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Several aspects of the forest carbon cycle have not been examined in detail, including sources of variation in carbon dioxide (C[O.sub.2]) emissions from coarse woody material (CWM). To address this knowledge gap, we examined C[O.sub.2] emissions from Acer saccharum Marshall logs within four harvesting treatments, using closed chambers fitted to the logs. We found that C[O.sub.2] emissions were highest for logs in small (31.8 [+ or -] 20.4 [micro]molC[O.sub.2][m.sup.- 3][s.sup.-1]) and large gaps (29.6 [+ or -] 24.4 [micro]molC[O.sub.2][m.sup.-3][s.sup.-1]) compared to those in control (13.9 [+ or -] 8.3 [micro]molC[O.sub.2][m.sup.-3][s.sup.-1]) and thinned matrix (13.6 [+ or -] 8.0 [micro]molC[O.sub.2][m.sup.-3] [s.sup.-1]) treatments. C[O.sub.2] flux rates did not differ between gap sizes, but they increased with temperature, which was higher in the small gap treatment. In addition, two individual logs fitted with multiple closed chambers revealed significant within-log variability in C[O.sub.2] emissions. On a subset of logs repeatedly sampled throughout the day, we found that log surface temperature generally peaked at midday and was positively correlated with C[O.sub.2] emissions, although this relationship was weak in one log. This study provides insight into sources of variation in C[O.sub.2] emissions from CWM while improving our understanding of the forest carbon cycle. Key words: carbon dioxide, carbon flux, forest carbon cycle, woody material, wood decomposition, Introduction Forests are important contributors to the global carbon cycle, both as a sink of carbon dioxide (C[O.sub.2]) through photosynthesis as well as an emitter of C[O.sub.2] as these carbon [...]

Tree fecundity and recruitment have not yet been quantified at scales needed to anticipate biogeographic shifts in response to climate change. By separating their responses, this study shows coherence across species and communities, offering the strongest support to date that migration is in progress with regional limitations on rates. The southeastern continent emerges as a fecundity hotspot, but it is situated south of population centers where high seed production could contribute to poleward population spread. By contrast, seedling success is highest in the West and North, serving to partially offset limited seed production near poleward frontiers. The evidence of fecundity and recruitment control on tree migration can inform conservation planning for the expected long-term disequilibrium between climate and forest distribution.

Statistical confidence in estimates of timber volume, carbon storage, and other forest attributes depends, in part, on the uncertainty in field measurements. Surprisingly, measurement uncertainty is rarely reported, even though national forest inventories routinely repeat field measurements for quality assurance. We compared measurements made by field crews and quality assurance crews in the Forest Inventory and Analysis program of the U.S. Forest Service, using data from 2790 plots and 51740 trees and saplings across the 24 states of the Northern Region. We characterized uncertainty in 12 national core tree-level variables; seven tree crown variables used in forest health monitoring; three variables describing seedlings; and 11 variables describing the site, such as elevation, slope, and distance from a road. Discrepancies in measurement were generally small but were higher for some variables requiring judgment, such as tree class, decay class, and cause of mortality. When scaled up to states, forest types, or the region, uncertainties in basal area, timber volume, and aboveground biomass were negligible. Understanding all sources of uncertainty is important to designing forest monitoring systems, managing the conduct of the inventory, and assessing the uncertainty of forest attributes required for making regional and national forest policy decisions. Key words: carbon accounting, Forest Inventory and Analysis, forest inventory, measurement uncertainty, forestry, 1. Introduction Forest inventories have historically been performed for many purposes (Labau et al. 2007), including estimating merchantable timber, determining risk of fire, evaluating habitat for wildlife, and assessing biodiversity. [...]

Although climate change is expected to drive tree species toward colder and wetter regions of their distribution, broadscale empirical evidence is lacking. One possibility is that past and present human activities in forests obscure or alter the effects of climate. Here, using data from more than two million monitored trees from 73 widely distributed species, we quantify changes in tree species density within their climatic niches across Northern Hemisphere forests. We observe a reduction in mean density across species, coupled with a tendency toward increasing tree size. However, the direction and magnitude of changes in density exhibit considerable variability between species, influenced by stand development that results from previous stand-level disturbances. Remarkably, when accounting for stand development, our findings show a significant change in density toward cold and wet climatic conditions for 43% of the species, compared to only 14% of species significantly changing their density toward warm and arid conditions in both early-and late-development stands. The observed changes in climate-driven density showed no clear association with species traits related to drought tolerance, recruitment and dispersal capacity, or resource use, nor with the temperature or aridity affiliation of the species, leaving the underlying mechanism uncertain. Forest conservation policies and associated management strategies might want to consider anticipated long-term species range shifts alongside the integration of contemporary within-distribution density changes. [ABSTRACT FROM AUTHOR]

