Juniperus horizontalis



INTRODUCTORY


  1997-2001, Mark Brand, University of Connecticut
AUTHORSHIP AND CITATION:
Gucker, Corey L. 2006. Juniperus horizontalis. 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/ (2007, January 16).

FEIS ABBREVIATION:
JUNHOR

NRCS PLANT CODE [110]:
JUHO2

COMMON NAMES:
creeping juniper
creeping cedar
creeping savin

TAXONOMY:
The scientific name of creeping juniper is Juniperus horizontalis Moench. (Cupressaceae) [39,44,47,48,61,65,101,113].

Creeping juniper may hybridize with eastern redcedar (J. virginiana) and Rocky Mountain juniper (J. scopulorum) where distributions of the species overlap [1,2,39,40,40,44,47,69,85,113]. The Rocky Mountain juniper creeping juniper hybrid is recognized as J. fassettii Boivin [44]. Fassett [40] suggests that overlapping populations of eastern redcedar and creeping juniper on the Coast of Maine and in the Driftless area of Wisconsin may be hybrid swarms.

SYNONYMS:
Juniperus prostrata Pers. [65]

LIFE FORM:
Shrub

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
As of 2006, creeping juniper is considered endangered in Illinois, New Hampshire, and New York. It is threatened in Iowa and Vermont. Information on state-level protected status of plants in the United States is available at Plants Database.

DISTRIBUTION AND OCCURRENCE

SPECIES: Juniperus horizontalis
GENERAL DISTRIBUTION:
Creeping juniper occurs in the northern portion of the contiguous United States, throughout most of Canada, and in interior and coastal Alaska. Distribution is limited in the interior of Alaska. In the contiguous United States, creeping juniper's western limit is western Montana, and the southern limit is likely Nebraska [3,16,47,48,61,101,102,103,113]. Some suggest that creeping juniper may extend as far south as Colorado [3,48,80,112]. Creeping juniper occurs in the Great Lakes states and in the New England states as far south as Pennsylvania [3,16,47,48,56,61,101,102,103,113]. Creeping juniper's distribution throughout its range is disjunct and spotty. Several states list creeping juniper as a rare species. See Plants Database for a distributional map of creeping juniper.

Juniperus fassettii is reported from Banff in Alberta, near Bridger in Montana, and near the Missouri River and Amidon in North Dakota [1,2]. Creeping juniper eastern redcedar hybrids have been found on the coast of Maine and in the Driftless area of Wisconsin [40]. Hybrid populations discussed here do not likely represent an exhaustive distribution treatment.

ECOSYSTEMS [45]:
FRES10 White-red-jack pine
FRES11 Spruce-fir
FRES15 Oak-hickory
FRES17 Elm-ash-cottonwood
FRES18 Maple-beech-birch
FRES19 Aspen-birch
FRES20 Douglas-fir
FRES21 Ponderosa pine
FRES23 Fir-spruce
FRES28 Western hardwoods
FRES35 Pinyon-juniper
FRES36 Mountain grasslands
FRES37 Mountain meadows
FRES38 Plains grasslands
FRES39 Prairie

STATES/PROVINCES: (key to state/province abbreviations)
UNITED STATES
AK CT DE IL IA MA ME MI MN MT
NE NH NJ NY NC ND PA RI SD VT
WI

CANADA
AB BC MB NB NF NT NS ON PE PQ
SK YK


BLM PHYSIOGRAPHIC REGIONS [11]:
8 Northern Rocky Mountains
9 Middle Rocky Mountains
10 Wyoming Basin
11 Southern Rocky Mountains
14 Great Plains
15 Black Hills Uplift
16 Upper Missouri Basin and Broken Lands

KUCHLER [71] PLANT ASSOCIATIONS:
K011 Western ponderosa forest
K012 Douglas-fir forest
K016 Eastern ponderosa forest
K017 Black Hills pine forest
K024 Juniper steppe woodland
K063 Foothills prairie
K064 Grama-needlegrass-wheatgrass
K066 Wheatgrass-needlegrass
K067 Wheatgrass-bluestem-needlegrass
K069 Bluestem-grama prairie
K074 Bluestem prairie
K075 Nebraska Sandhills prairie
K093 Great Lakes spruce-fir forest
K094 Conifer bog
K095 Great Lakes pine forest
K096 Northeastern spruce-fir forest
K100 Oak-hickory forest
K107 Northern hardwoods-fir forest
K108 Northern hardwoods-spruce forest

SAF COVER TYPES [38]:
1 Jack pine
16 Aspen
18 Paper birch
37 Northern white-cedar
42 Bur oak
46 Eastern redcedar
107 White spruce
201 White spruce
202 White spruce-paper birch
203 Balsam poplar
209 Bristlecone pine
210 Interior Douglas-fir
217 Aspen
219 Limber pine
220 Rocky Mountain juniper
236 Bur oak
237 Interior ponderosa pine
239 Pinyon-juniper
251 White spruce-aspen
252 Paper birch
253 Black spruce-white spruce
254 Black spruce-paper birch

