Three Invasive Plant Species to Really Watch Out For

by Michael Bald

People sometimes ask which invasive plant species give me the greatest cause for alarm. They often have their own list or landscape perspective, but frequently we’ll agree on one or two. For me, it’s a fairly simple question, but first I frame the response with a touch of personal / professional experience. It’s highly unusual for me to encounter a landscape with only a single “issue”, because much of our non-forested landscape is compromised in so many ways. One particular species may be drastically impacting the site, but there are doubtless other factors at play. And of equal importance would seem to be the human element: what do we seek from this piece of land and how does that serve larger visions or system function?

A tree farm in central Vermont. How does one safely manage these evergreens through a sea of wild parsnip?

So with all that in mind, I return to my baseline guiding principle: Stewardship = Presence. My active management seeks to guide or steer the site over time, favoring known native species over clearly disruptive and invasive non-natives. In order for me to have that Presence, however, I need safe access to the land. Wild parsnip (Pastinaca sativa) complicates this requirement, for me as well as for essentially all landowners, visitors, and recreational users. The photo-activated sap, and the deep enduring blisters that develop after an exposure, are seriously hazardous. There is also risk to the eyes, and although giant hogweed and wild chervil also require some sap-awareness, wild parsnip is the one that seems most dangerous in my professional opinion. It is common across New England and New York, and the most effective pulling approach has to allow time for the stem to harden off, which brings the plant up to head and face level.

I cannot manage multi-flora rose or barberry or phragmites safely if wild parsnip is sprinkled about a site. Nor can a school host sporting events when the playing field is bordered by wild parsnip. Changing a bicycle tire, walking the dog, enjoying a picnic, chopping and baling hay; all of these activities become high-risk scenarios in presence of parsnip. So as much as I admire the plant and its tenacity in the quest to flower, wild parsnip is a species of major concern.

The other two on my list are high-impact species that drastically alter the places they inhabit. True, we humans do the same, trying to maintain lawns and forcing our will onto land that may not best fit the intent, but so be it. I look at the effect of Japanese knotweed (Polygonum cuspidatum) on riparian areas and even on our necessary infrastructure. The plant clearly serves some purpose, and even offers multiple uses for humans, but the effects of a knotweed infestation are dramatic: erosion patterns, mono-cultures, loss of biodiversity, and many more. I have seen riverbanks and hilltops, forests and fields with and without Japanese knotweed; I have also seen a few before-and-after scenarios, and the differences are immense.

Black swallow-wort in a woodland setting, central Vermont. Open field populations are even more dense and tend to achieve greater seed production.

My final nominee for the honor of most-alarming terrestrial plant species is actually a combination of two non-natives: black swallow-wort (Vincetoxicum nigrum) and Oriental bittersweet (Celastrus orbiculatus). One may not encounter them often, but when they appear together the effect is catastrophic. Black swallow-wort can smother acres of ground under a dense mat of deep-green, impenetrable vines. Although small in diameter and not lengthy, the vines wrap around anything they encounter and allow for little germination or regeneration of other plants. When that dilemma is coupled with the much-larger Oriental bittersweet weighing down the overhead canopy, the forest is truly compromised and highly unsafe. This tends to occur on edges, where the fields transition to sugarbush or woodlot or forest, but even long driveways and singular homesteads are enough of an opening for this dual infestation to begin. Both vines are difficult to eradicate in stone walls and densely matted, compacted pastures; black swallow-wort is even wind dispersed from seed pods to add to the management challenge.

Those are my three attention-getters, admittedly somewhat biased. But with our dependence on resilient natural systems, we have to put full energy into preserving biodiversity. We can agree to cooperate and learn the nuances of the land, but a safe setting for that work is a clear must.

About the Author

Mike Bald has worked with invasive species since 2003 and founded his company (Got Weeds?) in early 2011. Got Weeds? is a Vermont company that uses manual and non-synthetic control methods to eradicate, contain, or suppress non-native, invasive plants. Mike believes that fine-tuned ecosystems can be protected with vigilance, persistence, patience, education, humility, respect, and cooperation. Mike’s focus is on long-term site stewardship, soil health, native plant diversity, and education of landowners. Cooperation across multiple ownerships is also crucial to the control effort. Mike appreciates the importance of healthy habitats, site specificity, and ecosystem resilience; his goal with the treatment programs at Got Weeds? is to demonstrate (with comprehensive documentation) that manual/mechanical methods can succeed over extended timeframes.

***

Each author appearing herein retains original copyright. Right to reproduce or disseminate all material herein, including to Columbia University Library’s CAUSEWAY Project, is otherwise reserved by ELA. Please contact ELA for permission to reprint.

Mention of products is not intended to constitute endorsement. Opinions expressed in this newsletter article do not necessarily represent those of ELA’s directors, staff, or members.