Symphoricarpos occidentalis



INTRODUCTORY


  Photo courtesy of the Wisconsin State Herbarium and Kitty Kohout.
AUTHORSHIP AND CITATION:
Hauser, A. Scott. 2007. Symphoricarpos occidentalis. 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:
SYMOCC

NRCS PLANT CODE [156]:
SYOC

COMMON NAMES:
western snowberry
western wolfberry
wolfberry
buckbrush

TAXONOMY:
The scientific name of western snowberry is Symphoricarpos occidentalis Hook. (Caprifoliaceae) [23,35,56,58,60,78,84,90,100,161]. There are no western snowberry varieties or subspecies.

SYNONYMS:
None

LIFE FORM:
Shrub

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
Information on state-level protected status of plants in the United States is available at Plants Database.

DISTRIBUTION AND OCCURRENCE

SPECIES: Symphoricarpos occidentalis
GENERAL DISTRIBUTION:
Western snowberry occurs from Northwest Territories, Canada, throughout most of the southern Canadian provinces and northern United States, south to Texas, but excluding most of the southeastern and southwestern states [23,35,56,58,60,78,84,90,100,161]. Plants Database  provides a distributional map of western snowberry.

HABITAT TYPES AND PLANT COMMUNITIES:
Western snowberry is described as a dominant species in the following vegetation classifications and locations.

Idaho:

Iowa: Montana: Nebraska: North Dakota: South Dakota: Wyoming: Great Basin: Great Plains: Alberta: Manitoba: Saskatchewan:

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Symphoricarpos occidentalis
GENERAL BOTANICAL CHARACTERISTICS:
This description provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available (e.g., [23,56,60,71,78,79,100,144,147,159,167]).

Western snowberry is a stiffly erect and freely branching shrub [35,79,144] that grows from 1 to 5 feet (0.3-1.5 m) tall [23,35,60,71,78,79,100,144,167] and commonly forms dense, low thickets [79,144]. When young, the branches are minutely hairy [60,71,100,167]. As shrubs mature, bark forms on the branches that becomes shreddy with age [144,147,159]. Leaves are deciduous, 0.8 to 3 inches (2-8 cm) long, and 0.6 to 2.2 inches (1-5.5 cm) wide [23,60,71,79,144,147,159,166,167]. Juvenile shoots sometimes produce larger leaves that are 4 inches (10 cm) long and 3 inches (8 cm) wide [60]. Flowers, born in racemes [35,79,167], occur in dense clusters of 2 to 10 at the end of branches and in the axils of leaves [60,71,100,117,144,165,166]. The fruits of western snowberry occur in crowded clusters and are berrylike drupes that each contain 2 nutlets [117,144]. Fruits are 6 to 9 millimeters in diameter, approximately 2.5 to 3.5 millimeters long, and 1.5 to 2.5 millimeters wide [35,60,71,79]

Colonies: Western snowberry forms dense colonies along ditches, streams, and floodplains; and in moist, open, grassy swales on mesas and plains [35,56,58,60,71,159,165,166,167]. Colonies range from 3 to 700 feet (1-200 m) or greater in diameter [25,83,117,122].

Rhizomes: Pelton [117] provides a detailed description of western snowberry rhizomes in 2 colonies in Minnesota. Western snowberry rhizomes tend to be very long and sparsely branched, and typically grow to a depth of 14 inches (35 cm). A rhizome from a 4-year-old plant at the periphery of a western snowberry colony measured 30 inches (80 cm) long, and roots from the rhizomes extended 5.09 feet (1.55 m) belowground. New sprouts from rhizomes develop in spring at approximately the same time shoots develop on older stems. In the first year of growth, new sprouts commonly attain the same height of mature stems and sometimes produce "abundant" fruit. Rhizome sprouts are generally reproductively mature for several years before the rhizome connection with the parent plant severs or decays. Rhizomes in the interior of one colony were approximately 20 years old [117].

RAUNKIAER [123] LIFE FORM:
Phanerophyte

REGENERATION PROCESSES:
Western snowberry primarily reproduces by rhizomes [1,35,60,79,83,117,122,147,151,152], but can also reproduce by seeds [1,24,25,122,151,159,164].

Pollination: Western snowberry is generally insect-pollinated [59,117]. However, self-pollination may take place when pollen falls on stigmas from horizontal or pendulous flowers [59].

Breeding system: Western snowberry has perfect flowers [144,147].

Seed production: There is little information on seed production of western snowberry. Near Minneapolis, Minnesota, mean fruit production of western snowberry increased with size and age [117].

Mean number of western snowberry fruits/stem in relation to stem height, diameter, and age [117]
Measurement Size or age class Total # of stems Mean # of fruits
Height (cm) 0-24 7 0
25-49 58 0
50-74 110 5.5
75-99 117 18.8
100-124 120 35.3
125 + 88 104.6
Diameter (cm) 0-0.19 13 0
0.20-0.39 139 2.1
0.40-0.59 174 15.3
0.60-0.79 102 53.3
0.80-0.99 43 142.4
1.0 + 21 174.3
Age (years) 1 114 4.1
2 116 19.9
3 45 22.2
4 67 26.9
5 114 62.5
6 + 37 75.3

Seed dispersal: Western snowberry seeds are dispersed primarily by small mammals and birds [103,117,149], though wind and water may play a small part in their dispersal. In a feeding trial, 10.7% of 150 western snowberry nutlets passed through the digestive tract of domestic chickens intact and viable. Western snowberry nutlets will float in water for approximately 48 hours before sinking [117].

Seed banking: Little information is available on western snowberry seed banking. Pelton [117] claims that western snowberry utilizes a seed bank "limitedly". The fruit of western snowberry can remain on the plant for a year or more [117].

