Our Capital Naturalist, Alonso Abugattas, recently took action in response to a misinformed article that ran last week in a Virginia paper touting the benefits of invasive, non-native plants. We thought his comments deserving of a wider audience and he has kindly given us permission to print his letter to the editor of that paper, which was published there as well.
To the Editor:
Please note that no one considers all non-native plants to be invasive, that is not the definition of an invasive plant. No one suggests we get rid of all non-natives or that we shouldn’t have any non-native plants around. Rather that we manage the invasives, and where possible eliminate them, because they do outcompete (partially because they do not support the same diversity of native wildlife, and partially because some invasives are allelopathic and alter the chemistry to allow them to survive and reduce competition with natives) many native plants. Everything said that follows is about invasive plants, not just any non-native.
That native plants cannot make use of disturbed soil conditions is also false, they certainly can and would do so better in absence of invasive competition. Plants have evolved in Virginia to make use of just about every niche, that is why we are blessed with such a great diversity in the Commomwealth.
Since some invasive plants such as garlic mustard are allelopathic and alter soil conditions, the idea that leaving invasives because they improve the soil for natives later is not likely to happen. Rather more invasives will fill that new soil type, since the invasives will alter the soil as they decompose and release chemicals to resemble their country of origin rather than native soils full of mycorrhizal fungi and other soil components symbiotic with our native plants. The vast majority of our natives have evolved not just with certain insect species dependent on them, but also fungi, something that invasives do not promote and some actually inhibit. As you observe in your article, that is another reason you see so many inavaisves growing among the invasives and “competing” with them. This is not soil rehabilitation that will help native plants as you suggest.
Native plants evolved with native insects and fungi and so are codependent. Many of our insects need them as host plants, unable to feed anywhere near to the same extent as on invasives. These are not only caterpillars and other leaf feeders, but also about a third of our native bees that need the particular pollen of host flowers in order to reproduce (they are oligolectic). Invasives almost never provide the required chemicals or pollen types to serve as hosts for these native species, and so are detrimental to the habitat and wildlife diversity in that manner as well. Not only do the vast majority of birds then feed on these insects sometime during their lives, but all 17 of our bat species do as well. So the effects of invasives are widespreading throughout the environment.
You mention Japanese Knotweed as an example. I’ll use it as well then. It does NOT serve as a host plant or bee-specific pollen source for very many species (any?). In fact, studies have shown that amphibian species such as green frogs decline where it is dominant, many believe because it does not support sufficient insect life for them. You also forget to mention that Japanese Knotweed is one of the allelopathic plants. It exudes chemicals that impede and help it compete with native plants. Some believe this same chemical warfare results in deleterious affects to developing tadpoles by the way as well.
It is factors such as allelopathy, rapid growth, lack of natural insect predators, and out-competing of natives that make invasives such an issue. This also does allow them to invade pristine habitats and take over at the expense of natives and all the life that depends on them. This is why control and not planting of invasives (not all non-natives) is vital. That it takes the judicious application of herbicide to sometimes do so outweighs any negative effects in many situations. Just as not all uses of non-native plants results in harm, so also not all use of herbicide results in harm; well, except to the invasive of course. I have made this much too long a response already, but I hope you see that there are many points that are in contention at least, and some clarifications that also should be made. I will not go on, though there are many other points that can be made. Thank you.
Thank YOU, Alonso for taking action; along with VNPS President, Nancy Vehrs, and our VNPS Invasive Species Educator, Ruth Douglas
This might be a good time to remind folks that the Mid Atlantic Invasive Plant Council’s 2015 Conference is open for registration now. The two-day event takes place August 4 and 5 at Juniata College in Huntingdon, PA. New research, best practices: