest ecosystems in the face of changing climate and disturbance regimes represents a grand challenge for forest managers and policy makers. To address this challenge, a range of adaptation approaches have been proposed centered on conferring ecosystem resilience and adaptive capacity; however, considerable uncertainty exists regarding how to translate these broad and often theoretical adaptation frameworks to on-the-ground practice. Complicating this issue has been movement away, in some cases, from other recent advances in forest management, namely ecological silviculture strategies that often focus on restoration. In this paper, we highlight the areas of compatibility and conflict between these two frameworks by reviewing the four principles of ecological silviculture (continuity, complexity and diversity, timing, and context) from the perspective of global change adaptation. We conclude that given many commonalities between the outcomes of ecological silviculture and conditions conferring adaptive capacity, the four principles remain a relevant starting point for guiding operationalization of often theoretical adaptation strategies.

The emerald ash borer (EAB) has killed ash species (Fraxinus L.) in much of eastern North America, but it has yet to reach the vast ash wetlands in northern Minnesota, USA. In these wetlands, a single species, black ash (Fraxinus nigra Marsh.) comprises a majority of trees and has a foundational role in controlling ecosystem function. Given the likelihood of wide-spread mortality of black ash from EAB and the likelihood of severe ecosystem impacts, we examined the potential for co-occurring tree species to replace black ash, either through gap filling in the overstory or release from the understory. We addressed this objective by examining woody plant communities in 32 mature black ash sites located across a large geographic region and inclusive of two distinct wetland types as defined by hydrologic regime. Our results indicate a region-wide lack of species capable of replacing black ash in both wetland hydrologic types; thus there is very low existing potential for replacement of black ash from expansion in the overstory or through release in the understory. These results point to an urgent need for silvicultural intervention to identify and establish future-adapted non-ash tree species so as to promote resilience in the face of EAB by maintaining aspects of the foundational role of black ash in controlling ecosystem functions.

As part of the Carrefour Forêts 2019 Conference, the forest research branch of Quebec’s Ministère des Forêts, de la Faune et des Parcs and the Canadian Wood Fibre Centre of Natural Resources Canada organized jointly the symposium “Adaptive silviculture to climate change: from concepts to reality”. The symposium brought together a hundred actors from the forest sector including engineers, biologists, technicians, private woodlot owners, professors, researchers and students. Speakers from different regions of Quebec and Vermont shared current knowledge related to adaptive silviculture in order to nurture reflexion and dialogue about actions that can be taken today to help forests to adapt with the anticipated changes. The symposium covered the theoretical framework of adaptive silviculture, then offered case studies of different ecosystems, innovative tools or research initiatives. The symposium also included presentations by practitioners who described the challenges and opportunities offered by adaptive silviculture in their professional practice. Based on an interactive discussion, participants identified increased drought events, partial cuttings and mixed-species plantations as important topics on which researchers and practitioners should interact in years to come.

Dans le cadre du Carrefour Forêts 2019, le colloque Sylviculture d’adaptation aux changements climatiques : des concepts à la réalité, organisé conjointement par la Direction de la recherche forestière du ministère des Forêts, de la Faune et des Parcs du Québec et le Centre canadien sur la fibre de bois de Ressources naturelles Canada, a rassemblé une centaine d’acteurs du milieu forestier incluant des ingénieurs forestiers, des biologistes, des techniciens forestiers, des propriétaires de boisés, des professeurs, des chercheurs et des étudiants. Des conférenciers de différentes régions du Québec et du Vermont ont partagé les connaissances actuelles en rapport avec la sylviculture d’adaptation afin d’amorcer la réflexion et le dialogue quant aux actions pouvant être entreprises dès maintenant pour favoriser l’adaptation des forêts aux changements anticipés. Les présentations ont abordé les fondements théoriques de la sylviculture d’adaptation, pour ensuite présenter des réflexions ou des études de cas portant sur différents types d’écosystèmes, des outils innovants ou des initiatives de recherche. Le colloque a également laissé une place aux praticiens qui ont pu décrire les défis et les occasions qu’offre la sylviculture d’adaptation dans leur pratique professionnelle. Au terme d’une activité interactive, les participants ont ciblé les sécheresses accrues, les coupes partielles et les plantations mélangées comme des thèmes importants qui devraient animer les échanges entre les chercheurs et les praticiens dans les années à venir.

