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Silvicultural thinning can lead to rapid microclimatic changes for residual trees. Despite the benefits of decreased competition, thinning may induce 'thinning shock'--temporary negative physiological responses as trees acclimate to new conditions. We examined the impact of thinning on the microclimate and physiology of residual, previously shaded red spruce (Picea rubens Sarg.) trees relative to non-thinned controls. Both daily maximum temperature and vapor pressure deficit increased post thinning, with larger increases observed on hotter and drier days. In response to these environmental changes, we found clear evidence of physiological declines. At 1.7 weeks post thinning, we found a 0.59 MPa reduction in average midday water potential relative to control trees, which lasted for an additional 1.4 weeks. Thus, the trees in the thinning treatment were at or beyond published estimates of needle turgor loss. Thinning decreased the photosynthetic efficiency of current-year needles by 3.8% after 2 weeks, and it declined by 1.3% per week for the remainder of the growing season. These results suggest that thinning shock occurs in red spruce, a shade-adapted, climate-sensitive species. Thinning shock may contribute to the lagged growth responses commonly observed post thinning, and these effects may be more extreme in novel future climates. Key words: Picea rubens, water potential, silvicultural thinning, photosynthesis, microclimate, vapor pressure deficit, Introduction In the northeastern United States (US), climate change is driving warming and increasing the likelihood of extreme weather events (Vose et al. 2016; Karmalkar and Horton 2021). Average annual [...]

Despite the importance of financial outcomes to stand-level forest management decision-making, long-term assessments are rare. We compared the quality and value of mixed, northern conifer (Picea-Abies-Tsuga) stands in Maine, USA, treated with a range of silvicultural systems and exploitive cuttings for 65 years. Ten replicated treatments--single-tree selection and uniform shelterwood systems, commercial clearcutting, fixed and guiding diameter-limit cutting, and no cutting--were assessed for quality and value of standing and harvested trees. Selection systems resulted in good tree quality and high stand value, particularly when applied on a short cutting cycle, but small harvest volumes were not always commercially operable. Shelterwood system resulted in good tree quality, but changes in species values over time influenced financial outcomes. In contrast, commercial clearcutting and fixed diameter-limit cutting resulted in poor tree quality and low residual stand value after multiple harvests. Guiding diameter-limit cutting resulted in high stand value and is more appropriately characterized as a silvicultural system than exploitive harvesting when applied with harvest volume limits and seed tree retention. Overall, treatments focused on short-term financial gain led to degraded stand conditions, while those that sought to grow high-quality trees resulted in desirable outcomes over the long term. Key words: spruce-fir, shelterwood, selection cutting, exploitation, forest management. Malgre l'importance des resultats financiers resultant des prises de decisions en gestion forestiere des peuplements, les evaluations a long terme sont rares. Nous avons compare la qualite et la valeur de coniferes septentrionaux sur pied mixtes (Picea-Abies-Tsuga) dans le Maine, aux Etats-Unis, traites avec un eventail de systemes sylvicoles et de coupes d'exploitation durant 65 annees. Dix traitements reproduits--systemes de coupe progressive uniforme et de jardinage d'arbres individuels, coupes a blanc commerciales, coupes de diametre limite fixes et generales et absence de coupes--ont ete evalues en fonction de la qualite et de la valeur des arbres sur pied et des arbres recoltes. Les systemes de selection ont eu comme resultat une bonne qualite d'arbres et une valeur elevee des arbres sur pied, particulierement lorsqu'ils etaient appliques a un cycle court de coupes, mais les volumes reduits de recoltes n'etaient pas toujours exploitables sur le plan commercial. Le systeme de coupe progressive a eu comme resultat une bonne qualite d'arbres, mais les changements dans les valeurs des especes au fil du temps ont influence les resultats financiers. Par contre, la coupe a blanc commerciale et la coupe limitee a un diametre fixe ont eu comme resultat une mauvaise qualite d'arbres et une faible valeur residuelle des arbres sur pied apres de nombreuses recoltes. La coupe de diametre limite generale a eu comme resultat une valeur elevee des arbres sur pied et elle est caracterisee de maniere plus appropriee comme un systeme sylvicole plutot qu'une recolte d'exploitation lorsqu'elle est appliquee avec des limites du volume des recoltes et une sauvegarde des semenciers. Dans l'ensemble, les traitements axes sur les gains financiers a court terme ont entraine des conditions de degradation des arbres sur pied alors que ceux qui visaient a accroitre une qualite elevee des arbres ont mene a des resultats souhaitables a long terme. [Traduit par la Redaction] Mots-cles: epinette-sapin, coupe progressive, coupe de jardinage, exploitation, gestion forestiere., Introduction Forest landowners and managers make decisions about whether and how to manage forests based on a number of short- and long-term considerations. For commercial landowners, return on investment or [...]

