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We integrate a carbon net sink and stand-level wood production to analyze their simultaneous optimization as an economic problem. Carbon is included in living trees, wood products, and forest soil. Forestry is specified by a size-structured model for optimizing thinning timing and intensity, rotation period, and the optimal choice of rotation versus continuous cover forestry. The optimal inclusion of a carbon net sink increases the carbon pool mainly in living trees and forest soil, while the effect on the product carbon pool remains minor. With a 3% interest rate, increasing the C[O.sub.2] price to 40 [euro] per tC[O.sub.2] increases the total steady-state carbon pool by 131% and the soil carbon accounts for ca. 60% of the increased carbon storage. Omitting soil carbon, as in previous studies, leads to underestimates of the carbon sink, significantly decreasing the optimal total C[O.sub.2] net sink and achievable economic net gain from joint wood production and carbon management. The inclusion of soil carbon suggests that, in contrast to previous results, a higher C[O.sub.2] price does not necessarily favor continuous cover forestry. Key words: carbon sequestration, economic profitability, soil carbon, continuous cover forestry, rotation forestry, optimal rotation, 1. Introduction Climate change and the aim of limiting global warming have strongly increased the attention given to forests as carbon sinks (Shukla et al. 2019). Compared with the tropics, [...]

This article applies the tools of bibliometric analyses to explore the evolution and strategic orientation of research focusing on the temporal dynamics of land use, which can be considered as an important proxy to assess soil vulnerability. With 1416 papers published in 417 different journals, the investigation showed a growing interest in the subject during the period ranging from 2001 to 2020. The main countries working on that topic are the USA, China, and certain countries of the European Union with a worldwide collaboration regarding coauthors. A cluster analysis of the keywords generated 6 main themes of research, each focusing on different issues and approaches, that is, greenhouse gas emissions, soil nutrients, climate change, erosion risk, human disturbances as well as resilience of soil functioning. Finally, it appears that the effect of land use legacy is poorly considered in the context of climate change, which could represent a future line of research. Key words: Bibliometrics, historical ecology, land use legacy, agricultural activities, forest soils, soil functioning, 1. Introduction In 2015, the United Nations (UN) member states adopted the '2030 Agenda for Sustainable Development' containing 17 Sustainable Development Goals (SDGs) (UN General Assembly 2015). These objectives include [...]

Most forest soils contain substantial amounts of gravel. However, unlike the more widely known root resource uptake behaviors which respond to resource patches in substrate without gravels, how roots respond to substrate containing different gravel levels is poorly understood. We grew roots in substrates with five gravel levels (0%, 10%, 20%, 30%, and 40% of volume) in a subtropical Schima superba Gardn. et Champ plantation, determined fine root dynamics and turnover rate with minirhizotrons, measured fine root morphological, architectural, mycorrhizal colonization, chemistry, and mass allocation. The presence of gravel in the substrate delayed the timing of peak root growth. In the substrate with higher gravel content, plants produced more in roots in autumn, but there were fewer roots in summer and the roots tended to exhibit lower fine root turnover rate and mycorrhizal colonization, but higher root biomass allocation. The higher root biomass in the substrate with higher gravel content was associated with higher root carbon/nitrogen ratio. Our findings emphasize the complexity of root resource uptake behavior in response to gravel content and suggest that incorporating substrate gravel content into root studies may help to improve the prediction of patch exploitation and nutrient acquisition in stony soils. Key words: heterogeneous patches, root phenology, root morphology, root architecture, mycorrhizal colonization. La plupart des sols forestiers contiennent des quantites substantielles de gravier. Cependant, contrairement aux comportements plus largement connus concernant le prelevement des ressources par les racines qui reagissent a des ilots riches en ressources dans un substrat exempt de gravier, la facon dont les racines reagissent a un substrat qui contient differentes quantites de gravier est mal connue. Nous avons fait croitre les racines dans des substrats contenant differentes proportions (cinq) de gravier (0%, 10%, 20%, 30% et 40% du volume) dans une plantation subtropicale de Schima superba Gardn. et Champ; determine la dynamique et le taux de renouvellement des racines fines a l'aide de minirhizotrons; mesure la morphologie, l'architecture, la colonisation mycorhizienne et les caracteristiques chimiques des racines fines ainsi que la repartition de la biomasse. La presence de gravier dans le substrat a retarde le moment ou la croissance des racines a atteint son niveau maximum. Dans le substrat contenant le plus de gravier, la plus forte croissance est survenue dans les racines a l'automne. Par contre les racines etaient moins abondantes durant l'ete et le taux de renouvellement ainsi que la colonisation mycorhizienne des racines fines avaient tendance a etre plus faibles, mais l'allocation de biomasse racinaire etait plus prononcee. La biomasse racinaire plus elevee dans le substrat contenant le plus de gravier etait associee a un rapport carbone:azote plus eleve dans les racines. Nos resultats font ressortir la complexite du comportement relie au prelevement des ressources par les racines en reaction a la teneur en gravier et indiquent que l'incorporation de la teneur en gravier du substrat dans les etudes portant sur les racines pourrait contribuer a ameliorer la prediction de l'exploitation des ilots riches en ressources et l'acquisition des elements nutritifs dans les sols pierreux. [Traduit par la Redaction] Mots-cles : ilots heterogenes, phenologie racinaire, morphologie racinaire, architecture racinaire, colonisation mycorhizienne., 1. Introduction Resources in soil are heterogeneously distributed. Understanding fine root resource uptake strategies in heterogeneous patches is of primary importance for predicting plant growth and adaptation to changing environments [...]

