Biotic invasion

Some of the most pressing problems in ecology get little discussion in the public realm. Such is the case with invasive plants and animals. The fall season brought visual reminders of the relentless expansion of this problem in the northeastern US, and other parts of the country are not doing much better. This year’s poster child plant was, for me, Japanese Knotweed.

Japanese Knotweed. October, Danville, Vermont

After the deciduous forest dropped its leaves, knotweed stood out like a sore thumb, with its coppery color, its broad leaves, and its domination in the patches it has conquered, where no other plant, let alone native plant, can survive.

The Winooski River flowing through Marshfield, Vermont. The copper-colored stand at center is Japanese Knotweed.

Our wonderful local broadcast program, Brave Little State, just did a really nice piece on the infernal Japanese Knotweed. It’s been in Vermont for about a century. Growing steadily, it now occupies streambanks and roadsides in almost every part of Vermont.  The problem is largely independent of anthropogenic climate warming.

Many people, my late mother included, dismiss the introduction of foreign plants as a charming and inoffensive little issue. After all, there are so many more pressing problems, like the re-election of Trump and the destruction of property by floods. But one does not have to look very hard to find documented cases of invasive plants costing billions of taxpayer dollars to fight. Or introduced pests that threaten agricultural products, which raise the cost of your grocery bill.

Many, perhaps all, invasive plants are champions of the mechanism of spread by disturbance. When a creek floods and tears out a section of vegetation on the bank, the seeds of the invasives are quick to take advantage. With the intense summer rainstorms of 2023 and 2024, Danville and St Johnsbury are now bearing witness to the power of Japanese Knotweed to become the sole occupant of large stretches of streambank. But these invasives don’t care if the disturbance is natural or man-made. Roadsides that have been worked over by earth-moving equipment are just the right stimulus for a new patch. Often it is a homeowner improving the view by carelessly tearing out trees and bushes, and buying into a problem that will take thousands of dollars to remedy.

Residential property in Lyndon, Vermont, succumbing to a forest of Japanese Knotweed.

To emphasize the nature of this problem for native plants, it’s important to realize that knotweed and other invasives displace natives completely. If we did nothing at all, every streambank in Vermont would end up being 100% knotweed – a catastrophe of immense consequence. All of the grasses, sedges, forbs, and trees that currently provide shelter, food, and camouflage for native wildlife would be gone. Japanese Knotweed provides none of these because there has been no evolutionary overlap with native wildlife. Our river banks would be no better than if paved with asphalt. Knotweed does not stabilize the stream banks that it smothers: it leads to further flood erosion, which makes space for even more knotweed. Clever, positive-feedback strategy!

There is more to write about invasive plants and animals than there is ink to write with. Many of them exact enormous costs on us. There are also many cases where the costs are yet to come. Perhaps one of these is the Asian Ladybug, a yearly visitor to our house and yard. Superficially, they look just like native ladybugs – not unpleasant at all. When the weather turns cold, though, these pests invade our house in numbers that strike fear and loathing in us. Their extreme abundance makes me worry about which native insects have been displaced to accommodate them. This may be an issue not well studied.

Asian Ladybugs trying to winter in my garage, November 2024.

What can you do? First of all, don’t be part of the problem of propagation. Look in your own yard and identify unfamiliar plants. We use the phone app Seek, which taps into a phenomenal knowledge bank about plant identification and distribution. Yank any plants that are labelled by Seek as “Introduced” (although check the map and the written description to be sure). Be careful about plants that you buy at a commercial nursery. Ask the salesman about the potential for that attractive little plant in the pot to become invasive. If you get a shrug of the shoulders, assume the worst, and put it back on the shelf. When you ask a lot of questions, you will begin to discover the fact that only a few nurseries exist that specialize in native plants, and they deserve the money from your wallet. Many of the sprawling, bargain-basement commercial plant sellers (including Lowe’s and Home Depot) are not reputable. In our area, Fedco is a good one. Prairie Nursery delivers native seeds and plants from their Wisconsin location. In New Mexico, for years we went exclusively to Plants of the Southwest and Agua Fria Nursery. They are more expensive, but there is a good reason for that, since they expend a lot more effort investigating problems and nursing along the slow-growing natives.

Second, give your support to local eradication programs. These government-sponsored efforts use taxpayer money to do their work. They are the only effective means of preventing future invasive problems. The programs are expensive, but will save compared to much larger programs that start after the problem has gotten out of hand. One of my favorite riparian birding spots in Galisteo, New Mexico was the site of a Russian Olive eradication effort to restore willows and cottonwoods. When the heavy equipment finished its job of pulling stumps, a few locals were upset that the floodplain looked denuded. They should have known better. I’ve been told that it is now a much wetter environment, spurring the growth of valuable and declining riparian species of trees and shrubs. On our trip to Kruger National Park in South Africa, we learned that  eradication of exotics is a large and important part of the budget. Our guide pointed to the many roadside crews we saw, busy with tree and plant removal. This effort is an important source of income for local workers.

Third, educate yourself about invasive issues in your area, and become an advocate for eradication. Support the removal of feral cats in your town. In the world of birds, one effort that has run into misguided opposition is the removal of Mute Swans. People who don’t know take notice of their elegant form and assume they deserve protection. They do not. They were introduced to North America over a century ago, and are now displacing native ducks and geese, as well as native swans on wintering grounds. They are shockingly aggressive toward ducks and even people (when nesting), and they are overeating aquatic plants that natives rely on. Animal rights groups have filed lawsuits  to prevent agencies from shooting them, which only further reduces the budgets needed to restore habitat. Feral horses roam parts of the western US, and contribute to overgrazing on public lands. Perhaps the most distressing example of invasive animals is the case of feral pigs in Hawaii, which have decimated the fragile ecosystem of the islands by their tendency to rip out roots. Regrettably, many people find it fun to hunt them, and this lobby has prevented the removal of the pigs. An insane tragedy of misunderstanding. Be open to the kind of eradication measures that may at first seem aggressive. Chemicals, hormonal injections, trapping, shooting, even (as in the case of Tamarisk) the introduction of another pest species. Be patient and listen to the agency personnel’s case carefully – they have been studying the issue far longer than you have.