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. Key words: mixed-species forests, deciduous-coniferous mixtures, silvicultural systems, tree regeneration, shade tolerance. Les forets mixtes (melanges de feuillus et de resineux) temperees du centre et de l'est des Etats-Unis et du Canada peuvent etre classees en deux categories principales : celles qui sont composees de resineux tolerants a l'ombre maintenus par des perturbations legeres a moderees et celles qui sont composees de resineux intolerants et semi-tolerants a l'ombre maintenus par des perturbations moderees a severes. La premiere categorie comprend l'epinette rouge (Picea rubens Sarg.), le sapin baumier (Abies balsamea (L.) Mill.) ou la pruche du Canada (Tsuga canadensis (L.) Carr.) en melange avec des especes de feuillus nordiques; la deuxieme categorie comprend des melanges de pins (Pinus) et de chenes (Quercus). Ces forets possedent une valeur socio-economique interessante, un potentiel d'habitat faunique ou une capacite d'adaptation, mais leur amenagement est difficile parce que la presence d'au moins une espece resineuse dans chaque categorie peut etre limitee par un manque de semences, des exigences de regeneration trop strictes ou une faible capacite concurrentielle. Les systemes sylvicoles qui sont appropries varient en fonction de la composition de ces forets et dependent de la tolerance a l'ombre et de l'intensite des perturbations associees aux resineux critiques, a la qualite de la station et au degre d'herbivorie. La durabilite de la composition des forets mixtes necessite que la structure et la composition des peuplements soient amenagees a chaque rotation de facon a maintenir des arbres vigoureux d'especes ayant des longevites et des taux de croissance differents et a favoriser le developpement de la regeneration preetablie ou d'arbres semenciers d'especes desirees. Quel que soit le systeme sylvicole, il est essentiel de maintenir des sources de semences des resineux critiques, de creer des substrats de germination appropries et de maitriser la concurrence. Dans cet article, nous decrivons les points communs entre les forets mixtes temperees du centre et de l'est de l'Amerique du Nord et presentons une marche a suivre pour leur amenagement. Mots-cles: forets mixtes, melanges de feuillus et de coniferes, systemes sylvicoles, regeneration des arbres, tolerance a l'ombre., Introduction Silviculture must integrate knowledge of forest ecology, growth and yield, and operations while accounting for multiple goals depending on the context of application (Puettmann et al. 2009). The design [...]

Mixedwood forest composition, or co-dominance of hardwood and softwood species, has been interpreted as both stable and unstable. Through review of existing theory, we propose a conceptual model to understand mixedwood compositional stability in boreal and temperate forests of eastern North America. We first review the current theory that the strength of neighborhood effects (i.e., species ability to self-replace under their own canopy) is essential to understanding stability such that when self-replacement is strong for both dominant hardwood and softwood species, composition is stable except at extreme disturbance severities. In contrast, when mixedwood forests are dominated by negligible or weak affinities to self-replace, composition is unstable and sensitive to changes in disturbance. Our new concept further posits that changes in both the disturbance severity and its vertical direction are essential to understanding stability. For example, where moderate-severity surface fires (which impact forests from below) cease and are replaced by moderate-severity blowdowns (which impact forests from above), instability can occur even when disturbance severity is unchanged. We therefore pose and discuss an extension to current theory to provide a new unifying concept of stability for mixedwood forests and, more broadly, for mixed-species forests. Key words: mixed-species forests, deciduous-coniferous mixtures, regeneration strategy, neighborhood effects, compositional resilience. La composition des forets mixtes, dans lesquelles il y a codominance d'especes feuillues et resineuses, a ete decrite comme etant stable ou instable. En se fondant sur la theorie existante, nous proposons un modele conceptuel pour comprendre la stabilite de la composition des peuplements mixtes dans les forets boreale et temperee de l'est de l'Amerique du Nord. Nous explorons d'abord la theorie actuelle selon laquelle la force des effets de voisinage (c'est-a-dire la capacite des especes a s'autoremplacer sous leur propre couvert) est essentielle pour comprendre la stabilite. Ainsi, lorsque l'auto-remplacement est fort pour les especes dominantes de feuillus et de resineux, la composition est stable sauf si l'intensite des perturbations est extreme. En revanche, lorsque les forets mixtes sont dominees par des especes dont la capacite a s'auto-remplacer est negligeable ou faible, la composition est instable et sensible a des changements de perturbation. De plus, notre nouveau concept postule que des changements d'intensite de la perturbation et de sa direction verticale sont necessaires pour comprendre la stabilite. Par exemple, lorsque des feux de surface d'intensite moderee (qui affectent les forets par le bas) cessent et sont remplaces par des chablis d'intensite moderee (qui affectent les forets par le haut), un etat instable peut s'etablir meme si l'intensite de la perturbation demeure inchangee. Par consequent, nous proposons et discutons d'une extension de la theorie actuelle pour introduire un nouveau concept unificateur de stabilite pour les forets composees de feuillus et de resineux et, plus generalement, pour les forets composees de plus d'une espece. Mots-cles : forets mixtes, melanges de feuillus et de resineux, strategie de regeneration, effets de voisinage, resilience compositionnelle., Introduction Forests cover approximately one-third of the Earth's land area, support biodiversity and ecosystem processes, and provide jobs, commodities, materials, food, and fuel to societies (FAO and UNEP 2020). Tree [...]