Germination: Western snowberry has embryo dormancy, requiring an afterripening period for adequate germination [117]. Warm stratification at room temperature for 3 to 4 months followed by cold stratification at 41 F (5 C) for 4 to 6 months increases germination [72,117]. Pelton [117] notes that western snowberry seeds likely require more than 1 summer and winter in the soil to break dormancy.

Western snowberry seeds appear to favor cool season germination. Western snowberry seed germination rates under constant and alternating temperatures are presented below. In the alternating temperature experiment, the western snowberry seeds were exposed to the high temperature for 8 out of each 24 hours.

Percent germination of western snowberry seeds under alternating and constant temperatures [117]

Alternating temperatures (C) -5/5 -5/10 5/10 5/15 5/20 10/15 10/20 10/25 15/20 15/25
Germination (%) 0 0 45.2 45.7 35.3 45.8 37.0 29.4 22.3 20.1
Constant temperatures (C) 5 10 15 20 25
Germination (%) 35.5 44.1 40.1 18.7 5.9

Seedling establishment/growth: Western snowberry rarely establishes by seedlings [24,117,122]. In Minnesota, western snowberry seedlings growing in "poor" soil reached a height of 4 inches (9 cm) by the end of the first growing season. During the same time period, seedlings grown in "rich" potting loam reached a height of 18 inches (45 cm). While the seedlings in the potting loam grew "vigorously", they did not produce rhizomes or flowers during the first growing season [117]. In a review by Moles and Westoby [106], the cause of western snowberry seedling mortality during 1 growing season in a grazed pasture in Minnesota was discussed. Major mortality agents included fungal attack (18.9%), herbivory (32.8%), and drought (29.9%).

Vegetative regeneration: Western snowberry regenerates vegetatively by rhizomes [1,35,60,79,147,151,159]. It can be propagated by stem and root cuttings [159] and will sprout following mowing or cutting [164]. Research on other sprouting species indicates that development of new shoots on shrubs is controlled by apical dominance. The death of apical buds removes the hormonal control of lateral buds on rhizomes [6].

SITE CHARACTERISTICS:
Western snowberry is commonly found in riparian areas such as alluvial floodplain terraces, upland ravines, swale-like depressions, and along streams and rivers [35,41,42,43,71,78,79,167]. It is also common in open deciduous woods, open prairies, rocky bluffs, pastures, and along roadsides and railway embankments [41,42,43,60,71,73,78,79,144,147,159].

Climate: Western snowberry occurs in continental-type climates characterized by extreme temperature ranges and light to moderate precipitation [32,117]. Western snowberry is adapted to survive moderate drought conditions [163,164].

Extensive climatic data are available for the aspen parklands of central Canada [18] and the prairie province mixed grasslands [31,32,34] where western snowberry is common.

Elevation: The elevational range of western snowberry by state or province is presented below.

Elevation range of western snowberry
State/province Elevation (feet)
Colorado 3,500-8,500 [71,134]
Montana 1,950-4,000 [70]
New Mexico 5,000-8,500 [100]
North Dakota 800-1,800 [174]
South Dakota 4,125-7,000 [21,115]
Utah 1,525-7,000 [58,167]
Wyoming 7,525-9,900 [48]
Alberta 2,000-4,685 [4,169]

Grasslands: Western snowberry is a common shrub component in mixed-grass prairies. In a mixed-grass prairie in The Gap Community Pasture near Regina, Saskatchewan, density of western snowberry was significantly (P<0.05) lower in plots with "low" water availability than in plots with "normal" to "high" water availability [88].

Invasive species: In Theodore Roosevelt National Park, the effect of leafy spurge on species richness was estimated in floodplain communities where western snowberry is an indicator species. Species richness was 19% lower in infested sites than in noninfested sites [29].

Soil: Western snowberry occurs on most soil textures except for loose sands [63]. On floodplains where it occurs, alluvial soils are generally fine textured, composed primarily of silt with moderate quantities of clay and fine sand [63]. It may also occur on infertile sand or rocky substrates, rich loams, or compact clays [117,126,164]. It can tolerate "imperfectly" drained soils and considerable flooding but is intolerant of prolonged flooding or permanent high water tables. Western snowberry is common on mildly alkaline to slightly acidic soils [22,67,164].

Detailed analyses of soils where western snowberry occurs in Minnesota [117], eastern North Dakota [124], wooded draws of the southern Great Plains [160], and southwestern North Dakota [55] are available.

Topography: In the more humid parts of its range, western snowberry occurs on drier topographic sites such as exposed bluffs, open hillsides, and south and west facing slopes. In drier areas, western snowberry is most commonly found on moister sites such as depressions, ravines, the shores of lakes and sloughs, along stream banks and floodplains, at the base of steep slopes susceptible to runoff, and on north or east facing slopes [117].

SUCCESSIONAL STATUS:
Western snowberry occurs in climax communities [25,101] but is generally found in seral communities on immature soils and in the transition zones between grasslands and forests [117]. Western snowberry is most commonly found where full or nearly full sunlight is available. However, it is also frequently found at forest borders where it can survive under partial to dense shade [67,117].

Disturbed sites: Western snowberry thrives following disturbances such as fire [57,109,119], logging [15], animal activity [18,150], and various other soil disturbances [144,161]. On alluvial floodplains in northwestern Montana, the western snowberry community type generally represents a disturbance-induced seral stage of the interior ponderosa pine/red-osier dogwood (Cornus sericea) and/or Rocky Mountain Douglas-fir/red-osier dogwood habitat types [22].

