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Wildlife, Animals, and Plants
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BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Artemisia tridentata spp. vaseyana
| Mountain Big Sagebrush
Mountain big sagebrush is a long-lived (50+ years), woody, aromatic, native, evergreen shrub [7,11]. Shrubs often appear flat-topped from a distance because of the nearly equal height of flowering stalks [68]. The fruit is a small, easily shattered achene that falls or is blown near the parent plant [111,151]. Root length of mature plants was measured to a depth of 6.5 feet (2 meters) in alluvial soils in Utah [105]. Greenhouse grown plants had roots 22.3 feet (6.8 meters) long at 6 months [136]. Mountain big sagebrush roots are colonized by fungi that form symbiotic vesicular-arbuscular mycorrhizae [24,121]. Aboveground tissues host an unidentified, pathogenic snowmold fungus that decreases shrub cover and productivity [55,92].
Phanerophyte
Mountain big sagebrush usually flowers in late summer and fall, but some strains may flower as early as July. Seed matures from September through October [71]. Mature seeds fall or are blown from inflorescences during autumn and winter and emergence occurs in winter or spring [75,80,151]. Seeds are short-lived (less that 5 yr in warehouse) and probably do not form a persistent seed bank [82,151]. Average annual seed production in western Nevada was 29 pounds per 2.5 acres (1.3 kg/0.1 ha) over a 4 year period [154].
Recently harvested seeds are nondormant but require light for germination [82]. Cold, moist conditions and exposure to light increase germination [75,76,82]. Germination response varies between populations of mountain big sagebrush growing in different habitats. Meyer and others [80,81,82] observed strong, significant correlations (P < 0.05) between percent germination and climate variables (light and cold). Seed collections from habitats with long, severe winters germinated slowly and incompletely, whereas seed collections from sites with shorter, milder winters germinated rapidly and completely.
Results of a western Nevada seed bank study showed the number of (greenhouse) germinable seeds of mountain big sagebrush decreased sharply as winter progressed and fell below detectable levels by June. Seeds did not persist in the soil seed bank. For 4 consecutive years there were no detectable seed reserves in the soil from June to November. Dispersal began in December and hundreds of newly dispersed mountain big sagebrush seeds were counted in seed traps near individual plants. Seedling emergence in the study plots began in February, but all seedlings died by June. No successful seedling establishment of mountain big sagebrush (nor basin big sagebrush) was observed in any of the permanently marked plots during the 4 years of the study [151].
To examine yearly variation in germinability, Harniss and McDonough [51] quantified percent germination in unstratified, laboratory-germinated seeds collected from the same 10 plants of mountain big sagebrush for 3 consecutive years. They detected no significant (P < 0.05) year-to-year difference in average germination, which ranged from 11% to 17%.
Mountain big sagebrush can reproduce vegetatively by layering [7,8,53,71]. It does not resprout when aboveground tissues are killed by fire or other means [10,11,94].
In the Intermountain west, mountain big sagebrush usually occurs in the upper elevational range of the big sagebrush zone in montane valleys and on foothills, slopes and high ridges [5,6,11,71,148]. In northerly parts of its range, this species occurs in mountain valleys and on mountain slopes and ridges as high as 9,840 feet (3,000 m) [71]. It has been reported as low as 2,600 feet (780 m) in Idaho. West and others [144] report that although mountain big sagebrush is the most common sagebrush in the Great Basin pinyon-juniper woodlands, only the wettest and coolest areas of the higher and larger mountain masses have mountain big sagebrush in their woodlands. Soils are moderately deep, well-drained, slightly acid to slightly alkaline and characterized by late-melting winter snow cover and summer moisture [6,11,19,20,71,124,144]. This shrub grows in full sun but tolerates shade, often occurring in association with mature conifers [96,144].
In a landscape-scale study in Wyoming, soils in topographic depressions occupied by mountain big sagebrush had higher organic matter, nutrients and microbial biomass than soils in more exposed (windblown) areas occupied by other vegetation, including basin and Wyoming big sagebrush. The effect was attributed to greater snow accumulation, leading to greater plant and litter biomass accumulation [19,20,21].
