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Wildlife, Animals, and Plants |
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BOTANICAL AND ECOLOGICAL CHARACTERISTICS
GENERAL BOTANICAL CHARACTERISTICS:Basin big sagebrush is an erect, rounded or somewhat spreading evergreen shrub which normally grows 3 to 10 feet (1-2 m) in height [110]. It occasionally occurs as a dwarf shrub or can be treelike in appearance, reaching a height of 16 feet (5 m). Maximum stature is reached on deep, well-drained soils in sheltered areas. Variability in plant height occurs along a moisture gradient, with larger plants occurring on more mesic sites [6]. Basin big sagebrush has a multistemmed form with a relatively thick trunk and an irregular crown. It is often characterized by a discernible main trunk [44]. It commonly reaches 40 to 50 years of age, and some plants may exceed 100 years. Slow-growing individuals on unfavorable sites attain the greatest age. The root systems of all subspecies of big sagebrush are well adapted to extract moisture from both shallow and deep portions of the soil profile. This makes them highly competitive with associated grasses and forbs [19,101]. Basin big sagebrush exhibits greater plant height, crown cover, production, and annual leader growth than Wyoming big sagebrush
RAUNKIAER [87] LIFE FORM:Phanerophyte
REGENERATION PROCESSES:Basin big sagebrush reproduces from seed. None of the subspecies of big sagebrush resprout after fire or other disturbance [93]. Flowers are self- or wind-pollinated [42,94,121]. Plants 2 to 3 years of age are capable of producing viable seed. Approximately 90% of big sagebrush seed is dispersed within 30 feet (9 m) of the parent shrub [42]. Few seeds are carried more than 100 feet (30 m) [94]. Density falls off rapidly away from the parent shrub, with maximum seed dispersal at approximately 108 feet (33 m) [42,94]. The rate of seed dispersal depends on wind and storm activity after seeds reach maturity [94]. Wind is the primary dispersal agent, although animal and water dispersal can also occur. Animals can serve as a minor dispersal agent when seeds are dislodged as the animals brush against branches. Seeds of big sagebrush contain a small air space which permits floatation in water. Rates of seed dispersal are slower in basin big sagebrush than in other subspecies. Seed dispersal takes approximately 8 weeks [94]. Seed of basin big sagebrush is short-lived and lasts less than 5 years when stored in a warehouse [77]. Some seedbanking occurs in other subspecies of big sagebrush [74], so seedbanking in basin big sagebrush is probable. Some basin big sagebrush seeds remained viable after prescribed burning in Utah. Emergence of basin big sagebrush seedlings on burned soil was reduced, however, compared to emergence of Wyoming and mountain big sagebrush. It was also reduced compared to emergence of basin big sagebrush on unburned control soil [26]. Germination may occur during winter or even late fall at mild winter sites such as the Mojave Desert, but at cold winter sites, it may be delayed until snowmelt [75,77]. Big sagebrush seeds germinate within a wide range of temperature. Rates of germination of unstratified seed vary according to temperature, with basin big sagebrush requiring 2 to 3 days at all temperatures [72]. According to Meyer and others [77], big basin sagebrush seed from cold winter populations germinate much more slowly at near-freezing temperatures than do seeds from warm winter populations and also exhibit dormancy under autumn temperature regimes. Basin big sagebrush also shows annual variation in germination [48]. Basin big sagebrush is a more prolific seed producer than is Wyoming big sagebrush [76]. Studies suggest that sufficient basin big sagebrush seed was present for adequate germination each year even at the lowest germination rates observed [48]. Specific details on germination rates are available [75,77]. Seedlings emerge in early spring soon after snowmelt [75]. Seedling survival often depends on precipitation. Seedlings under mature sagebrush plants are more likely to survive [83]. Seedling survival tends to be lower in grazed, unsheltered areas [85].