We report a molecular crystal that exhibits four successive phase transitions under hydro-static pressure, driven by aurophilic interactions, with the ground-state structure re-emerging at high pressure. The effect of pressure on two polytypes of tris(μ2-3,5-diiso-propyl-1,2,4-triazolato-κ2N1:N2)trigold(I) (denoted Form-I and Form-II) has been analysed using luminescence spectroscopy, single-crystal X-ray diffraction and first-principles computation. A unique phase behaviour was observed in Form-I, with a complex sequence of phase transitions between 1 and 3.5 GPa. The ambient C2/c mother cell transforms to a P21/n phase above 1 GPa, followed by a P21/a phase above 2 GPa and a large-volume C2/c supercell at 2.70 GPa, with the previously observed P21/n phase then reappearing at higher pressure. The observation of crystallographically identical low- and high-pressure P21/n phases makes this a rare example of a re-entrant phase transformation. The phase behaviour has been characterized using detailed crystallographic theory and modelling, and rationalized in terms of molecular structural distortions. The dramatic changes in conformation are correlated with shifts of the luminescence maxima, from a band maximum at 14040 cm-1 at 2.40 GPa, decreasing steeply to 13550 cm-1 at 3 GPa. A similar study of Form-II displays more conventional crystallographic behaviour, indicating that the complex behaviour observed in Form-I is likely to be a direct consequence of the differences in crystal packing between the two polytypes.

Introduction: Mounting evidence suggests that geographic ranges of tree species worldwide are shifting under global environmental changes. Little is known, however, about if and how these species' range shifts may trigger the range shifts of various types of forests. Markowitz's portfolio theory of investment and its broad application in ecology suggest that the range shift of a forest type could differ substantially from the range shifts of its constituent tree species. Methods: Here, we tested this hypothesis by comparing the range shifts of forest types and the mean of their constituent species between 1970-1999 and 20002019 across Alaska, Canada, and the contiguous United States using continent- wide forest inventory data. We first identified forest types in each period using autoencoder neural networks and K-means cluster analysis. For each of the 43 forest types that were identified in both periods, we systematically compared historical range shifts of the forest type and the mean of its constituent tree species based on the geographic centroids of interpolated distribution maps. Results: We found that forest types shifted at 86.5 km-decade-1 on average, more than three times as fast as the average of constituent tree species (28.8 km-decade-1). We showed that a predominantly positive covariance of the species range and the change of species relative abundance triggers this marked difference. Discussion: Our findings provide an important scientific basis for adaptive forest management and conservation, which primarily depend on individual species assessment, in mitigating the impacts of rapid forest transformation under climate change. [ABSTRACT FROM AUTHOR]

Successional, second-growth forests dominate much of eastern North America; thus, patterns of biomass accumulation in standing trees and downed wood are of great interest for forest management and carbon accounting. The timing and magnitude of biomass accumulation in later stages of forest development are not fully understood. We applied a "chronosequence with resampling" approach to characterize live and dead biomass accumulation in 16 northern hardwood stands in the White Mountains of New Hampshire. Live aboveground biomass increased rapidly and leveled off at about 350 Mg/ha by 145 years. Downed wood biomass fluctuated between 10 and 35 Mg/ha depending on disturbances. The species composition of downed wood varied predictably with overstory succession, and total mass of downed wood increased with stand age and the concomitant production of larger material. Fine woody debris peaked at 30–50 years during the self-thinning of early successional species, notably pin cherry. Our data support a model of northern hardwood forest development wherein live tree biomass accumulates asymptotically and begins to level off at ∼140–150 years. Still, 145-year-old second-growth stands differed from old-growth forests in their live (p = 0.09) and downed tree diameter distributions (p = 0.06). These patterns of forest biomass accumulation would be difficult to detect without a time series of repeated measurements of stands of different ages. [ABSTRACT FROM AUTHOR]

