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Adrian Watson
Adrian Watson

Black Greasewood _TOP_

The following grasses are common associates and often codominant with black greasewood: saltgrass (Distichlis spicata), basin wildrye (Leymus cinereus), Salina wildrye (L. salinus), alkali sacaton (Sporobolus airoides), alkali muhly (Muhlenbergia asperifolia), western wheatgrass (Pascopyrum smithii), bluebunch wheatgrass (Pseudoroegneria spicata), bottlebrush squirreltail (Elymus elymoides), and bluegrasses (Poa spp.) [7,13,33,38,60,69,92,93,93,96,105,128,141,142,143,155].

black greasewood

In Washington, black greasewood is commonly found with spiny hopsage, big sagebrush, saltgrass, and cheatgrass (Bromus tectorum) [71]. Black greasewood is dominant or codominant with big sagebrush in the northern plains; other associates include shadscale, Nuttall's saltbush (Atriplex nuttallii), western snowberry (Symphoricarpos occidentalis), rubber rabbitbrush, fourwing saltbush, winterfat, western wheatgrass, blue grama (Bouteloua gracilis), slender wheatgrass (E. trachycaulus), bluebunch wheatgrass, saltgrass, Sandberg bluegrass (P. secunda), and thickspike wheatgrass (E. lanceolatus) [9,12,76].

Photo courtesy Gerald and Buff Corsi@ California Academy of Sciences. GENERAL BOTANICAL CHARACTERISTICS:The following description of black greasewood provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available (e.g. [84,85,149]).Black greasewood is a native flowering perennial [83,107,112,116]. Its growth form is erect to low and spreading, reaching 10 feet (3 m) tall [5,15,16,47,48,66,74,96,103,107,112,116] and 3 to 6 feet (0.9-1.8 m) across [78]. The multiple branches are brittle and spinescent; the ends of smaller branches taper to sharp thorns [15,16,17,47,48,50,66,74,96,103,107,116]. Deciduous leaves are fleshy and narrow, and are 0.4 to 1.6 inches (1-4 cm) long [15,16,17,47,48,50,66,66,74,96,103,103,107,116]. Black greasewood seeds have long wings and are 0.16 to 0.2 inch (4-5 mm) long and 0.39 inch (1 cm) wide (including wing margin) [17,66].

Where groundwater is present, maximum rooting depth of black greasewood is governed by the depth to a saturated zone. It is normally deep rooted but has some shallow roots near the soil surface [71]. Black greasewood consistently forms deep, branched taproots [68,78,116]. Branching increases toward the soil surface; taproots typically penetrate downward to the capillary fringe overlying the water table. Black greasewood is clonal and may have a number of major stem clones arising from 1 large clump. These clones in turn produce numerous taproots [68]. In a Colorado study, the majority of roots grew to a soil depth of 4.4 feet (13.5 m), though some reached the water table at 12 feet (3.7 m) [20]. In California, black greasewood roots also reached the water table, 9.8 to 16.4 feet (3-5 m) below surface [40]. Others report roots reaching 20 feet (6 m) deep [116,128]. The dense shallow root system of black greasewood has lateral roots that may extend many meters beyond the canopy [40]. At a site in Utah where the root system of a black greasewood plant was exposed, the 6-foot-tall (1.8 m) shrub had roots 18 feet (5.5 m) deep with a 3-inch (7.6 cm) diameter taproot reaching to 6 feet deep [128].

Black greasewood height, canopy coverage, and total leaf surface area are inversely related to depth to water. A study in south-central Washington compared greasewood transpiration on a site where groundwater was 23 feet (7 m) deep (site A) to a site where groundwater was approximately 42 feet (13 m) deep (site B). Black greasewood on site A had higher crown density and closer shrub spacing, shading the interior leaves and reducing water vapor transport. Black greasewood on site B, where groundwater was deeper, were more widely spaced with thin crowns. The reduction of root growth with increasing soil depth and internal resistance to water movement may also affect efficient and effective use of water by black greasewood [71]. Seasonal fluctuations in surface water also impact black greasewood; low moisture levels in the top 5 feet (1.5 m) of soil have been correlated with internal-plant stress on sites in Colorado. Interestingly, this study found little fluctuation in the water table at 12 feet (3.7 m) during the growing season, indicating little use of the groundwater by black greasewood [20].

Breeding system: Some authors report that black greasewood is monoecious [15,16,48,50,96,134], while others describe it as generally monoecious but occasionally dioecious [17,42,74,103,116,120]. On monoecious plants, pistillate flowers are borne in leaf axils below staminate catkin-like spikes [15,16,48,50]. Staminate flowers are borne high on the plant in small, conelike structures at the ends of the smaller branches. Pollen production is generally high [116]. Female flowers are borne singly at the juncture of stem and leaf back from the tip of the small branches [103]. Black greasewood is cross-pollinated [103,120].

