Vicious Vegetation: Invasive Plants-- the Negative Nuances of Forceful Flora and Belligerent Blossoms

In the past our forests fell solely by the ax of the lumberman—a quick and clean end that had some utility. Today, the destruction is brought about by a far more insidious foe that slowly sickens and displaces once robust and diverse native plant life with alien invaders that usurp our native variety. Invasive species, while typically unassuming individually, given time and the chance to propagate, can bring about more change to ecosystems unconsciously than we can do with even the most ambitious plan. Apart from the harm invasives cause to native habitats, to hikers and trail maintainers, they pose an incredible nuisance by forming dense and impenetrable thickets that not only cause physical harm and annoyance, but are responsible for the destruction of equipment and the engulfment of trail and shelter land. You don’t have to be an ecologist to see the damage invasives inflict.

While many of us have heard the term “invasive” used before and have a general idea of the subject, what exactly constitutes an invasive species?

An invasive plant is one that that was never present in an ecosystem prior to its transport by human aid; typically has a high tolerance range to a wide variety of habitats; can thrive in adverse environmental conditions, such as hostile weather and low quality or contaminated soil; and finally, possesses an extremely high fecundity, where the plants are capable of producing vast amounts of offspring year after year. Not all non-native plants are invasives, and not all invasives are from some far away continent—even plants from North America transported to somewhere out of its normal range (perhaps only a few hundred miles) have the capability of developing invasive qualities. Native species, many of which do not have such weedy traits and have no means to resist the invaders, are generally outcompeted and displaced.

A majority of these detrimental plants were brought to this country for use as ornamentals. Many continue to be bought and planted despite the well known invasiveness they pose if they escape cultivation. We further lend a hand whenever we degrade the land. Environmental disturbance and invasives are synonymous.

Some of the major offenders along the Appalachian Trail need no introduction. Kudzu in the Southern states is one such example. It’s so widespread and its damage is so familiar it doesn’t even warrant a description here. Other species that rival it in forest alteration but remain in the shadows, both literally and figuratively, should be brought to light.

Major Offenders

Japanese Barberry

Japanese barberry is one of the largest nuisances to hikers. Being a small shrub that averages about waist high, its thorny branches often lead to painful scrapes and where present in dense quantities can lead to higher rates of Lyme disease. Recent research has shown that ticks thrive in the shady and damp confines of the bushes.

In addition to human impacts, the leaves can alter soil chemistry, and due to how thick the shrub grows, will often exclude native species from the understory. Its bright red berries that are produced in the fall are a tempting treat to wildlife. Birds and deer rapidly disperse the seeds.

This species is one of the most popular invasive ornamentals still planted, much to the consternation of ecologists. It is worryingly easy to buy. Visit any nursery and it is likely to be found there.

Even state officials can be ignorant. Decades ago, not long after the creation of Bear Mountain State Park in New York, barberry was planted along several trails to keep visitors from wandering off them. Today, barberry is rampant throughout the park and can be found in prodigious amounts all along the Appalachian Trail as a result. Though it is now being removed, mostly through the efforts of the NY-NJ Trail Conference and volunteers, it is now so prevalent it will remain a permanent staple of our forests. Cutting the stems is only a seasonal solution—in the spring they will resprout. The only effective removal method is to dig up the roots, a strenuous and slow process. Prevention is the best cure.

Multiflora Rose

Another invasive similar to Japanese barberry is multiflora rose, although everything about it is of a larger magnitude. It can easily form clumps as long as a car and tower well above head height. Its thorns are formidable and pierce the flesh like needles. They are often referred to as “fish hooks.” Its modest white blossoms hardly warrant an excuse to plant this bush with all the inconvenience that comes along with it. Each bush can produce up to a million seeds annually that have the capability of surviving buried in the soil for 20 years.

 

 Swallow-wort (Black and Pale)

Based on its nickname of dog-strangling vine, swallow-wort is a species that is not to be underestimated.  This plant favors forest gaps and other openings that allow ample light to penetrate to the forest floor. In optimal conditions, swallow-wort can become so dense that walking through a patch proves challenging, as the vines are tough enough to resist being broken or uprooted and can easily trip a person, or seriously ensnare wildlife as the nickname suggests. In early autumn its seed pods, similar in appearance to those of milkweed, open up and cotton-like seeds are dispersed by the wind as easily as those of a dandelion.

