SPECIES: Artemisia cana
Artemisia cana spp. bolanderi (Gray) G.H. Ward [12,75,92,117]
Bolander silver sagebrush
Artemisia cana ssp. cana plains silver sagebrush
Artemisia cana ssp. viscidula (Osterh.) Beetle [12,92,117] mountain silver sagebrush
Within this summary, "silver sagebrush" refers to the species as a whole. Infrataxa are referred to by the 3 common names listed above. Not all authorities recognize infrataxa within silver sagebrush [38,190].
Hybrids: The sagebrush genus is evolving rapidly, and hybridization is an important factor in its evolution [96,97,113,116,188]. Silver sagebrush readily hybridizes with other woody sagebrush species (Artemisia subgenus Tridentatae) including threetip sagebrush (A. tripartita), big sagebrush (A. tridentata) [117,188,190,191], and low sagebrush (A. arbuscula) [12,117,190]. Silver sagebrush × mountain big sagebrush (A. t. ssp. vaseyana) and silver sagebrush × Lahontan sagebrush (A. a. ssp. longicaulis) hybrids form stable, self-reproducing populations that some authorities classify as distinct taxonomic entities (snowfield sagebrush (A. spiciformis Osterh.) and coaltown sagebrush (A. argilosa Beetle), respectively) [12,114,116,118,163]. Silver sagebrush infrataxa also hybridize with each other, although Bolander silver sagebrush is geographically isolated from the other 2 subspecies and does not do so naturally [12,38,114]. Sagebrush hybrids are important ecologically as well as evolutionarily, often tolerating a broader range of ecological conditions than either parent . Fire effects to silver sagebrush hybrids are discussed in that section of this review.LIFE FORM:
The Nature Conservancy ranks silver sagebrush communities of the Great Plains as regionally endangered .
Subspecies: Bolander silver sagebrush occurs from north-central Oregon, where it occurs in montane meadows of the Ochoco and Blue mountains and on the eastern slope of the Cascade Range , south through mountainous regions and the eastern edge of the Great Basin to Inyo and Tulare counties, California, and east to Humboldt and Washoe counties, Nevada. Bolander silver sagebrush populations are disjunct from the other 2 subspecies [30,71,92,93,112,126].
Plains silver sagebrush occurs from southern British Columbia east to southwestern Manitoba and south to western Nebraska, eastern Colorado, central Wyoming, and south-central Montana [71,92,190]. Most common east of the Continental Divide, it is widely distributed in the northern Great Plains. Common in Saskatchewan, it becomes increasingly sparse to the south except along watercourses and bottomlands, where it may be locally abundant [90,112]. Distributions of plains and mountain silver sagebrush overlap in eastern Idaho, western Montana, across Wyoming, and in north-central Colorado. Outlying populations occur in west-central Colorado and the eastern Dakotas .
Mountain silver sagebrush is most common west of the Continental Divide. It is distributed from central Idaho and western Montana east to central Colorado, south to northeastern New Mexico and north-central Arizona, and west to central Nevada and eastern Oregon [71,92,112,126,190].ECOSYSTEMS :
Bolander silver sagebrush: There are few descriptions of Bolander silver sagebrush communities in the literature. Bolander silver sagebrush types on the Toiyabe National Forest of west-central Nevada and east-central California are codominated by Douglas' sedge (Carex douglasii) and/or Baltic rush (Juncus balticus) . Descriptions of Bolander silver sagebrush communities in California are particularly sparse, although a community codominated by mat muhly (Muhlenbergia richardsonis) has been documented in Lassen County . In nearby Plumas County, Bolander silver sagebrush co-occurs with mountain big sagebrush, Nebraska sedge (Carex nebrascensis), and tufted hairgrass (Deschampsia cespitosa) . In central Oregon, Bolander silver sagebrush/mat muhly communities occur on seasonal ponds, expanding and contracting as climate drives water levels. Big sagebrush, Sierra lodgepole pine (Pinus contorta var. murrayana), and quaking aspen (Populus tremuloides) border and may invade the community . In meadows of the Ochoco and Blue mountains, Bolander silver sagebrush often codominates with big sagebrush. Cusick's bluegrass usually dominates the understory; western yarrow (Achillea millefolium) is a constant associate . Bolander silver sagebrush is classified as a major indicator shrub for riparian zones in central Oregon .
Plains silver sagebrush: Species diversity tends to be low in plains silver sagebrush communities [78,127,177]. There are few other shrub species; the communities are mostly composed of silver sagebrush, bunchgrasses, and other graminoid associates. Forbs are typically infrequent [78,177] but occasionally important. Nelson  reported 20% forb cover in a plains silver sagebrush community in the Badlands of North Dakota. In Saskatchewan, plains silver sagebrush dominates sandhill prairies, and is common in the blue grama-green needlegrass (Bouteloua gracilis-Nassella viridula) association . Plains silver sagebrush dominates mesic mountain steppes in the northwestern portion of its range, often mixed with Wyoming big sagebrush (Artemisia tridentata var. wyomingensis). It merges with and associates in western wheatgrass-Idaho fescue (Pascopyrum smithii-Festuca idahoensis) and bluebunch wheatgrass (Pseudoroegneria spicata)-Idaho fescue mountain grasslands  and in black greasewood (Sarcobatus vermiculatus) communities . Plains silver sagebrush-dominated communities are often upslope from black cottonwood (Populus balsamifera ssp. trichocarpa) floodplains throughout the subspecies' distribution , and may codominate with willow (Salix) species on meandering drainages . Plains silver sagebrush sometimes dominates understories of open narrowleaf cottonwood (Populus angustifolia) stands . In the shortgrass prairie, plains silver sagebrush communities occur on or upslope from floodplains. Western wheatgrass is the most common codominant; other frequently codominating or associated grasses include green needlegrass, prairie sandreed (Calamovilfa longifolia), and blue grama [21,31,64,127,139,177]. Nelson  found blue grama codominated upland sites in the Badlands of North Dakota, while a plains silver sagebrush-western snowberry (Symphoricarpos occidentalis)/western wheatgrass formation occurred on bottomlands. Japanese brome (Bromus japonicus) and cheatgrass (B. tectorum) are fairly constant invaders in plains silver sagebrush communities . Thatcher  reported that plains silver sagebrush in eastern Wyoming was the only woody sagebrush species growing in association with basin wildrye.
