Without active stewardship, invasive species can spread aggressively, displacing native plants that provide food and habitat to wildlife, and degrading cultural and economic resources. Invasive species often use more water and resources than native plants, ignite more easily, and contribute to more severe, destructive wildfires.

Removing invasive plants also creates safer access along the roads for firefighters and residents, and fosters diverse, more resilient habitats by reducing competition for native species.

When & Where to Manage Invasive Species

Invasive species are usually a higher priority where fire has occurred; where soil has been disturbed by digging, scraping, grading, landslides, or vehicle traffic; or where rare or sensitive plants might be over-run by invasives.

Invasive species often establish from seeds that germinate in disturbed soil–along a road cut, after heavy equipment work, or after a landslide–or seeds that are accidentally spread along frequently traveled roads. 

There are four general strategies for invasive species management, depending on the extent of the problem, as shown in the invasion curve infographic above. They are listed from lesser to greater investment. 

1. Prevention

• When leaving an area where there might be invasive plants, it is important not to transport any seeds, fruit, or root pieces. Wash or brush your boots before leaving a potentially contaminated area. Request decontamination from any crews coming to work on the property; include this language in any contract. (Cal-IPC.org provides a check-list of gear, tools, and equipment to clean.)
• Retain healthy native vegetation to fend off invasive species. This strategy has the most benefits and fewest downsides. Healthier, more biodiverse landscapes can present biotic resistance, meaning they are more resistant to invasive species.
• Some nurseries sell invasive plants, often in their “exotic” or “decorative” sections. Check out this page for ideas on which invasive species to avoid and what to plant instead.

2. Early eradication

• Early detection, rapid response –  stopping invasions early is always easier than removing a population that has spread widely.

[Web designer: 1. This graphic should be placed next to or very near the sentence above that starts with “there are four general strategies…”. 2. please caption the “Invasion Curve” graphic as: Infographic from National Park Service, adapted from Invasive Plants and Animals Policy Framework, State of Victoria, Australia.]

3. Containment

• Prioritize species and populations based on most important locations to protect and available resources
• Start with satellite populations around the edges of infestations; progress towards older, denser populations and/or the source of the infestation

4. Long-term management

• Create stability in heavily degraded areas and reestablish a trajectory of proper ecological functioning
• Often a mix of the above strategies are used simultaneously across different sites on a property.

• The seed bank often flushes or germinates after fire, creating huge infestations, but it’s important to know that the infestation was not brought by the fire. Seeds remain viable for decades, so repeat treatment and consistent monitoring are critical. Treatments and monitoring are only needed every other year, because it takes that long for new plants to create viable seed.
• Successive flushes of the seed bank over two to three years usually greatly diminish the number of seedlings that germinate each year, reducing the work needed to control broom in that area.
• Manual removal is most effective in spring or early summer before flowers turn to seeds; large plants require tools that remove roots.
• Generally, cutting or mowing mature broom does not kill it, and increases the difficulty of manually removing the roots. However, mowing young broom plants (those that have not been cut before and are under 12 inches in height) at ground level in the spring, with follow-up in the fall of the same year, can often kill them.

Other widespread invasive plants are listed here. Click each link to see plant information, management guides, and articles and research. 

• Ivy: English (Hedera helix), Algerian (Hedera canariensis), and Cape (Delairea odorata)
• Himalayan (or Armenian) Blackberry (Rubus armeniacus)
• Silver Wattle (Acacia dealbata, Acacia sp.)
• Tree of Heaven (Ailanthus altissima)
• Poison Hemlock (Conium maculatum)
• Giant Reed (Arundo donax)
• Pampas (or Jubata) Grass (Cortaderia selloana, C. jubata)
• Stinkwort (Dittrichia graveolens)
• Thistles: Yellow Star (Centaurea solstitialis), Italian (Carduus pycnocephalus), Milk (Silybum marianum) and Bull (Cirsium vulgare)
• Grasses: Medusa Head, Barbed Goat, Harding, 
• Periwinkle (Vinca major)
• European beachgrass (Ammophila arenaria)
• Ice plant (Carpobrotus edulis)

Variations on this Practice

The appropriate mix of methods depends on how dominant the invasive species are compared to desirable native plant species. When timed correctly, Beneficial Fire can be a useful tool to manage many invasive species.

Timing for Managing Invasive Species

[Click image to view full size graphic]
By Jason M. Mills, Senior Restoration Contractor, Ecological Solutions

If plants are large enough that managing them will cause a disturbance, it’s best not to do the work during bird nesting season, March through August. If substantial disturbance must be done during nesting season, consider Nesting Bird Surveys.

Equipment

Personal Protective Equipment (PPE)

• Long pants
• Long sleeve shirt
• Boots
• Helmet
• Leather gloves
• Eye and ear protection

Tools

• Hand saw
• Pruner
• Loppers
• Digging tools, such as pick-mattocks, pulaskis, or shovels, weed wrenches, hard rakes or Mcleods
• Tarps for transportation of materials

Observing the land regularly by walking along common routes of transmission (roads and trails, neighboring land uses), as well as around known populations of invasives can help reduce further spread or new invasions.

“Maintenance is about preventing further outbreaks from occurring and establishing. Monitoring historic problem spots along roads and other access points, limiting movement of equipment and vehicles through infested areas during wet season and seed season, and being knowledgeable about where materials such as gravel or rock are coming from are all important steps to maintaining your hard work.” -Tori Norville, UCCE.