Search

Silvicultural regeneration methods focus on manipulating the forest canopy, but success can depend on the use of site preparation to control competing vegetation, including the density of advance regeneration, and create suitable microsite conditions for germination and seedling establishment. Tip-up mounds are known to provide favorable conditions for some tree species, but the creation of tip-up mounds as a method of site preparation has scarcely been investigated. We assessed effects of artificial tip-up mounds on tree seedling composition across a gradient of regeneration methods and residual overstory densities 2-4 years post-implementation. We found that tree seedling communities on mounds in some treatments were compositionally distinct from untreated reference plots. However, no tree species exhibited a strong affinity for mounds when analyzed independently from the regeneration method, and much of the difference in composition was associated with lower dominance of maples (Acer spp. L.) on mounds. As maples are strong competitors in forests regenerated with selection systems, reduced maple competition on artificial mounds could advantage desired under-represented species and aid in natural regeneration over time. Therefore, in stands where promoting tree species diversity is desirable, implementing artificial tip-up mounds as part of a long-term strategy may be beneficial. Key words: site preparation, seedling composition, forest regeneration, Acer saccharum, shelterwood, Introduction Natural forest regeneration is a complex process influenced by factors that interact across space and time scales. These factors can interact with life history characteristics, including seed size and [...]

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

Increased emphasis on forest complexity, resilience, and biodiversity has renewed interest in northern hardwood forests. In parallel, there is concern of impacts of traditional, timber-oriented regeneration methods on successional trajectories and tree communities. To ensure compatibility of emerging goals with site biological capacity, assessment of common silvicultural methods across forest conditions is imperative. This work utilizes a long-term dataset of 407 sampling plots from the Bartlett Experimental Forest in New Hampshire, USA, over 70 years. Topographic and meteorological variables were utilized to test the effects of site conditions and silviculture on tree species diversity and composition. Results show a decline in diversity over time that reflects a shift toward dominance of late successional species, which vary with site-specific conditions. The effect of silviculture was not detectable, and differences in tree communities were attributed to pre-existing conditions of site variables prior to installation of experimental treatments. Tree diversity and composition for both 1932 and 2003 measurements were correlated with solar insolation, local wind speed, and hydrological catchment area. The collective findings highlight the long-term stability of species under past silvicultural regimes, that some areas are more facilitative/limiting to goals of enhancing tree biodiversity and emerging technologies can capture species-site interactions in northern hardwoods. Key words: silviculture, succession, biodiversity, remote-sensing, forest management, Introduction The northern hardwood forests of Northeastern North America have long been utilized for timber and fiber commodity production, and primarily managed through even- and uneven-aged natural regeneration systems adopted [...]

Precommercial thinning could be a valuable tool for climate change adaptation, as it can promote stand diversity while increasing productivity. Softwood and hardwood stands are usually thinned following different methods, and we lack recommendations for application in mixedwood stands. We evaluated the effects of precommercial thinning on the growth and composition of balsam fir (Abies balsamea L.)-birch stands dominated by paper and yellow birch (Betula papyrifera Marsh. and Betula alleghaniensis Britt.), comparing methods and production objectives (systematic release-softwood, systematic release mixedwood, crop-tree release-mixedwood, and crop-tree release-hardwood) in Quebec (Canada). Precommercial thinning increased tree-level and stand-level growth, especially for both birches. Compared to the non-thinned control, thinning increased tree diameter at breast height annual increments by 60%-107%, with similar results among modalities. Thinning changed initial stand composition, but mixedwood production plots composition was similar to that of the control 15 years after treatment. Promoting diversity is often perceived to be made at the expense of wood production. Our results suggest that we can obtain both increased growth and maintain diversity. Precommercial thinning is currently suggested as an adaptation tool that can foster drought resistance. Based on our study, we suggest it could serve another purpose in climate-adapted forest management, that is, maintaining diversity and thus increasing resilience to disturbances. Key words: Adaptive forest management, balsam fir, mixed wood silviculture, paper birch, tree species diversity, Introduction Diversity is increasingly perceived as a key element for the adaptation of managed forests to global change, as it could increase the resistance and resilience of stands to stressors [...]

Individual tree recruitment is an important element needed to understand stand dynamics, as it influences both stand composition and productivity. Forest growth simulators usually include recruitment models. The quality of recruitment predictions can have long-term impacts on estimations of forest growth, ecosystem health and the commercial utility of managed forests. The main objective of this study was to develop a recruitment model for commercial-size trees (i.e., trees with a diameter at breast height > 9 cm) of 10 species groups using different dendrometric and environmental variables. The resulting model will be included in a growth simulator used to support forest management planning. We hypothesized that accounting for sapling density as a covariate would improve the recruitment model's predictive performance. Using empirical data from periodically measured permanent sample plots (1982-2019) located throughout the managed mixed hardwood forests of Quebec, we constructed models with and without sapling-related covariates and compared them on the basis of cross-validation model performance statistics. Our results show that including sapling density significantly improved model performance. From this, we conclude that adding sapling density as a covariate can significantly improve a recruitment model's predictive power for eastern mixed hardwood forests. Key words: model comparison, negative binomial distribution, northern hardwoods, Quebec, SaMARE, zero-inflated model, 1. Introduction The hardwood forest of the province of Quebec, Canada, is important in terms of commercial uses and ecosystem services. Located in the northern temperate forest zone, south of [...]

Basic wood density (BWD) is a functional characteristic important to quantify carbon storage and is related to tree growth and its survival. We investigated BWD variability among tree species, populations, and forest types across the Atlantic Forest biome in Rio de Janeiro state, Brazil. We sampled and measured 576 trees of 83 species in 28 natural ecosystems in the Dense Ombrophilous Forest, Seasonal Semi-deciduous Forest, and the Restinga Forest. Stem wood from two different heights at each tree was acquired using a drill borer; discs were removed from branches in 20% of the height from 39 trees. BWD means increased from 0.42 for the most humid ecosystem to 0.675 g*[cm.sup.-3] from the driest ecosystem. We identified changes in the wood as a result of climatic variables particular to different typologies, such as increased wood density in areas with lower precipitation and higher temperatures, were also observed within species, but with little difference in means. We identified three groups of species according to their BWD, different in mean height and diameter. The branches can be used to estimate tree wood density. Key words: biodiversity, branches, functional trait, non-destructive sampling, stem wood La densite de base du bois (DBB) est une caracteristique fonctionnelle importante pour quantifier le stockage du carbone et est liee a la croissance et a la survie des arbres. Dans cette etude, nous avons examine la variabilite de la densite de base du bois parmi les especes d'arbres, les populations et les types de forets dans le biome de la foret atlantique de l'Etat de Rio de Janeiro, au Bresil. Nous avons echantillonne et mesure 576 arbres de 83 especes dans 28 ecosystemes naturels de la foret ombrophile dense, de la foret semi-decidue saisonniere et de la foret de Restinga. Le bois de la tige a deux hauteurs differentes de chaque arbre a ete acquis a l'aide d'une foreuse (methode non destructive), de plus, des disques ont ete preleves sur les branches a 20% de la hauteur de 39 arbres. Les moyennes de densite de base du bois ont augmente de 0,42 pour l'ecosysteme le plus humide a 0,675 g*[cm.sup.-3] de l'ecosysteme le plus sec. Nous avons identifie des changements dans le bois resultant de variables climatiques particulieres aux differentes typologies, comme l'augmentation de la densite du bois dans les regions ou les precipitations sont plus faibles et des temperatures plus elevees ont egalement ete observees au sein d'une meme espece, mais avec peu de difference entre les moyennes. Nous avons identifie trois groupes d'especes en fonction de leur DBB, differentes en hauteur et en diametre moyens. De plus, les branches representent la densite des tiges des especes de la foret atlantique et, par consequent, peuvent etre utilisees pour estimer la densite du bois des arbres. [Traduit par la Redaction] Mots-cles : biodiversite, branches, trait fonctionnel, echantillonnage non destructif, bois de tige, Introduction The Atlantic Forest is an important hotspot with high conservation priority (Myers et al. 2000; Rezende et al. 2018). Its biodiversity is influenced by geological, pedological, and climatic heterogeneity [...]

The longevity of a single 22.4 Mg * [ha.sup.-1] application of dolomitic limestone at four northern hardwood stands was evaluated over 30 years (1986-2016) to determine whether changes in soils, foliage, and tree growth were sustained on the unglaciated Allegheny Plateau in northern Pennsylvania, USA. In limed plots, soils, sampled to 45-55 cm depth, and sugar maple (Acer saccharum Marsh.) and black cherry (Prunus serotina Ehrh.) foliage had significantly (P [less than or equal to] 0.05) greater concentrations of calcium (Ca) and magnesium (Mg) through 2016 compared with samples from unlimed plots. Ca and Mg capitals (g * [m.sup.-2]) in the Oi through A horizons combined were greater on limed plots than unlimed plots, largely due to increases in the thickness and nutrient concentration in the A horizon. Over 30 years, sugar maple basal area increment ([cm.sup.2] * [year.sup.-1] BAINC) was greater in limed plots (30.6 [cm.sup.2] * [year.sup.-1] vs unlimed 13.3), American beech (Fagus grandifolia Ehrh.) BAINC was unaffected by lime application, and black cherry BAINC was reduced in limed plots compared with unlimed plots. The sustained effect of this one-time lime treatment shows the strong role of efficient nutrient cycling in forests and suggests that the benefits over a substantial portion of a stand rotation may increase the feasibility of operational liming. Key words: forest liming, base cations, exchangeable calcium (Ca) and magnesium (Mg), percent carbon (C) and nitrogen (N), basal area increment, sugar maple, American beech, black cherry. La longevite d'une application unique de 22,4 Mg * [ha.sup.-1] de calcaire dolomitique dans quatre peuplements de feuillus nordiques situes dans la partie non glaciere du plateau des Alleghany dans le nord de la Pennsylvanie, aux Etats-Unis, a ete evaluee sur une periode de 30 ans (1986-2016) pour determiner si les changements dans le sol, le feuillage et la croissance des arbres ont persiste. Dans les parcelles qui avaient ete chaulees, les sols echantillonnes jusqu'a une profondeur de 45-55 cm, ainsi que le feuillage de l'erable a sucre (Acer saccharum Marsh.) et du cerisier tardif (Prunus serotina Ehrh.), avaient des concentrations de calcium (Ca) et de magnesium (Mg) significativement plus elevees (P [less than or equal to] 0,05) jusqu'en 2016 comparativement aux echantillons provenant de parcelles non chaulees. Les capitaux en Ca et Mg (g * [m.sup.-2]) dans les horizons Oi a A combines etaient plus eleves dans les parcelles chaulees que dans les parcelles non chaulees, surtout a cause de l'augmentation de l'epaisseur et de la concentration des nutriments dans l'horizon A. Sur 30 ans, l'accroissement de la surface terriere (AST [cm.sup.2] * [an.sup.-1]) de l'erable a sucre etait plus eleve dans les parcelles chaulees (30,6 contre 13,3 [cm.sup.2] * [an.sup.-1] dans les parelles non chaulees). L'application de chaux n'a pas eu d'effet sur l'AST du hetre d'Amerique (Fagus grandifolia Ehrh.) et a reduit l'AST du cerisier tardif dans les parcelles chaulees comparativement aux parcelles non chaulees. L'effet persistant de cette application unique de chaux illustre le role majeur du recyclage efficace des nutriments dans les forets et indique que les benefices qui perdurent pendant une partie importante de la periode de revolution d'un peuplement peuvent augmenter la faisabilite du chaulage operationnel. [Traduit par la Redaction] Mots-cles : chaulage en foret, cations basiques, calcium (Ca) et magnesium (Mg) echangeables, pourcentage de carbone (C) et d'azote (N), accroissement de la surface terriere, erable a sucre, hetre d'Amerique, cerisier tardif., Introduction Forest liming is used to alter soil acidity, counter effects of long-term acidic inputs, and improve the growth and health of trees (Long et al. 2011; Court et al. [...]

