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Climate-smart forestry (CSF) is an emerging branch of sustainable adaptive forest management aimed at enhancing the potential of forests to adapt to and mitigate climate change. It relies on much higher data requirements than traditional forestry. These data requirements can be met by new devices that support continuous, in situ monitoring of forest conditions in real time. We propose a comprehensive network of sensors, i.e., a wireless sensor network (WSN), that can be part of a worldwide network of interconnected uniquely addressable objects, an Internet of Things (IoT), which can make data available in near real time to multiple stakeholders, including scientists, foresters, and forest managers, and may partially motivate citizens to participate in big data collection. The use of in situ sources of monitoring data as ground-truthed training data for remotely sensed data can boost forest monitoring by increasing the spatial and temporal scales of the monitoring, leading to a better understanding of forest processes and potential threats. Here, some of the key developments and applications of these sensors are outlined, together with guidelines for data management. Examples are given of their deployment to detect early warning signals (EWS) of ecosystem regime shifts in terms of forest productivity, health, and biodiversity. Analysis of the strategic use of these tools highlights the opportunities for engaging citizens and forest managers in this new generation of forest monitoring. Key words: climate change, early warning signals, ecosystem regime shifts, wireless sensor network, Internet of Things, citizen science, green technologies. La foresterie intelligente face au climat est une branche emergente de la gestion forestiere adaptative et durable dont l'objectif est d'accroitre la capacite des forets de s'adapter au changement climatique et d'en attenuer les effets. Cela comporte beaucoup plus d'exigences en termes de donnees que la foresterie traditionnelle. Ces exigences en matiere de donnees peuvent etre satisfaites grace a de nouveaux appareils qui permettent de surveiller la foret in situ en continu et en temps reel. Nous proposons un reseau complet de capteurs, c.-a-d. un reseau de capteurs sans fil, qui peut faire partie d'un reseau mondial d'objets interconnectes individuellement adressables, un Internet des objets (IdO) qui peut rendre les donnees disponibles presque en temps reel a de nombreux interesses, incluant des scientifiques, des forestiers et des gestionnaires forestiers, et qui peut en partie motiver les citoyens a participer a une importante collecte de donnees. L'utilisation de sources in situ de donnees de suivi comme donnees d'entrainement validees sur le terrain pour des donnees de teledetection peut favoriser la surveillance des forets en augmentant les echelles spatiale et temporelle, permettant ainsi une meilleure comprehension des processus forestiers et des menaces potentielles. Certains des developpements et applications cles de ces capteurs sont presentes dans cet article avec des directives pour la gestion des donnees. Des exemples de leur deploiement pour detecter les signaux d'alerte rapide des changements de regime des ecosystemes en ce qui a trait a la productivite, l'etat de sante et la biodiversite de la foret sont presentes. L'analyse de l'utilisation strategique de ces outils met en evidence les occasions d'interesser les citoyens et les gestionnaires forestiers a cette nouvelle generation de suivi des forets. [Traduit par la Redaction] Mots-cles : changement climatique, signaux d'alerte rapide, changement de regime des ecosystemes, reseau de capteurs sans fil, Internet des objets, science participative, technologies vertes., 1. Introduction Forests have traditionally been managed as large blocks with uniform treatments. This approach simplifies management but may miss shifts in forest dynamics over time; however, new technology permits [...]

Remote sensing (RS) and Geographic Information Systems (GISs) provide significant opportunities for monitoring and managing natural resources across various temporal, spectral, and spatial resolutions. There is a critical need for natural resource managers to understand the expanding capabilities of image sources, analysis techniques, and in situ validation methods. This article reviews key image analysis tools in natural resource management, highlighting their unique strengths across diverse applications such as agriculture, forestry, water resources, soil management, and natural hazard monitoring. Google Earth Engine (GEE), a cloud-based platform introduced in 2010, stands out for its vast geospatial data catalog and scalability, making it ideal for global-scale analysis and algorithm development. ENVI, known for advanced multi- and hyperspectral image processing, excels in vegetation monitoring, environmental analysis, and feature extraction. ERDAS IMAGINE specializes in radar data analysis and LiDAR processing, offering robust classification and terrain analysis capabilities. Global Mapper is recognized for its versatility, supporting over 300 data formats and excelling in 3D visualization and point cloud processing, especially in UAV applications. eCognition leverages object-based image analysis (OBIA) to enhance classification accuracy by grouping pixels into meaningful objects, making it effective in environmental monitoring and urban planning. Lastly, QGIS integrates these remote sensing tools with powerful spatial analysis functions, supporting decision-making in sustainable resource management. Together, these tools when paired with in situ data provide comprehensive solutions for managing and analyzing natural resources across scales. [ABSTRACT FROM AUTHOR]

