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Contemporary forest harvesting practices, specifically harvesting woody biomass as a source of bioenergy feedstock, may remove more woody debris from a site than conventional harvesting. Woody debris, particularly smaller diameter woody debris, plays a key role in maintaining ecosystem nutrient stores following disturbance. Understanding nutrient concentrations within woody debris is necessary for assessing the long-term nutrient balance consequences of altered woody debris retention, particularly in forests slated for use as bioenergy feedstocks. Nutrient concentrations in downed woody debris of various sizes, decay classes, and species were characterized within one such forest type, Populus tremuloides Michx.-dominated forests of northern Minnesota, USA. Nutrient concentrations differed significantly between size and decay classes and generally increased as decay progressed. Fine woody debris (â¤â7.5 cm diameter) had higher nutrient concentrations than coarse woody debris (>â7.5 cm diameter) for all nutrients examined except Na and Mn, and nutrient concentrations varied among species. Concentrations of N, Mn, Al, Fe, and Zn in coarse woody debris increased between one and three orders of magnitude, while K decreased by an order of magnitude with progressing decay. The variations in nutrient concentrations observed here underscore the complexity of woody debris nutrient stores in forested ecosystems and suggest that retaining fine woody debris at harvest may provide a potentially important source of nutrients following intensive removals of bioenergy feedstocks.

Several aspects of the forest carbon cycle have not been examined in detail, including sources of variation in carbon dioxide (C[O.sub.2]) emissions from coarse woody material (CWM). To address this knowledge gap, we examined C[O.sub.2] emissions from Acer saccharum Marshall logs within four harvesting treatments, using closed chambers fitted to the logs. We found that C[O.sub.2] emissions were highest for logs in small (31.8 [+ or -] 20.4 [micro]molC[O.sub.2][m.sup.- 3][s.sup.-1]) and large gaps (29.6 [+ or -] 24.4 [micro]molC[O.sub.2][m.sup.-3][s.sup.-1]) compared to those in control (13.9 [+ or -] 8.3 [micro]molC[O.sub.2][m.sup.-3][s.sup.-1]) and thinned matrix (13.6 [+ or -] 8.0 [micro]molC[O.sub.2][m.sup.-3] [s.sup.-1]) treatments. C[O.sub.2] 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 C[O.sub.2] 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 C[O.sub.2] emissions, although this relationship was weak in one log. This study provides insight into sources of variation in C[O.sub.2] emissions from CWM while improving our understanding of the forest carbon cycle. Key words: carbon dioxide, carbon flux, forest carbon cycle, woody material, wood decomposition, Introduction Forests are important contributors to the global carbon cycle, both as a sink of carbon dioxide (C[O.sub.2]) through photosynthesis as well as an emitter of C[O.sub.2] as these carbon [...]

The persistence of many saproxylic (wood-living) species depends on a readily available supply of coarse woody debris (CWD). Most studies of CWD inputs address stand-level patterns, despite the fact that many saproxylic species depend on landscape-level supplies of CWD. In the present study we used dated CWD inputs (tree mortality events) at each of 14 Norway spruce (Picea abies) dominated woodland key habitat sites to analyze the spatial and temporal patterns of CWD additions between 1950 and 2002 within a small landscape in central Sweden. We found that inputs were episodic within sites, where local windstorms created pulses in CWD input. Pulses occurred simultaneously in many sites, yielding landscape-level synchrony of CWD input. These synchronous pulses, and importantly, the breaks between pulses, may have negative implications for saproxylic species that are dependent on large volume inputs of freshly killed Norway spruce. In addition, the inherent small size and relative isolation of these sites may further increase extinction risks due to stochastic events. However, background CWD input rates occurring between pulses varied substantially among sites, presumably the result of the sitesâ varied histories and structural characteristics. This finding suggests that the different sites have varied abilities to provide habitat for saproxylic species during periods with low landscape-level input of CWD.