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 onequarter 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 Juniperas. 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. Key words: hardwood, softwood, deciduous, coniferous, Forest Inventory and Analysis (FIA). Au fur et a mesure qu'augmente l'interet pour l'amenagement et le maintien des forets mixtes dans le nord des Etats-Unis, la comprehension de leur abondance et de leur repartition devient de plus en plus importante. Dans le but d'obtenir de l'information, nous avons analyse les donnees du programme d'inventaire forestier et d'analyse portant sur les forets mixtes de 24 Etats du nord des Utats-Unis, a partir du Maine vers le sud jusqu'au Maryland et vers l'ouest jusqu'au Kansas et au Dakota du Nord. Les forets mixtes, c'est-a-dire les forets composees a la fois de feuillus et de resineux, dont la proportion n'excede pas 75 a 80% dans un cas comme dans l'autre, representent plus de 19 millions d'hectares, ce qui correspond a plus du quart des forets du nord des Etats-Unis. Elles sont plus frequentes dans les provinces ecologiques des Adirondacks en Nouvelle-Angleterre, Laurentienne et du Nord-Est, mais elles sont aussi presentes ailleurs dans les provinces ecologiques dominees par les feuillus. Les forets mixtes sont courantes meme dans les types forestiers categorises nominalement comme etant feuillus ou resineux. Les feuillus les plus courants dans ces forets sont des especes des genres Quercus et Acer alors que les resineux les plus courants sont des especes des genres Pinus, Tsuga et Juniperus. Bien que la superficie totale des forets mixtes soit demeuree stable au cours de notre periode d'analyse, les gaules de feuillus etaient predominantes, ce qui indique que la composition d'une forte proportion de ces forets pourrait tendre vers une dominance des feuillus s'il n'y a pas de perturbations favorisant la regeneration de la composante resineuse. Nos analyses indiquent que meme si la plupart des parcelles de forets mixtes sont demeurees des forets mixtes, la recolte de bois modifie generalement la composition des forets mixtes vers des types de couvert domines par des feuillus ou des resineux, mais la comprehension des causes de ces changements necessite de l'information plus specifique. Mots-cles: feuillus, resineux, especes decidues, coniferes, programme d'inventaire forestier et d'analyse (FIA)., Introduction Forests with both hardwoods and softwoods (i.e., generally broadleaf, deciduous, and needle-leaf, evergreen trees, respectively) present but neither exceeding 75%-80% of basal area, crown cover, or other metric are [...]

Although northern white-cedar (Thuja occidentalis; henceforth cedar) is thought to have few insect pests, arborvitae leafminers (primarily Argyresthia thuiella) have been known to cause leaf necrosis. Yet, historical evidence for leafminer outbreaks is limited. We combined leafminer larval surveys conducted between 1950 and 1992 with tree-ring analyses from eight cedar stands to reconstruct a history of leafminer outbreaks in Maine, USA. Our tree-ring data show distinctive 2- to 3-year growth reductions that we attribute to leafminers. Several such growth reductions correspond to peak leafminer larval abundances, providing evidence that the reductions are reliable indicators of leafminer activity. Outbreak severity within a site was unrelated to cedar abundance. Outbreak periods thus identified (beginning ca. 1919, 1937, 1950, 1962, mid-1970s, but not at all sites) suggest that leafminer damage may have been more prevalent (albeit patchy) than previously thought. This historical information is relevant given current outbreaks in Maine and elsewhere. [ABSTRACT FROM AUTHOR]

Selection cutting is defined as a tool for uneven-aged silviculture. Dependence on diameter distribution by forestry practitioners for identifying stand conditions has led to misuse of selection-like cuttings in even-aged northern hardwood stands. Our study used several long-term data sets to investigate the temporal stability in numbers of trees per diameter class in uneven-aged northern hardwood stands treated with single-tree selection and in 45-year-old second-growth stands treated with selection-like cuttings. We analyzed data from New York, Michigan, and Wisconsin to determine changes through time in number of trees across 2.5 cm diameter classes, shifts in the shape and scale of the three-parameter Weibull function used to describe the diameter distributions, and dynamics of associated stand attributes. Findings showed that single-tree selection cutting created and sustained stable diameter distributions and uniformity of conditions through consecutive entries in unevenaged stands. By contrast, these characteristics varied through time in the second-growth stands that had been treated with selection-like cuttings. Analysis also showed that the Weibull shape and scale parameters for stands under selection system migrated towards those of the recommended target diameter distribution in the uneven-aged stands. These parameters diverged from the target with repeated use of selection-like cuttings in the second-growth even-aged stands. Key words: structural stability, single-tree selection, diameter distribution, northern hardwood stands, long-term study. La coupe de jardinage est consideree comme un outil de la sylviculture inequienne. L'utilisation de la distribution des diametres par les praticiens forestiers pour determiner l'etat des peuplements a conduit a une mauvaise application de coupes ressemblant au jardinage dans les peuplements equiennes de feuillus nordiques. Notre etude a utilise plusieurs jeux de donnees a long terme pour analyser la stabilite temporelle du nombre d'arbres par classe de diametre dans des peuplements inequiennes de feuillus nordiques traites par jardinage par pied d'arbre, ainsi que dans des peuplements de seconde venue ages de 45 ans qui ont ete traites a l'aide d'une coupe ressemblant au jardinage. Nous avons analyse des donnees provenant des etats de New York, Michigan et Wisconsin afin de determiner les changements temporels du nombre d'arbres par classe de diametre de 2,5 cm, les changements de forme et d'echelle de la fonction de Weibull a trois parametres utilisee pour decrire la distribution des diametres, et la dynamique des autres attributs des peuplements. Les resultats ont montre que le jardinage par pied d'arbre creait et maintenait des distributions diametrales stables et une uniformite des conditions par des entrees consecutives dans les peuplements inequiennes. Par contre, ces caracteristiques ont varie au fil du temps dans les peuplements de seconde venue traites a l'aide d'une coupe ressemblant au jardinage. L'analyse a egalement montre que les parametres de forme et d'echelle de la fonction de Weibull des peuplements jardines se dirigeaient vers les cibles de distribution diametrales recommandees pour les peuplements inequiennes. Ces parametres ont diverge de la cible a la suite de l'utilisation repetee de coupes ressemblant au jardinage dans les peuplements equiennes de seconde venue. [Traduit par la Redaction] Mots-cles: stabilite structurale, jardinage par pied d'arbre, distribution diametrale, peuplements de feuillus nordiques, etude a long terme., Introduction Selection system in the United States Conceptually, the selection system creates and maintains a consistent diameter distribution, a high degree of vertical structural diversity, and stable stand conditions over [...]