Cold-air pooling is a global phenomenon that frequently sustains low temperatures in sheltered, low-lying depressions and valleys and drives other key environmental conditions, such as soil temperature, soil moisture, vapor pressure deficit, frost frequency, and winter dynamics. Local climate patterns in areas prone to cold-air pooling are partly decoupled from regional climates and thus may be buffered from macroscale climate change. There is compelling evidence from studies across the globe that cold-air pooling impacts plant communities and species distributions, making these decoupled microclimate areas potentially important microrefugia for species under climate warming. Despite interest in the potential for cold-air pools to enable species persistence under warming, studies investigating the effects of cold-air pooling on ecosystem processes are scarce. Because local temperatures and vegetation composition are critical drivers of ecosystem processes like carbon cycling and storage, cold-air pooling may also act to preserve ecosystem functions. We review research exploring the ecological impacts of cold-air pooling with a focus on vegetation, and then present a new conceptual framework in which cold-air pooling creates feedbacks between species and ecosystem properties that generate unique hotspots for carbon accrual in some systems relative to areas more vulnerable to regional climate change impacts. Finally, we describe key steps to motivate future research investigating the potential for cold-air pools to serve as microrefugia for ecosystem functions under climate change.

Attributes of deadwood in forests, including quantity, landscape position, and state of decay, influence numerous ecosystem processes such as wildfire behavior, tree regeneration, and nutrient cycling. Attributes of deadwood that vary over subdiurnal time steps, including moisture, have not been routinely measured despite the profound effects they have on ecosystem processes. To improve our understanding of forest deadwood subdiurnal moisture dynamics, we installed an intensive time-domain reflectometry (TDR) sensor network in a log and surrounding soil within a northern hardwood forest in New England, United States. Intensive monitoring during a partial growing season indicated that deadwood moisture was dynamic but similar to that of surrounding soils at 15-min intervals, especially during wetting and drying events. Field results and bench analysis of the sample log revealed numerous challenges when attempting to monitor deadwood moisture with TDR such as heterogeneous and (or) advanced decay confounding TDR moisture measurements in logs. An efficient, high-frequency TDR sensor network was demonstrated to record deadwood and soil moisture fluctuations, which provides an opportunity to refine our understanding of deadwood dynamics in the context of global change such as changing precipitation regimes.

Standardizing gross volume increment on periodic height increment of the dominant trees is a means of minimizing the effects of site quality and age in growth–growingstock relations; however, volume increment per height increment contains more information than just a normalization method for fitting growth models. This study builds on previous work suggesting that the cumulative sum of the ratios between individual-tree volume increment and height increment may be a direct measure of stand density. We used data from several levels of growing-stock studies for Douglas-fir, ponderosa pine, and red pine to explore this hypothesis. Regression analysis indicated that the sum of the ratios is proportional to (Dqx · N), the underlying equation form of Reineke’s stand density index. Stem growth is a function of canopy dynamics, and additional analyses showed that volume added per unit of height growth was also related to canopy architecture, increasing with decreasing live-crown ratio and increasing foliage density. The linkages between growth, canopy architecture, intermediary canopy dynamics, and (Dqx · N) support the hypothesis that the sum of the tree ratios between volume increment and height increment is a direct measure of site occupancy due to its association between growth and corresponding resource use. Study Implications: Stand density indices are fundamental to managing the development of forest stands to achieve habitat and production goals, and advanced statistical techniques are providing silviculturists with more precise tools to manage density. However, the increased precision is only available with data from self-thinning stands, rare in managed forests. Furthermore, silviculturists must assume that constant fractions of relative stand density are parallel to fitted self-thinning trajectories. The results of this study show that the slope of the stand density gradient can be determined without data from self-thinning stands and the gradient in stand density runs parallel to the trajectory of self-thinning stands.

1. Increasing heat and aridity in coming decades is expected to negatively impact tree growth and threaten forest sustainability in dry areas. Maintaining low stand density has the potential to mitigate the negative effects of increasingly severe droughts by minimizing competitive intensity. 2. However, the direct impact of stand density on the growing environment (i.e. soil moisture), and the specific drought metrics that best quantify that environment, are not well explored for any forest ecosystem. We examined the relationship of varying stand density (i.e. basal area) on soil moisture and stand-level growth in a long-term (multi-decadal), ponderosa pine Pinus ponderosa, forest management experiment. We accounted for the influence of stand-level density on moisture availability by measuring and modelling soil moisture using an ecosystem water balance model. 3. To quantify the growing environment, we developed metrics of ecological drought that integrate the influence of moisture availability in the soil with moisture demand by the atmosphere. We paired these results with stand-level dendrochronological data, avoiding the potential bias introduced from individual tree-based assessments, and used critical climate period analysis to identify the timing and duration of these drought metrics that most relate to forest growth. 4. We found that stand-level growth is highly responsive to the combination of high temperature and low soil moisture. Growth in all stands was negatively related to temperature and positively related to moisture availability, although the sensitivity of growth to those conditions varied among stand density treatments. Growth enhancement during cool years is greatest in low density stands. In addition, low density stands displayed substantially higher long-term average growth than higher density stands and maintained higher growth even when temperatures were high. Growth in low density stands also increased more than higher density stands in response to greater long-term moisture availability. 5. Synthesis and applications. We quantified the influence of stand-level density on the environmental conditions that determine tree growth and related forest growth to patterns of moisture supply and demand. Our drought metrics, and analytical approach for quantifying drought impacts on forest growth, are a novel approach for assessing forest vulnerability to drought under climate change. These results provide new perspective on the potential for density management to mitigate drought stress and maintain forest stand growth during and after drought events in water-limited forests.

