Factors influencing fall leaf color
 
UT Arboreum bench in autumn

The outstanding fall color is wonderful to behold from a bench along a trail at the UT Arboretum. Photo by R. Evans, courtesy UTIA.

 


KNOXVILLE, Tenn. – New York, Paris and Milan all have their fashion weeks scheduled to the minute months in advance, but the annual fashion week for Tennessee forests can be much less predictable.


Everyone wants to know when will be the best time to view autumn’s big show, but leaf color predictions can be quite tricky says Wayne Clatterbuck, professor of forest management in the Department of Forestry, Wildlife and Fisheries with the University of Tennessee Institute of Agriculture.

"Environmental factors that influence leaf color are hard to predict, so just when the the colors will peak is an annual mystery,” Clatterbuck said. “Most of the factors that influence leaf color are related to weather conditions prior to and during the leaf color change. Specific weather conditions are difficult to forecast in advance.”

But certain fall characteristics can be counted on, Clatterbuck admits. “Changing leaf color is triggered by the shorter days of sunlight - called the photoperiod - which is constant from year to year, then influenced by temperature and moisture,” he said.  In general, Clatterbuck says these weather conditions generally yield specific results:


● Warm, dry weather with extended droughts or moisture deficits
Fall color that is not as vibrant, is short lived (a week or so) and the timing can be delayed a week or more.

● Cool nights and warm days
Cool nights with temperatures in the 40s and low 50s (but not freezing) with daytime highs in the 60s and 70s tend to retain leaf color longer, and the colors are more pronounced, especially if the days are sunny.

● Sunny days vs. overcast days
Sunny days create more vibrant leaf color. Several rainy or overcast days in a row when leaves are turning color will cause them to be more dull.

● Adequate moisture
A little rain will yield a longer period of leaf color.


● Freezing overnight temperatures and early frost
Flashy forest fashion will quickly fade. Leaves will turn brown and die.


The color of leaves changes first at the higher elevations where it is cooler, then progresses to the valleys at the lower elevations. Color in the mountains of East Tennessee usually begins during the second week of October and advances to the valleys and the Coastal Plain of West Tennessee by the end of October. It can even last into the first two weeks of November. Thus, leaf color can peak at various dates depending on your location in the state or region.

Are you looking for some more information on how to identify the trees by their leaves? Check out the simple online guide provided by the UT Forest Resources AgResearch and Education Center and Arboretum in Oak Ridge.

The UT Forest Resources AgResearch and Education Center is celebrating its 50th year of service. If you want to check out the facility and fall color for yourself, visit UT Arboretum. There are walking trails that can be combined for hikes of various lengths. Most are very family friendly and interpretive signs describe points of interest along the way. There is no admission fee. Visit the Arboretum’s website for details.

The UT Institute of Agriculture provides teaching, research and outreach through the colleges of Agricultural Sciences and Natural Resources and Veterinary Medicine; UT AgResearch, including its system of 10 research and education centers; and UT Extension with offices in every Tennessee county.

###

Contact:

Dr. Wayne Clatterbuck, UT Department of Forestry, Wildlife and Fisheries, 865-974-7346, wclatter@utk.edu

Dr. Kevin Hoyt, UT Forest Resources AgResearch and Education Center, 865-483-3571, UTforest@utk.edu

###