SPECIES: Atriplex canescens

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Atriplex canescens: INTRODUCTORY

INTRODUCTORY

SPECIES: Atriplex canescens
  Br. Alfred Brousseau, St. Mary's College

AUTHORSHIP AND CITATION:
Howard, Janet L. 2003. Atriplex canescens. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ []..

FEIS ABBREVIATION:
ATRCAN

SYNONYMS:
Atriplex canescens var. aptera (Nels.) Hitchc. [88,98]
     = Atriplex aptera Nels. [107]
Atriplex canescens ssp. canescens [97]
     = Atriplex canescens var. canescens [98,107]
Atriplex canescens ssp. linearis (S. Wats.) Hall & Clements [84,97]
     = Atriplex canescens var. linearis (S. Wats.) Munz [107]
Atriplex canescens var. occidentalis (Torr. & Frem.) Welsh & Stutz [213]
     = Atriplex canescens var. canescens [107]

NRCS PLANT CODE [194]:
ATCA2
ATCAA3
ATCAC
ATCAG4
ATCAL2
ATCAL4
ATCAM

COMMON NAMES:
fourwing saltbush
four-wing saltbush
chamiso
chamiza
thinleaf fourwing saltbush (Atriplex canescens var. linearis)

TAXONOMY:
The scientific name of fourwing saltbush is Atriplex canescens (Pursh.) Nutt. (Chenopodiaceae) [52,80,97,98,107,109,213]. Varieties are as follows:

Atriplex canescens var. angustifolia (Torr.) Wats. [107]
Atriplex canescens var. canescens [98,107]
Atriplex canescens var. gigantea Welsh & Stutz [107,213
Atriplex canescens var. laciniata Parish [107]
Atriplex canescens var. linearis (S. Wats.) Munz [107,137]
Atriplex canescens var. macilenta Jepson [107]

Ploidy levels within fourwing saltbush range from 2n to 12n and form a partial basis for segregation of infrataxa [163,184] . The infrataxa are interfertile [97]. Morphological overlap occurs among the varieties [84], and geographic distributions of the varieties overlap in the Southwest and California [107]. Some authorities do not recognize fourwing saltbush infrataxa [106].

Hybrids: North American saltbushes (Atriplex spp.) are evolving rapidly. Hybridization, polyploidy, and introgression are common mechanisms of evolution within the genus [86,124,136,186]. Fourwing saltbush hybridizes more often than any other saltbush. Even nonwoody saltbush species may cross with fourwing saltbush and produce fertile offspring [24,86,186] in the Great Basin [186]. Common fourwing saltbush crosses are with New Mexico saltbush (A. obovata) and sickle saltbush (A. falcata) [86,108,174,186]. Several hybrids are described as distinct, established taxa [86,107,186,213]:

Atriplex aptera Nels., moundscale (fourwing Nuttall's saltbush (A. nuttallii))
Atriplex bonnevillensis Hanson, Bonneville saltbush (fourwing sickle saltbush on the Lake Bonneville lakebed)
Atriplex laciniata L., frosted orache (fourwing cattle saltbush (A. polycarpa))
Atriplex odontoptera Rydb. (fourwing Gardner's saltbush (A. gardneri))

Other important fourwing saltbush hybrids form swarms. Although common, some of these hybrids are too genetically flexible to be considered distinct taxa. Others are waiting nomenclatural designation. They include [86,186]:

fourwing saltbush armed saltbush (A. acanthocarpa)
fourwing saltbush shadscale (A. confertifolia)
fourwing saltbush basin saltbush (A. tridentata)

LIFE FORM:
Shrub

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
Atriplex canescens var. gigantea is on BLM's sensitive plant species list for Utah [197]. Populations are located on the Little Sahara National Recreation Area and are threatened by recreational vehicle use on the sand dunes [198].


DISTRIBUTION AND OCCURRENCE

SPECIES: Atriplex canescens
GENERAL DISTRIBUTION:
Fourwing saltbush is the most widely distributed native woody species in North America [108,136,185]. Its native range extends north-south from southern Alberta to central Mexico and east-west from the Missouri River to the Pacific Coast [98,107,135,177,219]. Fourwing saltbush is widely planted in temperate regions of North America as an ornamental, and is locally naturalized east of the plains grasslands, its native boundary [108]. Plants database provides a distributional map of fourwing saltbush and its infrataxa.

Fourwing saltbush is planted worldwide to increase forage production on arid rangelands. It has naturalized on cold, warm, and hot deserts throughout the world [2,16,18].

ECOSYSTEMS [71]:
FRES21 Ponderosa pine
FRES29 Sagebrush
FRES30 Desert shrub
FRES32 Texas savanna
FRES33 Southwestern shrubsteppe
FRES34 Chaparral-mountain shrub
FRES35 Pinyon-juniper
FRES38 Plains grasslands
FRES39 Prairie
FRES40 Desert grasslands

STATES/PROVINCES: (key to state/province abbreviations)
UNITED STATES
AZ CA CO ID KS MT NE NM
ND OK OR SD TX UT WA WY

CANADA
AB BC

MEXICO
B.C.N. Chih. Coah. Dgo. S.L.P. Sin. Son. Zac.

BLM PHYSIOGRAPHIC REGIONS [21]:
3 Southern Pacific Border
5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range
8 Northern Rocky Mountains
9 Middle Rocky Mountains
10 Wyoming Basin
11 Southern Rocky Mountains
12 Colorado Plateau
13 Rocky Mountain Piedmont
14 Great Plains
15 Black Hills Uplift
16 Upper Missouri Basin and Broken Lands

KUCHLER [113] PLANT ASSOCIATIONS:
K011 Western ponderosa forest
K016 Eastern ponderosa forest
K017 Black Hills pine forest
K019 Arizona pine forest
K022 Great Basin pine forest
K023 Juniper-pinyon woodland
K024 Juniper steppe woodland
K027 Mesquite bosques
K031 Oak-juniper woodland
K032 Transition between K031 and K037
K033 Chaparral
K035 Coastal sagebrush
K036 Mosaic of K030 and K035
K037 Mountain-mahogany-oak scrub
K038 Great Basin sagebrush
K039 Blackbrush
K040 Saltbush-greasewood
K041 Creosote bush
K042 Creosote bush-bur sage
K043 Paloverde-cactus shrub
K044 Creosote bush-tarbush
K045 Ceniza shrub
K053 Grama-galleta steppe
K054 Grama-tobosa prairie
K055 Sagebrush steppe
K056 Wheatgrass-needlegrass shrubsteppe
K057 Galleta-threeawn shrubsteppe
K058 Grama-tobosa shrubsteppe
K059 Trans-Pecos shrub savanna
K060 Mesquite savanna
K061 Mesquite-acacia savanna
K062 Mesquite-live oak savanna
K064 Grama-needlegrass-wheatgrass
K065 Grama-buffalo grass
K066 Wheatgrass-needlegrass
K067 Wheatgrass-bluestem-needlegrass
K068 Wheatgrass-grama-buffalo grass
K069 Bluestem-grama prairie
K070 Sandsage-bluestem prairie
K072 Sea oats prairie
K073 Northern cordgrass prairie
K074 Bluestem prairie
K075 Nebraska Sandhills prairie
K076 Blackland prairie
K077 Bluestem-sacahuista prairie
K085 Mesquite-buffalo grass
K086 Juniper-oak savanna
K087 Mesquite-oak savanna
K088 Fayette prairie
K090 Live oak-sea oats

SAF COVER TYPES [59]:
66 Ashe juniper-redberry (Pinchot) juniper
68 Mesquite
219 Limber pine
220 Rocky Mountain juniper
222 Black cottonwood-willow
235 Cottonwood-willow
237 Interior ponderosa pine
238 Western juniper
239 Pinyon-juniper
240 Arizona cypress
241 Western live oak
242 Mesquite

