• IMMEDIATE FIRE EFFECT ON PLANT
• DISCUSSION AND QUALIFICATION OF FIRE EFFECT
• PLANT RESPONSE TO FIRE
• DISCUSSION AND QUALIFICATION OF PLANT RESPONSE
• FIRE MANAGEMENT CONSIDERATIONS

IMMEDIATE FIRE EFFECT ON PLANT:

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:

PLANT RESPONSE TO FIRE:

Harrod and others [40] suggested that fire might reduce the ability of diffuse knapweed to produce seed in the current year, since many bolting stems appeared to be reverted back to a rosette stage after fire. This might allow grasses (which appear to be stimulated by fire) to gain a competitive advantage [40]. A single fire in northern Washington, however, increased the cover and density of both diffuse and spotted knapweed without enhancing desired species [97,99]. Roche and Roche [85] suggest that diffuse knapweed can resprout even after intense wildfire at bolting or flowering stages, although they provide no experimental evidence for this assertion. They further suggest that fire may damage desirable residual species while stimulating knapweed (Centaurea spp.) populations.

Reproduction by abundant seed gives diffuse knapweed an advantage in fire-prone environments. Spotted knapweed seeds demonstrate some resistance to high temperatures [1]. This may also be true for diffuse knapweed. Diffuse knapweed seeds may persist in the soil and germinate after fire. Where diffuse knapweed plants are left standing, seeds may be present above ground as well. This "aerial seed bank" may or may not be an advantage after fire, depending upon the characteristics of the fire. Renney and Hughes [84] suggest that burning shows some promise for diffuse knapweed control, especially since the viability of seeds held above ground in the seedhead is considerably reduced by heat, though they give no reference to experimental evidence for this conclusion. Watson [129] notes that seed collected from diffuse knapweed plants in an area burned by a mid-August wildfire was not viable.

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

FIRE MANAGEMENT CONSIDERATIONS:

Others suggest that burning may be an effective means of controlling diffuse knapweed in areas where seasonal or occasional fires are part of the natural ecosystem [16]. Watson and Renney [128] cite Popova (1960) as reporting that fire provides effective control of diffuse knapweed, with vigorous grass regrowth after burning in the Crimea. Additionally, repeated burning of prairie and dune sites in Michigan has proven to encourage growth of native vegetation and reduce spotted knapweed density [61]. Repeated burns may also prevent new seed production and eventually deplete the seed bank.

Postfire colonization potential: Diffuse knapweed has the potential to invade an area following fire. Fire provides an ideal seedbed by removing shade and exposing mineral soil. Therefore, if diffuse knapweed was present on or near the site prior to the fire, there is potential for its establishment. It is a good idea to survey the surrounding area for diffuse knapweed skeletons that may contain seed that could be dispersed through tumbleweed action. Diffuse knapweed is 1 of the introduced species mentioned as "taking over large tracts of logged, burned, or otherwise disturbed lands in British Columbia" [119].

The USDA Forest Service's "Guide to Noxious Weed Prevention Practices" [120] provides several fire management considerations for weed prevention in general that apply to diffuse knapweed. 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.

When planning a prescribed burn, inventory the project area and evaluate the cover and phenology of any diffuse knapweed present on or adjacent to the site, and avoid ignition and burning in areas at high risk for diffuse knapweed establishment or spread due to fire effects. Avoid creating soil conditions that promote weed germination and establishment. Discuss weed status and risks in burn rehabilitation plans.

Related categories for SPECIES: Centaurea diffusa | Diffuse Knapweed