Intermediate disturbances are an important component of many forest disturbance regimes, with effects on canopy structure and related functions that are highly dependent on the nature and intensity of the perturbation. Ice storms are an important disturbance mechanism in temperate forests that often result in moderate-severity, diffuse canopy damage. However, it has not previously been possible to distinguish the specific effect of ice storm intensity (as ice accretion) from predisturbance stand characteristics and physiographic factors. In this study, we utilized a novel experimental ice storm treatment to evaluate the effects of variable ice accretion levels on forest canopy structure. Our results verified significant impacts of ice storm disturbance on near-term canopy structural reorganization. Canopy openness, light transmission, and complexity increased significantly relative to predisturbance baselines and undisturbed controls. We documented variable impacts with disturbance intensity, as significant canopy changes largely occurred with ice accretion levels of [greater than or equal to]12.7 mm. Repeated ice storm disturbance (two consecutive years) had marginal, rather than compounding, effects on forest canopy structure. Our findings are relevant to understanding how ice storms can affect near-term forest canopy structural reorganization and ecosystem processes and add to a growing base of knowledge on the effects of intermediate disturbances on canopy structure. Key words: intermediate disturbance, canopy structure, complexity, ecosystem function. Les perturbations intermediaires sont une composante importante de plusieurs regimes de perturbation des forets qui ont des effets sur la structure du couvert forestier et les fonctions qui y sont reliees lesquels dependent fortement de la nature et de l'intensite de la perturbation. Les tempetes de verglas qui causent des dommages diffus et moderement severes dans le couvert forestier constituent un mecanisme important de perturbation dans les forets temperees. Cependant, il n'a pas precedemment ete possible de distinguer l'effet specifique de l'intensite d'une tempete de verglas (sous forme d'accumulation de glace) des facteurs physiographiques et des caracteristiques du peuplement avant d'etre perturbe. Dans cette etude, nous avons utilise un nouveau traitement experimental qui reproduit une tempete de verglas pour evaluer les effets de differents niveaux d'accumulation de verglas sur la structure du couvert forestier. Nos resultats ont permis de constater les impacts importants de la perturbation due a une tempete de verglas sur la reorganisation structurale a court terme du couvert forestier. L'ouverture, la transmission de la lumiere et la complexite du couvert forestier ont significativement augmente par rapport a la situation anterieure a la perturbation et aux temoins non perturbes. Nous avons observe des impacts variables selon l'intensite de la perturbation alors que des changements importants dans le couvert forestier sont surtout survenus avec des niveaux d'accumulation de verglas [greater than or equal to] 12,7 mm. Des perturbations repetees (deux annees consecutives) dues a une tempete de verglas ont eu des effets marginaux plutot que conjugues sur la structure du couvert forestier. Nos resultats sont pertinents pour comprendre de quelle facon les tempetes de verglas peuvent avoir un impact a court terme sur la reorganisation structurale du couvert forestier et alterer les processus de l'ecosysteme. Ils contribuent au developpement de la base de connaissances sur la structure du couvert forestier. [Traduit par la Redaction] Mots-cles : perturbation intermediaire, structure du couvert forestier, complexite, fonction de l'ecosysteme., Introduction Moderate-severity disturbances are an important driver of ecosystem functioning, structural development, and successional change in forest ecosystems (Frelich 2002; Cohen et al. 2016). Disturbances that result in damage to [...]

