SPECIES: Rhus trilobata
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USDA-NRCS PLANTS Database
© 1995 Saint Mary's College of California
AUTHORSHIP AND CITATION:
Anderson, Michelle D. 2004. Rhus trilobata. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: www.fs.fed.us/database/feis .
Rhus aromatica var. pilosissima 
= Rhus trilobata var. pilosissima [76,115]
Rhus aromatica var. simplicifolia (Greene) Cronq. 
= Rhus trilobata var. simplicifolia [76,155]
Rhus aromatica Aiton ssp. trilobata (Nuttall) Weber 
= Rhus trilobata
Rhus aromatica var. trilobata (Nutt.) Gray [58,153]
= Rhus trilobata var. trilobata [76,115,155]
NRCS PLANT CODE :
The currently accepted scientific name of skunkbush sumac is Rhus trilobata Nutt. (Anacardiaceae) [47,48,69,71,76,77,115,155]. Infrataxa are as follows:
R. t. var. anisophylla (Greene) Jepson [76,155], skunkbush sumac
R. t. var. pilosissima Engelm. [76,115], pubescent skunkbush sumac
R. t. var. quinata (Greene) Jepson [76,155], Grand Canyon skunkbush sumac
R. t. var. racemulosa (Greene) Barkl. , skunkbush sumac
R. t. var. simplicifolia (Greene) Barkl. [76,155], skunkbush sumac
R. t. var. trilobata, skunkbush sumac
FEDERAL LEGAL STATUS:
|R. t. var. anisophylla||Washington south to California, east to Utah and New Mexico|
|R. t. var. pilosissima||California east to Texas, north to Colorado and Kansas|
|R. t. var. quinata||Washington south to California, east to Nevada and New Mexico|
|R. t. var. racemulosa||Arizona and New Mexico|
|R. t. var. simplicifolia||Washington south to California, east to Colorado, New Mexico, and Oklahoma|
|R. t. var. trilobata||entire range|
Grassland: Common associates in mixed-prairie communities are thickspike wheatgrass (Elymus lanceolatus), needle-and-thread grass (Hesperostipa comata), prairie Junegrass (Koeleria macrantha), western wheatgrass (Pascopyrum smithii), plains reedgrass (Calamagrostis montanensis), Sandberg bluegrass (Poa secunda), sedges (Carex spp.), green needlegrass (Nassella viridula), Indian ricegrass (Achnatherum hymenoides), hairy grama (Bouteloua hirsuta), blue grama (B. gracilis), little bluestem (Schizachyrium scoparium), dropseeds (Sporobolus spp.), big bluestem (Andropogon gerardii var. gerardii), and switchgrass (Panicum virgatum) [1,26]. Woody plant associates include cherry (Prunus spp.), smooth sumac (Rhus glabra), lead plant (Amorpha canescens), golden currant (Ribes aureum), snowberry (Symphoricarpos spp.), American elm (Ulmus americana), and hackberry (Celtis occidentalis) .
Shrubland: Skunkbush sumac is frequently found with sagebrushes (Artemisia spp.) and rabbitbrushes (Chrysothamnus spp.) . In mountain shrub communities, skunkbush sumac is associated with Gambel oak (Quercus gambelii), chokecherry (P. virginiana), true mountain-mahogany (Cercocarpus montanus), bluegrass (Poa spp.), needlegrass (Nassella spp.), Indian ricegrass, and broom snakeweed (Gutierrezia sarothrae) . In Colorado steppe communities, common associates include sleepygrass (Achnatherum robustum), western wheatgrass, blue grama, buffalo grass (Buchloe dactyloides), fourwing saltbush (Atriplex canescens), and rubber rabbitbrush (Chrysothamnus nauseous) .
