Tom's Blog

Wednesday, August 11, 2010

Watch out for the clones!

We have been inclined to think that the invasive plants we have to deal with in restoration ecology are nonnative, but it turns out that most of the clonal species we contend with are native.

Here are a few of the native clonal species we have battled over the years at Pleasant Valley Conservancy:

Woody species:
Prickly ash
Gray dogwood
Rubus sp. (especially red raspberry)
Big-toothed and trembling aspen

Herbaceous species:
Canada goldenrod
Woodland sunflower
Pale Indian plantain
Common milkweed

Some other clonal natives at Pleasant Valley Conservancy that have not been a problem (at least yet; all herbaceous):
Missouri goldenrod
Coreopsis palmata
Wild sarsaparilla
Big bluestem
Canada anemone
Bluejoint grass
Pennsylvania sedge
Grass-leaved goldenrod
Wild strawberry
Western sunflower
Showy sunflower
Whorled loosestrife
Whorled milkweed
May apple
Teuchrium canadense
Typha latifolium

How do you recognize a clonal species?
1. They grow in patches
2. They are perennial
3. They spread primarily by vegetative means (rhizomes or stolons)
4. Because of #3, flowering and seed formation may be relatively uncommon. There will often be many nonflowering stems

One characteristic of a clonal species is its ability to send up new stems from underground rhizomes, a process called "root suckering". This property occurs during clonal growth, but it will also occur if the above-ground stems are eliminated by cutting and/or herbicide treatment.

Research on aspen and black locust, which are notorious for root suckering, has shown that auxin, the plant hormone, plays an important role in root suckering. During normal growth, auxin produced by growing stems is translocated to the rhizomes, where it inhibits suckering. If auxin is eliminated by removal of the stems, the inhibition is abolished and growth of new shoots from rhizomes ensues.

For instance: I got rid of a whole clone of sumac by cutting and treating the cut stems with herbicide. Within a month, new shoots had started to appear and they continued to appear the following year. Eventually, over 200 new stems had arisen from a clone of about 100 stems that I had cut. Obviously, if one is going to eradicate the clone, one has to kill all these new root suckers, which requires returning to that clone again and again, until its resources are exhausted. It may take several years, but eradication can be accomplished.

One of the herbaceous species on the list above is pale Indian plantain (Arnoglossum atriplicifolia). In an earlier post, I described some draconian methods we had used to eradicate a large patch of this plant. In that post, I expressed puzzlement as to why this native species was giving us difficulties. At that time, I had not known that this was actually a clonal species with an impressive rhizome system. Recently, I discovered a research paper that showed very clearly that pale Indian plantain is clonal, and capable of spreading extensively. (Athey and Pippen, 1987. Michigan Botanist Volume 26, pp. 3-15.) Now that I know this is a clonal species, I am looking at our large patches in a different way.

Unfortunately, that patch we eradicated in the earlier post has already started to root sucker, as the photo below shows (two weeks after the patch was eradicated). Note that this is not a resprout from a cut stem, but new growth from somewhere else in the area of the clone. (The cut stems had been treated with herbicide and did not resprout.)

I'll have more to say about the pale Indian plantain problem in a later post.


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