Grazing: Western snowberry sometimes occurs in communities characterized as a moderately disturbed secondary successional stage following grazing and/or browsing [63]. On low-elevation riparian and wetland sites in central and eastern Montana, prolonged browsing of eastern cottonwood/red-osier dogwood communities leads to the disturbance-induced eastern cottonwood/western snowberry community-type [65]. In eastern Idaho, continued grazing or browsing pressure in narrowleaf cottonwood/red-osier dogwood and black cottonwood/red-osier dogwood communities leads to a grazing disclimax narrowleaf cottonwood/western snowberry community and black cottonwood/red-osier dogwood community. If grazing or browsing is heavy enough, all shrubs will be eliminated, leaving an herbaceous understory dominated by Kentucky bluegrass (Poa pratensis), timothy (Phleum pratense), smooth brome (Bromus inermis), and variety of "weedy" forbs [63].

Grasslands: When western snowberry spreads onto grasslands, it reduces forage production [25]. Pelton [117] states that western snowberry's most important successional role is that it can successfully invade grasslands to the point where it shades out grasses, thereby facilitating the invasion of trees. In Canada, the invading tree is quaking aspen (Populus tremuloides), while in Iowa and Nebraska it is primarily bur oak.

SEASONAL DEVELOPMENT:
Flowering dates for western snowberry are presented below.

Western snowberry flowering periods in the United States and Canada
Illinois June-August [105]
Minnesota June-September [117]
Nebraska June-July [152]
New Mexico May-August [100,159]
Oklahoma May-July [159]
South Dakota June-July [163]
Texas May-July [159]
Great Plains June-August [60,151]
Intermountain West June-August [35]
North-central Plains June-August [147]
Northeastern United States and adjacent Canada June-August [56]
Pacific Northwest June-August [79]
Uinta Basin, Utah May-July [58]
Ontario July-August [144]

The fruiting period of western snowberry across its range is generally from August through October [144,147,159,163].

From 1979 to 1984 first-flowering dates and flowering periods for western snowberry were observed and reported in a mixed-grass prairie near Woodworth, Stutsman County, North Dakota. Flowering dates and periods for western snowberry are presented below [30].

First-flowering dates and periods for western snowberry [30]
Earliest first bloom Latest first bloom Median date of first 10 plants with flowers Median date of full flowering Median date when flowering 95% complete Length of flowering period
13 May 1980 10 July 1979 25 June 6 July 28 July 33 days

The phenological development of western snowberry in a prairie habitat northwest of Lincoln, Nebraska was observed by McMillan and Pagel [102] in 1956 and 1957.

Phenological development of western snowberry during 1956 and 1957 [102]
Observation year Leaf bud opening Initial anthesis
1956 26 March-21 April 16 June-22 July
1957 13 April-21 April 23 June-22 July

FIRE ECOLOGY

SPECIES: Symphoricarpos occidentalis
FIRE ECOLOGY OR ADAPTATIONS:
Fire adaptations: Western snowberry is fire-tolerant [63,67,70] and sprouts after fire [6,27,53,57,63,140,141,142,145]. While the stems of western snowberry are sensitive to fire, the rhizomes and stem bases can survive fire due to their depth in the soil (0.8-14 inches (2-35 cm)) [7,117].

Fire regimes: There is little information directly relating to western snowberry fire regimes. Western snowberry may occur where the fire-return interval is as short as 1 year and as long as 500 years.

Northern Great Plains/Mixed-grass prairie: Fire has played an important role in northern Great Plains mixed-grass prairies, where western snowberry occurs. The historically large tracts of continuous mixed-grass prairie, which occur in hot, dry areas, accumulated much fine fuel and were susceptible to frequent lightning fires. Early records kept by explorers, trappers, and settlers noted a high occurrence of fires, both natural and anthropogenic [140], with frequent low-severity fires occurring at intervals of 5 to 10 years [37,116,173]. In a review by Sieg [140], the fire-return interval for level to rolling topography in the northern Great Plains is 5 to 10 years. On more dissected topography, such as breaks and rivers, the fire-return interval ranges from 20 to 30 years. In mixed-grass prairies of Badlands National Park, South Dakota, frequent low-intensity surface fires occurred at frequencies of 1 to 25 years [37]. Since the early 1900s, fire has been excluded and nonnative species, including Japanese brome (Bromus japonicus), smooth brome, Kentucky bluegrass, crested wheatgrass (Agropyron cristatum), and Canada thistle (Cirsium arvense), are widely established in the area [37]. Fire exclusion has also allowed the encroachment of western snowberry into grasslands of the northern Great Plains [114,117].

Western snowberry-dominant communities: Fire has played an active role in shaping the interior ponderosa pine/western snowberry and Rocky Mountain Douglas-fir/western snowberry communities of the Little Rocky Mountains [131] and the Rocky Mountain Douglas-fir/western snowberry communities of the Bear's Paw Mountains [130]. In a review by Fischer and Clayton [49], it is suggested that the fire frequency of interior ponderosa pine communities with a shrub understory is "considerably" less than 50 years, and that of Rocky Mountain Douglas-fir ranges from 5 to 20 or more years. Long-term exclusion of surface fires has altered Rocky Mountain Douglas-fir sites, creating more flammable conditions. On Bureau of Land Management lands in southern and eastern Idaho, narrowleaf cottonwood/western snowberry and black cottonwood/western snowberry communities typically burn during the late summer and fall [63].