Following timber harvests in bottomland mixed-oak (Quercus L.) stands, desirable oak advance regeneration can be overgrown by shade-intolerant pioneer species. We investigated the effects of group selection opening size on composition of tree regeneration 19 years postharvest in an oak-dominated bottomland forest and compared results with earlier findings to evaluate development trends. In response to six opening sizes (7-40 m radii), we evaluated regeneration density and dominance of four tree species groups: conifers, hard mast, shade-intolerant hardwoods, and shade-tolerant hardwoods. Our objectives were to determine the optimum gap size for regenerating oaks and test the delayed oak dominance hypothesis, in which oaks slowly gain dominance as pioneer species undergo self-thinning. Opening size influenced conifer regeneration but minimally affected hardwoods. Hard mast species density was less than that of either intolerant or tolerant species regardless of opening size. Future stem density trends suggest increasing intolerant species and constant mast and tolerant species. Modeled future height trends suggest increasing mast species dominance over intolerant pioneers after 30 years. Our results suggest that gap-based silviculture can be used to regenerate bottomland hardwood stands with desirable species including oaks; larger gaps favor conifers but there was no optimum size to enhance oak regeneration. Key words: dominance hypothesis, group selection, opening size, Quercus, self-thinning., Resume : Apres la recolte de bois dans des peuplements mixtes de chenes (Quercus L.) etablis sur des basses terres, la regeneration preetablie du chene que l'on souhaite conserver peut [...]

Forested wetlands may represent important ecosystems for mitigating climate change effects through carbon (C) sequestration because of their slow decomposition and C storage by trees. Despite this potential importance, few studies have acknowledged the role of temperate treed swamps in the C cycle. In southwestern Nova Scotia, Canada, we examined the role of treed swamps in the soil C cycle by determining C inputs through litterfall, assessing decomposition rates and soil C pools, and quantifying C outputs through soil greenhouse gas (GHG) emissions. The treed swamps were found to represent large supplies of C inputs through litterfall to the forest floor. The swamp soils had substantially greater C stores than the swamp-upland edge or upland soils. We found growing season C inputs via litterfall to exceed C outputs via GHG emissions in the swamps by a factor of about 2.5. Our findings indicate that temperate treed swamps can remain a C sink even if soil GHG emissions were to double, supporting conservation efforts to preserve temperate treed swamps as a measure to mitigate climate change. Key words: forested wetland, treed swamp, carbon sink, carbon sequestration, greenhouse gas flux. Les milieux humides boises pourraient s'averer d'importants ecosystemes pour attenuer les effets du changement climatique en sequestrant du carbone (C) a cause de la lenteur de la decomposition et du stockage de C dans les arbres. Malgre cette importance potentielle, peu d'etudes ont reconnu le role des marecages arborescents en zone temperee dans le cycle du C. Dans le sud-ouest de la Nouvelle-Ecosse, au Canada, nous avons etudie le role des marecages arborescents dans le cycle du C dans le sol en determinant les apports de C provenant de la chute de litiere, en evaluant les taux de decomposition et les reservoirs de C dans le sol, et en quantifiant la production de C par l'entremise des emissions de gaz a effet de serre (GES) en provenance du sol. Nous avons observe que les marecages arborescents fournissaient d'importantes quantites d'apports de C dans la couverture morte par l'entremise de la chute de litiere. Les sols des marecages emmagasinaient substantiellement plus de C que les sols situes a la limite entre les marecages et les terres hautes ou ceux des terres hautes. Nous avons observe que les apports de C durant la saison de croissance par l'entremise de la chute de litiere excedaient la production de C due aux emissions de GES dans les marecages par un facteur d'environ 2,5. Nos resultats indiquent que les marais arborescents en zone temperee peuvent demeurer un puits de C meme si les emissions de GES du sol devaient doubler, ce qui supporte les efforts de conservation visant a preserver les marecages arborescents en zone temperee comme mesure d'attenuation du changement climatique. [Traduit par la Redaction] Mots-cles : milieu humide boise, marecage arborescent, puits de carbone, sequestration du carbone, flux de gaz a effet de serre., Introduction Wetlands may be key ecosystems for mitigating the effects of fossil fuel emissions on climate through carbon (C) sequestration (Mitsch and Hernandez 2013). Although they cover only a small [...]

Predator-prey interactions influence behaviors and life-history evolution for both predator and prey species and also have implications for biodiversity conservation. A fundamental goal of ecology is to clarify mechanisms underlying predator- prey interactions and dynamics. To investigate the role of predator sensory mechanisms in predator-prey interactions, specifically in predator detection of prey, we experimentally evaluated importance of visual and olfactory cues for an apex predator, the coyote (Canis latrans Say, 1823). Unlike similar studies, we examined use of sensory cues in a field setting. We used trail cameras and four replicated treatments--visual only, olfactory only, visual and olfactory combined, and a control--to quantify coyote visitation rates in North American deciduous forests during fall 2016. Coyote visitation was greatest for olfactory-only and visual-only cues, followed by the combined olfactory-visual cue; all cues attracted more coyotes than the control (i.e., olfactory = visual > olfactory-visual > control). Our results suggest this apex predator uses both olfactory and visual cues while foraging for prey. These findings from a field study of free-roaming coyotes increase understanding of predator foraging behavior, predator- prey interactions, and sensory ecology. Our study also suggests future directions for field evaluations of the role of different sensory mechanisms in predator foraging and prey concealment behaviors. Key words: Canis latrans, coyote, foraging ecology, habitat selection, habitat use, olfactory concealment, predator-prey interactions, sensory cues, visual concealment. Les interactions prédateurs-proies influencent les comportements et l'évolution du cycle biologique tant pour les espèces de prédateurs que pour celles de proies et sont également importantes pour la conservation de la biodiversité. La détermination des mécanismes qui sous-tendent les interactions et la dynamique prédateurs-proies constitue un objectif fondamental de l'écologie. Pour examiner le rôle des mécanismes sensoriels des prédateurs dans les interactions prédateurs- proies, plus précisément dans la détection de proies par les prédateurs, nous avons évalué de manière expérimentale l'importance de signaux visuels et olfactifs pour un prédateur de niveau trophique supérieur, le coyote (Canis latrans Say, 1823). Contrairement à d'autres études semblables, nous avons examiné l'utilisation de signaux sensoriels sur le terrain. Nous avons utilisé des caméras de chasse et quatre traitements répliqués--visuel seulement, olfactif seulement, visuel et olfactif combinés et un témoin--pour quantifier la fréquence de visites de coyotes dans des forêts de feuillus d'Amérique du Nord à l'automne 2016. La fréquence des visites de coyotes était la plus grande pour les signaux seulement olfactif et seulement visuel, suivis par les signaux olfactif et visuel combinés; tous les signaux attiraient plus de coyotes que le témoin (c.-à-d., olfactif = visuel > olfactif- visuel > témoin). Nos résultats indiqueraient que ce prédateur de niveau trophique supérieur utilise des signaux olfactifs et visuels dans sa quête de proies. Ces constatations tirées de l'étude sur le terrain de coyotes en liberté accroissent la compréhension du comportement de quête de nourriture des prédateurs, des interactions prédateurs-proies et de l'écologie sensorielle. L'étude suggère également de futures directions pour l'évaluation sur le terrain du rôle de différents mécanismes sensoriels dans les comportements de quête de nourriture des prédateurs et de dissimulation des proies. [Traduit par la Rédaction] Mots-clés : Canis latrans, coyote, écologie de la quête de nourriture, sélection d'habitat, utilisation de l'habitat, dissimulation olfactive, interactions prédateurs-proies, signaux sensoriels, dissimulation visuelle., Introduction Predator-prey interactions are a key class of community interactions that influence ecosystem dynamics (Dulvy et al. 2004; Beauchamp et al. 2007; Ripple and Beschta 2012), drive behavioral and life-history [...]

Bats exploit forest resources based on species-specific adaptations, resulting in differences in activity across forested landscapes. Forest management practices alter forests, impacting species differently and presumably affecting bat activity. Application of forest management that promotes species-specific bat conservation requires further understanding of bat response to silvicultural practices. We surveyed timber harvest treatments on two Indiana State Forests to compare bat activity across forest management treatments, in forests adjacent to harvests, and at locations across the harvest-forest gradient from May to July in 2013 and 2014. We used Wildlife Acoustics Song Meter SM2BAT+ detectors and Kaleidoscope Pro analysis software to survey bats in relation to four treatment types: clear cut, patch cut, shelterwood preparatory cut, and intact forest. Detectors were deployed at two points within each treatment and three points on the forested periphery of treatments and recorded for three consecutive nights. We examined bat activity using Admixture models that estimate abundance and probability of detection for an open population and used Akaike's Information Criterion to select the best models. Based on identification of acoustic calls, eastern red bats and hoary bats were more active in harvest treatments than control treatments. Big brown, eastern red, and tri-colored bats were most active at harvest edges. Northern long-eared and Indiana/little brown bats were most active at harvest edges and in adjacent forest and hoary bats were most active at harvest centers. Differences in bat activity across these managed forests suggest bat assemblages benefit from management that employs an array of silvicultural methods, provides edge habitat, and maintains adjacent forest stands. Our results can be used to predict effects of forest management practices on species-specific bat activity to maximize bat usage of forests., INTRODUCTION Approximately 75% of forest cover has been lost in the state of Indiana over the last two centuries due to agricultural expansion, logging practices, urban development, and human population [...]

