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Wildlife, Animals, and Plants
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BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Artemisia tridentata ssp. wyomingensis
| Wyoming Big Sagebrush
Wyoming big sagebrush is a native shrub [6,34,39,64]. It is the most drought tolerant of the 3 major big sagebrush subspecies [94]. Plants are generally 18 to 30 inches (46-76 cm) tall, with rounded, uneven crowns. The main stem is usually branched at or near ground level into 2 or more substems [11,112]. Wyoming big sagebrush is technically an evergreen but is semideciduous in habit. It develops 2 types of leaves: large ephemeral leaves and smaller, perennial leaves produced from ephemeral leaf axes [96]. The inflorescence is an open, many-flowered spike [11]. The fruit is a small, easily shattered achene [116].
The root system is deep and well developed, with many laterals and one or more taproots. The majority of roots (about 35% of the total root system) are in the upper 1 foot (30.5 cm) of soil. Some roots may penetrate as far as 6 feet (1.8 m) [51,85,124]. Roots are infected with the vesicular-arbuscular mycorrhizae (VAM) Glomus microcarpus and Gigaspora spp. [16,36,71].
Wyoming big sagebrush is a long-lived species. In an undisturbed Wyoming big sagebrush community in southern Wyoming, plants ranged from 26 to 57 years of age; average age was 42 years [124]. Plants in long-undisturbed communities of New Mexico typically reach 50 years of age [135]. Maximum life span may exceed 150 years [50].
Identification of big sagebrush subspecies based upon morphology is difficult and often faulty. This is especially true for Wyoming big sagebrush, which is intermediate in several characteristics used to distinguish basin and mountain big sagebrush [67,129,132,139,149]. Chemical analyses are more reliable, but they cannot be conducted in the field and sometimes give indeterminate results [140]. Combining field identification with chemical analysis produces the most positive identification of subspecies. Laboratory techniques used to identify Wyoming and other big sagebrush subspecies include paper chromatography [78,115], UV absorption [120,121], and DNA analysis [89].
Phanerophyte
Wyoming big sagebrush reproduces from seed; it does not sprout or layer [12,90,112]. Pollination is mostly by outcrossing, but plants can also self pollinate [56]. Shrubs produce large quantities of small seeds beginning at 3 to 4 years of age [90,129]. Goodwin [60] estimated that a moderate-sized plant produces about 350,000 seeds in a season, and a large one produces over a million. Big sagebrush seed is disseminated mostly by wind, with some seed spread by animals and water [60,116]. The seed floats, so seedlings may establish along watercourses [60,98]. Most seed shatters within a week of maturation [60] and travels less than 100 feet (30 m) from the parent plant [10,129]. Some viable seed is retained on the parent and disseminates slowly over the winter [98]. Establishment occurs mostly from the seedbank [67]. Wyoming big sagebrush seed stored in the warehouse has retained viability for at least 6 years [116]; viability in the field is unknown. On burns, Wyoming big sagebrush that escape fire are an important seed source [29]. If the seedbank is destroyed over a large area by repeated fires or other means, Wyoming big sagebrush eventually seeds in from adjacent areas, but such a strategy may take several decades [129].
Seeds are nondormant, but a short (< 4 week) stratification period and light improve germination [92,93,98]. Germination rates in the laboratory are high over a broad range of temperatures (50-95
oF (10-35 oC)) [40,116]. Fresh seed collected over 5 western states showed germination rates of 69 to 100% [93]. Year-to-year seed viability seems more than adequate; germination rates of fresh seed collected in 3 successive years near Dubois, Idaho, ranged from 43 to 70% (mean=54%) [61].
A light litter layer favors seedling establishment; heavy litter retards establishment. Drought conditions favor establishment of Wyoming big sagebrush over perennial bunchgrasses [10]. Seedling growth is slow compared to growth of other subspecies and is probably under genetic control. Wyoming big sagebrush seedlings grow slowly even when water and nutrients are not limiting [17,20]. In the greenhouse, well-watered Wyoming big sagebrush seedlings stopped growth earlier in the growing season and attained less height than mountain and basin big sagebrush seedlings. Under drought conditions, Wyoming big sagebrush seedlings were not only shorter in stature, but also had smaller aboveground parts, than the other 2 major subspecies [20]. Seedling mortality can be high under drought conditions [40]
Although Wyoming big sagebrush seedlings outcompete mature bluebunch wheatgrass for water, mature crested or desert wheatgrass (Agropyron cristatum, A. desertorum) outcompetes Wyoming big sagebrush seedlings. In northwestern Utah, mortality of Wyoming big sagebrush seedlings was 8 times greater when transplanted into desert wheatgrass than when transplanted into bluebunch wheatgrass. Growth was best when Wyoming big sagebrush was planted alone [44].
Wyoming big sagebrush is most common on foothills, undulating terraces, slopes, and plateaus, but also occurs in basins and valley bottoms [34,39,54,69,128]. Aspect varies, but shrubs are most common on south- to west-facing slopes [28,128,131].
Soils: Wyoming big sagebrush occurs on frigid, mesic, and xeric soils of silty, clayey, skeletal, and mixed textures [54,69,70,103,150]. Soil parent material is highly variable [131]. Soil pH ranges from moderately acidic to moderately basic [70,75]. In riparian zones, Wyoming big sagebrush communities usually develop on gravelly outwashes and high floodplains [46,54]. Where Wyoming, basin, and mountain big sagebrush ranges overlap, Wyoming big sagebrush tends to grow on shallowest, most well-drained, and hottest soils relative to the other 2 subspecies. Basin big sagebrush tends to occupy the deepest, most fertile soils, and mountain big sagebrush tends to occupy moderately deep soils that are wetter and cooler than those occupied by Wyoming big sagebrush [7,19,150].
