Noxious and Invasive Weeds

A Nationwide Threat

Spotted Knapweed is a delicate pink flower.Noxious weeds and invasive plant species pose an increasing threat to native ecosystems, croplands, and other plant communities throughout the United States. While weeds have long been recognized as a problem for agriculture, the potential impact to other plant communities, including wildlands, is receiving greater attention.
There are an estimated 2,000 invasive and noxious weed species already established in the United States. Escalating worldwide trade and travel will only increase the risk of further invasions. All ecosystems urban, suburban and rural, including wildlands, rangelands, forests, riparian areas, and wetlands are vulnerable to invasion.
Experience and research have shown that invasive and noxious weeds can no longer be considered a problem only on disturbed sites. Noxious and invasive plant species have become established within relatively undisturbed ecosystems, including entire ecosystems such as the Florida Everglades. Noxious weeds pose an increasing threat to the integrity of wildland ecosystems, including specially designated areas such as wilderness and research natural areas.
A large meadow at the base of the mountains has been taken over by Yellow StarthistleOn Federal lands in the Western United States, it is estimated that weeds occur on more than 17 million acres, with similar infestations occurring in Canada and Mexico. Good estimates are not available for the Eastern United States. On National Forest System (NFS) lands, an estimated 6-7 million acres are currently infested and potentially increasing at a rate of 8 to 12 percent per year. The noxious weed situation in the United States has been described by many as a biological disaster, "an explosion in slow motion" (Wyoming Department of Agriculture).
On the Modoc National Forest - Proactive management, before it's too late!
Noxious weeds and invasive exotic plants are an increasing threat to the function, composition, and structure of our native ecosystems here on the Modoc National Forest. In the past, noxious weeds have traditionally been considered primarily rangeland and agricultural problems in Modoc, Lassen and Siskiyou County. However, many conservation organizations now recognize invasive exotic species as a threat to wildland biodiversity and ecosystem integrity.
Scotch Thistle is a pink flower with barbs.Throughout California, one thousand and twenty-five species of the flora are exotic and this number continues to increase at an alarming rate. All ecosystems (rangelands, forests, grasslands, riparian areas, wetlands, lakes, and streams) are vulnerable to invasion by non-native weed species. Noxious weeds and invasive exotic plants are a serious biodiversity issue of great significance to human and natural resource conditions on the Modoc National Forest.
Aggressive noxious weed species often out-compete native plants for water, nutrients, sunlight, and space. Many species contain chemical compounds that prevent other plant seeds from germinating at the same site. When noxious weeds dominate sites, the composition, structure, and function of the entire ecological community is altered. Weed infestations affect wildlife by reducing important food plants and modifying habitat characteristics such as cover and movement corridors. Noxious weed altering of habitat and competition for resources adversely affects more than 50% of all threatened and endangered species in the United States.
A major habitat and source of dispersal for weeds is roads. The constantly disturbed cut and fill slopes of a road prism and associated high traffic create ideal conditions for many weed species. Forested habitats are not immune from weed invasion. Intact forest ecosystems are less vulnerable to invasion, but both natural and human-related disturbances such as fire, floods, mineral extraction, grazing, and timber harvest can create opportunities for weeds to become established and spread.
Dalmatian Toadflax has yellow flowers on a tall stock.On the Modoc National Forest, the numbers of exotic invasive plant species and areas infested are relatively small compared to other parts of the west. This is fortunate, because we still have an opportunity to prevent extensive weed infestation and spread if aggressive, consistent treatment is employed. The species of highest priority for treatment (e.g. the knapweeds, leafy spurge, Dalmatian toadflax) are in relatively small, scattered populations on the scale of hundreds of gross acres. Conversely, in the Rocky Mountain States (Idaho, Montana, Wyoming, etc.), these species occupy millions of acres and are essentially beyond eradication or control. Prevention is recognized as the best, most cost-effective strategy, but once infestation has occurred, actions must be taken to prevent further establishment and spread of the alien species.

Want to know more?  Here are some Frequently Asked Questions about noxious and invasive weeds.