|
Wildlife, Animals, and Plants
|
|
BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Purshia tridentata
| Antelope Bitterbrush
Antelope bitterbrush is a native, deciduous shrub [30]. The fruit is an achene, 0.13 to 0.5 inch (3-13 mm) long. Antelope bitterbrush has two common ecotypes, both present throughout its range: multiple-stemmed, decumbent plants, and single-stemmed, columnar plants [30,44,169,191]. Plants may reach 12 to15 feet (3.6-4.5 m) in height, but usually grow to 3 or 4 feet (0.9-1.2 m) [20]. The decumbent form is more prevalent at higher elevations. Antelope bitterbrush is long lived. Nord [176] reported a 115-year-old plant that was 10 inches (25 cm) high and spread over 7 square feet (1.8 m2). At a lower elevation, Nord found a 128-year-old plant that was 12 feet (3.6 m) high and 20 feet (6 m) across.
Antelope bitterbrush has a long taproot or taproots [19, 58] that reach up to 15 to 18 feet (4.5-5.4 m) in length [158,176], and few shallow roots [12].
Antelope bitterbrush sometimes has nitrogen-fixing root nodules, a result of a symbiotic association with Frankia spp. actinomycetes [2,46,151,169,192,195,238]. Degree of nodulation depends on site conditions including soil moisture content and salinity, presence of inoculants, and available nitrogen [171,192,193]. Presence of nodules, even in high numbers, does not necessarily indicate that significant amounts of nitrogen are being added to the soil [130,131,195]. Trappe [132] claims antelope bitterbrush has vesicular-arbuscular mycorrhizae, not nodule-forming actinorrhizae.
Phanerophyte
Regeneration is by seed, stem layering, and sprouting [20,30,169,205]. Sprouting ability of antelope bitterbrush varies. Reports of sprouting in the literature mostly relate to fire and are discussed in "PLANT RESPONSE TO FIRE" below.
Antelope bitterbrush reaches seed-bearing age in 8 to 10 years, depending on local site conditions [105]. Flowers are pollinated by insects [21,30,] except where plants are crowded and wind pollination is possible [182]. Antelope bitterbrush is highly self-incompatible [30].
Achenes fall beneath parent plants when mature and dry [105]. The papery cover prevents seed germination until the cover rots away, which usually occurs over winter [85]. Seeds are dormant and require cool-moist stratification or damage to the seedcoat by mechanical scarification, chemical treatment, or soaking in aerated water for 1 to 2 weeks to break dormancy [33,84,163,250,246]. Four to six weeks of chilling at 36 degrees Fahrenheit (2 degrees C) is sufficient to germinate antelope bitterbrush seeds [163,248]. Seeds may enter a second dormancy if chilling requirements are not met [162,163,246,251]. Stevens and Jorgensen [212] found that 74% of antelope bitterbrush germinated after 25 years of storage. There is no available information regarding antelope bitterbrush persistence in seedbanks. Natural seedling establishment occurs only in years with normal to above-normal spring precipitation [84,133]. Artificial seeding processes that do not bury the seed are rarely successful because conditions needed for germination do not usually exist for long on the soil surface.
Rodent caches are often crucial to natural regeneration of antelope bitterbrush [55,83,85,126,199,201,204,229,236,248]. Rodents and ants may stash the entire crop of seed. Accumulation of litter and duff in forested antelope bitterbrush habitats discourages rodent caching and therefore decreases seedling regeneration [85]. Rodents return in spring to eat the sprouting cotyledons, which are a rich source of carotene. Uneaten seeds are a key source of new plants [85,169]. Rodent and insect herbivory are significant causes of establishment failure, however [85,161]. Clements and Young [55] found rodents preferred antelope bitterbrush cotyledons to millet (Panicum millaceum) seed, which is usually a preferred food. Rodent herbivory reduced ability of antelope bitterbrush seedlings to reach true leaf stage by 47 to 87% in test plots.