Understanding patterns of aboveground carbon storage across forest types is increasingly important as managers adapt to threats of global change. We combined field measures of aboveground biomass with lidar to model fine-scale biomass in deciduous forests located in two watersheds; one watershed was underlain by sandstone and the other by shale. We measured tree and shrub biomass across three topographic positions for both watersheds and analyzed biomass using mixed models. The watershed underlain by shale had 60% more aboveground biomass than the sandstone watershed. Although spatial patterns of biomass were different across watersheds, both had higher (between about 40% and 55%) biomass values at the toe-slope position than at the ridge-top position. To model fine-scale spatial patterns of biomass, we tested the effectiveness of leaf-on and leaf-off lidar combined with topographic metrics to develop a spatially explicit random forest model of tree and shrub biomass across both watersheds. Leaf-on variables were more important for modeling shrub biomass, while leaf-off variables were more effective at modeling tree biomass. Our model of tree and shrub biomass reflects the distribution of biomass across both watersheds at a fine scale and highlights the potential of abiotic factors such as topography and bedrock to affect carbon storage. Key words: biomass, lidar, understory, carbon, shrub. Il est de plus en plus important de comprendre les profils de sequestration aerienne du carbone qui caracterisent les differents types de foret alors que les gestionnaires s'adaptent aux menaces associees au changement global. Nous avons combine des mesures de biomasse aerienne prises sur le terrain avec le lidar pour modeliser la biomasse a petite echelle dans des forets decidues situees dans deux bassins versants : un des bassins reposait sur du gres et l'autre sur du schiste. Nous avons mesure la biomasse des arbres et des arbustes dans trois positions topographiques dans les deux bassins et analyse la biomasse a l'aide de modeles mixtes. Le bassin qui reposait sur le schiste avait 60 % plus de biomasse aerienne que le bassin reposant sur le gres. Bien que la repartition spatiale de leur biomasse differe, les deux bassins avaient des valeurs de biomasse plus elevees (environ 40 a 55 %) au pied qu'au sommet de la pente. Pour modeliser la repartition spatiale a petite echelle, nous avons teste l'efficacite du lidar en presence et en l'absence du feuillage jumele a des donnees topographiques pour elaborer un modele forestier aleatoire, spatialement explicite, de la biomasse arborescente et arbustive dans les deux bassins. Les variables mesurees en presence du feuillage etaient plus importantes pour modeliser la biomasse des arbustes tandis que les variables mesurees en l'absence du feuillage etaient plus efficaces pour modeliser la biomasse des arbres. Notre modele de biomasse arbustive et arborescente reflete la repartition de la biomasse a petite echelle dans les deux bassins et met en evidence l'influence potentielle des facteurs abiotiques, tels que la topographie et le substrat rocheux, sur la sequestration du carbone. [Traduit par la Redaction] Mots-cles : biomasse, lidar, sous-bois, carbone, arbuste., 1. Introduction Understanding patterns of carbon storage across forest types is increasingly important as managers adapt to the diverse threats of global change. Forests are vital components of the global [...]

The Regional Estimates of VEgetation Abundance from Large Sites (REVEALS) model was used to quantify Holocene changes in vegetation cover in the deciduous forest of southeastern Quebec, Canada. The Extended R-Value (ERV) model was used to obtain relative pollen productivity estimates (PPEs) for eight tree taxa and to determine the relevant source area of pollen (RSAP) for lakes in this ecosystem. Modern vegetation was estimated using pollen data from 16 small ( Key words: relative pollen productivity estimates (PPEs), REVEALS model, pollen-vegetation relationship, Holocene, Quebec. Le modèle REVEALS ([much less than] Regional Estimates of VEgetation Abundance from Large Sites [much greater than]) a été utilisé afin de quantifier les changements de la couverture végétale durant l'Holocène dans une forêt décidue du sud-ouest du Québec, Canada. Le modèle ERV ([much less than] Extended R-Value [much greater than]) a été utilisé pour obtenir l'estimation de la productivité pollinique (PPE, [much less than] pollen productivity estimates [much greater than]) de huit taxons d'arbres et déterminer la source pollinique pertinente (RSAP, [much less than] relevant source area of pollen [much greater than]) pour les lacs de cet écosystème. La végétation moderne a été estimée à l'aide des données polliniques de 16 petits lacs ( Mots-clés : estimation de la production pollinique, modèle REVEALS, relation pollen-végétation, Holocène, Québec., Introduction Traditional paleoecological studies depend on pollen percentage diagrams, pollen concentration, or pollen accumulation rates, which provide insight into the vegetation history of a region. However, the nonlinear relationship between [...]

Northern hardwood trees display a wide variety of stem forms and defects, which can substantially reduce their financial value and also complicate their silviculture. While attributes of stem form and defect have been incorporated into tree classification systems, their ability to assess product value and recovery in standing trees has not been adequately tested. To address this issue, we classified stem form and risk using a system developed by the Northern Hardwoods Research Institute (NHRI) for four species across several locations in Maine, New Hampshire, and New Brunswick: sugar maple (Acer saccharum Marsh.), red maple (Acerrubrum L.), yellow birch (Betula alleghaniensis Britton), and northern red oak (Quercus rubra L.). Using these data, we (i) quantified interspecific and regional variation in stem form and damage, (ii) related potential sawlog recovery to tree size, form, and risk, and (iii) compared the efficacy of the NHRI system with a commonly used classification system and a continuous measure of stem quality. High variation in both stem form and damage among the species was found, with red maple showing the largest range. A simplified NHRI system including three form classes proved to be sufficient in differentiating sawlog potential in individual trees, while a model using a continuous measure of stem quality (estimated merchantable sawlog height) performed best. Key words: stem form, risk, northern hardwoods, classification systems, sawlog potential. Le tronc des feuillus nordiques presente une variete de formes et de defauts qui peuvent reduire substantiellement leur valeur financiere et aussi compliquer leur sylviculture. Bien que les attributs de la forme et des defauts du tronc aient ete incorpores dans des systemes de classement des arbres, leur capacite a estimer le rendement et la valeur des produits chez les arbres sur pied n'a pas ete adequatement testee. Pour aborder ce probleme, nous avons classe la forme du tronc et le risque de perte de vigueur a plusieurs endroits dans le Maine, le New Hampshire et le Nouveau-Brunswick en utilisant un systeme developpe par l'Institut de recherche sur les feuillus nordiques (IRFN) pour quatre especes : l'erable a sucre (Acer saccharum Marsh.), l'erable rouge (Acer rubrum L.), le bouleau jaune (Betula alleghaniensis Britton) et le chene rouge (Quercus rubra L.). A l'aide de ces donnees nous avons (i) quantifie la variation interspecifique et regionale de la forme de la tige et des dommages, (ii) relie le rendement potentiel en billes de sciage a la taille de l'arbre, la forme du tronc et le risque de perte de vigueur et (iii) compare l'efficacite du systeme de l'IRFN a celle d'un systeme de classement generalement utilise ainsi qu'a la mesure continue de la qualite du tronc. Nous avons trouve une grande variation de la forme du tronc et des dommages parmi les especes; l'ampleur de la variation etait la plus importante chez l'erable rouge. Le systeme de l'IRFN simplifie comportant trois classes de de forme s'est avere suffisant pour differencier les billes de sciage potentielles chez les arbres individuels tandis qu'un modele utilisant la mesure continue de la qualite du tronc (hauteur marchande estimee en billes de sciage) etait le plus performant. [Traduit par la Redaction] Mots-cles: forme du tronc, risque de perte de vigueur, feuillus nordiques, systeme de classement, bille de sciage potentielle., Introduction The northern hardwood forest type covers approximately 8.1 million ha in the United States (US), spanning from New York into portions of Canada adjacent to this region (Leak et [...]

Bryophytes are dominant components of boreal forest understories and play a large role in regulating soil microclimate and nutrient cycling. Therefore, shifts in bryophyte communities have the potential to affect boreal forests' ecosystem processes. We investigated how bryophyte communities varied in 83 forest stands in interior Alaska that ranged in age (since fire) from 8 to 163 years and had canopies dominated by deciduous broadleaf (Populus tremuloides Michx. or Betula neoalaskana Sarg.) or coniferous trees (Picea mariana Mill B.S.P.). In each stand, we measured bryophyte community composition, along with environmental variables (e.g., organic layer depth, leaf litter cover, moisture). Bryophyte communities were initially similar in deciduous vs. coniferous forests but diverged in older stands in association with changes in organic layer depth and leaf litter cover. Our data suggest two tipping points in bryophyte succession: one at the disappearance of early colonizing taxa 20 years after fire and another at 40 years after fire, which corresponds to canopy closure and differential leaf litter inputs in mature deciduous and coniferous canopies. Our results enhance understanding of the processes that shape compositional patterns and ecosystem services of bryophytes in relation to stand age, canopy composition, and changing disturbances such as fire that may trigger changes in canopy composition. Key words: boreal forest, succession, moss, chronosequence, leaf litter, canopy effects, fire, bryophyte. Les bryophytes sont des elements dominants du sous-bois de la foret boreale et jouent un grand role dans la regulation du recyclage des nutriments et du microclimat dans le sol. Par consequent, les changements dans les communautes de bryophytes peuvent avoir un impact sur les processus de l'ecosysteme de la foret boreale. Nous avons etudie de quelle facon les communautes de bryophytes variaient dans 83 peuplements forestiers de l'interieur de l'Alaska, dont l'age (depuis un feu) allait de 8 a 163 ans et dont le couvert etait domine par des feuillus (Populus tremuloides Michx. ou Betula neoalaskana Sarg.) ou des coniferes (Picea mariana Mill B.S.P.). Dans chaque peuplement, nous avons mesure la composition des communautes de bryophytes, ainsi que des variables environnementales (p. ex., la profondeur de l'horizon organique, la couverture de la litiere de feuilles, l'humidite). Les communautes de bryophytes etaient initialement semblables dans les forets de feuillus et de coniferes mais divergeaient dans les peuplements plus vieux en lien avec la profondeur de l'horizon organique et la couverture de litiere de feuilles. Nos donnees indiquent qu'il y a deux points de bascule dans la succession des bryophytes : un lors de la disparition des taxons pionniers 20 ans apres un feu et l'autre 40 ans apres un feu, moment qui correspond a la fermeture du couvert forestier et a l'apport different de litiere de feuilles dans les couverts matures de feuillus et de coniferes. Nos resultats ameliorent la comprehension des processus qui determinent les patrons de composition et les services de l'ecosysteme des bryophytes en relation avec l'age du peuplement, la composition du couvert forestier et les differentes perturbations, telles que le feu, qui peuvent declencher des changements dans la composition du couvert forestier. [Traduit par la Redaction] Mots-cles: foret boreale, succession, mousse, chronosequence, litiere de feuilles, effets du couvert forestier, feu, bryophyte., Introduction In high-latitude ecosystems such as boreal forests, bryophytes (mosses, liverworts, and hornworts) are dominant and ubiquitous components of the understory and account for a significant proportion of plant diversity [...]

