|A fallen Cottonwood tree|
It was not that trees could not grow on the prairie. Rather, it was that the prairie fires that swept across the plains burned whatever seedlings managed to root in the prairie soil before they could mature. Once settlers arrived, they protected the trees by plowing fire guards around their trees and crops, which reduced the risk. When fire was seen on the horizon, neighbors rushed to help however they could. If they had horses, they plowed fire breaks, and those neighbors without horses and implements battled the creep of fire in the matted prairie grass with blankets or the coats off their backs, if that was all they had to slow the fire. (See "Prairie Fires," 11-21-2013 in the blog archives.)
|Cottonwood Leaf Beetle|
However, it wasn't just prairie fires that were a threat to Isaac Werner's trees. Cottonwood trees attracted two particular pests. Cottonwood Leaf Beetles cause damage two ways. The adults eat the leaves, but they also lay their yellow, oval-shaped eggs on the undersides of the leaves, and when the larvae hatch they feed on the leaves. The risk of these feeding beetles and their larvae is unlikely to kill the tree, but severe infestation can cause defoliation.
Isaac wrote in his journal that something was eating the leaves of his cottonwood trees, and it worried him. However, he made no later mention of severe damage to the trees. Today there are chemical controls available; however, natural enemies of the beetles may be the best protection, and chemicals could kill these predators. Stink bugs, assassin bugs, ants, wasps, spiders, lacewings, lady bugs, and parasitic tachinid flies are natural enemies of the cottonwood leaf beetle.
Another cottonwood pest is the Cottonwood Borer, which also uses the cottonwood tree as its host both as an adult and as larvae. The adults chew the leaves, stems, and new twigs, but unlike the beetles, the borers chew small pits near the base of the trees in which to lay their eggs. The larvae burrow into the tree, first feeding on the roots and then burrowing through the heartwood near ground level. As adults, perhaps 2 years later, they chew their way out of the tree and then dig up to ground level. If the larvae are numerous they can weaken a young tree and cause it to fall in high winds. As for the adults, their chewing on tender twigs can cause malformation of new branches. The harm to more mature trees is unlikely to be significant, but since Isaac was growing young cottonwoods from rooting cuttings, his trees may have suffered some damage. (See "Isaac Plants Cottonwood Trees," 12-2-2011 in the blog archives.)
|Cottonwood rotted in the center|
However, it was neither the beetle nor the borer that felled the old cottonwood tree pictured at the top of this blog. Rather, it was rot. Common rot which starts at the base of the tree and gradually rots the inner core of the tree is perhaps the most common cause of mature trees falling. The photograph at left is the same tree pictured at the beginning of this blog, and you can see how rot has eaten the center of the tree away.
One day last summer we watched a raccoon climb quickly up an old silver maple tree in our front yard and disappear. As we continued to watch, the raccoon popped its head out of what from the ground had appeared to be the flat base where a large limb had been sawn off. Only when the raccoon peeked out of the cavity did we realize that the removal of the large limb had cause the trunk below to rot. It made a nice nest for the raccoon, but the trunk has been weakened and we do not know how deeply the cavity extends downward. Our mature row of silver maples may suffer the same fate as the rotted cottonwood.
(Photo credits to to Whitney Cranshaw for the beetle and Jim Mason for the borer.)