| | |
 |
|
| 
| ||
 |
|
|
|
 |
|
Wildlife, Animals, and Plants |
|
|||
|
BOTANICAL AND ECOLOGICAL CHARACTERISTICS
GENERAL BOTANICAL CHARACTERISTICS:Blackbrush is a native, aromatic shrub with soft wood [109], growing from 1 to 6 feet (0.3-2 m) tall [16,27,38,79,84,85,90,117,123]. It shows compact, erect growth, with a symmetrically round form [16,118]. The scientific name refers to the unusual sheath or torus around the ovary (Coleogyne) and to its many-branched morphology (ramosissima) [17]. The common name is derived from the color of the dense branches, which have gray bark that turns black with age or when wet [8,16,17,90]. The terminal branches grow for a few years then die, drying back for several centimeters from the tip and resulting in the characteristically tangled spinescence of blackbrush [16,17,79,84,85]. Apical dominance is removed when the terminal buds die, allowing development of lateral branches [16,78,79,84,85]. The shrub undergoes stem-splitting, in which the main stem splits into several smaller portions [16,17]. These clusters of multi-stemmed segments also correspond to separate segments of the root system [118]. Blackbrush has a diffuse and shallow root system [63]. The greatest root biomass of blackbrush is found at a soil depth of 4 to 12 inches (10-30 cm), with few roots penetrating the fractured caliche layer, if present [16,79,84,85]. Large supporting roots are located directly beneath the plant, and root biomass tends to decrease with increasing distance from the plant and with increasing soil depth [79,84,85]. Shallow soils often result in a low root:shoot ratio and limited root development in blackbrush communities [58]. Blackbrush is evergreen [1,27,79,84,85,89,94,109], though it may lose substantial leaf area during the dry summer season [96]. Blackbrush is drought-deciduous, avoiding water stress by becoming temporarily dormant and shedding older leaves as stress intensifies during the dry season [54]. After leaf drop, it enters a long summer dormancy [54] Atypical of the rose family [8,17], blackbrush flowers typically lack petals [38,68,90,123]. Blackbrush flowers are perfect, solitary, and terminal on the young branchlets [16]. The fruits are dry, leathery achenes, 3 to 4 mm long, with a bent and twisted style [38,90,117]. Blackbrush has a "long" life span [92,121], and its life history emphasizes maintenance of existing individuals; establishment from seed is rare [121]. Blackbrush-dominated stands are generally monotypic, simple communities where shrub cover is high. Close spacing permits little growth of other vegetation [8,16,17,41,45,58,79,84,85,94].
RAUNKIAER [88] LIFE FORM:Phanerophyte
REGENERATION PROCESSES:Blackbrush regenerates from wind-pollinated seed [64,102]. Fruits are large and heavy with no visible means of rapid dispersal; the only obvious means of dispersal are rodent activity and storm runoff [9,16,64,121]. Blackbrush is a mast species, and although winter precipitation initiates flowering, size of the resulting fruit crop is a function of available stored resources [102]. The scarcity of blackbrush seedlings on sites in southwestern Utah indicates that blackbrush reproduction occurs infrequently [23]. Blackbrush seed germination occurs in February or March and can occur from relatively deep in the soil [16,17,53]. Seedlings often appear in clusters from rodent caches [9,16,17,53,121]. Few seedlings are actually present in blackbrush stands. Due to several factors most seedlings do not survive past their cotyledon stage. Destruction by rodents digging up the cache for remaining seeds, soil erosion that exposes seeds and then covers them with debris, and limited soil moisture in the summer cause seedling mortality [16,17,60]. Infrequent and inconsistent seed set and seedling establishment may also result from herbivore browsing [40]. Blackbrush generally has a low germination rate [9,121], but with heavy, early spring rains, blackbrush seeds germinate in relatively large numbers. These may be the only conditions under which substantial germination occurs, suggesting that "pulse" climatic events are needed for establishment [9,10,121]. Soil moisture is required before seeds will break dormancy; watering at 2-week intervals was found to increase germination more than watering at 1- or 