Lepidium draba L. (1753)

More info for the terms: cover, fire management, fire suppression, forbs, invasive species, phenology, prescribed burn, restoration, severity, wildfire

Postfire colonization potential: It has been suggested that hoary cress may initially appear following fire [71], although no specific cases are documented. Information regarding hoary cress seed longevity, heat tolerance, location of populations in the proximity of the burn area, fire suppression activities, and potential for seed dispersal into the burned area is needed to predict postfire colonization potential [12].

Fire as a control agent: Rosenfels and Headley [82] report that hoary cress was successfully controlled in many areas by searing plants with a hand-held burner. They say that in several cases, searing caused a deterioration of the root several inches below the crown. In field trials using a commercial, coil-type burner at intervals of 2, 3, 4, and 8 weeks, hoary cress plants were eradicated in about 2.5 seasons at every interval except 8 weeks. It appeared that plants seared every 8 weeks or more would live indefinitely. They conclude that under the conditions of these tests, searing can be regarded as an acceptable substitute for hoeing, but not as a method giving quick results [82].

Land managers should always be cautious when using fire to control invasives because it may promote the establishment of other fire-tolerant invasive species [12].

Preventing postfire establishment and spread: The USDA Forest Service's "Guide to Noxious Weed Prevention Practices" [97] provides several fire management considerations for weed prevention in general that apply to hoary cress.

When planning a prescribed burn, preinventory the project area to evaluate cover and phenology of any hoary cress or other invasive plants present on or adjacent to the site, and avoid ignition and burning in areas at high risk for hoary cress establishment or spread due to fire effects. Avoid creating soil conditions that promote weed germination and establishment. Areas of soil disturbance (e.g. those brought about by fire suppression activities) are especially susceptible to invasive plant establishment. Weed status and risks must be discussed in burn rehabilitation plans. Also, wildfire managers might consider including weed prevention education and providing weed identification aids during fire training; avoiding known weed infestations when locating fire lines; monitoring camps, staging areas, helibases, etc., to be sure they are kept weed free; taking care that equipment is weed free; incorporating weed prevention into fire rehabilitation plans; and acquiring restoration funding. Additional guidelines and specific recommendations and requirements are available [32,97].

Preventing invasive plants from establishing in weed-free burned areas is the most effective and least costly management method. This can be accomplished through early detection and eradication, careful monitoring, and by limiting invasive plant seed dispersal into burned areas by [6,32,97]:

• Re-establishing vegetation on bare ground as soon as possible
• Using only certified weed-free seed mixes when revegetation is necessary
• Cleaning equipment and vehicles prior to entering burned areas
• Regulating or preventing human and livestock entry into burned areas until desirable site vegetation has recovered sufficiently to resist establishment of undesirable vegetation
• Detecting weeds early and eradicating before vegetative spread and/or seed dispersal
• Eradicating small patches and containing or controlling large infestations within or adjacent to the burned area

In general, early detection is critical for preventing establishment of large populations of invasive plants. Monitoring in spring, summer, and fall is imperative. Eradicate established hoary cress plants and small patches adjacent to burned areas to prevent or limit seed dispersal into the site [6,32,97].

The need for revegetation after fire can be assessed on the basis of the degree of desirable vegetation displaced by invasive plants prior to burning, and on postfire survival of desirable vegetation. Revegetation necessity can also be related to invasive plant survival as viable seeds, root crowns, or rhizomes capable of reproduction. In general, postfire revegetation should be considered when desirable vegetation cover is less than about 30% [32].

Goodwin and others [31,32] provide guidelines for determining burn severity, revegetation necessity, and establishing and managing competitive plants. The following paragraphs provide some general guidelines for invasive species management after fire. See Integrated Noxious Weed Management after Wildfires for a more detailed source of this information. More research is needed specific to fire tolerance and response of hoary cress in specific sites and ecosystems in which it occurs.

When prefire cover of hoary cress is absent to low, and prefire cover of desirable vegetation is high, revegetation is probably not necessary after low- and medium-severity burns. After a high-severity burn on a site in this condition, revegetation may be necessary (depending on postfire survival of desirable species), and intensive monitoring for invasive plant establishment is necessary to detect and eradicate newly established invasives before they spread [32].

When prefire cover of hoary cress is moderate (20-79%) to high (80-100%), revegetation may be necessary after fire of any severity if cover of desired vegetation is less than about 30%. Intensive weed management is also recommended, especially after fires of moderate to high severity [32].

Fall dormant broadcast seeding into ash will cover and retain seeds. If there is insufficient ash, seedbed preparation may be necessary. A seed mix should contain quick-establishing grasses and forbs (exclude forbs if broadleaf herbicides are anticipated) that can effectively occupy available niches. Managers can enhance the success of revegetation (natural or artificial) by excluding livestock until vegetation is well established (at least 2 growing seasons) [32].