The Impact of Invasive Plants

Myths and Facts | What You Can Do

Why Should You Care About Invasive Plants?

…if you own a farm or ranch:

• Invasive plants crowd out crops and rangeland forage. These invaders can be low in nutrition or even toxic to livestock.
• Invasion can cause land values to drop, and management is often costly. Nationwide, invasive weeds in pastures and farmland cost an estimated $33 billion per year.

…if you enjoy the outdoors and watching wildlife:

• Invasive plants can blanket waterways, trails, and scenic landscapes, making boating, hiking and biking difficult, and lowering the land's value for photography and wildlife viewing.
• Invasive plants can significantly degrade wildlife habitat. Nationally, invasive species are the second-greatest threat to endangered species, after habitat destruction.

…if you hunt or fish:

• Invasive plants reduce habitat for game species. This stress on wildlife reduces hunting and fishing resources.
• Invasive aquatic plants form dense mats that restrict boat access and kill fish by reducing oxygen in the water.

…if you live in the city or suburbs:

• Invasive ornamentals such as Scotch broom, pampasgrass, and eucalyptus increase fire fuel loads and are dangerous near homes.
• Plants like giant reed (Arundo donax) clog creeks throughout California, reducing their water-carrying capacity and increasing the risk of floods during winter storms.

…if you're a public official:

• Some invasive plants generate higher fuel loads than native plants. When these plants invade, wildfires can be more frequent and sometimes catastrophic. Towns and wildlands may need decades to recover from these dangerous, costly fires.
• Some invasive plants consume enormous quantities of water. This water is lost to wildlife, agriculture, and drinking supply, at a high price. For example, saltcedar trees along the Colorado River cost southern California over 68 billion gallons of water per year.

Myths and Facts About Invasive Plants

Myth: These species increase biological diversity.

Fact:  Many invasive species form monocultures (dense stands of one plant) that push out native species and reduce food and shelter needed by native wildlife, including endangered species. Although the total number of species may increase, habitat quality and ecosystem health decline.

Myth: Invasive species are here and there's nothing we can do about it.

Fact:  Many projects across the state are achieving success at removing invasive plants to restore native habitat. These projects vary from multi-million dollar efforts like the Invasive Spartina Project in San Francisco Bay to the many smaller projects implemented by local Weed Management Areas (WMAs).

Myth: The cost of prevention and removal isn't worth it.

Fact:  Prevention, early detection, and rapid response against invasive plants are excellent investments for California. Control costs increase exponentially over time as infestations spread. Weed Management Areas have surveyed many new populations of invasive plants, allowing them to be treated quickly, before control costs rise. It is especially important to manage invasive plants in settings with particular natural resource values, such as state and national parks.

Myth: Species are always on the move, so "non-native" species moving into new habitat is natural.

Fact:  The rich diversity of species that have evolved on the planet today is the result of ecological isolation due to geographic barriers (such as Darwin's finches on different islands in the Galapagos). Over geologic time, a few major events (such as large meteorites) created distinct breaks in this slow evolutionary process. As humans began to move organisms around the globe, helping them cross geographic barriers, some organisms were able to spread unchecked in the absence of natural enemies with whom they evolved in their home range. Today, international travel and trade are moving a greater number of organisms greater distances in ever shorter times. This is greatly increasing the potential for invasive species. This is "natural" in the same way that a major planetary event is natural, but probably not desirable.

What You Can Do

1. Avoid using known invasives in gardens or landscaping. See our Don't Plant a Pest! program for attractive alternatives to invasive plants.
2. Learn which invasive plants your local Weed Management Area is tracking so you can report new infestations whenever you see them.
3. Educate others about invasive plants (see our brochures).
4. Encourage your local nursery not to sell invasives.
5. Volunteer with creek groups, parks, or your local land conservancy to remove invasive plants in your area.
6. Become a Cal-IPC member!

References

Bossard, C. C., J. M. Randall, and M. C. Hoshovsky (eds.) 2000. Invasive Plants of California's Wildlands.

Pimentel, D. L. Lach, R. Zuniga, and D. Morrison. 2000. Environmental and economic costs of nonindigenous species in the United States. BioScience 50:53-65

Wilcove, D.S., D. Rothstein, J. Dubow, A. Phillips, and E. Losos. 1998. Quantifying threats to imperiled species in the United States. BioScience. 48:607-615

Zavaleta, E. 2000. Valuing Ecosystem Services Lost to Tamarix Invasion. In: Invasive Species in a Changing World. Mooney, H. A. and R. J. Hobbs, (eds.)

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