Invasion of Undesirable Plant Species (Weeds)

After initial introduction, invasive plants are capable of spreading to cover large areas. This invasion poses a serious threat to the integrity and productivity of rangelands. An example from the United States serves to illustrate the nature and extent of the problem (Box 1), but the problem itself occurs world-wide. | Environmental Assessment: Pressure State Response Indicators Policy Pressures and Policy Options Technology Options

Box 1 Of the thousands introduced plant species currently established in the United States, 1400 are scientifically recognised as pests. Ninety of these species are officially recognised as Federal Noxious Weeds and many more species are designated on State Noxious Weed lists. Experts estimate that invasive plants already infest well over 100 million acres and continue to increase by 8 to 20 percent annually. This means 3 million acres, an area twice the size of the state of Delaware, may be lost to invasive plants each year. In particular, invasive plants are recognised as a direct threat to agricultural production and biodiversity in the United States. Invasive plants adversely impact croplands, rangelands, forests, parks, preserves, wilderness areas, wildlife refuges and urban spaces. The habitat of two-thirds of all threatened and endangered species is threatened by invasive species. Invasive plants have encroached upon millions of acres, in every region of the US, causing billions of dollars in lost revenue and control costs. In 1993, total direct control costs for noxious weeds were estimated between $3.6 to $5.4 billion annually, with an additional $1 billion in indirect costs. In agricultural production, invasive plants out-compete crops for soil and water resources, reduce crop quality, interfere with harvesting operations, and reduce land values. The estimated annual loss in productivity of 64 crops is estimated at $7.4 billion. On rangelands, invasive plants crowd out more desirable and nutritious forage, cause soil erosion, and poison some wildlife and livestock species. In natural areas, invasive plants reduce habitat for native and endangered species, degrade riparian areas, create fire hazards, and interfere with recreational activities. Aquatic invasive plants clog lakes and waterways and adversely affect fisheries, public water supplies, irrigation, water treatment systems, recreational activities, and shipping. Source: Federal Interagency Committee for the Management of Noxious and Exotic Weeds (1998). National Strategy for Invasive Plant Management. http://refuges.fws.gov/FICMNEWFiles/NatlWeedStrategyTOC.html

Any effort to devise a response to this potentially serious problem must bring together a complex set of interests that includes both private and communal landowners, industry, and government agencies at all levels. Education and awareness are important components of an overall plan of action.

References

Bureau of Land Management. 2000. Invasive Weeds: A Growing Pain. http://www.blm.gov/education/weed/weed.html

USDA APHIS Plant Protection and Quarantine. 2000. Noxious Weeds Home Page. http://www.aphis.usda.gov/ppq/weeds/weedhome.html

NSW Agriculture, 1999. Noxious Weeds Act 1993. This Act provides for the identification, classification and control of noxious weeds in New South Wales, Australia. http://www.agric.nsw.gov.au/general/acts/weeds.htm

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