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The green menace

Food For Thought

Many years ago, I enrolled in an art class to learn more about painting with watercolors. I’d majored in art in college and had concentrated more on oil painting, but had always wished I knew more about this more portable form of painting. The watercolor class was in the summer and most of the sessions were held outdoors. I became acutely aware of the many different shades and variations of green there are in our landscape and eventually became seriously tired of green paint.
As a result of that experience, I still tend to make note of the different shades of green in our summer plants– even though all the leaves of a tree are basically the same color, we see them as variations, some darkened by different degrees of shadow and others glowing with the kiss of sunlight. I’ve often wondered, if we didn’t have our Iowa winters to interrupt the growth of greenery, how long it would take before we would become engulfed in a botanical jungle.
Some plants grow at almost alarming rates and would clearly overtake and crowd out less hardy ones. And count on it– those plants are mostly classified as weeds or invasive species, and most of those are not native to Iowa or even to the North American continent. We’ve been told that the dandelion was imported by European colonists who wanted to be sure they would have that familiar and useful plant available in the new world. Most of the annual grain, vegetable, and fruit crops grown in the United States are nonnative species that originated in the tropics. Many grasses used today as forage for livestock were brought in deliberately and have proven superior to the native grasses. Unfortunately, a great many plants have sneaked in by other means and many of those have proven to be nuisances if not disasters.
Plants have been imported and propagated here for reasons other than food, however. Kudzu, that hardy vine notorious in our southern states was first imported from Asia to help control erosion. Its aggressive roots spread rapidly and help hold the soil in place; however it is now out of control, crowds out other plants and is very difficult to eradicate. We are all familiar with the problems created by the wild multiflora rose, once touted as a desirable hedge plant and now declared a nuisance.
Those invasive alien plants damage native species in different ways. Some successfully compete with native plants for nutrients, light or water. An invader may alter the local environment to the extent that the site is no longer suitable for the native plants. For example, the decaying leaves of purple-flowering musk thistle release into the soil substances that suppress the growth of competing plants and create bare patches where only thistle seed can sprout. In this way, that exotic thistle has invaded rangelands and displaced forage grasses on vast stretches of our western range. Other unwanted plants have arrived as contaminants in seed shipments. These invaders include Russian thistle, the tumbling tumbleweeds of song and legend, and certain Eurasian grasses, which have overwhelmed the native sagebrush of our west since the 1880s. Ranchers have mixed feelings about these grasses because for six to eight weeks in the spring they provide needed food for cattle when other grasses are not hardy enough. (Remember, cattle are also imports and their overgrazing has helped invasive species take over the rangelands from native plants.)
Declining habitat and invasive species often are mutually exacerbating and make the area vulnerable to infestations of weeds and other pests, thus making it less able to sustain the native plant life. Eventually this could lead to what has been referred to as the “McDonaldization” of our plant life– with a limited “menu” of the same items available everywhere. It has been estimated that over half the species of plants declared endangered are in peril because of the impact of invasive species of plant and animal life on their environment.
Efforts to control animal and insect pests can indirectly affect native plants as in the near-eradication of the bumblebee through the use of pesticides. The only bee with a tongue long enough to reach the nectar of the red clover blossom, it is the only insect that pollinates that plant. (Red clover is one of the “good” plants that has been introduced to our continent from Europe, and it is an important plant in pastures and hay fields.) The bumblebee and the red clover plant depend on each other, though the bumblebee is also an important pollinator of other plants including strawberries and tomatoes.