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Holodiscus dumosus

• INTRODUCTORY
• DISTRIBUTION AND OCCURRENCE
• BOTANICAL AND ECOLOGICAL CHARACTERISTICS
• FIRE EFFECTS AND MANAGEMENT
• MANAGEMENT CONSIDERATIONS
• APPENDIX: FIRE REGIME TABLE
• REFERENCES

INTRODUCTORY

	AUTHORSHIP AND CITATION FEIS ABBREVIATION NRCS PLANT CODE COMMON NAMES TAXONOMY SYNONYMS LIFE FORM
Photo by Mary Ellen (Mel) Harte, Bugwood.org

The Holodiscus taxonomy is confused because rockspirea, creambush oceanspray (H. discus), and small-leaved rockspirea (H. microphyllus) are taxonomically and morphologically similar [15,54,61]. Authorities separating these 3 closely related taxa do so based on different leaf morphologies [15,54] and distributions [54]. This review follows the taxonomy of Lis (in [33]), who is authoring the Flora of North America's [23] Holodiscus chapter. In Lis's treatment, rockspirea, creambush oceanspray, and small-leaved rockspirea are treated as separate and distinct species [33]. Some systematists lump either rockspirea and creambush oceanspray [39,67,89], creambush oceanspray and small-leaved rockspirea [38], or all 3 [88] into single species.

DISTRIBUTION AND OCCURRENCE

• GENERAL DISTRIBUTION
• HABITAT TYPES AND PLANT COMMUNITIES

Coniferous communities: Rockspirea is often characteristic to dominant in the understories of Rocky Mountain Douglas-fir [1,4,53], southwestern ponderosa pine (includes interior ponderosa pine and Arizona pine (P. p. var. arizonica)) [58,62,64], and mixed-conifer [69] forests and woodlands. It often dominated the shrub layer of low-elevation Rocky Mountain Douglas-fir/Gambel oak [62] and interior ponderosa pine/Gambel oak (Quercus gambelii) [66] communities of the Southwest. Kuchler describes rockspirea as a characteristic to dominant shrub of southwestern ponderosa pine-Rocky Mountain Douglas-fir forests in the southern Rocky Mountains [45], Great Basin bristlecone pine-limber pine (P. aristata-P. flexilis) [44] forests and woodlands in high elevations of the Great Basin, and southwestern ponderosa pine forests in Arizona [43].

Great Basin: In western Nevada, rockspirea grows in Rocky Mountain Douglas-fir, Great Basin bristlecone pine [44], and red fir (Abies magnifica) [39] communities. Welsh and others [89] call it "nearly ubiquitous" in coniferous and other plant communities of Utah.

Colorado: Rockspirea occurs in Colorado pinyon-juniper/soapweed yucca/blue grama (P. edulis-Juniperus spp./Yucca glauca/Bouteloua gracilis)) woodlands of western Colorado [14] and in Engelmann spruce (Picea engelmannii)-Rocky Mountain Douglas-fir and Rocky Mountain bristlecone pine (Pinus aristata) forests of west-central Colorado [1]. It is occasional in blue spruce/sprucefir fleabane (Picea glauca/Erigeron eximius) habitat types of the San Juan Mountains [17].

Arizona: Rockspirea grows in Rocky Mountain Douglas-fir [4], pine (Pinus spp.) [40], spruce (Picea spp.) [40], and white fir (A. concolor) [62] forests and woodlands of Arizona. In the Santa Teresa Mountains, it is a component of sky-island Rocky Mountain Douglas-fir and interior ponderosa pine communities [10]. In the Rincon Mountain Wilderness, rockspirea occurs in mixed-conifer forests dominated by Rocky Mountain Douglas-fir and white fir on north- and northeast-facing slopes and by southwestern white pine (P. strobiformis) and interior ponderosa pine on northwest-facing slopes. Quaking aspen (Populus tremuloides) stands are often interspersed among these coniferous forests. Southern aspects, on which rockspirea may also grow, are typically dominated by southwestern white pine and oaks, including Arizona oak (Q. arizonica), Emory oak (Q. emoryi), and silverleaf oak (Q. hypoleucoides) [4]. On the Gunnison National Forest, rockspirea had 2% to 6% average cover in Rocky Mountain Douglas-fir habitat types [41]. It is characteristic in Engelmann spruce/Rocky Mountain maple (Acer glabrum) habitat types of the Chiricahua Mountains [62].

