Redwood National and State Parks Exotic Plant Control Techniques

Control Techniques

Park staff research exotic plant control techniques described by The Nature Conservancy (TNC), other resource management agencies and universities. The most promising control techniques are tested on high priority species. Following NPS IPM guidelines, the following classes of control techniques are options for individual species under the parks' Exotic Plant Management Plan:

No Action

This option is elected if the ecological threat from an exotic species is insignificant (the species is innocuous), or if no further action is needed to achieve or maintain control of the species.

Mechanical Controls

Heavy equipment: Machinery such as bulldozers, backhoes, cable yarders and loaders may be used in areas where exotic plant density is high, native species are absent, and impacts to other natural or cultural resources are negligible.
Power tools: Chain saws, weed whips, winches.
Hand tools: Shovels, pulaskis, loppers, Weed Wrenches ^TM, grip hoists, machetes, chokers.
Manual removal: Manual removal of herbaceous and shallowly-rooted plants is relatively inexpensive and can control some species.
Draught animals: Mules, horses can be used for plowing or pulling out large individual plants.
Prescribed Fire: Prescribed burning consumes above-ground vegetation and my kill seeds of exotic species or break their dormancy, allowing later removal of the plants. Fire affects the composition of native flora, and this may be manipulated to re-establish and support its natural resistance to invasion by non-native species. Personnel working in exotic plant management will work closely with prescribed burn staff to accomplish the multiple objectives of each burn. Rehabilitation of fires and firelines are planned carefully to avoid establishment and spread of exotic species from surrounding areas.
Cautions for mechanical controls:
Some exotic species, such as Scotch broom, deposit long lived seeds into the soil and these seeds may be in mud from infested locations. Before departing an infested worksite, crews are directed to clean their boots, tools, tires and machinery in order to prevent seed dispersal.
People, equipment, noise and smoke may disturb rare, threatened and endangered wildlife, including the spotted owl, marbled murrelet and snowy plover. Therefore, all plans to use mechanical controls are reviewed and carefully timed to avoid any adverse impacts to sensitive species, in compliance the Endangered Species Act.

Cultural Controls

"Cultural control" means educating people and encouraging them to adjust their activities and surroundings (insofar as possible) to minimize the spread of harmful plants.

Cleanliness: Vehicles and equipment can disperse seeds great distances. There may be long lived seeds of species, such as Scotch broom, in mud, debris and crops from infested locations. If just one seed germinates and the plant matures to reproductive age, it can start a new population. Before working in a vulnerable ecosystem, such as the Bald Hills prairies, earth moving equipment used for any purpose, including road construction, maintenance and watershed rehabilitation, should be thoroughly cleaned and inspected by park staff to prevent seed dispersal.
Disposal of plant debris: Exotic plants that have been removed from the ground can be either left on site for consumption during a prescribed burn, or moved to another area for pile burning at a later date. Ultimately, the debris should be either burned or used as mulch so that it does not add to solid waste. Extra care is necessary when such debris is moved off-site in order to avoid contaminating other areas with live plants and seed.
Information: Information is provided to the public and park employees in the form of signs, interpretive displays, brochures, and programs on the threat of exotic species and the need to control them. This helps to limit spread. Information is included on how to differentiate exotic from native species with the same general appearance.
Developments and Cultural Landscapes: Where exotic species are features of park developments or National Register eligible cultural landscapes, staff asses the ecological risk of these species (i.e. will they spread into adjacent landscapes or create undesirable wildlife/human interactions) and the cost of maintaining the cultural landscape and preventing their spread outside this boundary. Exotic plants that to pose no significant threat or nuisance in surrounding natural areas are exempt from control efforts within the boundaries of developments and cultural landscapes. Exotic plants that pose a threat or are a nuisance will be managed as appropriate, taking cultural and historic resource needs into account, to prevent further natural resources management problems.

Biological Controls

Natural Enemies: Certain insects or pathogens (e.g., fungus, bacteria) attack specific plants and limit their growth or reproduction. Introductions must be carefully controlled so as not to harm other native plants or species of economic importance, and are introduced only after several years of scientific evaluation.
Vegetation succession: Canopy closure by native evergreen conifers and/or hardwoods suppresses or eliminates shade-intolerant exotic species. Succession can be encouraged.

Chemical Controls

Soil chemistry and microflora: Soils can be managed toward conditions that favor native species or that selectively target invasive species when the natives and invasives have differing soil requirements. Plant-available nutrients, salinity, acidity, and oxygen can be managed, and native symbiotic microflora can be re-introduced. For example, a hot surface fire tends to kill native mycorrhizae and to release much plant-available nitrogen. Abundant nitrogen favors weedy pioneers, such as thistles, foxglove, and fireweed. A dense stand of competing weeds, combined with a lack of native seed and mycorrhizae slows re-establishment of native plant species. Introducing a little topsoil from the undisturbed surroundings may be enough to re-introduce native seed and mycorrhizae, and a light surface application of natural litter or sawdust will cause decomposer fungi to multiply and to remove excess plant-available nitrogen from the soil.
Herbicides: An herbicide may be considered as a means to control an invasive plant species if it is determined that alternative mechanical, physical, cultural, or biological means are either not acceptable or not feasible. Herbicides will not be considered for control in natural vegetation unless other control techniques prove ineffective. If herbicides are used, they are applied in strict accordance with IPM guidelines under the supervision of the park IPM coordinator by a trained, certified pesticide applicator. To the extent possible, herbicides are used only as a last resort.