Invasive Plants

September 10, 2006

The pleasures of the tasty fruit that Himalayan blackberry produces, the sweet tropical fragrance that the blooms of French and Scot's broom emit and the rich yellow flowers of gorse that add color to the Caspar Headlands is clouded by these plants being invasives. An invasive species is a non-native that propagates itself in the wild without human intervention and whose introduction may cause economic or environmental harm or harm to human health. Other familiar invasive plant species that occur locally include pampas grass, yellow star thistle, English ivy, periwinkle, black locust, iceplant, giant reed, Harding grass and tansy ragweed.

Ironically, invasive plants have a home. In the ecosystems where they are native, competition, biological controls (e.g. herbivores or disease-causing microorganisms) and environmental conditions (e.g climate), keep them well behaved. Hearty traits such as producing large quantities of seed or plant parts (e.g. rhizomes that support asexual reproduction), producing seed that remains viable for decades, thriving in disturbed soil or in over-grazed pasture, growing aggressive root systems that spread long distances and producing reproductive parts that are suited for transport by effective vectors including water, wind, birds, animals and humans are possessed by some invasive plant species. However, many non-invasive plant species possess these same hearty attributes. So it stands to reason there is more to the story of why invasive plants are successful outside their native ecosystems. Peter Warner, environmental scientist for the California Department of Parks and Recreation, adds human commerce and the rapid, deliberate and incidental movement of both entire plants and propagules (e.g. seeds, rhizomes, etc.) and human accelerated disturbance combine with these traits to increase the spread of invasives. Mild, moist climates are also especially susceptible to invasion by greater numbers of invasive species. Peter states further, in general, the spread of species to new regions and ecosystems is not novel in a long-term historical context, but the rate of introduction and spread have far outpaced the evolutionary resiliency of native species and their ecosystems to withstand this external pressure.

Concern over invasive plants is rising because they can cause decline of endangered or threatened species; invasive plants compete directly with native species for moisture, sunlight, nutrients and space; overall plant diversity can be decreased; invasive plants degrade wildlife habitat; diminish productivity on agricultural lands; degrade water quality; increase soil erosion and increase fire hazard.

So what do we do? The lowest hanging fruit is prevention. Ways you can prevent the spread of invasives, include choosing non-invasive plant species for your gardens and landscaping, disposing of yard waste properly, not picking and transporting the flowers of invasives, cleaning your boots or vehicle if they are carrying invasive plant material and use feed for livestock and mulch for erosion control free of invasive plant seed. You can also support programs to eradicate invasive plants or habitat restoration programs by donating time and/or money, and request that governments do the same.

To get more information about invasive plants ask for the invasive plants brochure at the Navarro River Resource Center at 895-3230. To see how you can get involved locally, visit the Mendocino Coast Cooperative Weed Management Area website at www.mcwma.org, for example in late September an Arundo removal workday is planned at Lake Mendocino. To learn what ishappening state-wide, visit the website of the California Invasive Plant Council at cal-ipc.org.

A portion of this production was gleaned from the United States Forest Service website on Invasives Plants at www.fs.fed.us/wildflowers/invasives and communication with Peter Warner of the California Department of Parks and Recreation and Tara Athan, botanist for the Mendocino Coast Cooperative Weed Management Area.

I welcome responses as well as ideas for future Tree Tips. You can also get an email version by contacting me at thembi@mcn.org or go to www.nwwg.org, click on Resources and click on Tree Tips.

Thembi Borras is a Registered Professional Forester living and working in Mendocino County, CA USA.