New Mexico: In the White Mountains, rockspirea is important in interior ponderosa pine-Gambel oak/New Mexico locust (Robinia neomexicana) communities [26,27]. In the Rio Grande Wild and Scenic River Recreation Area, big sagebrush, broom snakeweed (Gutierrezia sarothrae), and rockspirea codominate the understory of a canyon-bench interior ponderosa pine woodland [76]. Rockspirea is occasional in blue spruce/sprucefir fleabane habitat types of the Sangre de Cristo Mountains [17].

Mexico: In the Sierra Occidentale of Nuevo Leon, rockspirea occurs in subalpine border pinyon (P. culminicola) scrub [5].

Riparian hardwood and other hardwood communities: Among hardwood communities, rockspirea is reported most often in riparian communities but is also common in mesic montane and canyon-bottom communities. It occurs in riparian quaking aspen/willow (Salix spp.) communities of northeastern Nevada [12] and in quaking aspen woodlands of Rocky Mountain National Park, Colorado [11]. On the Coronado National Forest, Arizona, rockspirea grows in Arizona sycamore-velvet ash/mule fat (Platanus wrightii-Fraxinus velutina/Baccharis salicifolia) riparian communities [14]. In southwestern New Mexico, it grows along the Mimbres River in cottonwood/Goodding willow (Populus spp./Salix gooddingii) woodlands communities below about 7,450 feet (2,270 m). Fremont cottonwood (P. fremontii), narrowleaf cottonwood (P. angustifolia), and/or lanceleaf cottonwood (P. × acuminata) are overstory dominants [7]. Rockspirea is common in canyon bottomlands of Canyon de Chelly National Monument, Arizona. Overstory species in these canyon-bottomland communities include boxelder (Acer negundo) and shrub live oak (Quercus turbinella) [29].

Shrublands: Rockspirea grows in big sagebrush (Artemisia tridentata), woody draw, and mountain shrub communities. In western and central Nevada, it is characteristic of upper-elevation big sagebrush-grass communities that occur above the pinyon-juniper (Pinus-Juniperus spp.) zone. This big sagebrush zone may extend from 5,000 to over 9,800 feet (1,500-3,000 m) elevation [6]. In northeastern Nevada, rockspirea is an important component of big sagebrush communities in and just upland from riparian zones [57]. In Colorado it is generally rare east of the Front Range, but it is a characteristic component of mixed-shrub associations that occur in woody draws of the eastern foothills [85]. On plateaus east of Pike's Peak, rockspirea is a characteristic species of skunkbush sumac (Rhus trilobata)-Gambel oak foothill thickets within the plains grassland ecosystem [72]. In studies across Utah, rockspirea was a minor species in curlleaf mountain-mahogany (Cercocarpus ledifolius) communities [16]. In the Organ Mountains of New Mexico, it occurred in hairy mountain-mahogany/yucca-canyon sage (Cercocarpus breviflorus/Yucca spp.-Salvia ramosissima) communities, and it had low cover (2%) but high frequency (51%) in Gambel oak/snowberry (Symphoricarpos spp.) associations [18]. On the summit of Mt Livermore in western Texas, it is a component of a bald-hill formation of scrubby shrubs and sparse herbs. Just below the summit, rockspirea codominates on talus slopes with Gambel oak [34].

Vegetation classifications describing plant communities in which rockspirea is dominant are listed below.

