Tom's Blog

Friday, May 23, 2014

Good time for aspen eradication

Although native, quaking aspen (Populus tremuloides) is completely undesirable in any restored natural area in the Midwest and should be eradicated. Girdling is the only effective procedure and the next few weeks are the ideal time to carry this out.

The primary growth of aspen is asexual by underground runners. The typical aspen "grove" is a multi-stemmed clone in which all the roots are interconnected. If an injury to a root occurs, there will be a rapid response by the clone, and new shoots ("suckers") will be sent up all over the area. New shoots have been known to arise as far as 50 feet from the nearest aspen tree! The clone may expand simultaneously in several directions, as influenced by environmental conditions.

If a single tree or a whole aspen clone is cut, massive numbers of new shoots (called root suckers) will be sent up. An area that had perhaps 5 or 10 large aspen trees will soon have hundreds of small aspen stems. There is only one certain way of killing an aspen clone and this is by girdling.

Girdling means stripping a layer of bark and the underlying cambium and phloem in a band around the trunk. The phloem vessels translocate sugars and other nutrients to the roots, so if the phloem tubes are broken, the roots become starved of food. The xylem vessels, which translocate water to the leaves, are not affected by girdling. With girdling, the upper part of the tree still remains alive, since photosynthesis can continue. Eventually, however, the roots die, and the whole tree dies. The first year after girdling, the clone may appear almost normal, but by the second year the clone usually dies. The dead trunks can then be cut without stimulating resprouting.

In contrast to cutting, girdling does not induce the formation of root suckers. (There is an interesting but  complex plant hormonal process involved in root sucker formation.)

Depending on the size of the tree, different tools can be used in girdling an aspen, but we have found the most effective is a discarded truck spring that is sharpened on one side, which helps in making the initial cut. Once the bark is penetrated, it is peeled back all around the trunk, as the photo shows. It is essential that a complete ring is made, otherwise the tree may be able to repair the damage. Also, every tree in the clone must be girdled.

After girdling, one must wait a year or so for the tree to die. The dead trees can then be cut and stacked for later burning. (Aspen logs do not make very good firewood.)

Although the process described above will eradicate the aspen clone, not all the roots are killed, so that scattered root suckers may appear in subsequent years. (We have had scattered aspen root suckers from a clone as long as 25 years later.) Thus the site should be monitored, and new suckers killed. The best way to kill these small suckers is with basal bark treatment with Garlon 4 (15-20%) in oil. (My preferred way is to apply the herbicide by a paint stick.)

The U.S. Forest Service has an excellent publication on aspen growth and ecology. Although dealing mainly with Western aspen, it does include information on Lake States populations. It is available as a PDF for download at the U.S.F.S. publications web site as General Technical Report RM-119. There is also a nice treatment of aspen in the volume on Silvics in North America. The aspen chapter can be downloaded at the following link:


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