The following table provides fire regime information on vegetation communities in which western snowberry may occur:

Fire regime information on vegetation communities in which western snowberry may occur. For each community, fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Models [92]. These vegetation models were developed by local experts using available literature, local data, and/or expert opinion as documented in the .pdf file linked from the name of each Potential Natural Vegetation Group listed below. Cells are blank where information is not available in the Rapid Assessment Vegetation Model.
Pacific Northwest Great Basin Northern Rockies
Northern Great Plains
 
Pacific Northwest
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Northwest Grassland
Bluebunch wheatgrass Replacement 47% 18 5 20
Mixed 53% 16 5 20
Idaho fescue grasslands Replacement 76% 40    
Mixed 24% 125    
Northwest Woodland
Ponderosa pine Replacement 5% 200    
Mixed 17% 60    
Surface or low 78% 13    
Northwest Forested
Ponderosa pine (xeric) Replacement 37% 130    
Mixed 48% 100    
Surface or low 16% 300    
Dry ponderosa pine (mesic) Replacement 5% 125    
Mixed 13% 50    
Surface or low 82% 8    
Great Basin
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Great Basin Grassland
Great Basin grassland Replacement 33% 75 40 110
Mixed 67% 37 20 54
Mountain meadow (mesic to dry) Replacement 66% 31 15 45
Mixed 34% 59 30 90
Great Basin Shrubland
Mountain shrubland with trees Replacement 22% 105 100 200
Mixed 78% 29 25 100
Great Basin Woodland
Ponderosa pine Replacement 5% 200    
Mixed 17% 60    
Surface or low 78% 13    
Great Basin Forested
Interior ponderosa pine Replacement 5% 161   800
Mixed 10% 80 50 80
Surface or low 86% 9 8 10
Ponderosa pine-Douglas-fir Replacement 10% 250   >1,000
Mixed 51% 50 50 130
Surface or low 39% 65 15  
Aspen with conifer (low to midelevation) Replacement 53% 61 20  
Mixed 24% 137 10  
Surface or low 23% 143 10  
Douglas-fir (warm mesic interior) Replacement 28% 170 80 400
Mixed 72% 65 50 250
Stable aspen-cottonwood, no conifers Replacement 31% 96 50 300
Surface or low 69% 44 20 60
Stable aspen without conifers Replacement 81% 150 50 300
Surface or low 19% 650 600 >1,000
Northern Rockies
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Northern Rockies Grassland
Northern prairie grassland Replacement 55% 22 2 40
Mixed 45% 27 10 50
Northern Rockies Shrubland
Riparian (Wyoming)
Mixed 100% 100 25 500
Mountain shrub, nonsagebrush Replacement 80% 100 20 150
Mixed 20% 400    
Northern Rockies Forested
Ponderosa pine (Northern Great Plains) Replacement 5% 300    
Mixed 20% 75    
Surface or low 75% 20 10 40
Ponderosa pine (Northern and Central Rockies) Replacement 4% 300 100 >1,000
Mixed 19% 60 50 200
Surface or low 77% 15 3 30
Ponderosa pine (Black Hills, low elevation) Replacement 7% 300 200 400
Mixed 21% 100 50 400
Surface or low 71% 30 5 50
Ponderosa pine (Black Hills, high elevation) Replacement 12% 300    
Mixed 18% 200    
Surface or low 71% 50    
Ponderosa pine-Douglas-fir Replacement 10% 250   >1,000
Mixed 51% 50 50 130
Surface or low 39% 65 15  
Douglas-fir (xeric interior) Replacement 12% 165 100 300
Mixed 19% 100 30 100
Surface or low 69% 28 15 40
Douglas-fir (warm mesic interior) Replacement 28% 170 80 400
Mixed 72% 65 50 250
Douglas-fir (cold) Replacement 31% 145 75 250
Mixed 69% 65 35 150
Northern Great Plains
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval
(years)
Minimum interval
(years)
Maximum interval
(years)
Northern mixed-grass prairie Replacement 67% 15 8 25
Mixed 33% 30 15 35
Northern Plains Woodland
Northern Great Plains wooded draws and ravines Replacement 38% 45 30 100
Mixed 18% 94    
Surface or low 43% 40 10  
Great Plains floodplain Replacement 100% 500    
*Fire Severities:
Replacement=Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed=Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects.
Surface or low=Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area [64,91].

POSTFIRE REGENERATION STRATEGY [148]:
Rhizomatous shrub, rhizome in soil
Ground residual colonizer (on-site, initial community)


FIRE EFFECTS

SPECIES: Symphoricarpos occidentalis
IMMEDIATE FIRE EFFECT ON PLANT:
Western snowberry is typically top-killed by fire [117]. While the stems of western snowberry are sensitive to fire, the rhizomes and stem bases can usually survive fire due to their depth in the soil (0.8-14 inches (2-35 cm)) [7,117].

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
No additional information is available on this topic.

PLANT RESPONSE TO FIRE:
Western snowberry sprouts from rhizomes or the stem base after top-kill from fire [6,27,53,57,63,140,141,142,145]. Postfire sprouting can begin within 2 weeks following fire [74]. While western snowberry may establish from seeds after fire, no mention of this is found in the literature. The fire studies discussed below present mixed results concerning western snowberry's response to fire.

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Repeated burning: While several sources claim that spring burning increases western snowberry cover [49,157,172], a long-term study in the aspen parklands of Alberta [3,4] and a shorter duration study in Minnesota [14] found that annual spring burning either caused a decrease or fluctuation in cover, a decrease in density, and a reduction in height.

Annual early spring burning significantly (P<0.005) reduced western snowberry cover and density in east-central Alberta [3,4]. Prescribed burning took place for at least 24 years in an aspen parkland composed of a mosaic of quaking aspen groves and grasslands dominated by rough fescue and shortbristle needle-and-thread. Before and after burning, western snowberry had the greatest stem density and cover of any shrub on the site. Burns were conducted in April when soil moisture was normally high. Frequency and cover measurements were obtained in July and August of the same year. Frequency and canopy cover of western snowberry were analyzed on sites which had been burned annually and on sites where burning had not occurred during the study period. Western snowberry frequency and canopy cover were 56% and 31%, respectively, on unburned sites and 52% and 2%, respectively, on burned sites. Western snowberry density was 25.0 stems/m on unburned sites and 17.8 stems/m on burned sites [3,4].

