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Wildfires are increasing in importance in many regions of the Canadian boreal forest and are an ongoing risk for forest management activities. We simulated the effects of fires on long-term harvest levels on the 59 forest management units of the province of Québec, Canada, for the 2020–2100 period. Different climate change pathways (stable, RCP 4.5 or 8.5) and salvage logging rates (20% or 70% of mature burned stands) were simulated. Changes in forest flammability due to climate change, species migration, and forest management were also considered. Under stable climatic conditions, the decline in potential harvest levels due to fire, based on 50 simulations per scenario, ranged between 3% and 33% (mean = 11%) when high salvage logging rates were simulated, compared to 6%–45% (mean = 20%) for low salvage rates. Climate change caused increases in burn rates between −3% and 39% for RCP 4.5 and between 33% and 69% for RCP 8.5 at the end of the 21st century, depending on fire zones. However, the effects of these modified burn rates on harvest levels did not differ substantially from those of baseline burn rates, probably because the projected burn rates were highest during the later part of the simulations (2070–2100), when their impacts on harvest level calculations were limited. This study indicates that potential harvest levels calculated without considering wildfires are likely to be non-sustainable. [ABSTRACT FROM AUTHOR]

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

If the modern climate trend continues for an additional 20–40 years, forests along the southern border of Canadian taiga may shift into new ranges of annual temperature and precipitation that are similar to the modern climate of central New York State, United States. Here we investigate the possible future response of white spruce (Picea glauca (Moench) Voss) to a warmer climate by studying trees planted 90 years ago near the southern limit of their climate tolerance in central New York, 300 km south of the boreal forest where this species is prevalent. We employed high-frequency recording dendrometers to determine radial growth phenology of six mature white spruce trees during 2013–2017. The results demonstrate significant reductions in the length of radial growth periods inversely proportional to the number of hot days with air temperature exceeding 30 °C. During years with very hot summers, the start of radial growth began about 3 days earlier than the 2013–2017 average. However, in those same years, the end of radial growth was also about 17 days earlier resulting in a shorter (70 days versus 100 days) radial growth season. Abundant (350–500 mm) summer precipitation, which resulted in soil moisture values of 20%–30%, allowed us to dismiss drought as a factor. Instead, a likely cause of reduced radial growth was mean temperature that exceeded optimal growth ranges, exacerbated by temperature extremes in ranges that lead to photoinhibition. The latter case was evident in the two warmest growing seasons (2013 and 2017), marked by extended periods of high daytime temperature (>30 °C) followed by early cessation of radial growth independent of seasonal precipitation. [ABSTRACT FROM AUTHOR]

In this paper, we examine the implications of managing for sustained yield in a world characterized by growing risk and uncertainty. We review the history of sustained yield (SY) forestry in North America, with an emphasis on economic benefits and the persistence of the SY paradigm today, despite a publicized shift towards managing for a wider range of forest values called sustainable forest management (SFM). We show that current forest management goals around sustainability as well as SFM indicators are still predicated on maximizing harvest levels and timber flows. We build a simple model to explore the implications of SY under extreme (fat-tailed) risk assumptions to show that maximizing a level of harvest without adequately accounting for risk leads towards the depletion of the forest stock with a corresponding decline in the forest economy. We discuss these results in relation to real-world events such as the increase in catastrophic fires and pest outbreaks like the mountain pine beetle in Western Canada. We then examine the theoretical and practical implications that flow from this model and analysis. [ABSTRACT FROM AUTHOR]

Droughts driven by global change are triggering worldwide forest dieback, a phenomenon that is predicted to worsen. We combined genome-wide single nucleotide polymorphisms (SNPs) and dendrochronological approaches to assess genetically-based individual tree vulnerability to past extreme droughts that caused massive mortality of coihue (Nothofagus dombeyi (Mirb.) Blume) forests in northern Patagonia, Argentina. We collected fresh leaves and wood cores from pairs of trees, one with a healthy crown (HC) and another with a partially affected crown (PA), at four sites impacted by droughts in 1998, 2008, and 2014. We used dendrochronological techniques to estimate parameters in terms of growth trends due to drought and genomic analysis to assess the relationship of genomic variation with water stress. While 5155 neutral loci did not differentiate PA from HC trees, a set of 33 adaptive SNPs did, 8 of which were related to water stress. Association analysis between genomic variants and dendrophenotypic traits yielded 6 SNPs that were associated with a growth measure as resilience to cope with drought. Our preliminary results indicate that susceptibility to drought in N. dombeyi could be determined at the genomic level. The combination of these approaches provides a framework for the identification and analysis of candidate genes for stress response in non-model species. [ABSTRACT FROM AUTHOR]

