• FIRE ECOLOGY OR ADAPTATIONS
• POSTFIRE REGENERATION STRATEGY

FIRE ECOLOGY OR ADAPTATIONS:

Fire regimes: Diffuse knapweed occurs primarily in bunchgrass and open ponderosa pine forest community types in the northwestern United States and southern British Columbia. The historical fire regimes of these communities were relatively frequent, low-severity surface fires. Diffuse knapweed did not occur in these communities at the time in which these fire regimes were functioning, but has established since fire exclusion began. It is unclear how this type of fire regime might affect diffuse knapweed populations. It is also unclear how the presence of diffuse knapweed might affect these fire regimes, though it has been observed that closely related species, such as spotted knapweed (see the spotted knapweed summary in FEIS), do not carry fire as readily as grasses [61,134]. If this holds true for diffuse knapweed, dense infestations may change the fire regime by changing the fuel characteristics and reducing the fire return interval at a given site.

The following table provides fire regime intervals for some of the communities in which diffuse knapweed may be found.

Community or Ecosystem	Dominant Species	Fire Return Interval Range (years)
grand fir	Abies grandis	35-200 [7]
sagebrush steppe	Artemisia tridentata/Pseudoroegneria spicata	20-70 [75]
basin big sagebrush	A. t. var. tridentata	12-43 [92]
mountain big sagebrush	A. t. var. vaseyana	15-40 [8,12,62]
Wyoming big sagebrush	A. t. var. wyomingensis	10-70 (40**) [124,135]
desert grasslands	Bouteloua eriopoda and/or Pleuraphis mutica	5-100
plains grasslands	Bouteloua spp.	< 35
blue grama-needle-and-thread grass-western wheatgrass	B. gracilis-Hesperostipa comata-Pascopyrum smithii	< 35
grama-galleta steppe	B. g.-Pleuraphis jamesii	< 35 to < 100
cheatgrass	Bromus tectorum	< 10
western juniper	Juniperus occidentalis	20-70
Rocky Mountain juniper	J. scopulorum	< 35 [75]
Engelmann spruce-subalpine fir	Picea engelmannii-Abies lasiocarpa	35 to > 200 [7]
pinyon-juniper	Pinus-Juniperus spp.	< 35 [75]
Rocky Mountain lodgepole pine*	P. contorta var. latifolia	25-300+ [6,7,89]
Colorado pinyon	P. edulis	10-49 [75]
Jeffrey pine	P. jeffreyi	5-30
western white pine*	P. monticola	50-200
Pacific ponderosa pine*	P. ponderosa var. ponderosa	1-47
interior ponderosa pine*	P. p. var. scopulorum	2-10 [7]
mountain grasslands	Pseudoroegneria spicata	3-40 (10**) [6,7]
Rocky Mountain Douglas-fir*	Pseudotsuga menziesii var. glauca	25-100
California mixed evergreen	P. m. var. m.-Lithocarpus densiflorus-Arbutus menziesii	< 35
western redcedar-western hemlock	Thuja plicata-Tsuga heterophylla	> 200
mountain hemlock*	T. mertensiana	35 to > 200 [7]

*fire return interval varies widely; trends in variation are noted in the species summary
**mean

POSTFIRE REGENERATION STRATEGY [109]:

Related categories for SPECIES: Centaurea diffusa | Diffuse Knapweed