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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.

The amount of logging residues left on site after clear‐felling has been shown to influence the state of soil nutrient resources, but this effect may depend on soil conditions. In three regions of the boreal zone of Quebec, with contrasting soil characteristics, soil and foliar nutrient status of young (15–20 yr old) stands were compared among sites that were clear‐felled at two harvesting intensities, that is, stem‐only (SOH) and whole‐tree harvesting (WTH). Balsam fir (Abies balsamea) stands were studied in the Forêt Montmorency and Gaspésie regions, while black spruce [Picea mariana (Mill.) B.S.P.] and jack pine (Pinus banksiana Lamb.) were studied in the Haute‐Mauricie region. Whole‐tree harvesting resulted in lower cation exchange capacity (CEC) compared with SOH, but this effect could be linked to decreased levels of organic C only in the Haute‐Mauricie region, where soils had intrinsically low organic matter content. Lower soil and foliar Ca concentrations after WTH were observed in all three regions. Foliar Ca status was most strongly affected by harvesting intensity in Gaspésie, where soils exhibited the lowest concentration of total Ca in the parent material. In Haute‐Mauricie, where the parent material contained a low level of Mg, foliar nutrition for this element was significantly poorer under WTH compared with SOH. Harvesting intensity did not influence the biogeochemical cycles of K and N. Foliar analysis revealed that jack pine exhibits the strongest nutritional difference between WTH and SOH. Results suggested that the tree species regenerating the harvested sites, as well as the total Ca and Mg contents of the parent material are better indicators of a site's susceptibility to nutritional alteration by WTH than soil available nutrient status.

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Harvest residues are an attractive woody biomass feedstock for bioenergy production. A portion of the total harvest residues are generally left in the cutblock due to technical and profitability constraints. A better understanding of the factors influencing the variability of residue operational recovery rate is important to inform accurately policy development on sustainable forest biomass procurement practices. We compiled the results of field trials from boreal and temperate forests to quantify the range of variation of residue recovery rates and to identify the main factors explaining this variability. The average recovery rate was 52.2%, with minimum and maximum values of 4.0 and 89.1%, and a near-normal distribution around the average. The main factor contributing to this variation was country of operations, which encompasses aspects of bioenergy policy and markets, technological learning, and forestry context. A shift in bioenergy policy, a growth in (and a change in access to) bioenergy markets, and upward movements along the technological learning curve could increase residue recovery rates approaching the highest values observed in this study, such as those in Nordic countries (72% residue recovery), or even higher if economic and technological conditions keep improving. However, local stand conditions, especially in North America where natural variability is high among forest stands, may continue to constrain operational recovery of harvest residues. Our results suggest the need for the development of policies that define practices and thresholds based on the ecological suitability of ecosystems, with clear definitions and explicit standards for harvest residue inventory, quantification, and retention.

Accurately assessing the delay before the substitution of fossil fuel by forest bioenergy starts having a net beneficial impact on atmospheric CO 2 is becoming important as the cost of delaying GHG emission reductions is increasingly being recognized. We documented the time to carbon (C) parity of forest bioenergy sourced from different feedstocks (harvest residues, salvaged trees, and green trees), typical of forest biomass production in Canada, used to replace three fossil fuel types (coal, oil, and natural gas) in heating or power generation. The time to C parity is defined as the time needed for the newly established bioenergy system to reach the cumulative C emissions of a fossil fuel, counterfactual system. Furthermore, we estimated an uncertainty period derived from the difference in C parity time between predefined best-and worst-case scenarios, in which parameter values related to the supply chain and forest dynamics varied. The results indicate short-to-long ranking of C parity times for residues < salvaged trees < green trees and for substituting the less energy-dense fossil fuels (coal < oil < natural gas). A sensitivity analysis indicated that silviculture and enhanced conversion efficiency, when occurring only in the bioenergy system, help reduce time to C parity. The uncertainty around the estimate of C parity time is generally small and inconsequential in the case of harvest residues but is generally large for the other feedstocks, indicating that meeting specific C parity time using feedstock other than residues is possible, but would require very specific conditions. Overall, the use of single parity time values to evaluate the performance of a particular feedstock in mitigating GHG emissions should be questioned given the importance of uncertainty as an inherent component of any bioenergy project.

Boreal forests in northern Alberta have a growing anthropogenic footprint due to a rapidly growing oil sands mining industry. Although land reclamation is a necessary aspect of responsible industrial development, these activities nearly always affect higher order landscape components such as the broader landform, and its hydrology and biogeochemistry. Recent anthropogenic impacts are then believed to result in new environmental conditions and obstacles under which the boreal forest is developing, potentially leading to irreversibly different environments that could be characterized as novel ecosystems. Reflecting an emerging trend across the field of restoration ecology, these novel ecosystems are not necessarily undesirable. Instead, they are an unavoidable consequence of pervading anthropogenic effects on natural ecosystems. It is our view that successful reclamation outcomes can still be derived so long as policy and regulatory requirements are afforded the necessary scope and economic flexibility to account for the development of hybrid and novel ecosystems among highly disturbed mine sites. Hence, this analysis seeks to situate current and anticipated challenges affecting the reclamation of boreal forest following oil sands mining by describing (i) how regulatory criteria shape reclamation practices and targeted end goals and (ii) how these approaches embody latest trends and priorities in the area of restoration ecology.Key words: land reclamation, equivalent land capability, boreal forest, oil sands, novel ecosystems. Résumé :Les forêts boréales du nord de l'Alberta subissent une empreinte anthropique croissante due à l'expansion rapide de l'industrie des sables bitumineux. Alors que la réhabilitation des sites est un aspect essentiel d'un développement industriel responsable, ces activités affectent presque toujours des composantes majeures du paysage telles que son relief, son hydrologie et sa biogéochimie. On suppose que les impacts anthropiques récents créent des conditions environnementales et des obstacles nouveaux pour le développement de la forêt boréale, ce qui pourrait mener à des environnements irréversiblement différents qui pourraient être qualifiés d'écosystèmes nouveaux. Reflétant une tendance émergente en écologie de la restauration, ces nouveaux écosystèmes ne sont pas nécessairement indésirables. Ils sont plutôt une conséquence inévitable des effets anthropiques invasifs sur les écosystèmes naturels. Nous sommes d'avis que la réhabilitation des sites peut encore donner de bons résultats dans la mesure où on accepte que les exigences politiques et réglementaires aient l'ampleur et la flexibilité économique nécessaires pour prendre en compte le développement d'écosystèmes hybrides et nouveaux dans des sites miniers hautement perturbés. Ainsi, cette analyse vise à identifier les défis actuels et anticipés de la réhabilitation de la forêt boréale à la suite de l'exploitation des sables bitumineux en décrivant (i) la manière dont les critères réglementaires influencent les pratiques...