3-week intervals [53]. Germination of blackbrush seeds requires cold stratification without light [16,17,53]. Germination has been found to increase from 53% with no treatment to 83% after 7 weeks of cold stratification at 39 degrees Fahrenheit (4 oC) [16,17,29,53]. Seeds have also been found to respond to a moist storage at 41 degrees Fahrenheit (5 oC) and germinate at that temperature [118]. Germination patterns vary as a function of climate and elevation. Seeds collected from low-elevation sites were less dormant than seeds from high elevation sites in southern Utah and Nevada; the seeds from the 3,930-foot (1200 m) sites required a shorter chilling period to increase germination response than those from the 5,085-foot (1550 m) sites [53]. This relationship between dormancy status and site elevation may indicate that blackbrush has evolved ecotypes [53,75]. Dreeson and Harrington [29] found that substantial age and source differences are apparent in regard to population germination and/or stratification requirements. The sensitivity of seeds to salinity may be a limiting factor governing the distribution of blackbrush [17,118]. Blackbrush has a slow growth rate [57,121] that may be the result of shallow soils and an often-present caliche layer, which impede root growth and soil moisture [57].
SITE CHARACTERISTICS:Blackbrush ranges typically occur at elevations between 2,500 and 8,000 feet (760-2440 m) [6,16,57,58,106,118], and distribution is strongly related to differences in precipitation, temperature, and soils [17]. The upper elevation limit may be set by colder air temperatures, while the lower limit may be determined by cold air draining from adjacent mountain slopes into the valley bottoms [57,58], or by low soil moisture [17,57,58]. Average annual precipitation on blackbrush sites ranges from 4.5 to 11.5 inches (114-292 mm) [1,2,9,23,36]. The greatest precipitation on Utah sites generally falls from November through March; April, June, and October are dry; May has variable precipitation; and July and August experience summer storms [17]. Blackbrush sites are characterized by high summer and low winter temperatures, ranging from -11 to 116 degrees Fahrenheit (-24 to 47 oC) [17,23]. Blackbrush stands occur on well-drained sites including alluvial and colluvial slopes, washes, valley bottoms, lowlands, and flatlands of mild slope, and derived from limestone, sandstone, gneiss, and basalt [1,2,5,6,8,10,15,16,23,47,51,55,58,106,107,118,123,124]. Soils supporting blackbrush are generally shallow, poorly developed, and coarse textured, often with abundant exposed rock and high sand content [5,6,8,17,23,44,51,98,118,123]. These sites are also calcareous, moderately alkaline, and low in salinity [9,17,94,118] with pH ranging from 7.8 to 8.5 [16,17,23]. Blackbrush has a low tolerance for salinity, excessive soil moisture, and impeded soil aeration [124]. Shrubs are often clustered on small mounds, evidently created by entrapment of wind-blown material [121]. There is typically a well-developed microphytic crust on the soil surface between shrubs [125]. The shallowness of soil may in part determine the abundance and distribution of blackbrush [23,55]. Blackbrush is abundant on shallow soils with caliche layers [2,8,12,16,17,23,55,118,125], but is more abundant on adjacent, deeper soils [118]. Blackbrush occurs on ancient granitic debris flows in California, with the cover and density of blackbrush increasing with the age of the debris [120,121]. On the oldest depositional area, blackbrush is nearly monospecific, and the only physical differences between the flows studied are those resulting from difference in geologic age; notably, the intermediate and oldest flows had caliche layers [120,121]. The association of blackbrush with old soils and the lack of it on young basalt flows implies either an allogenically controlled succession with blackbrush dominating [121] or an affinity of blackbrush for calcium carbonate irrespective of the age of the surface [121,125]. Blackbrush individuals alter the soil chemistry around their bases [16,17,121]. Bowns [16] found that percent totals of nitrogen and available phosphorus are higher in soil beneath blackbrush plants than in the spaces between, and both nutrients decrease with increasing soil depth [16].