We evaluated shoot nonstructural carbohydrate (NSC) concentrations, stem wound closure, and radial growth of sugar maple (Acer saccharum Marsh.) and red maple (Acer rubrum L.) trees in a novel ice storm experiment in which five storm treatments (0, 6.4, 12.7, and 19.1 mm of radial ice accretion in 1 year and 12.7 mm of ice in two consecutive years) were applied within a mature northern hardwood forest. We tested for changes in physiology at two levels: (1) associated with plot-level ice treatments and (2) with crown damage classes of individual trees. Few differences in NSC or wound closure associated with treatment were found. Growth decreased for red maple in the medium and high treatments and sugar maple in the high treatment but no other treatments. Changes in physiology were more evident when assessed using crown damage classes. Two NSC components were elevated in sugar and red maples with high (≥50%) crown damage. Wound closure was less for red maples with high damage, and separation among damage classes was even greater for sugar maple. Red maples with moderate (<50%) and high crown damage showed gradually declining growth, whereas sugar maples with high damage showed ∼80% reduction in growth the first year after injury. [ABSTRACT FROM AUTHOR]

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

Ice storms are an important natural disturbance within forest ecosystems of the northeastern United States. Current models suggest that the frequency and severity of ice storms may increase in the coming decades in response to changes in climate. Because of the stochastic nature of ice storms and difficulties in predicting their occurrence, most past investigations of the ecological effects of ice storms across this region have been based on case studies following major storms. Here we report on a novel alternative approach where a glaze ice event was created experimentally under controlled conditions at the Hubbard Brook Experimental Forest, New Hampshire, USA. Water was sprayed over a northern hardwood forest canopy during February 2011, resulting in 7-12 mm radial ice thickness. Although this is below the minimum cutoff for ice storm warnings (13 mm of ice) issued by the US National Weather Service for the northeastern United States, this glaze ice treatment resulted in significant canopy damage, with 142 and 218 g C*[m.sub.-2] of fine and coarse woody debris (respectively) deposited on the forest floor, a significant increase in leaf-on canopy openness, and increases in qualitative damage assessments following the treatment. This study demonstrates the feasibility of a relatively simple approach to simulating an ice storm and underscores the potency of this type of extreme event in shaping the future structure and function of northern hardwood forest ecosystems. Resume: Les tempests de verglas sont la cause d'une perturbation naturelle importante dans les ecosystemes forestiers du nodes des etats-Unis. Les modeles actuels indiquent que la frequence et la severite des tempetes de verglas pourraient augmenter au cours de la prochaine decennie en reaction aux changements climatiques. Parce que les tempetes de verglas sont par nature aleatoire et que leur occurrence est difficile a predire, la plupart des travaux de recherche passes portant sur les effets ecologiques des tempetes de verglas dans cette region ont ete bases sur des etudes de cas a la suite de tempetes majeures. Cette etude porte sur une approche alternative originale qui consiste a produire experimentalement dans des conditions controlees un episode de verglas a la foret experimentale de Hubbard Brook, au New Hampshire, e.-U. La canopee d'une foret de feuillus nordiques a ete arrosee avec de l'eau en fevrier 2011 provoquant la formation de glace dont l'epaisseur radiale a atteint 7 a 12 mm. Bien que cela soit sous le seuil minimal (13 mm de glace) pour que le Service meteorolo-gique nationale des etats-Unis lance un avis de tempete de verglas pour le nord-est des etats-Unis, ce traitement a provoque des dommages importants entranant le depot sur la couverture morte de respectivement 142 et 218 g C*[m.sub.-2] de debris li-gneux fins et grossiers, une augmentation significative de l'ouverture de la canopee feuillue et des augmentations dans les evaluations des dommages qualitatifs a la suite du traitement. Cette etude demontre la faisabilite d'une approche relative-ment simple pour simuler une tempete de verglas et fait ressortir la capacite de ce type d'evenement extreme d'influencer de facon determinante la structure et la fonction a venir des ecosystemes forestiers de feuillus nordiques., Introduction Extreme events Human-induced climate change has the potential to alter the prevalence and severity of extreme climate events such as heat waves, cold waves, wind storms, floods, and droughts [...]

