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Wildlife, Animals, and Plants |
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BOTANICAL AND ECOLOGICAL CHARACTERISTICS
GENERAL BOTANICAL CHARACTERISTICS:Rubber rabbitbrush is an erect round or pyramidal native shrub that typically reaches 12 to 90 inches (31-229 cm) in height [17,55]. Certain populations have been reported to reach heights of 10 to 12 feet (3.3-3.6 m) [77]. Plant spread is generally between 0.2 and 3.3 feet (0.6-1 m) [60]. Several more or less upright stems arise from the base and branch to give plants a rounded appearance. Rubber rabbitbrush exhibits a number of adaptations for surviving in an arid environment. Leaves and stems are covered with a felt-like layer of trichomes that insulate the plant and reduce transpiration [3]. Leaves are linear and less than 0.04 inch (0.1 cm) wide [17]. Rubber rabbitbrush has a deep taproot with less well-developed laterals [8,18,19]. Flowers are perfect [17]. Stanton [123] reports that plants may be "full grown" within 4 years. Botanical characteristics such as leaf and flower characters vary considerably among the subspecies of rubber rabbitbrush [141]. Two separate series are recognized within Chrysothamnus nauseosus, a gray form and a green form. Green forms are characterized by glabrous involucres and greenish leaves and stems (i.e., C. n. ssp. consimilis, graveolens, leiospermus, and mohavensis. Gray forms have tomentose involucres and gray to whitish foliage and stems (i.e., C. n. ssp. albicaulis, bigelovii, hololeucus, and nauseosus [7].
RAUNKIAER LIFE FORM:Phanerophyte
REGENERATION PROCESSES:Rubber rabbitbrush establishes from seed and by sprouting. Sprouts originate at or near the soil surface from epicormic buds located on the stem and root crown [91,147,149]. For more information on sprouting, see "PLANT RESPONSE TO FIRE" below. Seed ripens in autumn [31,85,90]. The wind-dispersed seed may be carried up to 165 yards (151 m). Rubber rabbitbrush usually produces an abundance of seed, although fruit fill varies by plant and year [88]. Good seed crops generally occur every year or every 2 years [133]. Mild weather in late fall and early winter can enhance the percentage of seed which is viable [96]. Seeds do not persist in a seedbank [85]. Seeds germinate in winter or spring after snow melt. Seed dormancy in rubber rabbitbrush is described as conditional and temperature-dependent [88]. Germination occurs over a broad range of temperatures but over a narrow range of moisture conditions [109]. A stratification period is not necessary for rubber rabbitbrush but may speed germination. Stratification period may extend to 120 days [70]. Without stratification, germination begins within 5 to 20 days after planting [27]. In laboratory tests, germination rates are highest at 58 to 86 degrees Fahrenheit (20-30 oC) and lowest at 50 degrees Fahrenheit (10 oC) [109]. A specific light regime is not required, but germination can be inhibited by high saline concentrations [67,138]. Germination rates vary dramatically by seed source [85]. For example, the length of time required for 50% germination ranged from 5 to 96 days for seed obtained from California, Arizona, Nevada, Utah, and Montana [79]. Subspecies from the same location generally show similar germination response to temperature [88]. Subspecies with wide ecological amplitude often show a wide range of germination response [88]. Specific germination characteristics by subspecies are as follows [67,114]: Chrysothamnus nauseosus ssp. bigelovii - excellent germination at or below 91 degrees Fahrenheit (32.5 oC) C. n. ssp. consimilis - mean germination time = 5.9 days; germination at constant or alternating temperatures; best germination at 57 to 86 degrees Fahrenheit (25-30 oC) Seeds from southern or warm desert populations germinate more rapidly than do those from northern or montane and high-elevation populations [79,138]. Meyer and McArthur [88] report that under laboratory conditions of 37 degrees Fahrenheit (3 oC), seed collections from warm desert habitats required less than 2 weeks