In forested ecosystems, topography and tree species contribute to spatial variability in carbon (C) dynamics through differential rates of C uptake and storage; therefore, estimates of species-specific and spatial variability in C can strengthen ecosystem budgets. To produce such estimates, we deconstructed watershed-scale C and component pools (e.g., wood biomass, litter) and fluxes at a fine scale using a small mixed deciduous forest catchment to determine the variation due to topographic position and species. Factors affecting fluxes included aspect, slope curvature, tree species contributions, and litter production. Annual C uptake into wood varied across the catchment from 0 to 34 kg C x [year.sup.-1] and was 20% greater on southern aspects than northern ones and 33% greater in swales than non-swale slopes. Of the more than 20 tree species found in the forest canopy of the catchment, highest C uptake in woody biomass was measured in Quercus rubra L. growing in swales, followed by Quercus prinus L. syn. growing on the southern aspect, with the lowest aboveground wood increment measured in Pinus at higher elevations on non-swale slopes. Quercus leaf litter moved from where it dropped into litter traps to where it settled on the forest floor, shifting the location of litter C inputs to the soil. Local variation in aboveground C rivals regional variation across regions and has the potential to introduce error when scaling C measures from points to landscapes. Key words: aboveground net primary productivity, basal area, litterfall, Quercus, Acer, Carya. Dans les ecosystemes forestiers, la topographie et les especes d'arbres contribuent a la variability spatiale de la dynamique du carbone (C) par le biais de taux differentiels d'absorption et d'emmagasinage du C; par consequent, les estimations de la variability specifique et spatiale du C peuvent ameliorer les bilans ecosystemiques. Pour produire de telles estimations, nous avons decompose le C a l'echelle du bassin versant ainsi que les pools constitutifs (p. ex. biomasse ligneuse, litiere) et les flux a une echelle fine en utilisant un petit bassin couvert d'une foret feuillue mixte pour determiner la variation due a la position topographique et a l'espece. Les facteurs qui influencent les flux incluaient l'exposition, la courbure de la pente, la contribution des especes d'arbres et la production de litiere. L'absorption annuelle de C dans le bois variait a travers le bassin de 0 a 34 kg C x [an.sup.-1] et etait 20 % plus elevee sur les versants exposes au sud comparativement aux versants exposes au nord et 33 % plus elevee dans les pentes avec baissieres que dans les pentes sans baissieres. Parmi plus de 20 especes d'arbres presentes dans le couvert forestier du bassin, la plus forte absorption de C dans la biomasse ligneuse a ete mesuree chez le Quercus rubra L. croissant dans les baissieres suivi du Quercus prinus L. syn. croissant sur les versants exposes au sud. Les plus faibles accroissements dans le bois au-dessus du sol ont ete mesures chez le Pinus a des altitudes elevees sur des pentes sans baissieres. La litiere de feuilles du Quercus se deplacait de l'endroit ou elle etait tombee dans les trappes a litiere jusqu'a l'endroit ou elle se fixait dans la couverture morte, modifiant ainsi la localisation des apports de C de la litiere dans le sol. La variation locale du C aerien egale la variation regionale entre les regions et pourrait introduire une erreur lorsqu'on transpose des mesures ponctuelles de C aux paysages. [Traduit par la Redaction] Mots-cles: productivite primaire nette aerienne, surface terriere, Quercus, Acer, Carya., 1. Introduction Carbon (C) storage is a valued ecosystem service driven largely by the composition and structure of the biotic community. Many studies have estimated carbon fluxes in forest ecosystems [...]

Terrestrial orchids are especially susceptible to population declines, and hence are the focus of plant conservation efforts worldwide, but the life history and demography of heterotrophic orchids is not well understood. Our objective was to quantify life stage transition rates for a species pair of rare round-leaved orchids (Platanthera spp.) in a northern hardwood forest. Marked individuals were measured over 5 years, and metrics included: leaf area, damage by herbivores and pathogens, flowering, and seed production. Germination trials were also conducted. Vital rates were very similar for the two species, which were about equally abundant despite large differences in seed production. Mortality was twice as high for juvenile as for adult stages, and juvenile abundance was markedly lower than for adults. Both species are vulnerable to leaf damage by invertebrates and fungi and exhibit clear leaf area thresholds for progression across life stages, both suggesting a delicate carbon balance for these mixotrophic orchids. The likely role of mycosymbiont distribution in facilitating seedling establishment deserves further detailed study to inform conservation efforts as these and other orchid species face an uncertain future owing to rapid environmental change and increasing pressure from white-tailed deer herbivory in the northern part of their range. Key words: orchid, demography, conservation, herbivory threshold, life stage. Les orchidees terrestres sont particulierement exposees aux declins de populations et sont ainsi au centre des efforts de conservation des plantes a travers le monde, mais le cycle biologique et la demographie des orchidees heterotrophes ne sont pas bien compris. L'objectif des auteurs etait de quantifier les taux de transition des etapes du cycle biologique chez une paire d'especes rares d'orchidees a feuilles rondes (Platanthera spp.) dans une foret septentrionale de feuillus. La surface foliaire, le dommage par les herbivores et les pathogenes, et la production de fleurs et de graines ont ete documentes chez des individus marques pendant 5 ans. Des tests de germination ont aussi ete menes. Les taux de survie des deux especes etaient tres similaires, lesquelles etant tout aussi abondantes malgre des differences importantes dans la production de graines. La mortalite etait deux fois plus elevee au stade juvenile comparativement au stade adulte et les juveniles etaient beaucoup moins abondants que les adultes. Les deux especes etaient vulnerables au dommage foliaire cause par les invertebres et les champignons et presentaient des seuils clairs de surface foliaire necessaire pour progresser a travers les etapes du cycle biologique, suggerant une balance sensible en carbone chez ces orchidees mixotrophes. Le role probable de la distribution de mycosymbiotes dans la facilitation de l'etablissement des plantules merite d'etre etudie de facon plus detaillee afin d'alimenter les efforts de conservation car ces orchidees et d'autres especes d'orchidees font face a un avenir incertain en raison des changements environnementaux rapides et d'une pression croissante venant de l'herbivorisme pratique par le cerf de Virginie dans la partie septentrionale de sa distribution. [Traduit par la Redaction] Mots-cles : orchidees, demographie, conservation, seuil d'herbivorisme, etapes du cycle biologique., Introduction Orchids are the focus of plant conservation efforts worldwide because they are highly susceptible to population declines, owing largely to their complex interactions with other organisms (Fay et al. [...]

Climate models require an understanding of ecosystem-scale respiration and photosynthesis, yet there is no way of measuring these two fluxes directly; here, new instrumentation is used to determine these fluxes in a temperate forest, showing, for instance, that respiration is less during the day than at night. Seasonal variation in forest productivity Much of the carbon dioxide emitted into the atmosphere is taken up by forest ecosystems. Forest carbon sink estimates are based on the idea that ecosystem respiration is greater during the day than at night and that the efficiency of photosynthetic light use declines after spring. Rick Wehr et al. determine ecosystem photosynthesis and daytime respiration in a temperate deciduous forest over a three-year period on the basis of the isotopic composition of net ecosystem exchange. The work reveals that ecosystem respiration is in fact lower during the day than at night -- evidence of the inhibition of leaf respiration by light (the Kok effect) at the ecosystem scale. The authors argue that current approaches for estimating photosynthesis and daytime respiration do not take this effect into account and therefore overestimate ecosystem photosynthesis and daytime respiration at their forest site, and portray ecosystem photosynthetic light-use efficiency as declining when it is in fact stable. The findings may have implications for estimates of biospheric productivity and carbon cycle-climate interactions. Terrestrial ecosystems currently offset one-quarter of anthropogenic carbon dioxide (CO.sub.2) emissions because of a slight imbalance between global terrestrial photosynthesis and respiration.sup.1. Understanding what controls these two biological fluxes is therefore crucial to predicting climate change.sup.2. Yet there is no way of directly measuring the photosynthesis or daytime respiration of a whole ecosystem of interacting organisms; instead, these fluxes are generally inferred from measurements of net ecosystem-atmosphere CO.sub.2 exchange (NEE), in a way that is based on assumed ecosystem-scale responses to the environment. The consequent view of temperate deciduous forests (an important CO.sub.2 sink) is that, first, ecosystem respiration is greater during the day than at night; and second, ecosystem photosynthetic light-use efficiency peaks after leaf expansion in spring and then declines.sup.3, presumably because of leaf ageing or water stress. This view has underlain the development of terrestrial biosphere models used in climate prediction.sup.4,5 and of remote sensing indices of global biosphere productivity.sup.5,6. Here, we use new isotopic instrumentation.sup.7 to determine ecosystem photosynthesis and daytime respiration.sup.8 in a temperate deciduous forest over a three-year period. We find that ecosystem respiration is lower during the day than at night--the first robust evidence of the inhibition of leaf respiration by light.sup.9,10,11 at the ecosystem scale. Because they do not capture this effect, standard approaches.sup.12,13 overestimate ecosystem photosynthesis and daytime respiration in the first half of the growing season at our site, and inaccurately portray ecosystem photosynthetic light-use efficiency. These findings revise our understanding of forest-atmosphere carbon exchange, and provide a basis for investigating how leaf-level physiological dynamics manifest at the canopy scale in other ecosystems., Author(s): R. Wehr [sup.1] , J. W. Munger [sup.2] , J. B. McManus [sup.3] , D. D. Nelson [sup.3] , M. S. Zahniser [sup.3] , E. A. Davidson [sup.4] , [...]

Forest health deteriorated in eastern North America as a result of depletion of available soil base cations by elevated inputs of acid deposition. We experimentally restored available calcium (Ca) to soils of a forested watershed at Hubbard Brook, New Hampshire, and measured the response of fine root biomass 14 years after treatment. In this northern hardwood forest, fine root ( Key words: acidification, allocation, leaf area index, mycorrhizae, production. L'etat de sante des forets de l'est de l'Amerique du Nord s'est deteriore a la suite de l'epuisement des cations basiques disponibles dans le sol cause par des apports eleves de depots acides. Nous avons experimentalement restaure le calcium (Ca) disponible dans le sol d'un bassin versant boise a Hubbard Brook, au New Hampshire, et mesure la reaction de la biomasse de racines fines (diametre < 1 mm) 14 ans apres le traitement. Dans cette foret de feuillus nordiques, la biomasse de racines fines a diminue de facon significative en reaction a l'apport de Ca relativement a la situation qui prevalait avant le traitement et a celle d'une foret temoin. La diminution etait la plus prononcee dans les zones feuillues situees a une altitude intermediaire a elevee dans le bassin versant, oU les sols sont plus minces et la saturation en bases et les reserves de Ca echangeables sont les plus faibles. La restauration du Ca dans le sol semble avoir reduit l'allocation de C au systeme racinaire et a coincide avec l'augmentation de la biomasse aerienne et de la productivite. Par consequent, nous croyons que l'allocation relativement plus elevee de C aux racines a contribue dans le passe a la baisse de productivite aerienne observee dans les ecosystemes forestiers de feuillus nordiques sous l'effet des depots acides. [Traduit par la Redaction] Mots-cles: acidification, allocation, indice de surface foliaire, mycorhizes, production., Introduction Soils and surface waters in industrialized regions have been acidified as a result of high atmospheric deposition of strong acids derived primarily from the burning of fossil fuels (Likens [...]

