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Forest management activities are increasingly analyzed through a lens that quantifies their effects on soil carbon (C) and nitrogen (N) storage because forest soils are an important C sink. Data on the longer-term impacts of repeated interventions are often lacking. At the Petawawa Research Forest, Ontario, Canada, treatments to evaluate the effect of repeated thinnings on wood quality of red pine (Pinus resinosa Aiton) and white pine (Pinus strobus L.) were initiated in 1918 with the first experimental plots in Canada: permanent sample plots 1 (thinned) and 2 (control). In 2005, 16 years after the last thinning in 1989, we observed that repeated thinnings reduced soil C and N stocks in the surface L, F, and Ah horizons. Contrary to our hypotheses, concentrations and stocks of C and N increased in the Bm1 horizon, indicating that these elements could be accumulated in deeper horizons after surface disturbance and potentially increased decomposition associated with thinning. However, total C and N accumulation in the profile to 30 cm contributed to reduced storage (-35% for C and -30% for N). Many forest sites in the Great Lakes Forest Region that are selectively cut repeatedly over decades could experience this level of soil C and N decline. Key words: thinning treatment, soil organic carbon, total soil nitrogen, long-term plots, soil horizons. Les activites d'amenagement forestier sont de plus en plus analysees sous l'angle de la quantification de leurs effets sur le stockage du carbone (C) et de l'azote (N) dans le sol parce que les sols forestiers sont un important puits de carbone. Toutefois, les donnees sur les impacts a long terme d'interventions repetees font souvent defaut. A la Foret experimentale de Petawawa, en Ontario, au Canada, des traitements visant a evaluer l'effet d'eclaircies repetees sur la qualite du bois des pins rouge (Pinus resinosa Aiton) et blanc (Pinus strobus L.) ont ete amorces en 1918 en etablissant les premieres parcelles experimentales au Canada, les placettes echantillons permanentes 1 (eclaircie) et 2 (temoin). En 2005, 16 ans apres la derniere eclaircie appliquee en 1989, nous avons observe que les eclaircies repetees reduisaient les stocks de C et de N du sol dans les horizons de surface L, F et Ah. Contrairement a nos hypotheses, les concentrations et les stocks de C et de N ont augmente dans l'horizon Bm1, ce qui indique que ces elements pourraient s'accumuler dans les horizons plus profonds apres une perturbation de surface et pourraient possiblement augmenter la decomposition associee a l'eclaircie. Cependant, l'accumulation totale de C et de N jusqu'a 30 cm dans le profil a contribue a reduire le stockage (-35 % pour C et -30 % pour N). De nombreuses stations forestieres de la region forestiere des Grands Lacs qui ont subi plusieurs coupes de jardinage au cours des dernieres decennies pourraient connaitre ce niveau de declin de C et de N dans le sol. [Traduit par la Redaction] Mots-cles : traitement d'eclaircie, carbone organique du sol, azote total du sol, placettes suivies a long terme, horizons du sol., 1. Introduction Soil organic matter is a key component of terrestrial ecosystems (Batjes 1996). It contains three times more carbon (C) than the atmosphere (Schmidt et al. 2011) and is [...]

Plant species distribution and plant community composition vary along environmental gradients. At the continental scale, climate plays a major role in determining plant distribution, while at the local and regional scales vegetation patterns are more strongly related to edaphic and topographic factors. The projected global warming and alteration of the precipitation regime will influence tree physiology and phenology, and is likely to promote northward migration of tree species. However the influence of soil characteristics on tree species migration is not as well understood. Considering the broad tolerance of most tree species to variations in soil factors, soils should not represent a major constraint for the northward shift of tree species. However, locally or regionally, soil properties may constrain species migration. Thus, while climate change has the potential to induce a northward migration of tree species, local or regional soil properties may hinder their migratory response. These antagonistic forces are likely to slow down potential tree migration in response to climate change. Because tree species respond individualistically to climate variables and soil properties, new tree communities are likely to emerge from climate change. Key words: climate change, tree migration, soil properties, temperate forest, boreal forest. La distribution des especes et la composition des communautesveegetales varient le long de gradients environnementaux. A l'eechelle continentale, le climat joue un riale primordial dans la distribution des especes vegetales, alors qu'aux echelles locale et regionale la distribution des especes est surtout influenceee par les variables edaphiques et la topographie. Le rechauffement climatique projete et l'alteration du regime des precipitations sont susceptibles d'influencer la physiologie et la pheenologie des arbres, et d'entrainer leur migration vers le nord. Toutefois, l'influence des caracteeristiques des sols sur le potentiel migratoire des arbres est peu connue. Puisque la plupart des especes d'arbres possedent une grande tolerance aux variations edaphiques, les sols ne devraient pas constituer un obstacle majeur a leur migration vers le nord. Toutefois, localement ou regionalement, les sols pourraient posseder des proprietes qui pourraient restreindre la migration des especes. Alors que les changements climatiques ont le potentiel de provoquer la migration des especes vers le nord, localement ou regionalement les proprietes des sols pourraient limiter leur capacite; migratoire. Ces forces en opposition pourraient restreindre le potentiel migratoire des arbres en reponse aux changements climatiques. Parce que les especes d'arbres repondent de maniere individuelle aux variables climatiques et aux proprietes des sols, de nouvelles communautes d'arbres pourraient resulter des changements climatiques. Mots-cles: changements climatiques, migration des arbres, proprietes des sols, foret temperee, foret boreale., Introduction Plant species distribution and plant community composition vary along environmental gradients (Allen and Hoekstra 1990; Levin 1992), and several community and landscape studies have linked species responses to environmental [...]