The invasion by emerald ash borer (Agrilus planipennis) of extensive black ash wetlands in the upper Great Lakes region of North America is expected to alter plant community structure and composition and, therefore, abiotic factors like temperature and hydrology. We conducted two experiments to examine how changes in leaf litter could alter ecosystem function via 1) changes in litter breakdown and 2) aquatic invertebrate feeding. For the first experiment, we placed litter bags containing black ash (Fraxinus nigra), swamp white oak (Quercus bicolor), and lake sedge (Carex lacustris), in either control or clear-cut black ash plots. We found that black ash litter broke down 2-3 times faster than other species and broke down faster in control plots than in clear-cuts. There was no effect of clear cutting on swamp white oak or lake sedge breakdown rates. For the second experiment, we fed shredding caddisfly larvae (Limnephilus indivisus) one of six species: black ash, swamp white oak, lake sedge, balsam poplar (Populus balsamifera), American elm (Ulmus americana), or speckled alder (Alnus incana) for 14 days. Caddisflies had the highest survival and greater resource use when given black ash or speckled alder, which are abundant in black ash wetlands. These results suggest that loss of black ash will alter ecosystem processes via changes in the physical environment, changes in leaf litter properties, and changes in shredder processing rates of leaf litter.

Silvicultural decisions and forest-management practices in Minnesota represent the collaboration and partnership between forest managers from multiple organizations and forest researchers. To better understand current practices, trends, needs, and opportunities, Minnesota has invested in the collection of quantitative data on the application of silvicultural systems and forest-management activities in 1991, 1996, 2008, and 2017. Drawing on those data, the goal of our study is to summarize 26 years of data to characterize and quantify trends in forest-management practices. During this period of time, timberland ownership (acres) has increased, whereas harvested volume has decreased (cords). Across state, federal, county, forest industry, and tribal forest lands, which collectively represent the majority of timberlands in Minnesota, the clearcut system decreased from 91% of the harvested area in 1991 to 72 percent in 2017. In contrast, the proportion of total harvested area as part of shelterwood, seed tree, selection, and thinning treatments all more than doubled from 1991 to 2017. Factors influencing the changes relate to forest health and diseases, shifts in ownership structure, and shifts in organizational policy and/or goals. The factors identified mirror many of the trends forest managers are experiencing in other regions, nationally and internationally.

Do trees adjust support costs to the stem in order to maintain or boost allocation to foliage to compete for light? This question was addressed with data collected from three, long-term studies investigating the growth effects of controlled levels of competition for Alnus rubra, Pseudotsuga menziesii, and Pinus resinosa. Costs and benefits of marginal height were defined as the stem volume and foliage added when trees grew 1 m in height, respectively. Effects of competition effects on the distribution of these variables within tree populations were evaluated with growth dominance indexes (Gdv/dh and GdAl/dv, respectively). Competition effects on the distribution of relative height growth (Gdg) were also evaluated to verify mode of competition. The hypothesized simple tradeoff between marginal height cost and marginal height benefit was not supported with these data. Instead, Gdv/dh and GdAl/dh were linearly related for all three species. The values of Gdh were generally positive for all species supporting asymmetric competition within these plots. The strength of support for this hypothesis varied by species, however, with the shade intolerant A. rubra providing the strongest support and the more shade tolerant P. menziesii providing the least support. The age-adjusted values of P. menziesii of Gdh were only significantly greater than zero in the unthinned, control plots. The results suggest that competition effects on marginal height benefit translate to marginal height cost through biomechanical relationships between crown size and structure and stem dimensions. Competitive effects on stand dynamics can therefore be linked to a basic tree morphology that scales with height. Realized additions of stem volume and foliage per growing season are subsequently determined by the distribution of relative height growth.