Moving from the southwest to the northeast, temperatures decrease by an average of about 10 F. Moisture, on the other hand, decreases from the southeast to the northwest. Well, the deciduous forest is something like the story of the Three Bears. Parts of northern Minnesota are just too cold. The northern coniferous forest grows in those areas. Parts of southern and western Minnesota are too dry.
Prairie does best there.
Only frequent fire, or the activities of humans, prevent these areas from remaining primarily forest. Minnesota's deciduous forest is on the western edge of a biome that stretches to the Atlantic coast. It is characterized by tall trees that form a dense canopy in summer, and which drop their leaves in response to the shortening day length of autumn. Some of these types, such as those containing aspens and birch, are early-successional communities, which grow after a disturbance by fire or logging. These trees grow quickly, and form a canopy that is less dense than that of later-successional forests.