Invasive sandbar willow in a wetland

Now that we have invasive brush mostly under control in our upland sites, we are starting to do some  work in our wetlands. Unfortunately, the habitat and the species are different in the wetlands, requiring new approaches.

Although we have found scattered buckthorn and honeysuckle in the wetland, the principal woody plants have been several species of willows. Some, such as pussy willow (Salix discolor), are benign, even desirable. However, the sandbar willow (Salix interior) is another matter. It forms large, dense clones that crowd out any other species. A scan of the literature brought up no control articles, but a lot of work on how to get this species established in order to stabilize stream banks and other erodible areas. Thus, when we started to work on sandbar willow we were starting from deep ignorance.

Except for the burns, most of our work is done in the winter, when cold weather provides a firm footing. Most of the sandbar willow stems are of fairly small diameter, so that a brush cutter can usually be used. All cut stems are treated with 20% Garlon 4 in oil, which is our standard procedure for upland shrubs.

Although this procedure  killed the dormant buds of the cut stems, we were ignorant of the fact that this species of willow root suckers prolifically. By late summer the clones were bright green with new shoots, as the photo below shows.

The bright green is due to a large number of root suckers in a sandbar willow clone that had been cut and treated.

I felt rather foolish, because we have had a lot of experience dealing with other root suckering species (aspen, sumac), and I should have anticipated this. Well, nobody told us either.

Now that we know about root suckering, we can also predict that prescribed fire will be ineffective in eradicating this species. The photo below shows a clone just after prescribed fire in April 2013. The fire effectively top-kills, but the roots, of course, are unharmed. In fact, running fire through these clones may be exactly the wrong thing to do. The second bright green patch in the photo above is probably a willow clone that was burned in our 24 April 2013 spring burn.

Clone of sandbar willow just after a prescribed burn. The fire burns primarily around the edges of the clone, since because of shading there is less fuel in the center.

To eradicate root-suckering aspen, girdling is the solution. However, girdling a large, dense clone of sandbar willow would seem to be a daunting task! Any suggestions?