SRM (RANGELAND) COVER TYPES [100]:
301 Bluebunch wheatgrass-blue grama
302 Bluebunch wheatgrass-Sandberg bluegrass
303 Bluebunch wheatgrass-western wheatgrass
304 Idaho fescue-bluebunch wheatgrass
306 Idaho fescue-slender wheatgrass
307 Idaho fescue-threadleaf sedge
308 Idaho fescue-tufted hairgrass
309 Idaho fescue-western wheatgrass
310 Needle-and-thread-blue grama
311 Rough fescue-bluebunch wheatgrass
312 Rough fescue-Idaho fescue
313 Tufted hairgrass-sedge
323 Shrubby cinquefoil-rough fescue
411 Aspen woodland
412 Juniper-pinyon woodland
601 Bluestem prairie
602 Bluestem-prairie sandreed
603 Prairie sandreed-needlegrass
604 Bluestem-grama prairie
606 Wheatgrass-bluestem-needlegrass
607 Wheatgrass-needlegrass
608 Wheatgrass-grama-needlegrass
609 Wheatgrass-grama
610 Wheatgrass
613 Fescue grassland
614 Crested wheatgrass
906 Broadleaf forest
917 Tall shrub swamp
920 White spruce-paper birch

HABITAT TYPES AND PLANT COMMUNITIES:
Creeping juniper is a dominant or subdominant in the following vegetation classifications:

United States

Montana:
North Dakota: South Dakota: Northern Great Plains: Rocky Mountains:

Canada

Alberta: Manitoba: Saskatchewan:

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Juniperus horizontalis

 

  James L. Reveal, University of Maryland

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. [3,16,47,48,61,101,102,103,113]).

Aboveground description: Creeping juniper is an evergreen prostrate shrub with long, trailing or creeping branches [3,16,61,80,103,112,113]. Horizontal branches reach lengths of 10 to 20 feet (3-5 m) or more and send up many short erect stems that are typically less than 10 inches (30 cm) tall [99,101,112]. Stems are typically less than 1.5 mm in diameter, although rapidly growing stems may measure 2 mm [103,112]. Small and/or young stems are covered with scale-like leaves [103,112]. Wood is not distributed evenly within the branches; 33% of wood occurs on the up side of branches while the rest occurs on the soil-facing side [12]. The bark on mature branches is thin, scaly, and shredding [48,101,103].

Many of the characteristics used to identify creeping juniper are variable. These characters can vary as much in a stand or colony as they do in the entire species. Often a number of plants and plant parts are necessary for positive identification. For instance, not all peduncles attached to the female cone are curved, but 60% or more will be. Not all seeds are pitted, but likely 50% or more will be [40].

This mat-forming shrub may measure up to 20 feet (7 m) across but rarely exceeds a height of 20 inches (40 cm) [33,103]. Creeping juniper is considered slow growing [12]. In Montana, researchers found that plant size was related to climate and site conditions. Thirty widely separated creeping juniper-dominated stands were evaluated. Shrubs averaged 2.5 inches (6.4 cm) tall, and height range was 1.9 to 3.8 inches (4.8-9.6 cm). Tallest plants occurred on dry, low-elevation sites with low grass and forb cover. Shortest plants occurred on mesic, high-elevation sites with high grass and forb cover. Terminal growth averaged 1.4 inches (34.5 mm)/growing season, and most occurred in June and July. Lateral growth averaged 0.4 inch (9.0 mm)/growing season and was slow and without spurts. Shrubs on northern slopes produced the longest twigs, while the shortest twigs occurred on sites with a tree canopy. Dead crown area averaged 3.5% [79]. A study of 52 plants in central Montana revealed an average shrub age of 56.7 years and a range of 20 to 140 years. Young plants were scarce in the study area. Browsing may have been a factor in the limited regeneration [76].

Leaves are opposite, appressed, and overlap in a scale-like pattern; on juvenile plants, however, leaves are spreading and needlelike [3,18,33,99,101]. On mature plants, leaves overlap in a clasping manner and measure 1 to 3 mm long by 0.5 to 1 mm wide. Juvenile shrubs have longer leaves (3-7 mm long by 0.6-1.3 mm wide) that are spreading. Immature and mature leaves typically have sharp points. Leaf color can vary from bright green to bluish. Glands occur on the undersides of leaves [16,47,48,61,92,102,103,112]. Creeping juniper is dioecious and produces male and female cones on the ends of 1st- and 2nd-year branches. Staminate cones are a cluster of umbrella-shaped or cylindrical stamens that measure 3.5 to 5 mm long and 1 to 2 mm in diameter. Female cones require 2 growing seasons to mature. In the 1st year of development, female cones are a cluster of 3 to 8 scales. Upon spring fertilization, scales come together and protect the ovules in a round berrylike cone that measures 6 to 10 mm in diameter. In the fall of the next growing season, the green, fleshy, berrylike cone matures and turns a blue color. These cones occur on short curved stalks. Berrylike cones contain between 1 and 6 seeds [3,47,48,79,80,101,102,103,103,112]. Seeds are oval to round with ridges and sharp points. Typically seeds are flat on one side and measure 3 to 5 mm long and 2 to 4 mm in diameter [47,48,79,103,112].