When Wyoming big sagebrush occurs with smaller sagebrush species, Wyoming big sagebrush often occupies the relatively deeper soils. In Wyoming, black (A. nova), low (A. longiloba), and three-tip (A. tripartitia) sagebrush communities interface with Wyoming big sagebrush, with the dwarf sagebrush communities occupying the shallower soils [131]. On the
Humboldt National Forest, Nevada, sites dominated by Wyoming big sagebrush tend to be Mollisols with intermediate surface soil thickness, while black sagebrush dominates sites with little to no upper soil horizon, and mountain or basin big sagebrush dominates sites with deep surface soil horizons [72].
Precipitation: In the Snake River Plains of southern Idaho, Wyoming big sagebrush communities occur on sites with greater than 7 inches (200 mm) of annual precipitation. Sites receiving less precipitation are dominated by shadscale and/or winterfat [66]. Where the ranges of Wyoming and mountain big sagebrush overlap, Wyoming big sagebrush generally occurs where precipitation is less than 12 inches (300 mm), whereas mountain big sagebrush occurs on wetter sites [26,27,65,67]. In the southern Rocky Mountains, Wyoming big sagebrush occurs on low- to mid-elevation sites receiving most precipitation as rain, whereas mountain big sagebrush occurs above 7,000 feet (2100 m), and most precipitation is snow [85].
Elevational ranges of Wyoming big sagebrush are as follows:
California: up to 7,260 feet (2200 m) [64]
Idaho: 2,500 to 6,500 feet (700-1980 m) [149]
Utah: 5,030 to 6,530 feet (1525-1980 m) [144]
Wyoming: 5,000 to 7,000 feet (1500-2100 m) [11]
East of the Continental Divide: below 7,000 feet (2100 m) [112]
Wyoming big sagebrush is a mid- to late-seral species [41,54,125].
Period of Wyoming big sagebrush establishment after a stand-replacing event such as fire is typically about a decade but varies with site [125]. Prior to re-establishment of Wyoming big sagebrush, disturbed Wyoming big sagebrush communities are mostly populated with associated grasses. Principal component analysis of Wyoming big sagebrush steppe on the Thunder Basin National Grassland of Wyoming produced this successional model (intervals between seres were not quantified) [13]:
early: forbs
early intermediate: blue grama
late intermediate: western wheatgrass
late seral: Wyoming big sagebrush
Wyoming big sagebrush/cheatgrass associations are most common on frequently disturbed sites. In the Trout Creek Mountains of Oregon, the type occurs on floodplains with large amounts of bare ground cover [46].
Wyoming big sagebrush may lose dominance on some steppe that have not experienced fire or other stand-replacing events for half a century or more. Kindschy [81] noted that in pristine Wyoming big sagebrush/bluebunch wheatgrass on Oregon's Jordan Crater Natural Research Area, most sites with a preponderance of dead Wyoming big sagebrush were the oldest seres. Old seres were primarily populated with long-established perennial herbs, with a few decadent Wyoming big sagebrush.
VAM associated with Wyoming big sagebrush are killed by heating or chemical alteration of the soil, and they may take several years to recolonize after fire or other soil-altering disturbance [148]. Absence of VAM probably inhibits Wyoming big sagebrush establishment on disturbed soils. For example, 2.5 years after restoration work, VAM had not yet colonized a coal-mined site in south-central Wyoming even though stockpiled topsoil was replaced. When VAM-infected and noninfected Wyoming big sagebrush seedlings were transplanted on the site, there was no significant difference in growth between the 2 groups: both showed poor establishment. In the greenhouse, however, biomass gain of the infected group was significantly greater (about 1.5 times more, p=0.05) compared to the uninfected group. This suggests that on the disturbed site, VAM were unable to survive anywhere but inside Wyoming big sagebrush roots, and establishment of VAM and host Wyoming big sagebrush probably will not occur until the chemistry of lower soil horizons changes [122].
Wyoming big sagebrush develops ephemeral leaves in early spring and retains them until onset of summer drought. Perennial leaves develop slowly, from late spring until July. Perennial leaves are generally retained until their 2nd year, when they are shed during summer drought. By retaining about 1/3rd of its perennial leaves over winter and then developing ephemeral leaves early in the growing season, Wyoming big sagebrush begins photosynthesis and height growth earlier than most herbaceous associates [38,96]. Relatively more leaves are shed in dry years compared to wet ones, and new leaves tend to be smaller in dry years [85]. Flowering begins in late summer (Aug. or Sept.), and fruits ripen in fall (mid-Oct. to mid-Nov.) [116,149]. Flowering continues until the onset of cold weather. Most seed is shed in fall, but some seed shed may continue until early winter [98].
Phenology of Wyoming big sagebrush in the Curlew Valley of northern Utah was as follows [51]:
root elongation April - mid-May
shoot elongation May - mid-Aug.
flowering mid-July - Sept.
fruiting mid-Aug. - Sept.
Related categories for
SPECIES: Artemisia tridentata ssp. wyomingensis
| Wyoming Big Sagebrush
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