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There are concerns about the effect of increasing resource extraction and other human activities on the soils and vegetation of the boreal zone. The review covers published papers between 1974 and 2012 to assess the effects of natural disturbances and human activities on soils and tree nutrition and growth of the Canadian boreal zone. Changes in soil and foliar nutrients following disturbance were also analyzed by meta-analysis. When sufficient replicated studies were not available for a given disturbance or nutrient, response assessments or narrative summaries are presented. The majority of fertilization studies in the boreal zone showed a positive tree growth response to nitrogen (N) and phosphorus (P) fertilization either individually or in combination. Large amounts of N may be lost through volatilization following fire depending on the severity and frequency of the fire. This may contribute to N limitation in the boreal zone. Available soil P and extractable calcium (Ca) and magnesium (Mg) increased in the surface horizons following fire. In contrast, extractable P decreased following harvest. Harvesting had no effect on total or inorganic N except in mixedwoods where total N decreased in the surface organic horizon following harvest. These are potential areas of concern given tree growth responses to N and P fertilization. Potassium (K) in the forest floor did not change following fire or harvesting; thus, K availability for tree nutrition should not be at risk, since its cycle is rapidly restored. Mercury (Hg) cycling may be altered in the boreal zone as a result of flooding and if fire return intervals and intensities increase. Interactions of multiple disturbances may increase the risk of nutrient depletions, but there is currently little information on these interactions in the boreal zone. Evidence to date suggests the soils of the Canadian boreal zone have not been adversely affected except in localized areas. However, there is the risk of nutrient loss if soils are not considered in our forest management strategies, particularly where multiple disturbances may interact. The potential for off-site movement of nutrients and contaminants into the atmospheric and aquatic ecosystems, in addition to on-site environmental issues, is also a concern. Key words: boreal, disturbances, nutrient cycling, nitrogen, phosphorus, base cations, mercury, soils. En region boreale, l'augmentation du nombre de projets d'extraction des ressources ainsi que des autres activites humaines souleve des inquietudes quant aux impacts sur les sols et la vegetation. Cette synthese traite des articles publies sur ce sujet entre 1974 et 2012 afin d'evaluer l'effet des perturbations naturelles et d'origine anthropique sur les sols et sur la croissance et la nutrition des arbres de la zone boreale canadienne. Les changements au niveau des sols et de la nutrition foliaire a la suite des perturbations ont aussi ete analyses par meta-analyse. Lorsque le nombre d'etudes repetees n'etait pas suffisant pour evaluer de maniere statistique un type de perturbation ou de nutriment, l'evaluation se limite a la presentation des resultats ou a un resume de la situation. La plupart des etudes de fertilisation en zone boreale ont montre une reponse positive de la croissance des arbres a la fertilisation en azote (N) et en phosphore (P) applique individuellement ou ensemble. Des quantites importantes de N peuvent etre perdues par volatilisation lors des feux de foret, tout dependants de l'intensite et de la frequence de ces feux. Ceci pourrait contribuer a maintenir l'azote dans un etat limitatif en foret boreale. La disponibilite en P, ainsi qu'en calcium (Ca) et en magnesium (Mg) extractibles augmente dans les horizons de surface a la suite d'un feu. A l'oppose, le P extractible decroit a la suite de la recolte. On n'a pas observe d'effets de la recolte sur le N total ou inorganique, sauf dans le cas des forets mixtes ou le N total decroit dans l'horizon organique de surface apres la recolte. Ceci peut etre considere comme etant preoccupant si l'on considere la reponse du taux de croissance des arbres a la fertilisation en N et P. Le potassium (K) de la couche organique du sol n'a pas change a la suite de feu ou de la recolte, indiquant ainsi que la disponibilite de K pour la nutrition des arbres ne devrait pas etre a risque puisque son cycle est rapidement restaure. Le cycle du mercure (Hg) peut etre altere par l'ennoiement et lorsque l'intensite et la frequence des feux de foret augmentent. L'effet combine de plusieurs perturbations peut augmenter les risques de baisse de la disponibilite des nutriments, mais il n'existe que tres peu d'information a ce sujet en zone boreale. A ce jour, il n'y a pas d'evidences que les sols de la zone boreale canadienne ont ete affectes negativement, sauf dans certains endroits bien precis. Cependant, ilyaunrisque d'appauvrissement des sols si ceux-ci ne sont pas consideres dans nos strategies d'amenagement, tout particulierement dans les situations ou de multiples perturbations peuvent interagir entre elles. En plus des enjeux a l'echelle du site, le deplacement potentiel de nutriments et de contaminants hors des sites forestiers vers l'atmosphere ou vers les ecosystemes aquatiques est aussi une source de preoccupations. Mots-cles: boreal, perturbation, cycle des nutriments, azote, phosphore, cations basique, mercure, sols., 1. Introduction Soil (pedosphere) is part of the Earth's critical zone where interaction occurs with the lithosphere, atmosphere, hydrosphere, and biosphere (Yaalon 2007; National Research Council 2009). The ecological processes [...]

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There are concerns about the effect of increasing resource extraction and other human activities on the soils and vegetation of the boreal zone. The review covers published papers between 1974 and 2012 to assess the effects of natural disturbances and human activities on soils and tree nutrition and growth of the Canadian boreal zone. Changes in soil and foliar nutrients following disturbance were also analyzed by meta-analysis. When sufficient replicated studies were not available for a given disturbance or nutrient, response assessments or narrative summaries are presented. The majority of fertilization studies in the boreal zone showed a positive tree growth response to nitrogen (N) and phosphorus (P) fertilization either individually or in combination. Large amounts of N may be lost through volatilization following fire depending on the severity and frequency of the fire. This may contribute to N limitation in the boreal zone. Available soil P and extractable calcium (Ca) and magnesium (Mg) increased in the surface horizons following fire. In contrast, extractable P decreased following harvest. Harvesting had no effect on total or inorganic N except in mixedwoods where total N decreased in the surface organic horizon following harvest. These are potential areas of concern given tree growth responses to N and P fertilization. Potassium (K) in the forest floor did not change following fire or harvesting; thus, K availability for tree nutrition should not be at risk, since its cycle is rapidly restored. Mercury (Hg) cycling may be altered in the boreal zone as a result of flooding and if fire return intervals and intensities increase. Interactions of multiple disturbances may increase the risk of nutrient depletions, but there is currently little information on these interactions in the boreal zone. Evidence to date suggests the soils of the Canadian boreal zone have not been adversely affected except in localized areas. However, there is the risk of nutrient loss if soils are not considered in our forest management strategies, particularly where multiple disturbances may interact. The potential for off-site movement of nutrients and contaminants into the atmospheric and aquatic ecosystems, in addition to on-site environmental issues, is also a concern. [ABSTRACT FROM AUTHOR]

Human-induced changes in atmospheric composition are expected to affect primary productivity across terrestrial biomes. Recent changes in productivity have been observed in many forest ecosystems, but low-latitude upper tree line forests remain to be investigated. Here, we use dendrochronological methods and isotopic analysis to examine changes in productivity, and their physiological basis, in Abies religiosa (Ar) and Pinus hartwegii (Ph) trees growing in high-elevation forests of central Mexico. Six sites were selected across a longitudinal transect (Transverse Volcanic Axis), from the Pacific Ocean toward the Gulf of Mexico, where mature dominant trees were sampled at altitudes ranging from 3200 to 4000 m asl. A total of 60 Ar and 84 Ph trees were analyzed to describe changes in growth (annual-resolution) and isotopic composition (decadal-resolution) since the early 1900s. Our results show an initial widespread increase in basal area increment (BAI) during the first half of the past century. However, BAI has decreased significantly since the 1950s with accentuated decline after the 1980s in both species and across sites. We found a consistent reduction in atmosphere to wood (13) C discrimination, resulting from increasing water use efficiency (20-60%), coinciding with rising atmospheric CO2 . Changes in (13) C discrimination were not followed, however, by shifts in tree ring δ(18) O, indicating site- and species-specific differences in water source or uptake strategy. Our results indicate that CO2 stimulation has not been enough to counteract warming-induced drought stress, but other stressors, such as progressive nutrient limitation, could also have contributed to growth decline. Future studies should explore the distinct role of resource limitation (water vs. nutrients) in modulating the response of high-elevation ecosystems to atmospheric change., (© 2013 Blackwell Publishing Ltd.)