What is biodiversity and why is it important to us?
All living things have evolved to live in various places on the Earth as a result of millions of years of responses to atmospheric, geologic, hydrologic, climatic and other conditions and biological interactions with other species. These forces have shaped the natural ecosystems and habitats present today and the plants, animals, fungi, bacteria and other organisms associated with them. The United States has an incredible array of wild natural areas including coniferous and deciduous forests, swamps, bogs, marshes, rivers, streams, lakes, prairies, barrens, deserts and montane habitats comprised of diverse groups of native species adapted to particular habitats and conditions. These species comprise our native biodiversity. Many of our parks, nature preserves and wildlife refuges provide some of the best examples of these living communities and species assemblages.

Healthy ecosystems are essential for maintaining native wildlife populations and the native plants that provide the food and shelter they require. As global travel and trade have expanded humans have been moving species to new areas, introducing them to places they would not likely have been able to reach by means of wind, water or wildlife. Some exotic species have escaped from plantings and are able to reproduce on their own in the wild and some of these naturalized species have become weedy or ‘invasive.’ As these species establish and spread they are replacing native plants and altering natural habitats, often with disastrous consequences for the plants and animals dependent on them. Habitats are being damaged, degraded and sometimes completely destroyed as a result of invasion by exotic species.

Maintaining healthy ecosystems is also vital for human survival and quality of life. Healthy ecosystems help provide clean air and water and reduce loss of vital soil resources to erosion. Wild areas are also great places for humans to enjoy, relax and recreate. For many, spending time in nature provides inspiration, spiritual enrichment, and opportunities for personal development. Restoration of invaded ecosystems offers some hope for the future but will require a large and long-term commitment of resources, labor and determination. Patches of disturbed land including small woodlots, landscaped areas and backyards can sustain native wildlife, if managed, designed and maintained properly. Management and reduction of white-tailed deer populations in areas where they are overabundant is critical to the success of restoration efforts and long term conservation of our natural areas and biodiversity.

What are native species?
A native species is one that occurs in a particular place without human intervention. Species native to North America are generally recognized as those occurring on the continent prior to European settlement. Non-native (alien, exotic) species are ones that have been introduced by people, from other continents, ecosystems, or habitats to places where they don’t occur and would not likely have been dispersed to by wind, water, wildlife or other natural means. Many non-native plants have great economic value for agriculture, forestry, horticulture and other industries and pose little environmental threat. However, others have become invasive and are having a serious and measurable ecological impact.

What are invasive species?
Invasive species are alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health. Invasives often benefit immensely from arriving in new places without the assortment of natural controls (e.g., herbivores and diseases) in their native ranges that serve as a check on their survival. Many also have one or more of the following: 1) adaptation to disturbance; 2) broad tolerance for environmental conditions and extremes of light, pH, and moisture; 3) production of large numbers of seeds; 4) high seed germination success; and 5) ability to spread by runners or rhizomes.

An infestation of garlic mustard (Allaria petiolata) displaces spring wildflowers.Photo of a garlic mustard infestation. Photo by Bill Johnson.
Bill Johnson

Why are invasive plants a problem in natural areas?
Like an invading army, invasive plants are taking over and degrading natural ecosystems and wreaking havoc on the intricate and complex web of life involving native plants, animals and other organisms. Invasive species compete for limited natural resources including soil, water, light, nutrients and space. They displace native plants, replace wildlife food sources with exotic plants that are inedible, toxic, or otherwise harmful, draw pollinators away from native plants, hybridize with native species, push rare species closer to extinction and cause an overall reduction in native biodiversity. Some invasive species spread rapidly and unabated, changing forests, meadows, wetlands and other natural plant communities into landscapes dominated by a single species. Such “monocultures” have little ecological value. Invasive plants also impede recreational activities such as boating, fishing, swimming, hiking and bike riding when they overgrow trails and riparian areas or form impenetrable tangles in shallow water areas. Once established over large areas, invasives require enormous amounts of time, labor and money to manage and most are difficult if not impossible to eliminate. One estimate of the economic impact of invasive species is $142 billion annually.

An infestation of purple loosestrife (Lythrum salicaria) appears pretty, but reduces local biodiversity, endangers rare species and provides little value to wildlife.
Photo of purple loosestrife infestation.  Photo by Bill Johnson.
Bill Johnson

How are invasive plants introduced?
People introduce exotic plants intentionally and by accident, through a variety of means. Plants are introduced for food, medicine, landscaping, erosion control, forage, windbreaks and many other purposes. For example, kudzu was introduced to the U.S. from Japan in 1876 at the Philadelphia Centennial Exposition for forage and ornamental uses. From 1935 to the early1950s, farmers in the South were encouraged to plant kudzu to reduce soil erosion, and Franklin D. Roosevelt’s Civilian Conservation Corps planted it widely for many years. Kudzu was recognized as a pest weed by the U.S. Department of Agriculture and, in 1970, was removed from its list of permissible cover plants. By then its vigorous growth was widely recognized and it had earned the infamous moniker “the vine that ate the South.”

Many ornamental species have escaped from plantings to become significant environmental weeds. About two-thirds of the almost 1,200 plants currently reported to be invasive in natural areas in the U.S. were imported for their horticultural value. Japanese barberry, bamboos, privets, Chinese and Japanese wisteria, porcelain-berry, Oriental bittersweet and Princess tree were introduced and planted for ornamental purposes and are now major weeds of natural habitats, requiring significant resources to attempt to control. Other species have come in unknowingly on various imported products or in soil, water and other materials used for ship ballast or packing materials. Japanese stiltgrass, one of our most insidious invasive grasses, was used as packing material for porcelain and likely got a start when some material containing seed was deposited outdoors.