SRM (RANGELAND) COVER TYPES [173]:
105 Antelope bitterbrush-Idaho fescue
107 Western juniper/big sagebrush/bluebunch wheatgrass
205 Coastal sage shrub
206 Chamise chaparral
210 Bitterbrush
211 Creosote bush scrub
212 Blackbush
310 Needle-and-thread-blue grama
314 Big sagebrush-bluebunch wheatgrass
315 Big sagebrush-Idaho fescue
316 Big sagebrush-rough fescue
317 Bitterbrush-bluebunch wheatgrass
318 Bitterbrush-Idaho fescue
319 Bitterbrush-rough fescue
320 Black sagebrush-bluebunch wheatgrass
321 Black sagebrush-Idaho fescue
322 Curlleaf mountain-mahogany-bluebunch wheatgrass
401 Basin big sagebrush
403 Wyoming big sagebrush
405 Black sagebrush
406 Low sagebrush
407 Stiff sagebrush
408 Other sagebrush types
412 Juniper-pinyon woodland
414 Salt desert shrub
415 Curlleaf mountain-mahogany
416 True mountain-mahogany
417 Littleleaf mountain-mahogany
422 Riparian
501 Saltbush-greasewood
502 Grama-galleta
503 Arizona chaparral
504 Juniper-pinyon pine woodland
505 Grama-tobosa shrub
506 Creosotebush-bursage
507 Palo verde-cactus
508 Creosotebush-tarbush
509 Transition between oak-juniper woodland and mahogany-oak association
601 Bluestem prairie
602 Bluestem-prairie sandreed
603 Prairie sandreed-needlegrass
604 Bluestem-grama prairie
605 Sandsage prairie
606 Wheatgrass-bluestem-needlegrass
607 Wheatgrass-needlegrass
608 Wheatgrass-grama-needlegrass
609 Wheatgrass-grama
610 Wheatgrass
611 Blue grama-buffalo grass
612 Sagebrush-grass
613 Fescue grassland
614 Crested wheatgrass
615 Wheatgrass-saltgrass-grama
701 Alkali sacaton-tobosagrass
702 Black grama-alkali sacaton
703 Black grama-sideoats grama
704 Blue grama-western wheatgrass
705 Blue grama-galleta
706 Blue grama-sideoats grama
707 Blue grama-sideoats grama-black grama
708 Bluestem-dropseed
709 Bluestem-grama
710 Bluestem prairie
711 Bluestem-sacahuista prairie
712 Galleta-alkali sacaton
713 Grama-muhly-threeawn
714 Grama-bluestem
715 Grama-buffalo grass
716 Grama-feathergrass
717 Little bluestem-Indiangrass-Texas wintergrass
718 Mesquite-grama
719 Mesquite-liveoak-seacoast bluestem
720 Sand bluestem-little bluestem (dunes)
721 Sand bluestem-little bluestem (plains)
722 Sand sagebrush-mixed prairie
723 Sea oats
724 Sideoats grama-New Mexico feathergrass-winterfat
725 Vine mesquite-alkali sacaton
727 Mesquite-buffalo grass
728 Mesquite-granjeno-acacia
729 Mesquite
733 Juniper-oak
734 Mesquite-oak
735 Sideoats grama-sumac-juniper

HABITAT TYPES AND PLANT COMMUNITIES:
Fourwing saltbush is an important species in Great Basin, Intermountain, Great Plains, and southwestern desert communities. More often an associate than a plant community dominant [17,25], it may dominate some sites [85]. It is commonly dominant in sand dune communities of the Great Basin, Mojave, and Sonoran deserts [116].

Fourwing saltbush occurs in Great Basin communities including sagebrush (Artemisia spp.), salt-desert shrubland, blackbrush (Coleogyne ramosissima), black greasewood (Sarcobatus vermiculatus), mountain brushland, and Colorado pinyon-oneseed juniper (Pinus edulis-Juniperus monosperma) [3,211]. Fourwing saltbush-dominated communities are typically imbedded within sagebrush or other nonsalt-desert shrub types in the Great Basin [31]. Halogeton (Halogeton glomeratus) has invaded some fourwing saltbush communities [158]. Fourwing saltbush merges with sagebrush and creosotebush-white bursage (Larrea tridentata-Ambrosia dumosa) communities, becoming increasingly dominant in the Great Basin-Mojave Desert transition zone in southern Nevada [17,51,84,109,200,211]. It is also common in other Great Basin-Mojave Desert transition communities including Nevada ephedra (Ephedra nevadensis), Anderson wolfberry (Lycium andersonii), blackbrush, and creosotebush-white bursage, shadscale (Atriplex confertifolia), and pale wolfberry-Shockley's desert-thorn (Lycium pallidum-L. shockleyi). On the Nevada Test Site, fourwing saltbush codominates with winterfat (Krascheninnikovia lanata) and is a component of rabbitbrush (Chrysothamnus spp.), big sagebrush (Artemisia tridentata), black sagebrush (A. nova), and singleleaf pinyon (P. monophylla) communities [85].

In the Mojave and Sonoran deserts, fourwing saltbush may dominate or codominate salt-desert scrublands and alkali sinks. Silverscale saltbush (Atriplex argentea), allscale (A. polycarpa), and shadscale codominate in scrublands, while iodinebush (Allenrolfea occidentalis), fewleaf spiderflower (Cleome sparsiflora), and Parish's glasswort (Salicornia subterminalis) codominate on sinks. Fourwing saltbush sometimes codominates stabilized and partially stabilized sand dunes. Typical sand dune codominants include sand verbena (Abronia villosa), creosotebush, and white bursage [99]. It is a component of Joshua tree (Yucca brevifolia) and pinyon-juniper (Pinus-Juniperus spp.) communities [17,51,84,109,211].

Fourwing saltbush also occurs in coastal sage scrub in southern California [84]. In coastal and interior sage scrub, fourwing saltbush may associate or codominate with chamise (Adenostoma fasciculatum), California sagebrush (Artemisia californica), and California brittlebush (Encelia californica) [99].

In the Chihuahuan Desert of Texas and New Mexico, fourwing saltbush occurs in honey mesquite (Prosopis glandulosa)-fourwing saltbush scrub and alkali scrub communities [94]. Important associates in honey mesquite-fourwing saltbush include ironwood (Olneya tesota), blue palo verde (Cercidium floridum), creosote bush, and tarbush (Flourensia cernua) [61]. Honey mesquite-fourwing saltbush grades into alkali scrub, tobosa (Pleuraphis mutica), or wetland types [157,190]. Fourwing saltbush, other saltbushes (Atriplex spp.), and other shrubs may codominate in alkali scrub, including tubercled saltbush (A. acanthocarpa), New Mexico saltbush, and iodinebush [94]. Fourwing saltbush/alkali sacaton communities occur on the Trans-Pecos, High Plains, and South Plains regions of Texas. Important associates include frankenia (Frankenia jamesii), alkali muhly (Muhlenbergia asperifolia), and saltgrass (Distichlis spicata) [32,190]. In New Mexico, fourwing saltbush is most common in salt-desert shrublands. Fourwing saltbush-black greasewood /alkali sacaton is the most common salt desert shrub association across the state. In the north, where the Great Basin attains its southernmost distribution, big sagebrush-fourwing saltbush communities dominate. Fourwing saltbush also occurs in and sometimes dominates plains sand scrub and mesa sand scrub of New Mexico [51].

