• 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:

Antelope bitterbrush is very susceptible to fire kill. It is considered a weak sprouter and is often killed by summer or fall fire [27,35,51,52,173,176]. Antelope bitterbrush in some areas may sprout after light-severity spring fire [1,29,35,44,20]. Scholten [201] reports 70 and 91% of plants killed, respectively, in two separate Idaho wildfires, with 26% sprouting after the first fire and only 2% after the second fire.

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:

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PLANT RESPONSE TO FIRE:

Reports conflict on antelope bitterbrush's ability to sprout in response to fire [13,14,28,36,37,50,53,60,111,118,125,139,169,200,208,227,242]. Geographic and ecotypic variation is considerable. Sprouting is common in eastern Idaho, occasional in Utah, and rare in Oregon, California, and Nevada [244]. In an eastern Idaho study, 50% of burned plants and 72% of top-clipped plants sprouted. However, 33 and 21%, respectively, of those sprouts died within a few years, so sprouting may not result in good long-term survivorship rates [29]. Postfire mortality is higher in central and southeastern Idaho than in southwestern Idaho and Nevada [184]. Britton and Wright [38] claim antelope bitterbrush above 7,500 feet (2,250 m) elevation is resistant to fire due to low fuels loads.

Sprouting ability is affected by fire severity and season; plant genetics, carbohydrate stores, and age; competition; soil moisture and type; and air temperature [51,154,191]. Decumbent plants seem to sprout better [14,35,37,44,52] than columnar forms [18,96]. Columnar forms sprout either from the root crown and/or from aboveground calluses of meristematic tissue, whereas decumbent forms sprout from the root crown and from points where branches layer [44]. Columnar types sprout best when fire severity is low and postfire soil moisture is high [19].

In Idaho and Montana, Bunting and others [44] found decumbent antelope bitterbrush sprouted more frequently than columnar forms. Sprouting frequencies on spring- and fall-burned sites averaged 55 and 42%, respectively. Greatest sprouting potential was found in plants in mountain shrub and conifer (Douglas-fir or ponderosa pine) communities (60% for shrub and 49% for conifer, respectively), where plants were mostly decumbent. Decumbent antelope bitterbrush also dominated mountain big sagebrush communities, but sprouting was lower in that group, possibly due to more xeric conditions. Predominantly columnar antelope bitterbrush in basin big sagebrush and juniper (western or Utah) communities sprouted the least. Seedling success paralleled sprouting success, except that average density of antelope bitterbrush seedlings in the conifer type was much higher than average density of antelope bitterbrush sprouts. Lowest seedling density was found in the juniper communities, possibly due to seed predation by rodents.

Season of burning and environmental conditions impact antelope bitterbrush ability to survive fire and sprout. Driscoll [75] measured postfire sprouting ability of antelope bitterbrush in several Oregon burns. Sprouting success ranged from 1 to 80%. Sprouting success was less after a July fire than after a September fire. In Nevada, an August burn defoliated plants, but due to high moisture content of stemwood, plant crowns did not burn. At the same site in October, a repeat fire consumed stemwood up to 0.25 inch (0.6 cm) in diameter and all plants were killed [187,190]. Murray [170] found that postfire yields of antelope bitterbrush were less after a spring fire than a fall fire, and speculated that sprouting after a spring fire would be greater than after summer fire. When soils are moist at the time of the burn, the root crown incurs less damage. Additionally, sprouting is more likely if fires are followed by rain [36,176,242]. Clark and others [52] found mortality was higher on watered fall-burned plots than on spring-burned plots.

More plants sprouted following a light August burn than a light July burn in southern Idaho, which the authors attributed to greater carbohydrate storage in the roots in August. Most moderately and heavily burned plants were killed [225].

High fuel consumption increases antelope bitterbrush mortality and therefore favors seedling establishment [36,44]. A low intensity, high frequency fire regime favors sprouting, whereas higher intensity, less frequent fires favors seedling regeneration [78]. Driver [77], who found high sprouting rates on his study plots in Washington, suggests that successfully sprouting columnar ecotypes may have been selected on habitats with high fire frequencies. According to Agee [1], nonsprouting antelope bitterbrush is now widespread in ponderosa pine ecosystems due to fire exclusion.

Soil texture affects the thermal transfer properties of soil and therefore the ability of antelope bitterbrush to sprout from undamaged underground buds [177]. Fire is more damaging to antelope bitterbrush on fine-textured calcareous soils than on coarse-textured, well-drained soils [37]. In several Oregon burns, Driscoll [75] found plants on northerly slopes with loose, coarse-textured, nonstony soils without pumice sprout best. Plants on fine-textured, stony soil sprouted poorly.