Afforestation and reforestation are considered important tools for mitigating fossil fuel emission; however, establishment of plantations necessarily involves several silvicultural treatments that may influence soil organic C sequestration and, potentially, its relative stability. An experimental design established 20 yr ago, consisting of plantations of white pine (Pinus strobus L.) and white spruce [Piceaglauca (Moench) Voss] was used to determine midterm impacts of blade scarification, fertilization, application of an herbicide, and tree species on soil C stocks and on the fraction of labile C determined by measurement of C mineralization on laboratory incubations. Twenty years after treatment, blade scarification had the greatest effect on soil organic C stock and stability. Carbon content was 54.2% lower in the F/H layer (equivalent to Oi and Oe/Oa layers) of blade-scarified plots compared with plots without blade scarification. Effects on the mineral soil layers were less obvious and partly mitigated by the addition of fertilizer on the surface. Blade scarification affected the general quality of C in the F/H layer because it significantly increased by 21.1% the fraction of labile C to total C; nevertheless, labile C content was 51.9% lower in the blade-scarified treatment. Vegetation control by herbicide as well as tree species had minor effects on C stocks and stability. A 9.0% decrease in mineral soil C content was observed with vegetation control. The F/H layer C concentration was 18.6% higher under white spruce than under white pine but these differences did not lead to a difference in C content. The small effects of treatments on surface mineral soil C could be explained by the limited capacity of this coarse-textured soil to sequester more silt- and clay-associated C. doi: 10.2136/sssaj2009.0273

: In boreal black spruce (Picea mariana (Mill.) BSP) dominated stands, careful logging around advance regeneration contributes to protect the shrub layer while increasing light availability. Therefore, it may promote expansion of bog Labrador tea (Rhododendron groenlandicum (Oeder) Kron & Judd), which can impair black spruce growth by direct competition for nutrients and by alteration of soil biochemical conditions. Such harvesting approaches may not be suited for irregular, uneven-aged black spruce stands in the context of ecosystem-based management. Our objectives were to evaluate the effects of different intensities of partial harvest on critical resource availability and to compare the physiological and morphological responses of black spruce and Rhododendron to different intensities of partial harvest treatments. Two years after harvest, photosynthesis rate of black spruce was unchanged and was lower than that of Rhododendron, which was 63% higher after harvest. Nitrogen and water use efficiency were, respectively, 171% and 42% higher in Rhododendron than in black spruce after logging. Following harvest, black spruce physiology appeared to be regulated by the atmospheric humidity deficit, but for Rhododendron, physiology was regulated by light availability. The high plasticity of Rhododendron leaf traits could be indicative of the future advantage of this species in these stands following canopy removal associated with harvest. Resume: Dans les peuplements boreaux domines par l'epinette noire (Picea mariana (Mill.) BSP), la coupe avec protection de la regeneration preetablie contribue a proteger la strate arbustive tout en augmentant la disponibilite de la lumiere. Ainsi, cette coupe peut favoriser l'expansion du the du Labrador (Rhododendron groenlandicum (Oeder) Kron & Judd), ce qui peut reduire la croissance de l'epinette noire causee par la competition directe pour les nutriments et de l'alteration des conditions biochimiques du sol. Dans un contexte d'amenagement ecosystemique, de telles approches de recolte peuvent ne pas convenir aux peuplements d'epinette noire irreguliers et inequiens. Nos objectifs consistaient a evaluer les effets de differentes intensites de coupe partielle sur la disponibilite des ressources critiques et a comparer les reactions physiologiques et morphologiques de l'epinette noire et du Rhododendron aux differentes intensites de coupe partielle. Deux ans apres coupe, le taux de photosynthese de l'epinette noire est demeure inchange et etait plus faible que celui du Rhododendron qui etait 63% plus eleve apres la coupe. Les valeurs d'efficacite d'utilisation de l'azote et de l'eau du Rhododendron apres la coupe etaient, respectivement, 171% et 42% plus elevees que celles de l'epinette noire. Apres la coupe, la physiologie de l'epinette noire semblait controlee par le deficit hydrique de l'atmosphere alors que la lumiere controlait celle du Rhododendron. La grande plasticite des traits foliaires du Rhododendron pourrait etre un indice que cette espece serait avantagee dans le futur par l'elimination du couvert a la suite d'une coupe dans ces peuplements. [Traduit par la Redaction], Introduction Bog Labrador tea (Rhododendron groenlandicum (Oeder) Kron & Judd, previously referred to as Ledum groenlandicum Oeder) is a widely distributed, light-intolerant, perennial understory shrub of the North American boreal [...]