Both nutrient concentrations and pre- and post-harvest pool sizes were determined across down woody debris decay classes of several hardwood and softwood species in a long-term, natural disturbance based, silvicultural experiment in central Maine. Concentrations of N, P, Ca, Mg, Cu, Fe, and Zn generally increased 2- to 5-fold with increasing decay class. Concentrations of Mn, Al and B did not differ among decay classes, while K decreased by 20â44% from decay class 1 to class 4. C:N-ratios declined with increasing decay class, while N:P-ratios increased from decay class 1 to 2 and then plateaued with further decay. Within decay classes, softwoods generally had lower nutrient concentrations and higher C:N-ratios than hardwoods; N:P-ratios did not differ between hardwoods and softwoods. Although gap harvesting increased the size of the overall down woody debris nutrient pools, mostly through a large pulse of decay class 1 material, harvesting generally reduced the nutrients held in advanced decay classes. Pre-harvest down woody debris pools for N, P, K and Ca were 11.0, 0.6, 2.1 and 21.1 kg ha, respectively, while postharvest were 20.0, 1.3, 6.2 and 46.2 kg ha, respectively. While the gap-based silvicultural systems sampled in this study doubled the size of the pre-harvest, downed woody debris nutrient pools, the post-harvest pools were estimated to be only 3.2â9.1% of aboveground nutrients.â1â1

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 [...]

Multi-year drought and climate change can impact tree growth, especially in California's Mediterranean climate where growing season rainfall is limited or absent. Active forest restoration has the potential to mitigate climate impacts by reducing stand density and conversion towards more resilient species' composition. We used dendrochronology methods to examine climate-growth relationships for coast Douglas-fir (Pseudotsuga menziesii var. menziesii) trees in mixed multiaged stands near the species' natural southern range margin. We found positive correlations of ring width with spring-early summer and prior October precipitation and an evapotranspiration index. Additionally, cooler spring temperature was negatively correlated with growth. We also studied tree resistance, resilience, and recovery from two multi-year drought events. Restoration treatments enhanced resistance and resilience to drought relative to trees growing in untreated plots. We did not detect differences in drought resistance and resilience between two common restoration methods, giving managers options for restoration to lessen drought impacts on tree growth. Key words: climate-growth, dendrochronology, drought resistance, frill treatment, partial harvest, thinning, Introduction Warmer and drier future climates are expected to reduce productivity of most conifer forests (Song et al. 2021), raising particular concerns over the maladaptation and potential loss of trees [...]

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. Key words: black ash, dendroecology, emerald ash borer, gap dynamics, stand dynamics, moderate-severity disturbance Les forets de frenes noirs (Fraxinus nigra Marsh.) du centre-nord de l'Amerique du Nord sont actuellement menacees par l'agrile du frene (Agrilus planipennis, EAB), une espece non indigene. Malgre la large distribution des ecosystemes de F. nigra et l'inquietude concernant l'impact de l'agrile du frene, on sait peu de choses sur leur structure et la dynamique naturelle des peuplements. Nous avons echantillonne six peuplements anciens de F. nigra pour evaluer la structure, la composition, le recrutement des arbres et les perturbations passees. Les resultats dendrochronologiques ont revele que les taux de perturbation ont fluctue de facon marquee au cours des 200 dernieres annees ou plus, mais sont restes relativement faibles, ce qui suggere des perturbations a petite ou moyenne echelle. Les structures d'age du recrutement ont revele que (i) F. nigra est capable de maintenir une dominance a long terme grace a une longevite prolongee en tant qu'arbre de la canopee, et (ii) ces systemes ont un recrutement assez continu dans le temps, la plupart des sites montrant un recrutement de F. nigra dans chaque decennie de la chronologie. Nous supposons que le recrutement est couple aux fluctuations de la nappe phreatique, en plus de la perturbation de la canopee, car ces peuplements sont soumis a la fois a des inondations frequentes et a une secheresse effective du sol (etant donne la faible profondeur des systemes racinaires). Les faibles taux de perturbation de la canopee dans le passe et le remplacement par F. nigra qui y est associe soulignent le potentiel de changements dramatiques dans ces systemes apres l'invasion de l'agrile du frene et la mortalite subsequente des arbres de la canopee. [Traduit par la Redaction] Mots-cles : frene noir, dendroecologie, agrile du frene, dynamique des espaces, dynamique des peuplements, perturbation de gravite moderee, 1. Introduction Forest ecosystems can be dramatically altered when nonnative insects eliminate a foundational tree species, thereby causing shifts in food webs, energy flux, hydrology, and biodiversity (Ellison et al. [...]

