[en] There are several million hectares of marginal agricultural lands available for afforestation in Canada. A fully implemented afforestation program could sequester as much as 28.6 megatons (Mt) of carbon per year (C/y) in above ground biomass alone. Opportunities for carbon storage or, ultimately, feedstock for biofuel production, are likely to be greatest in intensively managed stands of rapidly growing tree species. To achieve high rates of C sequestration, climate and soil conditions in our northern temperate and boreal regions favor poplar and willow. Hybrid poplars, in particular, can reach very high rates of growth. Unfortunately, most available hybrids are adapted to relatively mild climates. Our native forests, however, support four of the five native North American poplar species. Prospects for developing stress-resistant, cold-climate adapted, fast-growing hybrids or intra-species crosses are thus very good. Appropriate selections could greatly increase the potential area that can be successfully planted to poplar. Associated with afforestation using poplar will be a reduced reliance on old-growth and ancient natural forests (and the carbon already banked there) to supply wood fiber for conventional uses. Our aim is to contribute to a national afforestation effort through the development of rapid, cost-effective analyses to identify native poplar genotypes for purposes of carbon sequestration and/or biofuel production. We are investigating plant hormone profiles, carbon isotopic composition, photosynthesis, frost hardiness, and several other physiological parameters in native clones and populations of poplar and cottonwood to form a basis for selecting stock and developing breeding strategies. Experimental crosses will be field tested and successful genotypes entered into field progeny trials. (author)