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You are here >1Up Info > Wildlife, Animals, and Plants > Plant Species > Shrub > Species: Ambrosia deltoidea | Triangle Bursage
 

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BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Ambrosia deltoidea | Triangle Bursage
GENERAL BOTANICAL CHARACTERISTICS : Triangle bursage is a native, drought-deciduous, microphyllous shrub growing up to 1.65 feet (50 cm) tall [24, 29]. Innumerable slender and brittle branches spring up from the base forming a compact, roughly hemispherical crown [27, 35]. Mature triangle bursage crowns contain many dead branches which are shed only as a result of weathering [27]. The branches and young leaves of triangle bursage are tomentulose and resinous. Leaves become glabrous above with age. Leaf length is 0.6 to 0.8 inches (1.5-2 cm) or smaller [24,27]. Staminate heads are borne terminally. Two-flowered, pistillate involucres are clustered below the staminate spikes or on lateral branches. They produce globose, spiny achenes [24,27]. Triangle bursage possesses one long taproot with well-developed laterals [35]. Triangle bursage roots are slender, brittle, and longitudinally ridged with cork [6]. They are confined to the soil above the caliche hardpan--about 8 to 16 inches (20-40 cm) deep [6,35]. Besides roots arising from the main root, Cannon [6] found 50 adventitious roots about 0.12 inches (3 mm) in diameter which arose from the root crown, growing horizontally. Filamentous rootlets formed on many roots of triangle bursage after the soil had been moistened by rains, but such rootlets were short lived [6]. Triangle bursage is relatively short lived for a desert shrub. It has an observed longevity of about 50 years [10,27]. RAUNKIAER LIFE FORM : Phanerophyte REGENERATION PROCESSES : Triangle bursage reproduces sexually. Seed is produced abundantly, and seedlings establish in open space. In the Sonoran Desert, the relative abundance of triangle bursage seedlings was some 45 times the density of mature triangle bursage plants. The density of mature triangle bursage was similar to that of mature creosotebush, but 1,001 triangle bursage seedlings were counted while only 124 creosotebush seedlings were found [17]. Triangle bursage seeds are spiny and are probably dispersed by mammals. One study reports that triangle bursage has very limited ability to sprout after top-kill [18]. No other research describes the ability of triangle bursage to sprout. Triangle bursage reproduces from cuttings with the application of auxin [15]. SITE CHARACTERISTICS : Triangle bursage commonly grows in open spaces [17] on pediments, upper bajada surfaces, and basin floors on a variety of substrates including volcanic, granitic, metamorphic, alluvial, and caliche soils. There was no significant difference in cover of triangle bursage among volcanic, granitic, metamorphic, and alluvial substrates [21]. Triangle bursage is a frequent dominant on gravel outwashes, bajadas, and the ecotone between upper and lower bajadas [3,17,35]. Triangle bursage occurs almost entirely on very coarse soils that are relatively uniform in composition with little differentiation into horizons [3,14,15], although it occurs rarely on sand [27]. Precipitation percolates rapidly through the soil and drains quickly away along the underlying caliche layer [1,35]. Rainfall averages 4 to 12 inches (100-300 mm) annually with a bimodal distribution [16,25]. Temperatures at Organ Pipe National Monument and elsewhere in the Sonoran Desert fluctuate daily and seasonally. The mean frost frequency at the monument from 1956 to 1985 was 17 frosts per year (standard deviation=7, range=5-34) [21]. Parker [22] studied the soil characteristics of sites dominated by triangle bursage at Organ Pipe National Monument. Overall, triangle bursage was most abundant on flat terrain, but its cover was reduced on the lower bajadas and in the western portion of the Monument where pH was relatively high [22]. In the Ajo Mountains on south-facing slopes, sites had low pH and high available magnesium. In the Blanco Mountains, Senita Basin, and Quitobaquito Hills, available magnesium was low. In the Bates Mountains, Puerto Blanco Mountains, lower elevations of the Ajo Mountains, and flats in Senita Basin, triangle bursage grew on north-facing slopes in volcanic soil. In the Sonoyta Mountains, triangle bursage grew on northwest- to northeast-facing slopes. Leitner [14] found that triangle bursage preferred the cooler, more humid conditions of north-facing slopes at Punta Cirio, Sonora, Mexico, although it occurred on both north- and south-facing slopes. Triangle bursage grows from 1,000 to 3,000 feet (300-900 m) [13]. SUCCESSIONAL STATUS : Facultative Seral Species Triangle bursage is often the first plant to occupy an open area. Recruitment of other species rarely occurs in the open. Once established, triangle bursage acts as a nurse plant for other species, providing improved microhabitat and protection from herbivory [17,9]. Most mature triangle bursage plants have an associated perennial. Eighty-two out of 103 triangle bursage plants lacking associated perennials were small (and presumably young)--2 inches (5 cm) or less in root crown diameter. Only 2 of 101 triangle bursage plants that had other perennials associated with them had basal diameters of 2 inches (5 cm) or less [17]. Succession in the desert is difficult to characterize. Although changes in relative abundances of species may occur, plants rarely disappear from the ecosystem altogether because severe disturbance is usually lacking [17]. McAuliffe [17] described changes in desert vegetation in terms of community dynamics instead of succession. For instance, in communities codominated by triangle bursage, triangle bursage colonizes open space and acts as a nurse plant for other perennial shrubs. Some larger, presumably older individuals within the population bear no evidence of former associations with triangle bursage, probably because they have outlived it. Triangle bursage continues to colonize other open space. Relative abundance of species may be altered, but triangle bursage presence is maintained [17]. Triangle bursage is known to establish on overgrazed desert grasslands. Tueller [31] suggested that partial or complete protection from grazing on triangle bursage-invaded rangeland will promote secondary succession. Secondary succession results in the establishment of climax grasses and palatable shrubs and a decrease in unpalatable shrubs such as triangle bursage. When growing among creosotebush and jumping cholla (Opuntia fulgida), triangle bursage occupies a distinct root zone so interspecific competition is minimized [35]. In one study, no roots of neighboring plants grew near triangle bursage roots [6]. SEASONAL DEVELOPMENT : Most new leaves on triangle bursage develop and mature during the winter and early spring [29]. Triangle bursage flowers from February to July [33]. Seeds are produced after both summer and winter rains [27].

Related categories for Species: Ambrosia deltoidea | Triangle Bursage

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Information Courtesy: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory. Fire Effects Information System

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