Skunkbush sumac is a common constituent of Arizona chaparral communities. Associates include shrub live oak (Q. turbinella), Emory oak (Q. emoryi), Palmer oak (Q. dunnii), true and birchleaf mountain-mahogany (Cercocarpus montanus var. glaber, C. betuloides), pointleaf and Pringle manzanita (Arctostaphylos pungens, A. pringlei), desert ceanothus (Ceanothus greggii), catclaw acacia (Acacia greggii), catclaw mimosa (Mimosa biurcifera), Bigelow's nolina (Nolina bigelovii), sugar sumac (Rhus ovata), jojoba (Simmondsia chinensis), redberry buckthorn (Rhamnus crocea), California coffeeberry (R. californica), and Wright and chaparral silktassel (Garrya wrightii, G. congdonii) [25,33,34,68,98,137,150]. Chaparral associates in Baja California include Parry pinyon (Pinus quadrifolia), singleleaf pinyon (P. monophylla), Muller oak (Q. cornelius-mulleri), redberry buckthorn, sugar sumac, flannelbush (Fremontodendron californicum), and desert agave (Agave deserti) .
Forest: Associates in Rocky Mountain forest communities include ponderosa pine (P. ponderosa), limber pine (P. flexilis), Douglas-fir (Pseudotsuga menziesii), Rocky Mountain juniper (Juniperus scopulorum), rubber rabbitbrush, prairie rose (Rosa arkansana), common snowberry (Symphoricarpos albus), true mountain-mahogany, chokecherry, wax currant (Ribes cereum), big sagebrush (Artemisia tridentata), silver sagebrush (A. cana), and antelope bitterbrush (Purshia tridentata) [94,121].
In pinyon-juniper (Pinus spp.-Juniperus spp.) communities, skunkbush sumac is commonly found with Colorado pinyon (P. edulis), oneseed juniper (J. monosperma), Bigelow sagebrush (A. bigelovii), true mountain-mahogany, groundcherry (Physalis spp.), agarito (Mahonia trifoliolata), wolfberry (Lycium spp.), galleta grass (Pleuraphis jamesii), blue grama, and creeping muhly (Muhlenbergia repens) [4,43]. Associates in Rocky Mountain juniper communities are chokecherry, silver buffaloberry (Shepherdia argentea), silver sagebrush, and shrubby cinquefoil (Dasiphora floribunda) .
Classifications listing skunkbush sumac as a plant community dominant include the following:
New Mexico [45,136]
South Dakota [39,132]
Plant community codominants include Arizona white oak (Q. arizonica), Colorado pinyon, oneseed juniper, New Mexico muhly (M. pauciflora) in the Southwest [15,45,136]; narrowleaf cottonwood (Populus angustifolia) in Nevada and southern California ; Rio Grande cottonwood (P. deltoides ssp. wislizeni)  and mountain muhly (M. montana) in Colorado ; bluebunch wheatgrass (Pseudoroegneria spicata) in Montana  and Wyoming ; and true mountain-mahogany , bur oak (Q. macrocarpa), bluebunch wheatgrass, and Idaho fescue (Festuca idahoensis)  in the Black Hills of South Dakota.
Skunkbush sumac is a deciduous, flowering native shrub [22,34,74,75,76,86,131]. It grows 2 to 12 feet (0.6-3.6 m) tall, averaging 4 feet (1.2 m) tall [34,40,56,105,107,115,144,150]. Taller shrubs are found on more favorable habitats [22,56]. Growth form is erect to spreading with a dense crown [40,74,107,135]. Shrub width may reach 6.5 feet (2 m) . Skunkbush sumac has many irregularly branched stems, and leaves are formed by 3 leaflets . The fruit of skunkbush sumac is a 1-seeded drupe .
Skunkbush sumac has a taproot  and a fibrous root system [74,75]. Roots
are deep and extensively branched with somewhat shallow, spreading woody
rhizomes . Individual shrubs and patches of skunkbush sumac may be
connected by underground structures that can exceed 20 feet (6 m) in length
and 30 years in age . It sprouts readily from the root crown [74,107].
