Trees
Trees are single-stemmed, perennial, woody plants taller than 3 m and exceeding 8 cm in diameter at breast height; shrubs are multistemmed and smaller. These definitions are somewhat arbitrary, since many species (eg, willow, alder, cherry, maple) can grow as trees or shrubs, depending on the environment. Counting the 30-odd shrubs that assume tree form under favourable conditions, there are about 140 native Canadian trees.