WashU Expert: How climate change impacts fall foliage

Many people believe that climate change is pushing back the start of fall leaf color to later in the year. But that does not appear to be the case. Instead, fall foliage might become less brilliant under warming conditions, according to a WashU expert.

“Warmer temperatures in September and October reduce anthocyanin production in leaves, which could mean that fall colors would become less brilliantly red or purple,” said Susanne S. Renner, honorary professor of biology in Arts & Sciences at WashU.

This effect is well documented in certain species, such as sugar maple, where experimental cooling of branches increases anthocyanin concentration and color brilliance.

Under some climate change scenarios, we might actually see leaves turning red and yellow earlier, Renner explained.

“Trees drop their leaves earlier if they have had a very productive spring and summer,” she said. “This overrides any delaying effects of a warm fall.

“The end result is that leaves still start to die after about the same amount of time on the tree as they have in years and even decades past.”

Renner co-authored a 2020 study in the journal Science that showed that increased growing-season productivity drives earlier autumn leaf senescence — the process through which plants break down and reabsorb key nutrients that had been deployed in leaves — in temperate trees.

Renner is available to answer questions about:

• How temperature and moisture conditions affect leaf color
• Which kinds of trees are experiencing changes in color dynamics
• Where in the world autumn leaves are most likely to be affected by climate change

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Contact [email protected] to schedule an interview with Susanne Renner.