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]

Understanding the influence of post‐disturbance forest management on tree regeneration is critical for assessing ecosystem recovery and guiding future responses. In particular, the influx of elevated coarse woody material (CWM) following wind disturbance, if left in situ, may impede herbivore access, thereby protecting saplings from browsing damage through a natural 'exclosure effect'.In 2013, a tornado in northcentral Maine, United States and subsequent salvage logging operations created three clear 'treatments' for evaluation of the exclosure effect: blowdown, blowdown plus salvage logging and an undamaged control. Nine years post‐tornado, we inventoried tree regeneration within these treatments to evaluate differences in sapling abundance, species composition, size structure and browsing intensity. We also inventoried CWM, including the height above forest floor.Results revealed significant differences in sapling composition and browsing intensity among treatments. The salvage treatment had the highest proportion of browsed saplings (56 ± 28%; mean ± standard error), followed by the control (9 ± 10%) and blowdown (5 ± 8%). Blowdown had by far the greatest mean (50 ± 9 cm) and average maximum (169 ± 43 cm) heights for CWM. Binomial generalized linear models revealed that browsing probability was a function of mean CWM height and an interaction between sapling density and proportion of sapling hardwoods. Thus, browsing damage was less likely in plots with greater CWM heights and more likely in plots with greater sapling density and more hardwood saplings.Synthesis and applications. This study furthers our understanding of ecosystem recovery following blowdown and salvage logging. Results suggest that salvage logging created important differences in coarse woody material (CWM) abundance and height distribution, when compared to un‐salvaged areas, and that these differences in turn altered sapling size structure and browsing intensity. These findings highlight the potential long‐term effects of successive disturbances, as the differences evident in these early stages may persist for decades or longer. Importantly, we provide evidence of the exclosure effect, suggesting that CWM retained in the un‐salvaged area protected saplings from moose browsing. Thus, in post‐disturbance areas where browsing threatens regeneration, we recommend that managers consider retaining CWM to serve as a natural exclosure. [ABSTRACT FROM AUTHOR]

Wildfires, insect outbreaks, and windstorms are increasingly common forest disturbances. Post-disturbance management often involves salvage logging, i.e., the felling and removal of the affected trees; however, this practice may represent an additional disturbance with effects on ecosystem processes and services. We developed a systematic map to provide an overview of the primary studies on this topic and created a database with information on the characteristics of the retrieved publications, including information on stands, disturbance, intervention, measured outcomes, and study design. Of 4341 retrieved publications, 90 were retained in the systematic map. These publications represented 49 studies, predominantly from North America and Europe. Salvage logging after wildfire was addressed more frequently than after insect outbreaks or windstorms. Most studies addressed logging after a single disturbance event, and replication of salvaged stands rarely exceeded 10. The most frequent response variables were tree regeneration, ground cover, and deadwood characteristics. This document aims to help managers find the most relevant primary studies on the ecological effects of salvage logging. It also aims to identify and discuss clusters and gaps in the body of evidence, relevant for scientists who aim to synthesize previous work or identify questions for future studies. Key words: salvage harvesting, sanitation logging, wildfire, insect outbreak, windthrow. Les feux de foret, les epidemies d'insectes et les tempetes de vent sont des perturbations forestieres de plus en plus frequentes. A la suite d'une perturbation, l'amenagement implique souvent une coupe de recuperation, c.-a-d., l'abattage et le prelevement des arbres endommages. Cependant, cette pratique peut constituer une perturbation additionnelle et avoir des effets sur les services et processus de l'ecosysteme. Nous avons developpe une carte systematique destinee a fournir un apercu des etudes originales sur ce sujet et cree une base de donnees contenant de l'information sur les caracteristiques des publications retenues, incluant des informations sur les peuplements, la perturbation, l'intervention, les resultats mesures et la methodologie de l'etude. Des 4341 publications trouvees, 90 ont ete retenues dans la carte systematique. Ces publications representaient 49 etudes menees principalement en Amerique du Nord et en Europe. La coupe de recuperation apres feu a ete etudiee plus frequemment qu'apres des epidemies d'insectes ou des tempetes de vent. La plupart des etudes portaient sur la coupe apres une seule perturbation et le nombre de repetitions de peuplements recuperes depassait rarement 10. Les variables reponse les plus frequentes etaient la regeneration de la strate arborescente, le couvert vegetal et les caracteristiques du bois mort. Ce document vise a aider les gestionnaires a trouver les etudes les plus pertinentes portant sur les effets ecologiques de la coupe de recuperation. Il vise aussi a identifier et examiner les points forts et les lacunes parmi l'ensemble des arguments pertinents pour les scientifiques qui cherchent a synthetiser les travaux anterieurs ou a identifier les sujets de futures etudes. [Traduit par la Redaction] Mots-cles : coupe de recuperation, coupe d'assainissement, feu de foret, epidemie d'insectes, chablis., Introduction Large, episodic, severe forest disturbances such as those caused by wildfires, insect outbreaks, and windstorms are part of the natural dynamics of forest ecosystems across the world (Noss et [...]

