• 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:

Wyoming big sagebrush ignites readily and produces a very hot fire [98,101,135]. Fire kills it [27,29,32,43,53,101,105,137,152].

PLANT RESPONSE TO FIRE:

Wyoming big sagebrush is not an initial colonizer. It may be slow to establish on a burn, especially when compared to other big sagebrush subspecies, because of the relatively drier sites it normally occupies [21,24,27]. Additionally, the VAM upon which Wyoming big sagebrush depend for healthy growth are harmed by fire, and may take several years after fire to recover [71,109]. Wicklow-Howard [148] found that on the Snake River Birds of Prey Area of southern Idaho, fewer of the VAM associated with Wyoming big sagebrush were killed by low-intensity fire than by moderate-intensity fire.

In southwestern Montana, Wyoming big sagebrush seedlings were still absent from a prescribed burn site 6 years after fire [137]. In the Missouri River Breaks of central Montana, wildfire removed the Wyoming big sagebrush from a Wyoming big sagebrush/bluebunch wheatgrass community, and it was not found during vegetation sampling performed at postfire year 14. Total coverage at that time was 50% grasses, with the remainder consisting of forbs and bare ground. Shrub cover was "minimal" [43].

Wyoming big sagebrush frequency declined significantly after late-summer (Sept. 21, 1983) prescribed fire near Elko, Nevada. Fire and Wyoming big sagebrush frequency data were as follows [29]:

Fire Parameters
temperature               70oF            
relative humidity         15%                     
windspeed                 1-3 miles/h         
fuel moisture             3%                         
live sagebrush moisture   93%             
soil moisture             8%                          

Wyoming big sagebrush Frequency (%)
Fire treatment              Unburned control
-----------------------     ----------------
year before fire     28     22
postfire year 1      2      18
postfire year 3      5      no data

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

Prescribed burning in Wyoming big sagebrush has been accomplished on patches as little as 0.3 acre (0.05 ha) [105] and as much as 14,500 acres (5800 ha). The 14,500-acre fire, on the Upper Snake River Plain of Idaho, burned about 57% of the area and reduced Wyoming big sagebrush and threetip sagebrush (Artemisia tripartita) cover from approximately 20 to 11% [53]. The small patchy fires, on the East Fork of the Salmon River in south-central Idaho, reduced Wyoming big sagebrush from a prefire frequency of 100% to and average of 40% in postfire year 1. Wyoming big sagebrush seedlings had not recolonized by postfire year 3 [105].

Wyoming big sagebrush may be less able to benefit from the increased nutrient load on recently burned sites than associated grasses. In a greenhouse study, cheatgrass and bottlebrush squirreltail seedlings showed a significant increase (p = 0.05) in total biomass when grown on soil collected from a new burn compared to growth on soil from an adjacent unburned site. Biomass of Wyoming big sagebrush seedlings was slightly (but not significantly) less when grown on soil from the burn compared to biomass when grown on soil from the unburned site [17].

FIRE MANAGEMENT CONSIDERATIONS:

Burning is the oldest method of big sagebrush control in the West, and it is still effective and relatively inexpensive. Sites generally need reburning every 15 to 30 years in order to control big sagebrush [85,112]. Composition of herbaceous vegetation is largely unaffected by burning, whereas herbicide control may reduce herb production by 45 to 65% [4,85]. Unlike burning in other big sagebrush types, burning in Wyoming big sagebrush usually does not usually increase forb density or diversity [53,58,151].

Fuels and Fire Guidelines: Prescribed burning may be difficult on some sites due to low fuel loads, but under the right combination of wind and high temperature, sparsely fueled Wyoming big sagebrush communities can burn [150]. On Wyoming big sagebrush rangeland in southern Idaho, prescribed burning in April, when fine fuels left over from the prior growing season carry a relatively "cool" fire, has been successful. Autenhreith and others [4] recommend burning in strips of not more than 50 yards (45 m) wide and 100 yards (90 m) in length in order to preserve some big sagebrush for wildlife. They do not recommend winter burning in sage grouse habitat, as winter availability of sagebrush is crucial to the birds.

Frandsen [55] developed a model estimating fuel load of Wyoming big sagebrush for fire behavior predictions. Britton and others [24] present a big sagebrush canopy cover-herbaceous fuel load curve representing proportions of big sagebrush cover and herbaceous fuels needed to produce a successful burn. Brown [25] has developed a model for fuel and fire behavior prediction in Wyoming and mountain big sagebrush based on sampling in Montana and Idaho.