• Rocky Mountain Douglas-fir/rockspirea scree forest associations of northern and central New Mexico [53]
• corkbark fir (Abies lasiocarpa var. arizonica)/rockspirea habitat type on the Gila National Forest; probably occurs elsewhere in Arizona and New Mexico [22]
• Rocky Mountain Douglas-fir/rockspirea scree habitat type on the Gila National Forest [22] and Rocky Mountain Douglas-fir/rockspirea scree forest associations of central Arizona [53]

• rockspirea phases of the white fir/Gambel oak/Rocky Mountain maple, white fir/Gambel oak, and Rocky Mountain Douglas-fir/Gambel oak habitat types on the Lincoln National Forest; these phases are especially common in the Sacramento Mountains [2]
• white fir/rockspirea scree habitat type in the San Mateo Mountains and on the Cibola National Forest [22]
• low-elevation interior ponderosa pine-Gambel oak/rockspirea/mountain muhly (Muhlenbergia montana) associations above the San Augustin Plains [66]

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

GENERAL BOTANICAL CHARACTERISTICS SEASONAL DEVELOPMENT REGENERATION PROCESSES SITE CHARACTERISTICS SUCCESSIONAL STATUS

Photo by Dave Powell, USDA Forest Service, Bugwood.org

Form and woody parts: Rockspirea is a deciduous [15,87] shrub from 1.6 to 20 feet (0.5-6.2 m) tall [15,39,89]. It is generally shorter than creambush oceanspray [75]. Its form is spreading [32,54]; mature plants may reach 5 to 10 feet (1.5-3 m) across [79]. Main branches arise from the root crown [79]. Terminal branches may be weakly spinescent [15]. Bark is shreddy [55]. The roots are dense and spreading [75,79]. Its roots reach at least 12 inches (30 cm) below ground [83].

Leaves and reproductive organs: The leaves occur mainly on spur branches; they range from 0.4 to 0.9 inch (1-2.3 cm) long and 0.2 to 0.5 inch (0.4-1.2 cm) wide [15,87]. Rockspirea leaves and inflorescences are smaller than those of creambush oceanspray [75]. Its inflorescence is a panicle or a raceme [15,40,90] from 2 to 8 inches (5-20 cm) long [87]. The flowers are small [32,90], about 2 mm across [55,87]. The fruit is an achene [15,19,54,89] from 1.4 to 2.2 mm long [15], bearing 1 seed [15,67].

Life span and physiology: Life span of rockspirea is reported as "moderate" [79,83]. Rockspirea is drought tolerant [79,83].

Vegetative regeneration: Rockspirea sprouts [83] from the root crown [8]. Its sprouting ability is not well documented [75]. Since creambush oceanspray and rockspirea are closely related (see Taxonomy) and sprouting is the primary method of regeneration for creambush oceanspray [56,78], sprouting it is likely rockspirea's primary method of regeneration as well.

Pollination and breeding system: Rockspirea flowers are perfect [73,89]. They are pollinated by insects [73].

Seed production: Kearney and others [40] describe rockspirea's flower production as "ample" [40].

Seed dispersal: Wind disperses rockspirea seeds [8,75].

Seed banking: Rockspirea probably maintains a soil seed bank [75], although this was not documented as of 2010. Creambush oceanspray establishes from soil-stored seed [81] occasionally; rockspirea likely establishes from seed as well.

Germination: Seed viability may be low in rockspirea. One study found seed soundness averaged 7% for rockspirea (King 1947 cited in [75]). Seeds are dormant and probably require overwinter stratification in the field. Stratification for 18 weeks at 41 °F (5 °C) broke rockspirea seed dormancy in the greenhouse [75]. Shaw and others [73,75] speculate that heat from fire may break dormancy of rockspirea seed, although this has not been documented.

Seedling establishment and plant growth: On the Wasatch Plateau in central Utah, Plummer [65] found that rockspirea established from planted seed spread as the artificial regeneration matured and produced its own seed. Rockspirea seedlings generally grow slowly [74].

Soils: Rockspirea is most common on medium-textured soils [79] but also grows in coarse soils. It prefers clays, clay loams [65], and loams [76] but is reported on sandy soils in Tsegi Canyon, northeastern Arizona [35]. On the Lincoln National Forest, rockspirea grows on alluvial deposits and on sideslopes with colluvial parent materials [2]. According to fact sheets, soils supporting rockspirea are neutral to alkaline [47,73], and rockspirea tolerates carbonate and low-fertility soils [83].