Five years of annual, low-severity spring burning of western snowberry caused fluctuation in percent cover and reduction in shrub height at Pipestone National Monument in southwestern Minnesota [14]. Burning took place from mid- to late April, except for 1987 when burning was conducted in early May. At the time of burning in 1987, western snowberry had considerably more foliage than at the time of burning in other years, which may account for the reduced cover during the summer of 1987. The researchers note that average western snowberry height was reduced from 3 feet (1 m) to 1.5 feet (0.5 m) due to burning. While not clear, height measurements were likely taken in summer 1987. Thus, the reduction in height of western snowberry is probably a short-term effect of annual burning [14].

Pre- and postburn western snowberry cover during 5 years of annual spring burning [14]
Season of measurement 1983 1984 1985 1987
Spring (Preburn) 3.7 6.3 9.5 N.D.*
Summer (Postburn) 10.0 9.6 N.D. 5.2
*N.D.=No data

On the Lostwood National Wildlife Refuge, western snowberry height and canopy cover was reduced by late growing season, alternate year prescribed burning. Burning was conducted either during full western snowberry leaf maturity when root reserves are lowest, or late in the growing season when it is too late for regrowth to replenish root reserves, thus producing winterkill. Following 3 burns over 6 years, average height of live woody stems had been reduced by about 60% and maximum height and canopy cover reduced by 55%. However, postfire sprouting had increased the number of live woody stems by 30% [143].

Prior to 1975, Willa Cather Prairie, a mixed-grass prairie in Nebraska, had been moderately grazed for an unknown number of years. Between 1975 and 1992, The Nature Conservancy greatly reduced grazing on the prairie and conducted 9 burns. Western snowberry cover increased from an average of 0.27% in 1975 to 3.42% in 1992 on all sites (lowland, limy upland, and silty upland) combined [112].

Single burns: Abundance of western snowberry typically increases in the short-term (3 months to 2 years) after a single fire. Effects of a single fire on canopy cover and height are more variable, as illustrated by the following studies.

A single, high-intensity burn in a plains cottonwood forest community in Dinosaur Provincial Park, British Columbia, significantly (P<0.05) reduced western snowberry cover. The fire occurred on 15 August 1989 and postfire measurements were taken in August 1990. Western snowberry cover on unburned sites was 46.33% and 8.8% on burned sites [110].

Following a single burn near Minneapolis in mid-April, all western snowberry plants on the site were top-killed. By fall of the same year, new shoots averaged just half the height and diameter of stems on unburned sites, but stems density was 2.5 times greater on burned versus unburned sites. During the second year, stems on the burned area had reached 75% the height of stems on unburned sites. Stem density on burned sites was lower than in postfire year 1 but was still appreciably higher than on the unburned site [117].

A single spring fire caused little change in western snowberry cover and frequency either 3 months or 2 years after fire, but caused a significant (P<0.01 and P<0.05) increase in stem density [6]. Burn plots were established in a western snowberry community located at the University of Alberta Ranch. The western snowberry community is part of a larger rough fescue grassland. Two prescription fires were conducted on separate plots; one in May 1970 and the other in May 1971. Western snowberry cover, frequency, and stem density were measured 1 and 2 years following the 1970 burn, and 3 months following the 1971 burn. Measurements on burned and unburned sites for both the 1970 and 1971 fires were taken during August. Western snowberry began sprouting 2 weeks after the prescribed fire was conducted. The increase in stem density on both the 1970 and 1971 burned sites is attributable the destruction of western snowberry apical buds by fire. The removal of apical dominance likely accounted for the increased number of woody stems following burning [6].

Cover, frequency, and density of western snowberry on unburned and burned sites following a single burn [6]

Burn date May 1971 May 1970
Sample date August 1971
(3 months after fire)
August 1970
(3 months after fire)
August 1971
(1 year after fire)
August 1972
(2 years after fire)
Treatment Burned Unburned Burned Unburned Burned Unburned Burned Unburned
Frequency (%) 99 100 100 100 100 100 100 100
Cover (%) 87 78 95 95 90 90 89 89
Density (stems/m) 102 22 236 86 199 65 170 66

Fall and spring low-severity prescribed fires caused little overall change in western snowberry cover and height, but an increase in number of individuals and crown width in Wind Cave National Park, South Dakota [20]. Fires were conducted at two separate sites on 17 October 1979 and 14 April 1980. Due to the similarity in results of fire effects on vegetation, data from both fires were combined. Data collection occurred in June of 1979 (preburn), 1980, and 1981 [20].

Fire effects on western snowberry following 2 fires [20]
Measurement Treatment June 1979 (preburn) June 1980 June 1981
Cover (%) Burn 0.8 0.3 0.4
Control 0.6 0.5 0.3
# of individuals Burn 1,226 1,305 1,120
Control 466 497 418
Mean height (cmSD) Burn 24.911.8* 17.39.0 18.48.0
Control 20.510.1 17.59.3 18.810.0
Mean maximum crown width (cmSD) Burn 16.59.3 10.56.3 13.79.1
Control 16.09.9 15.58.8* 15.28.8
*Significantly (P<0.05) greater than other treatment within year

Western snowberry cover decreased the first year after a fire in central Alberta (26 May 1968). In the months preceding the fire, temperatures were 10 F (6 C) above average in February and March and precipitation was 56% of normal in April and May. The summer before the fire, western snowberry cover was 3.9%; 15 months after fire, it was 1.7% [85].

Western snowberry density changed little during the 1st and 2nd growing seasons following a single, spring (17 April) prescribed fire in four bur oak woodlands in the Black Hills of South Dakota. Western snowberry density on burned versus unburned plots, respectively, was 13.02.3 and 11.80.4 shrubs/m (SE) the first postfire season; and 13.31.7 and 12.71.7 shrubs/m (SE) the second postfire growing season [141].