Gap dynamics facilitate recruitment of late-successional species such as northern white-cedar (Thuja occidentalis L.). For this reason, harvests that result in partial rather than complete canopy removal have been suggested for cedar. However, success of regenerating cedar following partial harvests is uncertain, especially where there is heavy browsing by white-tailed deer (Odocoileus virginianus Zimmerman) or snowshoe hare (Lepus americanus). Efforts to understand how partial harvests and browsing interact to affect natural regeneration of cedar have been limited. We inventoried partially harvested stands along a gradient of 1–11 years since harvest in New Brunswick, Canada, in an area where deer frequently overwinter. Cedar regeneration was negatively influenced by browsing, but positively influenced by years since harvest and sapling basal area. Cedar seedling survival was assessed over a 2-year period and found to be primarily a function of height at initial measurement, with little influence of browsing. Annual vertical gain of cedar seedlings (a surrogate for height growth) decreased with increasing years since harvest and was influenced by distance from gap edge. In gaps, vertical gain increased with distance to gap edge, while distance to gap edge had a negative influence on vertical gain of seedlings in the matrix (between-gap areas). Many tagged cedar seedlings disappeared prior to remeasurement. These were likely completely consumed by browsers, limiting our ability to determine relative influences of partial harvest and browsing on cedar regeneration. We conclude that partial harvests, as applied in this study, increase cedar abundance and vertical gain, but browsing may necessitate seedling protection. We suggest monitoring to confirm sufficient cedar regeneration in partially harvested stands, using exclosures where browsing is a concern, and retaining or at least delaying removal of seed-bearing cedar overstory trees until regeneration has reached heights safe from browsing. [ABSTRACT FROM AUTHOR]

Rehabilitation of cutover stands is often a management objective of landowners who desire improved stand conditions and increased value from future harvest revenues. We evaluated crop tree growth response and quality following precommercial rehabilitation treatments in mixedwood stands degraded through repeated exploitive cutting in Maine, USA. Treatments included control (no rehabilitation), moderate rehabilitation (crop tree release), and intensive rehabilitation (crop tree release plus timber stand improvement). Paper birch (Betula papyrifera Marsh.), red spruce (Picea rubens Sarg.), and eastern hemlock (Tsuga canadensis (L.) Carriere) crop tree diameter increments 0 to 9 years after treatment were greater following rehabilitation than in the control. Diameter increment did not differ between intensities of rehabilitation for any species. For conifers in the lower strata, crop tree height growth and change in crown length were negatively correlated with basal area in larger trees. The occurrence of epicormic branches on paper birches was greater in the rehabilitation treatments than the control. However, most epicormic branches occurred above the height corresponding to the first sawlog. These findings indicate that rehabilitation of mixedwood stands with similar characteristics can result in improved growth of crop trees without jeopardizing the quality of the lower bole in paper birches. Key words: crop tree release, timber stand improvement, commercial clearcut, epicormic branches, mixedwood. La rehabilitation des parterres de coupe est souvent un objectif d'amenagement des proprietaires forestiers qui souhaitent ameliorer les conditions du peuplement et augmenter les revenus de la recolte future. Nous avons evalue la reaction de croissance et la qualite des arbres d'avenir a la suite de traitements precommerciaux de rehabilitation dans des peuplements mixtes degrades par des coupes abusives repetees dans le Maine, aux Etats-Unis. Les traitements comprenaient un temoin (pas de rehabilitation), une rehabilitation moderee (degagement des arbres d'avenir) et une rehabilitation intensive (degagement des arbres d'avenir et amelioration du peuplement). L'accroissement en diametre des tiges d'avenir de bouleau a papier (Betula papyrifera Marsh.), d'epinette rouge (Picea rubens Sarg.) et de pruche du Canada (Tsuga canadensis (L.) Carriere) de0a9 ans etait plus grand apres la rehabilitation que dans le temoin. L'accroissement en diametre n'etait pas different selon l'intensite de rehabilitation chez toutes les especes. Dans le cas des coniferes de la strate inferieure, la croissance en hauteur et le changement dans la longueur de la cime des arbres d'avenir etaient negativement correles a la surface terriere chez les plus gros arbres. Des gourmands etaient davantage presents sur les bouleaux a papier ayant profite d'un traitement de rehabilitation que dans le temoin. Toutefois, la plupart des gourmands sont apparus au-dessus de la hauteur delimitant l'extremite de la premiere bille de sciage. Ces resultats indiquent que les traitements de rehabilitation peuvent ameliorer la croissance des arbres d'avenir sans compromettre la qualite de la partie inferieure du tronc des bouleaux a papier dans les peuplements mixtes ayant des caracteristiques similaires. [Traduit par la Redaction] Mots-cles : degagement des arbres d'avenir, amelioration du peuplement, coupe a blanc commerciale, gourmands, peuplement mixte., Introduction In the forests of northeastern North America, removal of the most commercially desirable species and trees began during colonial times with the harvesting of large eastern white pine (Pinus [...]

