Blue Ridge Naturalist: “Invasive Plants”: A Book Review and Commentary


© Marlene A. Condon

The miniscule flowers of a nonnative Cinnamon Vine feeds a tiny hover fly. Photo: Marlene A. Condon.
The miniscule flowers of a nonnative Cinnamon Vine feeds a tiny hover fly. Photo: Marlene A. Condon.

Even though I disagree with the premise that there are “invasive” plants, I must give high praise to the revised and updated second edition of Invasive Plants by Sylvan Ramsey Kaufman and Wallace Kaufman.

Published by Stackpole Books, this heavy tome is a wonderful guide to the identification of common nonnative plants that tend to grow in disturbed areas, such as along roadways, hiking trails, fields, sidewalks, lawns, and gardens.

Filled with photographs that often show the growth habit of a plant as well as its flowers and leaves, this book makes identification particularly easy. For example, I had admired for many years a vine I’d see growing here and there along a nearby road, but I had never been able to identify it. I hadn’t ever seen flowers, which is the typical starting point for using books to make an identification of a flowering plant.

But looking through the photos in this guide, I immediately recognized the distinctive heart-shaped leaves with the very long pointed tips of a plant called Cinnamon Vine or Chinese Yam (Discorea oppositifolia), the tiny flowers of which are easily overlooked from a distance. That explained why I’d never noticed them!

Invasive Plants contains a treasure trove of information about each plant. In addition to providing the identifying characteristics of each species, the authors have included the habitat and range where each plant grows, information on how these nonnative species reached North America, and references you can look up for yet more information.

The only issue I have with this book (which is the same issue I have with the movement against so-called invasive plants in general) is its description for each plant regarding its impact upon the ecosystem and how the plant should be managed. The write-ups suggest that particular plants, such as the Cinnamon Vine, are always a problem, no matter where they grow: “Vines quickly overgrow shrubs and small trees, blocking light to the ground. Plant species diversity declines under heavy cinnamon vine cover. Vines can grow so thickly that branches break under their weight.”

But this horror story does not necessarily play out. For example, I’ve been admiring the Cinnamon Vine along the roadway where I’ve exercised for almost three decades now. These plants have remained few and far between.

Although I’m sure the authors’ statements do apply in particular situations where conditions are just right for the growth of Cinnamon Vine, it’s misleading to give the reader the idea that the Cinnamon Vine (or any nonnative plant) is simply going to take over wherever it starts growing.

Unfortunately, this kind of misleading information about numerous nonnative but naturalized plants, which preys upon people’s emotions by inducing fear, has itself caused disastrous consequences for our world.

The insidious effect of numerous authors, extension agents, government agencies, and environmental groups recommending the use of pesticides over the past decade or so is a huge increase in the application of poisons that are far more harmful to our environment than alien plants will ever be.

The reality is that these so-called invasive plants start growing, thriving, and providing habitat where there would otherwise be mostly bare ground with an extremely limited variety of widely separated native plants.

When early European colonists arrived in North America, they beheld an ancient landscape of huge trees that were growing on nutrient-dense dark soil composed of humus. Much decomposition had occurred throughout the eons to produce the rich soil required by the plants growing beneath the leaf canopy.

When settlers cleared the land, they opened the canopy and planted crops that immediately began to deplete the aged soils of their nutrients. Many of the flower seeds brought, intentionally or unintentionally, by human immigrants produced naturalized plant citizens.

Over time, these new plants spread, moving into the clearings where native plants were no longer able to grow because conditions had been altered. And throughout the next 500 years, people continued to change the landscape as well as bring in new plants that could take advantage of disturbed areas created by man (and sometimes by nature).

Now such plants are considered invasive and are much maligned. But do they truly invade and destroy habitat for wildlife? This perception is unequivocally wrong except perhaps in very particular situations.

Physics tells us that no two objects can simultaneously occupy the same space. Therefore alien plants move into areas only where open space is available for them to start growing.

If a plant is woody and large, such as Autumn Olive (Eleagnus umbellata), then of course it will eventually fill an area, just as the Eastern Redcedar (Juniperus virginiana) has always done in fallow Virginia fields.

Autumn Olive is a nonnative counterpart to our native juniper. In fields where they coexist, it turns what would otherwise be a monoculture into a more diverse habitat that can support many more species of wildlife.

Diversification of plant and animal life does not hold true, however, in wetlands where soil profiles have been disturbed by man or weather. Here particular alien plant species can create immense monocultures because the environmental conditions are so ideal for their growth. This, of course, limits the diversity of wildlife within that ecosystem.

Thus this is the one place where human intervention usually needs to take place. However, people need to acknowledge that the “invasive” species only became a problem once the substrate was corrupted.

Away from wetlands, so-called invasive plants should be viewed as survivors that can withstand poor-quality habitat (such as highway medians and most yards), polluted areas (dredge spoil, sewage sludge, and mining tailings) and the well-trodden and compacted soil of hiking trails (in national parks and forests) and farmers’ fields (where half-ton cattle wander).

In these situations, the plants are not invaders that take over important habitat for wildlife. Rather, these plants have moved into damaged or degraded areas created by human activities where native plants can no longer grow well, if at all. The best way to deal with such situations is to leave the nonnative plants. Over time they add organic matter to the soil and thus rehabilitate it. To try to replace aliens too soon with native plants in such areas is misguided, serving only to impede the necessary rehabilitative process.

Once rehabilitation is accomplished, our native plants have the opportunity to move back into these areas. This statement is not hypothetical; it’s empirical. I have watched this process play out along roadways and river banks, in farmers’ fields, and in my own yard for over three decades.

All of this is not to say that people should deliberately plant non-native species. It is extremely important to maintain our native diversity of insects, many of which are dependent upon a very limited selection of plants to survive. Folks should certainly incorporate native plants into their landscapes as much as possible.

But it’s foolish to root out alien plants in degraded areas where they can and do provide habitat for numerous mammal, bird, amphibian, reptile, insect, arachnid, and uncountable other invertebrate species. That’s something bare ground will never be able to do.