Parent materials: Rockspirea is common on soils of volcanic origin [47,60]. It grows in sandstone-derived soils in Zion National park, Utah [31]. Rockspirea frequently grows in rock and rock fragments [89]. It grows in rock crevices in Zion National Park [30]. In the Rio Grande Wild and Scenic River Recreation Area, it grows on rock outcrops and talus slopes [76]. On the Gila National Forest, corkbark fir/rockspirea and Rocky Mountain Douglas-fir/rockspirea habitat types occur in scree. White fir/rockspirea habitat types occur on scree in the San Mateo Mountains and on the Cibola National Forest [22].

Moisture: Rockspirea occupies regions that are generally drier than the habitats of creambush oceanspray [21]. However, it is most common on relatively mesic sites within desert and other arid ecosystems. Slopes supporting rockspirea are generally well drained (review by [79]).

Rockspirea's occurrence on relatively mesic sites is well documented. It was rare in an 1898 survey of the Red Desert of southern Wyoming, occurring only below permanent winter snowdrifts [63]. Rockspirea is dominant in interior ponderosa pine-Gambel oak communities above the San Augustin Plains of New Mexico, but it does not occur in lower-elevation Colorado pinyon-alligator juniper (Juniperus deppeana) associations. The author attributed this to higher soil moisture levels in the interior ponderosa pine association [66]. East of the Front Range of Colorado, rockspirea grows in woody draws that are more mesic than surrounding plains grasslands [85]. Engelmann spruce (Picea engelmannii)/Rocky Mountain maple habitat types of the Chiricahua Mountains, in which rockspirea is characteristic, occur on cold, moist to mesic slopes at high elevations [62]. The Rocky Mountain Douglas-fir/Rocky Mountain maple habitat type of south-central Arizona also occurs on cool, moist slopes [62].

Topography and aspect: Rockspirea is common in canyons and on rocky ledges, cliffs, plateaus, and escarpments [19,39,61,67,88,89]. In the Rio Grande Wild and Scenic River Recreation Area, it grows on very steep to vertical slopes [76]. Rockspirea frequently grows on cliffs in Arizona; it is especially common in the Grand Canyon [40]. It grows in canyon bottomlands of Canyon de Chelly National Monument, Arizona [29] and on canyon slopes in the Rio Grande Wild and Scenic River Recreation Area [76].

Rockspirea favors slopes that provide protection from extreme weather, with aspect often varying with elevation. In Colorado and New Mexico it occurs in blue spruce habitat types, which occur on slopes that are protected from extreme sun and wind [17]. In Zion National Park, rockspirea was more common in rock crevices receiving low amounts of direct sunlight than in crevices receiving moderate or high amounts of direct sunlight (x =2.3, 0.2, or 0.5 plants/m of crevice, respectively) [31]. It is most frequent on north-facing slopes at either low elevations or in its southernmost distribution. Aspect is generally southerly at high elevations [79]. In ponderosa pine-Douglas-fir/Gambel oak communities of the White Mountains, New Mexico, rockspirea occurs on north- and east-facing slopes [27]. On the Lincoln National Forest, the rockspirea phases of white fir/Rocky Mountain maple and Douglas-fir/Gambel oak habitat types are most common in cool drainages at low elevations and on ridges and knolls at high elevations. These phases occur mostly on north- and northwest-facing slopes but also on westerly slopes if the slopes are cool and wet [2]. Rockspirea is restricted to north-facing volcanic cliffs in the Sierra Juarez of Baja California Norte [90]. On Cerro la Parra, a volcanic mountain in the Sierra Juarez, rockspirea was rare and found only on north-facing slopes [60]. In hairy mountain-mahogany associations of the Organ Mountains, New Mexico, rockspirea occurs on west-facing slopes at intermediate elevations (6,700-7,600 feet (2,000-2,300 m)) and on south-facing slopes above 7,600 feet (2,300 m) [18]. On the Gila National Forest, a Rocky Mountain Douglas-fir/rockspirea habitat type occurs on southerly slopes at 9,600 feet (2,926 m) elevation, and a corkbark fir/rockspirea habitat type occurs on a south-facing, 54% slope at 9,900 feet (3,018 m) elevation. On the Gila National Forest, a corkbark fir/rockspirea habitat type occurs on a south-facing, 54% slope at 9,900 feet (3,018 m) elevation. In New Mexico, white fir/rockspirea habitat types of the San Mateo Mountains and the Cibola National Forest occur on south-facing, 50% to 60% slopes from 9,200 to 9,240 feet (2,804-2,816 m) elevation [22].