Fourwing saltbush is dominant or, more commonly, sparsely interspersed with grasses in plains grassland communities [29]. Fourwing saltbush-dominated communities are a minor series on the Great Plains [114,131]. In Kansas, fourwing saltbush/blue grama (Bouteloua gracilis) communities occur on shallow, dry soils in association with hairy grama (B. hirsuta), fragrant sumac (Rhus aromatica), and western poison-ivy (Toxicodendron rydbergii) [114]. On the Comanche National Grassland of southeastern Colorado, fourwing saltbush/blue grama communities occur on hilly sites with deep soils. Plains prickly-pear (Opuntia polyacantha), galleta (Pleuraphis jamesii), and alkali sacaton (Sporobolus airoides) are common associates. Other plains grassland communities in Colorado include fourwing saltbush/western wheatgrass (Pascopyrum smithii)-blue grama and fourwing saltbush-Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis)/western wheatgrass. On the western slope of the Rocky Mountain Front, fourwing saltbush/needle-and-thread grass (Hesperostipa comata) communities occur on foothill slopes [105].

Fourwing saltbush occasionally occurs in desert grasslands, especially those bordering salt-desert shrublands. By the Green and Colorado rivers, fourwing saltbush is an associate in galleta-threeawn (Pleuraphis jamesii-Stipeae) shrubsteppe. Important species in galleta-needle-and-thread grass shrubsteppe of Canyonlands National Park, Utah, are green ephedra (Ephedra viridis), winterfat, scarlet globemallow (Sphaeralcea coccinea), and blue grama [214]. 

Fourwing saltbush is sometimes a component of ponderosa pine (Pinus ponderosa) communities in the Southwest [213].

Vegetation classifications describing communities dominated by fourwing saltbush are listed below by state and administrative region.

California [99,200]
Colorado [105]
Idaho [54]
Kansas [l113]
Nevada [56,141]
New Mexico [51,66,67]
Texas [94,190]
Wyoming [191]
Region 3 [131]

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Atriplex canescens

 drawing courtesy of USDA, NRCS PLANTS Database [194] and Britton and Brown [28]


GENERAL BOTANICAL CHARACTERISTICS:
Morphology: Fourwing saltbush is a native woody shrub [136]. As a general pattern, fourwing saltbush is erect and round in form, with rigid, brittle stems. It is heavily branched, with tight, thin bark. Lateral branches may bear spines at the tips [90,136,180]. However, fourwing saltbush is extremely variable in physiology, form, and other characteristics. Ecotypes differ in growth rate, winter-deciduousness, drought and cold hardiness, and palatability [74,75,124,126,130,230]. Plants range from low (1 foot (0.3 m)) and semiwoody in South Dakota to tall (>10 feet (3 m)) and woody in parts of the Colorado Desert of Utah and Colorado [88,136,140,183,213]. Common garden experiments using accessions from the northern Great Basin, Sonoran, and Chihuahuan deserts show population differences in stature and other characteristics are primarily driven by genetics [188].

Fourwing saltbush is extremely variable in leaf and fruiting bract morphology [108,136,213]. Leaves range from 0.8 to 2 inches (2-5 cm) long. Young leaves are covered with scales that protect against water loss [136]. Mature leaves have epidermal trichomes (hairlike epidermal outgrowths) that concentrate and exude salts, and on saline sites leaves become covered with a salty covering or scurf [196,208]. Plants are evergreen (in warm climate) to winter-deciduous (in cold climates) [140,208]. Staminate flowers are borne in dense, 2- to 3-mm-wide spikes, and pistillate flowers form 2- to 16-inch-long (5-40-cm) panicles [52,136,213]. The fruits are 0.3- to 0.4-inch-long (0.8-1 cm) utricles, with 0.4- to 1-inch-square (9-25 mm2) bracts [180,213]. Fourwing saltbush is the only species in the genus with 4 large wings on the fruits [108]. Seeds are tightly contained within the utricles, and do not separate from the utricles at dispersal. Seeds measure approximately 1 2 mm [180,213], with 17 to 120 seeds/fruit [19].

The root system consists of a taproot and small lateral feeder roots occupying upper soil layers [15]. Where soils allow, taproots often extend more than 20 feet (6 m) [109,140]. In a Colorado pinyon-oneseed juniper community of New Mexico, fourwing saltbush showed the greatest average rooting depth (=12.9 ft (3.92 m), range=3.61-25.0 ft (1.10-7.62 m)) of 7 excavated shrub species [65]. In southern California deserts, fourwing saltbush taproots have been found as far as 40 feet (12 m) below the soil surface [47]. Barrow [15] found rhizomatous fourwing saltbush populations in New Mexico.

The above description of fourwing saltbush provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keying out saltbushes, particularly fourwing saltbush, is challenging due to intraspecific variation and introgression with other saltbush species. For example, the type specimen (collected by Meriwether Lewis in 1804 in what is now South Dakota) appears introgressed with Gardner's saltbush [184]. Keys for identifying fourwing and other saltbushes are available (e.g. [52,90,97,108,213]).

Stand structure: Salt desert types with a fourwing saltbush component are generally comprised of scattered shrubs representing few species. Herbaceous cover is sparse; biological soil crusts fill the interspaces in nondegraded systems [31]. For example, on the carbonaceous shale badlands of the Cheyenne River Basin, Wyoming, fourwing saltbush is the only important species. Shrubs are widely spaced, and cover of other shrub species is slight. Few grasses and forbs are present in the understory, and herb reproduction is poor [191]. However, fourwing saltbush ecotypes are highly site-adapted [189], and stand structure can vary considerably with site. Once established, invasive annuals like cheatgrass (Bromus tectorum) and red brome (B. madritensis ssp. rubens) can contribute considerable understory biomass in salt-desert communities [31].

Physiology: Fourwing saltbush is salt, cold, and drought resistant [4,167]. Southern ecotypes may show superior drought resistance compared to northern ecotypes [130]. In the Hopi and Navajo reservations of northeastern Arizona, fourwing saltbush showed the 2nd most negative internal water potential ( -3.19 MPa) of 7 shrubs tested; only shadscale showed a quantitatively greater ability to withstand water stress [220]. Saline tolerance also varies among populations and infrataxa. For example, some Atriplex canescens var. linearis populations in Sonora, Mexico, grow on high tidelines of Gulf of Mexico estuaries, while inland populations of A. c. var. canescens are less salt tolerant [74]. Polyploid fourwing saltbush populations have experimentally shown greater osmotic capability than diploid populations, whereas in mesic environments, diploid populations show greater growth rates compared to polyploid populations [163]. Generally, increasing chromosome number slows growth, decreases size and palatability, and increases woodiness, frost, and drought tolerance [184,187].

Life span: Fourwing saltbush is long lived. Permanent plots on the Desert Laboratory near Tucson, Arizona, show survivorship of individual shrubs for at least 29 years [76]. Repeat photo series from the Grand Canyon document individual fourwing saltbush surviving over 100 years [27].

RAUNKIAER [156] LIFE FORM:
Phanerophyte

REGENERATION PROCESSES:
Fourwing saltbush reproduces from seed, by sprouting, and by layering. Seed spread is the most common form of reproduction [129,140,185,187]. Fourwing saltbush sprouts from the root crown, but it is generally a weak sprouter [208]. Rarely, populations spread from rhizomes or by layering [15,213].

Breeding system: Fourwing saltbush is mostly dioecious, but some populations are predominantly dioecious with a monoecious component that ranges from individuals that are entirely staminate or pistillate to hermaphroditic [13,136,140,213]. Some individuals may change sex (from female to male) in response to environmental stress such as cold, drought, heavy browsing, or prior heavy seed set, reverting to female expression when conditions improve [41,44,68,121,150]. Species ability to change gender is rare. Fourwing saltbush's dioecious-monoecious-hermaphrodite gender system has been termed trioecy [50,123,124,130]. Preferential browsing may alter natural regeneration patterns. On the Central Plains Experiment Range of Colorado, male plants were more common on grazed sites than on sites where cattle were excluded [41]. High ploidy levels are thought to decrease palatability [187], so browsing selection may favor individuals with higher ploidy levels in populations where multiple ploidy levels coexist [44].