The conic-paraboloid volume equation is receiving increased use with downed coarse woody material (CWM), but the consequences for taper have not been identified mathematically. Requiring that subdivision of a conic-paraboloid yields two smaller conic-paraboloids leads to an exact taper equation intermediate between those of cones and second-order paraboloids. This exact taper equation does not have an explicit inverse, however. An alternative, naive approach does have an explicit inverse, but subdivision does not yield two conic-paraboloids. The exact conic-paraboloid is closely approximated by Fermat's paraboloid with exponent 7/5. The exact and naive conic-paraboloids match in volume; differences in taper are [less than or equal to] 2.2% of large-end cross-sectional area and [less than or equal to] 5.9% of large-end diameter, while differences in inverse taper are [less than or equal to] 3.7% of total length. Fermat's paraboloid is always within 1.2% of total volume; differences in taper are [less than or equal to] 0.8% of large-end cross-sectional area and [less than or equal to] 2.0% of large-end diameter, while differences in inverse taper are [less than or equal to] 1.1% of total length. Such differences are negligible given the variety of CWM shapes and practical measurement challenges. Either the exact conic-paraboloid or the corresponding Fermat's paraboloid provides appropriate equations for estimating the volume and taper of CWM that is intermediate between conical and ordinary paraboloid frusta. Key words: coarse woody debris, downed dead wood, carbon accounting, forest inventory. L'equation du volume d'un paraboloide conique est de plus en plus utilisee pour le materiel ligneux grossier (MLG) au sol mais les repercussions sur la conicite n'ont pas ete identifiees du point de vue mathematique. Exiger que la subdivision d'un paraboloide conique engendre deux paraboloides coniques plus petits mene a une equation exacte de la conicite, intermediaire entre celle des cones et celle des paraboloides du second ordre. Cependant, cette equation exacte de la conicite n'a pas d'inverse explicite. Une approche alternative, naive, n'a pas d'inverse explicite mais la subdivision n'engendre pas deux paraboloides coniques. Le paraboloide de Fermat, avec un exposant 7/5, produit une tres bonne approximation du paraboloide conique exact. Les paraboloides exact et naif ont un volume semblable; la differences de conicite est [less than or equal to] 2,2 % de la surface de la section au gros bout et [less than or equal to] 5,9 % du diametre au gros bout tandis que la difference de conicite inverse est [less than or equal to] 3,7 % de la longueur totale. Le paraboloide de Fermat est toujours en dedans de 1,2 % du volume total, la difference de conicite est [less than or equal to] 0,8 % de la surface de la section au gros bout et [less than or equal to] 2,0 % du diametre au gros bout, tandis que la difference de conicite inverse est [less than or equal to] 1,1 % de la longueur totale. De telles differences sont negligeables etant donne la variete des formes du MLG et les defis pratiques que represente leur mesure. Soit le paraboloide conique exact, ou le paraboloide correspondant de Fermat, fournissent des equations adequates pour estimer le volume et la conicite du MLG qui est intermediaire entre le tronc de cone du paraboloide conique et celui du paraboloide ordinaire. [Traduit par la Redaction] Mots-cles: debris ligneux grossiers, bois mort au sol, bilan du carbone, inventaire forestier., Introduction Downed coarse woody material (CWM) has become a focus of substantial research and management attention in the past three decades (Harmon et al. 1986; Russell et al. 2015). The [...]