Timely and accurate knowledge of species-level biomass is essential for forest managers to sustain forest resources and respond to various forest disturbance regimes. In this study, maps of species-level biomass in Chinese boreal forests were generated by integrating Moderate Resolution Imaging Spectroradiometer (MODIS) images with forest inventory data using k nearest neighbor (kNN) methods and evaluated at different scales. The performance of 630 kNN models based on different distance metrics, k values, and temporal MODIS predictor variables were compared. Random Forest (RF) showed the best performance among the six distance metrics: RF, Euclidean distance, Mahalanobis distance, most similar neighbor in canonical correlation space, most similar neighbor computed using projection pursuit, and gradient nearest neighbor. No appreciable improvement was observed using multi-month MODIS data compared with using single-month MODIS data. At the pixel scale, species-level biomass for larch and white birch had relatively good accuracy (root mean square deviation < 62.1%), while the other species had poorer accuracy. The accuracy of most species except for willow and spruce was improved up to the ecoregion scale. The maps of species-level biomass captured the effects of disturbances including fire and harvest and can provide useful information for broad-scale forest monitoring over time. Key words: species-level biomass, MODIS, Chinese boreal forest, Random Forest (RF), kNN. Une connaissance precise et en temps opportun de la biomasse de chaque espece est essentielle pour permettre aux amenagistes forestiers d'effectuer un amenagement durable des ressources forestieres et pour s'ajuster aux divers regimes de perturbations forestieres. Dans cette etude, des cartes de biomasse par espece ont ete generees dans les forets boreales chinoises en integrant des images MODIS (spectroradiometre imageur a resolution moyenne) a des donnees d'inventaire forestier au moyen de l'approche des k plus proches voisins (kNN) et evaluees a differentes echelles. Les performances de 630 modeles kNN ont ete comparees en fonction de differentes metriques de distance, valeurs de k et variables predictives temporelles de MODIS. Les forets d'arbres decisionnels (RF) ont fait ressortir les meilleures performances parmi les six metriques de distance : la distance RF, la distance euclidienne, la distance de Mahalanobis, le plus proche voisin dans l'espace de correlation canonique, le plus proche voisin calcule par poursuite de projection, et le plus proche voisin par gradient. L'utilisation de donnees MODIS sur plusieurs mois n'a apporte aucune amelioration notable en comparaison de l'utilisation des donnees MODIS d'un seul mois. A l'echelle des pixels, la biomasse par espece avait une precision relativement bonne pour le meleze et le bouleau blanc (ecart quadratique moyen < 62,1%), tandis que la precision etait plus faible pour les autres especes. Pour la plupart des especes, a l'exception du saule et de l'epinette, la precision s'est amelioree jusqu'a l'echelle de l'ecoregion. Les cartes de la biomasse par espece ont capte les effets des perturbations, y compris les feux et la recolte, et peuvent fournir des informations utiles pour la surveillance des forets a une vaste echelle au fil du temps. [Traduit par la Redaction] Mots-cles: biomasse par espece, spectroradiometre imageur a resolution moyenne (MODIS), foret boreale chinoise, forets d'arbres decisionnels (RF), methode des k plus proches voisins (kNN)., 1. Introduction The boreal forest is the second largest terrestrial biome in the world, covering 33% of forest area and holding 23% of terrestrial carbon stocks (Carlson et al. 2009; [...]

Mechanical site preparation is assumed to reduce soil C stocks by increasing the rate at which the displaced organic material decomposes, but the evidence is equivocal. We measured rates of C loss of forest-floor material in mesh bags either placed on the surface or buried in the mineral soil at four sites in different regional climates in British Columbia. During the 3-year incubation, buried forest-floor material lost between 5% and 15% more C mass than material on the surface, with the greatest difference occurring at the site with the lowest annual precipitation. Studies of the long-term fate of buried and surface humus are needed to understand the net effects of site preparation on soil C stocks. Key words: humus, decomposition, soil, carbon, site preparation. On assume que la preparation mecanique de terrain reduit les reserves de C dans le sol en augmentant le taux de decomposition de la matiere organique qui a ete deplacee mais les indices sont equivoques. Nous avons mesure le taux de perte de C dans les materiaux de la couverture morte a l'aide de sacs-filets places en surface ou enfouis dans le sol mineral, a quatre endroits sous differents climats en Colombie-Britannique. Durant les trois annees d'incubation, les materiaux de la couverture morte qui avaient ete enfouis ont subi des pertes 5 a 15 % plus elevees que les materiaux places en surface; la plus grande difference a ete observee a l'endroit ou la precipitation annuelle etait la plus faible. Des etudes sur le destin a long terme de l'humus enfoui et en surface sont necessaires pour comprendre les effets nets de la preparation de terrain sur les reserves de C dans le sol. [Traduit par la Redaction] Mots-cles: humus, decomposition, sol, carbone, preparation de terrain., Introduction Mechanical site preparation such as scarification, mounding, or harrowing is commonly practiced following clearcut harvesting of northern forests; for example, in 2016, soil scarification was carried out on 155 [...]

Tropical forests play a key role in the global carbon cycle. However, little is known about carbon cycling in the substantial portion of tropical forests that are low-lying, with shallow and fluctuating water tables. This study aimed to determine what factors control emissions of C[O.sub.2] from soil in a riparian rainforest in Queensland, Australia. Emissions were measured over the course of I year, using static chambers. Emission rates were significantly related to soil temperature (0-0.1 m depth), soil water content (0-0.12 m depth) and depth to water table. The most efficient linear model of emissions as a function of measured parameters, which also included soil pH (0-0.1 m depth), had [r.sup.2] = 0.355. C[O.sub.2] emissions were highest (5.2-7.5 µmol [m.sup.-2] [s.sup.-1]) at moderate soil temperature (24-28 °C), water table depth (0.2-1.5 m) and soil water-filled porosity (0.25-0.79). They were lowest ( Additional keywords: carbon cycling, hydrology, soil respiration, tropical rainforest, soil moisture. Received 6 February 2015, accepted 10 August 2015, published online 13 April 2016, Introduction Tropical forests are a major pool of terrestrial carbon, and the cycling of carbon through forest soils is a key part of the global carbon cycle (Cleveland et al. [...]

Quantifying soil organic carbon (SOC) inputs in the surface soil is a critical component for assessing the potential for carbon sequestration of managed pine forests. This study used a sequential exclusion of aboveground litter inputs (L, litter exclusion) and aboveground plus belowground inputs (LR, litter and root exclusion) to segregate carbon sources contributing to the development and maintenance of SOC in the surface soil supporting juvenile loblolly pine (Pinus taeda L.) in its rapid growth phase. The study spanned the 7th to 10th year of stand growth. Soil physical size fractions (>2 mm, ≤2 mm, 2000-250 µm, 250-150 µm, 150-53 µm, and Key words: carbon accretion, leaf litter, mineralization, Pinus taeda L., soil size fraction. Il est essentiel de quantifier les apports de carbone organique du sol (COS) dans le sol de surface pour evaluer le potentiel de sequestration du C dans les forets de pin amenagees. Dans cette etude nous avons eu recours a l'exclusion sequentielle des apports aeriens de litiere (L, exclusion de la litiere) et des apports aeriens et souterrains (LR, exclusion de la litiere et des racines) pour separer les sources de C qui contribuent au developpement et au maintien du COS dans le sol de surface qui supporte le pin a encens (Pinus taeda L.) juvenile dans sa phase de croissance rapide. L'etude couvrait de la 7e a la 10e annee de croissance du peuplement. Les classes granulometriques du sol (>2 mm, ≤2 mm, 2000-250 µm, 250-150 µm, 150-53 µm et Mots-cles: accumulation du carbone, litiere de feuilles, mineralisation, Pinus taeda L., classes granulometriques du sol., Introduction Soil organic carbon (SOC) content is a keystone soil quality parameter and plays a significant role in the global carbon (C) cycle. Yet, the role of root turnover and [...]

