The Threat by Non-Native Invasive Species to Colorado's Native Plants

by P.K. Graves

When one thinks of the environment, the conservation of species such as bears, eagles, or hummingbirds comes to mind. What is not immediately apparent is the basic connection between these species and the native grasses, berries, or flowers upon which they depend and how those connections impact our own and future generations.

The United States is home to about 15,300 vascular plant species, or about 7% of the global total. Of these, approximately 4,000 species are endemic to the U.S., which means they are found nowhere else on earth. In Colorado, home to approximately 3,000 native species, 400 are listed as being under special concern, threatened, or endangered.

Native plants form a primary foundation for the ecology in Colorado. They produce food, fiber, medicine, and anchor the ecosystems upon which we depend for services such as water purification, crop pollination, and erosion control. Native plants are essential to wildlife, often developing extremely specialized relationships with the animal, bird, or insect that relies on them. Unfortunately, native plants are in decline, due in part to influence of invasive species.

It is estimated that 4,600 acres of federal lands each day are colonized by non-native species. More than 250,000 acres in Colorado are infested with non-native species, a level that increases at a rate of 8-12% per year. Non-native invasive species, also known as noxious weeds, are estimated to be the 2nd greatest cause of native species decline and extinction, second only to direct habitat conversion. They degrade wildlife habitat by replacing the plants upon which the wildlife depends. For example, Saltcedar, or Tamarisk, on the Colorado Plateau has spread and replaced thousands of acres of native Cottonwood/willow gallery forests, resulting in a significant decrease in the numbers of breeding bird species. Because native plants are often specifically adapted to their environment, the introduction of non-native species interferes with their ability to function. Non-native species are also known to deplete water tables, compete with natives for limited soil nutrients, and substantially increase the risks of erosion, slope failure, and fire. Cheatgrass, an annual noxious weed, germinates opposite the cycle followed by the native perennial grasses, which allows it to quickly develop a large root system early in the spring and take most of the water out of the top 12" of soil. Its ability to burn easily causes early and abundant wildfires, after which the early-maturing cheatgrass seeds take advantage of the nutrients the fire released, allowing larger and more productive seed crops. The insects, viruses, bacteria, and fungal diseases which accompany invasive species also destroy native plants, as the native species do not have adequate defenses against them. American Chestnut, American Elm, and the California Black Oak are a few of the tree species devastated by exotic fungal diseases.

To counter this threat, some land management agencies and wildlife conservation groups such as the Audubon Society often replace non-native plants with natives to restore the habitat. Other times a quarantine of the infected area is sufficient. Burning eradicates some species; others respond to herbicides, and some to a combination of actions. Before any steps can be taken, what is or is not an invasive species must be identified.

Several resources exist to aid the landowner in weed identification. As part of the Colorado Weed Management Act, passed in 1990 and revised this year, each county and municipality is required to adopt a noxious weed management plan for its jurisdiction as well as appointing advisory boards to develop weed management plans and identify certain plants as noxious for its area. Lists of plants that have been designated as "noxious" are available from county weed supervisors. The list of supervisors is available at: www.ag.state.co.us/dpi/weeds or by writing or calling the Colorado Department of Agriculture at: 700 Kipling St., Suite 4000, Lakewood, CO, 80215-8000. Telephone: (303) 239-4100. A copy of Creating An Integrated Weed Management Plan: A Handbook for Owners and Managers of Lands with Natural Values can be obtained by stopping by the offices of Colorado State Parks, 1313 Sherman, Room 618, Denver, CO, 80203 or by sending $2.26 in stamps to them. This book contains steps to develop a weed management plan, guidelines to herbicide use, and an index, with illustrations, of 182 noxious weeds. Other noxious weed information can be accessed for free on the Internet.

Managing non-native invasive species extends beyond just what we get rid of. We also need to be equally aware of what to plant in our gardens. Not all water-wise species are native-wise. Russian Olive, for example, while an excellent grower and a lovely flowering tree, is discouraged in many counties. Dame's Rocket, with its white or purple flowers and sweet scent, appears in many gardens and wild places, yet is considered to be a noxious weed in Colorado, as is Chicory, which grows so well along the roadsides, and Common Teasel, with its distinctive prickly head. For so long gardeners in Colorado have focused on what will grow, in our short season with often limited water, that we've lost sight of what should grow. Gardeners can help manage noxious weeds by learning to identify and manage them, by reporting their locations to local weed managers, by reseeding and revegetating with native species, and by not planting noxious weeds as ornamentals.

Colorado's ecology is a multi-integrated system geared to maximize the interspecies relationships that have been developed over millions of years. With the introduction of non-native species we change, and can damage, those relationships ultimately to our own detriment. Encouraging or reintroducing our native species is the best long-term means to ensure that our environment will exist for the use of generations to come.

References

Colorado Native Plant Society
1997 • Rare Plants of Colorado. Helena, MT: Falcon Press Publishing Co.

Colorado Natural Areas Program
2000 • Creating An Integrated Weed Management Plan: A Handbook for Owners and Managers of Lands with Natural Values. Colorado Natural Areas Program, Colorado State Parks, Colorado Department of Natural Resources, and the Division of Plant Industry, Colorado Department of Agriculture. Denver, CO.

Roberson, E.B.
2002 Barriers to Native Plant Conservation in the United States: Funding, Staffing, Law. Native Plant conservation Campaign, California Native Plant Society, Sacramento, CA, and Center for Biological Diversity, Tucson, AZ.

Spackman, S.B., et al.
1997 • Colorado Rare Plant Field Guide. Prepared for the BLM, the U.S. Forest Service, and the U.S. Fish and Wildlife Service by the Colorado Natural Heritage Program.