RAUNKIAER  LIFE FORM:
Skunkbush sumac propagates by seed and root sprouts . It sprouts readily from the root crown after severe disturbance [74,107] but is unlikely to reproduce vegetatively in the absence of disturbance . Skunkbush sumac reproduces only rarely from seed [74,94].
Breeding system: Skunkbush sumac has been reported as dioecious  and as polygamomonoecious .
Pollination: Skunkbush sumac is animal-pollinated , presumably by small mammals.
Seed production: Skunkbush sumac reportedly has low seed production . It was estimated that only 5 to 15% of skunkbush sumac flowers in a North Dakota shrub community actually produced fruit. Branches from 6 to 10 years of age produced the most viable fruit .
Seed dispersal: Seeds are eaten and dispersed by birds and animals [107,110,134].
Seed banking: No information is available on this topic.
Germination: Skunkbush sumac seeds have both seed coat impermeability and embryo dormancy [18,89,131,151]. They germinate poorly without scarification which is necessary to crack or soften the hard seed coat. Little evidence exists that skunkbush sumac seeds are physiologically dormant. Breaking embryo dormancy may require a cold stratification [18,107,151]. High temperatures (>180 oF (82oC)) associated with fire have been shown to break seed dormancy in greenhouse experiments . Some laboratory experiments have demonstrated that neither temperature or light stratification affects germination rates . However, Keeley  found that germination of skunkbush sumac was significantly decreased (p<0.001) by the absence of light.
A study of skunkbush sumac seeds found seeds ingested by bears and deposited in scat had much higher germination rates than noningested seeds. Furthermore, chilling the seeds resulted in even lower germination rates. Prewarming of seeds, on the other hand, significantly increased germination of seeds (p<0.05) .
Skunkbush seeds remain viable in cool storage (37-41 oF/3-5 oC) for 5 years .
Seedling establishment/growth: Seedling establishment may be rare in established skunkbush sumac stands [74,107,123]. Seedlings are very susceptible to damping-off fungus .
The primary means of short-range skunkbush sumac dispersal is vegetative [40,123,150];
shrubs in North Dakota up to 20 feet (6 m) apart were found to be connected
. Skunkbush sumac may form thickets as large as 30 feet (9 m) in diameter
[123,131,143,150]. Undisturbed plants produce few sprouts, while those subject to
browsing, trampling or burning produce many sprouts [40,94,150].
Skunkbush sumac grows on dry, rocky hillsides and sandhills, as well as along streams, canyon bottoms, and wetlands [40,56,75,76,91,105,131,135,137,144,150,153]. It is found in grassy flats and openings in woodland areas [63,74,75,76,94].
Elevation: Skunkbush sumac grows principally from 3,500-9,000 feet (1,065-2,740 m), though it also occurs at lower elevations [75,144]. The following table gives the elevation range of skunkbush sumac by state:
|Arizona||2,500-7,500 feet (760-2,285 m)||[34,77,137]|
|California||500-6,000 feet (152-1,830 m)||[40,74]|
|Montana||<6,000 feet (1,830 m)|||
|Southern New Mexico and southern Texas||4,220-6,000 feet (1,286-1,830 m)|||
|Utah||2,900-7,700 feet (885-2,350 m)||[110,153]|
The relationship between skunkbush sumac and slope aspect is ambiguous. It is reportedly more prevalent on north slopes in the mixed-prairie, where it is protected from prevailing winds and receives more water from wind-drifted snow . It is also more abundant on north-facing slopes in pinyon-juniper communities in the Southwest . In Alberta coulees, however, skunkbush sumac is largely restricted to south-facing slopes . In Montana, it is also found more often on south slopes, with slope gradients between 40 and 80% . In another study, skunkbush sumac in the North Dakota badlands had higher relative densities on steep southwest slopes; however, it was denser and larger on northeast slopes .