Surface mining in the Canadian boreal forest involves the removal of vegetation and soils, resulting in the local loss of biodiversity and ecosystem functioning. Ectomycorrhizal (EM) fungi are critical to ecosystem processes; however, their recovery following reclamation is not well understood. This study investigated the importance of reclamation cover soils (forest floor material, peat, and subsoil) and tree seedling species (Populus tremuloides Michx., Pinus banksiana Lamb., and Picea glauca (Moench) Voss) in structuring the community composition of EM fungi. We used 1-year-old seedlings to assay cover soils in the field for 3 months, and grew seedlings in each of the cover soils in a growth chamber assay for 5 months. Nonmetric multidimensional scaling indicated host identity structured the community composition of EM fungi in the field, while both host identity and cover soil influenced the composition of EM fungi in the growth chamber. However, pre-colonization of seedlings by nursery fungi complicates interpretation of field results. The rate of EM fungus colonization of seedlings collected across both assays was relatively low, approximately 23%. Our results indicate cover soils used in reclamation of surface-mined landscapes retain propagules of EM fungi, and using a wide variety of tree species in upland boreal forest restoration may increase the diversity of EM fungi recovered. Key words: Populus tremuloides, Pinus banksiana, Picea glauca, ITS rDNA, Sanger sequencing, reclamation, plant-soil links. L'exploitation miniere de surface dans la foret boreale canadienne implique l'ablation de la vegetation et des sols resultant en une perte locale de la biodiversite et du fonctionnement de l'ecosysteme. Les champignons ectomycorhizes (EM) sont critiques aux processus de l'ecosysteme ; cependant leur retablissement a la suite de la rehabilitation du terrain n'est pas bien compris. Cette etude s'est penchee sur l'importance de la rehabilitation des sols de surface (matiere du tapis forestier, tourbe et sous-sol) et des especes de semis d'arbres (Populus tremuloides Michx., Pinus banksiana Lamb. et Picea glauca (Moench) Voss) dans la structuration de la composition de la communaute des champignons EM. Les auteurs ont utilise des semis ages d'un an pour tester les sols de surface sur le terrain pendant 3 mois, et ils ont cultive les semis sur chacun des sols de surface lors d'un test en chambre de croissance pendant 5 mois. Une mise a l'echelle multidimensionnelle non metrique a indique que l'identite de l'hote structurait la composition des champignons EM sur le terrain, alors que l'identite de l'hote et le sol de surface influencaient la composition des champignons EM dans les chambres de croissance. Cependant, la pre-colonisation des semis par des champignons de pepiniere complique l'interpretation des resultats sur le terrain. Le taux de colonisation des semis par les champignons EM recoltes a travers les deux tests etait relativement faible, soit approximativement 23%. Les resultats des auteurs indiquent que les sols de couverture utilises en rehabilitation des terrains miniers de surface conservent des propagules de champignons EM, et que l'utilisation d'une grande variete d'especes d'arbres pour la restauration de la foret boreale situee en hauteur peut accroitre la diversite des champignons EM recuperes. [Traduit par la Redaction] Mots-cles: Populus tremuloides, Pinus banksiana, Picea glauca, ADNr de l'espaceur transcrit interne, sequencage de Sanger, rehabilitation, liens vegetal-sol., Introduction Surface mining, a relatively new disturbance in the Canadian boreal forest, involves the removal of vegetation and soils, resulting in the local loss of biodiversity and ecosystem functioning. Prior [...]

The availability of phosphorus (P) for the growth of plants often depends on the solubilisation of inorganic phosphates (P fractions) in the soil. The aim of this study was to investigate soil P fractions in terms of availability and soil characteristics of mangrove soil compared with the Atlantic forest and restinga soils that occur at Cardoso Island, Brazil. Soil samples were collected during summer at depths of 0-2, 2-5 and 5-10cm. Except for Ca-P, the quantity of P fractions in the soils decreased in the order: Atlantic forest > mangrove > restinga. Principal components analysis showed that treatments were clustered into two groups based on ecosystem proprieties; P in mangrove soil was associated with pH, moisture and salinity, and P in Atlantic forest soil with soil organic matter (SOM). The P in restinga soil was not associated with any variable. Among fractions, iron (Fe)-P was dominant, followed by calcium (Ca)-P and aluminium (Al)-P. The most recalcitrant P fractions, reductant Fe-P, occluded (o) Fe-P and oAl-P were detected in minor amounts. Soluble (sol)-P was detected only in the Atlantic forest soil. Soil P fractions varied little with depth in the mangrove and restinga soils. The P fractions from Atlantic forest soil were found at depths of 0-2 cm (Fe-P, Ca-P) and 2-5 cm (sol-P, Al-P, Fe-P, oAl-P and oFe-P). Positive correlation was obtained for all P fractions with moisture (except sol-P and Fe-P) and SOM (except Ca-P) contents and negative correlation with soil pH (except Ca-P) and salinity (except Fe-P and Al-P). Quantities and qualities of the P fractions varied among the studied ecosystems, influenced by the parent material and physico-chemical characteristics of the soil and vegetation. Additional keywords: depth, moisture, natural ecosystems, organic matter, pH., Introduction In self-sustaining systems, the availability of phosphorus (P) to plants depends on the mineralisation of organic P or solubilisation of inorganic P, and may vary depending on the source [...]

Deficiency in availability of phosphorus (P) in forest soils of southern China, where Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) stands have been established, greatly affects Chinese fir productivity. Deploying clones with high P-use efficiency could be a more attractive option than P fertilization to enhance the commercial productivity of Chinese fir. Thus, an understanding of the adaptive responses of roots to spatiotemporal variability of P, which is often ignored in previous studies, is essential. In this study, we report the root responses of a Chinese fir clone with high P-use efficiency to the spatially heterogeneous P availability in soil during various periods of time when P availability was controlled. The results showed significantly (p < 0.05) more root proliferation in the form of root length, root surface area, root volume, and root dry matter accumulation in P-replete than in P-poor patches when the patch persisted for a short period of time (50 days). As the patches persisted longer (100-200 days), root proliferation in P-replete patches appeared to decline. P-replete patches that persisted for short (50 days) and long (200 days) periods resulted in high root P accumulation, whereas P-replete patches that persisted for 100-150 days resulted in lower root P accumulation than other patches. It seems that the observed responses in the roots of the Chinese fir clone to heterogeneous P availability might include a comprehensive adjustment of root growth and intraroot P translocation in patches so as to maintain internal P homeostasis, as well as a trade-off between energy cost and production of new roots when the patch persists longer. Key words: Chinese fir, P-use efficiency, phosphorus plaques, root, nutrient heterogeneity. La carence en phosphore disponible (P) dans les sols forestiers du sud de la Chine oU des peuplements de sapin de Chine (Cunninghamia lanceolata (Lamb.) Hook.) ont ete etablis a un impact important sur la productivite de cette essence. Le recours a des clones a forte efficacite d'utilisation du P pourrait etre une option plus attrayante que la fertilisation en P pour ameliorer la production commerciale du sapin de Chine. Par consequent, il est essentiel de comprendre la variation spatiotemporelle du P, ce qui a souvent ete ignore dans les etudes precedentes. Nous presentons dans cet article les resultats d'une etude de cas realisee avec un clone de sapin de Chine a forte efficacite d'utilisation du P. L'etude portait sur la reaction des racines a l'heterogeneite spatiale de la disponibilite du P dans le sol pendant differentes periodes de temps durant lesquelles la disponibilite du P a ete controlee. La proliferation des racines en termes de longueur, de surface, de volume et d'accumulation de matiere anhydre etait significativement plus grande (p Mots-cles : sapin de Chine, efficacite d'utilisation du P, plaques de P, racine, elements nutritifs., Introduction Phosphorus (P) is an essential plant nutrient that is indispensable in terrestrial ecosystems (Cordell et al. 2009). Plants absorb P as orthophosphate; however, orthophosphates can easily bind to iron, [...]

