Integrated Pest Management

Read Yosemite's current Integrated Pest Management Plan [8 MB PDF]

The goal of the Invasive Plant Management program is to provide a comprehensive framework to protect the park’s natural and cultural resources from the impacts of non-native invasive plants. Yosemite resource managers use Integrated Pest Management (IPM), a sustainable approach to managing pests by combining the best available science and tools in a way that minimizes risk, whether human health, environmental, or economic . Elements of IPM include prevention, inventory, prioritization, treatment, monitoring, and education and outreach. Managers implement IPM through adaptive management which promotes flexible decision making to allow for program adjustments in the face of uncertainties and with an aim to reduce uncertainty over time via monitoring. This process allows resource objectives to be met while information is gathered and lessons are learned, in hopes of continually improving future management.


Prevention is the first line of defense against invasive species. Some of the nearly 4 million people visiting Yosemite each year bring invasive plant seeds into the park on their vehicles, bicycles, pack animals, pets and hiking boots. Preventing new infestations can be as simple as inspecting and removing seeds from your socks or pet’s coat, or washing mud, which often contains invasive plants seeds, from your vehicle before you visit Yosemite. Once invasive plants are introduced, control can require significant funding and personnel that must be sustained over many years. Invasive species brought in on construction or firefighting equipment can be thought of as a slow-moving emergency, and can pose a far greater long-term threat than fire to the park’s natural and cultural resources. Prevention measures include identifying weed-free sources for gravel, fill, topsoil, and other construction materials to reduce the spread of current infestations and the number of new infestations. An additional preventative measure is Yosemite National Park and DNC Parks & Resorts at Yosemite using certified weed-free forage to feed stock. Yosemite does not exist as an island, and therefore needs to work with other management entities to detect and prevent weeds from entering the park. Yosemite is working on developing stewardship initiatives with owners in and adjacent to the park and park visitors. At present, Yosemite is actively working with Sierra and Stanislaus National Forests to treat patches of yellow star-thistle that occur across our western political boundaries. The park also works with contractors on two separate prevention programs, equipment inspection [63 Kb PDF] and pre-procurement gravel-pit inspection [190 kb PDF]. Prevention programs cannot provide full-proof protection; the park must also have an inventory program to ensure new infestations do not occur.


There are numerous ways in which invasive plants seeds can slip through the cracks of even the most rigorous prevention systems. Therefore, a system of early detection is necessary to enable a rapid management response to new invasions. The goals of the inventory component of IPM are to: 1) survey the park for new priority infestations; 2) document the spread of existing infestations; 3) document the effectiveness of treatments; and 4) to provide the data needed to plan invasive plant treatment operations.

Catching infestations early enables managers to respond while populations are still relatively small. This is critically important because the probability of eradication is much greater when invasions are still small, and the treatments are much more effective. The management response, therefore, requires far fewer personnel and equipment and monetary resources, and would potentially use tools that are less invasive. In the figure below, one can see how dramatically the cost of control increases with increasing infestation size while the chance of success declines.


As infestation size increases, effort to control, measured in hours (and dollars) increases, while success of eradication decreases.

Non-native invasive plant inventories inform resource managers about the presence and absence of target species. Both are important and provide essential baseline data by which the success of management action or inaction can be assessed. Because it is not practical to inventory each of the 761,266 acres within Yosemite National Park, the inventories focus on areas most likely to be invaded, but include enough other sampling areas to inform managers about where invasive species occur or do not occur. Gathering this information mandates strategic surveying methods and allocation of limited resources to receive the greatest results. For example, high probability areas include both natural and manmade disturbance sites, particularly those exposed to a ready source of invasive plants propagules. All survey efforts should be tracked even when no target species are found in order to improve the reliability of the mapping effort, and to improve our understanding of the likelihood of habitats to become invaded. Identifying pathways for invasive species entry and spread can help managers make informed management decisions regarding park prevention systems and early detection efforts. Maintaining an invasive species inventory is an ongoing process. Sophisticated mapping technology allows managers to inventory and document areas of concern and catalog how infestations respond to treatment over time. Unfortunately, Yosemite National Park has no dedicated funding for early detection survey work at the present time, hence, survey work as well as treatment work has to be carefully prioritized.


Despite the limited nature of invasive plants surveys in Yosemite, more than 200 species have already been documented. The majority of exotics are relatively harmless as they are restricted to non-natural habitats, such as compacted roadside shoulders. Plants that do not alter the natural community structure or ecosystem function are also more of a nuisance rather than of real management concern. This is fortunate because the park cannot control all non-natives and has to concentrate its limited resources on the most harmful species it can effectively manage. Resource managers use a modified Alien Plants Ranking System (USGS 2000) to assess the degree that invasive species affect natural systems to focus management actions on those that pose the greatest threat to park resources. Resource managers use this analytical tool to separate the innocuous species from the invasive ones and strategically prioritize individual plants as a 'high', 'medium' or 'low' based on the potential threat to park resources, extent of species and ability to mitigate the spread of the invasive species. Park managers can then focus limited resources where they are needed most. Species, such as Himalayan blackberry, are ranked 'high priority' as they form dense, uniform stands that exclude native species or alter natural disturbance regimes. Some highly invasive species (e.g., some Mediterranean grasses) are already so widespread within Yosemite and surrounding areas that their control is not currently feasible, and attempts to control them would be a waste of resources. Those species then are assigned a lower priority.