Understanding forest structural changes resulting from postdisturbance management practices such as salvage logging is critical for predicting forest recovery and developing appropriate management strategies. In 2013, a tornado and subsequent salvage operations in northern Maine, USA, created three conditions (i.e., treatments) with contrasting forest structure: blowdown, blowdown + salvage, and control (undisturbed). We sampled forest structure in five stands representing each of these three treatments. Our results document obvious and predictable changes to forest structure caused by the blowdown and salvage operations; however, they also include unexpected findings: downed coarse woody debris volume remained quite high in the salvaged areas, although its vertical distribution was markedly reduced; salvage operations did not reduce fine woody debris volume; and the salvage operation itself reduced the abundance of upturned root masses. Our study contributes to a growing body of literature highlighting the fact that outcomes of salvage operations vary considerably from situation to situation. Nevertheless, they suggest that salvage logging has important implications for residual stand structure and regeneration potential and that these implications should be considered carefully when weighing postdisturbance management options. Key words: fire risk, fuel loads, pit-and-mound, Picea rubens, wind disturbance, woody debris. Il est essentiel de comprendre les changements dans la structure de la foret qui resultent des pratiques d'amenagement, telles que la coupe de recuperation, appliquees a la suite d'une perturbation pour etre en mesure de predire le retablissement de la foret et d'elaborer des strategies d'amenagement appropriees. Une tornade survenue en 2013 et les operations subsequentes de recuperation dans le nord du Maine, aux Etats-Unis, ont engendre trois types de situations (c.-a-d. traitements) comportant differentes structures de la foret: chablis, chablis + recuperation et temoin (non perturbee). Nous avons echantillonne la structure de la foret dans cinq peuplements representatifs de chacun de ces trois traitements. Nos resultats temoignent des changements evidents et previsibles dans la structure de la foret causes par le chablis et les operations de recuperation. Cependant, ils incluent egalement des surprises : comparativement au chablis non recupere, la coupe de recuperation n'a pas reduit davantage l'abondance des arbres vivants; le volume de debris ligneux au sol est demeure relativement eleve dans les zones de recuperation bien que sa distribution verticale ait ete nettement reduite; les operations de recuperation n'ont pas reduit le volume de debris ligneux fins; et l'operation de recuperation elle-meme a reduit l'abondance des masses de racines renversees. Notre etude s'ajoute au nombre croissant de publications mettant en evidence le fait que les resultats des operations de recuperation varient considerablement d'une situation a l'autre. Neanmoins, ils indiquent que la coupe de recuperation a d'importantes consequences sur la structure et la capacite de regeneration du peuplement residuel et que ces consequences devraient serieusement etre prises en compte lorsque vient le temps d'evaluer les options d'amenagement a la suite d'une perturbation. [Traduit par la Redaction] Mots-cles: risque d'incendie, charges de combustibles, creux et buttes, Picea rubens, perturbation causee par le vent, debris ligneux., Introduction Natural disturbances alter forest structure, function, and composition across a range of scales. Severe wind storms in particular damage or kill standing trees, creating pulses in downed woody debris [...]

