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At the landscape scale, one of the key indicators of sustainable forest management is the age-class distribution of stands, since it provides a coarse synopsis of habitat potential, structural complexity, and stand volume, and it is directly modified by timber extraction and wildfire. To explore the consequences of several landscape-scale boreal forest management strategies on age-class structure in the Mauricie region of Quebec, we used spatially explicit simulation modelling. Our study investigated three different harvesting strategies (the one currently practiced and two different strategies to maintain late seral stands) and interactions between fire and harvesting on stand age-class distribution. We found that the legacy of initial forested age structure and its spatial configuration can pose short-(<50 years) to medium-term (150-300 years) challenges to balancing wood supply and ecological objectives. Also, ongoing disturbance by fire, even at relatively long cycles in relation to historic levels, can further constrain the achievement of both timber and biodiversity goals. For example, when fire was combined with management, harvest shortfalls occurred in all scenarios with a fire cycle of 100 years and most scenarios with a fire cycle of 150 years. Even a fire cycle of 500 years led to a reduction in older forest when its maintenance was not a primary constraint. Our results highlight the need to consider the broad-scale effects of natural disturbance when developing ecosystem management policies and the importance of prioritizing objectives when planning for multiple resource use.Résumé : À l'échelle du paysage, un des indicateurs clés d'un aménagement forestier durable est la distribution des classes d'âges des peuplements étant donné qu'elle fournit un aperçu grossier des habitats potentiels, de la complexité structurale et du volume du peuplement et qu'elle est directement modifiée par le prélèvement de matière ligneuse et les feux de forêt. Nous avons utilisé un modèle de simulation spatialement explicite pour étudier les conséquences de plusieurs stratégies d'aménagement forestier à l'échelle du paysage en forêt boréale sur la structure des classes d'âges dans la région de la Mauricie, au Québec. Nous avons étudié trois stratégies de récolte (celle présentement utilisée dans la pratique et deux autres stratégies visant à maintenir les peuplements de fin de succession) et les interactions entre le feu et la récolte sur la distribution des classes d'âges des peuplements. Nous avons constaté que l'héritage laissé par la structure d'âge initiale de la forêt et sa configuration spatiale peuvent constituer des défis à court (<50 ans) et moyen (150-300 ans) termes pour arriver à concilier l'approvisionnement en bois et les objectifs écologi-ques. De plus, les perturbations dues aux feux, même avec des cycles relativement longs comparativement aux cycles passés peuvent compliquer encore davantage l'atteinte des objectifs de production de bois et de conservation de la biodiversité. Par exemple, lor...

To determine the nature of the negative influence of Kalmia angustifolia L. on black spruce (Picea mariana (Mill.) BSP) seedling growth and foliar nutrient concentrations, the effect of proximity to Kalmia on spruce seedlings was studied on two Kalmia-dominated sites of contrasting soil characteristics in central Newfoundland. Spruce seedlings and the soil at the base of their stems were sampled, and spruce leader length and foliar N and P concentration, as well as various physicochemical soil characteristics, were determined. Path analysis was used to determine the strength of direct and indirect relationships among variables hypothesized to be causally linked. Path diagrams were generated based on current knowledge of nutrient cycling in boreal ecosystems and mechanisms previously hypothesized to account for the influence of Kalmia on black spruce. On the wetter and richer site, proximity to Kalmia was associated with reduced spruce growth and humus extractable NH4-N, suggesting nutrient competition. On the drier and poorer site, results were consistent with a direct negative effect of Kalmia on the N nutrition of spruce. On both sites, we also found evidence for a direct effect of Kalmia on spruce growth that is consistent with allelopathic effects on spruce function.

The effect of different harvesting practices on soil acid–base status was evaluated in black spruce (Picea mariana (Mill.) BSP) forests of Quebec by comparing soil from five pairs of whole-tree and stem-only harvested plots 3 years after harvest. Stem-only harvesting contributed to the enrichment of the exchangeable base cation pool, particularly in the forest floors of the pairs where whole-tree harvested plots showed the highest exchangeable Al3+. In the mineral soil, divergence between treatments was low, perhaps because these acidic soils were strongly saturated with Al3+ (about 90%), which did not favour cationic exchange reactions. Although the effects of treatment may not persist over time, improved base cation nutrition may benefit stands during the early stages of development. Over a forest rotation of about 85 years, the estimated loss of alkalinity due to whole-tree harvesting was estimated to be low (less than 20%) when compared with the effect of acidic deposition.

The cumulative impacts of human and natural activity on forest landscapes in Alberta are clear. Human activity, such as forestry and oil and gas development, and natural processes such as wildfire leave distinctive marks on the composition, age class structure and spatial configuration of the forest. Also, other processes such as climate change may be slowly and subtly modifying forest dynamics and may lead to important changes over time. Given the importance and ubiquitous nature of these cumulative impacts, a forest management plan that does not adequately take such impacts into account cannot be expected to adequately manage the forest, neither its components nor its processes. In order to address the question of cumulative impacts in the context of forestry, a landscape model was designed and built in order to simulate forestry, oil and gas, climate change, wildfire, and demographic change for the Whitecourt forest management area over a long time horizon. This paper presents the model and the forest landscape states it forecasted with cumulative impacts, and evaluates the fate of some key indicators of biodiversity and forest productivity. Simulations of harvesting as the only disturbance, the nearest analogue to the current approach to forest management planning, yield results that differ greatly, in every respect, from the results of simulations of harvesting combined with other disturbance agents. The simulation of multiple disturbance agents together allows for the detection of interactions among disturbance agents, and indeed, there are important interactions between the processes of fire and oil and gas. Results also show that climate and demographic change will intensify the impact of fire on the supply of timber and other values. Also, the continued development of petroleum resources will lead to an important erosion of the forest landbase. Overall, this paper makes a strong case for cumulative impacts assessment and the use of spatial and temporal stochastic modelling in forest management.Key words: cumulative impacts, forest management, climate change, landscape modelling, APLM RÉSUMÉLes impacts cumulatifs des activités humaines et naturelles sur le paysage forestier en Alberta sont évidents. L'activité humaine, telle la foresterie et les développements pour le pétrole, et les processus naturels tel le feu laissent une marque distincte sur la composition, la structure des classes d'âge, et la configuration spatiale de la forêt. De plus, d'autres processus tels les changements climatiques influencent peut-être aussi subtilement et tranquillement la dynamique forestière et pourront mener à des changements importants avec le temps. Étant donné l'importance et l'ubiquité de ces impacts cumulatifs, un plan d'aménagement forestier ne prenant pas compte de ces impacts ne pourra aménager de façon satisfaisante ni la forêt, ses composantes, ni ses processus. Pour adresser la question des impacts cumulatifs dans le contexte de la foresterie, un modèle de paysage a été conçu et construit pour simuler...