Fourwing saltbush shows extreme genetic diversity across geographic and elevational gradients, and has been called the most adaptable shrub in North America [136,184,185]. Genetic changes have facilitated its radiation from its central Mexico geographic center of origin to as far north as southern Canada. Evolving rapidly and showing superior ability to adapt to changing environmental conditions, fourwing saltbush employs every known mechanism of evolution including hybridization, introgression, rapid rates of mutation, and multiple ploidy levels. Diploid individuals (probably the original chromosome state for the species) are now rare, and seldom breed successfully, in northern populations [184,185,188].

Pollination: Flowers are pollinated by wind [69,130,184]. Coupled with easy formation of polyploids, wind pollination facilitates intra- and interspecific hybridization of fourwing and other saltbushes [184,185]. However, dioecy and trieocy tend to reduce rates of successful pollination [189].

Seed production: Fourwing saltbush produces numerous seeds, may of which are unfilled and therefore unviable [12,130]. Polyploid populations tend to produce more unfilled seed than diploid populations [189]. Seed production is often further reduced because browsing animals find the fruits so palatable [43,101,109,196]. There are several insect seed predators that may reduce seed production in fourwing saltbush [134].

Seed dispersal: The abscised fruit, with seed inside, disperses by wind, floodwater, and animal transport [11,14,64,93]. As the only species in the genus with winged fruit, the potential for long-distance wind dispersal is greater for fourwing saltbush seed than seed of other saltbushes [93]. In a southwestern Wyoming experiment, Chambers [40] found fourwing saltbush seed was highly mobile on soil surfaces. Best seed retention occurred in large-diameter (50-cm-wide 10-cm deep) holes [40]. Dust devils may carry fourwing saltbush fruit for miles [93]. Animals ingest and then disperse the palatable seed in feces. In so doing, they may improve germination rates. Fourwing saltbush seed ingested by cattle and recovered from their droppings showed improved germination compared to noningested seed (=14% and 8%, respectively) [11].

Seed banking: Direct studies on fourwing saltbush are not available of this writing (2003). Seed dry-stored in open warehouses was still viable after 15 [130] and 19 years [100], suggesting that fourwing saltbush seed may survive in arid soil seed banks.

Germination: Seed is dormant; fruit bracts and seedcoats present mechanical barriers to germination [189]. Seeds also have chemical dormancy from saponins in the utricle [139]. Seeds therefore require stratification, leaching, and/or scarification for germination [130,139,189,207]. When dormancy breaks, seeds germinate when enough moisture for seed imbibition accompanies warm temperatures [176]. After stratification in the laboratory, 1st germinant emergence was 7 days after sowing; last emergence was 21 days after sowing. Favorable germination temperatures varied with seed source. Best germination occurred at 64 to 75 oFahrenheit (18-24 oC) for seeds colleted in California; at 61 to 64 oFahrenheit (16-18 oC) for New Mexico seeds; and 32 to 37 oFahrenheit (0-3 oC) for seeds from Utah. There are intrapopulation differences in germination requirements. For example, Springfield [176] found that while scarification increased germination of some seed lots, it decreased germination of other seed lots. Atriplex canescens var. gigantea shows higher rates of germination compared to other varieties of fourwing saltbush [136]. In the lab, germination improves when the seed wings are removed or worn away [19]. In the field, intact utricles may favor germination when soil-borne mycorrhizal associates infect fourwing saltbush fruit. Fourwing saltbush seed collected in New Mexico showed significantly better germination and subsequent seedling growth (p<0.01) when left in the utricle compared to seed that was excised from the utricle. Mycorrhizal decay of the utricle probably improves nutrient and water status of both the fungi and their germinant host [12]. Light has no effect on fourwing saltbush germination [176].

Seedling establishment/growth: In arid environments, microtopography that provides partial shade, such as pits and furrows, may be crucial for establishment [129]. On the Jornada Experimental Range, New Mexico, seedling emergence was best (p<0.05) on partially shaded dunes compared to open sites between dunes. Seed planting depth ( 2 or 5 mm) did not affect emergence (p<0.05) [92]. Seedlings from seed collected at different elevations showed genetic adaptation to freezing temperatures. In the greenhouse, all seedlings from 3,000-foot (900-m) elevation died when exposed to freezing temperatures, while 6% of seedlings from 4,000-foot (1,200 m) elevation survived, and 100% of seedlings from 5,900-foot (1,800-m) elevation survived (Young, J. A., as cited in [136]).

Seedlings on favorable sites show rapid growth. Along the Colorado River in Arizona, mean height of seedlings started from outplanted seed ranged from 1 to 1.5 inches (2.5-3.7 cm) in their 1st growing season [6]. Browsing can reduce seedling growth and survivorship [196]. Seedling survival on plots subjected to grasshopper, rabbit, and deer browsing was only 67% of survival on protected control plots [176]. Stands require 3 or 4 years to fully establish [140].

Asexual regeneration: Ability of fourwing saltbush to vegetatively reproduce is genetically variable. Fourwing saltbush may sprout from the root crown after top-growth is removed by fire or browsing [132,216]. However, sprouting vigor varies among populations and is difficult to predict based upon geographic location. Some populations show only a weak sprouting response; others no not sprout at all [47,57]. Basal and branch sprouting is probably an adaptation to browsing [23,45]. Pieper and Donart [153] found plants in south-central New Mexico did not produce basal sprouts when completely protected from browsing. Over 4 years, plants protected from browsing for a year produced 4 times more basal sprouts than continuously-browsed plants [15].

Rarely, populations reproduce by layering or sprouting from rhizomes [15,213]. Atriplex canescens var. gigantea populations in Utah survive on unstable sand dunes by rapidly elongating partially to completely buried stems, which then root [213]. Most fourwing saltbush populations do not rapidly elongate buried stems and apparently cannot  layer in the field [136]. Barrow [15] documented a rhizomatous population in New Mexico. Some populations near Alma, New Mexico, regenerate primarily through rhizomes; other, nearby populations appear to be seed-originated and nonrhizomatous.

SITE CHARACTERISTICS:
Climate/topography: Fourwing saltbush is adapted to desert climates. Temperature gradations across fourwing saltbush's distribution are great.  In northern salt-desert associations, annual precipitation ranges from 6 to 14 inches (150-350 mm); summers are hot and dry; and winters are cold [196]. Within fourwing saltbush's range, there are areas that rarely experience winter frosts. In other areas, winter temperatures may dip to -50 oFahrenheit (-46 oC) [86]. Ability of fourwing saltbush to tolerate cold (and therefore, cold deserts) varies with ecotype [140]. Topography includes dry plains, hills, bluffs, valleys, and riparian corridors [14,80]. In the Great Plains fourwing saltbush is common on barren sites, chalk bluffs, and grassland sites where sod is broken [180].

Water relations: Fourwing saltbush occurs on droughty sites. In the Chihuahuan Desert, fourwing saltbush occurs on deep, fine alluvium soils. Honey mesquite-fourwing saltbush communities occur on arroyos, bajadas, and sites where the water table is 10 to 30 feet (3-10 m) below the surface. Chihuahuan Desert sites where fourwing saltbush codominates with other saltbushes are usually internally drained sinks where chlorides, carbonates, and sulfates accumulate [94]. Johnston [105] describes a fourwing saltbush/western wheatgrass-blue grama community on the Pawnee National Grassland, northeastern Colorado, that occurs on floodplains with fine-textured soils. Fourwing saltbush cannot tolerate high water tables or late-season inundation [140].

Soils supporting fourwing saltbush vary from 10 inches (25 cm) to over 3 feet (0.9 m) in depth [196]. Fourwing saltbush is adapted to all soil textures [23,208]. It is most common on well-drained, sandy to rocky soils [52,80,108,137,196]. It also occurs on denser, clayey soils [196], especially when growing in association with black greasewood [136]. Generally, diploid populations are more likely to occur on sandy soils, while fourwing saltbush populations of higher ploidy level occur on clay substrates. Stutz [187] found diploid populations in the Great Basin grew above ancient (Pleistocene) lake levels, tetraploids occurred on ancient lakeshores, and other polyploids occurred on ancient lake bottoms. In the southern portion of the Guadalupe Mountains, Texas, fourwing saltbush occurs on heavy clay soils on the borders of old lakebeds [32].

