Ask the expert: How weather affects fall colors

As summer activities begin to wind down, Michiganders turn their attention to campfire gatherings, cool nights and some of the most spectacular fall color displays in the nation.

The beauty of Michigan’s fall colors can be attributed to the abundance of hardwood forested landscapes, which produce brilliant orange, yellow and red colors. While the shorter days provide the cue for leaves to begin their fall show of color, weather also plays an important role.

Julie Crick, natural resources educator with Michigan State University Extension, provides the following insight on fall colors and weather.

Why leaves change color

Leaves on a tree change color mainly in response to the decrease of daily sunlight. Photosynthesis, or the production of sugars that depends on sunlight, begins to slow down as the days become shorter. This leads to a reduction of chlorophyll, the pigment that supports photosynthesis and gives leaves their green color.

When chlorophyll is reduced, other pigments in the leaves begin to show or are produced. For example, the length of leaf color display time, as well as the extent of red color in the leaves, is directly related to temperature and moisture conditions that occur before and during the period when the amount of chlorophyll in the leaves is diminishing.

Weather plays a role

The most brilliant leaf displays follow a period of cool nights and warm days filled with sunshine. During this weather cycle, leaves photosynthesize and produce an abundance of sugars during the sunny days. The cooler nights and the gradual narrowing of leaf veins mean most of the sugars produced stay trapped in the leaf.

This abundance of sugars, coupled with full sun, leads to the production of anthocyanin pigments, which produce red, purple and crimson colors. The red hues are most vivid in leaves that receive full sun, as the pigment helps protect the photosynthetic structures from damage by the bright sunshine.

Conversely, yellow and gold leaf colors result from carotenoid pigments, which are always present in the leaf and only become visible when chlorophyll breaks down. We can always count on the yellow and gold fall leaf colors while red colors rely on the aforementioned weather conditions to present with vigor.

Soil moisture also plays a role in the timing and brilliance of leaf color. The best displays are produced when the soil has been adequately moist throughout the growing season coupled with the late summer weather described above.

Late spring or summer drought can delay the onset of color. Dry soils with a warm period during the last weeks of summer can also decrease the intensity of fall colors by triggering early leaf drop before the colors have had a chance to develop.

Additional factors

Other factors also cause leaves on trees to change color early or out of sync with their neighbors. Trees on the edge of low-lying areas, where cooler air collects at night, often display colors sooner than trees in an upland forested setting.

Trees that are diseased or in decline may also display fall colors earlier than their healthy neighbors. Look for other signs, such as dead branches, wounds to the trunk or areas of root compaction to provide more information about a tree health issue.

What will the colors be in your neck of the woods? The variability of the contributing conditions ensures that no two fall color displays will be identical year to year. However, scientists make predictions about the timing of fall colors and, yes, there is an app for that.

Michigan State University Extension professionals recommend that you check the timing, watch the weather and see if you can predict the intensity of your local fall color display.