Wind disturbance generates heterogeneous microsite structures, including downed logs, windthrow mounds, and pits. While these structures can provide opportunities for regeneration of certain tree species, the long-term influence of microsites and microsite heterogeneity on forest development has not been quantified. We used long-term measurements of a formerly old-growth Tsuga canadensis--Pinus strobus forest severely damaged by a category 3 hurricane in 1938 to quantify the impact of microsite conditions on overstory composition and structure. We asked (i) 'What are the patterns in live-tree size, growth, and mortality five and seven decades after disturbance?' and (ii) 'What roles do microsite heterogeneity and the presence of disturbance-generated microsites play in long-term forest development following disturbance?' We compared live-tree (>2 cm DBH) development and survival to microsite heterogeneity at the 100 [m.sup.2] scale. Microsite diversity was positively related to overstory species diversity and stem density and negatively related to average tree size. We propose that plots with higher microsite diversity may have experienced more severe local disturbance, which allowed more species and individuals to establish and created varied niches that allowed these individuals to coexist and generate greater stand-level diversity. These persistent relationships highlight how microsite conditions affect forest development after severe disturbances. Key words: downed woody debris, hemlock-pine forest, heterogeneity, large, infrequent disturbance, pit-and-mound microtopography. Les perturbations causees par le vent produisent des structures heterogenes de microsite, ce qui inclut des troncs d'arbre au sol de meme que des monticules et des depressions crees par les chablis. Bien que ces structures soient des occasions de regeneration pour certaines especes d'arbre, l'influence a long terme des microsites et de leur heterogeneite sur le developpement des forets n'a pas ete quantifiee. Nous avons utilise des mesures prises sur une longue periode dans une vieille foret initialement composee de Tsuga canadensis et de Pinus strobus, qui a ete fortement endommagee par un ouragan de categorie 3 en 1938, pour quantifier l'impact des conditions de microsite sur la composition et la structure du couvert dominant. Nous voulions savoir (i) quels etaient les patrons de taille, de croissance et de mortalite des arbres 50 et 70 ans apres la perturbation et (ii) quel role ont joue la presence et l'heterogeneite des microsites produits par la perturbation sur le developpement a long terme de la foret a la suite de la perturbation. Nous avons analyse le developpement et la survie des arbres (>2 cm de DHP) en fonction de l'heterogeneite des microsites a une echelle de 100 [m.sup.2]. La diversite des microsites etait positivement reliee a la diversite des especes du couvert dominant et a la densite des tiges, et elle etait negativement reliee a la taille moyenne des arbres. Nous croyons que les placettes associees a une plus grande diversite de microsites peuvent avoir subi une perturbation locale plus forte, ce qui a permis l'etablissement d'un plus grand nombre d'especes et d'individus, et que la variete de niches a permis a ces individus de coexister et de produire une plus grande diversite a l'echelle du peuplement. Ces relations persistantes mettent en evidence la facon dont les conditions de microsite influencent le developpement des forets apres de fortes perturbations. [Traduit par la Redaction] Mots-cles : debris ligneux au sol, foret de pruche et de pin, heterogeneite, perturbation de grande taille peu frequente, microtopographie formee de depressions et de monticules., Introduction Disturbance is a key driver of forest composition and structural dynamics, as resources are made available for species establishment or release following a disturbance event (Pickett and White 1985; [...]

