Controls of Invasive Plants

By Thembi Borras

Preventing the spread of invasive plants is easier said than done given the vast expanses of invasive plants with which we are faced. Harding grass, which grows much taller than the native grasses it replaced increases the fire danger in many of the steep grasslands in Rancho Navarro where I live. Each year I notice more and more brooms and star thistle along our roadways. According to an article recently published in the May 2006 issue of the Mendocino County Farm Bureau's publication medusa head and barbed goat grass have become increasingly problematic to wildlife and livestock by reducing native populations of desirable feed and giant reed, also known as Arundo, and Himalayan blackberry have been charged with clogging local waterways.

Faced with a small backyard population of invasive plants well timed manual control can be effective. However, addressing large populations is a challenge because treatments may require long term commitments from stakeholders, can be expensive and can in themselves adversely impact the environment. The trick is for land managers to decide which control method is most effective, while being the least damaging to the ecosystem. Controls being used include public education, manual and mechanical, grazing, prescribed fire, biocontrol, herbicides and Integrated Pest Management (IPM) which incorporates a combination of these controls.

Manual techniques which include cutting, pulling or grubbing, which means pulling out all the roots, are very labor intensive. The advantage is that people can be trained to discriminate between the native plants and invasives. Mechanical techniques include mowing and mastication and can be cost-effective but are limited to gentle terrain and like grazing may cause unacceptable levels of ground disturbance and compaction. Also, machines and animals may not be able to discriminate between the invasive plants being controlled and the native plants being retained. Fire is also being used to control invasive plant species most often as a facet of some integrated pest management approaches. If the invasive plant species being targeted produces a prolific amount of seed, timing these controls to prevent annual seed production will maximize control efforts. In biocontrol, a natural enemy such as a parasite, predator or disease organism is introduced into the environment of the invasive plant or, if already present, is encouraged to multiply and become more effective in reducing the number of invasive plants. However, some biocontrol programs have resulted in significant, irreversible harm to untargeted species and to ecological processes and must be used with caution informed by the lifecycles and complex interactions of targeted and nontargeted species. Finally, although chemical control, which involves the use of an herbicide to reduce invasive plant populations, is controversial, Peter Warner, environmental scientist for the California Department of Parks and Recreation, considers "herbicides to be one of many essential tools in reducing the spread of invasive plants". The Nature Conservancy provides a checklist to be used when considering the use of herbicides entitled, To Spray or Not To Spray? and is contained in the Weed Control Methods Handbook, which is an excellent resource that covers in depth each of the control methods. It can be downloaded from the website http://tncweeds.ucdavis.edu/handbook.html.

You can get an Invasive Plants brochure at the Navarro River Resource Center, the number for which is 895-3230. You can also visit the Mendocino Coast Cooperative Weed Management Area website at www.mcwma.org and see how you can get involved locally or visit the website of the California Invasive Plant Council at cal-ipc.org.

A portion of this production was gleaned from The Nature Conservancy Weeds website at tncweeds.ucdavis.edu 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.

Invasive Plants

By Thembi Borras

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 http://www.mcwma.org/. To learn what is happening 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 http://www.fs.fed.us/wildflowers/invasives/index.shtml 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.