Season of burning: Increases in density of western snowberry tend to be greatest after summer fires, and more variable on fall- and spring-burned sites. Western snowberry biomass growth tends to be greater on unburned sites than either spring- or fall-burned sites for several years following fire as illustrated in the research below.

Western snowberry density was highest on sites burned in summer, lowest on spring-burned sites and intermediate on fall-burned and control sites on the Kernan Prairie near Saskatoon, Saskatchewan. Prescribed fires were conducted during the spring (1998 May 6), summer (1998 June 26), and fall (1998 October 8). The area had been previously burned in 1991. At the end of the second growing season following burning, western snowberry stem density/m was measured on an unburned control site and the spring, summer, and fall burn sites. Western snowberry stem densities were 37.3, 28.7, 42.3, and 35.7, respectively [9]. For a detailed summary of this study, see the Research Project Summary Seasonal fires in Saskatchewan rough fescue prairie.

Another study on Kernan Prairie showed similar results on fall-burned plots, while spring-burned plots had higher stem densities than control plots  [132]. Burns were conducted in mid-October after western snowberry leaves had abscised, and in late April to early May before growth had begun. While stem density was greater on burned than unburned sites, the only significant (P<0.05) difference occurred between unburned and spring burned sites in postfire years 2 and 3.

Western snowberry stem density (live stems/m) on unburned and fall and spring burned sites [132]
Growing season Unburned Fall Spring
Preburn 36 39 38
Postfire year 1 39 72 122
Postfire year 2 43 67 111
Postfire year 3 46 62 95
Postfire year 4 46 57 51

Western snowberry biomass characteristics (total leaf area, new growth, old growth, and total biomass) during the first 3 growing seasons following the burns were generally greater on unburned than burned sites, except for new growth during the first postfire growing season. Total leaf area was significantly (P<0.05) greater on unburned sites than on spring burned sites in the second postfire growing season. New growth was significantly greater on unburned sites than on spring and fall burned sites in the second growing season. Old growth and total biomass were significantly greater on unburned than spring and fall burned sites during all 3 postfire growing seasons [132].

Western snowberry individual stem biomass characteristics on unburned and fall and spring burned sites during 3 postfire growing seasons [132]
Growth parameter Unburned Fall Spring

1st postfire growing season

Total leaf area (cm) 183 156 128
New growth (g) 0.7 1.4 1.2
Old growth (g) 6.1* 0.0 0.0
Total biomass (g) 8.8 3.1 2.5
2nd postfire growing season
Total leaf area (cm) 223* 133 102
New growth (g) 1.1* 0.6 0.5
Old growth (g) 6.2* 1.3 1.3
Total biomass (g) 10.1 3.4 3.0
3rd postfire growing season
Total leaf area (cm) 275 139 108
New growth (g) 1.7 0.4 0.4
Old growth (g) 7.7* 2.1 2.2
Total biomass (g) 13.2 4.0 3.9
*Significantly (P<0.05) greater on unburned than fall or spring burned sites

FIRE MANAGEMENT CONSIDERATIONS:
Fire behavior and fuel characteristics: To assess the maximum fire temperatures reached in western snowberry communities above and below ground, prescribed fires were conducted in late April and early May near Saskatoon, Saskatchewan [8]. At the time of the fires, air temperature ranged from 59 to 64 F (15-18 C), relative humidity from 30% to 40%, and wind speeds less than 3 meters/second. The fuel load was 1,029228 g/m dry weight ( SD) and fuel moisture content was 258 % ( SD) prior to the fires. At 3 measurement points above ground (4 inches (10 cm), 9.8 inches (25 cm), and 20 inches (50 cm)), fire temperatures exceeded 1,000 F (800 C). At all measurement points, maximum fire temperatures occurred within 2 to 3 minutes following ignition.

Average maximum fire temperatures and average duration of fire temperatures above 100 F (60 C) (SD) at selected heights in the western snowberry community [8]
Measurement height (cm) -5 0 10 25 50 100 150
Avg. maximum fire temperature (C) 4021 692118 84336 82443 83554 73511 69722
Avg. duration of fire temperatures above 60 C (minutes) 0.10 8.16.0 4.71.1 3.50.5 3.10.5 2.30.5 2.20.6

Bailey and Anderson [12] collected fuel and fire temperature data during April in a western snowberry community located within an aspen parkland in central Alberta. Fuels and temperatures at ground level during the fire at 3 locations within the western snowberry stand are presented in the table below. The inner third of the western snowberry community had significantly (P<0.05) greater western snowberry fuels and standing woody fuel and thereby a significantly higher surface temperature [12].

Fuel loading and fire temperature data in a western snowberry community in central Alberta [12]

Type of vegetation/fuel

Position in stand
Inner third Middle third Outer third
Western snowberry shrubland (kg/ha) 25,173* 16,857 14,732
Standing woody fuel (kg/ha) 14,906* 9,349 8,798
Ground surface fuel (kg/ha) 8,270 7,508 6,270
Fire temperature (C) 445* 368 381
*Significantly (P<0.05) greater than middle and outer third of stand

The researchers also took aboveground temperature readings during the western snowberry fire. Recorded headfire temperatures were higher than backfire temperatures. Fire temperatures for both head- and backfires were greatest at approximately 4 to 8 inches (10-20 cm) above ground. The mean and range of temperatures of the fires are presented in the table below. Both head- and backfires burned 100% of the area [12].

Temperature mean and range of head- and backfires in a western snowberry community [12]

Fire type

Mean temperature (CSE)

Temperature range (C)

Backfire 32519 204-427
Headfire 43517 232-704

Prescribed burning: Prescribed burning of western snowberry may be implemented to increase production, rehabilitate disturbed sites, and/or improve wildlife habitat.