Elevation: Rockspirea is mostly restricted to middle and upper elevations in the Southwest but grows on relatively cool sites at low elevations (for example, [2,18]).

FIRE EFFECTS AND MANAGEMENT

FIRE EFFECTS FUELS AND FIRE REGIMES FIRE MANAGEMENT CONSIDERATIONS
	Rockspirea growing in a slowly regenerating mixed-conifer forest 25 years after the 1977 Mt Elden Wildfire. Viewed from the Sunset Trail on the Coconino NF, with Mt Elden in background. Photograph © Lee Dittmann; used with permission from www.nazflora.org.

Fire adaptations and plant response to fire:
Fire adaptations: Rockspirea sprouts from the root crown [8] and establishes from seed [25] after fire. Seed source origins (seed bank, lightly burned patches, or seed transported from off site) were not documented as of 2010. Shaw and others [73,75] speculate that heat from fire can stimulate germination, but experimental evidence of this was lacking as of 2010.

Plant response to fire: In a review, Bradley and others [8] noted that postfire regeneration is poorly documented for rockspirea, but that rockspirea establishes after fire by sprouting from the root crown and likely from off-site, wind-dispersed seed as well. Further research is needed on the fire ecology of rockspirea. Postfire responses are better documented for creambush oceanspray, to which rockspirea is closely related. Many aspects of the fire ecology of creambush oceanspray that are reviewed in FEIS are likely applicable to rockspirea as well.

Succession may proceed slowly in conifer/rockspirea communities of the Southwest. Rockspirea established from seed following the 8,000-acre (3,000 ha) Saddle Mountain Fire on the Kaibab National Forest, Arizona. It showed 0.03% cover and 0.01% frequency in postfire year 45. Rockspirea established primarily in severely burned areas; the author suggested the seed was transported from parent plants on unburned or lightly burned areas [25].

In the White Mountains of New Mexico, rockspirea was present in Gambel oak-ponderosa pine and Gambel oak-Douglas-fir communities in postfire years 21 and 27, respectively. Its importance value was higher in Gambel oak-ponderosa pine than in Gambel oak-Douglas-fir communities. Both sites were on north aspects [27].

• Fuels
• Fire regimes

Alexander and others [2] found that the rockspirea phase of white fir/Gambel oak habitat types on the Lincoln National Forest generally had a well-developed litter layer. In west-central New Mexico, rockspirea abundance was low in an interior ponderosa pine-Gambel oak/rockspirea/mountain muhly community. Stand structure was open, with a poorly developed understory and ground layer. Other common understory species provided <2% total cover; herbaceous plants had ≤24% total cover [66].

Differences in shrub biomass between cattle-grazed and ungrazed plots were not significant in a riparian quaking aspen/willow (Salix spp.)/currant (Ribes spp.)-western snowberry community in northeastern Nevada. Rockspirea was an important component of the shrub layer. Biomass of grazed and ungrazed shrub understories is shown below. The authors also provide biomass measures for overstory, willow, and herbaceous components of the community [12].

Fire regimes: The coniferous and hardwood communities in which rockspirea occurs historically experienced mostly frequent, low- to mixed-severity fires. Fire-return intervals tend to lengthen from dry, low-elevation sites to cool, high-elevation sites [80]—where rockspirea is most common (see Site Characteristics)—but this trend may be weak. In fire studies across Arizona and New Mexico, Swetnam and others [80] found a wide range of fire frequencies within and among coniferous forests. Generally, southwestern ponderosa pine communities experienced fire at 2- to 10-year intervals, while higher-elevation, mixed-conifer communities experienced fire at 5- to 15-year intervals [80]. Southwestern shrubland ecosystems usually experience fire at <100-year intervals. Mountain shrub ecosystems tend to have shorter average fire-return intervals (20-50 years) [49] than Arizona chaparral (50-100 years) [48].