Empirical knowledge of long-term ecosystem response to single and compound disturbances is essential for predicting disturbance effects and identifying management practices to maintain productive capacity of managed and restored landscapes. We report on soil, foliar nutrition, and regeneration growth response to wildfire, clearcut harvesting, and postfire salvage logging, as well as undisturbed control stands within the first year following disturbance and 10-11 years after disturbance in trembling aspen--white spruce mixedwood forests near Lesser Slave Lake, north-central Alberta, Canada. The compound disturbance of salvage logging resulted in greater long-term impacts on forest floor properties than either wildfire or harvesting alone. Changes in forest floor properties such as carbon and nitrogen pools and cation exchange capacity under salvage logging have persisted for 10 years and exhibit a different recovery trajectory than fire or harvesting. Forest floor properties under harvesting, including depth, carbon content, pH, extractable ammonium, and extractable sulphur, were not different from the control condition 10 years after harvest. Effects on soil and foliar nutrition were not reflected in productivity (height and diameter) of regenerating vegetation. Our results show differences between short- and long-term responses to disturbance, among single natural and anthropogenic disturbances, and among single and compound disturbances. Key words: compound disturbance, salvage logging, soil carbon, soil nutrients, Boreal Plains Ecozone, boreal mixedwood forest. La connaissance empirique de la reponse des ecosystemes a des perturbations simples ou combinees est essentielle pour predire les effets et identifier les pratiques d'amenagement pour maintenir la capacite productive des paysages amenages et restaures. Nous rapportons les effets du feu, de la coupe totale et de la coupe de recuperation apres feu, ainsi que leur comparaison avec des sites non perturbes, sur les sols, la nutrition foliaire et la croissance de la regeneration, un an et 10-11 ans apres perturbation dans des forets mixtes de peuplier faux-tremble et d'epinette blanche pres de Lesser Slave Lake (centre-nord de l'Alberta, Canada). Par rapport au feu ou a la coupe, la coupe de recuperation apres feu, qu'on peut qualifier de perturbation combinee, a cause des impacts plus importants a long terme sur les horizons organiques de surface. Les changements dans les proprietes des horizons organiques, tels que les reservoirs de carbone et d'azote et la capacite d'echange cationique, ont persiste apres 10 ans, et montrent une trajectoire dans le temps differente de celles observees apres feu ou coupe. Dix ans apres perturbation, les proprietes des horizons organiques incluant l'epaisseur, le contenu en carbone, le pH et les concentrations en ammonium et soufre extractibles n'etaient pas differentes dans les sites coupes par rapport aux sites non perturbes. Les effets sur la nutrition des sols et des arbres ne se sont pas traduits par une plus grande productivite (hauteur et diametre) de la regeneration a ce stade precoce de la revolution du peuplement. Nos resultats montrent des differences entre la reponse a court et a long terme des ecosystemes suite a une perturbation, entre les perturbations d'origine naturelle et anthropique, et entre les perturbations simples et combinees dans les forets boreales mixtes de l'Ouest. Mots-cles: perturbation combinee, coupe de recuperation, carbone du sol, elements nutritifs du sol, Ecozone de la Plaine Boreale, foret boreale mixte., Introduction The western boreal mixedwood forest is experiencing an increasing anthropogenic footprint and an evolving suite of land-use pressures. It remains an important region of forest management for the sustainable [...]

Reintroductions of coarse woody debris (CWD) to Australia's temperate woodlands have been proposed to offset the impacts of long-term tree removal. However, the magnitude of the reduction in the rate of surface-soil moisture loss due to CWD is not known. Gravimetric soil moisture content was measured at different distances from CWD for 12 samples in a cleared temperate woodland. Sampling was conducted at regular intervals following a major rain event in late summer. Lower soil bulk densities near CWD indicated higher levels of soil carbon. A multivariate nonlinear statistical model was constructed to explain the observed soil moisture content as a function of time after rainfall, distance from CWD and CWD diameter. The model demonstrated that rates of soil moisture loss increased with increasing distance from CWD. Drying times near CWD were 40% longer than drying times at reference distances from CWD. The model also showed that CWD diameter influenced the rate of soil moisture loss, with larger diameters yielding reductions in soil moisture loss over greater distances from CWD. Locations of greater soil moisture availability associated with CWD may be particularly advantageous for organisms sensitive to low soil moisture levels and may increase productivity, particularly in water-limited ecosystems. Additional keywords: Eucalypt woodlands, south-east Australia, soil bulk density, soil moisture availability, coarse woody debris diameter., Introduction Coarse woody debris (CWD), consisting of fallen tree boles and branches with a small-end diameter >10 cm, contributes to the organic matter pool of forested ecosystems (Harmon el al. [...]