Fourwing saltbush tolerates saline, alkaline, boron, and gypsum soils but is not an indicator of such conditions [93,196]. Soil pH in fourwing saltbush communities ranges from slightly acid to slightly alkaline [105]. Maximum soluble salt that fourwing saltbush can tolerate is about 1,300 ppm [86]. On saline sites, the soil around fourwing saltbush plants increases in pH as rains wash the salty scurf from leaves [208].

Elevation: Overall range of fourwing saltbush is from below sea level in California and Texas to over 8,500 feet (2,600 m) in Wyoming [136,154,196]. It is most common from 4,500 to 6,000  feet (1,400-1,800 m) [196]. Elevations by state are as follows:

Arizona < 6,500 ft (2,000 m) [109]
California < 7,000 ft (2,100 m) [137]
Colorado 4,000-8,000 ft (1,200-2,400 m) [88]
Nevada 2,000-7,500 ft (2,000-2,300 m) [108]
New Mexico 3,000-6,500 ft (910-2,000 m) [120]
Texas sea level-7,000 ft (0-2,100 m) [154]
Wyoming >8,500 ft (>2,600 m) [136]
Utah 2,200-7,810 (670-2,380 m) [213]

SUCCESSIONAL STATUS:
Fourwing saltbush occurs in all stages of succession [70]. In early succession, it creates favorable microsites that can facilitate establishment of later-successional shrubs such as sagebrush [25]. On the proposed nuclear waste site at Yucca Mountain, Nevada, fourwing saltbush occurs in both early-successional creosotebush disturbed by heavy equipment and undisturbed creosotebush associations. In blackbrush communities on Yucca Mountain, it occurs on disturbed sites but is nearly absent from undisturbed sites [70]. Near Winnemucca, Nevada, Atriplex canescens var. gigantea is the 1st shrub to establish on active dunes that succeed to big sagebrush/Indian ricegrass (Achnatherum hymenoides) [227]; likewise, fourwing saltbush shows greatest shrub cover and percent composition in early old field succession on blue grama-buffalo grass (Buchloe dactyloides) prairie in northeastern Colorado [49]. Long-term livestock browsing pressure may favor less palatable shrubs. On cattle-grazed mine reclamation sites in Wyoming, seeded fourwing saltbush decreased greatly over 5 years, but facilitated establishment of less palatable taxa such as Wyoming big sagebrush [168]. Fourwing saltbush populations may remain stable or increase on open, relatively undisturbed shrublands. A 100-year repeat photo series from the Grand Canyon shows 89% mortality and 92% recruitment of fourwing saltbush [27].

Fourwing saltbush is somewhat shade tolerant [140] and may occur in open-canopy, mid- to late-successional woodlands and ponderosa pine forest communities [213]. Tress and Klopatek [192] found fourwing saltbush and Fremont's barberry (Mahonia fremontii) dominated the understory (18% cover) of a 90-year-old Colorado pinyon-Utah juniper (Juniperus osteosperma) woodland in north-central Arizona.

SEASONAL DEVELOPMENT:
Bud swell begins in early spring [206], with stem elongation resuming in mid- to late spring [140]. Seed germination occurs around the same time. Fourwing saltbush seeds outplanted along the Colorado River in Arizona germinated in March [6]. Flowering begins in mid- to late spring and may extend to early fall, depending upon latitude and elevation. Fruits and seeds mature 3 to 4 months after flowering: late summer (Aug.-Sept.) in the northern part of fourwing saltbush's range, and in fall and winter (Oct.-March) in the southern portion of its range [19,86,130,140,196]. Fruits are semipersistent, often remaining attached to the plant throughout winter. Fruits and seeds disperse as a unit in spring [135,196]. Phenological events reported by state are:

Area Leafs Flowers Fruits
California ---- May-Aug. [47,137] ----
Great Basin ---- May-mid-Aug. [86,136] fall [136]
Great Plains ---- May-Aug. July-Sept. [80,180]
Nevada late Feb.-April [1] Mar.-June [1,108] ----
Texas ---- April-Oct. [52] ----

FIRE ECOLOGY

SPECIES: Atriplex canescens
FIRE ECOLOGY OR ADAPTATIONS:
Fire adaptations: Given fourwing saltbush's evolutionary plasticity [136,184,185] and ability to establish in early succession [25,70], the species seems well equipped for survival in early postfire communities. With fourwing saltbush's high level of genetic diversity, however, ability to recover from fire vegetatively probably differs among and within populations. Fourwing saltbush population and genetic variation are well studied for a suite of ecologically important traits [74,75,124,126,130,230], but traits affecting fire recovery (ability to sprout and establish from naturally-dispersed seed in postfire environments) are not among them. Ironically, artificial regeneration studies on fourwing saltbush are numerous (see Value for Rehabilitation of Disturbed Sites). As of this writing (2003), studies documenting natural establishment of fourwing saltbush after fire or other disturbance are mostly anecdotal [47,132,216,225]. Given changing fire regimes in desert environments (see Fire Regimes below), fire ecology studies at the population level are badly needed for fourwing saltbush. Until further studies are published, this and other discussions of fourwing saltbush's adaptations to fire remain speculative.

Since seed is generally the most important method of fourwing saltbush reproduction [129,140,185,187], fourwing saltbush probably establishes primarily from seed after fire, with some populations also regenerating vegetatively. Fourwing saltbush shows good seedling establishment on disturbed arid lands [129,185,187]. Presumably, wind-, water-, and animal-dispersed seed begins growth on burns as soon as germination requirements are met.

Vegetative reproduction may be an important method of postfire regeneration in some populations. Some fourwing saltbush ecotypes sprout from the root crown after top-kill by fire [132,216,225]. Sprouting ability varies among fourwing saltbush populations, with sprouting response weak to nonexistent in some populations. For example, populations in southern California are limited to postfire seedling establishment because they do not sprout [47]. Geographic locations of sprouting populations, and the relative strength of their sprouting response, are sparsely documented in the literature.

A fourwing saltbush population in New Mexico is known to sprout from rhizomes [15]. This and other rhizomatous fourwing saltbush populations may be vigorous sprouters after top-kill, but fire studies on rhizomatous fourwing saltbush are lacking. Atriplex canescens var. gigantea layers in response to shifting sands [213], but the sparsely vegetated, unstable sand dune community where it grows rarely, if ever, experiences fire. Further studies are need on the mechanisms of natural fourwing saltbush recovery after fire and other disturbances.

Fuels: Leached fourwing saltbush litter is rated high in flammability [132]. Live shrubs do not easily ignite. With a high ash content and a moderate to high salt content, fourwing saltbush resists burning [30] and is characterized as moderately to highly fire resistant relative to other shrub species [47,130,132]. Moisture of fourwing saltbush is low, and ash and heat content of fourwing saltbush are high, relative to 2 associated southern California coastal sage shrubs ([138] and references therein):

Species May moisture content (%) Ash content (%), foliage & stems Heat content (BTU/lb), foliage & stems (0.25-0.50-in.)
foliage & current leaders (0.12-in. diameter) foliage & stems (0.25-0.50-in.)
fourwing saltbush 173 150 12.4 8,280-8,475
cattle saltbush 347 228 12.2 7,580-8,004
creeping sage (Salvia sonomensis) 277 213 9.8 7,900-8,100

Fuels production in salt-desert shrubland varies from year to year, depending upon precipitation. Production is also related to soil salinity and texture. Herbage production ranges from 0 to 500 lbs/acre (0-560 kg/ha) [216].