The Brown Creeper (Certhia americana Bonaparte, 1838) has been identified as one of the most sensitive passerines to partial forest harvest in North America. The effect of selection logging on Brown Creeper density, nest timing, nest survival, and nest and foraging site selection was examined in five silviculture treatments (intensive group selection, typical group selection, old single-tree selection, recent single-tree selection, and control forests) of Algonquin Provincial Park, Canada. As Brown Creeper nests under the bark of large, decaying trees, we hypothesized that Brown Creeper density, timing of breeding, nest survival, and nest and foraging site selection would be negatively affected by silviculture through the removal of large, decaying trees as part of providing safe conditions for loggers. We monitored 101 nests of Brown Creeper during the 2010 and 2011 breeding seasons, mapped territories to estimate density, and conducted foraging surveys. Brown Creeper density was reduced by about 42% in logged stands compared with control stands. Despite that, silviculture did not significantly alter timing of breeding or nest survival. However, the loss of large trees through partial harvesting meant that Brown Creeper nested closer to adjacent, small forested wetlands and often in balsam fir (Abies balsamea (L.) Mill.) in treated stands. In control stands, Brown Creeper nested further from forested wetlands, disproportionately in greater numbers in upland hardwoods, and preferentially in the bark of snags of yellow birch (Betula alleghaniensis Britton). The change in the species of tree used for nesting and the general forest type as a result of logging also resulted in consequences for the selection of foraging substrates. To maintain higher densities of Brown Creeper in logged stands in Algonquin Park, we recommend retaining larger diameter yellow birch, both snags and live trees, preferably within strategically located uncut reserves based on habitat supply planning, that maintains patches roughly the size of Brown Creeper territories (10 ha). Key words: Brown Creeper, selection silviculture, nesting ecology, foraging tree selection, forestry. Le grimpereau brun (Certhia americana Bonaparte, 1838) est reconnu comme un des passereaux les plus sensibles a la recolte forestiere partielle en Amerique du Nord. Nous avons etudie l'effet de la coupe de jardinage sur la densite d'individus, la chronologie de nidification, la survie des nids et la selection de sites de nidification et d'alimentation du grimpereau brun dans cinq traitements sylvicoles (jardinage habituel par bouquets, jardinage intense par bouquets, jardinage recent par arbre, jardinage ancien par arbre et foret temoin) dans le parc provincial Algonquin, au Canada. Comme le grimpereau brun niche sous l'ecorce de gros arbres en decomposition, nous avons pose l'hypothese que les pratiques sylvicoles, par le biais de la recolte des gros arbres en decomposition visant a procurer aux bucherons un environnement de travail securitaire, auraient un impact negatif sur la densite de grimpereaux, la chronologie de nidification, la survie des nids et la selection des sites de nidification et d'alimentation. Au cours des saisons de nidification 2010 et 2011, nous avons fait le suivi de 101 nids de grimpereaux, cartographie leurs territoires pour estimer la densite et effectue des releves de comportement alimentaire. La densite de grimpereaux etait inferieure de 42 % dans les peuplements traites par rapport aux temoins. Malgre cela, les interventions sylvicoles n'ont pas provoque de changements significatifs dans la chronologie de nidification ni dans la survie des nids. Toutefois, la perte de gros arbres causee par la coupe partielle a force les grimpereaux a nicher plus pres des petits milieux humides boises, souvent dans un sapin baumier situe dans un peuplement traite. Dans les peuplements temoins, le grimpereau a niche plus loin des milieux humides boises, disproportionnellement en plus grands nombres dans les peuplements feuillus bien draines et de preference sous l'ecorce de chicots de bouleau jaune. Le changement d'essence pour la nidification et les caracteristiques generales des peuplements a la suite de la recolte ont eu des consequences sur la selection des substrats d'alimentation. Pour maintenir de plus fortes densites de grimpereaux bruns dans les peuplements jardines du parc Algonquin, nous recommandons de conserver des blocs intacts contenant des gros chicots de bouleau jaune d'une superficie equivalente a un territoire de grimpereau (10 ha). [Traduit par la Redaction] Mots-cles : grimpereau brun, traitement en futaie jardinee, ecologie de la nidification, selection d'arbres d'alimentation, foresterie., Introduction Logging can negatively affect North American breeding bird populations (Vitz and Rodewald 2006). Management concerns for birds that breed in mature forests occur because logging can fragment and reduce [...]

ABSTRACT. Garlic mustard (Alliaria petiolata (M. Bieb.) Cavara & Grande) is a non-native plant that commonly invades hardwood forest understory plant communities. Such invasions have the potential of restructuring forest [...]

A major challenge in studies estimating stand water use in mixed-species forests is how to effectively scale data from individual trees to the stand. This is the case for forest ecosystems in the northeastern USA where differences in water use among species and across different size classes have not been extensively studied, despite their relevance for a wide range of ecosystem services. Our objectives were to assess the importance of different sources of variability on transpiration upscaling and explore the potential impacts of future shifts in species composition on the forest water budget. We measured sap velocity in five tree species (Fagus grandifolia Ehrh., Acer rubrum L., Acer saccharum Marsh., Betula alleghaniensis Britton, and Betula papyrifera Marsh.) in a mature stand and a young stand in New Hampshire, USA. Our results showed that the greatest potential source of error was radial variability and that tree size was more important than species in determining sap velocity. Total sapwood area was demonstrated to exert a strong controlling influence on transpiration, varying depending on tree size and species. We conclude that the effect of potential species shifts on transpiration will depend on the sap velocity, determined not only by radial variation and tree size, but also by the sapwood area distribution in the stand. Key words: sap velocity, stand transpiration, sapwood area, northern hardwood forest, diffuse-porous species. Les etudes dont le but est d'estimer l'utilisation de l'eau a l'echelle du peuplement dans les forets melangees font face a un defi majeur: comment passer efficacement de l'echelle des arbres individuels a l'echelle du peuplement. C'est le cas pour les ecosystemes forestiers dans le nord-est des Etats-Unis oU les differences dans l'utilisation de l'eau entre les especes et parmi les differentes categories de taille n'ont pas fait l'objet d'etudes approfondies malgre leur pertinence pour une vaste gamme de services de l'ecosysteme. Nos objectifs consistaient a evaluer l'importance des differentes sources de variation sur l'extrapolation de la transpiration et a explorer les impacts potentiels des changements futurs dans la composition en especes sur le bilan hydrique de la foret. Nous avons mesure la vitesse de la seve chez cinq especes d'arbre (Fagus grandifolia Ehrh., Acer rubrum L., Acer saccharum Marsh., Betula alleghaniensis Britton et Betula papyrifera Marsh.) dans un peuplement mature et dans un jeune peuplement au New Hampshire (E.-U.). Nos resultats ont montre que la plus grande source potentielle d'erreur etait la variation radiale et que la vitesse de la seve etait davantage determinee par la taille des arbres que par l'espece. La surface totale de bois d'aubier avait un effet tres determinant sur la transpiration qui variait selon la taille et l'espece d'arbre. Nous concluons que l'effet des changements potentiels dans la composition en especes sur la transpiration dependra de la vitesse de la seve qui est principalement determinee par la variation radiale et la taille des arbres mais aussi de la distribution de la surface de bois d'aubier dans le peuplement. [Traduit par la Redaction] Mots-cles: vitesse de la seve, transpiration du peuplement, surface de bois d'aubier, foret feuillue nordique, especes a pores diffus, methode du flux de chaleur., Introduction Forest ecosystems in the northeastern USA provide important ecosystem services to dense population centers in the region, including regulation of water quality and quantity (Campbell et al. 2011), carbon [...]

Deadwood in various stages of decomposition and diverse spatial arrangements provides habitat for numerous organisms. However, knowledge on the colonization of deadwood by vascular plants in mixed deciduous forests is insufficient. We carried out our study in an oak-lime-hornbeam forest in northeastern Poland. Downed logs were colonized by 49 vascular plant species, a number higher than reported from any other type of forest. Species richness and abundance of plants increased with log diameter and decomposition. The former was higher on broadleaf deadwood than on coniferous deadwood (46 vs. 38 species). The frequency and abundance on logs were higher for small-seeded plants ( Key words: forest ecology, disturbances, species richness, natural forest, tree regeneration. Le bois mort a divers stades de decomposition et dans divers arrangements spatiaux procure un habitat a de nombreux organismes. Cependant, nos connaissances sur la colonisation du bois mort par les plantes vasculaires dans les forets feuillues mixtes sont insuffisantes. Nous avons realise notre etude dans la foret de chene, de tilleul et de charme du nord-est de la Pologne. Les billes au sol etaient colonisees par 49 especes de plantes vasculaires, soit un nombre plus eleve que ce qui a ete rapporte dans n'importe quel autre type de foret. La richesse en especes et l'abondance des plantes augmentaient avec le diametre des billes et leur degre de decomposition. La richesse en especes etait plus grande sur le bois mort feuillu que resineux (46 vs 38 especes). La frequence et l'abondance des plantes avec de petites graines ( Mots-cles: ecologie forestiere, perturbations, richesse en especes, foret naturelle, regeneration arborescente., Introduction Long-lasting human pressure on forest ecosystems in the temperate regions of the Northern Hemisphere has not only caused a decrease in the area of forests, but also changed their [...]

This study examined the effects of temperature on soil nitrogen (N) dynamics and variation with slope aspect (northeast (NE) versus southwest (SW)) at two forested sites in West Virginia--Beech Fork Lake (BFL) and Fernow Experimental Forest (FEF)--with similar soil and overstory characteristics but with different latitudes and elevations. Previous work on mineral soil from both sites had shown sharp differences in microbial communities between SW slopes and NE slopes. Mineral soil was sampled from three and eight plots per aspect at FEF and BFL, respectively. Inorganic N was extracted from samples, which were then divided into polyethylene bags for 7-day incubations at 4 [degrees]C, 15 [degrees]C, 25 [degrees]C, and 35 [degrees]C. Following incubation, soils were extracted and analyzed for inorganic N. Net N mineralization varied significantly between aspects and temperatures but did not vary between sites; net nitrification varied significantly between aspects, temperatures, and sites. Net N mineralization increased with incubation temperature at all aspects and sites. Net nitrification rates increased with incubation temperature for BFL soils; however, maximum net nitrification rates occurred at 20-25 [degrees]C for FEF soils. Net nitrification was essentially undetectable for SW soils at either site. Results underline the complexities of the N cycle in temperate forest ecosystems, representing challenges in predicting alterations in soil N dynamics under conditions of global climate change. Key words: nitrogen mineralization, nitrification, forest ecology, global warming, temperate forests. Cette etude s'interesse aux effets de la temperature sur la dynamique de l'azote (N) dans le sol et sa variation selon l'exposition de la pente (nord-est (NE) vs sud-ouest (SO)) dans deux stations forestieres en Virginie-Occidentale : lac Beech Fork (LBF) et foret experimentale de Fernow (FEF), dont les caracteristiques du sol et de l'etage dominant sont similaires mais dont la latitude et l'altitude sont tres differentes. Des travaux anterieurs realises a chaque endroit ont montre qu'il y avait de nettes differences dans les communautes microbiennes du sol mineral entre les pentes SO et NE. Le sol mineral a ete echantillonne dans respectivement trois et huit placettes echantillons par exposition a la FEF et au LBF. L'azote inorganique a ete extrait des echantillons qui ont ensuite ete divises et places dans des sacs de polyethylene pour etre incubes pendant 7 jours a 4 [degrees]C, 15 [degrees]C, 25 [degrees]C et 35 [degrees]C. Les sols ont ete extraits apres l'incubation et analyses pour la presence de N inorganique. La mineralisation nette de N variait de facon significative selon l'orientation et la temperature mais pas selon la station; la nitrification nette variait de facon significative selon l'orientation, la temperature et la station. La mineralisation nette augmentait avec la temperature d'incubation peu importe l'orientation ou la station. La nitrification nette augmentait avec la temperature d'incubation dans les sols du LBF, mais les taux maximum ont ete observes a 20-25 [degrees]C a la FEF. La nitrification nette etait significativement reliee a la mineralisation nette de N dans les sols orientes NE dans les deux stations peu importe la temperature d'incubation, sauf 35 [degrees]C. La nitrification nette etait pratiquement indetectable dans les sols orientes NO dans les deux stations. Les resultats mettent en evidence la complexite du cycle de N dans les ecosystemes de foret temperee, ce qui represente un defi pour predire les modifications de la dynamique de N dans le sol dans le contexte du changement mondial. [Traduit par la Redaction] Mots-cles: mineralisation de l'azote, nitrification, ecologie forestiere, rechauffement climatique, forets temperees., Introduction Predicted increases in global temperatures have important implications for future changes in the dynamics of soil nitrogen (N) in many regions, especially those that are dominated by temperate forests [...]

