• 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:

Mountain big sagebrush is highly susceptible to injury from fire. Plants are readily killed in all seasons, even by light severity fires [10,11,93].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:

No entry

PLANT RESPONSE TO FIRE:

Mountain big sagebrush plants top-killed by fire will not resprout [10,94]. Regeneration of mountain big sagebrush is from on-site or off-site seed. Depending on circumstances of the environment and seed source, mountain big sagebrush seeds may sprout profusely the spring after burning [27,103], or very sparsely [10,50,67]. These relationships are not well understood. Seedlings can grow rapidly and may reach reproductive maturity within 3 to 5 years [18]. Where mountain big sagebrush is dominant and persistent (climax or long-term seral), fire often reduces its dominance and alters species composition for the first few years. If exotic species have not altered successional pathways, vegetation eventually reverts to its previous composition [1,11,17,88,94].

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

Early Response - Mountain big sagebrush regeneration from seed varies in the 1st postfire year. A high elevation (7,200 feet (2,200 m)) shrub-grass community in western Wyoming was burned in September, 1983, and evaluated 1 year later. The fire completely eliminated mountain big sagebrush cover on 50% of the site. Mean density of mountain big sagebrush seedlings on burned, east-slope plots was as high as 1,090 per acre (2,691/ha), compared to 97 seedlings per acre (240/ha) on paired, unburned plots. Measurements on west-facing slopes were impaired by sampling difficulties [103].

In contrast to the Wyoming study, Young and Evans [151] found no germination stimulating effect following wildfire in a stand of mountain big sagebrush in western Nevada. The August fire consumed all standing woody material. In September of the same year they collected 1000 soil samples from the interior of the burn and subjected them to a greenhouse germination test. No sagebrush germinated in any samples. At the end of the growing season following the fire, mountain big sagebrush seedlings in the field site were detected at a density of 4/acre (10/ha.).

Also in contrast to the Wyoming study, managers in California burned a high elevation meadow (8,202 feet (2,500 m)) to reduce shrub encroachment. The following spring only trace numbers of new mountain big sagebrush seedlings were present. Mature shrub species were replaced by an early seral grass-forb community [50].

Response Over Time - Mountain big sagebrush may return to preburn density and cover within 15-20 years following fire, but establishment after severe fires may proceed more slowly [18]. On some sites mountain big sagebrush may recover slowly in the first years after fire. A southern Idaho sagebrush steppe site experimentally burned in August, 1936, was studied in subsequent decades [10,11,52]. The site was identified as a mountain big sagebrush habitat type, free of cheatgrass. The burned area was protected from grazing for a year following burning and grazed conservatively thereafter. To the advantage of desirable forage species, big sagebrush was practically eliminated, and reestablishment was slow during the first 9 years, but during the next 18 years big sagebrush cover increased greatly. Researchers' summary statements are excerpted here:

"Almost all important species of shrubs, grasses and forbs decreased in yield from 1948 to 1966 as the big sagebrush recovered its dominance after the burn...From observation, sagebrush in the vaseyana habitat type sometimes reinvades an area immediately following a burn; so control benefits do not always exist as long as they have on the 1936 burn. The length of time between control measures depends on grazing practices and the undefined weather variables that favor sagebrush seedling survival and establishment" [52].

Fraas and others [40] quantified the effects of prescribed fire on vegetation 8 years after burning in an antelope bitterbrush-mountain big sagebrush-bluebunch wheatgrass community in Montana. Mountain big sagebrush canopy cover and stem density in the burned plot remained low. Both parameters were significantly greater (P < 0.01) in the unburned plot, indicating a high fire-induced mortality coupled with lack of postburn seedling establishment.

FIRE MANAGEMENT CONSIDERATIONS:

Prescribed fire can be an economically and ecologically sound method for meeting management objectives [11,17,18]. Low fine fuel loading is a common problem. Burning sagebrush shrubland may not result in intended increases in grass and forb production, but may instead result in unplanned and detrimental shifts in plant community composition. Concentrated large herbivore use should be expected and included in the planning process [17,40].

Fire does not result in substantial increases of herbaceous perennials on sites dominated by exotic annuals. The fuel load may be sufficient in such sites to sustain a fire, but the presence of annuals may prevent the establishment of perennial species. Annuals often increase following a fire, creating conditions where wildfires occur more frequently. Frequent fires prevent the reestablishment of shrubs and may reduce the existing perennial herb populations. Increasing the interval between fires allows time for perennials to establish, breaking the weed-perpetuating fire cycle [17].

In an Idaho prescribed burn conducted in winter, individual mountain and Wyoming big sagebrush plants burned easily when canopy fuel moisture was below 37%, air temperature was above freezing, relative humidity was below 45%, and skies were clear. In that study, only small areas burned because the canopy was not dense enough to carry fire. Where canopy cover was at least 50%, distance between plants was not greater than 50% of their average height, and effective wind speed was above 5 mph (8 km/hr), the fire carried successfully [93]. Britton and others [14] developed a big sagebrush canopy cover-herbaceous fuel load curve representing proportions of big sagebrush cover and herbaceous fuels needed to produce a successful burn.

Several monographs provide detailed information about managing fire in sagebrush. One of the monographs [15] provides information specific to mountain big sagebrush. The other 3 discuss mountain big sagebrush, but recommendations are general in scope, extending to other species of sagebrush.

Managing Intermountain rangelands--sagebrush-grass ranges [11]
Fire response of shrubs of dry forest habitat types in Montana and Idaho [96]
Guidelines for prescribed burning in sagebrush-grass rangelands in the northern Great Basin [18]
Fuel and fire behavior prediction in big sagebrush [15]

Please refer to other FEIS reports for discussions of fire management considerations for important co-occurring species, including Wyoming and basin big sagebrush, bitterbrush spp., bunchgrasses, and junipers. Related fire case studies for Wyoming big sagebrush and basin big sagebrush are available in the FEIS reports for those species.

Related categories for SPECIES: Artemisia tridentata spp. vaseyana | Mountain Big Sagebrush