Mountain silver sagebrush typically occurs in steppe vegetation. Species diversity and community production can be great in mountain silver sagebrush communities, which often border riparian zones and moist mountain meadows. The most common understory dominants in mountain silver sagebrush communities of Wyoming and Montana are tufted hairgrass and Idaho fescue . In the Gros Ventre area of Wyoming, high-elevation (> 7,000 ft. (2,000 m)) mountain silver sagebrush/Idaho fescue communities occur on moraines and landslides . Lower-elevation mountain silver sagebrush communities of Wyoming may be dominated by bluegrasses (Poa spp.) and bromes (Bromus spp.) . Shrubby cinquefoil (Dasiphora floribunda) is a common associate in mountain silver sagebrush communities, and usually the only other shrub present [20,143]. Shrubby cinquefoil is the only constant shrub associate in mountain silver sagebrush/Thurber fescue (F. thurberi) steppes of Colorado [176,178] and in mountain silver sagebrush/Idaho fescue steppes of central and eastern Idaho . Mountain silver sagebrush is locally dominant on mountain grassland clay soils of central Idaho, where it forms the "Camas Prairie" association with common camas (Camassia quamash) . Mountain silver sagebrush steppes in northern Utah and southern Idaho are codominated by tufted hairgrass, sheep fescue (F. ovina), and Kentucky bluegrass (P. pratensis). Mountain silver sagebrush/Kentucky bluegrass is probably a sere induced by heavy grazing [77,131]. Mountain silver sagebrush communities of Utah merge into open quaking aspen-Rocky Mountain Douglas-fir (Pseudotsuga menziesii var. glauca) parklands, where mountain silver sagebrush becomes an understory component . In eastern Oregon, Douglas' sedge and Cusick's bluegrass dominate mountain silver sagebrush understories. The mountain silver sagebrush community merges into upland mountain big sagebrush and streamside Kentucky bluegrass or sedge (Carex spp.) communities . In Nevada, mountain silver sagebrush steppes are codominated by slender wheatgrass (Elymus trachycaulus), Idaho fescue, beardless wildrye (Leymus triticoides), sedges, and Baltic rush [109,110].
Vegetation classifications describing silver sagebrush-dominated communities are listed below:
Silver sagebrush (covering both plains and mountain subspecies):
Bolander silver sagebrush:
Plains silver sagebrush:
Plant descriptions provided in this section present information relevant to fire ecology and are not meant as identification keys. Several florae [38,57,75,111,168,191] provide keys for identifying silver sagebrush.
Subspecies: Infrataxa are morphologically distinguished by plant height and relative leaf size, color, and hairiness of herbage [75,191]. Distinctions are not clear-cut, and there is considerable overlap in the subspecies' characteristics . Beetle  and Winward  provide keys for distinguishing silver sagebrush infrataxa. Gross differences in the subspecies' morphology follow.
Bolander silver sagebrush is a relatively low, thickly branched, round shrub . It is less than 3 feet (0.9 m) in height. Stems are woody at the base and bear relatively small (1- to 2-inch-long (3-5 cm)), narrow leaves. Fruits are less than 1.2 mm in length, and resinous . Bolander silver sagebrush is easily distinguished because of its restricted range .
Plains silver sagebrush is the tallest of the subspecies. It has an erect, freely branching growth form, typically reaching 3 to 4 feet (0.9-1 m) in height at maturity but sometimes as much as 4.9 to 6.6 feet (1.5-2 m) [57,90,168]. It has relatively larger, wider leaves (2-4 inches × 0.4 inch (4-9 × 1 cm)) with a denser, whiter covering of tomentum [38,89] compared to mountain silver sagebrush.
Mountain silver sagebrush is erect and freely branching in form . It grows from 0.3 to 1 foot (0.1-0.3 m) in height. It is differentiated from plains silver sagebrush by its relatively shorter stature, smaller (0.8-5.3 cm long), narrower, more strongly lobed leaves, and less silvery-white (often dark green) herbage [12,85,191].
Species' stand/age class structure: Silver sagebrush communities are usually structurally simple, consisting of silver sagebrush and an understory of graminoids. Silver sagebrush is often the only shrub [65,143,155,203], and forb cover is usually sparse [64,132]. Spacing varies from widely spaced silver sagebrush plants or clustered colonies to a close arrangement of shrubs [65,69,78,132,186]. Silver sagebrush in late succession can form nearly closed cover [69,198]. Hirsch  found a range of 674 to 4,519 silver sagebrush per hectare in a plains silver sagebrush-western wheatgrass community in southwestern North Dakota. Another western North Dakota study showed the few forbs in the community were most abundant near plains silver sagebrush, while bunchgrasses were more plentiful in shrub interspaces . Bare ground and biological soil crust cover tend to be low in undisturbed silver sagebrush communities [15,132]. On a mountain silver sagebrush community in eastern Oregon, mean bare ground and litter cover on undisturbed soils were < 3% and 80%, respectively. Maximum bare ground cover on disturbed soils was 17% .
