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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 [...]

Widespread changes in dissolved organic carbon (DOC) concentrations in lakes of the Northern Hemisphere are well documented, and there is a need to understand the ecological implications for changes in cold‐water refugia. DOC controls thermal structure in small, wind‐sheltered lakes, thus influencing the volume and persistence of the hypolimnion and cold‐water habitat. We explored the relationship between the quantity and quality of DOC and the availability of cold‐water habitat over the course of summer stratification in small lakes of varying depths. The ratio of the hypolimnetic volume to total lake volume was calculated to assess the relative changes in cold‐water habitat availability in each lake over time. DOC concentration, maximum lake depth, and the interaction between DOC concentration and maximum lake depth explained 87% of the variability in percent change in hypolimnion volume ratio across studied lakes. Hypolimnion compression was greater in shallow, low DOC lakes, whereas deeper, intermediate DOC lakes had more persistent hypolimnion volumes over the course of summer stratification. These results demonstrate that depth moderates the effect of DOC on the volume and persistence of cold‐water refugia availability in north temperate lakes, advancing our understanding of differing lake sensitivity in a rapidly changing physical and chemical environment. Key Points: Dissolved organic carbon concentration, maximum lake depth, and their interaction explained 87% of the variability in hypolimnion volume ratioThe relative change in hypolimnion volume ratio over the course of summer stratification had a strong, negative correlation with mean Schmidt stability [ABSTRACT FROM AUTHOR]

Quantifying changes in soil carbon (C) and nutrient stocks after timber harvesting is needed to inform C management and to ensure that forest productivity is sustained over time. Our objective was to assess changes in soil C, nitrogen (N), and phosphorus (P) 1 year after timber harvesting in temperate northern hardwood forests. We established permanent plots in forest stands for measuring forest attributes before and after harvesting. We collected soils from quantitative soil pits, which were associated with permanent plots, to determine total C, total N, and extractable P stocks and concentrations. Mean post‐harvest fine fraction organic (O) horizon C was less than the pre‐harvest stock, but we did not detect a statistically significant change in total O horizon or mineral soil C stocks. For the fine fractions of the O horizon and mineral soil from the 0–5 and 5–30 cm depth increments of the B horizon, total N and extractable P stocks were positively correlated with total C stocks. For all of these soil components, extractable P stocks and concentrations declined over time, which could be related to post‐harvest stand conditions that favored microbial activity and immobilization of available P. These findings indicate that P availability could be a concern in these forests and that long‐term monitoring is needed to consider potential management actions for ensuring that forest productivity is sustained. Core Ideas: We quantified changes in soils after harvesting in old forests to inform C and forest productivity objectives.For most of our operationally defined soil components, we did not detect a reduction in total C stocks.For all soil components, total N and extractable P stocks were positively correlated with total C stocks.We detected a reduction in soil extractable P stocks and concentrations 1 year after harvesting.Monitoring soils over time will be needed to determine future recovery or continued declines in extractable P. [ABSTRACT FROM AUTHOR]

We used P fractionation techniques to study the accumulation, mobilization, and availability of soil P in six watersheds of the eastern United States and Europe, two of which included paired long-term acidification experiments. Although total soil P concentrations varied widely among these watersheds, the proportions of P fractions were relatively uniform. The mean for the P fraction operationally defined as being associated with Al in the reference watersheds was 71% of total extractable P (SE [less than or equal to] 1%). Experimental whole-watershed acidification resulted in significant depletion of Al-P concentrations from the upper mineral soil in treated watersheds due to the dissolution of Al hydroxide by acidic solutions traveling along shallow flow paths. Acidic soil solutions mobilize both Al and P, leading to P depletion from the Al-P fraction in the mineral soils. Across this suite of watersheds, lower pH appears to decrease Al/P ratios in the Al-P fraction of these mineral soils through changes in Al solubility. Biocycling in these forests can play a critical role in linking subsurface mineral soil P to surface O horizon available P. In this study, sites with the lowest mineral subsoil Al/P ratios generally had the lowest mineral soil pH values and the highest O horizon available P concentrations. The net effect was to leave subsoil P more bioavailable at the lower pH values because of a lower Al/P ratio in the mineral subsoil at the pH range of 3.1 to 4.6 found in this study. These results suggest that changes in soil acidity due to management, air pollutants, or pedogenesis could shift P availability by altering acidity and the Al/P balance. Abbreviations: BBWM, Bear Brook Watershed in Maine; EB, East Bear; FEF, Fernow Experimental Forest; HB, Hadlock Brook; LP, Lesni Potok; MP, Mud Pond; SB, Strengbach; WB, West Bear. doi: 10.2136/sssaj2009.0267

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 [...]