The article offers information on forest evapotranspiration (ET) is one of the most important factors influencing the terrestrial hydrological cycle and is prone to being influenced by increasing drought events. Topics include the need to understand the interaction between global forest ET and drought, and decreasing forest ET to both restricted water supply and restricted water consumption by forests.

The article provides information on a study which examined the possible sensitivities of red oak growth to climate and potential pollution variables in the species' northern hardwood forest throughout Vermont. Topics discussed include anthropogenic drivers that can have a detectable influence on tree growth and relationships between whole ring widths (WRW), latewood (LW), and earlywood (EW) growth and environmental factors that may influence growth.

The article provides information on a study which examined the effect of annual variability in climatic conditions on the growth and performance of Pinus banksiana stands growing under different soil moisture conditions. Topics discussed include potential effect of forecasted climate for the region on the future growth of individuals, and whether P. banksiana should continue to be planted across these soil moisture gradients in the future.

Symptoms of forest decline, apparently due to climate change, have become evident in the last 10 years on the Trans-Mexican Volcanic Belt and northwestern temperate forest of Mexico, particularly at the xeric (low elevational) limit of several forest tree species. We review and provide recent evidence of massive infestation of timberline Pinus hartwegii Lindl. by the mistletoes Arceuthobium globosum Hawksw. & Wiens and Arceuthobium vaginatum (Humb. & Bonpl. ex Willd.) J.Presl; insufficient Abies religiosa (Kunth) Schltdl. & Cham. seedling recruitment at the Monarch Butterfly Biosphere Reserve; indications of inbreeding and defoliation in endangered Picea chihuahuana Martínez, Picea martinezii T.F. Patt., Picea mexicana Martínez, and extreme southern populations of Pseudotsuga menziesii (Mirb.) Franco; and the incidence of unusual pest and disease outbreaks (e.g., Dendroctonus Erichson, 1836 spp., Neodiprion autumnalis Smith, and Phytophthora cinnamomi Rands) in several conifer and oak species. We also discuss a difficult question: Is natural genetic variation sufficient to provide populations with the adaptive variation necessary to survive the natural selection imposed by projected climate change scenarios, or will phenotypic plasticity be exhausted and populations decline? Controversial ex situ conservation within natural protected areas, assisted migration, and translocation of species ensembles are discussed as options by which to accommodate projected climatic change impacts on the management and conservation practices of the megadiverse Mexican temperate forest. [ABSTRACT FROM AUTHOR]

The Bago Mountain Range in Myanmar is known as the "home of teak" (Tectona grandis L. f.) because of its bountiful, naturally growing teak-bearing forests. Accelerating forest loss and degradation are threatening the sustainable production of teak in the region. Changes in land cover between 2000 and 2017 in four reserved forests of the Bago Mountain Range were mapped using supervised classification of Landsat imagery and training data collected in the field. A stratified random sample was used to collect reference data to assess accuracy of the maps and estimate area. Based on the reference sample, it was estimated that the forest area declined from 71 240 ha (standard error (SE) = 1524 ha) in 2000 to 40 891 ha (SE = 4404 ha) in 2017, whereas the area of degraded forests increased from 88 797 ha (SE = 1694 ha) to 97 013 ha (SE = 5395 ha). The annualized rates of gross forest loss and gross forest degradation were 1.03% and 0.97%, respectively, indicating that forest degradation paralleled forest loss. In many degraded areas, there is an opportunity to ameliorate the situation through silviculture. The 2017 map identifies bamboo-dominated degraded forests where enrichment planting or reforestation is recommended. [ABSTRACT FROM AUTHOR]