A critical component of assessing the impacts of climate change on forest ecosystems involves understanding associated changes in the biogeochemical cycling of elements. Evidence from research on northeastern North American forests shows that direct effects of climate change will evoke changes in biogeochemical cycling by altering plant physiology, forest productivity, and soil physical, chemical, and biological processes. Indirect effects, largely mediated by changes in species composition, length of growing season, and hydrology, will also be important. The case study presented here uses the quantitative biogeochemical model PnET-BGC to test assumptions about the direct and indirect effects of climate change on a northern hardwood forest ecosystem. Modeling results indicate an overall increase in net primary production due to a longer growing season, an increase in N[O.sub.3.sup.-] leaching due to large increases in net mineralisation and nitrification, and slight declines in mineral weathering due to a reduction in soil moisture. Future research should focus on uncertainties, including the effects of (1) multiple simultaneous interactions of stressors (e.g., climate change, ozone, acidic deposition); (2) long-term atmospheric C[O.sub.2] enrichment on vegetation; (3) changes in forest species composition; (4) extreme climatic events and other disturbances (e.g., ice storms, fire, invasive species); and (5) feedback mechanisms that increase or decrease change. Une composante critique de l'estimation de l'impact des changements climatiques sur les ecosystemes forestiers implique la comprehension des changements associes au cycle biogeochimique des elements. Une recherche conduite dans les forets du nord-est de f Amerique du Nord montre clairement que les effets directs des changements climatiques entraineront des changements dans le cycle biogeochimique en alterant la physiologie des plantes, la productivite forestiere et les processus impliques dans la physique, la chimie et la biologie des sols. Les effets indirects engendres surtout par des changements dans la composition en especes, la longueur de la saison de croissance et le regime hydrique seront aussi importants. Une etude de cas est presentee ici a f aide du modele quantitatif biogeochimique PnET-BGC pour tester des hypotheses au sujet des effets directs et indirects des changements climatiques sur un ecosysteme forestier de feuillus nordiques. Les resultats des simulations permettent d' anticiper une augmentation generale de la production primaire nette causee par l'allongement de la saison de croissance, une augmentation du lessivage de N[O.sub.3.sup.-] due a de fortes augmentations de la mineralisation et de la nitrification nettes ainsi qu'une legere diminution de l'alteration des mineraux due a une reduction de l'humidite du sol. Les recherches futures devraient etre concentrees sur les incertitudes, lesquelles incluent les effets (1) des interactions multiples et simultanees des facteurs de stress (p. ex. : les changements climatiques, l'ozone, les depots acides), (2) de (enrichissement a long terme en C[O.sub.2] atmospherique sur la vegetation, (3) des changements de la composition en especes forestieres, (4) des evenements climatiques extremes et des autres perturbations (p. ex. : les verglas, le feu, les especes invasives) et (5) des mecanismes de retroaction qui augmentent ou diminuent ces changements. [Traduit par la Redaction], Introduction Human activity has increased atmospheric greenhouse gas concentrations since preindustrial times, which, in turn, has led to a positive radiative forcing of climate. Observed changes in climate include a [...]

Finally, stakeholders expressed the need for midterm (30-yr) projections of freezing rain changes, which is a time scale that is more actionable than longer-term (end-of-century) projections though also challenging given the large natural variability of freezing rain. Keywords: Winter/cool season; Freezing precipitation; Renewable energy; Risk assessment; Societal impacts; Transportation meteorology EN Winter/cool season Freezing precipitation Renewable energy Risk assessment Societal impacts Transportation meteorology E1265 E1267 3 08/24/23 20230701 NES 230701 B I What i b : Freezing rain scientists and stakeholders generated a road map of risk-relevant knowledge gaps in freezing rain science and critical avenues to fill those gaps B I When i b : 11-12 October 2021 B I Where i b : Online On 11-12 October 2021, Purdue University hosted the Purdue Ice Storm Risk Workshop, a 2-day interdisciplinary workshop bringing together over 20 experts from across weather and climate science and a wide range of sectors, including meteorology, climate, forestry, energy, aviation, agriculture, and economics. Finally, given the acute nature of freezing rain impacts, continued dialogue between on-the-ground stakeholders and weather/climate scientists is critical to ensure the science is addressing decision-relevant needs. [Extracted from the article]