SITE CHARACTERISTICS:Basin big sagebrush grows in relatively more mesic habitats than other subspecies of big sagebrush [6,72]. It commonly grows on well-drained soils in valley bottoms, lower foothill areas or in areas adjacent to drainages. Basin big sagebrush is associated with deep, seasonally dry, well-drained soils on plains, valleys, and foothills [5]. It frequently coincides with high water tables or deep moisture accumulations [96]. Basin big sagebrush occurs on stratified sandy loam soils on floodplains or on low stream terraces [53]. In southeastern Idaho, basin big sagebrush is most abundant on sandy soils or at the sandy end of a soil texture gradient [96]. Because it tends to grow in deep, fertile soils, basin big sagebrush is an indicator of productive sites. Many sites once dominated by basin big sagebrush are now farmland [84,118]. In farmlands, it is now restricted primarily to field edges, swales, and along drainage ways [24]. Precipitation on basin big sagebrush sites ranges from 10 to 18 inches (250-460 mm) per year [24]. Basin big sagebrush is considered intolerant of alkaline conditions, but some ecotypes do grow in association with salt-tolerant plants such as shadscale (Atriplex confertifolia), black greasewood (Sarcobatus vermiculatus), and saltgrass (Distichlis spp.) [9,52]. In Utah sites occupied by basin big sagebrush tend to be slightly alkaline whereas those occupied by mountain big sagebrush tend to be slightly acidic [108].
Elevational ranges are as follows [5,53,118]:
SUCCESSIONAL STATUS:Big sagebrush is the climax species on most of its present day range [23]. Research suggests that invasion into other vegetation types was uncommon [23,31,50,52,78,101,124]. Humphrey [57] describes big sagebrush as a "late successional" species in southeastern Idaho. Basin big sagebrush may increase in disturbed pastures which have been seeded to grasses such as crested wheatgrass (Agropyron cristatum) [85]. In many instances, basin big sagebrush shows only a moderate increase in density on disturbed sites, but may exhibit large increases in crown density [118]. Seedling establishment may begin immediately following a disturbance, but it usually takes a decade or more before big sagebrush dominates the site. Many basin big sagebrush sites are now depleted of "normal" perennial grasses and are now dominated by cheatgrass (Bromus tectorum) [24].
SEASONAL DEVELOPMENT:Primary new leaves develop along the main stem in spring. As vegetative growth continues, new short lateral branches form from the existing stem and support smaller leaves which persist throughout the next winter, long after the initial leaves are shed. In Utah, accentuated stem growth begins in early June, with maximum longitudinal stem growth occurring in early June. By the end of June, vegetative stem growth begins to decline as reproductive buds and shoots begin expansion [34]. The reproductive shoots form, mature, and bear seed within the span of a single growing season [34]. Basin big sagebrush flowers from late August to October [94]. In Utah, reproductive shoots reach maximum size and flowerbuds first appear in late July [34]. Basin big sagebrush tends to flower later than Wyoming big sagebrush [6]. High-elevation ecotypes flower and set seed earlier than do valley ecotypes [77]. The inflorescence may persist until the following season [120]. Seed production occurs from October to December [77]. Most seed is shed in the fall, although some may remain on the plant through the winter. Seeds germinate in the spring as early as April. Seasonal development in the valley of Alpowa Creek near Clarkston, Washington, was as follows [32]: Approx. Date Phenological Event ------------ ------------------ Mar. 4 No evidence of new shoot growth Apr. 1 1.5-2 in (4-5 cm) of new shoot growth Apr. 30 4-5 in (10-13 cm) of new shoot growth Jun. 2 4-10 in (10-25 cm) of new shoot growth Jul. 1 18 in (45 cm) of new shoot growth Aug. 1 Remaining leaves mainly in panicle or at branch tips Sep. 1 Flower buds formed Oct. 3 Pollination starting Oct. 31 Fruits immature Feb. 27 Dissemination ended, inflorescence brittle Mar. 15 Buds swelling
Related categories for SPECIES: Artemisia tridentata ssp. tridentata | Basin Big Sagebrush |
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