The consequences of forest fragmentation and edge effects on soil nutrient availability and nutrition of sugar maple (Acer saccharum Marsh.) forests remain understudied. We assessed soil chemistry (bulk pH, total carbon (C) and nitrogen (N), extractable phosphorus (P), exchangeable cations, and mineralizable N) and foliar nutrition (N, P, potassium (K), calcium (Ca), and magnesium (Mg)) of mature sugar maple forests along an edge–interior gradient (10, 20, 30, 50, 70, and 120 m from the forest edges) in seven sugar maple forest stands (three on sandstone and four on dolomite bedrock) that are embedded within an agricultural landscape in southern Quebec, Canada. We hypothesized that foliar nutritional imbalances of sugar maple forests would decline along this gradient. Foliar nutrition was analyzed using the diagnosis and recommendation integrated system (DRIS) and the compositional nutrient diagnosis with isometric log-ratio (CND-ilr) method. At the sandstone sites, rates of N mineralization and nitrification increased with increasing distance from the forest edge. Other soil chemical properties and all sugar maple foliar indices of nutritional diagnostics varied weakly along the edge–interior gradient. Assessment of sugar maple forest nutritional status through different nutritional indices revealed K and P deficiencies in all stands that were sampled and at all distances from the forest edge. Overall, we found weak forest-edge effects on soil chemical properties and sugar maple forest nutritional status. [ABSTRACT FROM AUTHOR]

In trees, wood anatomy is a more precise and informative measure of hydraulic responses to drought than radial growth. Tree populations located near the equatorial-range edge of their distribution (rear edge) are used to monitor responses to changes in hydroclimate; however, few studies have assessed the wood anatomy of these populations. We measured tracheid lumen diameter (LD) and cell wall thickness (CWT) in a rear-edge Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) population. We also evaluated the formation of intra-annual density fluctuations (IADFs), characterized by earlywood (EW) tracheids with narrow lumens. We expected that EW LD would be particularly sensitive to hydroclimate variability. We found that EW LD was directly related to precipitation during the previous year's late winter and the current year's spring. Wet conditions were associated with wider EW tracheids and improved growth. These correlations peaked when considering cumulative precipitation from January to May. EW IADFs were formed in response to dry conditions during March and April, suggesting that dry spring conditions limit tracheid expansion. The described associations in a rear-edge Douglas-fir population confirm that wood anatomy is highly responsive to drought. We conclude that EW LD is a valuable proxy for hydroclimate reconstruction in Douglas-fir. [ABSTRACT FROM AUTHOR]

The influence of water deficits and drought on tree physiological processes, growth, and survival has been the focus of substantial research efforts and debate over the past decades, but there is still a need to quantitatively link finer scale mechanistic explanations of the influence of water status with the physiological responses of trees, particularly for those past the sapling stage. Hence, the objective of this study was to link accumulated water stress during the growing season to leaf physiological response mechanisms of Juglans nigra L. trees. Results showed that trees subjected to higher cumulative water stress had lower maximum light-saturated photosynthesis (Amax), initiated net photosynthesis at higher light levels (Ic), and displayed reduced effectiveness of CO2 fixation per photons absorbed (Qe) at the bottom and upper positions along the vertical canopy gradient. Results suggest that water stress integral (Sψ), a variable that takes into account accumulated water deficits, would be useful to help future research efforts aimed at investigating responses to drought in trees past the sapling stage. [ABSTRACT FROM AUTHOR]

Forest decline is frequently associated with infection; however, infections habitually affect trees that have been previously debilitated by environmental stress. Nevertheless, the causes and physiology of noninfectious forest decline are not well known. Some Juniperus thurifera L. forests presented severe (noninfectious) declines, with defoliations over 50%. The goal of this study was to determine the causes and characterize the physiology of this noninfectious decline, and we hypothesized that it could be related to environmental stress from increasing interspecific competition resulting from land abandonment. We randomly assigned 60 trees to either a control group or one of two competition-release treatments, i.e., vegetation clearing or soil ploughing. We characterized the physiological state of the trees both before treatment application and 14 months after treatment application. The J. thurifera trees that were declining experienced significantly lower soil nutrient and water availability, which resulted in lower leaf nutrient concentrations, lower photosynthetic rates, higher water stress, and arrested growth and reproduction. We confirmed that competition release increased nutrient availability and acquisition, reduced water deficit, improved photosynthetic rates, and abruptly stopped defoliation. Competition plays an increasingly critical role in forest conservation, particularly with the reported increase in the number of species colonizing previously unfeasible habitats due to global change and the absence of traditional activities that used to buffer competition. [ABSTRACT FROM AUTHOR]

