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Observations of the rapid growth and slow decomposition of American chestnut (Castanea dentata (Marsh.) Borkh.) suggest that its reintroduction could enhance terrestrial carbon (C) sequestration. A suite of decomposition models was fit with decomposition data from coarse woody debris (CWD) sampled in Wisconsin and Virginia, U.S. The optimal (two-component exponential) model was integrated with generic growth curves and documented longevity and typical stem density to evaluate how CWD and biomass pools relate to decomposition. CWD decomposed faster in Wisconsin (4.3% ± 0.3% per year) than in Virginia (0.7% ± 0.01% per year), and downed dead wood decomposed faster (8.1% ± 1.9% per year) than standing dead wood (0.7% ± 0.0% per year). We predicted considerably smaller CWD pools in Wisconsin (maximum 41 ± 23 Mg C x [ha.sup.-1]) than in Virginia (maximum 98 ± 23 Mg C x [ha.sup.-1]); the predicted biomass pool was larger in the faster growing Wisconsin trees (maximum 542 ± 58 Mg C x [ha.sup.-1]) compared with slower growing trees in Virginia (maximum 385 ± 51 Mg C x [ha.sup.-1]). Sensitivity analysis indicated that accurate estimates of decomposition rates are more urgent in fertile locations where growth and decomposition are rapid. We conclude that the American chestnut wood is intermediate in resistance to decomposition. Due to the interrelatedness of growth and decomposition rates, CWD pool sizes likely do not depend on species alone but on how the growth and decomposition of individual species vary in response to site productivity. Key words: American chestnut, coarse woody debris, decomposition, carbon cycling, carbon sequestration, forest carbon simulations, forest growth, modeling, plantation development. Les observations ayant trait a la croissance rapide et a la decomposition lente du chataignier d'Amerique (Castanea dentata (Marsh.) Borkh.) indiquent que sa reintroduction pourrait accroitre la sequestration terrestre du carbone. Une serie de modeles de decomposition ont ete ajustes aux donnees de decomposition de debris ligneux grossiers (DLG) echantillonnes au Wisconsin et en Virginie, aux Etats-Unis. Le modele optimal (exponentiel a deux composantes), des courbes generiques de croissance, la longevite documentee et la densite typique de la tige ont ete integres pour evaluer comment les DLG et les reservoirs de biomasse sont relies a la decomposition. Les DLG se decomposaient plus rapidement au Wisconsin (4,3 ± 0,3 % x [an.sup.-1]) qu'en Virginie (0,7 ± 0,01 % x [an.sup.-1]) et les debris au sol se decomposaient plus rapidement (8,1 ± 1,9 % x [an.sup.-1]) que les debris sur pied (0,7 ± 0,0 % x [an.sup.-1]). Nous avons predit que les reservoirs de DLG seraient considerablement plus petits au Wisconsin (maximum de 41 ± 23 Mg C x [ha.sup.-1]) qu'en Virginie (maximum de 98 ±23 Mg C x [ha.sup.-1]); nous avons aussi predit que le reservoir de biomasse serait plus gros chez les arbres du Wisconsin qui croissent plus vite (maximum de 542 ± 58 Mg C x [ha.sup.-1]) comparativement a ceux de la Virginie (maximum de 385 ± 51 Mg C x [ha.sup.-1]). Une analyse de sensibilite a indique qu'il etait plus urgent d'obtenir des estimations precises du taux de decomposition dans les endroits fertiles oU la croissance et la decomposition sont rapides. Nous arrivons a la conclusion que le bois du chataignier d'Amerique a une resistance intermediaire a la decomposition. Etant donne l'interdependance des taux de croissance et de decomposition, la taille des reservoirs de DLG ne depend probablement pas seulement de l'espece mais de la facon dont la croissance et la decomposition de chaque espece varie en reponse a la productivite de la station. [Traduit par la Redaction] Mots-cles: chataignier d'Amerique, debris ligneux grossiers, decomposition, recyclage du carbone, sequestration du carbone, simulations du carbone forestier, croissance forestiere, modelisation, developpement des plantations., Introduction Forested ecosystems sequester atmospheric CO2 in living biomass, dead wood, leaf litter and other detritus, and soil carbon (C). Once disturbances are controlled for, the magnitude of C fluxes, [...]

