By Matt Kelley (Radio Iowa)
Most Iowans notice that some trees keep their dead, brown leaves on the branches all winter long, but it’s a safe bet few of us have heard the botanical term for it — marcescence.
Chip Murrow, an urban forestry program specialist with the Iowa Department of Natural Resources, says there are several species of trees where the petiole, or the stalk that connects the leaf to the branch, will hang on for months longer than all of the other trees.
“Part of the process of fall coloring is, the leaf will deteriorate, the petiole where it meets the stem of the branch, it falls off and that’s where you get the leaf scars that we talk about in forestry,” Murrow says. “Well some, like on some of the oaks that keep their leaves through the winter, that doesn’t sear off completely and it allows that leaf to stay on there so that the petiole covers the bud and protects it through the winter.”
Just like trees take cues from the environment around them to start the fall color show, the trees will also know in the spring when it’s time to — finally — dump those dead leaves.
Murrow says, “It’s something that the tree realizes, ‘Okay, it’s time for spring to start,’ and so it’ll drop the leaves so the buds can then elongate and form the new leaves and branches on the trees.”
Most of October has been unseasonably warm, which is helping to make for a longer autumn color show in Iowa that usual. He says leaf lovers should still be able to find plenty of Instagram-worthy locations for several days yet.
“One place was stating that last week was the color show weekend, but there’s still a couple places where, as I look around, I still see a little bit of green hanging on,” Murrow says, “so I think you still might get a little bit more toward the end of this week, into the weekend.”
On a recent visit to Walnut Woods State Park in West Des Moines, Murrow says it looked like winter without the snow as the majority of the walnut trees had already lost their leaves. It’s been an unusual fall, he says, as this warm October was preceded by one of the wettest Septembers on record.
“This is really the weather that we wanted to have in September to get that real good fall color, where you have the warmer days in that 70s range, but then the nights cool down,” Murrow says, “that’s what’s ideal to help with good coloration because that sunlight during the day helps the chlorophyll break down and then the cool nights.”
If you’re hoping to see the beautiful reds, yellows and golds of autumn for Halloween weekend, your best bet is to head south, as many trees across Iowa’s northern half are already bare, or they’re farther along in the process.