Climate: Skunkbush sumac is adapted to a wide range of climates, particularly the 10 to 20 inches (254-508 mm) annual precipitation zones [144,150]. In Montana, sites supporting skunkbush sumac have an average January temperature of 20 oF (-6.7 oC) and average July temperature of 64 oF (18 oC). Average annual precipitation is 14 inches (355 mm) per year, with 50% falling from May through July. The growing season varies from 50 to 130 days, with moderate to high density stands found on sites having 120 or more frost-free days . The climate in North Dakota has January temperatures averaging 11 oF (-11 oC) and July temperatures averaging 69 oF (20 oC). Average annual precipitation is 15.6 inches (396 mm), with 80% falling between April and September .
In contrast, the Arizona chaparral climate has cool, wet winters extending into March, followed by warm, dry weather for 2 or 3 months. Following summer rains, dry weather returns in October and persists until winter rains in December. Average annual precipitation ranges from 16 to 25 inches (406-635 mm), generally increasing with elevation. Average monthly temperatures range from less than 40 oF (4 oC) in January to more than 80 oF (26 oC) in July .
Skunkbush sumac is moderately drought tolerant [60,131,143,150], though seedlings may be severely affected by drought conditions . Acute drought may shorten twig growth and prevent fruit production .
Soils: Skunkbush sumac may grow to 2 to 3 feet (0.6-0.9 m) on dry sites,
and 10 to 12 feet (3-3.6 m) with more favorable moisture availability .
Skunkbush sumac is tolerant of most soil textures but prefers well-drained sites
[94,120,131,139,150,150]; it may be found in higher density at mid-slope
positions than at the bottom of slopes . Skunkbush sumac prefers deep
soil [74,94] or thin soils with a gravel base. Extensive stands have been
reported on steep slopes where topsoils were thin or absent . Soil pH is
often mildly alkaline [94,116]; in Montana, large stands were found on soil pH
of 7.4 . Soils may be high in potassium and low in organic matter,
phosphorus, and salt . Skunkbush sumac is intolerant of flooding and high
water tables .
Skunkbush sumac is commonly found on disturbed sites [18,24]. It prefers full sun or partial shade .
Annual growth of skunkbush sumac occurs primarily in spring and early summer [86,94,137,150]. In a North Dakota study, growth of new twigs was complete by July 9 . Skunkbush sumac flowers in early spring, 1 to 3 weeks before leaves appear [40,75,94,105,115,135,150]. Fruit matures July through October [18,22], and persists into winter . Seeds are dispersed from August through the following summer . Leaf drop occurs in October .
Fire regimes: No information is available regarding fire regimes in plant communities where skunkbush sumac is dominant, and little is known about its response to different fire regimes. Frequent or severe fires will restrict skunkbush sumac to protected sites or to areas of light fuel loadings, even though vigorous sprouting occurs after fire. The absence of fire allows seedling establishment on favorable microsites, and may result in an increase of skunkbush sumac on a site .
Skunkbush sumac grows in a wide variety of plant communities, where fire return intervals range from less than 10 years up to hundreds of years. Fire regimes for plant communities and ecosystems in which skunkbush sumac occurs are summarized below. For more information on the fire regimes of these communities, see the FEIS species summary for the dominant species listed below.
