SPECIES: Tetradymia spinosa


Tetradymia spinosa: INTRODUCTORY

INTRODUCTORY

SPECIES: Tetradymia spinosa

 

photos courtesy of:    

Christopher Christie Las Pilitas Nursery

AUTHORSHIP AND CITATION:
Howard, Janet L. 2002. Tetradymia spinosa. 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:
TETSPI

SYNONYMS:
No entry

NRCS PLANT CODE [55]:
TESP2

COMMON NAMES:
spiny horsebrush
shortspine horsebrush
catclaw-horsebrush
thorny horsebrush
cottonthorn

TAXONOMY:
The scientific name of spiny horsebrush is Tetradymia spinosa Hook. & Arn. (Asteraceae) [16,27,30,53,59,60]. Cronquist and others [16] recognize 2 varieties characterized by relatively short, recurved spines and relatively long, straight spines, respectively:

Tetradymia spinosa var. spinosa
Tetradymia spinosa var. longispina M. E. Jones

LIFE FORM:
Shrub

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
No entry


DISTRIBUTION AND OCCURRENCE

SPECIES: Tetradymia spinosa
GENERAL DISTRIBUTION:
Spiny horsebrush occurs from southeastern Oregon east to Wyoming and south to northwestern New Mexico, Utah, and southern California [16,60], where it is rare [30]. Tetradymia spinosa var. longispina occurs in southern Utah and Nevada, and in Mono County, California [16]. Plants database provides a distributional map of spiny horsebrush.

ECOSYSTEMS [21]:
FRES29 Sagebrush
FRES30 Desert shrub
FRES35 Pinyon-juniper

STATES:
CA CO ID MT NM NV OR UT WY

BLM PHYSIOGRAPHIC REGIONS [4]:
5 Columbia Plateau
6 Upper Basin and Range
7 Lower Basin and Range
10 Wyoming Basin
12 Colorado Plateau

KUCHLER [31] PLANT ASSOCIATIONS:
K023 Juniper-pinyon woodland
K024 Juniper steppe woodland
K038 Great Basin sagebrush
K040 Saltbush-greasewood
K041 Creosote bush
K042 Creosote bush-bur sage
K055 Sagebrush steppe

SAF COVER TYPES [18]:
238 Western juniper
239 Pinyon-juniper

SRM (RANGELAND) COVER TYPES [50]:
211 Creosote bush scrub
401 Basin big sagebrush
402 Mountain big sagebrush
403 Wyoming big sagebrush
404 Threetip sagebrush
405 Black sagebrush 
406 Low sagebrush
414 Salt desert shrub
501 Saltbush-greasewood
506 Creosotebush-bursage

HABITAT TYPES AND PLANT COMMUNITIES:
Spiny horsebrush is common throughout the Great Basin and Mojave deserts, but does not occur in pure stands. It is usually found as isolated individuals or small colonies in saltbush (Atriplex spp.) scrub, desert steppe, low-elevation sagebrush (Artemisia spp.), and pinyon-juniper (Pinus-Juniperus spp.) communities [3,30,37]. Common Great Basin associates of spiny horsebrush include shadscale (Atriplex confertifolia), winterfat (Krascheninnikovia lanata), and broom snakeweed (Gutierrezia sarothrae) [3]. In Utah it occurs in desert shrub, shrub-grassland, and Colorado pinyon-Utah juniper communities (P. edulis-J. osteosperma) [60]. It is a subdominant shrub on the Snake River Plain of southern Idaho, where it associates with big sagebrush (Artemisia tridentata), winterfat, and snakeweeds (Gutierrezia spp.) [33,40]. It is most common in black greasewood (Sarcobatus vermiculatus)-shadscale communities in Nevada [6,8], and in saltbush scrub deserts in California [27]. It also occurs in big sagebrush, creosotebush (Larrea tridentata), singleleaf pinyon (P. monophylla), and Joshua tree (Yucca brevifolia) communities in California [2,24].

Although spiny horsebrush is fairly constant in desert plant communities, it is usually not a community dominant. It showed 33% constancy in a spiny hopsage/green rabbitbrush/cheatgrass (Grayia spinosa/Chrysothamnus viscidiflorus/Bromus tectorum) community in north-central Nevada [5], and 38% mean cover on Mojave Desert sites in California [14]. It sometimes forms a Nevada ephedra (Ephedra nevadensis)-spiny horsebrush association in the Mojave Desert [13]. Branson and others [7] documented a spiny horsebrush-dominated community in west-central Colorado. It was the least productive and least diverse of the 13 Colorado Great Basin communities they studied.

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Tetradymia spinosa
GENERAL BOTANICAL CHARACTERISTICS:
Spiny horsebrush is a native subshrub or shrub with semiwoody to woody stem texture [30], reaching 4 feet (1.2 m) in height [16]. The leaves and young shoots are armed with spines [27,30,59] that are 0.2 to 0.6 inch (0.5-1.5 cm) long in the typical variety and 0.6 to 2 inches (1.5-5.0 cm) in Tetradymia spinosa var. longispina [16]. Horsebrushes (Tetradymia spp.) have 2 types of leaves: primary and secondary. Primary leaves occur on elongated stems, and secondary leaves grow from the axils of primary leaves [35]. Spiny horsebrush's inflorescence is a raceme with tubular, perfect flowers [16,35]. Fruits are 6- to 8-mm-long hairy achenes with bristly pappi [27]. Spiny horsebrush is rhizomatous, and shows a strong tendency to form colonies [53]. Horsebrushes are tap-rooted [32]. 

RAUNKIAER [47] LIFE FORM:
Phanerophyte

REGENERATION PROCESSES:
Spiny horsebrush regenerates from seed and by sprouting from rhizomes and the root crown [9,41,56,61,62]. Information on seed production, viability, and dispersal, seed banking, and seedling establishment is scant for spiny and other horsebrushes. Further research is needed on the reproductive ecology of this genus.

Breeding system: Spiny horsebrush may often be self-fertilized by individuals within a colony connected by rhizomes [53].

Pollination: Horsebrushes are pollinated by insect generalists including flies, moths, bees, and beetles [35].

Seed dispersal: Horsebrush seeds are wind dispersed [64]. The hairs on horsebrush pappi aid dispersal [20].

Seedling establishment/growth: Seedling establishment is rare in horsebrushes, probably due to harsh environments [53]. Spiny horsebrush seedlings were observed on a prescribed burned site in southeastern Oregon [62].

Asexual regeneration: Spiny horsebrush forms small colonies from rhizomes, which may extend 1 foot (30 cm) from the parent plant [37,53]. It also sprouts from the root crown [41,61].

SITE CHARACTERISTICS:
Spiny horsebrush occurs on dry, open foothills, plains, and alkali sinks [16,34]. It grows on skeletal to deep soils [5,24] with clay and loam textures [5,59]. Sites with a large spiny horsebrush component are often mostly bare ground. In west-central Colorado, a spiny horsebrush community showed 15% plant cover (9% of which was spiny horsebrush), 8% litter cover, and 77% bare soil. Although the soil was moist, it was the saltiest of 13 plant communities studied. Researchers speculated that most soil water was lost to evaporation [7]. A northeastern Utah study found spiny horsebrush dominance was correlated with bare ground and soils with poor cation exchange and high concentrations of soluble salts [10].

Spiny horsebrush generally occurs from 2,600 to 6,600 feet (800-2,000 m) elevation, although it is rarely found as high as 8,900 feet (2,700 m) [16]. Elevational ranges by state are:

CA 2,600-7,900 feet (800-2,400 m) [24,27]
CO 4,500-7,000 feet (1,400-2,100) [26]
UT 1,400-6,300 feet (1,250-1,925 m) [60]

Climate on spiny horsebrush sites is often harsh, with hot summers and cool to cold winters. A Nevada ephedra-spiny horsebrush site in the Owens Valley of California showed a mean weekly maximum summer temperature of 104 oFahrenheit (40 oC), 0.9 inch (240 mm) total summer precipitation, and mean total windspeed of 62.1 miles/day (99.9 km/day) [13].

SUCCESSIONAL STATUS:
Spiny horsebrush occurs in both seral and late-successional plant communities [44]. The rate of succession in many salt desert shrublands is very slow [58], and as a sprouting species, spiny horsebrush is more likely to be found in seral communities compared to nonsprouting desert shrubs. Spiny horsebrush is a nurse plant for seedling cholla cacti (Opuntia spp.) in the Mojave Desert [15].

SEASONAL DEVELOPMENT:
Spiny horsebrush flowers from April to June [16]; occasionally flowering extends into August [34]. Colonies usually have synchronous flowering [37,53]. Failure to flower or develop seed is apparently triggered by low rainfall. In very dry years, some individuals -- or entire colonies -- may not flower, or will flower and not set seed [53]. Spiny horsebrush is drought deciduous, shedding the secondary leaves 1st [23,53].

FIRE ECOLOGY

SPECIES: Tetradymia spinosa
FIRE ECOLOGY OR ADAPTATIONS:
Fire adaptations: Horsebrushes are "slightly damaged by fire" [45]: top-growth is removed. Spiny horsebrush sprouts from the root crown and rhizomes after fire [9,41,56,61]. It also establishes from seed after fire [62].

Fire regimes: Fires in the desert shrub ecosystems in which spiny horsebrush occurs were historically infrequent and stand replacing. Spiny horsebrush is most common on dry sites with sparse vegetation cover [7,10], and fires are rare on spiny horsebrush-dominated sites due to sparse fuels [41,42]. Fires in the pinyon-juniper types with a spiny horsebrush component were of mixed severity [42].

