What are “Invasive Plants” and why should you care?

Although exotic (non-native) species have been colonizing the state since the Mission era, there is now growing public awareness and concern about invasive plant species in California and the west. Why are these plants of such concern?  They often form monocultures that effectively exclude native species. This reduced diversity means loss of wildlife habitat, as food and shelter are eliminated. Gardeners may be most familiar with horticultural varieties that escape from cultivation. Notorious examples include Cortaderia (Pampas grass) along the Coast Highway and canyons, Vinca, widespread in wooded areas, and Pennisetum, lining roadways from the coast to the Utah canyonlands.

Less recognizable are accidentally introduced weedy species such as star and artichoke thistle, or deliberate erosion control introductions like Arundo, and Ammophila that got out of hand in the wild, congesting streams and monopolizing sand dunes, respectively. Even nominally “native “ species, used outside their natural range can become invasive, endangering or extirpating local species. This has occurred with the introduction of Lupinus arboreus to the dunes of far northern California, where it has initiated a cascade of disruptive biological events (Bossard, Randall, and Hoshovsy, 2000. Invasive Plants of California’s Wildlands). 

The environmental impact of invasive species is of course the exclusion of native species resulting in the loss of healthy biodiversity.  It is yet another factor in the shrinking of valuable and limited habitat here in Southern California.  The negative impact of invasive species is of course widespread throughout the west contributing to other troubling issues.

Millions of acres of agricultural and rangeland are now carpeted by invasive species, a huge economic issue throughout the west. Exotics typically increase costs by forcing greater herbicide use, displacing high quality forage, and some species are even toxic to grazing animals.

Invasive species contribute to increased wildfire intensity due to fuel accumulation, from exotic grasses. This issue was debated in the Los Angeles Times article: “Desert Fires’ Damage Will Last,” August 21, 2006. (http://www.latimes.com/news/local/la-me-desert21aug21,1,1200347.story?page=1&ctrack=1&cset=true.)  The interplay of wildfires, open spaces and invasive plants is of great importance to public safety. An in-depth examination of this complex issue can be found at the Defense Environmental Network and Information Exchange Website: (https://www.denix.osd.mil/denix/Public/ESPrograms/Conservation/Invasive/contents.html)

 At home:

• Eliminate known problem plants from your landscape.

• Use native plants: you will avoid the wild land invasion problem and create a little local habitat to enjoy!

In your community:

• Encourage neighbors, HOAs, and municipalities to substitute invasive plants with more appropriate selections.

• Request that your local nursery stop carrying invasive plants (Nursery wallet cards are available on cal-ipc.org - http://www.cal-ipc.org/landscaping/dpp/pdf/WalletCard.pdf ).

• Request a ‘Weed Watch Card’, (as pictured)*.  It includes a tear-off wallet card you can pass along to people who want (or need) to know.

www.cal-ipc.org, California Invasive Plant Council

http://tncweeds.ucdavis.edu/index.html, The Nature Conservancy’s Invasive Plant Initiative Page

http://www.asla-sandiego.org/content/Download/matrix.pdf, or http://www.asla-sandiego.org/content/plantguide.html San Diego ASLA Invasive Plant Matrix

If you feel a bit more energetic, working on local exotic removal projects is a fun and rewarding way to spend a few hours or a few days. Many conservation and park groups have ongoing programs that rely on volunteers, including individuals, families, and community organizations (www.invasivepecies.nbii.gov/outreach.html).

Clearly the problem of invasive plants is an issue that is too large for just one individual or even just one organization to solve.  However, unlike some environmental problems that seem overwhelming, the invasive plant battle can be fought successfully on many fronts. Any action you take will be constructive and helpful.  We hope that some of the resources we have provided here will help you understand the issues surrounding invasive plant species in Southern California and equip you to inform others!

*To order Weed Watch Cards, please contact Drew Ready at the Los Angeles San Gabriel Rivers Watershed Council by emailing him or calling 213.229.9951.