Invasive aquatic plants have been introduced by aquarium hobbyists who dump unwanted plants into waterways. Once established in a new environment and able to reproduce outside of cultivation, some exotic species are able to proliferate and expand over large areas, become invasive pests.

Kudzu (Pueraria montana var. lobata) grows vigorously over other plants and trees.
Photo of kudzu infestation.  Photo by Bill Johnson.
Bill Johnson

How do invasive plants spread?
Invasive plants can spread by seed and by vegetative means including rhizomes, runners, shoots, tubers and bulbs. Seeds and plant fragments may be dispersed by wind, water, wildlife and people. Some animals spread invasive plants by consuming the fruits and depositing seeds later or by transporting seeds or fruits on their fur and feet. People can spread invasive plants by carrying seeds and other plant parts on their shoes, clothing and equipment, or by using contaminated fill dirt and mulch. A common pathway for dispersal of invasive aquatic plants is through attachment to anchors, propellers, and wheel wells.

How you can prevent the spread of invasive plants
Become familiar with invasive plant species in your area and avoid using them. When selecting plants for landscaping, check the list before purchasing to avoid buying any that are known to be invasive or have a reputation for being weedy. Use native plants whenever possible that are native to the ecological region where you want to use them. Request nurseries to carry a wide variety of native species and offer some suggestions for plants you’ve been looking for. Consumer demand is a powerful tool that can be a major driver behind greater diversity and supply of natives – Use It! Lists of native plants are available from most state native plant societies and some state natural resources agencies. Some great sources of information on the importance and selection of native plants that provide food and shelter for native butterflies, birds, mammals and other wildlife are: 1) Bringing Nature Home: How You Can Sustain Wildlife with Native Plants, Updated and Expanded by Douglas Tallamy, 2) Native Plants for Wildlife Habitat and Conservation Landscaping, by the U.S. Fish and Wildlife Service, Chesapeake Bay Field Office, 3) Native Plants of the Northeast: A Guide for Gardening and Conservation, by Donald J. Leonard, 4) Designing Gardens with the Flora of the American Northeast, by Carolyn Summers, and 5) the Lady Bird Johnson Wildflower Center’s Native Plant Information Network (see References).

If you have invasive plants on your property, consider removing them and replacing them with native species, such as those suggested in this guide. When visiting a natural area, be alert for invasive species. If you see some, notify the agency or organization responsible for managing the land. Before you leave, avoid carrying “hitchhiking” plant material by taking time to brush seeds from clothing and shoes and remove plant material from boats, trailers and other items.

Herbicide Use
Taking action against invasive plants involves consideration of the various tools and techniques available for each plant and situation including site conditions, time of year, and resources available. Secondary and unintended consequences of control should also be considered, for example, if plants are pulled up, soil disturbance could bring more weed seed to the surface or facilitate invasion by additional invasive plants. The goal is to achieve effective long-term control and eventual restoration using approaches that pose the least risk of harm to people, especially those conducting the work, and to the environment including non-target plants and wildlife. And the bottom line is that the target species will be successfully controlled or at least reduced to a manageable level. This approach is referred to as integrated pest management (IPM) and sometimes integrated vegetation management (IVM). Often, the most effective method may be to do nothing at all until a suitable safe and well-thought-out tactic can be found.

Each method comes with its own set of risks. Cutting tools like pruning snips, hatchets, saws, weed whips, and mowers work great, but if not used with proper technique and care, can lead to serious injury. Use of herbicides poses additional risks and requirements associated with mixing, application, rinsing, disposal and storage. In order to avoid harm to yourself and others, to non-target plants and animals (including pets), and to the environment, especially in the case of an accidental spill, it is imperative that you are properly and sufficiently trained. No one should be applying herbicides without full knowledge about: 1) reading a pesticide label; 2) what the requirements for applying pesticides in your state are; 3) how to contact the company if there are questions about using the product; 4) how to measure the concentrate; 5) what type of personal protective equipment (PPE) is required during mixing and application; 6) what type of application equipment is recommended and most appropriate to your situation; 7) calibration of spray equipment, 8) rinsing and cleaning sprayers; and 9) disposal of unused mix, concentrate and containers.

Pesticide use by homeowners on their own property requires that the pesticide be allowed for residential use and that the product is not a Restricted Use pesticide, meaning it can only be applied by a licensed applicator. Application of pesticides on public lands and other properties generally requires certification with the Department of Agriculture in your state, which involves training and testing. Contact the agency in your state responsible for pesticides for more information.

This book provides a few of the generally lower risk methods available for control of many invasive plants. It is not intended to be the ultimate reference for control practices. Additional methods and approaches are available and can be obtained by contacting organizations and specialists in the region. It is up to each individual to know and abide by the regulations applicable to the area where herbicide applications will be done.

Use pesticides wisely: always read the entire pesticide label carefully, follow all mixing and application instructions and wear all recommended personal protective gear and clothing. Contact your state department of agriculture for any additional pesticide use requirements, restrictions or recommendations.

Mention of a trade name does not constitute the endorsement of the product by authors, agencies or organizations involved in the production of this publication.


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Last updated:11-Nov-2010