Invasive Plant Management

Stem of Velvet Grass in Field

Velvet grass

Prevention and early detection of invasive plants are the most important and economically feasible means to control the spread of invasive plants, as noted on our general invasive plants webpage. Yosemite National Park Service work crews, park partners and volunteers have been using techniques such as hand-pulling, lopping, and mowing to manage the park's most invasive species as part of a 2008 Invasive Plant Management Plan. Yosemite, in 2008, began using two herbicides--glyphosate and aminopyralid--as additional tools to manage the most threatening plants that manual methods have not effectively controlled.

Yosemite's removal efforts are focused on the control of nine high-priority species: yellow star-thistle; Himalayan blackberry; spotted knapweed; bull thistle; common velvet grass; cheat grass; French broom; Italian thistle; and perennial pepperweed.

In 2009, Yosemite's invasive-plant biological technicians treated 156 gross-infested acres (27 acres in wilderness) and mapped 231 acres of invasives so far this season. On the whole, invasive plant ecologists recorded 805 acres (285 in wilderness) of non-native plant infestations in Yosemite, but there's more to document. Some species, such as cheat grass, are so widespread that it's a challenge to map. Using GIS, the invasive-plant crew mapped 2,664 points, lines and polygons of invasive-plant infestations and treatments in 2009. Invasive-plant managers then incorporated these features into their planning map containing a total of 6,389 GIS features collected since 1995.


2015 Invasive Plant Management Program's Work Plan

View the 2015 Invasive Plant Management Plan [2.5 MB PDF] The work plan summarizes the 2014 field season and proposed 2015 treatments. The work plan describes the program's general approach as well as area specific plans. Thirty-five GIS maps [12 MB PDF] display invasive plant infestation locations and site-specific details on all proposed treatment actions.

Learn More about the Invasive Plant Management Plan

Green meadow filled with brown patches of invasive velvet grass

Velvet grass fills some of Yosemite's meadows(represented by light brown patches). Plant removal crew members, in the bottom center of photo, hand-pull the invasive plant.

The park's management of these invasive plants incorporates the following goals:

  • Prevent new invasions through early detection, equipment inspections, use of certified weed-free pack stock feed, and use of weed-free soil and rock for construction projects.
  • Eradicate existing infestations to minimize threats to natural and cultural resources and scenic values.
  • Preserve native plants and sites valued by American Indians.
  • Promote restoration of native species and habitats in ecosystems degraded by invasive plants.
  • Ensure the program is environmentally safe and supported by research.
  • Implement the most appropriate control technique for each species and
Single stalk of cheat grass

Cheat Grass

So, how exactly is Yosemite's invasive plant management one of the highest scientific concerns at Yosemite? In 2009, approximately 30 seasonal NPS crew members were involved in removing invasive plants—25 crew members, for example, removed star-thistle in June of 2009. In addition, Yosemite benefitted from 619 volunteers and 8,763 volunteer hours specific to invasive-plant removal in 2009.

Invasive species not only displace native plants, but they also can have severe negative impacts on many of the cultural and natural features. Invasive species are able to:

  • Affect Native Wildlife: Native animals are adapted to feed on native plants—with some animals very selective in the plants they eat—and to occupy well-defined plant habitats. Non-native plants can infest an area to the degree that food sources are displaced, resulting in adverse effects on wildlife. Conversely, some non-native plants can provide unnatural food abundance, affecting the distribution and behavior of animals. Thickets of Himalayan blackberry, for example, cover about 80 acres of Yosemite Valley, and their berries attract black bears.
  • Change Fire Regimes: Invasive species such as cheat grass can increase the frequency, seasonality, and intensity of fires. Many native plants and animals can be displaced by changes to the fire regime.
  • Alter the Visitor Experience: Invasive plants can transform spectacular displays of showy wildflowers into large, unattractive monocultures. Thorns and irritants on invasives can transform inviting and accessible areas into impassable and unattractive thickets of thorns and brambles.
  • Cause Impacts Beyond Park Borders: Invasive species have no regard for political boundaries. They can rapidly spread from Yosemite onto adjacent lands.
Drip torch setting fire to a field

The Following Methods or Techniques are Commonly used for Controlling Invasive Plants.

  • Mechanical removal includes hand-pulling, tilling, and mowing. Benefits: Selective if hand-pulling; only target species are affected. Disadvantages: Labor intensive; requires repeated treatments; disturbs ground.
  • Fire control includes both prescribed burns and hand-torching. Benefits: Can cover large area; reduces biomass. Disadvantages: Stimulates re-sprouting and germination of particular invasive plants; impacts air quality; can affect native species. (Learn more about fire ecology.)
  • Chemical control is the use of herbicides. Benefits: Effective to cover large areas; less labor intensive; potential to irradicate a population of invasive plants. Disadvantages: Can affect native species; training costs; potential toxicity.
  • Biological control uses the introduction of an herbivore (such as a beetle that consumes seeds) or pathogen (such as a fungus) that will infest invasive species. Benefits: Continues to work for many years; effective treating large infestations. Disadvantages: Potential threat to non-targe plants; introduces another exotic species.

Did You Know?