We analyzed arbuscular mycorrhizal fungal (AMF) communities in plant root samples from a natural forest ecosystem--a primeval forest in Jarvselja, Estonia. AMF small-subunit (SSU) ribosomal RNA genes were subjected to 454-pyrosequencing and BLAST-based taxonomic identification. Seventy-six AMF sequence groups (virtual taxa, VT) were identified from plant roots. Taken together with seven additional VT recorded in an earlier investigation of soil AMF communities at the site, this represents the highest number of AMF reported from a single ecosystem to date. The six study plant species hosted similar AMF communities. However, AMF community composition in plant roots was significantly different from that in soil and considerably more VT were retrieved from roots than from soil. AMF VT identified from plant roots as a whole and from individual plant species were frequently phylogenetically clustered compared with local and global taxon pools, suggesting that nonrandom assembly processes, notably habitat filtering, may have shaped fungal assemblages. In contrast, the phylogenetic dispersion of AMF communities in soil did not differ from random subsets of the local or global taxon pools. Key words: arbuscular mycorrhizal fungi, microbial ecology, microbial communities, symbionts, soil microbes. Les auteurs ont analyse les communautes de champignons mycorhiziens arbusculaires (CMA) dans des echantillons racinaires provenant d'un ecosysteme naturel--une foret vierge situee a Jarvselja en Estonie. Ils ont soumis les genes de la petite sous unite (PSU) d'ARNr au pyrosequencage 454 et effectue l'identification taxonomique par BLAST. Ils ont identifie 76 groupes de sequences de CMA (taxons virtuels, TV) a partir de racines de plantes. Pris ensemble avec 7 autres TV provenant d'une recherche antecedente conduite sur ce site portant sur les communautes CMA, ceci represente le nombre le plus eleve de CMA rapporte pour un ecosysteme donne, jusqu'ici. Les six plantes hotes etudiees hebergent des communautes similaires de CMA. Cependant, la composition des communautes de CMA dans les racines des plantes differe significativement de celle provenant du sol, ou on retrouve considerablement plus de TV dans les racines que dans le sol. Dans l'ensemble, les TV des CMA identifies a partir des racines des plantes ainsi que des especes de plantes individuelles montrent frequemment des clusters phylogenetiques en comparaison aux pools locaux et globaux de taxons. Ceci suggere l'existence de processus d'assemblage non aleatoires, notamment le filtre de l'habitat, qui pourraient avoir change l'assemblage des champignons. En revanche, la dispersion phylogenetique des communautes de CMA du sol ne different pas des sous-ensembles aleatoires des pools locaux ou globaux de taxons. [Traduit par la Redaction] Mots-cles: champignons mycorhiziens arbusculaires, ecologie microbienne, communautes microbiennes, symbiontes, microorganismes du sol., Introduction Arbuscular mycorrhizal fungi (AMF; phylum Glomeromycota) form a symbiosis with the majority of land plant species. The beneficial effects of these associations to plants include improved nutrition and growth, [...]

Exploring the relationship between the accumulation of soil organic carbon (C) and the form and availability of soil phosphorus (P) is important for improved understanding of soil P availability and its regulation of C storage in forest ecosystems. Here, we investigated the relationships among soil organic C, sequentially extracted P fractions and P sorption index in 32 surface soils (0-13.15 m depth) across eight mature subtropical forests (80-400 years) in Dinghushan, China. Results showed that soil organic P (Po) accounted for 40-63% (mean 54%) of soil total P. Soil organic C was significantly positively correlated with both the content and the percentage of soluble inorganic P (Pi), Al-Po and Fe-Po fractions and the content of the Al-Pi fraction. The content of soil total Po increased significantly with soil organic C, whereas the percentage of soil total Po tended to increase with soil organic C only when soil organic C was low ( Additional keywords: organic carbon, organic phosphorus, phosphorus sorption index, soil phosphorus fractionation, subtropical forest., Introduction Phosphorus (P) is one of the important nutrients determining the function and primary productivity of terrestrial ecosystems (Aerts and Chapin 1999; Elser et al. 2007). Despite the typically large [...]

Changes in total soil carbon (C), nitrogen (N) and natural-abundance N isotopes (δ[sup.15]N) were measured along three forest-to-pasture chronosequences on pumice soils in the Central North Island of New Zealand. On each of the three chronosequences, exotic pine forests had been converted to intensive dairy pastures 2-11 years before sampling and samples were also taken from remaining pine forests and long-term pastures (40-80 years old). The primary objective of the study was to test the hypothesis that surface-soil δ[sup.15]N would increase over time following conversion of forest to pasture, due to greater N inputs and isotope-fractionating N losses (e.g. ammonia volatilisation) in pasture systems. Results supported our hypothesis, with linear regression revealing a significant (P < 0.001) positive correlation between logtransformed pasture age ([log.sub.10][pasture age + 1]) and surface-soil δ[sup.15]N. There was also a positive correlation (P < 0.001) between pasture age and total soil C and N, and a negative correlation of pasture age with C: N ratio. Surface-soil δ[sup.15]N was also positively correlated (P Additional keywords: deforestation, land-use change, natural abundance, nitrogen isotope, pine forest., Introduction The understanding of soil properties and ecosystem development has been advanced by studying chronosequences, which are defined as 'a set of sites formed from the same parent material or [...]

Impacts of forest harvesting are often assessed in short-term studies that ignore the longer term changes associated with the disturbance. A chronosequence approach was taken to investigate changes in microbial community size and composition over ~20 years post-harvest in lodgepole pine (Pinus contorta Douglas ex Loudon) stands of the Boreal Plain. The LFH and mineral Ae horizons of Orthic Gray Luvisolic soils were sampled in six cutblocks, aged 1-19 years since harvest, in 2009 and 2010. Changes in microbial communities were assessed using phospholipid fatty acid analysis (PLFA) and 16S rDNA analysis. Physical and chemical soil parameters were measured to delineate microsite changes impacting microbial community shifts. Total microbial biomass (PLFA) was unaffected by harvesting disturbance, although fungal biomass was significantly larger in the oldest cutblock of the chronosequence. Microbial community composition did, however, differ between younger and older cutblocks as indicated by both lipid PLFA and 16S rDNA fingerprinting techniques. Forest soil microbial communities subject to clearcutting were observed to shift in overall community composition while remaining consistent in overall community size. The shift in community composition, which occurred in concert with the maintenance of biomass, indicated that the microbial community adapted sufficiently to the new post-harvest microsite conditions. Resume: Les impacts de l'exploitation forestiere sont souvent evalues dans le cadre d'etudes a court terme qui ignorent les changements a plus long terme associes a cette perturbation. Une approche chronosequentielle a ete utilisee pour etudier les changements dans la composition et la taille des communautes microbiennes survenus sur une periode de 20 ans apres une coupe dans des peuplements de pin tordu (Pinus contorta Douglas ex Loudon) de la plaine boreale. L'horizon LFH et l'horizon mineral Ae dans des luvisols gris orthiques ont ete echantillonnes dans six aires de coupe en 2009 et 2010, de 1 a 19 ans apres la coupe. Les changements dans les communautes microbiennes ont ete evalues par l'analyse des acides gras phospholipidiques (PFLA) et de l'ADNr 16S. Les parametres physiques et chimiques du sol ont ete mesures pour circonscrire les changements dans les microsites qui avaient un impact sur les modifications dans les communautes microbiennes. La biomasse microbienne totale (PFLA) n'etait pas influencee par la perturbation due a la recolte bien que la biomasse fongique ait ete significativement plus grande dans la plus vieille aire de coupe de la chronosequence. Cependant, il y avait une difference entre les aires de coupe les plus jeunes et les plus vieilles quant a la composition des communautes microbiennes, comme l'indiquaient les techniques de PFLA et d'empreinte genetique avec l'ADNr 16S. La composition d'ensemble des communautes microbiennes dans les sols forestiers a ete modifiee a la suite d'une coupe a blanc mais la taille globale des communautes est demeuree la meme. Le changement dans la composition des communautes qui s'est produit de concert avec le maintien de la biomasse indiquait que la communaute microbienne s'est suffisamment adaptee aux nouvelles conditions observees dans les microsites a la suite de la coupe. [Traduit par la Redaction], Introduction The forestry industry, like the agriculture industry, relies heavily on productive soils to yield fast-growing, healthy plants. Foresters, however, do not replace soil organic matter and nutrients as farmers [...]