We synthesize insights from current understanding of drought impacts at stand-to-biogeographic scales, including management options, and we identify challenges to be addressed with new research. Large stand-level shifts underway in western forests already are showing the importance of interactions involving drought, insects, and fire. Diebacks, changes in composition and structure, and shifting range limits are widely observed. In the eastern US, the effects of increasing drought are becoming better understood at the level of individual trees, but this knowledge cannot yet be confidently translated to predictions of changing structure and diversity of forest stands. While eastern forests have not experienced the types of changes seen in western forests in recent decades, they too are vulnerable to drought and could experience significant changes with increased severity, frequency, or duration in drought. Throughout the continental United States, the combination of projected large climate-induced shifts in suitable habitat from modeling studies and limited potential for the rapid migration of tree populations suggests that changing tree and forest biogeography could substantially lag habitat shifts already underway. Forest management practices can partially ameliorate drought impacts through reductions in stand density, selection of drought-tolerant species and genotypes, artificial regeneration, and the development of multistructured stands. However, silvicultural treatments also could exacerbate drought impacts unless implemented with careful attention to site and stand characteristics. Gaps in our understanding should motivate new research on the effects of interactions involving climate and other species at the stand scale and how interactions and multiple responses are represented in models. This assessment indicates that, without a stronger empirical basis for drought impacts at the stand scale, more complex models may provide limited guidance.

Global change drivers are altering forest dynamics, yet how these factors influence tree survival across early developmental stages (i.e., seedling to recruited sapling) over large geographies is not well understood. We developed a novel approach to evaluate controls on seedling and sapling survival. This approach was demonstrated on a set of systematic forest inventory plots across the northeastern USA in which seedlings were tallied within six height classes, allowing for a detailed assessment of the stages at which demographic bottlenecks in juvenile tree development are often observed. Forest inventory subplots containing a study species were divided into overlapping bins along an environmental or ecological gradient, and ratios of abundance between successive size classes were used to infer relative survival rates. Relationships between 10 common tree species and tree density, shrub cover, and mean annual temperature were assessed. As seedling height class increased, we observed shifts from positive to negative associations with shrub cover and large tree density. Our results suggest that observed patterns of sapling and tree abundance may belie complex and sometimes opposing influences on seedling survival that are important to quantify when predicting and managing for successful tree recruitment and future canopy tree composition. [ABSTRACT FROM AUTHOR]

Estimating the current status and future trends of carbon (C) stocks and stock changes in forests of the northeastern United States is desired by policy makers and managers as these forests can mitigate climate change through sequestration of atmospheric carbon dioxide (C[O.sub.2]). We developed C flux matrix models using tree and stand variables by tree diameter class and stand age class to compare size-structured models with age-structured models in their capacity to predict forest C dynamics that are central to policy decisions. The primary control variables for the C flux matrix models (diameter at breast height, stand basal area, stem density, and stand age) were all statistically significant at the [alpha] [less than or equal to] 0.05 level. Through comparing the simulation results and root mean square error of C flux matrix models by tree diameter class and stand age class, we found that tree diameter class more accurately predicted C stock change status across the broad compositional and structural conditions in the spatial and temporal domain. An uncertainty analysis revealed that predictions of aboveground C and soil C would be distinctively different whether using tree diameter class or stand age class with high certainty. Overall, this work may enable better integration of forest inventory data and remotely sensed data for the purpose of strategic-scale forest C dynamic simulations. Key words: forest C dynamic, matrix models, diameter class, age class, uncertainty. Les decideurs politiques et les amenagistes souhaitent avoir une estimation de l'etat actuel et des tendances futures des stocks de carbone (C) ainsi que des variations des stocks dans les forets du nord-est des Etats-Unis etant donne que ces forets peuvent attenuer le changement climatique en sequestrant le C[O.sub.2] atmospherique. Nous avons concu des modeles de matrice du flux de C a l'aide de variables de l'arbre et du peuplement fondes soit sur la classe de diametre des arbres, soit sur la classe d'age des peuplements dans le but de comparer les modeles structures par la taille et ceux structures par l'age quant a leur capacite a predire la dynamique du C forestier qui est au creur des decisions strategiques. Les variables de controle primaires dans les modeles de matrice du flux de C (le diametre a hauteur de poitrine, la surface terriere du peuplement, la densite des tiges et l'age du peuplement) etaient toutes statistiquement significatives ([alpha] [less than or equal to] 0,05). En comparant les resultats de la simulation et l'erreur quadratique moyenne des modeles de matrice du flux de C fondes sur la classe de diametre des arbres et ceux fondes sur la classe d'age des peuplements, nous avons trouve que la classe de diametre des arbres predisait avec plus d'exactitude la variation de l'etat des stocks de C pour l'ensemble des grandes conditions de composition et de structure dans les domaines spatial et temporel. Une analyse d'incertitude a revele que les predictions du C aerien et du C dans le sol seraient avec une grande certitude nettement differentes selon qu'on utilise la classe de diametre des arbres ou la classe d'age des peuplements. Dans l'ensemble cette etude peut aider a mieux integrer les donnees d'inventaire forestier et les donnees de teledetection pour simuler la dynamique du C forestier a une echelle strategique. [Traduit par la Redaction] Mots-cles: dynamique du carbone forestier, modeles de matrice, classe de diametre, classe d'age, incertitude., Introduction As forests are the largest terrestrial carbon (C) sink (Pan et al. 85/72011a) on Earth, nations have developed greenhouse gas (GHG) emission reduction targets inclusive of the land sector, [...]