to achieve 90% germination, whereas collections from montane habitats took up to 20 weeks. Similarly 50% germination at 37 degrees Fahrenheit (3 oC) took up to 100 days for seed from areas with severe winters. Mojave Desert seeds reached 50% germination in less than 1 week [85]. Collections from middle elevations exhibit asynchronous germination in the cold. Germination rates at near-freezing temperatures correlate with mean January temperatures at the collection site [90]. Seed collections from high elevation populations may show dormancy at autumn temperatures and may germinate slowly under the snow or at near-freezing temperatures. Collections from warm deserts germinate rapidly over a range of temperatures including near-freezing temperatures [88,90]. Rubber rabbitbrush seed retains good viability for 0 to 3 years [96,117]. In laboratory tests, germination declined from 80% to 14% from the second to fifth year of storage [67]. After 4 years of storage, viability dropped significantly as follows [125]: year % germination
2 80
3 65
4 34
5 14
7 11
10 7
Roots of new seedlings grow rapidly [82]. Early-season mortality is primarily caused by freezing, damping off, and improper rooting [31]. After early May, mortality is mostly due to water stress. Seedling emergence and establishment are severely limited in dry years [109]. Established seedlings do not persist unless late spring rains replenish soil moisture and roots elongate before surface moisture is depleted. In eastern Oregon, seedlings established in grass and litter on the northeast side of older shrubs. They also established on north sides of small mounds or indentations made by animals. Seedling mortality on these sites was greater than 50% by June.
SITE CHARACTERISTICS:Rubber rabbitbrush occurs in the cold deserts of the Colorado Plateau, throughout much of the Great Basin, and in warm deserts of the Southwest from lower-elevation Sonoran to subalpine zones [55,115]. Rubber rabbitbrush favors sunny, open sites throughout a wide variety of habitats including open plains, valleys, drainage ways, foothills, and mountains [26,60,123,142]. It is particularly common on disturbed sites [54]. Rubber rabbitbrush is cold hardy to temperatures of -40 degrees Fahrenheit (-40 oC) and tolerant of both moisture and salt stress [55,115]. The subspecies of rubber rabbitbrush may overlap in their ranges, but they often have somewhat different ecological requirements. Habitat preferences of Chrysothamnus nauseosus by subspecies are as follows [17,34,77,80,111,124] C. n. ssp. albicaulis - foothills, open slopes C. n. ssp. consimilis - hot, dry, alkaline lowlands, floodplains, and valley bottoms C. n. ssp. graveolens - foothills and valleys C. n. ssp. hololeucus - dry plains, valleys, and mountain slopes C. n. ssp. leiospermus - diverse habitats C. n. ssp. salicifolius - mountains, mountain brush Rubber rabbitbrush grows on a wide range of soils [47,54]. Soils tend to be medium to coarse-textured and somewhat basic, but may range from moderately acidic to strongly alkaline [60]. This shrub commonly grows on dry, sandy, gravelly or heavy clay [123]. Rubber rabbitbrush is somewhat salt tolerant [54,55]. Although rubber rabbitbrush often occurs on poor soils, it can also be found on some productive soils [55]. Soil preference varies according to subspecies as described below [4,32,62,78,111,112]: C. n. ssp. consimilis - pH of 5.6-8.6; common on deep, heavy soils and where water table ranges from 4.9-8.2 feet (1.5-2.5 m) C. n. ssp. hololeucus - pH of 6.5-8.9; soils often coarse, deep, well-drained C. n. ssp. iridis - barren seepage areas; gypsiferous soil C. n. ssp. turbinatus - restricted to sandy soils Rubber rabbitbrush grows across a wide elevational range. It grows from sea level to 10,500 feet (3,203 m) [138]. In the Great Basin, rubber rabbitbrush grows from 3,000 to 8,000 feet (900-2,400 m) [60]. In California, this species has been reported from 3,000 to 8,000 feet (914-2,438 m) in elevation [34]. Subspecific variation in elevational range is common. For example, where C. n. ssp. hololeucus and C. n. ssp. albicaulis occur within the same geographic area, C. n. ssp. albicaulis is found at higher elevations, usually over 6,000 feet (1,850 m), and C. n. ssp. hololeucus is restricted to lower elevation sites. Elevation range by subspecies is listed below [77]: C. n. ssp. albicaulis 2,000 to 7,000 feet (610-2135 m) C. n. ssp. consimilis 2,000 to 6,000 feet (610-1850 m) C. n. ssp. graveolens 3,000 to 6,000 feet (925-1850 m) C. n. ssp. salicifolius 6,000 to 9,000 feet (1,850-2745 m)