Fire Regimes: Fourwing saltbush is most common under regimes of infrequent fire and moderate browsing. Although fourwing saltbush responds to partial removal of branches with vigorous growth (a browsing response) [23,45], limited research shows a weak ability to sprout after heavy branch removal or complete removal of top-growth (such as fire accomplishes) [20,33,153]. Salt-desert shrub, desert shrub, and desert grassland communities with fourwing saltbush historically experienced infrequent, stand-replacement fires [147,223]. Although fourwing saltbush fingers into ponderosa pine ecosystems [213], which historically experienced frequent, nonstand-replacement surface fires [8,10,115], it is not common in ponderosa pine. Plains grassland is the one ecosystem with an historical fire regime of frequent, stand-replacement fire where fourwing saltbush is common. With fourwing saltbush's genetic plasticity, populations in plains grasslands may be well adapted to frequent fire. Studies comparing the relative sprouting ability of plains grassland ecotypes with fourwing saltbush ecotypes from less fire-adapted ecosystems may prove instructive. Fire regimes where fourwing saltbush is important are covered in more detail below.

Plains grasslands: Historical fire return intervals cannot be measured precisely in grasslands, but fires were historically prevalent in this type [63]. Mean fire return intervals are estimated at 4 to 20 years, depending upon fuels and ignition sources. Native Americans lighted fires for a number of reasons and were the primary source of ignition in high-use, low-elevation sites where fourwing saltbush grew in association with prairie grasses. Lightning was probably an important source of ignition where fourwing saltbush bordered forested and riparian communities. Shortgrass prairies would burn over large areas until a break in terrain or weather extinguished the fires. Incidence of fire in plains grasslands has greatly decreased since the 1800s due to modern grazing practices, cessation of Native American burning, and fire exclusion [82].

Salt-desert shrubland: Historic fire regimes in desert shrublands are equally difficult to quantify, but on sparsely vegetated salt-desert types, fires were historically rare except under unusual circumstances ([215] and references therein). There are still salt-desert shrublands in the western United States experiencing historic fire regimes. For example, as of this writing (2003) the well-studied salt-desert communities of  Raft River Valley, southwestern Idaho, have not experienced fire since at least the 1930s [216]. However, historic fire regimes are no longer operating on many salt-desert sites. Wet years such as those brought by El Nio encourage growth of fine fuels in salt-desert communities. In particular, annual grasses such as cheatgrass and red brome develop enough fine fuel biomass to support wildfires [31,149]. These and other exotic annual grasses have invaded some salt-desert ecosystems that historically experienced infrequent fire, increasing fine fuels and shortening fire return intervals [22,216,231]. Despite older perceptions [102], salt-desert shrublands burn with sufficient fine fuels and an ignition source, especially when fires are accompanied with high winds [216]. Once fire occurs, cover of annuals and probability of subsequent fire increase [31]. Salt-desert communities in Skull Valley, Utah, for example, have experienced cheatgrass-fueled wildfires. Harper [87] found little to no cheatgrass on saltbush and other desert shrub sites on the Desert Experimental Range of west-central Utah in 1959, a dry year. In 1990, a wet year, Sparks and others [175] found the same sites had converted to cheatgrass and other annual weeds "on a massive scale", and fuels were heavy enough to carry fire. Long recovery periods are needed when large-acreage fires occur in salt-desert shrub [30,31]. Frequent fire may preclude establishment of fourwing saltbush and other shrubs and increase the extent of the disturbed area.

Desert shrubland: Historic fire return intervals were variable, ranging between 10 and 100+ years in arid shrublands [218,222]. Fires were not historically important in desert shrublands where grasses were not abundant [103]. However, frequent fires fueled by exotic annuals are now common in desert shrublands, and involve larger acreages than in salt-desert types [218,228]. Fire in Wyoming big sagebrush, where fourwing saltbush is a common component, can spread into salt-desert types. Frequent fire has severely depleted sagebrush, fourwing saltbush, and other fire-sensitive shrubs in the Wyoming big sagebrush type [31].

The following table provides fire return intervals for plant communities and ecosystems where fourwing saltbush may be important. For further information, consult the FEIS summary on the community or ecosystem dominants listed below.

Community or Ecosystem Dominant Species Fire Return Interval Range (years)
California chaparral Adenostoma fasciculatum < 35 to < 100 [147]
bluestem prairie Andropogon gerardii var. gerardii-Schizachyrium scoparium < 10 [112,147]
Nebraska sandhills prairie A. gerardii var. paucipilus-S. scoparium < 10
bluestem-Sacahuista prairie A. littoralis-Spartina spartinae < 10 [147]
silver sagebrush steppe Artemisia cana 5-45 [96,155,224]
sagebrush steppe A. tridentata/Pseudoroegneria spicata 20-70 [147]
basin big sagebrush A. tridentata var. tridentata 12-43 [165]
Wyoming big sagebrush A. tridentata var. wyomingensis 10-70 (40**) [223,229]
coastal sagebrush A. californica < 35 to < 100
saltbush-greasewood Atriplex confertifolia-Sarcobatus vermiculatus < 35 to < 100
desert grasslands Bouteloua eriopoda and/or Pleuraphis mutica 5-100 [147]
plains grasslands Bouteloua spp. < 35 [147,224]
blue grama-needle-and-thread grass-western wheatgrass B. gracilis-Hesperostipa comata-Pascopyrum smithii < 35 [147,160,224]
blue grama-buffalo grass B. gracilis-Buchloe dactyloides < 35 [147,224]
grama-galleta steppe Bouteloua gracilis-Pleuraphis jamesii < 35 to < 100
blue grama-tobosa prairie B. gracilis-P. mutica < 35 to < 100 [147]
cheatgrass Bromus tectorum < 10 [151,218]
paloverde-cactus shrub Cercidium microphyllum/Opuntia spp. < 35 to < 100 [147]
curlleaf mountain-mahogany* Cercocarpus ledifolius 13-1,000 [9,166]
mountain-mahogany-Gambel oak scrub C. ledifolius-Quercus gambelii < 35 to < 100
blackbrush Coleogyne ramosissima < 35 to < 100
juniper-oak savanna Juniperus ashei-Quercus virginiana < 35
Ashe juniper J. ashei < 35
western juniper J. occidentalis 20-70
Rocky Mountain juniper J. scopulorum < 35
creosotebush Larrea tridentata < 35 to < 100
Ceniza shrub L. tridentata-Leucophyllum frutescens-Prosopis glandulosa < 35 [147]
wheatgrass plains grasslands Pascopyrum smithii < 5-47+ [147,155,224]
pinyon-juniper Pinus-Juniperus spp. < 35 [147]
Colorado pinyon P. edulis 10-400+ [62,78,110,147]
interior ponderosa pine* P. ponderosa var. scopulorum 2-30 [8,10,115]
Arizona pine P. ponderosa var. arizonica 2-15 [10,48,169]
galleta-threeawn shrubsteppe Pleuraphis jamesii-Aristida purpurea < 35 to < 100 [147]
mesquite Prosopis glandulosa < 35 to < 100 [128,147]
mesquite-buffalo grass P. glandulosa-Buchloe dactyloides < 35
Texas savanna P. glandulosa var. glandulosa < 10
oak-juniper woodland (Southwest) Quercus-Juniperus spp. < 35 to < 200 [147]
blackland prairie Schizachyrium scoparium-Nassella leucotricha < 10
Fayette prairie S. scoparium-Buchloe dactyloides < 10 [204]
little bluestem-grama prairie S. scoparium-Bouteloua spp. < 35 [147]
*fire return interval varies widely; trends in variation are noted in the species summary
**mean

POSTFIRE REGENERATION STRATEGY [182]:
Small to tall shrub, adventitious bud/root crown
Rhizomatous shrub, rhizome in soil (some ecotypes)
Initial off-site colonizer (off-site, initial community)
Secondary colonizer (on-site or off-site seed sources)

FIRE EFFECTS

SPECIES: Atriplex canescens
IMMEDIATE FIRE EFFECT ON PLANT:
Sustained surface fire top-kills or kills fourwing saltbush [47,223], depending upon ecotype.