Elevations reported in the literature are as follows:
4,500 to 7,400 feet (1,370-2,255 m) in Arizona [58]
5,905 to 9,840 feet (1,800-3,000 m) in California [56,118]
7,760 to 8,480 feet (2,365-2,585 m) in Colorado [13]
2,560 to 8,990 feet ( 780-2,740 m) in Idaho [71,146]
3,770 to 7,810 feet (1,150-2,380 m) in Montana and British Columbia [3,68,78,97]
5,445 to 10,170 feet (1,660-3,100 m) in Nevada [82,118,121,124,154]
3,500 to 9,000 feet (1,066-2,740 m) in Oregon [148]
7,250 to 8,040 feet (2,210-2,450 m) in Wyoming [20,25,29]
4,690 to 8,990 feet (1,430-2,740 m) in Utah [26,82]
On a geologic time scale, the big sagebrush species have probably reached their maximum post-glacial spread [6].
According to Bunting [17] and references therein, most recent research indicates that big sagebrush is the climax species on its present-day range, and that invasion into other types is uncommon. Alterations of historic fire regimes have resulted in major successional changes in regions dominated by mountain big sagebrush and other sagebrush species, and the introduction of exotic annual grasses has modified the role of fire. In general, fire is less common, but in some cases it is more frequent.
In some areas, especially where fire suppression has been a factor, stands of mountain big sagebrush are being invaded by juniper woodlands [17,23,83], lodgepole pine [6] and Douglas-fir [3].
In the juniper woodlands of southern Idaho, western juniper has invaded large areas of mountain big sagebrush shrubland. Burkhardt and Tisdale [22,23] reviewed possible causes, including destruction of grassland via livestock grazing, increased seed dispersal by sheep, climate change and a reduction of the historic fire return interval. In field sites they examined seed dispersal mechanisms, fire history, and juniper seedling establishment, and concluded that succession of sagebrush-grass shrublands to juniper woodlands is directly related to cessation of periodic fires. In the same region, Hironoka and others [57] identified 10 climax habitat types dominated by
mountain big sagebrush. Please see the Fire Ecology section of this report for more discussion of the Burkhardt and Tisdale study.
Beetle and Johnson [7] determined that most big sagebrush stands in Wyoming, including mountain big sagebrush, probably represent edaphic or topographic climax. Evidence indicates that stands were historically self-replacing after fire. In that area, mountain big sagebrush replaces pioneer grassland communities. Lodgepole pine, and occasionally Douglas-fir, were observed encroaching into established stands of mountain big sagebrush [6,7].
In Eastern Oregon and Washington, mountain big sagebrush forms climax shrub communities with snowberry, elk sedge, and Idaho fescue. Mountain big sagebrush climax shrublands occur in association with ponderosa pine and western juniper [60].
In southern British Columbia mountain big sagebrush sometimes dominates within openings in subalpine fir forests. These communities are characterized as edaphic climax [78].
Mountain big sagebrush is reported to have "a tendency" to increase in plant density or foliar cover following disturbance [57,146,147]. Beetle and Kendall [7] reported mountain big sagebrush has more potential for increasing in density than any other sagebrush species.
Please refer to the Fire Effects section of this report for information about short and long term responses of mountain big sagebrush to stand-replacing fires.
A study of sagebrush phenology in southern Idaho [146] showed marked differences in dates and rates of development among taxa. Mountain big sagebrush began growth approximately 2 weeks later and ripened seed at least 2 weeks earlier than basin and Wyoming big sagebrush. Blaisdell and others [11] reported that some strains of mountain big sagebrush start blooming as early as July, and that seed matures from September through October.
Generalized findings for mountain big sagebrush derived from the Idaho study are as follows [146]:
| late June |
early shoot development |
| early July |
medium shoot development |
| mid-July |
full shoot development |
| mid- to late July |
flowerheads green |
| early August |
flowerheads yellow |
| early September |
pollinating |
| late September |
seeds ripe |
Related categories for
SPECIES: Artemisia tridentata spp. vaseyana
| Mountain Big Sagebrush
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