FEIS Home Page |
SPECIES: Tetradymia canescens
Photo by Charles Webber, California Academy of Sciences. | Photo courtesy of Plants Database [67]. |
AUTHORSHIP AND CITATION:
Scher, Janette S. 2001. Tetradymia canescens. In: Fire Effects Information System, [Online].
U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station,
Fire Sciences Laboratory (Producer). Available:
https://www.fs.usda.gov/database/feis/plants/shrub/tetcan/all.html
[].
Revisions: On 5 July 2017, the common name of this species was changed from: gray horsebrush
to: spineless horsebrush in FEIS.
AZ | CA | CO | ID | MT | |||||
NV | NM | OR | UT | WA | |||||
WY |
BC |
Occasional dense stands of spineless horsebrush occur in the sagebrush zone [45], but stands with more than a few hundred individuals are rare. A typical colony size is 25 to 50 plants [64].
RAUNKIAER [56] LIFE FORM:Pollination: Spineless horsebrush is pollinated by generalists including moths, bees, flies, beetles, and other insects. Nearly all spineless horsebrush shrubs within a given colony flower within several days of each other. Flowering occurs relatively early in comparison to associated plants, minimizing competition for pollinators. Pollen fertility is high [43,64].
Seed production: Seed production is high [67].
Seed dispersal: Seeds are light (120,000 seeds per pound) [67] and wind dispersed [79]. The hairs on horsebrush pappi aid dispersal [21].
Seed banking: No information
Germination: No information
Seedling establishment/growth: Spineless horsebrush seedlings are somewhat rare, indicating a long colony turnover rate. This may be due to the harsh environments in which spineless horsebrush grows [42,64]. Though seedling vigor is rated low [67], numerous seedlings have been observed in recently burned areas [42].
Asexual regeneration: Spineless horsebrush sprouts from the root crown after top-growth removal by fire or other disturbances [5,19,30,34,69,76].
SITE CHARACTERISTICS:Elevation ranges for spineless horsebrush in some states in its range include:
Arizona | 6,000-7,000 feet (1,829-2,134 m) [32] |
California | 4,000-10,000 feet (1,219-3,048 m) [25,49] |
Colorado | 4,500-9,500 feet (1,372-2,896 m) [24] |
Montana | 4,000-7,000 feet (1,219-2,134 m) [16] |
New Mexico | 6,000-7,000 feet (1,829-2,134 m) [41] |
Utah | 5,000-10,335 feet (1,525-3,150 m) [71] |
Wyoming | 4,000-9,000 feet (1,219-2,743 m) [16] |
Arizona | July-October [32] |
California | July-August [49] |
New Mexico | July-September [41] |
The following spineless horsebrush phenology data are from a study in the Upper Snake River Plains of southern Idaho [8]:
Leaf growth starts | Twig growth starts | Flower buds visible | 1st bloom | Full bloom | Bloom over | Seed ripe | Dissemination over | Leaves drying | Leaf drop |
April 17 | May 27 | June 18 | July 17 | July 25 | Aug. 7 | Aug. 15 | Sept. 7 | Sept. 7 | Oct. 6 |
Fire regimes: Fires in the desert shrub and grassland ecosystems in which spineless horsebrush occurs were historically stand replacing. Fires in the forest types (ponderosa pine and Douglas-fir) were usually frequent surface fires, whereas fires in pinyon-juniper types were of mixed severity [52]. Fire return intervals for plant communities and ecosystems in which spineless horsebrush occurs are summarized below. Find further fire regime information for the plant communities in which this species may occur by entering the species name in the FEIS home page under "Find Fire Regimes".
Community or Ecosystem | Dominant Species | Fire Return Interval Range (years) |
sagebrush steppe | Artemisia tridentata/Pseudoroegneria spicata | 20-70 [52] |
basin big sagebrush | A. tridentata var. tridentata | 12-43 [57] |
mountain big sagebrush | A. tridentata var. vaseyana | 15-40 [3,11,44] |
Wyoming big sagebrush | A. tridentata var. wyomingensis | 10-70 (40**) [68,77] |
saltbush-greasewood | Atriplex confertifolia-Sarcobatus vermiculatus | < 35 to < 100 |
desert grasslands | Bouteloua eriopoda and/or Pleuraphis mutica | 5-100 |
plains grasslands | Bouteloua spp. | < 35 |
blue grama-needle-and-thread grass-western wheatgrass | B. gracilis-Hesperostipa comata-Pascopyrum smithii | < 35 |
blue grama-buffalo grass | B. gracilis-Buchloe dactyloides | < 35 |
grama-galleta steppe | Bouteloua gracilis-Pleuraphis jamesii | < 35 to < 100 |
blue grama-tobosa prairie | B. gracilis-P. mutica | < 35 to < 100 |
western juniper | Juniperus occidentalis | 20-70 |
Rocky Mountain juniper | J. scopulorum | < 35 |
pinyon-juniper | Pinus-Juniperus spp. | < 35 |
Colorado pinyon | Pinus edulis | 10-49 [52] |
Pacific ponderosa pine* | P. ponderosa var. ponderosa | 1-47 |
interior ponderosa pine* | P. ponderosa var. scopulorum | 2-10 |
Arizona pine | P. ponderosa var. arizonica | 2-10 [2] |
mountain grasslands | Pseudoroegneria spicata | 3-40 (10**) [1,2] |
Rocky Mountain Douglas-fir* | Pseudotsuga menziesii var. glauca | 25-100 [2] |
A study of big sagebrush-grass communities in Wyoming reported that while individual spineless horsebrush plants' production increased following a fire, an overall increase in density of the species was not observed by postfire year 2 [61]. Research in a big sagebrush community on the Upper Snake River Plains reported profuse sprouting by spineless horsebrush after a prescribed burn in August. By postfire year 3, sprout height exceeded height of prefire stems, and sprouts were producing seeds. Fifteen years later, spineless horsebrush production was significantly (p=0.05) higher on burned than on unburned plots, and highest yields tended to be associated with areas that burned more severely [7]. Results from a study of big sagebrush-Idaho fescue communities in Salmon National Forest, Idaho, suggest that "cool" burns may also enhance spineless horsebrush [37].