SUCCESSIONAL STATUS:Rubber rabbitbrush is generally regarded as an early seral species that rapidly invades and colonizes disturbed sites [55,134]. It is commonly found in seral communities such as along roadsides and on degraded rangelands [88,142]. Although it colonizes sites with little topsoil, it also invades fairly productive low-elevation riparian areas and deeper soils adjacent to drainage bottoms [23,86,122]. Rubber rabbitbrush often increases after the removal of big sagebrush [112]. On some sites, seedlings may be unable to become established until herbaceous pioneers increase soil stability [16]. Rubber rabbitbrush generally declines later in succession [135]. In the high desert of Oregon, it attains dominance only on highly disturbed early seral stands, but remains dominant for long periods on burned or abandoned agricultural lands [131]. Rubber rabbitbrush is considered a mid-seral species in some semi-arid sagebrush communities [84]. It was found to dominate the shrub layer on 35 to 65 year old pinyon-juniper sites in north-central Arizona [127]. During this time, rubber rabbitbrush cover declined from 22.03% to 10.1%. In shrub communities in Idaho, rubber rabbitbrush can remain dominant for 10 to 25 years after fire [149]. A "typical" successional pathway on sand dunes of Idaho is listed below [16]: stage 1 0 to 30 years pioneer species such as Elymus spp.
stage 2 10-70 years rubber rabbitbrush assumes dominance
stage 3 50-70 years antelope bitterbrush (Purshia tridentata)
stages 4-5 > 70 years big sagebrush, followed by antelope
bitterbrush
Meyer and McArthur [88] report that some of the geographically isolated subspecies form part of climax vegetation on dunes and shale barrens. Rubber rabbitbrush may continue as a minor component in stands near or at climax condition.
SEASONAL DEVELOPMENT:Bud burst usually occurs in late March or early April but may occur as early as late February. Restricted growth continues until May. Accelerated growth occurs from May until early or mid-August. Photosynthesis continues through the summer drought period [19]. Vegetative growth begins earlier and is more vigorous where competition is less [113]. Flower bud initiation takes place in early- to mid-summer, with flowering from mid-summer to fall [96,115]. Populations at higher elevations flower in July whereas those from low elevation Mojave Desert populations do not begin flowering until mid-October. Populations from cold deserts and northern pinyon-juniper woodlands are intermediate [88]. Seed ripens from late fall to early winter [96]. Seed set occurs in late September at higher elevations and in late November at low elevation Mojave Desert sites [88]. Seed dissemination starts before all flowers are fully mature. The rate of dissemination is affected by weather conditions, including wind and moisture. Fruit typically matures earlier on plants experiencing little competition. Germination occurs from March through June [133]. Generalized phenological events were reported as follows in a study conducted near Millican, Oregon [82]:
Phenological Event Date
Leaf development Mid-April to Mid-May
Flower bud initiation Mid-June to Mid-July
Bracts yellow Early Aug. to Early Sept.
Flowers mature Early Sept. to Early Oct.
Seed disseminated Early Sept. to Mid-Nov.
Phenological development of rubber rabbitbrush near Elko, Nevada was as follows [108]:
Date Event
7/18/53 Buds initiated
8/28/53 Mid-bloom
4/28/54 Dormant
6/3/54 2-4" Growth
6/30/54 3-6" Growth
Related categories for SPECIES: Chrysothamnus nauseosus | Rubber Rabbitbrush |
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