Ferguson and Medin [94] estimate that on an undisturbed Idaho range site dominated by antelope bitterbrush, only two antelope bitterbrush plants established per year due to competition from cheatgrass. They suggest, however, that antelope bitterbrush is likely to persist if it completes its first growing season without competition [123].
Decumbent antelope bitterbrush may layer. Layering is more prevalent above 7,000 feet (2,100 m) in California, where more than 30% of bitterbrush plants were found to layer. Only 12% did so below 7,000 feet. Layering is more common on fine-textured than coarse-textured soils [176].
Antelope bitterbrush is found on all slopes and aspects, usually on well-drained, permeable soils, from 3,100 to 10,000 feet (900-3,000 m) elevation. Average annual precipitation varies from 12 to 36 inches (300-910 mm) and usually falls as winter snow [205]. In Montana west of the Continental Divide, the antelope bitterbrush-bluebunch wheatgrass association occurs from 3,500 to 5,500 feet (1,000-1,650 m) elevation, generally on southern and eastern slopes. Annual precipitation ranges from 10 to 15 inches (250-380 mm) [109,205]. In Utah, antelope bitterbrush is common on dry rolling hills with northern exposures. In the basin big sagebrush cover type, antelope bitterbrush is found on deep, permeable soils below 7,000 feet (2,100 m) elevation [179].
Antelope bitterbrush survives on rocky and arid sites due to its long taproot or taproots [19, 58] and nitrogen-fixing capacity [12,192,205]. In Idaho, Murray [170] found more plants established on lava outcroppings than in swales with deeper soils. Antelope bitterbrush occurs on substrates with minimal root restriction. It is common on coarse-textured soils and on finer-textured soils with high stone content [77]. Antelope bitterbrush is found on slightly acid soils in California [175] but on basic soils in Utah [186]. It does not tolerate saline soils [176]. Seedlings have high tolerance for extremely high surface soil temperatures [91]. In eastern Oregon and western Nevada, antelope bitterbrush is important on upland sites. It is most frequent on highly calcareous, fine-textured sedimentary soils but also occurs on loamy sand and silty loam soils [7]. In Craters of the Moon National Monument, antelope bitterbrush dominates on old cinder cones, lava flows, and other substrates of volcanic origin [14].
Antelope bitterbrush is shade intolerant [14,154,159,208]. It is an early colonizer on disturbed sites [14,192], perhaps aided by its nitrogen-fixing capacity. In areas where antelope bitterbrush dominates and natural regeneration is not occurring, old, decadent antelope bitterbrush may be the climax community [218]. Biomass productivity in antelope bitterbrush declines after 70 years [14]. Stands without disturbance become senescent and decadent [56].
Antelope bitterbrush is generally replaced by western juniper where their ranges overlap [43]. In Colorado, antelope bitterbrush is much more prevalent in seral rather than climax Colorado pinyon-Utah juniper (Pinus edulis-Juniperus osteosperma) communities [81].
Hayward [115] identified antelope bitterbrush as a xerosere species in mountain shrublands.
Leopold [150] claims antelope bitterbrush is a seral species that would be replaced by bunchgrasses in eastern California if overgrazing by livestock and wildlife had not disrupted the natural succession.
Antelope bitterbrush flowers from early spring [21] to July. Fruits ripen from July to September, depending on elevation [30]. Old plants tend to put more energy into seed production than twig/canopy production unless stimulated by browsing [94].
Seasonal development in Wenatchee, Washington, is as follows [157]:
Growth stage Date
spring dormancy March 3-7
full leaf on old twigs May 8-12
full flower May 22-26
Rapid twig growth and early seed formation June 20-24
Seed maturity July 11-15
Cessation of growth September 2-7
leaf fall November 14-18
Related categories for
SPECIES: Purshia tridentata
| Antelope Bitterbrush
|
 |