Prioritization is a dynamic process, and occasionally, ranking of individual species may shift due to changes in plant behavior over time. For example, the exotic species velvet grass was first documented in Yosemite in 1919, but its non-invasive behavior did not warrant focused treatment for many decades. By 2006, managers recognized velvet grass was aggressively spreading from established patches and assigned it a high priority for control. Still other invasive species not yet been found in the park that are problem species in habitats similar to those found in the park are placed on a watch list [113 kb PDF] if their arrival in the park is anticipated. Park botanists and invasive plant staff specifically study such species so that they are readily noticed should they arrive. Effective prioritization results feeds directly into control operations.


Which control operation is implemented by managers can vary greatly from species to species depending on specific plant characteristics. Decisions for follow-up or modified treatments, as well as determining if there is even a need for future treatments can be informed by various types of monitoring.


Invasive plant control efforts are monitored to determine whether management objectives are being met and to ensure the effectiveness of control treatments. Monitoring data provides the necessary detail of post-treatment condition and compares it to pre-treatment data. The quality of monitoring is dependent on the sufficiency of baseline inventory information. The extent of monitoring can vary from year to year depending upon the needs of the program and the availability of funding and staff. Effective monitoring goals are those that are well-defined, easily quantifiable, and time specific. Trend monitoring includes the following:

  • Efficacy monitoring of control and prevention efforts helps determine whether or not objectives are being met through current management actions over a designated time.
  • Non-target effects monitoring evaluates the potential unintended consequences of management actions on non-target resources.
  • Ecological restoration monitoringevaluates the effectiveness of management actions for establishing natural ecosystem composition structure and ecosystem processes over a set time.
  • Corrective actions monitoring provides justification for eliminating actions that are not working, or modifying management tools and methods to improve their effectiveness.

Map showing pre- and post-treatment blackberry occurrence

Mapping a patch of Himalayan blackberry before herbicide treatment (left) provides baseline data that can be used to monitor treatment efficacy. The right image shows the extent of the blackberry patch one year after treatment.

The elements of monitoring allow for an adaptive approach so that park managers can adjust control methods as necessary to improve treatment success in the future. Monitoring is a crucial step in an iterative process that can benefit land managers in other parts of the Sierra Nevada and elsewhere. Land managers from other regions can learn from treatment success and failures documented in Yosemite, thus, informing and assisting with their management decisions. Additionally, this information can be synthesized in ways that incorporate diverse methods of outreach and education to reach a greater audience.

Research, Education, and Outreach

Inventory, monitoring and other methods of data collection inform invasive plant management decision making. Program managers conduct periodic literature reviews on published research relevant to invasion ecology and the management of invasive plants, which can be incorporated during annual review of the program's management objectives. Staff attend the California Invasive Plant Council invasive plant symposium annually which is also an excellent way to stay connected with IPM developments in California.

Education and outreach efforts can foster understanding of invasive plant prevention and control. These efforts are diverse and cater to a wide range of audiences. One method includes educating, training and using volunteers, who are essential to the invasive plant management in the park. One paid staff member can lead a work effort composed of many volunteers. Volunteer efforts allow the public to become stakeholders in solving park resource challenges, and many people return to volunteer year after year. The accomplishments of volunteers range from building fences to assisting with information technology to eradication of non-native invasive species. Yosemite would not be able to achieve the many goals set forth without volunteer devotion.

Additional efforts include incorporating invasive plant information into park operations such as planning and design, construction, interpretation, maintenance, American Indian consultation, staff training and resource management. Annual work plans are posted on the park's website, as well as in newspapers, journals, conferences, brochures, visitor center exhibits, and other announcements. This strategy allows invasive plant research and other information to be summarized and distributed to park staff, partners, and visitors. For example, information about the gravel pit inspection program [1.9 MB PDF], velvetgrass [1.1 MB PDF] and blackberry treatment [1.6 MB PDF] can be expressed through informative posters.

Park visitors can learn about invasive plant prevention and control through diverse opportunities. Interpretive programs and open houses educate the public about the threats posed by invasive plant species and actions taken to protect park resources from their introduction and spread. Partnerships with other park entities such as Delaware North Company, Yosemite Conservancy and Naturebridge are especially important for prevention and early detection of non-native invasive species. Several nationwide programs offer resources that aid efforts to combat invasive species: Inventory and Monitoring and Cooperative Weed Management Areas. In addition, 16 Exotic Plant Management Teams have been established across the country to work with 225 parks. These regionally specialized teams assist parks with ongoing efforts to remove invasive plants and provide management guidance for invasive plant control in individual parks. Other ideas include creating incentive programs to encourage invasive plant awareness, placing invasive plant awareness messages at trailheads and information kiosks, and including weed prevention guidelines on wilderness permits and construction and commercial use authorizations.

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