Fall foliage has shown up later than usual due to warmer weather at later points in the year.
Earth, Environment and Society Department Chair Susan Caplow said there has been longer summer-like weather and shorter winter-like weather in recent years. The longer stretch of warmer weather each year due to climate change results in leaves changing color and falling later in the season.
“It does vary year to year,” Caplow said. “Every year it’s a little bit different. It is, on average, getting to be later.”
September is a key time for leaves to change color, according to the Minnesota Department of Natural Resources. Fall colors in Minnesota normally peak from late September to mid-October.
St. Thomas grounds service worker Tony Grossman agreed that leaf-dropping weather conditions seem to be later this year.
“I watch leaves fall according to the climate and the weather. In my particular opinion, it seems late in the year, but not according to the weather,” Grossman said.
Grossman said the later the leaves fall, the more difficult his job becomes.
“We pivot real fast to snow removal,” Grossman said. “If the leaves are falling and it’s about ready to snow, that’s when we get stuck.”
Temperature is key in dictating when trees’ leaves will change color and eventually fall off; the amount of sunlight hitting trees also has an impact, according to the DNR.
“In general, the warming temperature interferes with the signals that both plants and animals use to make their decisions about what to do when. Part of the issue is that one of the cues being light, and one of the cues being temperature; those are getting mismatched more and more often, where the light is suggesting that it should be colder to the plant, but then the heat is not.” Caplow said.
As the amount of daylight decreases in the fall months, this causes leaves to change color and determines when they will fall off. However, Caplow said that more summer-like temperatures later in the year confuse trees.
Caplow said that plants, specifically trees native to Minnesota, are used to the climate, and when it changes, this stresses them out. Caplow said that this unpredictability of weather patterns is called climate weirding.
“The whole year of climate weirding is a stressor on the tree, and it can cause problems for it,” Caplow said.
Avery Mikolai can be reached at miko2197@stthomas.edu.