There is concern that changes in atmospheric deposition, climate, or land use have altered the biogeochemistry of forests causing soil base-cation depletion, particularly Ca. The Bear Brook Watershed in Maine (BBWM) is a paired watershed experiment with one watershed subjected to elevated N and S deposition through bimonthly additions of [(N[H.sub.4]).sub.2]S[O.sub.4]. Quantitative soil excavations in 1998 measured soil pools of exchangeable base cations 9 yr after treatments began. Stream sampling at the weirs on a weekly and event basis, and weekly precipitation sampling, were used for input-output estimates. The treated watershed had lower concentrations of exchangeable Ca and Mg in all horizons, with evidence for the greater depletion in the O horizon compared to underlying mineral soils, and in softwoods compared to hardwoods. This difference between watersheds is interpreted to be treatment-induced base-cation depletion, which was reinforced by model simulations. The difference between watersheds was 66 and 27 kg [ha.sup.-1] of exchangeable Ca and Mg, respectively, after accounting for soil mass differences between watersheds. This was comparable with the total cumulative excess stream Ca and Mg export in West Bear after 9 yr of treatment of 55 and 11 kg [ha.sup.-1] respectively. Model simulations of watershed response to treatments predicted excess soil exchangeable Ca and Mg losses in the treated watershed of 47 and 9 kg [ha.sup.-1] respectively. These results indicate that the response to a step-increase in N and S deposition during the first decade of treatments in this experimental forested watershed was to invoke cation-exchange buffering, resulting in a net decline in soil exchangeable base cations.

The Hubbard Brook Experimental Forest (HBEF) was established in 1955 by the U.S. Department of Agriculture, Forest Service out of concerns about the effects of logging increasing flooding and erosion. To address this issue, within the HBEF hydrological and micrometeorological monitoring was initiated in small watersheds designated for harvesting experiments. The Hubbard Brook Ecosystem Study (HBES) originated in 1963, with the idea of using the small watershed approach to study element fluxes and cycling and the response of forest ecosystems to disturbances, such as forest management practices and air pollution. Early evidence of acid rain was documented at the HBEF and research by scientists at the site helped shape acid rain mitigation policies. New lines of investigation at the HBEF have built on the long legacy of watershed research resulting in a shift from comparing inputs and outputs and quantifying pools and fluxes to a more mechanistic understanding of ecosystem processes within watersheds. For example, hydropedological studies have shed light on linkages between hydrologic flow paths and soil development that provide valuable perspective for managing forests and understanding stream water quality. New high frequency in situ stream chemistry sensors are providing insights about extreme events and diurnal patterns that were indiscernible with traditional weekly sampling. Additionally, tools are being developed for visual and auditory data exploration and discovery by a broad audience. Given the unprecedented environmental change that is occurring, data from the small watersheds at the HBEF are more relevant now than ever and will continue to serve as a basis for sound environmental decision‐making. [ABSTRACT FROM AUTHOR]

Ice storms are a type of extreme winter weather event common to north temperate and boreal forests worldwide. Recent climate modelling studies suggest that these storms may become more frequent and severe under a changing climate. Compared to other types of storm events, relatively little is known about the direct and indirect impacts of these storms on forests, as naturally occurring ice storms are inherently difficult to study. Here we describe a novel experimental approach used to create a suite of ice storms in a mature hardwood forest in New Hampshire, USA. The experiment included five ice storm intensities (0, 6.4, 12.7 and 19.1 mm radial ice accretion) applied in a single year, and one ice storm intensity (12.7 mm) applied in two consecutive years. Results demonstrate the feasibility of this approach for creating experimental ice storms, quantify the increase in fine and coarse woody debris mass and nutrients transferred from the forest canopy to the soil under the different icing conditions, and show an increase in the damage to the forest canopy with increasing icing that evolves over time. In this forest, little damage occurred below 6.4 mm radial ice accretion, moderate damage occurred with up to 12.7 mm of accretion, and significant branch breakage and canopy damage occurred with 19.1 mm of ice. The icing in consecutive years demonstrated an interactive effect of ice storm frequency and severity such that some branches damaged in the first year of icing appeared to remain in the canopy and then fall to the ground in the second year of icing. These results have implications for National Weather Service ice storm warning levels, as they provide a quantitative assessment of ice-load related inputs of forest debris that will be useful to municipalities creating response plans for current and future ice storms. [ABSTRACT FROM AUTHOR]