Yellow-cedar ( Chamaecyparis nootkatensis D. Don (Spach)) is currently undergoing a dramatic decline in western North America. Recent research suggests that site factors combined with a shift in climate have predisposed yellow-cedar trees to decline. We conducted the first landscape-level analysis of the decline in coastal British Columbia to assess relations between the decline and topographic variables. We used lasso-penalized logistic regression to model yellow-cedar decline presence and absence with topographic variables derived from a digital elevation model. Model results indicated that low elevation sites close to the coast, which are more exposed and have more variation in elevation, are more likely to show evidence of decline. The logistic model fit the data well (Nagelkerke R2 = 0.846) and had high predictive accuracy (AUC = 0.98). The topographic variables identified by the model influence degree of soil saturation, temperatures, and snowpack presence in a forest stand, supporting the proposed associations in the current decline hypothesis. The analysis also highlighted the utility of the lasso logistic model for selecting significant variables and mapping areas at high risk for decline. Knowledge of the determinants of the spatial pattern of decline will improve predictability and provide critical information for conservation and management of yellow-cedar. [ABSTRACT FROM AUTHOR]

Extreme climate events are frequently important factors associated with episodes of forest decline. A recent oak decline event and concurrent outbreak of a native wood-boring beetle, the red oak borer ( (Haldeman)), occurred throughout Arkansas Ozark and Ouachita Mountains. To investigate the role of drought and stand maturity on northern red oak ( L.) decline, we analyzed tree-ring growth patterns and their relationships to climate from 815 live and 161 recently dead Q. rubra. While younger Q. rubra exhibited faster growth rates and stronger climate relationships than older Q. rubra, some individuals within all stands that originated >60 years ago were susceptible to growth decline or mortality. A significant growth interaction occurred among the three age classes identified where currently healthy Q. rubra were initially growing at slower decadal rates than currently declining or recently dead Q. rubra and later transitioned to higher growth rates than the others. These differences appear to be related to carbon allocation patterns towards rapid aboveground and (or) belowground growth early in development that led to later decline and (or) mortality. Decline in growth and weakening tree growth - climate relationships appeared to be initiated by an unusually severe and sustained drought in the early 1950s. [ABSTRACT FROM AUTHOR]

To address hazardous fuel accumulations, many fuel treatments are being implemented in dry forests, but there have been few opportunities to evaluate treatment efficacy in wildfires. We documented the effectiveness of thinning and prescribed burning in the 2006 Tripod Complex fires. Recent fuel treatments burned in the wildfires and offered an opportunity to evaluate if two treatments (thin only and thin and prescribed burn) mitigated fire severity. Fire severity was markedly different between the two treatments. Over 57% of trees survived in thin and prescribed burn (thinRx) units versus 19% in thin only (thin) and 14% in control units. Considering only large-diameter trees (>20 cm diameter at breast height), 73% survived in thinRx units versus 36% and 29% in thin and control units, respectively. Logistic regression modeling demonstrates significant reductions in the log-odds probability of tree death under both treatments with a much greater reduction in thinRx units. Other severity measures, including percent crown scorch and burn severity index, are significantly lower in thinRx units than in thin and control units. This study provides strong quantitative evidence that thinning alone does not reduce wildfire severity but that thinning followed by prescribed burning is effective at mitigating wildfire severity in dry western forests. [ABSTRACT FROM AUTHOR]