Forest floor data are important for many forest resource management applications. In terms of fire and forest carbon dynamics, these data are critical for modeling direct carbon emissions from wildfire in Canadian forests because forest floor organic material is usually the greatest emissions source. However, there are very few data available to initialize wildfire emission models. Six data sets representing 41 534 forest stands across Canada were combined to provide summary statistics and to analyze factors controlling forest floor fuel loads and depths. The impacts of dominant tree species, ecozone, drainage-class, and age-class data on forest floor fuel loads and depth were examined using ANOVA and regression. All four parameters were significant factors affecting forest floor fuel load and depth, but only tree species and ecozone were substantially influential. Although forest floor depths summarized in this study are similar to those of previous studies, forest floor fuel loads are higher. Average forest floor fuel loads and depths are summarized by species and ecozone and can be used to initialize dynamic stand-level forest models. Resume: Les donnees sur la couverture morte sont importantes pour plusieurs applications en amenagement des ressources forestieres. En termes de dynamique du carbone forestier et du feu, ces donnees sont essentielles pour modeliser les emissions directes de carbone dues aux feux de foret dans les forets canadiennes parce que la matiere organique presente dans la couverture morte est habituellement la plus importante source d'emissions. Cependant, tres peu de donnees sont disponibles pour initialiser les modeles d'emissions dues aux feux de foret. Six jeux de donnees representant 41 534 peuplements forestiers a travers le Canada ont ete combines pour fournir des statistiques sommaires et analyser les facteurs qui determinent la charge et l'epaisseur des combustibles dans la couverture morte. Les impacts de l'espece d'arbre dominante, de l'ecozone, de la classe de drainage et des donnees de classe d'age sur la charge et l'epaisseur des combustibles dans la couverture morte ont ete etudies a l'aide des analyses de variance et de regression. Les quatre parametres avaient un impact significatif sur la charge et l'epaisseur des combustibles dans la couverture morte mais seules l'espece d'arbre et l'ecozone avaient une influence importante. Bien que les epaisseurs de couverture morte resumees dans cette etude soient semblables a celles des etudes precedentes, les charges de combustibles dans la couverture morte sont plus elevees. Les valeurs moyennes de charge et d'epaisseur des combustibles dans la couverture morte sont resumees par espece et par ecozone et peuvent etre utilisees pour initialiser les modeles forestiers dynamiques a l'echelle du peuplement., Introduction Forests cover almost 400 million ha of the Canadian land base, representing about 10% of the world's forest and 30% of the world's boreal forest (Natural Resources Canada 2011). [...]

Since plant growth in the boreal forest is often considered to be limited by low temperatures and low N availability and these variables are projected to increase due to climate warming and increased anthropogenic activities, it is important to understand whether and to what extent these disturbances may affect the growth of boreal trees. In this study, the hypotheses that wood phenology and anatomy were affected by increased soil temperatures and N depositions have been tested in two mature black spruce (Picea mariana (Mill.) BSP) stands at different altitudes in Quebec, Canada. For 3 years, soil temperature was increased by 4 ° C during the first part of the growing season and precipitations containing three times the current N concentration were added in the field by frequent canopy applications. Soil warming resulted in earlier onsets of xylogenesis and interacted with N addition producing longer durations of xylogenesis for the treated trees. The effect of warming was especially marked in the phenology of roots, while wood production, in terms of number of tracheids, was not affected by the treatment. Xylem anatomy and soil and needle chemistry showed no effect of the treatments, except for an increase of cell wall thickness in earlywood of treated trees. This short-term experiment with black spruce suggested that previous fertilization studies that used large and unrealistic rates of N addition may have overestimated the impact of N depositions on boreal forest productivity. Resume: Comme on considere souvent que les basses temperatures et la faible disponibilite du N limitent la croissance des plantes dans la foret boreale, et qu'une augmentation de ces variables est prevue a cause du rechauffement du climat et de l'augmentation des activites anthropiques, il est important de comprendre si, et dans quelle mesure, ces perturbations pour-raient influencer la croissance des arbres boreaux. Dans cette etude, les hypotheses que les augmentations de la temperature du sol et des depots de N ont un effet sur l'anatomie et la phenologie du bois ont ete testees dans deux peuplements matures d'epinette noire (Picea mariana (Mill.) BSP) situes a differentes altitudes au Quebec, Canada. Pendant 3 ans, la temperature du sol a ete elevee de 4 ° C durant la premiere partie de la saison de croissance et des precipitations contenant trois fois la concentration actuelle de N ont ete ajoutees au champ par de frequentes applications aeriennes. Le rechauffement du sol a entraine le declenchement plus hatif de la xylogenese et a interagi avec l'addition de N pour allonger la duree de la xylogenese chez les arbres traites. L'effet du rechauffement s'est fait particulierement sentir sur la phenologie des racines tandis que la production de bois, en termes de nombre de tracheides, n'a pas ete influencee par le traitement. Les traitements n'ont eu aucun effet sur l'anatomie du xyleme ni sur les caracteristiques chimiques du sol et des aiguilles, a l'exception d'une augmentation de l'epaisseur de la paroi cellulaire dans le bois initial des arbres traites. Cette experience a court terme avec l'epinette noire indique que les etudes precedentes de fertilisation, dans lesquels des taux eleves et irrealistes d'apport en N ont ete utilises, ont pu surestimer l'impact des depots de N sur la productivite de la foret boreale. [Traduit par la Redaction], Introduction The boreal forest is expected to experience a greater increase in surface temperature than any other forest ecosystem in the world (Stromgren and Linder 2002). For eastern Canada, recent [...]