Woody sagebrush species are long lived, with some species exceeding 100 years of age . As a cloning species, however, silver sagebrush probably does not fit this general pattern. Maximum life span and typical age class structure of silver sagebrush need further investigation. Wambolt and others  found age class structure of plains silver sagebrush in eastern Montana was as follows:
|Plant part||Mean age (yrs)||Standard deviation||Number of samples|
Flooding - Silver sagebrush has superior flooding tolerance compared to other woody sagebrush species .
Drought - Drought tolerance of silver sagebrush is uncertain. The species is markedly sensitive to water stress in the seedling stage [186,187], and has been noted as either drought intolerant  or tolerant [47,60] at maturity. Within the species, plains, mountain, and Bolander silver sagebrush have been ranked least to most drought tolerant, respectively . Anecdotal evidence from northern Great Plains studies during and after the "dust bowl" era (1937-1943) suggests that silver sagebrush is well adapted to survive severe, prolonged drought. On study sites across the northern Great Plains, adult postdrought survivorship of silver sagebrush was comparable to big sagebrush, and silver sagebrush showed better seedling establishment than big sagebrush after the drought had ended [47,144].RAUNKIAER  LIFE FORM:
Breeding system: Silver sagebrush's perfect flowers are uniformly fertile . Most breeding is accomplished by outcrossing, although some selfing occurs . DNA studies of plains silver sagebrush showed evidence of interpopulation outcrossing, but differences in genetic diversity among populations were not great. McArthur and others  state that large population sizes and wind-effected pollination tend to minimize between-population differences in silver sagebrush.
Pollination: Pollen is mostly spread by wind. Since bees, beetles, and flies regularly visit silver sagebrush flowers, some insect-mediated pollination probably occurs [112,115,182].
Seed production: Sagebrush species tend to have high fruit set, seed set, and germination rates. High seed production and germination rates help offset the genus' generally low rate of seedling establishment (see Seedling establishment) . Although a good fruit and seed producer, silver sagebrush has a lower rate of seed production than other species in its subgenus, with fruit set 18% lower than big sagebrush [71,179]. Silver sagebrush 1st starts producing seed at about 4 years of age .
Seed dispersal: At time of dispersal, the involucral bracts spread and release the ripe fruits . The single seed remains contained within the fruit, which falls beneath or slightly downwind of the parent plant. Some long-distance dispersal probably occurs when the sticky fruits adhere to passing animals [71,159]. Wind and water also disperse seed away from the parent plant [12,49,187]. Fruits that fall on crusted snow may be moved long distances by wind. Sagebrush seeds float, and water currents may also carry seeds considerable distances .
Seed banking: Studies on potential seed banking of silver sagebrush are sparse, but a few studies suggest that silver sagebrush may build up a short-term seed bank. Silver sagebrush seed retains its ability to geminate when stored under cool, dry conditions, but looses germinative capacity rapidly when exposed to unfavorable conditions. Eddleman  obtained better (73%) and faster germination from stratified, year-old seed than from unstratified 2-month-old seed (26% germination) in the laboratory. However, Romo and Young  found plains silver sagebrush seed rapidly lost its ability to germinate when exposed to field environments in Saskatchewan. Spring-sown seed showed significantly better emergence than fall-sown seed, which was more likely to be killed by fungi or drastic fluctuations in temperature. Some seeds that failed to germinate within the 1st year were still viable, and the authors suggest that silver sagebrush may have a small soil seed bank reserve on safe sites. Further studies are needed to determine ability of silver sagebrush to establish from soil-stored seed.
Germination: Silver sagebrush seed is immediately germinable, although best germination occurs when seeds are retained on the parent plant long enough to experience cold temperatures [45,186]. Seed germinates with or without light [184,186] over a wide range of temperatures . Plains silver sagebrush seed collected in Montana, stored at room temperature for 2 years, and sown in the greenhouse showed 51% and 64% germination on filter paper (without and with fungicide treatment, respectively). Optimum germination appears to occur with persistently cool soil temperatures. When sown in the greenhouse, seeds showed 93% germination at 68 oFahrenheit (20 oC) and 97% germination at 59 oFahrenheit (15 oC) . A Saskatchewan study found best germination of plains silver sagebrush occurred with stratification (> 28 days' duration) around 50 oFahrenheit (10 oC). Temperature range for germination was 41-77 oFahrenheit (5-25 oC) . In the Montana study, exposure to relatively high temperatures (86 oFahrenheit (30 oC) for 14 days) prior to planting resulted in loss of seed viability. Germination rates were best for seed planted 2.5 mm below the soil surface. No germination occurred in seed more than 7.5 mm below the soil surface. Seeds sown on the soil surface germinated readily but were highly susceptible to desiccation .
Seedling establishment/growth: Although silver sagebrush seed production is high, few plants survive the germination and seedling stages . Artificial plains silver sagebrush regeneration, established in southern Montana by seeding-in, showed mean 1st-year survivorship of 3.4% . Seedlings require open ground that is free from competition [71,147], and they are rare in undisturbed to lightly disturbed, mature stands [71,73]. On undisturbed steppes in the Badlands of North Dakota, plains silver sagebrush comprised 100% of total shrub cover, only 4% of which was seedlings . Good establishment occurs on soils disturbed by animal burrowing or tilling ; the incidence of postfire seedling establishment needs further study. Silver sagebrush seedling mortality is greatest in the 1st year, tending to level out after that [71,186]. Investigators in Saskatchewan  found that up to a critical mass, seedling establishment and growth rates of plains silver sagebrush seedlings increased with increasing weight of their originating seeds; however, plants from seeds weighting > 0.57 mg showed poor germination, and growth of seedlings from the heaviest seeds was slow. In a Saskatchewan study, Romo and Grilz  found that only 5-6% of sown silver sagebrush seed produced seedlings, but 85% of seedlings that survived their 1st year also survived their 2nd. Drought is the primary cause of seedling death. Seedlings require moist soil for establishment and growth [186,187], and pulses of seedling establishment have been noted in years of above-average precipitation .