Fourwing saltbush is fire-resistant compared to most associated shrubs. The salt scurf layer on leaves inhibits burning [47,130,132]. Ether extractives in leaves and stems promote shrub flammability. Rothermel [159] found low ether-extract content (1%, oven-dry weight) for fourwing saltbush. It was the lowest ether-extractive content recorded among 18 California shrub species [81].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
Whisenant [217] found fourwing saltbush seedlings did not sprout after fire in southern Idaho. Sprouting ability of mature fourwing saltbush in the area is not documented.

PLANT RESPONSE TO FIRE:
Fourwing saltbush may sprout after top-kill [223]. Some ecotypes fail to sprout, or show only a weak sprouting response [47]. Generally, fourwing saltbush  is poorly adapted to frequent fire [47,57]. It can recover from low-severity fire that mimics browsing by removing some branchwood. Some southwestern fourwing saltbush populations sprout after top-kill by fire [132,216,225]. In a review, Wright and Bailey [223] state fourwing saltbush sprouted after prescribed burning in the southern Great Plains, and was 'fully recovered' by postfire year 3. Conrad [47] reported that fourwing saltbush in southern California does not sprout.

Rhizomatous populations in New Mexico have a denser stand structure than nearby nonrhizomatous populations, presumably due to numerous underground rhizomes [15]. Healthy, rhizomatous fourwing saltbush populations probably recover top-growth rapidly after fire; however, postfire recovery studies have not been conducted on rhizomatous populations.

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
In scrublands of the Sonoran Desert, fourwing saltbush and other desert shrubs successionally replace annuals after fire. In saltbush, creosote bush, and mixed shrub communities, the general postfire successional sequence begins with Russian-thistle (Salsola kali); then annual mustards (Sisymbrium spp. and flaxleaf plainsmustard (Schoenocrambe linifolia)); exotic annual grasses (Schismus spp. and red brome); ruderal shrubs (e.g., desertbroom (Baccharis sarothroides) and goldenbush (Isocoma spp.)); and finally, dominance of fourwing saltbush and other important shrubs ([193] and references therein).

FIRE MANAGEMENT CONSIDERATIONS:
Restoration: Restoring desert and salt-desert shrublands severely altered by exotic annual grasses and frequent fire presents a great management challenge, and some authors do not believe it is possible [31,228]. Reestablishing fourwing saltbush and other native species means controlling competing vegetation through mechanical and/or herbicidal methods and restricting wildfire. Native species are then established through direct seedings and plantings [118]. Preventing the annual grass-frequent fire cycle through livestock management (restricting grazing to winter and eliminating it altogether during drought), fire prevention, and aggressive management of invasive species may prevent or slow alteration of desert and salt-desert shrublands [23,31]. Recruitment of native species on altered sites may require a decade or longer [31].

Fourwing saltbush is well suited for bare area recovery treatments because it establishes relatively easily from seed (see Value for Rehabilitation of Disturbed Sites). For example, in July 1981, a wildfire burned 62,000 acres (25,100 ha) of big sagebrush, mixed cold-desert shrubland, and Colorado pinyon-Utah juniper in Millard and Juab counties, central Utah. 'Rincon' fourwing saltbush, winterfat, 'Hobble Creek' big sagebrush, and antelope bitterbrush (Purshia tridentata) were seeded the following August. The fourwing saltbush cultivar showed good recruitment relative to the other shrub species. Best fourwing saltbush seedling establishment was on bottomlands dominated by black greasewood prior to wildfire. Relative shrub seedling recruitment and growth rates follow. Data are means from August, postfire year 3 [46].

  seedling recruitment (%) Seedling density/acre Height (in.) Crown volume (ft3)
'Rincon' fourwing saltbush 0.24a 1,260 10.9a 2.0a
'Hobble Creek' big sagebrush 0.38a 2,347 3.0b 0.1b
antelope bitterbrush 0.04b 660 5.6b 0.1b
winterfat 0.82c 4,080 6.9b 0.7b
Values in same column followed by different letters are significantly different at p<0.05.

Fire management: Since sprouting response varies among (and possibly within) fourwing saltbush populations [15,47,57,223], a prefire assessment of local population sprouting capacity is advised before prescribed fires are used. Postfire recovery time will vary, depending upon a population's relative ability to sprout after top-kill.

Fourwing saltbush is well adapted to recover from fire through seedling establishment. It shows good seed dispersal and early successional seedling establishment, even on harsh sites [6,11,14,38,64,93,140]. If an off-site seed source is nearby, natural regeneration from seed is likely to occur within 5 postfire years [140]. Rate of seedling establishment will probably be slower on large burns compared to small burns.

Due to its relatively low flammability, fourwing saltbush is sometimes planted in greenstrip (vegetative fuelbreak) mixes. Greenstripping is especially recommended to decrease spread and frequency of wildfires in desert areas infested with cheatgrass [132,148].

Hazlett [91] provides leaf area indices (useful in fuel modelling) for blue grama-fourwing saltbush shortgrass steppe of eastern Colorado.

MANAGEMENT CONSIDERATIONS

SPECIES: Atriplex canescens
IMPORTANCE TO LIVESTOCK AND WILDLIFE:
Fourwing saltbush provides valuable habitat and year-round browse for wildlife and livestock [83,101,108,130,136,213]. Its protein, fat, and carbohydrate levels are comparable to alfalfa (Medicago sativa) [37]. As an evergreen plant, it is especially valued in winter and during drought [84,111,130,136]. In southeastern Oregon, for example, mule deer preferred antelope bitterbrush over fourwing saltbush but browsed both. Fourwing saltbush showed better growth than antelope bitterbrush in drought years, providing more (and sometimes critical) forage [111]. Fourwing saltbush also provides browse and shelter for small mammals [73,83]. Additionally, the browse provides a source of water for black-tailed jackrabbits in arid environments [104]. Granivorous birds, including scaled and other quail species, grouse, and gray partridge, consume the fruits [140,154,196].

Palatability/nutritional value: Fourwing saltbush is 1 of the most palatable shrubs in the West [84]. It provides nutritious forage for all classes of livestock [26,101,154]. Wild and domestic ungulates, rodents, and lagomorphs readily consume all aboveground portions of the plant [95,104,136,180,230]. Palatability is rated good for deer, elk, pronghorn, bighorn sheep, domestic sheep, and domestic goats; fair for cattle; fair to good for horses in winter, and poor for horses in other seasons [53,162].

Shrub palatability varies within and among populations [143,184]. Within fourwing saltbush populations, plants with relatively high saponin content are least palatable [127]. Among populations, palatability tends to decrease with increasing ploidy levels [184]. Salt accumulated on leaf surfaces also decreases palatability; therefore, the physiological mechanism for salt tolerance tends to protect fourwing saltbush from overbrowsing during drought [25,77,208].

Browsers generally use fourwing saltbush most in fall and winter, when other green forage is scarce and protein, phosphorus, and energy content is high relative to associated shrubs and herbs [142,211]. In winter, fourwing saltbush browse is high in carotene, and leaves average about 18% total protein [140]. Nutritional variation in fourwing saltbush browse collected in the west-central Texas panhandle [72] and in central Utah [144] is given below. Data are means.