Northern red oak (Quercus rubra L.) seedling growth has been extensively studied. White oak (Quercus alba L.) and chestnut oak (Quercus prinus L.), however, are far less investigated despite their importance among upland oak species in eastern North American forests. We characterized white and chestnut oak seedling response to light and available soil nu-trients while using northern red oak as a benchmark. Germinants were grown within one of three shade treatments (25%, 18%, and 6% of full sun) in one of two native forest soil mixes over two growing seasons. Leaf area, shoot mass, and root mass of all three species showed positive growth responses to increasing light. Growth and biomass were higher for all spe-cies grown in the more nutrient-rich forest soil, but chestnut oak displayed the greatest positive responses to the higher nu-trient levels. White oak seedlings were the slowest growers and demonstrated the most root-centered growth, with root to shoot ratios almost twice that of either chestnut or northern red oak seedlings. The oak species evaluated here responded differently to changes in resource availability. Our study demonstrates the differential response of upland oaks to low light and nutrients. These differences need consideration when developing oak management prescriptions for specific oaks. La croissance des semis de chene rouge (Quercus rubra L.) a fait l'objet de plusieurs etudes. Toutefois, le chene blanc (Quercus alba L.) et le chene chataignier (Quercus prinus L.) ont ete beaucoup moins etudies malgre leur importance parmi les especes de chene de milieu sec dans les forets de l'est de l'Amerique du Nord. Nous avons caracterise la reaction des semis de chene blanc et de chene chataignier a la lumiere et a la disponibilite des nutriments du sol en utilisant le chene rouge comme reference. Les germinats se sont developpes pendant deux saisons de croissance dans un des trois traitements d'ombre (25 %, 18 % et 6 % de la pleine lumiere) et dans un des deux melanges de sol forestier preleves in situ. La crois-sance en surface foliaire, en biomasse des pousses et en biomasse racinaire des trois especes a augmente avec la disponibi-lite de la lumiere. La croissance et la biomasse des trois especes etaient plus elevees dans le sol forestier le plus riche, mais dans de telles conditions, la reaction du chene chataignier a ete la plus forte. La croissance des semis de chene blanc etait la plus lente et la plus axee vers le developpement racinaire avec un rapport entre la biomasse racinaire et celle des pousses presque deux fois plus eleve que ceux des semis de chene chataignier et de chene rouge. Les especes de chene de la pre-sente etude ont reagi differemment aux changements de disponibilite des ressources. Notre etude demontre que les chenes de milieu sec reagissent differemment a la faible disponibilite de lumiere et de nutriments. Ces differences meritent d'etre considerees pour mettre au point des prescriptions sylvicoles propres aux differentes especes de chene. [Traduit par la Redaction], Introduction A continuing problem in the Appalachian region of eastern North America is the sustainability and regeneration of oak species within forests as overstory oaks are eliminated through natural mortality [...]

To evaluate the effect of land use change from a natural broadleaf evergreen forest to Moso bamboo plantations and their management practices on soil [N.sub.2]O efflux in a subtropical region of China, [N.sub.2]O efflux was measured during June 2008 and May 2009 using static closed chamber method. The observed mean [N.sub.2]O fluxes were 0.230, 0.102 and 0.093 mg [N.sub.2]O/[m.sup.2]/h from the intensively managed bamboo forest (IM), conventionally managed bamboo forest (CM), and broadleaf evergreen forest (BL), respectively, and calculated annual cumulative [N.sub.2]O were 15.8, 8.7 and 7.2 kg [N.sub.2]O/ha, respectively. Soil temperature had significant influence on [N.sub.2]O flux. Whereas there was no correlation between [N.sub.2]O flux and soil water content. Conversion of the natural subtropical broadleaf evergreen forest to Moso bamboo did not increase soil [N.sub.2]O efflux, but intensive management practices such as regular tillage and fertiliser application, significantly increased soil [N.sub.2]O emission from bamboo soil. Keywords [N.sub.2]O flux * Greenhouse gas emission * Intensive management * Land use change * Bamboo plantation, Introduction [N.sub.2]O is a potent greenhouse gas with a global warming potential (GWP) 298 times greater than that of carbon dioxide (C[Osub.2]) on a 100-year interval (IPCC, 2007). Moreover, increasing [...]

In 2005/6, we conducted a remeasurement investigation of organic and mineral horizon Ca at 54 sites in forests of the Adirondack Mountains, New York. This network of plots represents northern hardwood, pine-dominated, and high-elevation spruce--fir stands typical of this region. Soil Ca had been measured at these sites twice (1930-1932 and 1984) in the previous 74 yr. Consistent with the original methods, we used measurements of dilute HCl (0.2 mol [L.sup.-1]) extractable Ca to make comparisons among the 1930 to 1932, 1984, and 2005/6 samples. Between 1932 and 2005/6, median HCl-extractable Ca content decreased significantly (78%) in organic horizons and in the whole profile (organic + mineral horizons, 64%), although significant decreases in mineral soil Ca content were confined to the upper 20 cm. Moreover, significant decreases in organic horizon (-1.5% [yr.sup.-1]), mineral horizon (-1.0% [yr.sup.-1]), and whole profile (-1.5% [yr.sup.-1]) Ca content between 1984 and 2005/6 indicated that Ca depletion has been sustained in recent decades. When stratified by forest type, there were significant decreases in extractable Ca concentrations and content in organic horizons and in the whole profile for all forest types between 1932 and 2005/6, although decreases between 1984 and 2005/6 were not necessarily significant. Overall, the rate of median whole-profile Ca depletion (~13.6 kg [ha.sup.-1] [yr.sup.-1]) was similar during all sampling intervals, suggesting that the combined Ca inputs from atmospheric deposition and mineral weathering have not kept pace with leaching and sequestration in biomass during much of the 20th and early 21st centuries in these plots. Abbreviations: HBEF, Hubbard Brook Experimental Forest; NC, Newcomb; NH, northern hardwood; OM, organic matter; PW, pine-dominated; SF, spruce--fir. doi: 10.2136/sssaj2009.0367

