First sweaters, now leaves? It’s the beginning of fall, which traditionally signifies the coming of brilliant fall colors. But as climate change drives major shifts — such as higher temperatures and severe drought — experts predict it could spell trouble for that annual burst of color.
Howie Neufeld, a professor of plant physiology at Appalachian State University, told LiveScience “climate change could dampen fall foliage by delaying the season, bleaching out red tones and ushering in invasive species.”
As Neufeld writes on his blog, there are several factors contributing to the risk of duller fall foliage. In addition to daylength, trees use temperature as one of their main cues for changing their colors in fall — if fall temperatures are cool, they speed the production of their fall color; if temperatures are warm, they delay. As climate change drives higher temperatures, it could delay the season and potentially mute the colors, especially if the disconnect between daylength and temperature becomes too great for trees to keep up.
According to Neufeld, a more dramatic change could stem from a rise in invasive species due to global warming. He explains that the hemlock woolly adelgid, an exotic aphid-like pest, is already devastating hemlock trees in the East. In the upper Midwest, the Asian longhorn beetle is killing hardwood trees. And in the West, climate change has fueled the explosion of the pine bark beetle, which has destroyed forests and worsened the damage caused by wildfires.
A 2012 U.S. Forest Service report found that these invasive species are changing the composition of entire forest ecosystems. Further, “climate change is exacerbating these changes by altering the amount and seasonal distribution of precipitation seasonal temperature patterns in ways that often favor the invasive species.”
Fall foliage, and trees in general, are also threatened by drought. As Climate Central explains, “drought puts enormous stress on trees, and while it’s much harder to kill a tree than it is, say, a corn or soybean field, arid conditions will make leaves turn brown and drop to the ground before they can flare into yellow or red for the tourists.”
With much of the U.S. still gripped in drought conditions, tree health and fall foliage are already changing. In Minnesota, the Lacrosse Tribune warned, “fall colors are showing up early again this year, and could be muted as a moderate drought in Houston and Winona counties continues on.”
As AccuWeather.com notes in its fall foliage forecast, “extreme drought can thwart fall colors … impacting the leaf size, vigor and physiology,” a fact that does not bode well for the western half of the U.S., “particularly along the Rocky Mountains, the primary color-producing area of the West.”
Diminished fall colors are not just an aesthetic change — they are a significant economic driver from the Midwest to New England. Last year, fall tourism brought over $1.5 billion to Maine alone, according to LiveScience. And Climate Central points out that “national statistics are hard to come by, but officials in New Hampshire estimate that leaf-peeping tourists pump up the state economy by about $1 billion each year” with the estimate being about the same for North Carolina.
While diminished fall colors are far from the most pressing impacts of global climate change, Neufeld explains they may be a sign of more severe changes to come: “Although less brilliant fall foliage displays may not rank high on the list of concerns about global change, those muted colors could be the canary in the mine shaft telling us that these shifts could be markers for more subtle, and potentially more consequential changes in our world.”