SUCCESSIONAL STATUS:Blackbrush is thought to be climax vegetation, occurring in late seral stages and generally dominating drier sites with residual or colluvial soil [16,17,107]. It forms stable vegetation assemblages on least disturbed geomorphic surfaces, and persists longer than other plant assemblages on these surfaces [54,107,121]. On some sites it is considered an invasive species, and may invade grasslands following overgrazing [8,16,17,122]. The occurrence of blackbrush on undisturbed, relict areas supports the idea that blackbrush is a climax species [45]. Where dominant on undisturbed sites, blackbrush cover and density are substantially higher than on adjacent disturbed sites [120,121]. In the blackbrush association of the northern Mojave Desert, 1 study found 3.2 plants/100 m2 on disturbed, early-successional sites, compared to 17.9 plants/100 m2 on undisturbed sites [34]. Blackbrush has been described as a mid- to late-seral species in California, increasing in occurrence at the expense of ephedra, wolfberry, and hopsage and forming nearly pure stands at the expense of all plant species except ephedra [120]. Succession to blackbrush replenishes the soil for annuals because it provides better soil moisture conditions early in the season and higher nitrogen levels under the shrub canopy [122].
SEASONAL DEVELOPMENT:Blackbrush initiates shoot growth and sets leaves in March [1,2,16,17]. Twig and leaf growth are normally restricted to late March through mid-June, but because blackbrush summer dormancy results from a combination of low soil moisture and high temperatures, heavy summer rains may result in resumed growth in September and October [2,16,17,59,118]. When watered at 104 degrees Fahrenheit (40 oC), no growth occurred; however, when temperature was dropped to 89 degrees Fahrenheit (31 oC) new growth was initiated [2]. In laboratory experiments, root growth and stem growth were better at 70 degrees Fahrenheit (21 oC) than at 61 (16 oC) or 82 degrees Fahrenheit (28 oC), indicating a narrow temperature tolerance [2,118]. Blackbrush flowers only in spring, probably the result of photoperiodism [1]. Flowering is induced by moderate to heavy winter precipitation [9,56]. Increases in winter precipitation and resulting soil moisture contribute to an abundance of flowers and seeds [16]. Flower buds begin to develop at the tips of terminal or lateral branches 2 weeks after the shoot growth begins and are fully open after 5 weeks [1,16,17]. By 6 weeks, 80 to 100% of the flowers are open, and no further twig elongation occurs once the flowers are fully developed [16,17]. Blackbrush at high elevations has a shorter flowering period than blackbrush at lower elevations, and flowering on individual plants is not synchronous, occurring over a 1- to 3-week period [56]. Fruits begin to develop in late April and early May [1,16,17]. After growth ceases in June, older outermost leaves yellow and dry out. Abscission occurs in July and August, causing a large buildup of organic matter [1,2,16,17]. Blackbrush may lose most of its leaves during summer dormancy, but retains enough leaves at the ends of branches to be considered an evergreen species [1,2]. Blackbrush phenophases vary according to location within its range. The following table lists the mean initial date of each phenophase along an elevation gradient from 4,900 to 5,900 feet (1,500-1,800 m) in southern Nevada. Standard errors and significant ( p£0.05) differences are denoted by a and b, respectively [56].
Related categories for SPECIES: Coleogyne ramosissima | Blackbrush |
 |
 | |
| |
| |
| Content on this web site is provided for informational purposes only. We accept no responsibility for any loss, injury or inconvenience sustained by any person resulting from information published on this site. We encourage you to verify any critical information with the relevant authorities. | |
| |
|
About Us | Contact Us | Terms of Use | Privacy | Links Directory |
| 1Up Info All Rights reserved. Site best viewed in 800 x 600 resolution. |