Abstract: An important tenet of the natural disturbance paradigm as a basis for sustainable forest management is that impacts of interventions fall within the range of natural variation observed for [...]

Understanding how silvicultural interventions affect soil spatial variability will improve our ability to predict forest ecosystem function in response to different degrees of management intensity. We demonstrate the use of spectral analysis, a geostatistical technique, to understand how management interventions affect soil spatial variability. The technique was applied to determine whether an intensive vegetation control treatment modifies the spatial patterns of soil microclimate and soil quality indicators: microbial biomass C (SMB-C) and N (SMB-N) as well as net N mineralization rate. A secondary objective was to investigate the contribution of soil microclimate factors to the explanation of spatial patterns of microbial biomass (C and N). Measurements were performed on transects laid out in two plots: a plot that was undisturbed since clearcut and replanted 11-yr earlier with white pine (Pinus strobus L.) and another plot which was subject to annual herbicide application during 4 yr following reforestation with white pine. Forest floor temperature (TEMP) and water content (WC), net N mineralization rate and SMB-C and SMB-N concentrations were measured every 25 cm along each transect. Spatial patterns were assessed using spectral analysis. In the two plots, microclimatic variables and SMB-N presented complex spatial patterns with several scales of spatial dependency, whereas SMB-C and net N mineralization did not demonstrate a spatial pattern at this scale of observation. In the herbicide-treated plot, the spatial pattern of SMB-N was influenced by the plantation grid. Herbicide applications markedly decreased spatial variability of forest floor properties. In some frequencies, SMB-N was markedly positively correlated with forest floor layer WC but not with forest floor TEMP.

Abstract: Large gaps (equivalent to twice the height of the trees, 1590 [m.sup.2]) originating from group selection cutting in mixed tolerant hardwood--eastern white pine (Pinus strobus L.) stands of Quebec [...]

The impacts of intensive silvicultural treatment on soil processes and fertility, as well as nutrition and growth of planted eastern white pine (Pinus strobus L.) and white spruce (Picea glauca (Moench) Voss) were examined 4 yr after planting and initial treatment. The impacts of three treatments, applied singly and in factorial combinations, were evaluated: (i) soil surface modification by scarification, (ii) fertilization, and (iii) vegetation control using herbicide. The most significant effects resulted from vegetation control. Nitrification increased significantly, soil total C and N declined, with accompanying decreases in soil pH and cation availability (K). With this same treatment, pine and spruce growth increased markedly in response to increases in light, moisture, and N. Scarification removed the nutrient reservoir in forest humus, resulting in decreased nutrient availability in the mineral soil, while fertilization had inconsistent effects on soil nutrient availability. However, neither scarification nor fertilization alone significantly affected growth; only their interactions with other treatments were important after 4 yr. During the period since planting, the effects of scarification and fertilization on conifer growth have declined, while effects of vegetation control have become much more prominent. The impact of losses of N and other nutrients as a result of vegetation control or scarification should become more evident as nutrient demand increases with plantation development.