Tree roots of northern hardwoods are shallow rooted, winter active, and minimally frost hardened; dieback is a winter freezing injury to roots incited by frost penetration in the absence of adequate snow cover and exacerbated by drought in summer. High soil water content greatly increases conductivity of frost. We develop a model based on the sum of z-scores of soil frost (December–February) and drought in summer (May–September) that accurately predicts timing and severity of dieback on sugar maple (Acer saccharum Marsh.), Betula spp., Fraxinus spp., and red spruce (Picea rubens Sarg.) in Maine, USA, during 1920–1995. Discrepancies between predicted and actual dieback relate largely to tree population dynamics. Extraordinary levels of dieback on Betula during 1935–1950 occurred under low stress but in mature populations; under high climate stress during 1951–1975, younger surviving Betula proved resistant and showed little dieback. Severe dieback in Acer stands during 1975–1995 may relate to extensive partial cutting, leaving stands open to frost and high water tables. Widespread use of forwarder feller/buncher and wheeled skidders after 1960 commonly left hummocky, irregular surfaces subject to pooling and accelerated frost penetration. Silvicultural applications include modifying harvesting practices to minimize frost complications and use of the model to track and map climatic risk to avoid conditions and locales subject to dieback. Les racines des feuillus nordiques sont peu profondes, actives en hiver et à peine endurcies au froid; le dépérissement est le résultat de dommages aux racines dus au gel hivernal qui pénètre dans le sol à cause d’un couvert nival insuffisant et ces dommages sont aggravés par la sécheresse estivale. Une teneur en eau élevée dans le sol augmente grandement la conductivité du gel. Nous avons élaboré un modèle basé sur la somme des écarts réduits du gel dans le sol (décembre à février) et de la sécheresse estivale (mai à septembre) qui prédit correctement le moment et la sévérité du dépérissement d’érable à sucre (Acer saccharum Marsh.), de Betula spp., de Fraxinus spp. et d’épinette rouge (Picea rubens Sarg.) dans le Maine de 1920 à 1995. Les divergences entre les dépérissements prédits et réels sont surtout reliées à la dynamique des populations d’arbres. Un dépérissement très sévère de Betula, de 1935 à 1950, est survenu dans des conditions de stress léger mais dans des populations matures. Dans des conditions de stress climatique sévère, de 1951 à 1995, de jeunes tiges de Betula qui ont survécu se sont avérées résistantes et ont subi peu de dépérissement. Le dépérissement sévère dans les peuplements d’Acer, de 1975 à 1995, est possiblement relié aux nombreuses coupes partielles qui ont rendu les peuplements plus vulnérables au gel et favorisé la remontée de la nappe phréatique. L’usage généralisé des abatteuses porteuses ou groupeuses et des débusqueuses à roue après 1960 a fréquemment laissé des surfaces irrégulières, avec des bosses et des creux, sujettes à l’accumulation d’eau et à la pénétration plus rapide du gel. Les applications sylvicoles incluent la modification des pratiques de récolte afin de minimiser les complications reliées au gel et l’utilisation de modèles pour détecter et cartographier les risques climatiques dans le but d’éviter les situations et les endroits sujets au dépérissement. [ABSTRACT FROM AUTHOR]

Presents three-ring analyses and forest health assessments in healthy and stressed aspen forests in Canada. Basis for reconstructing defoliation histories; Factors contributing the observed dieback of aspen forests; Threat of global change to the future health and productivity of aspen forests.

Focuses on Acer saccharum Marsh. (sugar maple) as one of only few arbuscular mycorrhizal trees to form extensive stands in northern temperate biomes. Recent maple decline could result from altered intensity and quality of root colonization by associated mycobionts or possible shifts in symbiotic fungal community composition following environmental stresses. In this study the effects on arbuscular mycorrhizal fungi of soil acidification, one of several proposed causal stresses underlying forest decline, and remedial liming were investigated under glasshouse conditions. Acer saccharum seedlings were grown in unsterilized, pH altered, forest soils from healthy and declining maple stands. Over a range of treatment pHs normally tolerated by A. saccharum, fungal populations and responses to pH changes differed between the two soils. The declining site with more acidic soil had an initially larger spore population but lower taxonomic diversity than the healthy site. However, liming stimulated sporulation of several taxa initially apparently absent from the declining site spore population. The quantity of colonization generally increased with pH for both sites. Five Glomus taxa and Scutellospora calospora (Nicol. & Gerd.) Walker & Sanders are added to the list of fungi known to form arbuscular mycorrhizas with A. saccharum, and the known range of Acaulospora cavernata Blaszkowski is extended from Poland to eastern North America.