It’s almost that time of year again. The days are getting shorter, and the nights are cooling down somewhat. So, where are the changing leaves?
Many people believe that climate change is pushing back the start of fall leaf color to later in the year. The general thinking is that the warmer conditions anticipated under climate change will mean that trees can hold on to their green, energy-producing leaves longer. However, scientists beg to differ. They do not actually see this happening across North American forests, according to an expert at Washington University in St. Louis.
“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. “This effect is well documented in certain species, such as sugar maple, where experimental cooling of branches increases anthocyanin concentration and color brilliance. If the first frost comes later than it used to, the brilliant foliage will appear later than it used to.
“However, she adds, “other factors counteract this. Most important is that trees drop their leaves earlier if they have had a very productive spring and summer. 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.”
In fact, under some scenarios we might even see leaves turning red and yellow earlier. Renner was the co-author of a 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.
“If climate warming continues unabated, the situation is likely to change after about 2040, with senescence then starting earlier than it does now,” Renner said.
Are you seeing the leaves change yet? In Central Texas we don’t get as much of a leaf-turning cavalcade during the fall as other areas, but … have you noticed any other colors on the trees besides brown and green? Feel free to start a conversation on our @AustinTreeServ, our Twitter Account. We’d love to hear from you.
