Q: Why do trees change color in the fall and what determines if we have a good display on a given year?
A: Those magnificent colors you see in the fall are actually there all summer, it's just you can't see them because of the chlorophyll in the leaves. As our days get shorter and the temperatures cool down, trees cease chlorophyll production causing the reds, oranges and yellows to show. Any sugars trapped in the leaf will react with each other in the presence of sunlight - thus the more sun, the more brilliant the colors. The best weather conditions are the same ones we enjoy in the fall - bright, cool days and chilly but not freezing nights. The slightest change - too hot, too cold, too wet or too dry - can slow the process, or cause trees to lose their leaves before they change color.
Minnesota is fortunate to have many excellent places to view the changing season - from the northern hardwood forests along the North Shore to the prairie regions of the state. To get the latest information on when and where the fall colors are expected to be at their peak, check out the DNR's Web site, www.dnr.state.mn.us.
- Linda Radimecky, Fort Snelling State Park Naturalist