Developing strategies for reducing atmospheric C[O.sub.2] is one of the foremost challenges facing natural resource professionals today. The goal of this study was to evaluate total ecosystem and harvested wood product carbon (C) stocks among alternative forest management treatments (selection cutting, shelterwood cutting, commercial clearcutting, and no management) in mixed-species stands in central Maine, USA. These treatments were initiated in the 1950s and have been maintained since, and ecosystem C pools were measured in 2012. When compared across managed treatments, the commercial clearcut had the lowest total ecosystem C stocks by 21%, on average (P < 0.05), while the selection and shelterwood treatments had similar total ecosystem C stocks. Including the C stored in harvested wood products did not influence observed differences in C storage among treatments. Total ecosystem C stocks in the reference stand were 247.0 ± 17.7 Mg x [ha.sup.-1] (mean ± SD) compared with 161.7 ± 31.3 Mg x [ha.sup.-1] in the managed stands (171.2 ± 31.7 Mg*[ha.sup.-1] with products C). This study highlights the impacts of long-term forest management treatments on C storage and indicates that the timing of harvests and the species and sizes of trees removed influence C stored in harvested wood products. Key words: carbon stocks, forest products, forest soils, coarse fragments, site quality. Le developpement de strategies visant a reduire le C[O.sub.2] atmospherique est un des principaux defis que doivent relever aujourd'hui les professionnels des ressources naturelles. Le but de cette etude consistait a estimer les stocks totaux de carbone (C) emmagasines dans l'ecosysteme et les produits forestiers recoltes dans des peuplements mixtes soumis a differents traitements d'amenagement forestier (coupe de jardinage, coupe progressive, coupe a blanc commerciale et aucun traitement) dans le centre du Maine, aux Etats-Unis. Ces traitements ont debute dans les annees 1950 et ont ete maintenus depuis. Les reservoirs de C dans l'ecosysteme ont ete mesures en 2012. Parmi les traitements d'amenagement, les stocks de C les plus faibles, de 21 % en moyenne (P < 0,05), etaient associes a la coupe a blanc commerciale tandis que les stocks totaux de C dans l'ecosysteme etaient similaires pour la coupe de jardinage et la coupe progressive. Inclure le C emmagasine dans les produits forestiers recoltes n'a pas influence les differences observees entre les traitements dans le stockage du C. Les stocks totaux de C dans l'ecosysteme atteignaient 247,0 ± 17,7 Mg x [ha.sup.-1] (moyenne ± ecart-type) dans le peuplement temoin comparativement a 161,7 [+ or -] 31,3 Mg x [ha.sup.-1] dans les peuplements amenages (171,2 ± 31,7 Mg x [ha.sup.-1] incluant le C dans les produits forestiers). Cette etude met en evidence les impacts a long terme des traitements d'amenagement forestier sur le stockage du C et indique que le moment de la recolte ainsi que l'espece et la taille des arbres recoltes influencent le C emmagasine dans les produits forestiers recoltes. [Traduit par la Redaction] Mots-cles : stocks de carbone, produits forestiers, sols forestiers, fragments grossiers, qualite de station., Introduction Concerns about climate change have increased interest in developing forest management strategies to produce a net reduction in atmospheric C[O.sub.2] and to make forests more resilient to future climatic [...]

Dead wood pools are strongly influenced by natural disturbance events, stand development processes, and forest management activities. However, the relative importance of these influences can vary over time. In this study, we evaluate the role of these factors on dead wood biomass pools across several forest management alternatives after 60 years of treatment on the Penobscot Experimental Forest in central Maine, USA. After accounting for variation in site quality, we found significant differences in observed downed coarse woody material (CWM; ≥ 7.6 cm small-end diameter) and standing dead wood biomass among selection, shelterwood, and commercial clear-cut treatments. Overall, total dead wood biomass was positively correlated with live tree biomass and was negatively correlated with the average wood density of nonharvest mortality. We also developed an index of cumulative harvest severity, which can be used to evaluate forest attributes when multiple harvests have occurred within the same stand over time. Findings of this study highlight the dynamic roles of forest management, stand development, and site quality in influencing dead wood biomass pools at the stand level and underscore the potential for various outcomes from the same forest management treatment applied at different times in contrasting stands. Key words: silviculture, tree mortality, spruce budworm, harvest severity index, woody debris. Les reservoirs de bois mort sont fortement influences par les perturbations, les processus de developpement des peuplements et les activites d'amenagement forestier. Cependant, l'importance relative de ces facteurs peut varier dans le temps. Dans cette etude, nous evaluons le role de ces facteurs sur les reservoirs de biomasse de bois mort en fonction de plusieurs options d'amenagement forestier apres 60 annees de traitement a la foret experimentale de Penobscot, dans le centre du Maine, aux Etats-Unis. Apres avoir tenu compte de la variation dans la qualite de station, nous avons observe des differences significatives dans les debris ligneux grossiers au sol (DLG; diametre au fin bout [greater than or equal to] 7,6 cm) et la biomasse de bois mort sur pied entre la coupe de jardinage, la coupe progressive et la coupe rase commerciale. Globalement, la biomasse totale de bois mort etait correlee positivement avec la biomasse des arbres vivants et negativement avec la densite moyenne du bois mort non recolte. Nous avons aussi developpe un indice d'intensite cumulative de recolte, qui peut etre utilise pour evaluer les attributs de la foret lorsque de multiples recoltes sont survenues avec le temps dans le meme peuplement. Les resultats de cette etude mettent en evidence les roles dynamiques de l'amenagement forestier, du developpement des peuplements et de la qualite de station quant a leur influence sur les reservoirs de biomasse de bois mort a l'echelle du peuplement et souligne la possibilite que le meme traitement d'amenagement forestier applique a differents moments dans differents peuplements produise differents resultats. [Traduit par la Redaction] Mots-cles : sylviculture, mortalite des arbres, tordeuse des bourgeons de l'epinette, indice d'intensite de recolte, debris ligneux., Introduction Dead wood is an important component of ecosystem structure and function (Harmon et al. 1986; McComb and Lindenmayer 1999; Siitonen 2001). Specifically, dead wood plays a key role in [...]