Dead woody material (DWM) plays numerous important roles in forest ecosystems; however, through the process of decomposition, it undergoes structural and chemical changes that progressively alter its function in these roles. Much remains unknown about how DWM mechanical strength and structural integrity change through decomposition in natural forest settings. We assessed changes in wood strength (bending strength, compressive strength, and surface hardness) using standard wood stakes of known initial mass from three species. The stakes were placed in forested settings for two and four years before collection for laboratory analyses. All three strength metrics decreased as stakes lost mass due to decay; however, bending strength had the strongest relationship with mass loss, a result that was consistent for all species, as well as species-pooled data. Results for all strength-loss metrics indicate that stakes had experienced ca. 10% strength loss before any detectable mass loss had occurred. Further, our results suggest that the decay class system typically used during field inventories--based in large part on tactile assessments of wood structural integrity--may provide a reasonable characterization of DWM mass loss, which is a critical assumption for carbon accounting and modelling based on inventory data. Key words: carbon accounting, decay class, decay stakes, forest fuels, wood decay, woody debris. Le materiel ligneuxgrossier (MLG) joue plusieurs roles importants dans les ecosystemes forestiers. Cependant, durant le processus de decomposition il subit des changements structuraux et chimiques qui modifient progressivement les fonctions associees a ces roles. Beaucoup de choses demeurent inconnues au sujet de la facon dont la resistance mecanique et l'integrite structurale du MLG changent durant sa decomposition en foret naturelle. Nous avons evalue les changements dans la resistance du bois (resistance a la flexion, resistance a la compression et durete superficielle) a l'aide de baguettes de bois standards dont on connaissait la masse initiale de trois especes. Les baguettes ont ete laissees en foret pendant deux et quatre ans avant d'etre recoltees pour les analyses en laboratoire. Les resultats des trois mesures de resistance ont diminue a mesure que progressait la perte de masse due a la decomposition des baguettes. Cependant, la resistance a la flexion etait le plus etroitement reliee a la perte de masse, un resultat constant chez toutes les especes ainsi qu'avec les donnees des especes regroupees. Les resultats pour toutes les mesures de perte de resistance indiquent que les baguettes avaient subi une perte de resistance d'environ 10 % avant que survienne une perte de masse detectable. De plus, nos resultats confirment que le systeme de classes de decomposition normalement utilise lors des inventaires terrestres, fonde en grande partie sur des evaluations tactiles de l'integrite structurale du bois, fournit une approximation raisonnable de la perte de masse du MLG, laquelle est essentielle pour la modelisation et la comptabilisation precise du carbone sur la base des donnees d'inventaire. [Traduit par la Redaction] Mots-cles: comptabilisation du carbone, classe de decomposition, baguettes de bois servant a mesurer la decomposition, combustibles forestiers, decomposition du bois, debris ligneux., Introduction Dead woody material (DWM) plays a crucial role in forest ecosystems where it contributes to carbon storage, nutrient cycling, and biodiversity maintenance (Harmon et al. 1986; Stokland et al. [...]

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. [ABSTRACT FROM AUTHOR]

: This study investigated the growth response of mature, isolated reserve trees (n = 528) in two multiaged silvicultural systems in the Acadian Forest Ecosystem Research Project (AFERP). Absolute and percent increases in basal area increment (BAI; [cm.sup.2] x [year.sup.-1]) were assessed for the five predominant reserve tree species in AFERP: Acerrubrum L., Picearubens Sarg., Pinusstrobus L., Thuja occidentalis L., and Tsuga canadensis (L.) Carriere. Absolute growth was significantly greater in the large-gap treatment (23.7 [+ or -] 1.1 [cm.sup.2] x [year.sup.-1]; mean [+ or -] SE) than in the small-gap treatment (16.3 [+ or -] 0.9 [cm.sup.2] x [year.sup.-1]). Percent growth increase was greater in the small-gap treatment (187.6% [+ or -] 15.8%) than in the large-gap treatment (143.4% [+ or -] 19.3%), and both treatments had greater percent increases than the unharvested control (9.6% [+ or -] 5.2%). Species differed in their response to treatment. Pinus strobus had the greatest absolute increase (large-gap, 52.5 [cm.sup.2] x [year.sup.-1]), while Tsuga canadensis (large-gap, 270% [+ or -] 71.6%) and Acerrubrum (small-gap, 262% [+ or -] 42.4%) had the greatest percent increases. Growth responses typically diminished with increasing tree size and pretreatment growth rate; however, reserve trees showed greater growth responses than their paired analogues in the control across all initial tree sizes and prior growth rates. The results suggest that these silivicultural systems accelerate the development of large trees. Key words: basal area increment, ecological forestry, restoration of large- diameter size classes, retention forestry, retention tree. Nous avons etudie le taux de croissance d'arbres de retention isoles et matures (n = 528) dans deux systemes sylvicoles multiages (a grandes ou petites trouees) du Projet de recherche sur les ecosystemes forestiers acadiens (PREFA). Les augmentations absolue et relative en accroissement de la surface terriere ([cm.sup.2] x [an.sup.-1]) ont ete evaluees pour les cinq especes d'arbres de retention predominantes dans la PREFA : Acer rubrum L., Picea rubens Sarg., Pinus strobus L., Thuja occidentalis L. et Tsuga canadensis (L.) Carriere. La croissance absolue etait significativement plus forte dans le systeme a grandes trouees (moyenne [+ or -] erreur-type de 23,7 [+ or -] 1,1 [cm.sup.2] x [an.sup.-1]) que dans le systeme a petites trouees (16,3 [+ or -] 0,9 [cm.sup.2] x [an.sup.-1]). Le pourcentage d'accroissement etait plus grand dans le systeme a petites trouees (187,6 [+ or -] 15,8 %) que dans le systeme a grandes trouees (143,4 [+ or -] 19,3 %), et le pourcentage d'accroissement de ces deux systemes etait plus eleve que dans le temoin non recolte (9,6 [+ or -] 5,2 %). La reaction aux traitements etait differente selon l'espece. La plus grande augmentation absolue a ete observee chez Pinus strobus (52,5 [cm.sup.2] x [an.sup.-1] dans les grandes trouees) alors que les plus grandes augmentations relatives ont ete observees chez Tsuga canadensis (270 [+ or -] 71,6 % dans les grandes trouees) et Acer rubrum (262 [+ or -] 42,4 % dans les petites trouees). Le taux de croissance a generalement diminue avec l'augmentation de la taille des arbres et du taux de croissance pretraitement. Toutefois, le taux de croissance des arbres de retention etait plus grand que celui des arbres qui leur etaient apparies dans le temoin et ce, peu importe la taille initiale des arbres et le taux de croissance pretraitement. Les resultats indiquent que ces systemes sylvicoles accelerent le developpement des gros arbres. [Traduit par la Redaction] Mots-cles : accroissement en surface terriere, foresterie ecologique, restauration des classes de gros diametre, foresterie de retention, arbre de retention., 1. Introduction The majority of the world's forests are managed as multifunctional forests, providing human commodities and other goods and services (Food and Agricultural Organization of the United Nations (FAO) [...]