Acclimated seedlings are cold-hardy. Plains silver sagebrush seedlings from Saskatchewan survived exposure to -38 oFahrenheit (-39 oC) temperatures after hardening-off, while nonacclimated seedlings did not survive exposure to 7 oFahrenheit (-14 oC) temperatures. The researchers suggested that seedlings germinating early in spring may show better winter survivorship than later-germinating seedlings, as older seedlings that have gradually acclimated to cooling temperatures have had more time to develop protection from freezing by lignifying cell walls and expanding twig buds .
Asexual regeneration: Cloning is silver sagebrush's most common method of reproduction [148,187]. With 3 methods of sprouting and the ability to layer [12,71,72,90,189], silver sagebrush is the strongest sprouter in its subgenus [71,186,200]. It sprouts from the roots [12,14,17,38,71,72,114,126], rhizomes [12,17,114,126,157,171,189], and the root crown [47,152,189] after disturbance damages stem tissue [38,72,126,157] and removes apical dominance. A strong sprouting response from buried organs increases silver sagebrush's ability to survive flood, ice scour, drought, and even severe fire damage [47,186,187]. Enlargement of colonies via sprouting and layering is nearly the sole method of silver sagebrush regeneration in the absence of disturbance; both seedlings and sprouts may occur on disturbed sites. Origin of excavated plains silver sagebrush plants in Montana was approximately 37% from seed (no connecting rhizomes) and 63% from sprouts (plants connected by rhizomes). An excavated colony consisted of 15 individuals, all connected by a rhizome running within 2 inches (5 cm) of the soil surface. Each plant had its own root system. Soil texture may affect ability to clone: the only sites where plants established from seed outnumbered those originating from rhizomes were those with very gravelly or very clayey soils . Similarly, another Montana study of plains silver sagebrush regeneration found plants started from seed outnumbered cloned plants only on sites with clay pans underlaid with gravel. Typical rates of establishment were 1/3rd from seed and 2/3rds from cloning .
Harvey  found layering was an important means of regeneration for silver sagebrush in eroded gullies. Stems that had been buried in silt by periodic floods were producing adventitious roots and sprouting; rhizomes were also producing sprouts.
Sprouting from the root crown is less frequently reported in the literature than sprouting from roots or rhizomes, but root crown sprouting may be an important adaptive response to drought and browsing. Approximately 3/5ths of the plains silver sagebrush plants on an eastern Montana site gradually died back to the root crown during the severe drought of the early1930s, sprouting back from the root crown in the spring of 1935. The remaining 2/5ths did not recover . In a study of the response of native shrubs to pruning (a surrogate for browsing), silver sagebrush responded to annual pruning to a height of 0.5 foot (0.2 m ) by "vigorous" sprouting from the root crown. The sprouts grew quickly: after 3 years of treatment, there was no difference in mean height between pruned and unpruned silver sagebrush plants (3 feet (0.9 m)), although crown area was significantly less in pruned vs. unpruned plants (03.2 vs. 42.4 ft2 (2.81 vs. 3.91 m2), respectively; p = 0.05). .
Hybrids: Silver sagebrush hybrids may inherit ability to sprout and layer [71,115]. For example, a natural mountain silver sagebrush × mountain big sagebrush hybrid from Gallatin County, Montana, produced root sprouts in the field and layered when moved to the greenhouse .SITE CHARACTERISTICS:
Soils: Silver sagebrush occupies moister, colder soils than any other woody sagebrush species in North America . Soil drainage is often slow. Silver sagebrush communities are also common on transitional wet-to-dryland sites [63,109] where soils dry by late summer. A mountain silver sagebrush/tufted hairgrass community in Yellowstone National Park was described as "the driest wetland community type" within the Park . Phosphorus, potassium, nitrogen, organic matter, and cation exchange capacity are often lower in silver sagebrush soils than in soils of surrounding communities. Silver sagebrush cannot tolerate strongly saline or calcareous soils [73,157,185]. Soil pH ranges from slightly acidic to strongly alkaline (6.0-8.5) [24,63,66,176]. Parent materials of soils supporting silver sagebrush include sandstones, shales, and granites ; soil textures include clay, silt, loam, sand, and gravel [71,85,187]. Silver sagebrush in Wyoming occurred on shallow to deep soil profiles, being most common (9/14 sites) in deep soils (depths of > 3 feet (1 m)) . Best growth occurs on well-drained, coarse-textured, alluvial soils that are moist in the upper 6 inches (20 cm) of the soil profile [63,185].
Elevation: Silver sagebrush's overall elevational range is from 5,000 to nearly 11,000 feet (2,000-3,000 m) elevation [17,157,198].
Bolander silver sagebrush is most common on pluvial lakebeds, internally drained basins with alkaline soils, and in snow catchments with granitic soils [71,91,113,163,203]. It also grows on meadows, streambanks, and moist, gravelly soils [17,75,98]. It is the only sagebrush in North America that can tolerate temporary inundation . Bolander silver sagebrush occurs from 4,400 to 11,000 feet (1,300-3,400 m) elevation [17,75,98]. In the Ochoco Mountains, it occurs on the margins of mid-elevation meadows (4,400-5,600 ft. (1,300-1,700 m)) and on lower-elevation, inactive floodplains . It occurs from 5,000 to 9,600 feet (1,500-2,900 m) elevation in Nevada .