Estimating the amount of standing deadwood in forests is crucial for assessing wildlife habitat and determining carbon stocks. In this analysis, snags (standing dead trees) in various stages of decay were inventoried across eight silvicultural treatments in eastern spruce-fir forests in central Maine nearly 60 years after treatments were initiated. Several modeling strategies were developed to estimate number of snags per hectare in various stages of decay. An unmanaged reference area displayed the highest basal area and volume of snags (5.4 [+ or -] 3.1 [m.sup.2] * [ha.sup.-1] and 29.4 [+ or -] 23.6 [m.sup.3] * [ha.sup.-1], respectively, (mean [+ or -] standard deviation)), while the lowest basal area and volume (0.9 [+ or -] 1.0 [m.sup.2] * [ha.sup.-1] and 3.1 [+ or -] 5.2 [m.sup.3] * [ha.sup.-1]) were observed in selection system with a 5-year cutting cycle. Models indicated that snag abundance was related to stand density, depth to water table, and the average harvest interval of the treatment. At a fixed stand density, approximately 140% more snags were predicted to occur in treatments with an average harvest interval of 55 compared with 5 years. An index of error reflecting the number of snags found in certain decay classes was reduced by 40% when predictions from count regression models fit with a mixed modeling strategy were used over ordinal regression. Results from these analyses can help to reduce the disparities between observed and modeled snag stocking levels and further our understanding of the relationships between live and standing dead trees inherent to eastern spruce-fir forests. Resume: Il est essentiel d'estimer la quantite de bois mort debout dans les forets pour evaluer l'habitat faunique et determiner les stocks de carbone. Dans cette etude, les chicots (arbres morts debout) a differents stades de decomposition ont ete inventories dans huit traitements sylvicoles dans des peuplements melanges d'epicea et de sapin situes dans le centre du Maine, presque 60 ans apres le debut des traitements. Plusieurs strategies de modelisation ont ete developpees pour estimer le nombre de chicots a l'hectare rendus a differents stades de decomposition. Une zone temoin non amenagee avait la surface terriere et le volume les plus eleves de chicots, soit respectivement (moyenne [+ or -] ecart type) 5,4 [+ or -] 3,1 [m.sup.2]*[ha.sup.-1] et 29,4 [+ or -] 23,6 [m.sup.3]*[ha.sup.-1], tandis que la surface terriere et le volume les plus faibles (0,9 [+ or -] 1,0 [m.sup.2]*[ha.sup.-1] et 3,1 [+ or -] 5,2 [m.sup.3]*[ha.sup.-1]) ont ete observes dans la coupe de jardinage avec une rotation de cinq ans. Les modeles indiquaient que l'abondance de chicots etait reliee a la densite du peuplement, a la profondeur de la nappe phreatique et a la l'intervalle moyen entre les recoltes. Avec une densite de peuplement fixe, les modeles predisaient approximativement 140% plus de chicots dans les traitements dont l'intervalle entre les recoltes etait de 55 ans comparativement a cinq ans. Un indice d'erreur refletant le nombre de chicots observes dans certaines classes de decomposition a ete reduit de 40% lorsqu'on utilisait les predictions des modeles de regression de variables explicatives de denombrement ajustes avec une strategie de modelisation mixte plutot que la regression ordinale. Les resultats de ces analyses peuvent contribuer a reduire les ecarts entre les niveaux observes de densite relative des chicots et ceux qui sont predits par les modeles et ameliorer notre comprehension des relations entre les arbres vivants et les arbres morts sur pied propres aux forets melangees d'epicea et de sapin. [Traduit par la Redaction], Introduction Snags (standing dead trees) play an important role in forest carbon dynamics (Harmon et al. 2011) and are key elements for maintaining forest biodiversity and providing a heterogeneous forest [...]

Equations to predict branch and tree leaf area, foliar mass, and stemwood volume were developed from 25 destructively sampled northern white-cedar (Thuja occidentalis L.) trees, a species whose production ecology has not been studied. Resulting models were applied to a large sample of 296 cored trees from 60 sites stratified across a soil gradient throughout northern Maine. Nonlinear regression analysis was used to assess alternative forms of the relationship between volume increment (VINC) and projected leaf area (PLA); analysis of covariance was used compare stemwood growth efficiency (GE) among soil-site classes, light exposure classes, and the presence of decay. Stem volume was estimated with Honer's equation (T.G. Honer. 1967. Forest Management Research and Services Institute) with refitted parameters. PLA was best predicted with Maguire and Bennett's nonlinear model (D.A. Maguire and W.S. Bennett. 