Prospects for 2007 Autumn Leaf Color

DNR QUESTION OF THE WEEK - August 28, 2007

Q: The switch from summer to fall is beginning but some trees have already made an unexpected transformation to their fall colors. Why is this? Does this mean this year's fall color display will be early and not as vibrant?

A: Some tree species, such as ash, are known to get a jumpstart on the fall color change. So it's not uncommon for people to see one or two ash trees in their neighborhood that have colored leaves. However, early coloration in other tree species can mean the tree is stressed, either from a disease or physiological stress, such as lack of water or too much of it. As a result, these trees will shut down operations for the year before other individuals of the same species. For example, stressed maples are prone to early coloration and will change color up to a month earlier than their healthy counterparts.

People who enjoy fall foliage should expect an early change in most areas of the state and, in fact, fall color change has just become noticeable in the northern part of the state. Even though a number of trees are already in the midst of their annual transformation, people should expect this year's fall colors display to be quite brilliant in most areas of the state, provided we have warm days and cool nights. For the latest information about fall colors, visit the Current Conditions section of the Minnesota Department of Natural Resources Web site.

- Jana Albers, Minnesota Department of Natural Resources Forest Health Specialist, Bemidji

DNR QUESTION OF THE WEEK - September 4

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, its just you can't see them because of the green chlorophyll in the leaves. As our days get shorter and the temperatures cool down, trees cease green chlorophyll production causing the reds to form, 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 red 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, visit the Current Conditions section of the Minnesota Department of Natural Resources Web site.

- Linda Radimecky, Minnesota Department of Natural Resources Naturalist, Fort Snelling State Park

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URL: http://climate.umn.edu/doc/journal/fall_colors_2007.htm
Last modified: August 31, 2007