Apart from manual removal, biocontrol agents are now being researched for use. Having the ability to use another species to control an invasive is often a much better option than by utilizing human labor. Biocontrol agents travel long distances on their own, can access sites we cannot, and are self-perpetuating, so that once released they will remain in the wild indefinitely, or until the food supply runs out.  It’s essentially having an army at your disposal that costs almost nothing.

Each biocontrol agent goes through a rigorous and lengthy research and review process. Before releasing a life-form into the wild, which is usually also of non-native origin, it must be made clear that the organism will only attack what we want it to. It would be incredibly counter-productive if what was released somehow itself became an invasive.

At the moment a noctuid defoliating moth (Abrostola clarissa) from Eurasia is being quarantined and tested at a site in the U.S. to see how effective and safe it will be to have it devour  swallow-wort at selected locations. It will be years until it is utilized if deemed entirely host-specific to swallow-wort.

Several other invasives are already being dealt with using different forms of biocontrol. Purple loosestrife and the nascent mile-a-minute vine are two species which are being successfully controlled also through the use of insects.

                                                                      Japanese Stilt Grass

Hikers are highly likely to spot Japanese stilt grass at shelter sites and along sunny reaches of the trail. When rolling fields or glades near the shelters are filled with nothing but stilt grass—which is quite often—it appears as though the site is cast adrift on a sea of green. While marginally stunning, the detritus left behind after the plants die off will result in an increased alkalinity of the soil and alter the nutrient availability. Grazing by wildlife, a natural control method, is by-passed by uninterested wildlife, enabling it to spread unchecked. The plant’s high stature and denseness is the perfect habitat for rodents, namely rats to infest. An increase in rodents close to human habitation is always worrisome, as the risk for disease rises in step with the pest’s abundance. Stilt grass is remarkably easy to pull by hand, but its prodigious populations make removing it an overwhelming and tedious task.

 

 

Forest Forensics

Quite often, being able to recognize certain combinations of invasives can lead to a past reconstruction of what an area once looked like. For example, many places in New England where the trail now passes through was formerly farmland. It may be hard to believe, but there is more forest today then there was a hundred years ago in the eastern half of the country. This is due to a change in agricultural preferences, where farmers understandably relish the flat, rich plains west of the Mississippi, over the stony and glaciated Northeast. Today, we hike through many abandoned fields that have once more reverted to a more natural state and apart from an occasional stone wall, leave seemingly nothing open to the imagination.  In the absence of fences, walls, and crumbling foundations, we can tell an area was once a planting field or pasture due to the presence of several invasives.  Finding Japanese barberry, multiflora rose, and black locust trees all present in the same general location can lead you to surmise that in the not so long ago past this patch of forest probably once supported someone’s family. Being able to indentify invasives and understand what they mean grouped together can be very rewarding.

Many invasives that we now encounter near the trail are present in extremely large quantities due to forest succession. After a vacant plot of land is abandoned it naturally begins reverting to forest. First, the herb layer sprouts, and is filled with native tall grasses, asters and goldenrods, and now without a doubt, invasives, possibly ranging from swallow-wort to thistle. A year or two after the field is left fallow the shrub layer emerges. Japanese barberry and multiflora rose predominate. Next, the trees make an appearance. The first native colonizers generally consist of tulip poplar, red maple, and black birch, among others. But in addition to the natives, we also have the foreigners like black locust trees that farmers used to mark their property boundaries with and now this tree sprouts as readily as the crops the farmers once planted. The Asian Tree-of-Heaven and the Norway Maple also have a hard time resisting the prime real estate that has just opened up.

Adding more forest to our fragmented landscape is overall beneficial, but with all positive things, something bad usually tags along. With all the invasives now released into this country, natives are at a disadvantage when it comes to repopulating vacant land, and the forests that emerge are usually of a lesser quality in terms of appearance and biodiversity. As the forests mature, the natives do generally gain slight advantages and the non-natives’ presence will deteriorate—but not completely.

This article has previously appeared in the September-October issue of A.T. Journeys.