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 [...]

Empirical knowledge of forest structure and development in early successional and range-margin populations is often lacking, limiting our ability to effectively model and manage these forests. Such is the case for jack pine (Pinus banksiana Lamb.) in central Minnesota, USA, where it reaches its southwestern range limit. Our objective was to quantify this population's historical range of variability of structural conditions and developmental pathways. We collected structural, spatial, and dendrochronological data on 0.25 ha plots from 10 jack pine dominated sites that initiated and developed outside of active management. Our results revealed a broad range of structural characteristics and developmental pathways, including rapid and protracted recruitment windows (5-50 years), with subsequent even- and uneven-aged structures, and random and clumped stem spatial arrangements. As such, these mature, early successional forests often displayed a degree of complexity more typically associated with old-growth forests. Our findings suggest that this population, like other southern range- margin populations with mostly nonserotinous cones, historically followed a variety of stand development pathways and did not solely follow the rapid establishment, even-aged pathway often attributed to this forest type. We suggest that even- and uneven-aged silvicultural systems should be used to reflect this historical range of developmental pathways and to increase resilience and adaptability. Key words: dendrochronology, early successional forest, jack pine, marginal population, range of variability. Le frequent manque de connaissances empiriques sur la structure et le developpement des forets en debut de succession et a la marge de leur aire de distribution limite notre capacite a les modeliser et les amenager efficacement. C'est le cas du pin gris (Pinus banksiana Lamb.) dans le centre du Minnesota, aux Etats-Unis, oU il atteint la limite sud-ouest de son aire de distribution. Notre objectif etait de quantifier l'etendue historique de la variabilite des conditions structurales et des trajectoires de developpement de cette population. Nous avons recueilli des donnees structurales, spatiales et dendrochronologiques dans des placettes de 0,25 ha etablies dans 10 peuplements domines par le pin gris dont l'origine et le developpement sont survenus sans amenagement actif. Nos resultats ont mis en evidence un large eventail de caracteristiques structurales et de trajectoires de developpement, incluant des periodes rapides et prolongees de recrutement (de 5 a 50 ans) suivies de l'etablissement de structures equiennes et inequiennes avec des arbres dont la distribution spatiale etait aleatoire et groupee. Ainsi, ces forets matures de debut de succession avaient souvent un degre de complexite generalement associe aux vieilles forets. Nos resultats indiquent que cette population, comme d'autres populations avec des cones generalement non serotineux et situees a la limite sud de leur aire de distribution, a dans le passe suivi une variete de trajectoires de developpement et non la seule trajectoire souvent attribuee a ce type de foret, soit un etablissement rapide et une structure equienne. Nous suggerons d'avoir recours a des systemes sylvicoles equienne et inequienne pour refleter cet eventail historique de trajectoires de developpement et accroitre la resilience et l'adaptabilite de ces forets. [Traduit par la Redaction] Mots-cles : dendrochronologie, foret de debut de succession, pin gris, population marginale, etendue de la variabilite., Introduction Plant populations located at their geographic range margins tend to display atypical species traits and population-level dynamics due to their proximity to suboptimal abiotic conditions and ecotonal community associations [...]