The following table provides fire return interval for plant communities and ecosystems with spiny horsebrush. For further information on fire regimes in these communities, see the FEIS summary on the dominant plant species listed below.

Community or Ecosystem Dominant Species Fire Return Interval Range (years)
sagebrush steppe Artemisia tridentata/Pseudoroegneria spicata 20-70 [42]
basin big sagebrush Artemisia tridentata var. tridentata 12-43 [48]
mountain big sagebrush Artemisia tridentata var. vaseyana 15-40 [1,11,36]
Wyoming big sagebrush Artemisia tridentata var. wyomingensis 10-70 (40**) [57,63]
saltbush-greasewood Atriplex confertifolia-Sarcobatus vermiculatus < 35 to < 100
western juniper Juniperus occidentalis 20-70
Rocky Mountain juniper Juniperus scopulorum < 35 
pinyon-juniper Pinus-Juniperus spp. < 35 [42]
**mean

POSTFIRE REGENERATION STRATEGY [51]:
Small shrub, adventitious bud/root crown
Rhizomatous shrub, rhizome in soil

FIRE EFFECTS

SPECIES: Tetradymia spinosa
IMMEDIATE FIRE EFFECT ON PLANT:
Fire rarely kills horsebrush species. It top-kills spiny horsebrush [43,45].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
No entry

PLANT RESPONSE TO FIRE:
Spiny horsebrush establishes after fire from seed and by sprouting from rhizomes and the root crown [9,41,56,61]. Spiny horsebrush seedlings were observed 1 year after prescribed burning in a Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis) community in southeastern Oregon [62]. Whether the seedlings established from the seed bank or from off-site sources was not known.

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
No entry

FIRE MANAGEMENT CONSIDERATIONS:
Fire exclusion on desert steppes has tended to favor sagebrush species over fire-tolerant shrubs such as spiny horsebrush [12,25,28]. Increased fire frequencies due to invasion of cheatgrass, red brome (Bromus madritensis ssp. rubens), and other annual grasses may favor spiny horsebrush and other sprouting shrubs over sagebrush.

MANAGEMENT CONSIDERATIONS

SPECIES: Tetradymia spinosa
IMPORTANCE TO LIVESTOCK AND WILDLIFE:
Palatability: Spiny horsebrush is not a toxic horsebrush species [19,49,52,54], but browsers seldom use it. Horsebrushes are unpalatable except early in the spring, when animals may consume young shoots and buds [29,49]. Domestic sheep on saltdesert shrublands in Utah browsed spiny horsebrush only incidentally. Use was 0.9% in the 1st year of the study and 0% in the 2nd [22]. Palatability of spiny horsebrush has been rated as follows [17]:

  CO MT UT WY
cattle ---- poor poor poor
domestic sheep ---- poor fair poor
horses ---- poor poor poor
pronghorn ---- ---- poor ----
elk poor ---- poor ----
mule deer poor ---- poor ----
small mammals ---- ---- fair ----
small nongame birds ---- ---- fair ----
upland game birds ---- ---- poor ----
waterfowl ---- ---- poor ----

Nutritional value: Mean nutritional content of spiny horsebrush browse is as follows [39]:

Nutrient %
ash 5.4
crude fiber 36.8
ether extract 6.3
N-free extract 42.8
Protein (N 6.25) 8.7
     cattle (digestible protein) 5.3
     domestic goats (digestible protein) 4.7
     horses (digestible protein) 4.9
     domestic rabbits (digestible protein) 5.4
     domestic sheep (digestible protein) 5.1
calcium 0.94
phosphorus 0.25

Cover value: Spiny horsebrush provides cover for small animals [34].

VALUE FOR REHABILITATION OF DISTURBED SITES:
Spiny horsebrush helps stabilize soil on erodible desert sites. Horsebrushes provide critically needed ground cover on dry sites that are otherwise often sparsely vegetated [34].

OTHER USES:
Spiny horsebrush is a honeybee plant [30]. Western Shoshone used spiny horsebrush concoctions as external medicine, and used the spines as piercing instruments [65].

OTHER MANAGEMENT CONSIDERATIONS:
Spiny horsebrush was affected by the massive shrub die-off in the Great Basin in 1977-1986. Besides high mortality, many plants showed signs of decline and low vigor. Causes of the die-off are not known; unlike other periods of shrub die-off in the Great Basin, it occurred during a period of unusually high precipitation [33,40]. Elevated levels of soil salinity, anaerobic conditions caused by waterlogged soils, and plant pathogens (viruses, fungi, and bacteria) have been suggested as causes. One result of the die-back was an escalated invasion of cheatgrass, which established in areas left bare by dead shrubs [40]. See cheatgrass for information on altered fire regimes due to that species.

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