The boreal zone and its ecosystems provide numerous provisioning, regulating, cultural, and supporting services. Because of its resources and its hydroelectric potential, Canada's boreal zone is important to the country's resource-based economy. The region presently occupied by Canada's boreal zone has experienced dramatic changes during the past 3 million years as the climate cooled and repeated glaciations affected both the biota and the landscape. For about the past 7000 years, climate, fire, insects, diseases, and their interactions have been the most important natural drivers of boreal ecosystem dynamics, including rejuvenation, biogeochemical cycling, maintenance of productivity, and landscape variability. Layered upon natural drivers are changes increasingly caused by people and development and those related to human-caused climate change. Effects of these agents vary spatially and temporally, and, as global population increases, the demands and impacts on ecosystems will likely increase. Understanding how humans directly affect terrestrial and aquatic ecosystems in Canada's boreal zone and how these effects and actions interact with natural disturbance agents is a prerequisite for informed and adaptive decisions about management of natural resources, while maintaining the economy and environment upon which humans depend. This paper reports on the genesis and present condition of the boreal zone and its ecosystems and sets the context for a detailed scientific investigation in subsequent papers published in this journal on several key aspects: carbon in boreal forests; climate change consequences, adaptation, and mitigation; nutrient and elemental cycling; protected areas; status, impacts, and risks of non-native species; factors affecting sustainable timber harvest levels; terrestrial and aquatic biodiversity; and water and wetland resources.Résumé : Le secteur de la zone boréale et ses écosystèmes fournissent de nombreux services dans les domaines de l'approvisionnement, de la régularisation, de la culture et du soutien. Compte tenu de ses ressources et de son potentiel hydroélectrique, la zone boréale est importante pour l'économie du Canada qui est basée principalement sur les ressources. La région présentement occupée par la zone boréale canadienne a connu des changements drastiques au cours des derniers trois millions d'années; un refroidissement du climat et des glaciations répétées ont affecté à la fois le biote et le paysage. Au cours des 7000 dernières années, le climat, les feux, les insectes, les maladies et leurs interactions ont constitué les forces naturelles les plus importantes de la dynamique des écosystèmes de la zone boréale, incluant la régénération, le cycle biogéochimique, le maintien de la productivité et la variabilité des paysages. À ces agents naturels, il faut ajouter les changements causés par les habitants et le développement ainsi que ceux reliés au changement climatique d'origine anthropique. Les effets de ces agents varient de façon spatio-temporelle et l'augmentation globa...

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