Understanding the patterns of tree recruitment is essential to quantifying the future health and productivity of forest ecosystems. Using national forest inventory information, we incorporated browse impact measurements into models of sapling (2.5-12.7 cm diameter at breast height (DBH)) and overstory tree (>12.7 cm DBH) ingrowth across the northern United States. Ingrowth was modeled with standard and zero-inflated techniques using discrete Poisson and negative binomial distributions. Zero-inflated models using stand attributes and browse impacts provided the best fit statistics for modeling the occurrence and frequency of ingrowth over a 5-year time period. Results indicate that stands with very high browse impact would contain 50.0% fewer ingrowth saplings compared with stands with no browse impact. Greater browse impacts similarly yielded a negative effect on overstory tree ingrowth, but to a lesser degree than saplings. Despite the stochastic nature of ingrowth observations, incorporating browse impacts may be essential in determining accurate levels of ingrowth in forests where herbivory constrains forest regeneration objectives. Key words: herbivory, white-tailed deer, regeneration, ingrowth, Forest Inventory and Analysis. Il est essentiel de comprendre les patrons de recrutement des arbres pour quantifier l'etat de sante et la productivity futures des ecosystemes forestiers. A partir des informations tirees de l'inventaire forestier national, nous avons incorpore des mesures d'impact du broutage dans des modeles de recrutement des gaules (2,5- 12,7 cm de diametre a hauteur de poitrine (DHP)) et des tiges ([greater than or equal to] 12,7 cm au DHP) dans l'etage dominant a travers le nord des Etats-Unis. Le recrutement a ete modelise a l'aide de techniques standards et avec une surrepresentation de zeros en utilisant les distributions de Poisson et binomiale negative. Les modeles avec une surrepresentation de zeros utilisant les attributs du peuplement et les impacts du broutage fournissaient les statistiques les mieux ajustees pour modeliser l'occurrence et la frequence du recrutement sur une periode de 5 ans. Les resultats indiquent que les peuplements severement impactes par le broutage contiendraient 50,0 % moins de recrues comparativement aux peuplements exempts de broutage. Des impacts plus importants dus au broutage ont de facon similaire eu un effet negatif sur le recrutement des tiges dans l'etage dominant, mais a un degre moindre que dans le cas des gaules. Malgre la nature stochastique des observations au sujet du recrutement, l'introduction des impacts du broutage peut s'averer essentiel pour determiner le degre exact de recrutement dans les forets ou le broutage menace les objectifs de regeneration forestiere. [Traduit par la Redaction] Mots-cles: broutage, cerf de Virginie, regeneration, recrutement, Analyse et Inventaire Forestier., Introduction Tree recruitment is the accretion of newly established trees of a certain size in forest stands. Quantifying tree recruitment is essential to forest managers and is an integral component [...]

Several aspects of the forest carbon cycle have not been examined in detail, including sources of variation in carbon dioxide (CO2) emissions from coarse woody material (CWM). To address this knowledge gap, we examined CO2 emissions from Acer saccharum Marshall logs within four harvesting treatments, using closed chambers fitted to the logs. We found that CO2 emissions were highest for logs in small (31.8 ± 20.4 µmol·CO2·m−3·s−1) and large gaps (29.6 ± 24.4 µmol·CO2·m−3·s−1) compared to those in control (13.9 ± 8.3 µmol·CO2·m−3·s−1) and thinned matrix (13.6 ± 8.0 µmol·CO2·m−3·s−1) treatments. CO2 flux rates did not differ between gap sizes, but they increased with temperature, which was higher in the small gap treatment. In addition, two individual logs fitted with multiple closed chambers revealed significant within-log variability in CO2 emissions. On a subset of logs repeatedly sampled throughout the day, we found that log surface temperature generally peaked at midday and was positively correlated with CO2 emissions, although this relationship was weak in one log. This study provides insight into sources of variation in CO2 emissions from CWM while improving our understanding of the forest carbon cycle. [ABSTRACT FROM AUTHOR]