What are Non-Native Invasive Species (NNIS)?
Non-native invasive species include plants, animals, and insects that are present in a geographic area but did not evolve with its associated natural systems. That is my definition, there are certainly others. NNIS is even defined in a presidential executive order. But the bottom line is that these organisms, once they are introduced into a new territory, are either directly or indirectly harmful to humans, their economies, and / or their environments. The organisms are sometimes referred to as “exotics”, and are frequently brought into new environments by the actions of people.
With everything in nature so intricately connected, it is not difficult to imagine how a single introduced species can upset the natural balance. Exotic species frequently arrive to a new area without the other species that would have kept them in check – other plants for example that would have competed for space, or insects that would have constrained them.
Why do we need to control these exotic species?
The issue with NNIS (or NNIP if we’re just talking about non-native invasive plants) is that they typically displace native species in a manner that causes the balanced system to break down. Natural systems are highly resilient in responding to disturbances such as fire or disease, but when non-natives upset the balance, that resilience is compromised. NNIP typically cause a significant drop in species diversity, and any sugarbush owner will confirm for you that a healthy sugarbush needs to have some diversity of tree species. Lose that diversity by maintaining only maple trees, and you leave the entire area open to disastrous diseases or other “unplanned events.”
Another example of the displacement caused by NNIP is with regard to milkweed. Several plants overwhelm milkweed in open fields – giant hogweed, black swallow-wort, wild parsnip, autumn olive – and without the presence of milkweed, there is no host plant for monarch butterflies to lay their eggs on. The monarch must then either adapt to the situation or move on to another location. Fish suffer the same fate when streamside vegetation becomes a non-native monoculture. They must either alter their diet, or find a new place to live…. both of those are risky moves.
So why do the invasive plants always seem to expand their area when I try to control their spread?
Yes, the critical question, and the one with the frustrating answer. By cutting the plants, or pulling them up, or digging them out, you have stressed them. Their response, for those that store energy underground and reproduce by rhizomes, is to grow laterally and re-sprout with new vigor. This alarms you, and you run away…. However, if you were to linger, and if you were to cut or dig or pull the plant again, you would find that you are weakening it over time. Look at the color of the re-growth…. not nearly as green or as vibrant as the original plants. So it may take a couple of years to get ahead of the plants – they sometimes have tremendous root stores – but steady action will starve out the plants. And if you begin to introduce native plants back into the area, or let them come up naturally, they will help in the effort to overwhelm the invader. Whacking everything in sight is not really helpful, so be prepared to spend some time in the effort. Read more…