Plains silver sagebrush occurs on low hillsides, riparian zones, and in valleys. Ranging from 4,000 to 7,000 feet (1,000-2,000 m) elevation, it is most common below 5,000 feet (1,550 m) on moist, sandy soil bordering prairie creeks, ephemeral water courses, and the bottoms of eroded hills [14,71,90,117,168]. Topography is usually flat to gently sloping . Scattered plants may occur on upland sites .
Mountain silver sagebrush is most common on mountain meadows, stream terraces, basins, and areas of heavy winter snowpack throughout its distribution. It is occasionally found on moist upland slopes [12,85,113,191]. In the Southwest it is most common in the mountains but also occurs on plains and in valleys . Mountain silver sagebrush is common on limestone-derived soils . It occurs from 6,000 to 10,000 feet (2,100-3,050 m) elevation across its range [17,71,191]. Ranges for mountain silver sagebrush by state are:
|AZ, NM||5,000-9,000 feet (1,500-2,700 m) |
|ID||6,000-8,000 feet (1,800-2,400 m) |
|MT||1,860-5,994 feet (567-1,827 m) [65,66]|
|NV||5,000-9,600 feet (1,500-2,900 m) |
|WY||1,000-10,000 feet (1,800-3,000 m) [20,85,130]|
Silver sagebrush may invade overgrazed mountain meadows . Silver sagebrush steppes of Utah occur on mountain rangelands disturbed by heavy grazing; the steppes are usually codominated by herbaceous invaders. In the absence of disturbance, the silver sagebrush steppes progress to stable, late-successional seres codominated by bunchgrasses .
Jakubos and Romme  noted invasion of Rocky Mountain lodgepole pine (Pinus contorta var. latifolia) into big sagebrush-silver sagebrush/sedge meadows in Yellowstone National Park. The authors attributed the tree invasion to a trend towards warmer climate since the late 1880s.SEASONAL DEVELOPMENT:
Phenology of plains silver sagebrush on 6 sites across southern Montana was as follows :
|dormancy ends||early to late March|
|apical bud enlargement||late March to mid-April|
|twig elongation||mid-April to mid-May|
|lateral branch bud enlargement||mid-May to mid-June|
|lateral branch elongation||late May to mid-Aug.|
|floral branch elongation||mid-June to mid-Aug.|
|floral bud enlargement||July|
|anther development||mid-July to mid-Aug.|
|flowering||mid-Aug. to early Sept.|
|fruit ripens||early Sept. to mid-Oct.|
|seed dissemination||mid-Sept. to mid-Oct.|
|onset of winter dormancy||mid-Oct. to mid-Nov.|
Although sprouting is silver sagebrush's primary method of postfire regeneration, some seedling establishment can occur if early postfire years are favorably wet during the growing season . Time required for postfire sprouts to begin seed production is undocumented, but given silver sagebrush's rapid rate of sprout growth , sprouting stems probably fruit and seed within 2 or 3 postfire years. Seeds produced from postfire sprouts are the most likely sources of seedling establishment, but wind, water, and animal transport of seed onto burns may also contribute to postfire seedling establishment [12,49,71,159,187].
Fuels: Occupying bottomlands and other areas that are wetter than surrounding vegetation, silver sagebrush communities often have heavier litter and vertical fuel loads than surrounding plant communities [132,177,186]. Fires tend to carry into and spread in silver sagebrush unless the community has been overgrazed [17,186]. Heavy litter build-up tends to decrease rhizomatous sprouting in silver sagebrush colonies, while removal of the litter by fire or other means encourages silver sagebrush sprouting and colonial expansion [185,187].
Fire regimes: Silver sagebrush steppes experience stand-replacement fires [14,134,195]. Fire frequencies are uncertain: fire histories for silver sagebrush communities are sparse to altogether lacking. Since plant productivity and community structure vary across the species' wide geographical distribution [65,69,78,132,186], historic fire intervals were probably similarly varied.
Bolander silver sagebrush: As of this writing (2002), there are no published fire history studies on Bolander silver sagebrush communities. Bolander silver sagebrush grows on sites with widely varying characteristics, including fuel loads. Fire was probably rare in Bolander silver sagebrush communities on alkali sinks in the rain shadow of the Sierra Nevada, and frequent on Bolander silver sagebrush meadows of the Ochoco and Blue mountains. Since even plant community composition, structure, and production are poorly described in the literature, a great deal of research is needed to understand fire effects and historic fire regimes for Bolander silver sagebrush communities. Fire and rangeland managers with experience in this type are encouraged to share their findings with Fire Effects Information System staff.
Plains silver sagebrush: Fire history studies of plains silver sagebrush-grama-needlegrass steppes of the northern Great Plains are based on historic records and tree fire scars obtained from adjacent, coniferous communities and a few lone, on-site conifers. These studies suggest that stand-replacement fires occurred frequently in plains silver sagebrush steppes. Wright and Bailey  estimated fire frequencies of 5 to 10 years on rolling-to-level topography, where plains silver sagebrush mostly occurs as widely scattered plants in a landscape dominated by mixed grasses . On topography dissected with breaks and rivers, where silver sagebrush is most common, they estimated fire return intervals of 20 to 30 years. Other researchers report similar fire return intervals for plains grassland steppes [27,52,192]. For example, fire return intervals range from 16 to 47+ years in relict western wheatgrass-green needlegrass-plains silver sagebrush communities of western North Dakota .
Most plains grassland fires historically occurred in summer or fall, with lightning and human ignition sources. Lightning-caused ignitions were most common in July and August. Sieg  suggests that for the northern Great Plains, the natural fire regime of low draws that were vegetated with sprouting species such as silver sagebrush was mostly late-growing-season fire, ignited after fine fuels had cured and dried. Late-season fires were probably "intense," but because natural fires also occurred in other seasons, the overall fire regime was highly variable. Native Americans traditionally set fires throughout the year, although April, September, and October were their peak ignition times .
