Updated: Apr 29, 2022
The colors of fall are a spectacular display that many look forward to each year. Some drive many miles to see the best of these displays. One type of tree that contributes to these colors are the aspens. If you look at our bluffs at this time of year and see large splashes of yellow-gold color, that is likely an aspen clone. And if you happen to get up close and see the leaves fluttering in tandem as the wind touches each leaf, it is even more likely to be an aspen. It almost seems as if the leaves are using their last gasp before falling to wave goodbye to the warm days of summer before heading into the cold of winter. Here is a photo of some aspen clones above the marsh just below and south of Miller Bluff:
In a previous blog posting, aspens were said to be a problem when they grow around a bluff prairie because they almost inevitably invade and take over the prairie. Elsewhere, however, the clones are a welcome site and provide excellent habitat for many species, especially the young trees as they move into new open territory. Aspens, especially the quaking aspen, are very successful having one of the widest distribution of any tree species in North America, mostly in the northern United States and Canada. It is a pioneer species colonizing open areas requiring full sunlight for new trees to grow. Ultimately, the clones are usually replaced by other trees as a forest matures. There are two types of aspen in the La Crosse area- quaking or trembling aspen (Populus tremuloides) and big-tooth aspen (Populus grandidentata). Both types flutter in the wind. The easiest way to tell them apart is to look at the leaves. The quaking aspen has smaller leaves that have a relatively smooth contour with small teeth compared to the big-toothed aspen which is larger and has bigger teeth. Some also call big-toothed aspen “sawtooth" aspen because the teeth look robust enough to saw through a log! Here is a picture of the two leaves, with the big-tooth on the left and trembling on the right:
Quaking aspens also form much larger clones than big-tooth, sometimes forming huge stands. One quaking aspen clone in Utah, known as Pando, is said to be a single organism, occupying a full 108 acres with a root system estimated to be up to 14,000 years old! Aspens are also dioecious meaning they come as either male or female. Pando is a male clone. Maybe some of those male trees in the middle of that 108 acres are a bit lonely! Both types of aspen leaves flutter in the wind. The fluttering comes from the peculiar shape of the petiole or the leaf stem. If looked at closely, the stems, unlike other trees, look kind of like a rudder with the flat side being perpendicular to the leaf. This produces an easy pivot point between the stem and leaf that allows the leaf to tremble in the slightest of breezes. Here are two pictures from different angles of the stem of a quaking aspen leaf:
Some say they can walk through a forest with eyes closed and know when they are beneath aspen trees by hearing the distinct sound of the fluttering leaves. Even better, put your ear on the trunk of an aspen and hear the beautiful music of the trembling leaves transmitted through the solid wood sounding like a miniature waterfall! First, to get the best sound, find an aspen with smooth bark. The bark of young aspen trees is smooth and creamy white with a hint of green but as the trees age the bark on the lower trunk changes to a deeply furrowed gray color (sound familiar?). Then, put your ear firmly against the trunk and wait for a brisk wind. Granted, you may look a bit peculiar and get some strange looks, but it will be worth it! When an aspen clone is near a prairie, the best way to eliminate the bigger trees and prevent it from taking over the prairie is to remove at least a 6 inch section of bark, best done in the early spring. Here is a tree near Zoerb Prairie that was girdled on May 15 of this year by a group of volunteers during a "girdling party":
I have heard some hikers near Zoerb Prairie wondering about the girdled aspen trees and speculating about what caused the patches of bark to be missing. Some thought it was done by porcupines. Others said beavers! But no, it was a crew of "busy beaver" volunteers with dull chisels or slightly sharpened leaf springs from old cars that debarked those trees! This girdling is preferred to just cutting the aspens down because cutting them stimulates the trees to sucker profusely. How does this happen? Well, there are two types hormones involved- cytokinins and auxins. Cytokinins encourage the growth of roots and therefore suckers, while auxins the growth of the tips of branches. There is usually a delicate balance between the two. But when a tree is cut or damaged, the clone responds by producing an abundance of cytokinins leading to root growth and a bunch of suckers. So, if you see a group of aspens missing some bark around a prairie, don't worry- it was done on purpose to protect the prairie. The work restoring and maintaining prairies is very labor intensive and done by members of Friends of the Blufflands, volunteers, and by hiring contractors. Please help Friends of the Blufflands in this effort by becoming a member, volunteering, or making a donation (see FriendsoftheBlufflands.org ). Thank you.