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

[CO.sub.2] efflux from forest soils is an important process in the global carbon cycle; however, effects of stand age and successional status remain uncertain. We compared soil respiration and its relationship to soil carbon content, forest floor mass, root biomass, soil temperature, and soil moisture content among three temperate forest ecosystems in Changbai Mountains, northeastern China, from 2003 to 2005. Forest types included an old-growth, mixed coniferous and broad-leaved primary forest (MN), a middle-aged, broad-leaved secondary forest (BL), and a young coniferous plantation forest (CP). Average annual soil [CO.sub.2] efflux at BL (1477.9 ± 61.8 g C*[m.sup.-2]*[year.sup.-1]) was significantly higher than at CP (830.7 ± 48.7 g C*[m.sup.-2]*[year.sup.-1]) and MN (935.4 ± 53.3 g C*[m.sup.-2]*[year.sup.-1]). Differences in soil temperature among those sites were not statistically significant but contributed to the differences in annual [CO.sub.2] efflux. In addition, the temperature response of soil [CO.sub.2] efflux was higher at MN ([Q.sub.10] = 2.78) than that at BL ([Q.sub.10] = 2.17) and CP ([Q.sub.10] = 2.02). Our results suggest that successional stage affects soil respiration by the differences in substrate quantity and quality, environmental conditions, and root respiration. Resume: L'emission de [CO.sub.2] par les sols forestiers est un processus important dans le cycle global du carbone. Cependant, les effets de l'age et du statut successionnel du peuplement demeurent incertains. Nous avons compare la respiration du sol et sa relation avec le contenu en carbone du sol, la masse de la couverture morte, la biomasse des racines, la temperature du sol et la teneur en humidite du sol dans trois ecosystemes de foret temperee dans les monts Changbai, dans le nord-est de la Chine, de 2003 a 2005. Les types de foret incluaient une vieille foret vierge mixte composee de coniferes et de feuillus (MN), une foret feuillue secondaire d'age intermediaire (BL) et une jeune plantation de coniferes (CP). Les emissions annuelles moyennes de [CO.sub.2] de BL (1477,9 ± 61,8 g C*[m.sup.-2]*[an.sup.-1]) etaient significativement plus elevees que celles de CP (830,7 ± 48,7 g C*[m.sup.-2]*[an.sup.-1]) et de MN (935,4 [+ or -] 53,3 g C*[m.sup.-2]*[an.sup.-1]). Les differences de temperature du sol entre ces sites n'etaient pas statistiquement significatives mais contribuaient aux differences entre les emissions annuelles de [CO.sub.2]. De plus, la reponse des emissions de [CO.sub.2] a la temperature du sol etait plus forte a MN ([Q.sub.10] = 2,78) qu'a BL ([Q.sub.10] = 2,17) et CP ([Q.sub.10] = 2,02). Nos resultats indiquent que le stade de succession influence la respiration du sol parce que la quantite et la qualite du substrat, les conditions environnementales et la respiration racinaire different. [Traduit par la Redaction], Introduction Soil respiration in forest ecosystems is an important flux in the global carbon cycle, accounting for approximately 70% of ecosystem respiration in temperate forests (Law et al. 1999). As [...]

Laboratory and field C[O.sub.2] efflux measurements were used to investigate the influence of soil organic C (SOC) decomposability and soil microclimate on summer SOC dynamics in seasonally dry montane forest and rangeland soils at the T.W. Daniel Experimental Forest in northern Utah. Soil respiration, soil temperature, and soil moisture content (SMC) were measured between July and October 2004 and 2005 in 12 control and 12 irrigated plots laid out in a randomized block design in adjacent forest (aspen or conifer) and rangeland (sagebrush [Artemisia tridentata Nutt.] or grass--forb) sites. Irrigated plots received a single water addition of 2.5 cm in July 2004 and two additions in July 2005. The SOC decomposability in mineral soil samples (0-10, 10-20, and 20-30 cm) was derived from 10-mo lab incubations. The amount of SOC accumulated in the A horizon (16 Mg [ha.sup.-1]) and the top 1 m (74 Mg [ha.sup.-1]) of the mineral soil did not differ significantly among vegetation type, but upper forest soils tended to contain more decomposable SOC than rangeland soils. The C[O.sub.2] efflux measured in the field varied significantly with vegetation cover (aspen > conifer = sagebrush > grass-forb), ranging from 12 kg C[O.sub.2]-C [ha.sup.-1] [d.sup.- 1] in aspen to 5 kg C[O.sub.2]-C [ha.sup.-1] [d.sup.-1] in the grass--forb sites. It increased (~35%) immediately following water additions, with treatment effects dissipating within 1 wk. Soil temperature and SMC, which were negatively correlated (r = -0.53), together explained ~60% of the variability in summer soil respiration. Our study suggests that vegetation cover influences summer C[O.sub.2] efflux rates through its effect on SOC quality and the soil microclimate. Abbreviations: SMC, soil moisture content; SOC, soil organic carbon. doi:10.2136/sssaj2009.0095

The role of forest soils in the biogeochemical cycling of C and N is most dynamic during the early stages of soil development. To define C and N trends that occur with soil development in a mixed coniferous forest, a chronosequence formed by debris flows was studied. The accumulation rates of total organic C (TOC) and total N (TN) were evaluated in soils on 10 debris flow deposits, ranging from < 1 to 244 yr old. Analysis of the mineral soils was restricted to the 30-cm depth, since this was the depth of the shallowest debris flows. Carbon was found to accumulate in the organic horizons at a rate of 26.5 g [m.sup.-2] [yr.sup.-1] throughout the time span of the chronosequence. Total organic C accumulation in the mineral horizons (0-30 cm) occurred from 0 to 82 yr at a rate of 13 g [m.sup.-2] [yr.sup.-1], and was nearly stable from 82 to 244 yr. Total N accumulated at a rate of 0.57 g [m.sup.-2] [yr.sup.-1] in the organic horizons and a rate of 0.17 g [m.sup.-2] [yr.sup.-1] in the mineral horizons (0-30 cm) throughout the 244 yr chronosequence. This study suggests that C accumulation in the upper mineral horizons of young forest soils occurs for < 100 yr, while N accumulation is a slower process that occurs for >250 yr. Carbon and N accumulation in the organic horizons, however, both follow a linear trend over the 244-yr period. The rates of C accumulation suggest a rapid recovery of the soil organic C pool following disturbance. Abbreviations: SDEF, San Dimas Experimental Forest; SMRNA, Shasta Mudflow Research Natural Area; TN, total N; TOC, total organic C.

The influence of forest operations on forest soil and water continues to be an issue of concern in forest management. Research has focused on evaluating forest operation effects on numerous soil and water quality indicators. However, poorly drained forested watersheds with organic soil surface horizons have not been extensively investigated. A study was initiated in the Tidewater region of North Carolina to gain a better understanding of the impact of harvesting operations on poorly drained organic soils. Soils on the study site, having >80% organic matter (OM) content to a depth of 60 cm below the soil surface, were classified as shallow organic soils. Soil physical properties were examined by collecting soil cores from control and treatment watersheds in a nested design. Compaction caused by the harvest operation increased bulk density ([D.sub.b]) from 0.22 to 0.27 g [cm.sup.-3], decreased saturated hydraulic conductivity ([k.sub.sat]) from 397 to 82 cm [h.sup.-1], and decreased the drained volume for a given water table depth. However, [D.sub.b] following the harvest remained low at 0.27 g [cm.sup.-3]. The drained volume at equilibrium following the lowering of the water table from the soil surface to a depth of 200 cm was reduced by 10% from that of control watershed as a result of harvesting.