Mountain silver sagebrush: The cool, moist montane sites supporting mountain silver sagebrush can be highly productive, with graminoids providing ample flashy fuels to carry fire . Fire ecologists estimate frequent stand-replacement fires in this type, with mean fire return intervals ranging from 3 to 45+ years [5,6,74]. Houston  estimated on Snake River Plains of Idaho, fires probably cycled about every 25 years in the wetter areas favored by mountain silver sagebrush.
The following table provides some fire return intervals for plant communities and ecosystems where silver sagebrush is a dominant or important component of the vegetation. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes".
|Community or Ecosystem||Dominant Species||Fire Return Interval Range (years)|
|silver sagebrush||Artemisia cana||5-45 [74,137,199]|
|sagebrush steppe||A. tridentata/Pseudoroegneria spicata||20-70 |
|basin big sagebrush||A. t. var. tridentata||12-43 |
|mountain big sagebrush||A. t. var. vaseyana||15-40 [7,29,122]|
|Wyoming big sagebrush||A. t. var. wyomingensis||10-70 (40**) [183,201]|
|saltbush-greasewood||Atriplex confertifolia-Sarcobatus vermiculatus||< 35 to < 100|
|plains grasslands||Bouteloua spp.||< 35|
|blue grama-needle-and-thread grass-western wheatgrass||B. gracilis-Hesperostipa comata-Pascopyrum smithii||< 35|
|blue grama-buffalo grass||B. g.-Buchloe dactyloides||< 35|
|cheatgrass||Bromus tectorum||< 10|
|western juniper||Juniperus occidentalis||20-70|
|Rocky Mountain juniper||J. scopulorum||< 35|
|wheatgrass plains grasslands||P. smithii||< 35 |
|interior ponderosa pine*||Pinus ponderosa var. scopulorum||2-30 [6,10,104]|
|eastern cottonwood||Populus deltoides||< 35 to 200 |
|quaking aspen (west of the Great Plains)||P. tremuloides||7-120 [6,58,121]|
|mountain grasslands||Pseudoroegneria spicata||3-40 (10**) [5,6]|
|Rocky Mountain Douglas-fir*||Pseudotsuga menziesii var. glauca||25-100 [6,7,8]|
Ground fires are rarely reported in silver sagebrush steppes; however, in Saskatchewan, Rowe  noted a September, lightning-ignited ground fire in a silver sagebrush/green needlegrass-blue grama-western wheatgrass association. In some spots, the fire burned into the taproots of silver sagebrush plants and killed them.PLANT RESPONSE TO FIRE:
Silver sagebrush requires an open, disturbed seedbed [71,147], and fire may prepare a favorable site for seedling establishment. In eastern Montana, plains silver sagebrush seedling establishment has been documented on sites disturbed by fire or ice scouring. Rhizome sprouting was more common, however (approximately 1 seedling per 3 sprouts) . In a rehabilitation study using artificial regeneration, mixed sagebrush steppe in Wyoming was treated to control invading Utah juniper (Juniperus osteosperma). Control methods included herbicide (picloram) application, bulldozing, tree harvest, and a fortuitous wildfire. After the treatments and the wildfire, native species including silver, big, and black (Artemisia nova) sagebrush were seeded in, with time of seeding (spring vs. fall) and seeding method (furrow vs. broadcast seeding) evaluated. All sagebrush species established best on burned plots compared to unburned plots; fall planting and broadcasting also favored the sagebrushes compared to spring seeding and furrowing .
Hybrids: Silver sagebrush hybrids may inherit the ability to sprout after fire and other top-killing events. Silver sagebrush × mountain big sagebrush and silver sagebrush × threetip sagebrush hybrids both sprout after fire [97,112]. Inadequately studied, postfire sprouting response of silver × threetip sagebrush hybrids is probably strong because each parent has genetic ability to sprout. Silver and threetip sagebrushes were once assumed to be closely related due to common sprouting ability [12,164]; however, DNA-based phylogenetic studies show a close genetic relationship among black sagebrush, low sagebrush, and silver sagebrush infrataxa (the silver sagebrush lineage) [96,97,120], and a more distant genetic relationship between the silver sagebrush lineage and the big sagebrush lineage (which includes threetip sagebrush and big sagebrush infrataxa) [96,97]. Studies on the sprouting ability of silver, black, and low sagebrush combinations are lacking, but such studies might provide insight into the genetic basis for sprouting in woody sagebrushes and ultimately, produce woody sagebrush plants that can survive on sites where exotic annual grasses have altered fire regimes. Sprouting, drought-tolerant sagebrush hybrids may be useful in rehabilitating sagebrush rangelands that have converted to annual grasslands dominated by cheatgrass or medusahead (Taeniatherum caput-medusae) after repeated, short-interval fires. Big and threetip sagebrush seedlings are more drought tolerant than silver sagebrush seedlings. Crosses among silver, big, and threetip sagebrush may produce sprouting plants that can survive on dry sites prone to reburns . McArthur and others  have produced a plains silver sagebrush × Wyoming big sagebrush hybrid with apparently fertile seed.DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Fire also favored silver sagebrush on the Grand Mesa National Forest, Colorado. A Gambel oak/common snowberry-Saskatoon serviceberry community (Quercus gambelii/Symphoricarpos albus-Amelanchier alnifolia) was prescribed burned, sprayed, and/or chained to reduce density and height of big game and cattle browse. Production of silver sagebrush (kg/ha) before and after treatments is given below .
|1 yr before||2 yrs after||5 yrs after||10 yrs after|
|spraying||data not given||----||----||----|
|burning, spraying, and chaining||1.20||0.53||0.60||2.00|
FIRE MANAGEMENT CONSIDERATIONS:
Beetle and Johnson  recommend prescribed fire to increase silver sagebrush density on rangelands. Blaisdell and others  provide general guidelines for burning in sagebrush-grasslands.