Thinning is believed to accelerate the development of late-successional attributes, thereby enhancing stand structural heterogeneity in young, secondary forests. By making use of a large-scale experiment implemented in 40- to 60-year-old coastal Douglas-fir (Pseudotsuga menziesii (Mirbel) Franco) forests, we addressed the following objectives: (i) determine the effect of three thinning treatments on the temporal dynamics (first 11 years after thinning) of key forest structure measures, (ii) evaluate the relationships between spatially explicit structural diversity measures and spatially nonexplicit stand metrics, and (iii) test the relationships between stand structure and observed periodic stand volume growth, ingrowth, and mortality. Treatments consisted of high-density, moderate-density, and variable-density thinnings-from-below, as well as a control. Differences in stand structural heterogeneity between treatments were mostly nonsignificant. However, our results suggest that variable- density stands displayed structural enrichment as tree size and tree species diversity increased throughout the study period as a result of continuous ingrowth of species other than Douglas-fir. Simple spatially nonexplicit metrics could not be used to reliably model spatially explicit structural diversity measures. The inclusion of structural and species diversity measures only rarely improved accuracy of sample plot level growth, ingrowth, and mortality prediction models. Despite the short-term nature of this study, we conclude that variable-density thinning shows promise in increasing structural heterogeneity in young even- aged stands. The inclusion of structural diversity measures in growth and mortality models may be beneficial, but further work is needed to clarify the underlying relationships, particularly at the individual-tree level. Key words: variable-density thinning, tree species diversity, tree size diversity, spatial tree arrangement, forest structure. L'eclaircie est censee accelerer le developpement des attributs de fin de succession, ameliorant ainsi l'heterogeneite structurelle des jeunes peuplements de seconde venue. A l'aide d'une experience a grande echelle etablie dans des forets cotieres de douglas de Menzies (Pseudotsuga menziesii (Mirbel) Franco) agees de 40 a 60 ans, nous avons poursuivi les objectifs suivants: (i) determiner l'effet de trois traitements d'eclaircie sur la dynamique temporelle (11 premieres annees apres l'eclaircie) des mesures cles de la structure forestiere, (ii) evaluer les relations entre des mesures spatialement explicites de diversite structurelle et des mesures de peuplements non spatialement explicites, et (iii) tester la relation entre la structure du peuplement et les valeurs observees de croissance periodique du volume, du recrutement et de la mortalite dans le peuplement. Les traitements etaient des eclaircies par le bas a densites forte, moderee et variable ainsi qu'un temoin. Les differences d'heterogeneite structurelle des peuplements entre les traitements etaient generalement non significatives. Cependant, nos resultats indiquent qu'un enrichissement structurel s'est produit dans les peuplements a densite variable puisque la diversite en taille et en espece d'arbre a augmente pendant la periode d'etude a cause du recrutement continu d'especes autres que le douglas de Menzies. Des mesures simples, non spatialement explicites, n'ont pu etre utilisees pour modeliser de facon fiable les mesures de diversite structurelle spatialement explicites. L'inclusion de mesures de diversite structurelle et specifique a rarement ameliore la precision des modeles de prevision de la croissance, du recrutement et de la mortalite a l'echelle de la placette echantillon. Malgre la courte echelle temporelle de cette etude, nous concluons que l'eclaircie a densite variable semble prometteuse pour augmenter l'heterogeneite structurelle dans les jeunes peuplements equiennes. L'inclusion de mesures de diversite structurelle dans les modeles de croissance et de mortalite peut etre benefique, mais d'autres travaux sont necessaires pour clarifier les relations sous-jacentes, particulierement a l'echelle de l'arbre individuel. [Traduit par la Redaction] Mots-cles: eclaircie a densite variable, diversite des especes d'arbre, diversite de la taille des arbres, distribution spatiale des arbres, structure forestiere., 1. Introduction Restoring structural heterogeneity in secondary forests as a means to increasing the provision of ecosystem services has become a major objective in forest management and a much-noticed topic [...]