|Community or Ecosystem||Dominant Species||Fire Return Interval Range (years)|
|California chaparral||Adenostoma and/or Arctostaphylos spp.||< 35 to < 100 |
|bluestem prairie||Andropogon gerardii var. gerardii-Schizachyrium scoparium||< 10 [83,109]|
|Nebraska sandhills prairie||Andropogon gerardii var. paucipilus-Schizachyrium scoparium||< 10|
|coastal sagebrush||Artemisia californica||< 35 to < 100 |
|silver sagebrush steppe||Artemisia cana||5-45 [67,117,156]|
|sagebrush steppe||Artemisia tridentata/Pseudoroegneria spicata||20-70 |
|basin big sagebrush||Artemisia tridentata var. tridentata||12-43 |
|mountain big sagebrush||Artemisia tridentata var. vaseyana||15-40 [6,32,97]|
|Wyoming big sagebrush||Artemisia tridentata var. wyomingensis||10-70 (40**) [147,157]|
|desert grasslands||Bouteloua eriopoda and/or Pleuraphis mutica||5-100 |
|plains grasslands||Bouteloua spp.||< 35 [109,156]|
|blue grama-needle-and-thread grass-western wheatgrass||Bouteloua gracilis-Hesperostipa comata-Pascopyrum smithii||< 35 [109,122,156]|
|blue grama-buffalo grass||Bouteloua gracilis-Buchloe dactyloides||< 35 [109,156]|
|grama-galleta steppe||Bouteloua gracilis-Pleuraphis jamesii||< 35 to < 100|
|blue grama-tobosa prairie||Bouteloua gracilis-Pleuraphis mutica||< 35 to < 100 |
|cheatgrass||Bromus tectorum||< 10 [111,154]|
|California montane chaparral||Ceanothus and/or Arctostaphylos spp.||50-100 |
|curlleaf mountain-mahogany*||Cercocarpus ledifolius||13-1,000 [8,127]|
|mountain-mahogany-Gambel oak scrub||Cercocarpus ledifolius-Quercus gambelii||< 35 to < 100|
|blackbrush||Coleogyne ramosissima||< 35 to < 100|
|western juniper||Juniperus occidentalis||20-70|
|Rocky Mountain juniper||Juniperus scopulorum||< 35 |
|cedar glades||Juniperus virginiana||3-22 [61,109]|
|wheatgrass plains grasslands||Pascopyrum smithii||< 5-47+ [109,117,156]|
|pinyon-juniper||Pinus-Juniperus spp.||< 35 |
|Mexican pinyon||Pinus cembroides||20-70 [102,140]|
|Rocky Mountain lodgepole pine*||Pinus contorta var. latifolia||25-340 [13,14,141]|
|Colorado pinyon||Pinus edulis||10-400+ [53,57,78,109]|
|Jeffrey pine||Pinus jeffreyi||5-30 |
|interior ponderosa pine*||Pinus ponderosa var. scopulorum||2-30 [5,10,87]|
|Arizona pine||Pinus ponderosa var. arizonica||2-15 [10,41,128]|
|galleta-threeawn shrubsteppe||Pleuraphis jamesii-Aristida purpurea||< 35 to < 100 |
|mesquite||Prosopis glandulosa||< 35 to < 100 [96,109]|
|mesquite-buffalo grass||Prosopis glandulosa-Buchloe dactyloides||< 35|
|Texas savanna||Prosopis glandulosa var. glandulosa||< 10 |
|Rocky Mountain Douglas-fir*||Pseudotsuga menziesii var. glauca||25-100 [5,6,7]|
|California oakwoods||Quercus spp.||< 35 |
|oak-juniper woodland (Southwest)||Quercus-Juniperus spp.||< 35 to < 200 |
|canyon live oak||Quercus chrysolepis||<35 to 200|
|blue oak-foothills pine||Quercus douglasii-P. sabiniana||<35 |
|California black oak||Quercus kelloggii||5-30 |
|bur oak||Quercus macrocarpa||< 10 |
|oak savanna||Quercus macrocarpa/Andropogon gerardii-Schizachyrium scoparium||2-14 [109,149]|
|shinnery||Quercus mohriana||< 35 |
|post oak-blackjack oak||Quercus stellata-Q. marilandica||< 10|
|blackland prairie||Schizachyrium scoparium-Nassella leucotricha||< 10 |
|little bluestem-grama prairie||Schizachyrium scoparium-Bouteloua spp.||< 35 |
Skunkbush sumac typically increases after fire, though average plant size is reduced in the short-term. The following table describes the impact of a 1979 prescribed fire on skunkbush sumac in a Black Hills ponderosa pine forest :
|1979 - preburn||1980||1981|
|Total # of plants||48||19||57||23||65||23|
|Mean max. height||28.2 cm||39.9 cm||28.6 cm||17.9 cm||30.6 cm||25.4 cm|
|Mean max. crown width||31.0 cm||33.2 cm||31.5 cm||17.7 cm||30.6 cm||25.4 cm|
Response of vegetation to prescribed burning in a Jeffrey pine-California black oak woodland and a deergrass meadow at Cuyamaca State Park, California, provides information on prescribed fire use and postfire response of many mixed-conifer woodland species including skunkbush sumac.FIRE MANAGEMENT CONSIDERATIONS:
Skunkbush sumac is also browsed by small mammals. Porcupines utilize it , and it is also browsed, sometimes heavily, by jackrabbits and cottontail [28,44], particularly after heavy snow when branches extend above drifts .