In the Rincon Mountain Wilderness of Arizona, Baisan and Swetnam [4] found that mixed-conifer forests of Rocky Mountain Douglas-fir-white fir and southwestern white pine-interior ponderosa pine had a history mostly of large (>500 acres (200 ha)) surface fires that occurred from May to July. The mean fire-return interval from 1748 to 1886 was 9.9 years, with a range of 3 to 19 years. Since fire exclusion, fires have become more infrequent and severe [4,10].

DeVelice and others [17] report "heavy disturbance" by fire and grazing is widespread in blue spruce/sprucefir fleabane habitat types of the San Juan and Sangre de Cristo mountains.

Jones [37] reports that fires were historically uncommon in the rockspirea phase of white fir/Gambel oak habitat types on the Lincoln National Forest. Conditions in these forests are generally wetter than other mixed-conifer types, and fires are mostly of low or mixed severity [37].

See the Fire Regime Table and FEIS reviews of interior ponderosa pine, Arizona pine, Rocky Mountain Douglas-fir, Great Basin bristlecone pine, Rocky Mountain bristlecone pine, white fir, and corkbark fir for further information on fire regimes of vegetation communities in which rockspirea may occur. 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".

MANAGEMENT CONSIDERATIONS

• FEDERAL LEGAL STATUS
• OTHER STATUS
• IMPORTANCE TO WILDLIFE AND LIVESTOCK
• VALUE FOR REHABILITATION OF DISTURBED SITES
• OTHER USES
• OTHER MANAGEMENT CONSIDERATIONS

Smaller mammals also eat rockspirea. Lagomorphs browse it (reviews by [74,75]). Rockspirea clippings were found in bushy-tailed woodrat middens in Gunnsion County, Colorado [24]. Rockspirea has also been collected in ancient woodrat middens [36].

Plant communities where rockspirea is common to dominant provide habitat for a variety of wildlife species. In the Rio Grande Wild and Scenic River Recreation Area, interior ponderosa pine/big sagebrush-broom snakeweed-rockspirea woodlands provide breeding habitat for at least 26 passerine bird species. Total passerine population density on study grids in these woodlands was 168 breeding pairs/40 ha [76]. Big sagebrush communities in and near riparian zones near Wells, Nevada, provide habitat for small mammals. Rockspirea is an important component of this vegetation [57]. Conifer/rockspirea scree habitat types of Arizona and New Mexico also provide habitat for small mammals [22,53]. Mixed-conifer/mixed-shrub forests of the Sacramento Mountains, in which rockspirea is important to dominant, provide habitat for the Sacramento Mountain salamander [71], a federally listed Species of Concern [84].

Palatability and/or nutritional value: Although common and browsed frequently on some sites, rockspirea is not as palatable as many associated browse species ([21,73,74], review by [75]). Ungulates may make little use of rockspirea if more palatable shrubs are available [21,73].

Cover value: No information is available on this topic.

Rockspirea is propagated from seeds [47,83,83,87], layering [87] or cuttings [47,83,87]. On the Wasatch Plateau of central Utah, Plummer [65] found rockspirea established and spread from planted seed. In relation to 19 other woody species, he rated its ability to establish as "medium" and its growth rate and ability to spread from seed as "good". Planting sites were ≥9,500 feet (2,900 m) in elevation [65].

As of 2010, restoration use of rockspirea was hindered by lack of commercially available seed [73,75,79,83]. Shaw and others [74] provide information on propagating rockspirea from cuttings or seed collected locally.

Information on the traditional uses of rockspirea is scant. Native Americans of the Great Basin ate the seeds, and pioneers made nails from the wood [73,74]. The Navajo used a decoction of the leaves to treat influenza [86]. The Tewa ate the fruits [87].

APPENDIX: FIRE REGIME TABLE

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