In the northern Great Plains, spring burning (May-June) generally causes western snowberry to sprout, while frequent fires may reduce western snowberry cover. Prescribed burning guidelines for the northern Great Plains are available [75].

Successful spring burning of western snowberry shrub communities in the aspen parklands of Alberta requires the following: 1) A minimum temperature of 55 F (13 C), 2) winds of 2 to 12/mph, 3) 50% maximum relative humidity, and 4) at least 4 days following a precipitation event [171].

To increase production and caloric content of western snowberry, a prescribed burn was conducted on the Oakvile Prairie, near Grand Forks, North Dakota. On an unburned upland site, western snowberry production was 26.3 g/m and caloric content was 4,822 kcal/g (ash-free) and 126,915 kcal/m. At postfire month 3 on burned sites, western snowberry production was 39.4 g/m and caloric content was 4,855 kcal/g (ash-free) and 191,190 kcal/m [62].

Site rehabilitation: The narrowleaf cottonwood/western snowberry streamside community type in eastern Idaho is "extremely" important in reducing sedimentation, stabilizing streambanks, and slowing flood waters. Overgrazing can lead to the complete removal of western snowberry and Wood's rose. Prescribed fire, if managed carefully, is a possible tool in maintaining or restoring this community type. If fire is used, livestock grazing should be excluded from the site for at least 5 postfire years and wildlife browsing should be closely monitored [63].

Wildlife: The effect of cool-season burns on wildlife was investigated in Wind Cave National Park, South Dakota. The fires, occurring on separate sites, were conducted on 17 October 1979 and 14 April 1980. Both fires were classified as low-severity. During the first postfire year, deer mice and songbird populations increased "dramatically". By the second postfire year, the effect disappeared or in some cases was reversed. Likely the deer mice and songbirds were attracted to the burn during postfire year 1 by an increase in food supply, which decreased by the second postfire year [19].

Following a prescribed fire in a rough fescue community at Kernen Prairie, Saskatchewan, the density of breeding pairs of birds was reduced for 3 postfire years. Western snowberry is a common shrub at the site. The fire was conducted in October 1986 and bird population counts were taken during the summers of 1987, 1988, and 1989. Averaging all 12 bird species counted on the burned and unburned sites, the density of breeding pairs on burned sites in the 3 years was 2.39, 2.47, and 2.95 breeding pairs/ha. On unburned sites, breeding pair density was 5.18, 5.22, and 4.24 breeding pairs/ha [121].


MANAGEMENT CONSIDERATIONS

SPECIES: Symphoricarpos occidentalis
 

 

Domestic goats grazing western snowberry in research plots at South Dakota State University. Photo courtesy of Alexander Smart.

IMPORTANCE TO LIVESTOCK AND WILDLIFE:
Livestock: In the eastern part of its range, western snowberry is rarely eaten by livestock, even when other forage is scarce [117]. Yet in the western part of its range, western snowberry is considered an important livestock browse species [117,122,145,158,159], particularly during winter [117,145]. Western snowberry is often more heavily utilized by livestock and wildlife in the first few years following fire [135]. Western snowberry may also be browsed by domestic goats [86]. Stands of western snowberry can become so thick that they exclude livestock and wildlife [63].

Small mammals/birds/insects: The fruits of western snowberry are an important source of food for some small mammals and birds [40]. Upland game birds heavily utilize western snowberry fruits since they persist on the plant through the winter [63,82,117,147]. In Minnesota, western snowberry fruits are eaten by waterfowl [117]. Western snowberry flowers are also a valued bee food [145,159].

Ungulates: Western snowberry is an important forage species for elk, mule and white-tailed deer, pronghorn, bighorn sheep, and moose [22,36,38,39,44,47,89,99,108,113]. In the Bridger Mountains of Montana, antelope bitterbrush (Purshia tridentata) and western snowberry are the 2 most important fall browse species for mule deer [168]. Western snowberry was the most important browse plant for white-tailed deer on the Charles M. Russell Wildlife Refuge, in north central Montana, during a yearlong study from June 1964 to June 1965. Western snowberry was found in 100% of summer, fall, and winter rumen samples and 85% of spring samples. Utilization of western snowberry is greatest in fall (55% total rumen sample volume), followed by winter (25%), summer (19%), and spring (10%) [2]. Western snowberry is a principal food source for white-tailed and mule deer in the Black Hills of South Dakota and Wyoming. An analysis of stomach contents showed that the frequency of occurrence of western snowberry ranged from a high of 62% for the period May through September to a low of 45% for the period October to December [76,77,117].

Palatability/nutritional value:
The palatability of western snowberry for cattle and domestic sheep is generally rated as "fair" [22,40,63,151] and "poor" for horses [22,40]. Western snowberry palatability for deer and elk is rated as "good" [40,63,76].

In northwestern Montana, western snowberry provides "fair" energy and protein value for livestock and wildlife [22]. The nutritional value for ungulates, small mammals, and birds in 5 western states is rated as follows [40]:

Western snowberry nutritional value rating [40]
Species Utah Colorado Wyoming Montana North Dakota
Elk Good Poor Fair Fair N.D.
Mule deer Good Poor Fair Good Fair
White-tailed deer N.D. N.D. Good Good Fair
Pronghorn N.D. N.D. Fair Fair Fair
Upland game birds Good N.D. Good Fair Fair
Waterfowl Poor N.D. Poor N.D. Poor
Small nongame birds Fair N.D. Good Fair N.D.
Small mammals Good N.D. Good Fair N.D.
N.D. = No Data

At the Ministik Wildlife Research Station near Edmonton, Alberta, seasonal changes in percent digestibility and crude protein of western snowberry leaves were measured in an aspen-dominated boreal forest [127].

