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Wildlife, Animals, and Plants |
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BOTANICAL AND ECOLOGICAL CHARACTERISTICS
GENERAL BOTANICAL CHARACTERISTICS:Gray horsebrush is a spineless, many-branched native shrub [26,35,37,54,55]. This perennial grows up to 6.5 feet (2 m) tall [35,37,54,69]. Leaves are 0.4-1.2 inches (1-3 cm) long and 0.04-0.16 inch (1-4 mm) wide [11,26,35,37,55]. Medium-sized flowerheads are borne on tips of numerous short branches in small, cymose clusters [11,26,35,37,55]. The plant produces light achenes that are 0.12-0.16 inch (3-4 mm) long [11,26,35,37,54,55]. Occasional dense stands of gray horsebrush occur in the sagebrush zone [37], but stands with more than a few hundred individuals are rare. A typical colony size is 25-50 plants [54]. RAUNKIAER [47] LIFE FORM:Phanerophyte REGENERATION PROCESSES:Breeding system: Gray horsebrush is a monoecious species with perfect flowers [35,54]. Pollination: Gray horsebrush is pollinated by generalists including moths, bees, flies, beetles, and other insects. Nearly all gray horsebrush shrubs within a given colony flower within several days of each other. Flowering occurs relatively early in comparison to associated plants, minimizing competition for pollinators. Pollen fertility is high [54]. Seed production: Seed production is high [56]. Seed dispersal: Seeds are light (120,000 seeds per pound) [56] and wind dispersed [69]. Seed banking: No information Germination: No information Seedling establishment/growth: Gray horsebrush seedlings are somewhat rare, indicating a long colony turnover rate. This may be due to the harsh environments in which gray horsebrush grows [35,54]. Though seedling vigor is rated low [56], numerous seedlings have been observed in recently burned areas [35]. Asexual regeneration: Gray horsebrush sprouts from the root crown after fire [15,24,28,59,66]. SITE CHARACTERISTICS:Gray horsebrush is found in dry, open places on hills, ridges, and plains [11,19,26,35,55] at elevations ranging from 1,300 to 10,800 feet (400-3,300 m) [15]. In the southern part of its range, gray horsebrush is found at higher elevations (5,800-9,700 feet, 1,800-3,000 m), while in the northern areas of its range, British Columbia and Washington, it is found at lower elevations (1,300-1,900 feet, 400-600 m) [54]. It is adapted to medium to coarse soils with a pH of 7 to 8 [56] and is most often found in gravelly or sandy loams [26,55] in semi-desert saline or alkali loam range sites [26]. However, 1 source characterizes gray horsebrush as salt intolerant. The annual moisture requirement of gray horsebrush is 5-12 inches (130-300 mm); it is considered highly drought tolerant [56]. The plant tends to occur least frequently on south-facing slopes but occurs equally on north, east, and west slopes [27]. Elevation ranges for gray horsebrush in some states in its range include:
SUCCESSIONAL STATUS:Though gray horsebrush can be found in nearly all successional stages, it is primarily considered a seral species [54]. One study reported that the species comprised greater than 5% of the cover only in early-mid successional stages [27]. It is not shade tolerant [56]. SEASONAL DEVELOPMENT:Gray horsebrush begins growth in spring and blooms in spring or summer [24]. It begins flowering in mid-June in the northern part of its range (British Columbia), while blooming begins in late July or early August in southern California and northern Arizona [35,37]. Blooming may continue until September in New Mexico [34] and as late as October in Arizona [26]. Leaf fall occurs in autumn [11]. Flowering dates in several states are as follows:
The following gray horsebrush phenology data are from a study in the Upper Snake River Plains of southern Idaho [6]:
Related categories for SPECIES: Tetradymia canescens | Gray Horsebrush |
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