Seed production: Seed production is typically low but occasionally abundant [15]. With removal of competing vegetation, seed production may increase dramatically. A Great Basin study documented 20% of black greasewood producing seed in an undisturbed stand, with an average of

Seed dispersal: Winged seeds allow for wind dispersal [47,56,58,116]. In a study at Mono Lake, California, where high windspeeds are common and there are few aboveground barriers, black greasewood seeds were dispersed at least 0.4 mile (700 m) from source plants [58]. It is unclear how far seeds might disperse in vegetated areas with numerous obstacles to trap seed [56].

Germination: Black greasewood seeds germinate well at cool temperatures and rates of germination are generally high (nearly 100% at 50 oF (10 oC)). Laboratory tests have shown optimum germination temperatures range from 50 to 77 oF (10 to 25 oC) [48]. One hundred percent germination was achieved with a constant temperature of 52 oF (11oC); 94% germination was achieved with 60 oF (15.5 oC) for 8 hours followed by 52 oF for 16 hours [121]. Seed from Oregon germinated best at 68 oF (20 oC) [48,117]. Seeds from Montana germinated at temperatures ranging from 41 to 104 oF (5-40 oC) [117], though high temperatures (>25 oC) reduced both germination rate and percentage germination, and abnormal seedlings developed [48,117]. Seeds from New Mexico germinated poorly at temperatures above 66 oF (19oC) [121].

Stratification of seeds is not necessary; laboratory trials have found that black greasewood germinates best at 50 oF without stratification and at 68 to 86 oF (20-30 oC) with stratification. Black greasewood seeds do require a period of afterripening lasting 30-60 days, and a short freeze/thaw cycle may encourage germination due to the breakdown of the pericarp [47].

The bracts of the seeds contain high levels of sodium which, along with other available sodium, is rapidly absorbed by the seedlings [48,49]. Eddleman and Romo [48,49] suggest that accumulating sodium is a means of adjusting the seedling's osmotic potential to cope with saline conditions during establishment. Adjustment of internal osmotic potential enables plants to maintain turgor, growth, and metabolic processes at low water potentials [49]. Germination may be reduced by decreasing osmotic potential, limiting most germination to periods when salts are diluted or leached and conditions are favorable for seedling growth (that is, spring) [118]. Laboratory experiments have demonstrated that black greasewood germinates under moisture stress, and establishment can be successful at low soil moisture levels near the soil surface if moisture at lower levels is sufficient for growth and development. At 0.0 MPa, 0.5% of seeds germinated; germination rates increased with increasing water stress to a maximum of 37.5% at -0.4 MPa. Germination decreased to 26% at -1.6 MPa [22]. Other tests have found that total germination may be high for black greasewood with water potential down to -0.13 MPa; however, the number of days required to reach high germination rates increases [121].

Asexual regeneration: Some authors describe sprouting from the root crown and roots after disturbance [48,78,116]; a study of a greasewood population at Mono Lake, California noted sprouting from wide-ranging lateral roots [56]. However, Harvey and Weaver [72] found no evidence of vegetative reproduction in Montana field experiments (established individuals).

Annual temperatures in the shadscale zone where black greasewood is often dominant may range from a maximum of 110 oF (43 oC) to a minimum of -30 oF (-34 oC). Daily temperature fluctuations may be 21 oF in January and 56 oF during summer months [11,52]. Black greasewood grows in areas receiving 3 to 20 inches (76-508 mm) of annual precipitation [11,52,107,112]. Precipitation is unevenly distributed, with most falling during 2 periods: March through May and July through August. Summer precipitation is often in the form of cloudbursts: quick, high volume showers that provide limited available water for plants due to high runoff and evaporation in high summer temperatures [52].

Black greasewood occupies sites ranging from wetlands to deserts and open to wooded areas [83]. In the Intermountain area, it is often confined to alkali soils on alluvial areas, floodplains, dry washes, and gullies where soil moisture is high. Black greasewood often dominates desert areas where runoff waters have accumulated [18,47,76,78,84,93,103]. In the northern Great Plains, black greasewood is common on bottomland flats, adjacent gentle slopes, and stream bottoms [9,66,134].

Soils: Soils supporting black greasewood include silt-clays, clay-loams, silt-loams, or deep fine sand-loams [47,76,93,134]. Black greasewood may grow on sandy soil in the northeastern part of its range, but it is most commonly associated with heavy textured soils of high salt content (0.05-1.6%) [15,16,48,48,78,85,116,131]. Black greasewood is halophytic [20,37,48] and often associated with saline [8,16,21,36,76,78,93] and alkaline soils [21,36,78] that may have a pH of 6.2 to 9.8 [8,36,47,76,131]. Donovan and Richards [39] found that black greasewood is more stress tolerant than rubber rabbitbrush, growing better on sites high in sodium and boron. Black greasewood frequently occurs in nearly pure stands in saline conditions [15,16,48,78]. Black greasewood is not, however, an infallible indicator of high soil salt content; it also grows well on nonsaline soils [27,48,128]. 041b061a72


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