More info for the terms: competition, density, fire exclusion, fire regime, fire severity, frequency, fuel, root crown, severity, shrub, xeric
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