Saginaw Forest in Ann Arbor, Michigan, includes the second-oldest eastern white pine plantation in the United States, with pioneering thinning experiments among the oldest in the country. With no additional silvicultural treatments occurring since at least the 1950s, we report on the current condition of four planting lots near their century mark to provide silvicultural, cultural, and historical perspectives. Stand density and tree diameter in 2017 were similar across the four lots, all having a significant number of trees > 50 cm diameter at breast height. Tree ring widths suggest that diameter growth was responsive to thinning treatments that occurred before 1955. Today, management geared towards site preservation as a cultural and historical landmark, with an emphasis on intensive invasive species and hardwood ingrowth control and native tree species regeneration, are likely more appropriate than a focus on silviculture. Study Implications Saginaw Forest in Ann Arbor, Michigan contains the second-oldest eastern white pine plantation in the United States. It underwent pioneering forest thinning experiments that pre-dated similar experiments in the oldest eastern white pine plantation at the Biltmore Estate in Asheville, North Carolina. Silvicultural treatments have not occurred since the 1950s, but the effects of historical thinning treatments are evident today across four planting lots. We summarize the current conditions of this important forestry site, noting a serious threat by invasive species and hardwood ingrowth that should be targeted as a means of preserving this important cultural and historical landmark. [ABSTRACT FROM AUTHOR]

: Extensive outbreaks of the mountain pine beetle (Dendroctonus ponderosae Hopkins) will alter the structure of many stands that will likely be attacked again before experiencing a stand-replacing fire. We examined a stand of lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Watson) in Grand Teton National Park currently experiencing a moderate-level outbreak and previously attacked by mountain pine beetle in the 1960s. Consistent with published studies, tree diame-ter was the main predictor of beetle attack on a given tree, large trees were preferentially attacked, and tree vigor, age, and cone production were unimportant variables for beetle attack at epidemic levels. Small trees killed in the stand were killed based mainly on their proximity to large trees and were likely spatially aggregated with large trees as a result of the previous outbreak. We concluded that the driving factors of beetle attack and their spatial patterns are consistent across outbreak severities but that stand structure altered by the previous outbreak had implications for the current outbreaks in the same location. This study should catalyze additional research that examines how beetle-altered stand structure affects future outbreaks-an important priority for predicting their impacts under climate change scenarios that project increases in out-break frequency and extent. Resume: De vastes epidemies du dendroctone du pin ponderosa (Dendroctonus ponderosae Hopkins) vont modifier la structure de plusieurs peuplements qui vont probablement etre attaques de nouveau avant d'etre detruits par un feu qui en-traine le remplacement du peuplement. Nous avons etudie un peuplement de pin pin tordu latifolie (Pinus contorta var. lati-folia Engelm. ex S. Watson) dans le parc national de Grand Teton qui subit presentement une epidemie moyennement severe et qui a dejaete attaque par le dendroctone du pin ponderosa dans les annees 1960. Conformement aux etudes pu-bliees, le diametre des arbres etait le principal predicteur de l'attaque de l'insecte sur un arbre en particulier; l'insecte pre fere les gros arbres et la vigueur de l'arbre, son age et la production de cones ne sont pas des variables importantes en lien avec l'attaque de l'insecte lors d'une epidemie. Les petits arbres qui ont ete tues dans le peuplement l'ont ete surtout parce qu'ils etaient situes a proximite de gros arbres et ils etaient probablement regroupes avec de gros arbres a cause de l'epide-mie precedente. Nous arrivons a la conclusion queles facteurs qui sont a l'origine de l'attaque de l'insecte et leur repartition spatiale sont les memes pour differents niveaux de severite, mais que la structure du peuplement qui a ete modifiee par une epidemie precedente avait des consequences sur l'epidemie actuelle qui sevit au mee endroit. Cette etude devrait susciter d'autres travaux de recherche pour determiner comment la structure du peuplement qui est modifiee par l'insecte influence les epidemies futuresune importante priorite pour predire leurs impacts dans l'optique de scenarios de changement cli-matique qui prevoient une augmentation de a frequence et de l'etendue des epidemies. [Traduit par la Redaction], Introduction Insect outbreaks are pervasive and significant disturbance agents that are important in shaping the structure of coniferous forests in western North America (Nigh et al. 2008; Axelson et al. [...]