General guidelines for burning big sagebrush types: For stand-replacing fire, Beardall and Sylvester [9] recommend fine fuels of 600 to 700 lbs/acre (674-786 kg/ha). Big sagebrush should be at least 1/3rd of total plant cover [104].

Success of winter broadcast burning (n=5 fires) in big sagebrush communities in southern Idaho was follows [101]:

Conditions                    Fire carried     Fire did not carry
Canopy cover (%)        72.1                 60.0
Density (plants/ha)       114,296           121,020
Biomass (g/plant)         1,634               1,496
Shrub height (cm)         103.8               108.3
Basal diameter (cm)     3.8                3.2
Distance between  
plants (cm)                 15.4                 37.5
Temperature (^oC)      9.0               9.0
Relative humidity (%) 49.3                46.6
Windspeed (km/h)     8.3                 6.6
Fuel moisture (%)     37.0                38.0

Postfire Management: Native species that have been successfully seeded in after fire on degraded Wyoming big sagebrush rangelands include bluebunch wheatgrass, fourwing saltbush (Atriplex canescens), scarlet globemallow (Sphaeralcea coccinea), and balsamroot (Balsamorhiza spp.). Russian wildrye (Psathyrostachys juncea), crested, and desert wheatgrasses have also been successfully seeded in [80,150]. Reoccupation of Wyoming big sagebrush is slower on sites seeded to crested or desert wheatgrass than on sites seeded to native grasses [112].

Deferment of grazing is recommended for 1 to 2 years after burning Wyoming big sagebrush/grass types to allow native grasses to recover [69,104,152].

Cheatgrass: While burning will remove Wyoming big sagebrush, it will not restore perennial grasses in areas where cheatgrass has become dominant [27]. Arid regions may be most susceptible to cheatgrass invasion. Hironaka and others [67] reported that in the Wyoming big sagebrush/bluebunch wheatgrass type, cheatgrass has been less invasive in eastern Idaho than in the drier regions of southern Idaho, eastern Oregon, and northern Nevada and Utah. To reduce cheatgrass invasion after burning, they recommend a gradual reduction in shrub cover so that bluebunch wheatgrass and other bunchgrasses regain vigor and produce a continuous supply of seed.

In general, burning in cheatgrass-infested big sagebrush types is not recommended if cheatgrass cover exceeds 50% or if cover of fire-resistant native grasses is less than 20%. Cheatgrass is more likely to invade after fire if the dominant native grass is not a fire-resistant species (for example, Thurber needlegrass or Idaho fescue) or if native grasses were in poor condition prior to fire [104,146]. Artificial seeding with native grasses is recommended after fire if cheatgrass was a major component of the prefire community or if it was a minor component and native grasses were in poor condition [146,155].

Communities in good condition may at least partially recover from temporary postfire increases in cheatgrass, especially when fire is followed by favorable precipitation. For example, a summer wildfire in central Utah occurred in a Wyoming big sagebrush/bluebunch wheatgrass community in good condition shortly after vegetation sampling was performed for a different study. Precipitation was above average in postfire years 1 and 2. Further vegetation sampling was done in postfire years 1 and 2 for a fire effects study. Wyoming big sagebrush was removed by fire. Bluebunch wheatgrass recovered quickly, almost equaling prefire coverage by postfire year 2. Cheatgrass coverage increased greatly on both burned and unburned control plots, with coverage on burned plots over twice that on unburned plots. The authors concluded that on this rangeland, postfire seeding would not have increased abundance of bluebunch wheatgrass and other native grasses relative to cheatgrass. Pre- and postfire coverages of Wyoming big sagebrush, bluebunch wheatgrass, and cheatgrass are given below. Data are means and 1 standard error [146].

            ----------------Burned----------------   
            Prefire    Postfire yr 1  Postfire yr 2       
sagebrush   6.5(1.3)   0              0           
wheatgrass  12.9(5.0)  6.5(1.7)       12.3(4.9)    
cheatgrass  6.6(1.5)   34.8(12.1)     56.8(5.4)        

            ------------Unburned Control----------
            Prefire    Postfire yr 1  Postfire yr 2
sagebrush   2.3(1.2)   3.7(1.2)       5.7(4.0)
wheatgrass  13.3(0.5)  16.0(1.)       13.3(5.9)
cheatgrass  6.8(1.1)   11.0(1.1)      24.0(8.2)

Related categories for SPECIES: Artemisia tridentata ssp. wyomingensis | Wyoming Big Sagebrush