We quantified the fine root length density of Lonicera maackii (Amur honeysuckle) and native trees at two depths on transects away from individuals of this invasive shrub and tested whether the invasive shrub L. maackii reduced water availability for other forest plants by either of two mechanisms: (1) intercepting rainwater during light rain events or (2) absorbing large amounts of water through its fine roots. To test the two hypothesized mechanisms, we selected plots near large L. maackii shrubs and control plots away from any large L. maackii shrubs in the forest understory. Within each plot we placed a trenched and an untrenched subplot and measured soil water content in each. We also measured precipitation above and below L. maackii canopies. We found that within 2 m of large maackii shrubs, this shrub accounted for a large fraction (22-25%) of the fine roots in the top 12 cm of soil. Reduced throughfall and soil moisture below shrubs supported the hypothesis that L. maackii competes with tree seedlings by interception. Findings were inconclusive regarding the hypothesis of competition by water uptake., INTRODUCTION Invasive plant species often cause deleterious effects on local communities, particularly by reducing native plant species diversity (Vila et al., 2011). However, the individual mechanisms underlying these reductions in [...]

The decomposition of coarse woody debris contributes to forest nutrient sustainability and carbon (C) balances, yet few field studies have been undertaken to investigate these relationships in northern hardwood forests. We used a paired-sample approach to study the decomposition of sugar maple (Acer saccharum Marsh.), American beech (Fagus grandifolia Erhr.), and yellow birch (Betula alleghaniensis Britt.) boles at the Hubbard Brook Experimental Forest in New Hampshire. Mass loss over 16 years followed a first-order exponential decay pattern with half-lives ranging from 4.9 to 9.4 years in bark and from 7.3 to 10.9 years in wood. Nitrogen (N) and phosphorus (P) concentrations increased significantly during decomposition, resulting in sharp decreases in C:N and C:P ratios. We did not, however, observe significant net increases in the amount of N or P stored in decomposing boles, as reported in some other studies. Calcium (Ca) concentration decreased by up to 50% in bark but more than doubled in wood of all species. The retention of Ca in decomposing wood helps maintain Ca pools in this base-poor ecosystem. Together, the exponential model for mass loss and a combined power-exponential model for changes in nutrient concentrations were able to simulate nutrient dynamics in decomposing boles after clear-cutting in an adjacent watershed. Key words: coarse woody debris, decomposition, nitrogen, carbon, calcium. La decomposition des debris ligneux grossiers contribue a la durabilite des nutriments et au bilan du carbone (C) dans les forets mais peu d'etudes sur le terrain ont ete entreprises dans le but d'examiner ces relations dans les forets feuillues nordiques. Nous avons utilise l'approche des echantillons apparies pour etudier la decomposition des troncs d'erable a sucre (Acer saccharum Marshall), de hetre d'Amerique (Fagus grandifolia Erhr.) et de bouleau jaune (Betula alleghaniensis Britton) a la foret experimentale de Hubbard Brook au New Hampshire. Sur une periode de 16 ans, la perte de masse a suivi un patron de decomposition exponentiel du premier degre avec une demi-vie allant de 4,9 a 9,4 ans dans l'ecorce et de 7,3 a 10,9 ans dans le bois. Les concentrations d'azote (N) et de phosphore (P) ont augmente de facon importante durant la decomposition entrainant une diminution rapide des rapports C:N et C:P. Nous n'avons cependant pas observe d'augmentation nette significative des quantites de N ou de P emmagasines dans les troncs en decomposition telle que l'ont rapportee d'autres etudes. La concentration de calcium (Ca) a diminue dans une proportion pouvant atteindre 50 % dans l'ecorce mais a plus que double dans le bois en decomposition de toutes les especes. La retention du Ca dans le bois en decomposition aide a maintenir les reservoirs de Ca dans cet ecosysteme pauvre en bases. Ensemble, le modele exponentiel pour la perte de masse et un modele combine de puissance et exponentiel pour les changements dans la concentration des nutriments pouvaient simuler la dynamique des nutriments dans les troncs en decomposition apres une coupe a blanc dans un bassin versant adjacent. [Traduit par la Redaction] Mots-cles: debris ligneux grossiers, decomposition, azote, carbone, calcium., Introduction Coarse woody debris (CWD) has long been recognized as an important ecological component of forest ecosystems (Harmon et al. 1986). During the decomposition of CWD, nutrients are returned to [...]

Silvicultural disturbance can lead to major shifts in biotic and abiotic characteristics of forests, with significant implications for wildlife. Many studies have demonstrated site occupancy and abundance of small mammals changes following silviculture, but few have identified the habitat characteristics associated with small mammal responses. We conducted a study in the central hardwood forest region of the U.S. to examine the relationship between small mammal habitat use and habitat variables at the microsite scale, before and after silvicultural disturbance, while explicitly accounting for imperfect detection. Following the creation of harvest openings, vegetation cover and coarse woody debris increased, and leaf litter depth decreased. Fewer changes occurred following the midstory removal stage of a shelterwood harvest. Eastern chipmunks (Tamias striatus) and white-footed mice (Peromyscus leucopus) were positively correlated with woody vegetation cover and coarse woody debris, and short-tailed shrews (Blarina brevicauda) were positively correlated with coarse woody debris and leaf litter depth. Careful consideration of experimental scale and incorporation of detection probability are necessary for successful identification of small mammal associations within microhabitats, as these relationships help to explain shifts in small mammal communities following silviculture., INTRODUCTION The impacts of silviculture on wildlife are an increasing concern for managers seeking to preserve ecosystem function in conjunction with forest management. Silvicultural techniques can exert a range of [...]

The regeneration ecology of sugar maple (Acer saccharum Marsh.) has been impacted by acid rain leaching of base cations from the soils throughout much of its range. We tracked the survival and causes of death for a natural cohort of sugar maple seedlings across 22 sites in the Hubbard Brook Valley in New Hampshire, USA, where soil acidification has been documented. Survival over 7 years averaged 3.4%; however, significant differences in survival were observed among sites, which were classified into three main groups based on the shape of their survival curves. These site groups differed in position on the landscape, seedling nutrition and leaf size, and the prevalence of damage agents, but not in soil Ca. First-season mortality was high (71%), and the main damage agents were fungal infection (Rhizoctonia spp.) and caterpillar herbivory (Geometridae). Other principal causes of mortality in order of importance were winter injury, mechanical damage, and rodent (Myodes gapperi Vigors, 1830) tunneling, and all damage agents varied significantly in severity between years. This study highlights the importance of landscape-level variation in biotic factors for predicting sugar maple regeneration success. Predictions of sugar maple regeneration will require a better understanding of controls on initial seedling growth and the suite of biotic agents that damages seedlings. Key words: Geometridae, Hubbard Brook Experimental Forest, mortality, Rhizoctonia, winter injury. Le lessivage des cations basiques du sol par les pluies acides a eu un impact sur l'ecologie de la regeneration de l'erable a sucre (Acer saccharum Marshall) presque partout dans son aire de repartition. Nous avons suivi la survie et les causes de moralite d'une cohorte naturelle de semis d'erable a sucre dans 22 stations de la vallee de Hubbard Brook au New Hampshire, E.-U., oU l'acidite du sol a ete documentee. Sur une periode de 7 ans, le taux moyen de survie a ete de 3,4 %; cependant, des differences significatives ont ete observees entre les stations qui ont ete classees en trois groupes principaux sur la base de leur courbe de survie. Ces groupes de stations se distinguaient par leur position dans le paysage, la nutrition et la taille des feuilles des semis ainsi que par la predominance des agents deteriorateurs mais non par le Ca du sol. La mortalite a ete elevee (71 %) durant la premiere saison et les principaux agents deteriorateurs etaient les infections fongiques (Rhizoctonia spp.) et l'herbivorisme des chenilles (Geometridae). Les autres causes principales de mortalite etaient en ordre d'importance: les blessures hivernales, les blessures mecaniques et les galeries de rongeur (Myodes gapperi Vigors, 1830) et la severite des dommages causes par tous les agents deteriorateurs etait significativement differente d'une annee a l'autre. Cette etude fait ressortir l'importance de la variation a l'echelle du paysage des facteurs biotiques pour predire la reussite de la regeneration de l'erable a sucre. Les predictions concernant la regeneration de l'erable a sucre necessitent une meilleure comprehension des facteurs qui regissent la croissance initiale des semis et la serie d'agents biotiques qui causent des dommages aux semis. [Traduit par la Redaction] Mots-cles: Geometridae, foret experimentale de Hubbard Brook, mortalite, Rhizoctonia, blessures hivernales., Introduction Temperate forests are confronted with an unprecedented combination of human-accelerated environmental changes, including climate warming (Dale et al. 2001), air pollution (Tomlinson 2003), and introduced pests and pathogens (Fischer [...]

