I like the opportunity to control a native invading species without the use of chemicals. Double-cutting within the growing season or multiple years offers one method of controlling some native clonal trees species. To be effective, you must be timing the cuttings correctly, be cutting all of the stems in the clone, and continue the process as long as needed.
Continuing on the theme of herbicide-free control methods, I'll talk about my experience with double-cutting. Again we look to the anatomy and physiology of the species to be controlled to understand how this works [for those of you that know why double cutting works, or don't care why it works, you can skip the next three paragraphs]. Clonal species form what looks like many plants when in fact it is a single plant with many stems. These clusters of stems often have larger older stems toward the center and smaller younger stems on the perimeter. No matter what the control method you use (mechanical or chemical), all stems of the clone need to be treated. Cutting off the stems in the winter results in the formation of new stems from adventitious nodes the next spring. Where there were tens (or hundreds) of stems prior to cutting, you might have hundreds (or thousands) after a winter cutting.
Cutting any plant when most of the energy stored in the roots has been translocated to above ground plant parts is advantageous. For most trees, this translocation occurs throughout the spring and early summer when it is building structures to 1) produce new energy, 2) to add to its size, and 3) for reproduction (leaves, trunk/branches, and flowers/fruit, respectively). After this annual use of energy from the roots is done, the tree begins translocating energy back to the roots at higher percentage. So, to deliver maximum hurt to the tree, cutting before energy starts going back to the roots is a good strategy. This maximum damage also minimizes prolific sprouting from adventitious nodes.
Even with a well-timed cutting, a tree still has enough energy in the roots to produce more above ground structure to assure it lives on. Here's where the double-cutting comes in. After the first cutting, the tree needs to again use the remaining energy in the roots to build all new structures for the purpose of gaining energy (reproduction is put on hold under these stressful times). Similar to the first cutting, this second cutting is timed to coincide with maximum translocation of energy from the roots, but again not waiting past the period where a lot of energy is translocated to the roots.
I read about doubled-cutting years ago, and have used it quite a bit. I generally follow the July 1 and August 1 timing for cutting, but have varied it a little depending on growth in a given year (e.g., first cutting for sumac is usually after flowering). I've done the “cutting” with a variety of methods. I've used a mower if clones are large, where mowing is feasible, and the clone is not in a high quality prairie. The point related to high quality prairie is that multiple years of repeated mowing can have negative effects on some desired species. I've found mowing to not be as effective, as it reduces competition for resprouts because everything gets cut. I've used a handheld brushcutter in native prairie areas, cutting each stem individually. It's not as quick as mowing, but less damaging to other prairie species and better than using hand loppers to cut each stem. Loppers are effective for small clones. I've found that with sumac, you can actually snap off the stems in many cases (but be prepared to have the juices stain anything it gets on). Depending on the size of the stems, a Parsnip Predator can be used to cut the stems.
Another variable to consider is the height of the cut. I've varied this as well, from ground level to 2-3 foot high. Cutting to ground level results in fleshy resprouts that can easily be second-cut with a Parsnip Predator. The really high cut was done to encourage resprouting only on the stem and to test if you get less new stems from the roots. This method allowed a second cut of a single stem, rather than the cluster of resprouts that come from the base. With this method, I found that the stem sprouts can sometimes just be snapped or stripped off, especially with sumac. The disadvantages are that some of the energy in the stem is retained, and the resprouts are not shaded by other vegetation. The method seemed to work as well as cutting lower on the stem in areas of sparser vegetation.
How effective is double-cutting on clonal species? I use it only on aspen and sumac; it's been found to be ineffective on black locust. Because these two species are native, I'm not really all that concerned with eradication. However, I have eradicated many clones using double-cutting (with no herbicide), but most of those required several years of double-cutting. In one case, a single double-cutting killed a sumac clone. This was an older clone, so include that as one of the variables that might contribute to success when using double-cutting.
You might consider herbicides if you want more certainty in eradication. However, as Tom Brock points out in his recent work (link to Tom's work), even with herbicide it is a multi-year effort. For myself, I like the opportunity to control a native invading species without the use of chemicals. However, for the double-cutting to be effective, you must be timing the cuttings correctly, be cutting all of the stems in the clone, and continue the process as long as needed.