The design of a precipitation monitoring network must balance the demand for accurate estimates with the resources needed to build and maintain the network. If there are changes in the objectives of the monitoring or the availability of resources, network designs should be adjusted. At the Hubbard Brook Experimental Forest in New Hampshire, USA, precipitation has been monitored with a network established in 1955 that has grown to 23 gauges distributed across nine small catchments. This high sampling intensity allowed us to simulate reduced sampling schemes and thereby evaluate the effect of decommissioning gauges on the quality of precipitation estimates. We considered all possible scenarios of sampling intensity for the catchments on the south-facing slope (2047 combinations) and the north-facing slope (4095 combinations), from the current scenario with 11 or 12 gauges to only 1 gauge remaining. Gauge scenarios differed by as much as 6.0% from the best estimate (based on all the gauges), depending on the catchment, but 95% of the scenarios gave estimates within 2% of the long-term average annual precipitation. The insensitivity of precipitation estimates and the catchment fluxes that depend on them under many reduced monitoring scenarios allowed us to base our reduction decision on other factors such as technician safety, the time required for monitoring, and co-location with other hydrometeorological measurements (snow, air temperature). At Hubbard Brook, precipitation gauges could be reduced from 23 to 10 with a change of <2% in the long-term precipitation estimates. The decision-making approach illustrated in this case study is applicable to the redesign of monitoring networks when reduction of effort seems warranted. [ABSTRACT FROM AUTHOR]

In the Northeastern U.S., drought is expected to increase in frequency over the next century, and therefore, the responses of trees to drought are important to understand. There is recent debate about whether land-use change or moisture availability is the primary driver of changes in forest species composition in this region. Some argue that fire suppression from the early twentieth century to present has resulted in an increase in shade-tolerant and pyrophobic tree species that are drought intolerant, while others suggest precipitation variability as a major driver of species composition. From this debate, an emerging hypothesis is that mesophication and increases in the abundance of mesophytic genera (e.g., Acer, Betula, and Fagus) resulted in forests that are more vulnerable to drought. This review examines the published literature and factors that contribute to drought vulnerability of Northeastern U.S. forests. We assessed two key concepts related to drought vulnerability, including drought tolerance (ability to survive drought) and sensitivity (short-term responses to drought), with a focus on Northeastern U.S. species. We assessed drought-tolerance classifications for species, which revealed both consistencies and inconsistencies, as well as contradictions when compared to actual observations, such as higher mortality for drought-tolerant species. Related to drought sensitivity, recent work has focused on isohydric/anisohydric regulation of leaf water potential. However, based on the review of the literature, we conclude that drought sensitivity should be viewed in terms of multiple variables, including leaf abscission, stomatal sensitivity, turgor pressure, and dynamics of non-structural carbohydrates. Genera considered drought sensitive (e.g., Acer, Betula, and Liriodendron) may actually be less prone to drought-induced mortality and dieback than previously considered because stomatal regulation and leaf abscission in these species are effective at preventing water potential from reaching critical thresholds during extreme drought. Independent of drought-tolerance classification, trees are prone to dieback and mortality when additional stressors are involved such as insect defoliation, calcium and magnesium deficiency, nitrogen saturation, and freeze-thaw events. Overall, our literature review shows that multiple traits associated with drought sensitivity and tolerance are important as species may rely on different mechanisms to prevent hydraulic failure and depleted carbon reserves that may lead to mortality. [ABSTRACT FROM AUTHOR]