A variety of fire treatments may be needed to mimic historic fire regimes. Because the fire regime of the northern Great Plains was highly variable, Sieg  recommends varying fire intensities and seasons, including use of mid-summer fire, to restore natural disturbance patterns. Howe  stated "the strategy should avoid a uniformity of timing of burns or in intervals between burns that artificially simplifies what was probably a more complex system."
Fall burning was conducted in early October of 1979, after summer drought "substantially reduced soil moisture throughout the soil profile." A backfire was used.
Fuel loadings and weather conditions were similar on the spring- and fall-burned sites. Fuel loads ranged from 300 kg/ha pm plains silver sagebrush/blue grama sites to more than 1,000 kg/ha on plains silver sagebrush/western wheatgrass sites. Temperature averaged 21 oC and wind speed was less than 8 km/hr.FIRE EFFECTS ON TARGET SPECIES:
Immediate fire effect: The fires accomplished partial to complete top-kill as described in the severity groups above. Silver sagebrush mortality was dependent upon fire severity and season. The spring fire killed approximately 1/3rd of the plants that were completely burned. Plants that were not completely top-killed sustained mortalities of less than 10%. The fall fire killed about 3/4ths of the completely burned plants, with 40% mortality of incompletely consumed plants. Mortality differences were highly significant (p<0.01) between seasons.Plant response to fire: Prefire plant size had no significant effect (p < 0.05) on either fire survival or postfire growth. Severe fire reduced height growth of postfire sprouts on top-killed plants compared to fires that only partially consumed plants. Plants that had only foliage removed tended to sprout more quickly than those also losing branches. Spring burning resulted in plants with relatively fewer sprouts, superior height growth, and greater canopy indices compared to fall burning. For spring-burned silver sagebrush, height growth by the next July was > 20 cm for top-killed plants, and > 30 cm for partially consumed plants. Canopy indices* (see above) were > 350 mm. For the fall burns, incompletely burned plants usually had > 10 sprouts per plant, and the sprouts were < 20 cm in height by the next July. Top-killed plants averaged 4 sprouts per plant, with sprouts < 4 cm in height by the next July. Mortality and postfire growth data are given below.
|Number of sprouts||Height (mm)||Canopy index (mm)|
|twigs & foliage consumed||3.8a||305a||424a|
|twigs & foliage consumed||13.3a||188a||279a|
|1Differences between values are significant (p < 0.05) when followed by a different letter.|
In regions with dry summers, livestock and wildlife may browse silver sagebrush when upland vegetation has already dried. In Modoc County of northeastern California, Bolander silver sagebrush communities were preferred summer-use areas for pronghorn, feral horses, and cattle . Although a common staple for wildlife, livestock use of silver sagebrush is variable depending upon availability of palatable herbs . Domestic sheep generally browse silver sagebrush more heavily than cattle . Cattle may prefer grazing in silver sagebrush steppes, however, because their relatively mesic soils promotes heavier grass cover than in adjacent communities, especially in summer . Livestock may actually make greater use of silver sagebrush when there is ample grass to go with it .
Silver sagebrush steppes are important habitat for wildlife. For example, they are the 2nd-most used habitat for sharp-tailed grouse in eastern Montana; the birds used only upland western wheatgrass-blue grama grassland habitats more than plains silver sagebrush steppes . Silver sagebrush communities also provide important corridors for wildlife traveling from riparian zones to forested or grassland communities [129,132]. Three wildlife species, pronghorn, sage-grouse, and a native grasshopper, sometimes rely on silver sagebrush steppes as their primary habitat, and on silver sagebrush browse as their primary forage.
Silver sagebrush is used as an indicator species in pronghorn habitat suitability index models . It provides winter maintenance and emergency forage [59,172]. Pronghorn also use silver sagebrush in the fall, particularly when vegetation on less mesic sites has dried [4,11,43]. For example, stomach samples of pronghorn taken during hunting season (Sept.-Oct.) in southeastern Montana were primarily sagebrush (plains silver and big sagebrush); several samples contained no other forage . Pronghorn in Saskatchewan were concentrated on fall rangelands where plains silver sagebrush and creeping juniper (Juniperus horizontalis) were available . Heavy livestock grazing can degrade silver sagebrush habitat conditions for pronghorn . Fires that top-kill large patches of silver sagebrush can adversely affect pronghorn habitat  until sprouts have attained a few years' growth.
When plentiful, silver sagebrush is important in the diet of sage-grouse [105,140]. Where it is the primary sagebrush cover, silver sagebrush communities are critical sage-grouse habitat . Crop analysis of adult sage-grouse in White Pine County, Nevada, showed the birds were consuming almost nothing but mountain silver sagebrush . Sage-grouse populations at the northern and eastern boundaries of the bird's distribution are most likely to be ecologically dependant on silver sagebrush . Sage-grouse in southeastern Alberta -- where other woody sagebrush taxa are uncommon -- nest under plains silver sagebrush almost exclusively, and silver sagebrush is their primary diet item .
Silver or sand sagebrush are the primary diet items of the sagebrush grasshopper (Melanoplus bowditchi). A North Dakota study showed crop contents of sagebrush grasshoppers were 97% silver sagebrush. High densities of sagebrush grasshoppers have never been recorded, suggesting few economic impacts and little damage to silver sagebrush populations are caused by the insect. However, little is known of the ecology and life history of sagebrush grasshopper, and further studies are needed to assess the ecological and economic impacts of the grasshopper .