1996. Can. J. For. Res. 26: 1991-2005) using sapwood area or crown length and the ratio of tree height to diameter at breast height. A sigmoid model form captured the relationship between VINC and PLA more precisely and with less bias than the simple power function; this implies that the relationship between GE and PLA reaches a peak rather than decreases monotonically. At PLAs >50 [m.sup.2], GE gradually declined with increasing crown size and was significantly influenced by site and light exposure. With PLA, site, and light held constant, decayed trees had a significantly lower (by 11%) GE than sound stems, a finding not previously reported for other tree species. Resume: Des equations de prediction de la surface foliaire des branches et de l'arbre, de la biomasse foliaire et du volume de la tige ont ete mises au point a partir d'un echantillonnage destructif de 25 thuyas occidentaux (Thuja occidentalis L.), une espece dont les caracteristiques ecologiques de production n'ont pas ete etudiees. Les modeles ainsi elabores ont ete appliques sur un vaste echantillon forme de 296 arbres carottes dans 60 stations reparties selon un gradient edaphique dans le nord du Maine, aux Etats-Unis. Une analyse de regression non lineaire a ete utilisee pour evaluer les differentes formes de relation entre l'accroissement en volume (AV) et la surface foliaire projetee (SFP). Une analyse de covariance a ete utilisee pour comparer l'efficacite de la croissance (EC) de la tige entre les classes de station, entre les classes d'exposition a la lumiere et en presence de carie. Le volume de la tige a ete estime a l'aide des equations de Honer (T.G. Honer. 1967. Forest Management Research and Services Institute) dont les parametres ont ete recalcules. Les meilleures predictions de la SFP ont ete obtenues avec le modele non lineaire de Maguire et Bennett (D.A. Maguire et W.S. Bennett. 1996. Res. can. rech. for. 26: 1991-2005) en utilisant la surface d'aubier ou la longueur de la cime et le rapport entre la hauteur de l'arbre et son dhp. Une meilleure precision et un plus petit biais ont ete obtenus lorsque la relation entre l'AV et la SFP etait calculee par une forme de modele sigmoide plutot que par la fonction simple de puissance. Cela implique que la relation entre l'EC et la SFP est caracterisee par l'atteinte d'une valeur maximale suivie d'une diminution non monotone. Pour des valeurs de SFP superieures a 50 [m.sup.2], l'EC diminue graduellement avec l'augmentation de la taille de la cime et est significativement influencee par la station et l'exposition a la lumiere. Pour des valeurs constantes de SFP, de station et de lumiere, les arbres caries avaient une EC significativement plus faible (de 11 %) que celle des arbres sains, un resultat qui n'avait encore jamais ete publie pour d'autres especes d'arbre. [Traduit par la Redaction], Introduction Northern white-cedar (Thuja occidentalis L.) is the fourth most abundant conifer in Maine after red spruce (Picea rubens Sarg.), eastern white pine (Pinus strobus L.), and balsam fir (Abies [...]

Understory growth dynamics of northern conifer species were studied in four stands managed under multiaged silvicultural systems in eastern Maine. Height growth of Picea rubens Sarg., Abies balsamea (L.) Mill., and Tsuga canadensis (L.) Carr. saplings between 0.5 and 6.0 m in height was related to the proportion open sky (POS), using sapling height as a covariate. Height growth of T. canadensis equaled A. balsamea and exceeded P. rubens under very low light levels (POS < 0.1) but is much less responsive to both increasing POS and taller heights, reaching 50% of its maximum height growth at a POS of only 0.09. Abies balsamea outgrew P. rubens under similar dark conditions; at higher light levels (POS > 0.10), both species grew similarly. Evidently, no feasible overstory manipulation of light alone can promote more rapid height development of P. rubens saplings over A. balsamea. A nonlinear light-prediction model using stand basal area is linked with height-growth prediction equations to quantify sapling development from 0.5 to 6 m. Depending on overstory density, P. rubens requires a height advantage of 0.14-0.33 m over a 0.5 m tall A. balsamea to reach a height of 6 m over the same time period. La dynamique de la croissance en sous-etage des coniferes nordiques a ete etudiee dans quatre peuplements soumis a un regime sylvicole multi-age dans l'est de l'Etat du Maine. Avec la hauteur des gaules comme covariable, la croissance en hauteur des gaules d'epinette rouge (Picea rubens Sarg.), de sapin baumier (Abies balsamea (L.) Mill.) et de la pruche du Canada (Tsuga canadensis (L.) Carr.) entre 0,5 et 6,0 m de haut est reliee au pourcentage d'ouverture du couvert (POC). La croissance en hauteur de T. canadensis egale celle de A. balsamea et depasse celle de P. rubens dans des conditions de tres faible luminosite (POC < 0,1). Mais la croissance en hauteur de T. canadensis est tres peu sensible a l'augmentation du POC et a une hauteur initiale plus elevee, atteignant 50 % de sa croissance maximale en hauteur a une valeur de POC de seulement 0,09. Abies balsamea depasse P. rubens dans des conditions similaires de luminosite; dans des conditions de plus forte luminosite (POC > 0,10), les deux essences croissent de facon similaire. Evidemment, en pratique aucune manipulation de l'etage dominant pour augmenter la luminosite ne peut favoriser une croissance en hauteur des gaules de P. rubens plus rapide que celle de A. balsamea. Un modele non lineaire de prediction de la luminosite base sur la surface terriere est relie aux equations de prediction de la croissance en hauteur pour quantifier le developpement des gaules de 0,5 a 6 m. Dependamment de la densite de l'etage dominant, une tige d'epinette rouge doit avoir 0,14 a 0,33 m de plus qu'une tige de sapin de 0,5 m de haut pour atteindre une hauteur de 6 m au cours de la mdme periode de temps. [Traduit par la Redaction], Introduction A natural disturbance regime dominated by gap dynamics and a long history of partial cutting have made multiaged, mixed-species forest structures common in the Acadian Forest of northeastern North [...]