Large-toothed Aspen - Populus grandidentata
This fast-growing, short-lived species is extremely important in regenerating forest growth after clearing or burning. Its fast-growing roots help to retain soil and trap moisture, and its branches provide shade for other species. Large-Toothed Aspen often look similar to Trembling Aspen, but can be distinguished by larger leaves edged with several large, coarse, and uneven teeth. Moose, elk, muskrats, and rabbits, amongst many other animals, will eat the buds, bark, and twigs year round, and many birds enjoy the downy fruits. 
The specific name, grandidentata, means large-toothed, and lends this species its common name. Like Trembling Aspen, these leaves are attached by flat stalks, which make them tremble in even the lightest breeze. Photo by Sean Fox.
Bark of the Largetooth Aspen is smooth and usually grey. In comparison to the Trembling Aspen the bark is much darker. This bark also becomes darker and furrowed with age. Photo by Jesse Wolf.
Buds of the Largetooth Aspen are 7-8 mm long, dull brown in colour and slightly hairy. Photo by Sean Fox.
Ontario Tree Atlas map of non-planted Largetooth Aspen. 1995-1999.
References
Farrar, J.L.. 1995. Trees in Canada. Fitzhenry & Whiteside Ltd. Toronto. ON. 504 pp.
Kershaw, L. 2001. Trees in Ontario: Including tall shrubs. Lone Pine Publishing. Edmonton. AB. 240 pp
Muma, W. 2011. Ontario Trees and Shrubs. [Online] Available: www.ontariotrees.com
OMNR, 2011. Ontario Ministry of Natural Resources: Ontario Tree Atlas. [Online] Available: http://www.mnr.gov.on.ca/en/Business/ClimateChange/2ColumnSubPage/267027.html
OMNR, 2008. Ontario’s Biodiversity: Species at Risk.