Texas site Crude protein (%) IVODM*  (%) Ca  (%) K (%) Mg  (%) Na  (%) P  (%)
Nov. 1985 18.9 (leaves) 66.2 1.6 2.3 1.0 2.7 0.19
8.4 (stems) 32.0 0.7 1.4 0.3 1.1 0.09
Feb. 1986 23.7 (leaves) 71.0 1.8 2.8 1.1 2.6 0.23
14.7 (stems) 45.4 1.2 2.2 0.5 1.4 0.16
May 1986 18.5 (leaves) 62.5 1.5 2.7 0.8 2.2 0.21
10.1 (stems) 36.9 1.1 2.4 0.4 1.3 0.10
Aug. 1986 11.6 (leaves) 61.7 1.3 2.5 0.7 2.7 0.18
4.6 (stems) 31.3 1.0 1.9 0.3 1.1 0.01
*In-vitro organic digestible matter

Utah site Crude protein (%) Digestible protein (%) Metabolic energy (Mcal/kg)
Sept. 14.5 7.9 ----
Oct. 16 8.9 ----
Nov. 15 8.2 ----
Dec. 14.6 8.1 ----
4-month mean ---- 8.24 1.42
Minimum requirement for pregnant ewe ---- 4.40 1.46

Mean nutritional composition (%) of fourwing saltbush grown on calcareous, saline soil in Egypt is given below [18]. Data are presented as an example of fourwing saltbush's high nutritional value on marginal lands.

Crude protein Crude fiber Ether extract Ash P Na K Ca Saponins
15.55 25.21 2.37 12.63* 0.04 2.39* 1.46 1.35 1.13
*Ash and sodium content were the lowest of 7 saltbush species planted.

Nutritional value varies among populations. In a common garden experiment in southern Idaho, Welch and Monsen [212] found significant (p=0.05) differences in winter protein levels, in-vitro digestibility, and productivity in fourwing saltbush accessions from Idaho, Utah, Wyoming, Colorado, New Mexico, and Arizona. Crude protein  ranged from 6.05 to 14.2%, in-vitro digestibility ranged from 29.1% to 46.9%, and productivity ranged from 6.95 oz/plant (197 g/plant) to 15.81 oz/plant (1,451 g/plant). There were no clear geographical patterns to the differences. Nutritional analysis has also been conducted for populations in the west-central panhandle of Texas [72].

Fruits and seeds are  highly nutritious and palatable. All classes of ungulates, and many bird and small mammal species, consume the utricles [162,196]. Fourwing saltbush seeds are commonly found in pocket mice and kangaroo rat scatterhoards near Reno, Nevada [117]. However, deer mice in western Nevada selected fourwing saltbush seed significantly less (p<0.1) than seed of associated species [58].

Fourwing saltbush is somewhat poisonous when consumed in large quantities without other forage, probably because of saponins in leaves and stems [84,108]. Cattle, particularly calves, feeding on little but fourwing saltbush may develop scours [47]. Angora goat yearlings fed only fourwing saltbush for 3 weeks lost weight (=2.5 lbs (1.1 kg)) [199]. As a component of a varied diet, fourwing saltbush is unlikely to have deleterious effects on livestock, especially after ruminal or cecal bacteria have adjusted to a saltbush diet [44].

Cover value: A variety of wildlife seek fourwing saltbush cover [136]. Coyote in southeastern Colorado preferentially seek fourwing saltbush/blue grama habitat along arroyos over open grassland [73]. Small mammals including common porcupine, ground squirrels, and lagomorphs use fourwing saltbush when resting and for shade [161,180,196]. Upland game birds (ring-necked pheasant, quail species, and gray partridge) use fourwing saltbush for thermal and roosting cover [172,196]. Fourwing saltbush cover in several states has been rated as follows [53]:

  CO MT UT WY
elk poor ---- fair poor
pronghorn ---- ---- poor poor
mule deer poor ---- fair poor
white-tailed deer ---- ---- ---- poor
small mammals fair fair good poor
small nongame birds ---- fair fair poor
upland game birds fair fair fair poor
waterfowl ---- ---- poor poor

Fourwing saltbush provides habitat and food for several at-risk species. For example, desert tortoises use fourwing saltbush habitats and browse its shubbery [125]. Mountain plover on the Pawnee National Grassland, Colorado, use fourwing saltbush/blue grama habitat for nesting [79]. Restoration ecologists planted fourwing saltbush, Fremont cottonwood (Populus fremontii), and red willow (Salix laevigata) on the Kern River Preserve, California, to improve habitat for the state-endangered yellow-billed cuckoo [5].

VALUE FOR REHABILITATION OF DISTURBED SITES:
Fourwing saltbush is widely used in rangeland and riparian improvement and reclamation projects [3,4,6,35,130,140], including burned area recovery [7,46,146,170,178]. It is probably the most widely used shrub for restoration of winter ranges and mined land reclamation [25,130]. Fourwing saltbush is drought and cold resistant, palatable, relatively easy to establish with artificial regeneration, and establishes on harsh (and even toxic) sites. Fourwing saltbush is adaptable on sites with declining water tables, brackish groundwater, or saline soils [38]. The deep roots help stabilize erodible soils [4,108,109,140]. It can facilitate establishment of native shrubs, such as sagebrush, that are more resistant to artificial regeneration. Booth [25] warns against overseeding, which may exclude other desirable shrubs. Caution is also recommended when planting fourwing saltbush on roadways because it attracts large browsing ungulates [196].

Fourwing saltbush is propagated from seed or stem cuttings [130]. Information on seed collection and storage, nursery practices for starting seedlings and cuttings, and field outplanting techniques is available [4,118,122,130,140,152,171,181,203,208,209,226]. Fourwing saltbush is often included in native seed mixes [35,39]. Because it shows ecotypic variation, using local plant sources is recommended when possible [130]. Several cultivars have been developed for regional uses, and the seed is commercially available [35,195].

OTHER USES:
Traditional: Fourwing saltbush is traditionally important to Native Americans. They ground the seeds for flour [52,108]. The leaves, placed on coals, impart a salty flavor to corn and other roasted food [201]. Top-growth produces a yellow dye. Young leaves and shoots were used to dye wool and other materials [55,201]. Branch ashes were added to blue corn dough to make green bread [36]. The roots and flowers were ground to soothe insect bites [47,201]. Navajo used the roots to treat coughs and toothaches. Navajo and Seri used the seeds and leaves for an enemetic tea [60,201]. Native tribes throughout the Southwest favored fourwing saltbush as forage for their livestock [36,55].

Landscaping: Fourwing saltbush us widely cultivated as an ornamental [108,213], and is used in xeriscaping [179].

For biological control: In Iraq, seed extracts of fourwing saltbush produced significant mortality (p<0.01) in Culex mosquito larvae [145].

OTHER MANAGEMENT CONSIDERATIONS:
Browsing effects: Fourwing saltbush is adapted to browsing, and may show compensatory growth after stem removal [104,180]. Old crown wood can produce vigorous sprouts after new growth is browsed [23,45]; however, plants declined when subjected to overuse (complete defoliation followed by 3 subsequent years of summer browsing) by domestic sheep and goats in Israel [20,33]. Pieper and Donart [153] found populations in south-central New Mexico suffered 25% mortality under continuous cattle browsing. They concluded fourwing saltbush populations do best when given year-long periodic respites from browsing. Humphrey [102] provides a photographic guide to accessing condition of fourwing saltbush/blue grama and other rangelands of northern Arizona.

Range productivity: There is considerable interest in using fourwing saltbush to improve production on marginal rangelands with very dry or saline soils [16,18,38,119]. As a result, fourwing saltbush is planted as forage on temperate and hot deserts throughout the world [2,16,18].

Shrub die-off: Great Basin shrubs are subject to periodic, massive die-offs, with fourwing saltbush often showing greatest mortality among affected shrub species [89,205]. Many factors that probably act synergistically are implicated in fourwing saltbush die-offs: increased soil salinity, high water table, and root anaerobiosis associated with El Nios; desert dodder (Cuscuta denticulata) infestation; fungal pathogens; and insect herbivory [89,205,210]. A variety of insects including grasshoppers, bugs, Lepidoptera, and Hemiptera feed on fourwing saltbush. Haws and others [89] identified insect herbivores on fourwing saltbush and associated shadscale, winterfat, and antelope bitterbrush during the 1988-1989 shrub die-off.

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