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

IMMEDIATE FIRE EFFECT ON PLANT:

Big sagebrush is readily killed when aboveground plant parts are charred by fire [55]. If sagebrush foliage is exposed to temperatures above 195 degrees Fahrenheit (90^oC) for longer than 30 seconds, the plant dies [18]. In some areas, scattered unburned basin big sagebrush may survive, particularly where the soil is thin and rocky and where sparse herbaceous biomass limits the fire's spread [22].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:

Site productivity affects the ease with which big sagebrush communities will burn. Highly productive sites have greater plant density and more biomass which, in turn, are likely to provide more fuel to carry a fire.

Among the three major subspecies of big sagebrush, basin big sagebrush is considered intermediate in flammability. Mountain big sagebrush is most flammable, and Wyoming big sagebrush is least flammable [18].

PLANT RESPONSE TO FIRE:

Basin big sagebrush does not resprout after fire. Because of the time needed to produce seed, it is eliminated by frequent fires [21]. Basin big sagebrush reinvades a site primarily by off-site seed or seed from plants that survive in unburned patches. The rate of stand recovery depends on the season of burn, as season affects the availability of seed, postfire precipitation patterns, and the amount of interference offered by other regenerating plant species [18,30,124]. Establishment may be delayed until favorable moisture conditions occur [55].

Sagebrush seed is not disseminated for great distances so off-site sources are probably less important than on-site seed [43]. Shrubs surviving within the perimeter of a disturbed area provide a more important seed source than those on the perimeter [60]. The vast majority of big sagebrush seed produced during fall is gone by spring and very few seeds persist. Seed of some subspecies of big sagebrush may persist in a seed bank [72]. However, unlike many of the other subspecies, emergence of basin big sagebrush seed appears to be reduced by exposure to heat [23].

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

In Wyoming, where big sagebrush has been removed by chemical means, it regained its pretreatment cover in 17 years on stands where grazing was not controlled [61].

FIRE MANAGEMENT CONSIDERATIONS:

Sapsis [90] reports "investigations of prescribed burning as an ecological agent in basin big sagebrush dominated systems are lacking." However, a number of studies have focused on big sagebrush in general. Fire as a management tool has primarily been used to reduce big sagebrush. Where sagebrush reduction is a desired goal, prescribed burns in basin big sagebrush communities tend to be more successful than those in Wyoming big sagebrush, but less successful than those in mountain big sagebrush [19]. In Nevada where "range improvements" were desired, best results have been obtained after spring or late fall burns [5]. Summer burns in big sagebrush communities can leave the soil bare and subject to erosion. Favorable results are often obtained after fire in basin big sagebrush is an adequate understory is present prior to the burn [21].

Britton and others [19] report that as a general rule for a successful prescribed burn in big sagebrush at least 20% canopy cover of big sagebrush should be present, with at least 200 to 300 lb. per acre of herbaceous fuel. Beardall and Sylvester [5] suggest that for prescribed burns to succeed in big sagebrush communities in Nevada, the following conditions should be met: 600 to 700 lb./acre fine fuels; ignition should occur when relative humidity is 60% or less; soil must be wet, winds must be 8 miles per hour or greater; and burning should stop when spring growth of grasses reaches 2 inches. Big sagebrush should be at least 1/3rd of total plant cover [84]. The presence of weedy annuals may prevent establishment of desirable perennial grasses and can increase future fire hazards [20].

Success of winter broadcast burning (n=5) in big sagebrush communities in southern Idaho was as follows [78]:

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 (C)       9.0             9.0
Relative humidity (%) 49.3            46.6
Windspeed (km/h)      8.3             6.6
Fuel moisture (%)     37.0            38.0

Removing sagebrush by fire or chemical treatment may release desirable undergrowth if the site is in good condition. However, many basin big sagebrush sites today are limited in extent and do not have a high density of undergrowth to respond if the overstory is reduced. Animals are attracted to burned areas and may damage low-vigor plants if the animals concentrate in a small area. In some cases, prescribed fire in big sagebrush communities can create mosaics that are beneficial to wildlife [21].

Several studies have examined big sagebrush as a fuel. Average fuel load for basin big sagebrush is reported as follows [38]:

 
                     fuel load (kg/m2)
                     leaves   1 hr  10 hr  100 hr
basin big sagebrush  0.084    0.12  0.14   0.16     

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