Seasonal digestibility and crude protein of western snowberry leaves [127]
  Late spring Summer Autumn
Digestibility (%) 57.4 61.3 59.5
Crude protein (%) 15.0 17.5 12.3

The cellulose and protein content of western snowberry at 3 stages of growth were evaluated in a rough fescue community in southwestern Alberta [16].

Nutritional content of western snowberry during 3 stages of growth [16]
Growth stage Cellulose (%) Digestible protein (%)
Leafing 15.5 4.0
Flowering 19.2 1.8
Seed ripe 15.5 1.1

Western snowberry fruit is an important fall and early winter food for sharp-tailed grouse. As the fruits dry, however, their nutritional value decreases substantially. Western snowberry fruit taken from the plant in South Dakota during fall, at a time when it is fed upon by sharp-tailed grouse, provided 4.916 kcal/g and 5.5% crude protein [46].

Composition of western snowberry on 4 dates in 1945 on the Black Hills, South Dakota [52]
Date Moisture (%) Carotene (g/g) Ash (%) Crude fat (%) Crude protein (%) Crude fiber (%) N-Free extract (%) Ca (%) P (%) Fe (ppm) Mn (ppm)
18 January 36.80 13.54 2.38 1.28 3.32 23.20 33.02 0.36 0.072 165.82 61.76
16 May 58.01 4.01 2.02 1.06 5.42 12.75 20.74 0.26 0.166 128.41 39.95
27 June 66.12 40.62 2.26 1.24 4.46 5.41 20.51 0.21 0.15 40.83 8.71
22 October 54.01 14.35 2.67 2.20 2.99 5.77 32.36 0.54 0.144 87.88 28.31

Cover value: Western snowberry communities provide cover for a variety of animal species, particularly small mammals and birds [10,22,73,117,122,132,147]. The narrowleaf cottonwood/western snowberry and black cottonwood/western snowberry grazing disclimax communities along streams provides cover for fish and other aquatic species [63]. Given the shrub's height, western snowberry only provides "poor" to "fair" cover for large ungulates [22,40].

Western snowberry stands are common nesting sites for waterfowl, wild turkeys, and sharp-tailed grouse [97,120,133]. In south-central North Dakota, western snowberry was found to occur at 62.8% of all sharp-tailed grouse nesting sites [61]. In northeastern South Dakota, western snowberry is an important cover species for nesting female Rio Grande and eastern wild turkeys. While shrub vegetation (primarily western snowberry) was the least available vegetation type (10%) at the study site, 54% of females chose this vegetation type for nesting cover [94].

VALUE FOR REHABILITATION OF DISTURBED SITES:
Western snowberry produces an extensive rhizome/root system, making it an excellent soil binder for the prevention of erosion [63,147,159,163,164]. It is also a good species for restoring disturbed sites [63,107,118,128,145]. If western snowberry is used to rehabilitate erosive sites, complete grazing exclusion may be necessary during establishment [63].

A western snowberry cultivar ('common') is available [111].

OTHER USES:
Western snowberry was used by Native Americans for food, arrow shafts, brooms, and treatment of certain eye diseases [117,139,152].

Western snowberry is used as an ornamental [81,159].

OTHER MANAGEMENT CONSIDERATIONS:
Browsing: Western snowberry is generally considered a browsing "increaser" [25,95,117,152].

The effect of heavy cattle browsing on western snowberry in early and late summer following burning was investigated on rough fescue grasslands at the University of Alberta Ranch [11,50,51]. Following a controlled burn on 15 May 1979, plots were either grazed heavily (5 AUM/ha leading to total removal of all edible vegetation) from 5 to 17 July 1979 and 31 May to 13 June 1980 (early treatment) or grazed heavily from 22 August to 1 September 1979 and 15 to 23 August 1980 (late treatment) [11,50,51]. Western snowberry production and density were generally greater on late grazing sites.

Western snowberry production and density under early and late grazing treatments [11,50,51]
Measurement date Grazing treatment Production (kg/haSE)* Density (plants/m)
May 1980 Early 417 21.6
Late 631501 31.2
August 1981 Early 524 28.2
Late 1,3641,073 23.1
July 1981 Early 792 36.1
Late 1,394770 46.9
*Standard error not given for early treatment

At the Central Grasslands Research Station in south-central North Dakota, western snowberry communities were subjected to 3 different grazing treatments (short duration, season-long, and twice-over rotation) between 1982 and 1986. The 3 treatments did not significantly alter western snowberry density, but western snowberry cover was significantly (P<0.05) reduced with the exception of the short duration treatment from 1982 to 1986. Further, western snowberry standing crop significantly increased on the short duration treatment. With little overall change between 1982 and 1986, the researchers suggest that western snowberry communities on the study site were relatively stable under the environmental and biological conditions present at the time of the study [87].

Herbicides: Western snowberry can be controlled by 2,4-D and metsulfuron methyl [24,25,25,45].

Insects: On a mixed-grass prairie at the Central Grasslands Research Center in south-central North Dakota, western snowberry was associated with white grub infestations. The infestation decreased grass standing crop 92% and facilitated a significant (P<0.05) increase in density of western snowberry for at least 1 year [98].

Invasive species: Western snowberry is an effective competitor for water against lens-podded hoary cress (Cardaria chalapensis) and globe-podded hoary cress (C. pubescens). On dry farming land in Saskatchewan, the extensive rhizome/root system of western snowberry was able to utilize subsoil moisture, thus reducing cover of both invasive species [137,138].

Mowing: Mowing western snowberry can partially control its spread. Near Lincoln, Nebraska, western snowberry was mowed annually in May while plants were in full leaf and new sprouts were 4 to 10 inches (10-30 cm) tall. In May of 1954, the fourth consecutive year of mowing, western snowberry cover was reduced by 30% to 52% [45].


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