What are invasive plants?
Across California, invasive plants damage wildlands. Invasives displace native plants and wildlife, increase wildfire and flood danger, consume valuable water, degrade recreational opportunities, and destroy productive range and timber lands.
Most of the plants used in gardens and landscaping do not invade or harm wildland areas. But a few vigorous species can - and do - escape from cultivation into open landscapes where they cause a variety of ecological problems. They crowd out native plants, insects and animals, clog waterways, and can lead to increased flooding, fire and crop losses.
When an aggressive plant is introduced to a new environment, the predators that would normally limit their growth in their home environment may not be present. This allows them to proliferate, spread, and take over natural habitats. Each invasive plant has its own strategy for growth and dispersal. Some have seeds that are spread by the wind, like pampas grass, whose seeds can be blown up to two miles away. Others have seeds that are carried by water or eaten by birds and animals that deposit them far from the parent plant. There are also species that reproduce vegetatively, like Arundo that sprouts new shoots from fallen stalks and plant fragments.
Invasive species are a leading threat to biodiversity, second only to habitat destruction. And the economic cost is as significant as the ecological cost: in California, more than $85 million goes to fighting invasive plant and animals every year1. A much-cited paper by Cornell researchers including David Pimentel estimates the economic impacts of invasive species to be $120 billion a year. If divided equally through the 50 states, the cost to each state averages $2.4 billion annually — and given California's size and resources, the actual impact is likely greater in our state2.
There have been various attempts to calculate the monetary costs of invasive species. Some of the factors that are included in these calculations are:
- the cost of equipment, chemicals and work hours required to control and eradicate invading populations
- loss of productivity of rangelands and crops
- decreased land value
- flooding, erosion, and fire near homes and businesses
- loss of recreational opportunities
- decreased water availability
It's important to remember that there are other costs to humans that are more difficult to quantify, such as:
- loss of aesthetic beauty of native lands
- decreased water quality
- volunteer time and energy to control invasions on public and private lands
The invasive plants identified by PlantRight came from the list of known invasive species from the California Invasive Plant Council. We identified the plants that are available in the horticultural trade and discussed each one to assess its effect on wildlands, range of distribution, and role in the industry. We vetted our conclusions with the horticultural industry professionals and academic scientists. The result is a concise list of the most critical invasive species in our state, which you can access by visiting our regional map and learning more about the invasive plants - and their beautiful non-invasive alternatives - in your area.
If you would like to learn more about invasive plants in California wildlands, including those of horticultural origin, please visit the website of the California Invasive Plant Council. Another excellent source of information is the Global Invasive Species Initiative of the environmental group The Nature Conservancy.
1 Invasive Species: Federal and Selected State Funding to Address Harmful, Nonnative Species. United States General Accounting Office, Report to Congressional Committees. August, 2000.
Note: The dollar figure at the top of our website - that California spends $85M per year fighting invasive species - came from this report on government spending from the US General Accounting Office. This conservative estimate has only increased since the report came out in 2000.
2 Pimentel, D., R. Zuniga & D. Morrison. 2005. Update on the environmental and economic costs associated with alien-invasive species in the United States. Ecological Economics 52: 273-288.
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