Vertebrate herbivores and omnivores modify forest regeneration not only via direct and indirect trophic pathways, but also via nontrophic pathways such as litter and soil disturbances that may favor the regeneration of some species but not others. Deer are overabundant throughout vast portions of the eastern deciduous forest, and turkeys, once nearly extirpated, are now far more common; their foraging habits disturb litter over large areas, though this has rarely been evaluated. We quantified the size and frequency of litter disturbances created by both deer and turkeys. In addition, we tested the hypothesis that excluding vertebrates via fences would cause a reduction in the abundance and size of litter disturbances. We tested this hypothesis inside and outside six exclosures and adjacent control plots in an old-growth deciduous forest in Pennsylvania. Bare soil patches were ~60% smaller and between 50% and 90% less abundant inside exclosures. The mean size of turkey litter disturbances was large (mean > 30 [m.sup.2]) and significantly greater than deer disturbances (p = 0.002), though turkey disturbances were less frequent. Our findings should apply broadly and are some of the first to demonstrate the extent of turkey disturbances. In addition, we demonstrate that exclosure studies reduce physical disturbances as well as browsing, both of which may synergistically act to cause changes in forest communities. We also caution that many deer fences exclude other vertebrates such as turkeys, which are important herbivores, seed predators, and major agents of disturbance. Consequently, we argue that studies that use fences to exclude deer should explicitly consider nontrophic indirect effects, particularly leaf disturbances and the potential impact of other large consumers as well (e.g., turkeys). Key words: deer, wild turkey, litter disturbance, nontrophic effects, exclosure studies. Les vertebres herbivores et omnivores modifient la regeneration forestiere non seulement via les chaines trophiques directes et indirectes, mais aussi via des effets non-trophiques tels la perturbation de la litiere et du sol qui peut favoriser la regeneration de certaines especes au detriment des autres. Le cerf est surabondant dans de vastes parties de la foret feuillue de l'Est tandis que le dindon sauvage, apres avoir frole la disparition, est maintenant beaucoup plus commun. Bien que les habitudes alimentaires de ces deux herbivores perturbent la litiere sur de vastes superficies, leurs effets n'ont a peu pres pas ete documentes. Nous avons quantifie la taille et la frequence des perturbations de la litiere par le cerf et le dindon. De plus, nous avons teste l'hypothese que l'exclusion des vertebres par des clotures devrait causer une reduction de l'abondance et de la taille des perturbations de litiere. Pour tester cette hypothese, nous avons dispose des places-echantillons dans six exclos et dans des sites temoins adjacents dans une foret feuillue ancienne en Pennsylvanie. Les plaques de sol denude etaient ~60 % plus petites et de 50 a 90 % moins abondantes dans les exclos. La taille moyenne des plaques de litiere perturbees par le dindon etait importante (moyenne > 30 [m.sup.2]) et significativement plus grande que celle des plaques perturbees par le cerf (p = 0,002), mais les plaques perturbees par le dindon etaient moins frequentes. Nos resultats devraient avoir une grande portee et sont parmi les premiers a demontrer l'importance des perturbations causees par le dindon. De plus, nous demontrons que les etudes faisant appel a des exclos reduisent les perturbations physiques et le broutement, deux agents de perturbation qui peuvent agir en synergie pour causer des changements dans les communautes forestieres. Nous soulignons aussi le fait que plusieurs clotures a cerf excluent aussi d'autres vertebres dont le dindon, un herbivore important, un predateur de graines et un agent majeur de perturbation. Par consequent, nous soutenons que les etudes qui utilisent des clotures pour exclure le cerf devraient formellement tenir compte des effets non-trophiques indirects, en particulier les perturbations du feuillage et l'impact potentiel des autres consommateurs de grande taille comme le dindon. [Traduit par la Redaction] Mots-cles: cerf, dindon sauvage, perturbation de la litiere, effets non-trophiques, exclos experimentaux., Introduction There is now overwhelming evidence that white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)) browsing has created depauperate and low-density plant communities throughout vast portions of the eastern deciduous forest (Waller [...]

Invasive Amur honeysuckle (Lonicera maackii) creates a dense shrub layer in eastern deciduous forests that negatively impacts native herbs and tree seedlings. Given the well-studied influence of habitat structure on spider abundance and guild composition, we examined the effects of this invasive shrub on spiders in forests of southwestern Ohio. Because spiders are sensitive to shrub architecture, we predicted that increased vegetative cover caused by invasion of L. maackii would increase diversity and abundance of spider taxa and guilds. We used paired plots (e.g., honeysuckle present and honeysuckle- absent) in ten deciduous forest locations to sample spiders and measured vertical cover of woody vegetation in the shrub layer. Abundance of spiders overall, spider families (Anyphaenidae, Araneidae, Salticidae, Theridiidae) and spider guilds (foliage runners, orb weavers, space web builders, stalkers), was higher in honeysuckle-present than in honeysuckle-absent plots, but diversity was not affected. Ordination of spider taxa and guilds significantly distinguished honeysuckle-present from honeysuckle-absent plots. Invasion by honeysuckle more than doubled the amount of vertical cover on honeysuckle-present plots compared to honeysuckle-absent plots. This increased vertical cover explained the significant increase in abundance of spiders and spider guilds on honeysuckle-present plots, likely because of increased complexity of vegetation. While a positive association between vegetation complexity, spider abundance, and guild structure has been documented for native habitats, our study extends this relationship to result from invasion by an exotic shrub. Because spiders are important predators in forest food webs, and their abundance is higher in areas containing honeysuckle, forests could be managed to retain some honeysuckle in the system, thereby preserving their positive effect on spider populations., INTRODUCTION Diversity and abundance of spiders (Arthropoda: Araneae) is affected by habitat structure, e.g., plant height, foliage density, number of leaves and branches, and number of inflorescences (Uetz, 1991; Souza [...]

A study over time provides a unique approach to investigate if landscape-environmental conditions can explain community resistance to invasion by nonnative plants in protected forest patches. This study investigated overall and intra-forest spatial patterns of change in nonnative Lonicera maackii (Amur honeysuckle) after 18 y in a 5.2 ha mature deciduous forest in southwestern Ohio. Changes in height-class abundances were measured in 60 permanent plots and mapped using GIS. Amur honeysuckle density increased from 3361 to 5472 individuals/ha (62.8%), but increases and decreases occurred at different sample plots. Greatest increases were for individuals 1 and, INTRODUCTION 'The modern synthesis of community ecology recognizes that all ecological ecosystems are inherently unstable' (Pickett et al., 1992, p. 66). Plant communities change over time in response to local [...]

Standing dead trees (snags) are an important component of forest ecosystems, providing foraging, nesting, and roosting substrate for a variety of vertebrates. We examined the effects of four forest regeneration treatments on residual snag density and compared those with densities found in unharvested, naturally regenerated forests (controls) during the second, fourth, and sixth year after timber harvest in mixed pine-hardwood forests of Arkansas and Oklahoma. Regeneration treatments were clearcut with snag creation, shelterwood, single-tree selection, and group selection. Density of large snags (≥25.0 cm DBH) differed only during the sixth year after harvest, with shelterwoods having a lower density of large snags (1.0 snags/ha) than the control or group selection stands (4.0 and 4.2 snags/ha, respectively). Density of small snags (10.0-24.9 cm DBH) mirrored residual basal area, with controls and group-selection stands having the greatest snag densities. Creation of snags in clearcuts by injection with herbicides caused initial snag density in these areas to be greater than other treatments, but density in clearcuts declined sharply by 6 years after harvest. In the absence of snag creation, treatments such as shelterwoods that remove most trees may have snag densities below that required to address some management objectives without additional snag creation. Resume: Les arbres morts sur pied (chicots) sont une composante importante des ecosystemes forestiers car ils servent de source de nourriture et de lieu de nidification et de repos pour de nombreux vertebres. Nous avons etudie les effets de quatre traitements de regeneration forestiere sur la densite residuelle de chicots et compare ces resultats a la densite de forets regenerees naturellement et non exploitees (temoins) au cours des deuxieme, quatrieme et sixieme annees apres la coupe de forets mixtes de pins et de feuillus de l'Arkansas et de l'Oklahoma. Les traitements de regeneration incluaient: une coupe a blanc avec creation de chicots, une coupe progressive d'ensemencement, une coupe de jardinage par pied d'arbre et une coupe de jardinage par groupe. La densite de gros chicots (diametre a hauteur de poitrine--DHP ≥ 25,0 cm) a ete differente seulement pendant la sixieme annee apres la coupe au cours de laquelle les coupes progressives contenaient une plus faible densite de gros chicots (1,0 chicot/ha) que les temoins et les coupes de jardinage par groupe (respectivement 4,0 et 4,2 chicots/ha). La densite de petits chicots (DHP = 10,0-24,9 cm) etait proportionnelle a la surface terriere residuelle, c'est-a-dire que les plus fortes densites etaient associees aux temoins et aux coupes de jardinage par groupe. La creation de chicots dans les coupes a blanc par injection d'herbicides a initialement produit une plus grande densite de chicots que les autres traitements, mais elle avait fortement diminue 6 ans apres la coupe. Sans creation additionnelle de chicots, des traitements comme la coupe progressive, qui preleve la plupart des arbres, peuvent engendrer une densite de chicots sous le seuil vise par certains objectifs d'amenagement. [Traduit par la Redaction], Introduction The importance of snags to vertebrates in forest ecosystems is widely known. Over 85 species of North American birds use snags for foraging or nesting (Scott et al. 1977), [...]

Leaf litterfall represents an important nutrient flux in forests, but separating leaves by species and collecting fresh litter annually for nutrient analysis is time-consuming and expensive. To quantify the sources of variation in litterfall nutrient estimates and guide optimal allocation of research effort, we analyzed nutrient concentration (5 years) and mass (6 years) of leaf litter for nine tree species in 13 northern hardwood sites. Coefficients of variation (CVs) in nutrient concentration were higher across sites than over time within sites for most elements; phosphorus was especially variable across sites (56% CV). Thus, to estimate litterfall nutrient fluxes accurately in forests of this type, nutrient analyses should be sitespecific as well as species-specific but may not need to be repeated annually (CVs over time averaged 17% for calcium, 21% for magnesium, 28% for potassium, and 32% for phosphorus concentration). Total leaf litterfall mass varied considerably from year to year, ranging from 234 to 370 g*m [sup-2] averaged over 13 sites. We recommend that litter collectors be elevated above the ground to avoid oversampling during extreme wind events. Use of species-specific allometric equations, or even basal area, to estimate the species composition of total litter mass may obviate the need to sort litter by species. Resume: La chute de litiere de feuilles represente un flux important de nutriments dans les forets mais la separation des feuilles selon l'espece et la collecte annuelle de litiere fraiche pour analyser les nutriments coutent cher et prennent beaucoup de temps. Afin de quantifier les sources de variation des estimations des nutriments presents dans la chute de litiere et de favoriserune allocation optimale des efforts de recherche, nous avons analyse la concentration des nutriments (5 ans) et la masse de litiere de feuilles (6 ans) pour neufespeces d'arbres dans 13 stations de feuillus nordiques. Les coefficients de variation (CV) de la concentration des nutriments etaient plus eleves entre les stations qu'entre les annees dans une meme station pour la plupart des elements; le phosphore etait particulierement variable d'une station a l'autre (CV = 56%). Par consequent, pour estimer avec precision les flux de nutriments dans la chute de litiere de ce type de foret, l'analyse des nutriments devrait etre specifique a chaque station et a chaque espece mais n'a pas besoin d'etre repetee a chaque annee (le CV entre les annees atteignait en moyenne 17% pour la concentration de calcium, 21% pour le magnesium, 28% pour le potassium et 32% pour le phosphore). La masse totale de chute de litiere de feuilles variait considerablement d'annee en annee, allant en moyenne pour les 13 stations de 234 a 370 g*m [sup-2] Nous recommandons que les collecteurs de litiere soient sureleves par rapport au sol pour eviter de surechantillonner lors d'episodes de vents violents. L'utilisation d'equations allometriques propres a chaque espece, ou meme de la surface terriere, pour estimer la composition en espece de la masse totale de litiere peut eviter d'avoir a trier la litiere selon l'espece. [Traduit par la Redaction], Introduction The mass and nutrient content of leaf production and turnover are important for estimating net primary productivity and nutrient cycling budgets in forested ecosystems (Whittaker et al. 1979; Clark [...]

