While snowshoeing through deep powder in a stand of aspen trees recently, I noticed black and deeply furrowed bark at the base of the oldest trees. I reflected back to what a friend once told me, “They say that marks the depth of the snow.” Humph I thought, “I wonder what causes the bark to turn black?” The answer took a couple of years to come forth.
Of course, elk eat aspen bark. It is the inner bark, or the cambium layer that the elk and others find to be nutritious. Elk chew-marks are mainly around chest level, or a comfortable height for an elk to scoop upward with its lower front teeth in a chisel-like fashion. But this doesn’t answer the question, “why do the aspen’s bark get rough and solid black for the bottom couple of feet?”
The answer finally arrived last spring, while I was telemark skiing in the LaSal Mountains near Moab, Utah with my good friend Donny Shefchik. It was the end of April, and we skinned up through an especially majestic stand of bright white-barked giant aspens. As we moved along I noticed where the snow had receded near the aspen trunks, many had been chewed upon at the base. There were fine teeth marks in the bark, which led me to believe that small rodents had chewed upon the bark. More convincing still were the piles of droppings surrounding those same trees.
Later that spring, I investigated several aspen saplings that had wilted brown leaves, and had seemed to have died. I found that the young aspen’s thin and tender bark had been girdled away by mice. If an animal eats a full-depth ring around the base of a tree or shrub, the nutrient flow from the roots is interrupted, and everything above the ring dies because it does not receive water.
Mice regularly burrow within the air-laden snow pack to feed on bark, seeds and fruit. Not only does the snow help to keep the mice warm, it keeps them out of sight of their predators as well. On mature aspen trees, the tiny mice teeth chew through a partial depth of the bark, leaving the bulk of the tree’s bark intact enabling it to continue nourishing the tree. Over time, scars on aspen trunks turn black whether from an elk, a human, or a mouse.
Some other fun things to keep yours eyes peeled for in an aspen grove are bear claw marks left by black bears ascending the aspen trunks. Or if you’re near a stream, you may find aspens felled by beavers. If you’re lucky, you’ll see a nuthatch bop headfirst down the trunk of an aspen as it gleans insect larvae.
I personally recommend frequent strolling (or skiing) through aspen groves as a way to clear the mind and brighten the spirit. Aspen groves are magical places that stir the imagination. Imagine yourself looking skyward, the powder-white bark of limbs contrasting with Colorado blue sky, the sun shines warmly on your chest, and the shadows cast long at your feet.