Weeds Essay ⋆ Environment Essay Examples ⋆ EssayEmpire

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John Leland, a natural historian, defines a weed as a “plant out of place.” The Bureau of Land Management (BLM) states that weeds constitute “any plant growing where it is not wanted.” Weeds can be native or nonnative, invasive or noninvasive, and noxious or nonnoxious. According to the Animal and Plant Health Inspection Service of the U.S. Department of Agriculture, a weed is “any plant that poses a major threat to agriculture and/or a natural ecosystem.” This particular definition is significant because it highlights the economic and ecological impact that weeds can have on human communities, landscapes, and natural ecosystems. Some weeds have been categorized as “noxious” by federal agencies and state and local governments. A noxious weed is a plant that poses a major threat to agriculture, public health, recreation, wildlife, or property. The BLM defines noxious weeds as those plants that are “competitive, persistent, and pernicious” and out of place.

Characteristics and Proliferation

Weeds can be found worldwide. A few of them, like plantain and henbit, have medicinal qualities. Others, such as dandelion, can be eaten. Most weeds, however, are nuisances and some pose severe problems to human communities and natural ecosystems. Each year, landowners spend billions of dollars on herbicides in a never-ending fight to eliminate weeds in their yards. Yards and lawns are not the only place to find weeds. In the United States, it is estimated that over 5,000 nonnative, exotic, and alien plants (which include many weed species) have escaped into natural ecosystems. Some of these weeds have been naturalized and assimilated into the forest community. Others, though, pose a severe threat to both land and aquatic ecosystems.

One of the most significant factors in the proliferation of weeds is human activity. Weeds came to North America with the early explorers and settlers. American colonists, for example, brought along with them plants for food and medicinal purposes, including dandelions, which, over time, became “naturalized” weeds. Some weeds came to the New World accidentally as stray seeds in livestock and human food supplies. Other American weeds, like crabgrass and Bermuda grass, came from early global networks involving Africa and the slave trade. During the late 19th century, a whole array of weeds, like kudzu, honeysuckle, and wisteria, came to the United States as ornamental plants. Commercial ventures, too, are responsible for the great profusion of weeds. The fish aquarium industry, for example, is directly linked to the accidental introduction of the Asian aquatic plant hydrilla to native ecosystems in the United States. Today, the introduction of weeds to new areas has significantly increased due to globalization and an exploding human population.

Although there exists an immense variety of weeds throughout the world, they all share certain characteristics. For one, weeds are hardy survivalists and are able to thrive in new habits due to their ability to adapt to adverse conditions, such as poor soils and extreme climates. For this reason, weeds have been identified in some of the world’s harshest natural environments. Since many invasive and noxious weeds are rapid colonizers of barren soil, they tend to favor habitats that have been disturbed through human activities and natural occurrences.

In addition to being resilient, weeds are aggressive, fast-growing plants, and they have a tendency to out-compete natural vegetation for essential nutrients, space, and light. Superior competition among invasive weeds may be enhanced by a lack of natural predators or the diseases that, in the weeds’ natural environment, would tend to keep them under control. Once established, aggressive weed species encroach on native vegetation and eventually endanger local plant communities. In some areas, weeds have completely replaced native plant species. Dense weed infestations tend to retard natural succession and reforestation and thus decrease biodiversity. According to the Nature Conservancy, 42 percent of the species listed as endangered or threatened under the Endangered Species Act are connected to invasive weeds and exotic plants.

Weeds thrive, also, because of superior reproduction capabilities. One of the most common means of reproduction among weeds is through seeds that have high germination rates, although this is not the only way that weeds propagate. In the southern states, Johnson grass utilizes both seeds and an expansive rhizome root system to form new colonies. In addition to seed and root reproduction, hydrilla can also replicate asexually through its leaves or leaf particles. To enhance their survival, some weeds, over time, hybridize with native plant species, altering their genetic make-up. Hybridization occurs when human activity inadvertently brings together two similar plant species. In many instances, the hybrid offspring is more competitive-and destructive-than either parent.

Dangers to the Environment

Weeds present many problems to both human and natural environments. In the United States alone, “alien” weeds make up nearly 65 percent of the total weed flora and the costs associated with their control are enormous. In 1994, it was estimated that Americans spent $20 billion on weed control. In that same year, agricultural losses due to weeds exceeded $10 billion.

The impact of weeds on ecological systems is tremendous. In many instances, they completely alter natural functions within ecosystems by modifying nutrient and hydrology cycles. In this respect, weeds have the potential to change natural habitats. One example of habitat alteration concerns the hybrid cattail, which has replaced native white top and wild rice in North American wetlands. European purple loosestrife, which came to North America during the 19th century as an ornamental plant, has invaded most of the wetland areas in the United States. Today, the plant has negatively impacted wetlands by reducing native plant species and threatening wildlife habitat. Consequently, native plant destruction caused by the European purple loosestrife has directly contributed to a decline in the box turtle population, due to a reduction in its natural food supply. It has also cost taxpayers $45 million annually in efforts to control its spread. Not only do weeds pose threats to endangered species of plants and animals, they also prevent or retard the natural succession of native vegetation by forming dense mats of infestation. Certain species of weeds, such as leafy spurge, are also toxic to cattle. Additionally, weeds like thistle have reduced native forage plants in pastures, rangelands, and forests and have had a significant impact on the ability of cattle to graze.

Bibliography:

Bureau of Land Management Weeds Website, www.blm.gov;
Federal Noxious Weed List, www.aphis.usda.gov;
“Invasive and Exotic Species,” www.invasive.org;
John Leland, Aliens in the Backyard: Plant and Animal Imports into America (University of South Carolina Press, 2005);
David Pimentel, Lori Lach, Rodolfo Zuniga, and Doug Morrison, “Environmental and Economic Costs Associated with Non-Indigenous Species in the United States” (1999), news.cornell.edu.