By Ethan Tapper, Chittenden County Forster
A big part of my job has become dealing with non-native invasive plants (also called “invasive exotic plants” or “invasives”) in the woods. While many of the plant species found in Vermont are non-native, only a small portion of these are “invasive” — outcompeting native species and negatively impacting natural communities.
So, what’s wrong with invasive plants?
We find ourselves in a strange and important moment in the history of our planet; in the midst of a mass extinction event, the sixth such event in history but the first caused by a single species. Today, an estimated 1 million animal and plant species are threatened with extinction, including more than 40 percent of amphibians, one-third of reef-forming corals and more than one-third of marine mammals. About 700 vertebrate species and at least 100,000 species of invertebrates have gone extinct since the 16th century, and, according to the World Wildlife Fund, global animal populations have declined an average of 68 percent since 1970.
The consensus in the scientific community is that the main contributors to this biodiversity crisis are all human-caused: climate change, deforestation/habitat loss, pollution, and biological invasions — non-native invasive plants, pests, pathogens and animals — are considered the main culprits. According to the National Wildlife Federation, 42 percent of endangered species are primarily threatened by invasives, and invasive organisms account for about half of extinctions of which the cause is known.
Why are invasives such a problem?
Within their native environments, each species occupies a unique niche; constrained by habitat limitations and by the other species that have adapted to prey on them, parasitize them and compete with them over thousands of years. They form communities: groups of species that share a complex evolutionary history. Species are not adapted to every other species on Earth — only to those with which they co-occur — and so ecosystems can harbor vast open niches.
For example, New Zealand’s ecosystems have no native terrestrial mammals and have been decimated by the introduction of rats and other mammals; Guam’s native birds are all functionally extinct due to the introduction of a single species of snake. In her Pulitzer Prize-winning book “The Sixth Extinction,” author Elizabeth Kolbert describes invasives as species released from the constraints of evolution, introduced into communities which are completely unprepared for them in an evolutionary sense.
While the gravity of non-native invasive pests and pathogens like emerald ash borer, chestnut blight and Dutch elm’s disease is relatively easy to understand, the way that invasive plants negatively impact ecosystems is much less obvious. The influence of non-native invasive plants can be just as disruptive — it’s just harder to visualize.
In forests and other ecosystems, invasives like common and glossy buckthorn, shrub honeysuckle, Japanese barberry, Asiatic bittersweet and multiflora rose outcompete native plants and trees, preventing regeneration and often forming dense monocultures. As they do so, invasives can displace and disrupt entire communities of organisms which have coevolved with native trees and plants for millennia. As forests and wildlife respond to our changed and changing world, invasives threaten their resilience — their ability to adapt, to regenerate, to stay healthy in a trying and stressful time.
While eradicating invasive plants across our landscape is not possible, invasive plants are actually much easier to deal with than most invasive animals, pests and pathogens. In most cases it is completely possible to control them, to lower populations of invasives to a level that minimizes the negative impacts they cause to a forest or other ecosystem. Controlling invasives is challenging and requires an ongoing commitment, but with the right tools it is fully achievable.
Protecting ecosystems is as much an act of self-preservation as environmentalism — our forests clean our air and our water, regulate our climate, underpin the biological and geochemical processes which make life on Earth possible, support our local communities and economies and safeguard our lives and our quality of life in countless ways. Controlling invasives, and protecting the integrity of ecosystems in general, is part of how we take responsibility for our ecosystems, for each other, and for future generations — how we build a better world for our children and our grandchildren to inhabit.
(Ethan Tapper is the Chittenden County Forester for the Vermont Department of Forests, Parks and Recreation. See what he’s been up to, check out his YouTube channel, sign up for his enews and read articles he’s written.)