Cheatgrass invasion has increased the amount of fine fuels in big sagebrush-antelope bitterbrush grasslands, and antelope bitterbrush is not adapted to the more frequent, high severity fires resulting from increased fuel loads. Cheatgrass may outcompete antelope bitterbrush after fire [227]. Murray [170] found prescribed burned plots in Idaho had less than half the average yields of antelope bitterbrush compared to unburned plots. He concludes that vigorous competition from grasses may have decreased seedling establishment of antelope bitterbrush.

Antelope bitterbrush seeds germinate and grow on mineral soil exposed by fire [35,108]. In the Black Hills of South Dakota, antelope bitterbrush survival was measured 10 years after planting on a burned site and in an unburned, open stand of ponderosa pine [74]. Establishment from seed and containerized seedlings was higher on burned plots:

Percent survival on:     Seeded      Planted from containerized seedlings
Burned                   22.0        20.0
Unburned                  8.3        11.0

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

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FIRE MANAGEMENT CONSIDERATIONS:

In ponderosa pine/antelope bitterbrush communities, antelope bitterbrush is more prevalent in communities where fire has been suppressed for decades than in communities that have occasionally burned [191]. However, when fire is completely excluded from ponderosa pine for a long time, antelope bitterbrush becomes decadent [10,144]. Its density declines because dying plants are not replaced [43,44,200]. Frequent Indian-set fires probably favored grasses over antelope bitterbrush on most sites. On dry or stony sites, however, fires would not have carried as well, and antelope bitterbrush probably dominated such sites [8]. According to Driver and Winston [78], frequent, low-intensity wildfire in ponderosa pine communities of north-central Washington encouraged sprouting and maintained antelope bitterbrush as a community dominant.

Following prescribed burns to restore pre-settlement condition of ponderosa pine at Lick Creek in western Montana, antelope bitterbrush mortality was 25% during the harvest phase of treatment and increased to 40% after the prescribed burning that followed. Plants surviving the treatments had greater live biomass and palatability than unburned plants [9]. Also in western Montana, burn treatments in a ponderosa pine community resulted in antelope bitterbrush mortality of 72%. Following spring fire, only two antelope bitterbrush seedlings were found on study plots. Browsing was heavy on these sites and may have reduced available seeds. Twelve percent of burned plants sprouted the first year after fire. Annual growth rate of antelope bitterbrush was greater on burned plots compared to unburned plots for the first 2 years after fire [18].

Blaisdell [28] found some antelope bitterbrush sprouting following prescribed burns in Idaho, but total production of antelope bitterbrush was far below prefire levels. Sprouting bitterbrush dominated big sagebrush 9 years after fire, since it outgrew big sagebrush regeneration from seed. Twelve years after the burn, antelope bitterbrush production was still lower on burned plots compared to unburned plots.

In western juniper-antelope bitterbrush associations, antelope bitterbrush appears more vigorous where fire has killed junipers [44,191]. Antelope bitterbrush has a low (6%) sprouting success rate, low seedling establishment, and short lifespan in western juniper communities [42]. In these communities, regular but not too frequent fires are required to clear out older, decadent antelope bitterbrush and western juniper; to establish new antelope bitterbrush seedlings; and/or to encourage sprouting [42,108].

In dry Douglas-fir habitat types, antelope bitterbrush requires fire to reduce competition from conifer seedlings [35]. Prescribed fire in mesic forest communities maintains a subclimax community type and therefore encourages antelope bitterbrush establishment [44].

Antelope bitterbrush recovery from fire often takes too long for fire to be a useful tool in managing antelope bitterbrush [15,49,170,181]. Gruell [108] claims a fire frequency of 5 to 20 years would result in sparse distribution and low density of antelope bitterbrush. Driver and Winston [78] found fire recovery in the Craters of the Moon National Monument to take 15 to 20 years. Barrington and others [14] claim antelope bitterbrush density remains lower than prefire density for over 30 years in ponderosa pine communities on the eastern slope of the Cascade Range in Washington. Wright [242] reported that antelope bitterbrush was not fully recovered 27 years after a fire in a ponderosa pine community on the Warm Springs Reservation, Oregon. In contrast, Davis and others [68] found that antelope bitterbrush established quickly in a burned ponderosa pine/antelope bitterbrush habitat type on the Lolo National Forest, Montana.

Rodent-cached seeds are an important source of antelope bitterbrush regeneration after fire [44,225]. Rodent caches near or in a burned area may suffer less from seed predation following a fire because of reduced cover for rodents [56].

In British Columbia, Demarchi and Lofts [73] evaluated the nutritional content of antelope bitterbrush following fire. They concluded that there was a 3-year increase in nitrogen; a 2-year increase in calcium; a 1-year increase in phosphorus, potassium, and zinc; a decrease in copper; and no change in manganese.

Related categories for SPECIES: Purshia tridentata | Antelope Bitterbrush