Tom's Blog

Monday, May 11, 2015

Aspen control: long-term survival of buried roots

Aspen is one of those plant species that you can either love or hate! It has extensive commercial value, and its fall color is greatly prized in the Rockies. But it forms large (often huge) clones which make it a menace in prairie and savanna restoration. The individual trees of the clone are connected by rhizomes, which also are responsible for the spread of the clone into new territory.

Unfortunately, aspen cannot be removed by simple cutting, since there are massive numbers of underground buds which are then released from dormancy and send up shoots. Cutting an aspen clone turns a site with a few dozen trees into a forest with hundreds (or thousands) of  shoots, each arising from one of those dormant buds.

The only way to remove an aspen clone is to girdle every tree. Girdling starves the roots of energy and nutrients and the roots eventually die. It may take two years for the girdled trees to die, after which they can be cut and removed. For details of how girdling works, see this link.

Unfortunately, not all the buried roots die. Some of these roots containing underground buds apparently survive and escape dormancy, sending up shoots. How long will these underground roots survive? I used to think "just a few years" but our experience at Black Earth Rettenmund Prairie indicates otherwise. What is the situation?

At the time the Nature Conservancy acquired Black Earth Rettenmund Prairie in 1986 (29 years ago) there was a fairly large aspen clone along the north edge of the Saddle area. This clone was removed by the conventional girdling procedure and by 1990 was completely gone.

In 2002  Kathie and I took over management of BE Prairie. In 2005 we found that a large number of aspen shoots had arisen in this area. Using hand clippers and glyphosate, volunteers cut and treated all these shoots. After that we began burning the Saddle almost every year, either with the North or South unit.

This year (2015) was the first time in some years that we left the Saddle unburned. By early May a large number of new aspen shoots had developed which had obviously arisen from viable dormant buds associated with buried rhizomes. In earlier years, when the Saddle was burned, any new shoots that had developed during the growing season would have been top-killed by the next spring's burn. But this year by allowing a second year of growth, these aspen shoots were now fairly large and easily visible.

My conclusion is that the new shoots have arisen from dormant buds that have remained alive since the aspen clone was eliminated in 1986-1987. Even remaining in the dark all these years, those buds have remained alive.

How long will they yet remain alive? Only time will tell, although I would bet they still have a long underground life yet!

Two aspen shoots treated 5 days before.
The wood lily is  undamaged.
What is the best way of eliminating these new aspen shoots? Since 2005 we have developed a much better and more efficient technique. These young aspen shoots are very sensitive to basal bark treatment with 20% Garlon 4 in oil. Our preferred application method is a sponge on the end of a wooden stick or PVC pipe. The sponge is kept soaked with herbicide from a spray bottle, and treatment consists of swiping up from the bottom along one side of the shoot for a distance of about 6". With this procedure there is no peripheral damage to other "good" species, and within 5 days the treated aspen shoot looks very moribund. Follow-up observations showed that no later new regrowth occurs at the bases of treated shoots. Each treated shoot is gone for good.

Aspen shoots basal barked 5 days before with 20% Garlon 4 in oil. Other species are unharmed.


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