Skunkbush sumac fruit is an important winter food source for birds, including songbirds, prairie chickens, Merriam turkeys, ring-necked pheasants, sage-grouse, ruffed grouse, sharp-tailed grouse, and bobwhite, valley, Gambel, and scaled quail [107,135,138,139]. Fruit is also eaten by black bears , and occasionally, white-tailed deer .
Palatability/nutritional value: Skunkbush sumac has poor palatability for domestic livestock throughout most of its range [46,135], but may be fair to good for cattle and domestic sheep in the Southwest and Colorado . It is highly palatable for domestic goats in the Southwest . Skunkbush sumac provides good browse for deer and pronghorn .
The National Academy of Sciences reports the following nutritional information for skunkbush sumac (% dry matter) :
|Ether extract||4.4||Digestible protein:|
A study in the southern Great Plains found the following monthly nutrient content for skunkbush sumac (5-year means, % dry weight) :
Monthly variation in crude protein content of skunkbush sumac from California samples was reported as follows (% oven dry weight) :
Skunkbush sumac provides useful cover and nesting sites for birds [75,139].
It provides poor to fair cover for elk; fair to good cover for white-tailed
deer, mule deer, and pronghorn; good cover for upland game birds, nongame
birds, and small mammals; and poor cover
for waterfowl .
VALUE FOR REHABILITATION OF DISTURBED SITES:
Skunkbush sumac is useful for landscape planting [60,73], wind barriers [75,139], and reclamation of disturbed areas . It is excellent for erosion control [74,143] and survives on untreated mine spoils . Skunkbush sumac is commercially available (e.g. cultivar "Autumn Amber") [73,146] and grows well from seed (especially when planted in fall and winter) or transplants . Skunkbush sumac has an average of 20,300 seeds per pound (44,750 seeds/kg) . For best survival, plant 2-0 container stock  in deep soil and full sun . Excellent transplant success has been reported (100% on 3 out of 4 sites) ; however, a study in the Tahoe Basin found poor transplant establishment and survival .
In laboratory experiments, optimum germination was achieved with both sulfuric
acid treatment and moist prechilling . Acid scarification is useful in encouraging
seed germination due to the impermeable seedcoat [90,151]. Other experiments found that
germination of skunkbush sumac was significantly decreased (p<0.001) by the absence
of light, while the addition of powdered, charred wood significantly increased (p<0.01)
germination rates .
Southwestern Native Americans ate the fruits of skunkbush sumac, either fresh or after being ground to form meal [16,35]. The berries have a distinct lemon flavor and could be mixed with various foods for seasoning  or dried and made into jam [36,49]. Berries were also mixed with water to make a beverage . Leaves of skunkbush sumac were dried and mixed with tobacco for smoking . The leaves were also used for medicinal purposes (stomachache, diuretic, toothache pain, bleeding, head colds, poison ivy rashes) [16,62,112].
Native Americans burned skunkbush sumac to stimulate production of long,
straight sprouts which could be used for making baskets and handcrafted
OTHER MANAGEMENT CONSIDERATIONS:
Reports regarding skunkbush sumac response to grazing are conflicting, with some authors reporting increased growth due to sprouting [94,135,150] and others reporting decreased growth [86,158].
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