Results from 1 postfire study in a big sagebrush-grass range on the Upper Snake River Plains, Idaho, are below. The table compares spineless horsebrush annual herbage production (lb/acre, air-dry) on unburned and burned areas for selected years following a 1936 burn. Overall, it shows that higher yields of spineless horsebrush were produced on burned plots than on unburned plots [23].
1936 | 1937 | 1939 | 1948 | 1966 | |
Unburned | 12 | 12 | 8 | 8 | 8 |
Burned | 33 | 10 | 38 | 70 | 36 |
Poisoning by spineless horsebrush has resulted in losses of as many as 1,000 domestic sheep at a time [15,64]. All parts of spineless horsebrush contain compounds (furanoeremophilanes) that are toxic to sheep, but they generally consume only young stems and buds. Spineless horsebrush is therefore most dangerous in its bud stage. After flowering, its toxicity appears to decrease [63]. Stems and leaves equaling as little as 0.5% of the animal's body weight [45] can cause liver damage and related photosensitization, leading to capillary breakage, edema, and swelling of the head known as bighead disease [9,28,45,63,64]. Photosensitization occurs when domestic sheep consume black sagebrush (Artemisia nova) and littleleaf horsebrush together [46,58,63,66], which seems to synergistically increase sheep sensitivity to the furanoeremophilanes [30]. Other effects include a lowering of wool quality [15] and abortion [15,30]. Domestic cattle are not poisoned by spineless horsebrush [9,30,45,64].
PALATABILITY:The degree of use shown by livestock and wildlife species for spineless horsebrush is rated as follows [16]:
CO | MT | UT | WY | |
Cattle | Poor | Poor | Poor | Poor |
Domestic sheep | Poor | Fair | Poor | Poor |
Horses | Poor | Poor | Poor | Poor |
Pronghorn | ---- | Poor | Poor | Fair |
Elk | Poor | Poor | Poor | Fair |
Mule deer | Poor | Poor | Poor | Good |
White-tailed deer | ---- | ---- | ---- | Fair |
Small mammals | ---- | ---- | Poor | Fair |
Small nongame birds | ---- | ---- | Poor | ---- |
Upland game birds | ---- | ---- | Poor | ---- |
Waterfowl | ---- | ---- | Poor | ---- |
CO | MT | UT | WY | |
Pronghorn | ---- | Poor | Poor | Fair |
Elk | ---- | Poor | Poor | Poor |
Mule deer | ---- | Poor | Poor | Poor |
White-tailed deer | ---- | ---- | ---- | Poor |
Small mammals | Fair | Poor | Fair | Good |
Small nongame birds | ---- | ---- | Fair | Good |
Upland game birds | ---- | ----- | Fair | Fair |
Waterfowl | ---- | ---- | Poor | Poor |
Control:
Root cutting, bulldozing [53,72], and tebuthiuron application, can reduce spineless horsebrush density
[13,50]. Application of 2,4-D in spring when plants are actively growing can help
control spineless horsebrush; however, retreatment is necessary to control sprouts
[72].
In rangelands where big sagebrush control is desired, care should be exercised with selection of
methods. Unless spineless
horsebrush is also controlled, it may increase in density [38,51,53,54,74].
Some control treatments may actually increase spineless horsebrush density. Single applications of
atrazine [18] or 2,4-D do not effectively control spineless
horsebrush [18,19,53]. In a big sagebrush community near Reno, Nevada, May
application of 2,4-D the spring after a July wildfire did not significantly (p=0.05)
reduce spineless horsebrush sprouting (plots were remeasured at posttreatment year
4). Livestock grazing significantly increased spineless horsebrush density
on both sprayed and unsprayed plots. Seeding with the perennial bunchgrasses
desert wheatgrass (Agropyron desertorum) and intermediate wheatgrass (Elytrigia
intermedia) significantly reduced spineless horsebrush density on grazed and
ungrazed plots [19]. Desert wheatgrass and intermediate wheatgrass are exotic
species [25]: native bunchgrasses may be more desirable rehabilitation
alternatives. The following control methods
are also generally ineffective at controlling spineless horsebrush: prescribed burning, cutting, beating, shredding, harrowing, railing,
and rolling brush cutting [53]. In 1 Utah study, prescribed burning,
rotobeating, application of 2,4-D, or railing each resulted in at least a 2-fold increase in spineless horsebrush
density compared with untreated plots [48].
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