Invasive species usurp habitat space at the expense of natives, reducing biodiversity and altering ecosystem function. The non-native invasive shrub Amur honeysuckle (Lonicera maackii) is known to have substantial effects on forest structure and biodiversity in Midwestern North America; however, its influence on nutrient cycling is relatively unexplored. We investigated throughfall volume and chemistry, and soil nutrients, under and away from L. maackii shrubs in random locations along transects in three patchily invaded second-growth forests. Significantly lower volumes of throughfall were found under L. maackii canopies than in sites located away from L. maackii. Cation concentrations in throughfall were significantly higher, and in some instances 3 x higher, under L. maackii than in 'away' locations. Despite lower throughfall volumes under L. maackii compared to 'away' locations, total deposition of cations in throughfall under L. maackii was also consistently higher than in adjacent areas of native forest canopy. In contrast, [NH.sub.4.sup.+]-N concentrations in throughfall were significantly lower under L. maackii than away, suggesting N transformation and assimilation as rainwater passed through the canopy. No differences were found in soil properties between 'under' and 'away' locations. In summary, L. maackii significantly reduced the volume of rainwater arriving at the forest floor and altered the chemistry of that rainwater causing an increase in cation concentrations and a reduction in [NH.sub.4.sup.+]-N. These results suggest that L. maackii invasion has the potential to cause significant alterations to nutrient cycling in forests., INTRODUCTION The invasion of forests by non-native species can substantially influence ecosystem composition and function (Evans et al., 2001; Mack et al., 2000). Invasive species rapidly expand into habitat space, [...]

I observed an exceptionally high density of Hermit Thrush (Catharus guttatus) nests (3.1 nests/ha) over two breeding seasons in an isolated 1.3-ha portion of an earthworm-free study site in the Chequamegon-Nicolet National Forest, Wisconsin. This density was much greater than the 0.1 to 0.6 nests/ha observed over the rest of the study area and exceeds by an order of magnitude most previously reported estimates for this species. The mean distance among Hermit Thrash nests in earthworm-free sites (215 m; 95% CI = 180-250 m) was lower than in invaded sites (250 m; 95% CI = 236-264 m); this difference was not statistically significant. Nest density did not differ significantly between categories. An abundance of suitable nest sites in a favored nesting substrate (clubmoss; Lycopodium spp.) could have contributed to the exceptionally high density of Hermit Thrush nests observed. High Hermit Thrush nest densities may occur in association with forest floor conditions that are characteristic of earthworm-free areas. Received 3 August 2011. Accepted 16 January 2012., Invasive European earthworms (Lumbricus spp.) are spreading through north temperate hardwood forests of North America that were previously glaciated and historically earthworm-free (James 2004). Lumbricus earthworms alter soil structure and [...]

We resurveyed a network of sampling plots (n = 371) 10 years after its establishment in Hubbard Brook Experimental Forest (New Hampshire, USA) to quantify recent trends in tree biomass and demography. We found no significant change in live-tree biomass during the decade. Total biomass was 246 [Mg * ha.sup.-1] (95%CI = 235 - 258) in 1995-1996 and 245 Mg * ha.sup.-1 (95%CI = 234 - 256) in 2005-2006. Annual mortality during the period for trees ≥ 10 cm diameter at breast height (1.37 m) averaged 9.7 [[trees * ha.sup.-1] * year.sup.-1] (95% CI of annual mortality rate = [1.36% - 1.84% * year.sup.-1]). Tree recruitment into the census pool was 8.4 [[trees * ha.sup.-1] * year.sup.-1] (95% CI = 5.8 - 10.6). Although overall forest biomass remained constant, there were marked shifts in the relative dominance of the canopy species. For example, the live biomass of Betula alleghaniensis Britton declined by 7%, whereas the live biomass of Picea rubens Sarg. increased by 6% and that of Acer saccharum Marshall increased by 4%. There was no instance of recruitment significantly exceeding mortality for the major species. Relative growth rates ranged from [1.03% * year.sup.-1] for Betula papyrifera Marshall to [1.99% * year.sup.-1] for Abies balsamea (L.) Mill. Our results confirmed earlier reports that the forest at Hubbard Brook is no longer aggrading. Current live-tree biomass is lower than expected. Although effects of novel disturbances documented on a regional level have not led to directional changes in tree demography at Hubbard Brook, we suggest that these novel stressors are depressing the biomass potential of the forest. Resume: Nous avons remesure un reseau de placettes echantillons (n 0371) 10 ans apres son etablissement a la foret experimentale d'Hubbard Brook (New Hampshire, E-U.) pour quantifier les tendances recentes de la demographie et de la biomasse des arbres. Nous n'avons observe aucun changement significatif dans la biomasse des arbres au cours de la decennie. La biomasse totale atteignait 246 [Mg * ha.sup.-1] (IC de 95 % = 235 - 258) en 1995 Underscore 1996 et 245 [Mg * ha.sup.-1] (IC de 95 % = 234 - 256) en 2005-2006. Pendant cette periode, la mortalite annuelle des arbres ≥ 10 cm de diametre a hauteur de poitrine (1,37 m) a ete en moyenne de 9,7 [[arbres * ha.sup.-1] * an.sup.-1] (IC de 95 % du taux annuel de mortaliteEqual 1,36 Underscore 1,84 [% * an.sup.-1]). Le recrutement d'arbres dans le bassin d'inventaire atteignait 8,4 [[arbres * ha.sup.-1] * an.sup.-1] (IC de 95 % = 5,8 - 10,6). Bien que la biomasse forestiere globale soit demeuree constante, il y a eu des changements marques dans la dominance relative des especes formant le couvert. Par exemple, la biomasse vivante de Betula alleghaniensis Britton a diminue de 7 % tandis que celle de Picea rubens Sarg. a augmente de 6 % et celle d'Acer saccharum Marshall de 4 %. Aucun episode de recrutement n'a excede la mortalite des principales essences. Le taux de croissance relatif variait de 1,03 [% * an.sup.-1] pour Betula papyrifera Marshall a 1,99 [% * an.sup.-1] pour Abies balsamea (L.) Mill. Nos resultats confirment les rapports anterieurs qui mentionnent que la foret d'Hubbard Brook n'est plus en train de s'ameliorer. La biomasse courante des arbres vivants est plus faible que prevu. Meme si les effets de nouvelles perturbations documentees a l'echelle regionale n'ont pas entraine de changements directionnels dans la demographie des arbres a Hubbard Brook, nous croyons que ces nouveaux stress reduisent la biomasse potentielle de la foret. [Traduit par la Redaction], Introduction Recent reports that live-tree biomass has stopped accumulating at the Hubbard Brook Experimental Forest in the White Mountains of New Hampshire, despite expectations of continued growth (Fahey et al. [...]

Stand structure is a key attribute of forest ecosystems. Mixed-tree plantations are widely felt to be the appropriate option for providing a broad range of goods and environmental services and to reduce susceptibility to natural hazards. However, the debate continues whether mixed plantations can achieve greater financial return than monocultures can. In this study, mixed-species stands of conifers and hardwood species were analyzed in consideration of economically relevant factors. Growth performance and resistance to hazards and pests are widely noted in the literature and are of general economic interest. Thus meta-analyses of relevant studies were conducted to test the following hypotheses: (1) mixing tree species has no significant influence on growth performance or resistance against hazards and pests and, if refuted, (2) mixing tree species causes mainly negative effects on growth performance and resistance against hazards and pests. However, a positive impact of mixing tree species was proven for resistance against windthrow and pests. The meta-analysis on growth performance just as well indicates a positive effect of mixing tree species. Overall, these positive results underscore the need for a large number of additional studies to examine different silvicultural systems to develop optimal management prescriptions to benefit from positive interactions. La structure du peuplement est un attribut cle des ecosystemes forestiers. Les plantations mixtes sont largement considerees comme une option appropriee pour fournir une large gamme de produits et de services environnementaux ainsi que pour reduire la predisposition aux catastrophes naturelles. Cependant, le debat persiste a savoir si les plantations mixtes peuvent procurer un meilleur rendement financier que les monocultures. Dans cette etude, des peuplements mixtes composes d'especes feuillues et resineuses ont ete analyses en tenant compte de facteurs pertinents du point de vue economique. La croissance et la resistance aux catastrophes et aux ravageurs sont couramment mentionnees dans la litterature et presentent un interet economique general. Des meta-analyses des etudes pertinentes ont par consequent ete realisees pour tester les hy-potheses suivantes: (1) le fait de melanger les especes d'arbre n'a aucun effet significatif sur la croissance ou la resistance aux catastrophes et aux ravageurs et si cette hypothese est refutee, (2) le fait de melanger les especes d'arbre a surtout des effets negatifs sur la croissance et la resistance aux catastrophes et aux ravageurs. Toutefois, un effet positif du melange des especes a ete demontre dans le cas de la resistance au chablis et aux ravageurs. La meta-analyse indique egalement que le melange des essences a un effet positif sur la croissance. Dans l'ensemble, ces resultats positifs soulignent la necessite d'ef-fectuer un grand nombre d'etudes additionnelles pour examiner differents systemes sylvicoles dans le but d'elaborer des prescriptions d'amenagement optimales pour beneficier des interactions positives. [Traduit par la Redaction], Introduction Until the end of the 18th century, central European deciduous forests were degraded. Although foresters as well as scientists have been discussing whether or not pure or mixed-species stands [...]

The role of the [O.sub.ie] horizon in calcium supply of sugar maple (Acer saccharum Marsh.) seedlings was evaluated. Forest floor [O.sub.ie] horizon was reciprocally transplanted on 1 [m.sup.3] quadrats between a Ca-treated (W1) and a reference (W3) watershed, and sugar maple seeds were planted on the quadrats. The [O.sub.ie] horizon in W1 exhibited a greatly increased Ca:Sr molar ratio compared with the reference W3 (550 vs. 220), allowing distinction of this Ca source in seedling tissues. Foliage and fine roots of maple seedlings growing on quadrats in W3 with [O.sub.ie] transplanted from W1 exhibited Ca:Sr ratios intermediate between the [O.sub.ie] and underlying native soil horizons, demonstrating the role of [O.sub.ie] in seedling Ca nutrition. However, apparently strong and temporally changing discrimination of Ca and Sr in seedling uptake and internal transport confounded quantitative evaluation. Resume: Nous avons evalue le role de l'horizon [O.sub.ie] dans l'approvisionnement en calcium des semis d'erable a sucre (Acer saccharum Marsh.). L'horizon organique forestier [O.sub.ie] a ete reciproquement transplante dans des quadrats de 1 [m.sup.2] etablis dans un bassin versant traite au Ca (W1) et un bassin de reference (W3) et des graines d'erable a sucre ont ete plantees dans chaque quadrat. Le rapport molaire Ca:Sr de l'horizon [O.sub.ie] du bassin W1 a fortement augmente comparativement a celui du bassin de reference W3 (550 vs. 220), ce qui a permis de distinguer cette source de Ca dans les tissus des semis. Les feuilles et les radicelles des semis d'erable croissant dans les quadrats du bassin W3, mais dans lesquels l'horizon [O.sub.ie] du bassin W1 a ete transplante, avaient un rapport Ca:Sr intermediaire entre l'horizon [O.sub.ie] et les horizons originels sous-jacents du sol, ce qui demontre le role de l'horizon [O.sub.ie] dans la nutrition en Ca des semis. Toutefois, la discrimination apparemment forte et variable dans le temps entre Ca et Sr lors de l'absorption par les semis et du transport interne a brouille l'evaluation quantitative. [Traduit par la Redaction], Introduction Long-term exposure of forest ecosystems to acid deposition has resulted in soil and surface water acidification on acid-sensitive sites in industrialized regions. Consequent depletion of soil base cations has [...]