Fractal symmetry is symmetry across scale. If one looks at a branch of a tree its branching pattern is reminiscent of the tree as a whole. Plants exhibit a number of different symmetries, including bilateral, rotational, translational, and fractal; deviations from each of these types has been associated with organisms developing in stressful environments. Here, we explore the utilization and meaning of fractal analysis on annual growth ring production in woody plants. Early detection of stress in plants is difficult and the compounding effects of multiple or severe stressors can lead to irreversible damage or death. Annual wood production was used to produce a time series for individuals from stands classified as either high vigor or low vigor (a general measure of health). As a measure of symmetry over time, the fractal dimension of each time series was determined and compared among vigor classes. We found that individuals obtained from low vigor sites had a significantly lower fractal dimension than those from high vigor sites. These results agree with patterns found in a variety of other organisms, and we argue that the reduced fractal dimension is related to a loss in system complexity of stressed individuals. [ABSTRACT FROM AUTHOR]

Forest insects and pathogens are major disturbance agents that have affected millions of hectares in North America in recent decades, implying significant impacts to the carbon ( C) cycle. Here, we review and synthesize published studies of the effects of biotic disturbances on forest C cycling in the United States and Canada. Primary productivity in stands was reduced, sometimes considerably, immediately following insect or pathogen attack. After repeated growth reductions caused by some insects or pathogens or a single infestation by some bark beetle species, tree mortality occurred, altering productivity and decomposition. In the years following disturbance, primary productivity in some cases increased rapidly as a result of enhanced growth by surviving vegetation, and in other cases increased slowly because of lower forest regrowth. In the decades following tree mortality, decomposition increased as a result of the large amount of dead organic matter. Net ecosystem productivity decreased immediately following attack, with some studies reporting a switch to a C source to the atmosphere, and increased afterward as the forest regrew and dead organic matter decomposed. Large variability in C cycle responses arose from several factors, including type of insect or pathogen, time since disturbance, number of trees affected, and capacity of remaining vegetation to increase growth rates following outbreak. We identified significant knowledge gaps, including limited understanding of carbon cycle impacts among different biotic disturbance types (particularly pathogens), their impacts at landscape and regional scales, and limited capacity to predict disturbance events and their consequences for carbon cycling. We conclude that biotic disturbances can have major impacts on forest C stocks and fluxes and can be large enough to affect regional C cycling. However, additional research is needed to reduce the uncertainties associated with quantifying biotic disturbance effects on the North American C budget. [ABSTRACT FROM AUTHOR]

Emerald ash borer (EAB) is an invasive beetle that kills native North American ash species, threatening their persistence. A classical biological control program for EAB was initiated in 2007 with the release of three specialized EAB parasitoids. Monitoring changes in the health and regeneration of ash where EAB biocontrol agents have been released is critical for assessing the success of EAB biocontrol and predicting future changes to the ash component of North American forests. We sampled release and control plots across southern Michigan over a three-year period to measure ash health and recruitment to begin assessing the long-term impact of EAB biological control on ash populations. We noted a reduced mortality of larger trees between 2012 and 2015 in release plots compared to control plots and increases in ash diameter, but our results were otherwise inconsistent. Ash regeneration was generally higher in release plots compared to control plots but highly variable among sites, suggesting some protection of ash saplings from EAB by parasitoids. We conclude that EAB biocontrol is likely to have a positive effect on ash populations, but that the study duration was not long enough to definitively deduce the long-term success of the biocontrol program in this region. [ABSTRACT FROM AUTHOR]