Palatability: Silver sagebrush is 1 of the
more palatable and nutritious sagebrush species [181,198]. With a mean of 11%, winter (Jan.-March) crude protein content of Bolander
silver sagebrush on the Fort Rock-Silver Lake winter mule deer range in central
Oregon exceeded that of either low or big sagebrush . Mule deer, fed 7
sagebrush taxa collected from the Silver Lake Range in fall and winter, showed
highest relative preference* for Bolander silver, low, and mountain big
sagebrush in both fall and winter feeding trials. Domestic sheep showed moderate
preference (browsed but did not prefer) for Bolander silver and mountain
big sagebrush in fall, and showed highest preference for Bolander silver, low, and
mountain big sagebrush in winter. Area of collection did not affect the animals' choices,
while taxa consistently did .
*relative preference index=% of diet/% composition available
Walton  has ranked Bolander, mountain, and plains silver sagebrush as most to least palatable, respectively.
Nutritional value: Nutritional content of silver sagebrush is greatest in the spring and declines slowly over winter. Silver sagebrush is rated "fair" in energy value and "fair to good" in protein value . Mean chemical composition of plains silver sagebrush on the Little Missouri National Grasslands, North Dakota, was as follows .
|Ca*||Mg*||K*||Cu*||Fe (ppm)||Mn (ppm)||Zn (ppm)|
Based upon nutritional content (protein, carbohydrate, fat, vitamin, and mineral ), palatability, and dependability of supply on rangelands, silver sagebrush is rated low to fair forage for cattle, fair to good for domestic sheep, and good for pronghorn, elk, and deer [63,145].
Cover value: Silver sagebrush provides thermal and hiding cover for small mammals, small nongame birds, and game birds [44,66]. At the lower end of its elevational range, it provides important sage-grouse nesting cover .VALUE FOR REHABILITATION OF DISTURBED SITES:
Rehabilitation projects show variability in silver sagebrush's ability to establish on coal mine spoils. In southern Montana, silver sagebrush sown on coal mine spoils showed poor survivorship and seedling growth compared to germinants on unmined plots . However, silver sagebrush cuttings transplanted on coal mine sites in Wyoming and Colorado showed good to excellent survivorship in their 1st year. Transplants on 2 Wyoming sites treated with topsoil showed 100% survivorship. In Colorado, transplants showed 50% survivorship on sites treated with topsoil and 100% survivorship on untreated coal mine spoils. Neither the Wyoming nor the Colorado coal mine sites were irrigated after transplanting . Poor results on some sites may be due to toxic soil contaminants and/or dry soils. Further information is needed on ability of silver sagebrush to establish on contaminated soils.
Information on seed collection, processing, storage, and planting is available for silver sagebrush [45,147,159,189].OTHER USES:
Silver sagebrush is listed as a heat and drought tolerant plant suitable for xeriscaping . Since young plants are not drought tolerant [186,187], generous dry-season irrigation is probably warranted for their 1st few years until plants establish a deep root system.OTHER MANAGEMENT CONSIDERATIONS:
Cunningham  found that productivity of silver sagebrush in northwestern Colorado was negatively correlated (r=-0.52, p<0.01) with productivity of associated graminoids; forbs were not correlated with silver sagebrush growth. Presence of extractable magnesium in the 12- to 24-inch (30-60 cm) soil layer increased silver sagebrush productivity (r=0.47, p<0.05), as did rock and gravel in the soil profile (r=0.25, p<0.05). A high percentage of sand in the 12- to 24-inch soil layer negatively affected growth (r=-0.15, p<0.01). Harvey  provides a model for predicting silver sagebrush productivity based upon leaf and woody tissue measurements.
Silver sagebrush may allelopathically inhibit germination of some herbaceous species, as well as its own seed. Aqueous extracts of silver sagebrush leaves reduced germination of 6 mixed-grass species, including silver sagebrush. Laboratory results using extracts do not necessarily indicate allelopathy under field conditions; however, a field study of plant species distributional patterns in western North Dakota suggests that some forb species are more likely to associate beneath or nearby silver sagebrush canopies. Other species, especially bunchgrasses, tend to segregate away from silver sagebrush . Possible allelopathy of silver sagebrush, and its effects on plant community composition and structure, need further investigation.
Control: Since silver sagebrush provides important wildlife forage and cover, controlling it is not generally recommended [134,198]. Silver sagebrush can obtain nearly closed cover on some sites , however, and control may be desired if silver sagebrush is so dense that it is excluding perennial grasses.
Chemical: Silver sagebrush can be controlled with 2,4-D or picloram [17,81,134,194]; 2-,4-D is most effective [17,196]. Follow-up spraying may be necessary to control sprouts . Mechanical controls such as plowing, disking, and chaining are not recommended for mature plants because they are likely to promote sprouting . They may be effective for young plants. White and Currie  obtained up to 67% control by plowing silver sagebrush less than 1 m3 in size.Fire: A single application of prescribed fire is not recommended for control, as it is likely to promote sprouting . Used in sequence, prescribed fire and herbicides may reduce silver sagebrush to desired levels. Using various combinations and rates of herbicides, Whitson and others  obtained a range of 8-91% control with fall prescribed fire followed by July application of herbicides to sprouts. Frequent reburning may also reduce silver sagebrush cover, and further studies are needed on the possibility of reduced silver sagebrush using repeated fires. Blaisdell and others  provide general guidelines for managing sagebrush-grass rangelands, including assessment of rangeland condition and recommendations for burning. See Fire Management Considerations for further information on managing silver sagebrush with fire.
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