Belowground description: The creeping juniper root system is shallow. While major roots typically come from the center of the shrub, there are several other major and many minor roots elsewhere. Adventitious roots typically appear 4 to 8 inches (10-20 cm) from branch tips. Depth of the major roots of shrubs in Montana averaged 8.8 inches (22.4 cm) and ranged from 5.1 to 14 inches (13-35 cm) [79]. Creeping juniper colonies studied in Sherburne County, Minnesota, had no main vertical taproot. Plants produced large horizontal roots with 0.8 inch (2 cm) diameters that were as long as 13 feet (4 m). These roots extended from the "gnarled stem base," and most were within 4.7 inches (12 cm) of the soil surface [12]. Available literature (2006) suggests that creeping juniper reproduces primarily by layering and the subsequent breakup of mature shrubs.

Hybrids: Juniperus fassettii in Banff, Alberta, were 12 to 39 inches (30-100 cm) tall with one or more upright stems measuring 71 to 120 inches (180-300 cm) [1,2]. For more information on properly identifying creeping juniper in areas where eastern redcedar and/or Rocky Mountain juniper co-occur, see [40].

RAUNKIAER [88] LIFE FORM:
Chamaephyte

REGENERATION PROCESSES:
Creeping juniper is capable of reproducing sexually and asexually; however, studies describing asexual regeneration are predominant in the limited research that addresses this topic.

Pollination: Cones are wind pollinated.

Breeding system: Creeping juniper is dioecious [48,103]. A researcher that studied creeping juniper stands throughout Montana determined that the sex ratio was 2:1 in favor of males. Shrubs averaged 23.5 ripe berrylike cones per 100 twigs, and the number of ripe "berries" ranged from 5.5 to 101.4. The researcher encountered just a single plant that failed to produce cones [79].

Seed production: Curtis [29] suggests that creeping juniper is a poor seed producer, but well-documented observations and/or experimental research are largely lacking.

Seed dispersal: Seeds are likely dispersed by wildlife and wind. A person collecting a creeping juniper specimen in Ohio observed birds dropping creeping juniper seeds along a fence line, and noted this observation on the herbarium voucher [18].

Seed banking: Creeping juniper seed dormancy suggests some persistence in the seed bank.

Germination: Creeping juniper seed germination studies are lacking. Seed collected in Montana and encouraged to germinate in the laboratory germinated at a very low percentage (0.1%). Just 9 of 9,500 new and 2-year-old seeds germinated. Seed treatments, if any, and laboratory conditions were not reported [79]. Curtis [41] indicates that the germination period is lengthy.

Pack [84] conducted laboratory germination studies on juniper (Juniperus spp.) and found that seed requires an after-ripening period at temperatures of 32 to 50 F (0-10 C). The stratification period was approximately 100 days at 41 F (5 C). Juniper seed germinated at 41 F (5 C) as well. When ripened seeds were subject to temperatures above 59 F (15 C), they experienced a 2nd dormancy. Once germination began, seedlings grew quickest at 77 F (25C), but germination was initiated earlier and seedlings appeared healthier when grown at 59 F (15 C). While many attempts were made to force seed germination before the after-ripening period, all failed [84].

Seedling establishment/growth: The limited number of studies that address creeping juniper seedling establishment suggest that it is a rare event. Waterman [116] reports that creeping juniper seed germinates in pure sand soils, but seedling survival on sand sites is rare. In an extensive study of 30 widely separated creeping juniper stands in Montana, just 6 shrubs were less than 10 years old and considered the result of seedling establishment. The researcher suggested that poor seedling establishment was likely a combination of 1 or more of following factors: low seed production, failure of seed to reach maturity, lack of germination, and/or high seedling mortality. It was also suggested that plants may rely heavily on vegetative reproduction or that successful seedling establishment may be episodic, which may not pose a problem for this long-lived species [79].

Growth: A couple of studies indicate that climate and site conditions can affect creeping juniper growth. The 1st study monitored numerous plants throughout Montana. Longest stems were produced by shrubs on north slopes, and shortest stems occurred on sites with an overstory [79]. Creeping juniper is a slow-growing species. In Minnesota, creeping juniper growth, measured as square millimeters of wood produced in a year, was slowest in the year that experienced a severe drought preceded by a record-breaking severe winter [12].

Vegetative regeneration: The available literature (2006) suggests that creeping juniper reproduces primarily by layering and the subsequent breakup of mature shrubs. However, information addressing creeping juniper reproduction is largely lacking. Regeneration was primarily vegetative in 30 widely separated creeping juniper stands in Montana. Seedlings or young plants were not as common as new plants resulting from the disconnection of mature shrubs [79].

SITE CHARACTERISTICS:
Creeping juniper prefers open, well-drained sites. In Nova Scotia creeping juniper occupies rocky headlands, cliffs, pastures, and beaches [92]. Creeping juniper is noted on sand dunes and shores and in open rocky woods and pastures in Ontario [101]. Habitats are similar in the Great Plains states and include open hillsides, eroded areas, and open woods [48,103]. Creeping juniper occurs in Glacier National Park, Montana, on east slopes at and above timberline [102]. Grimm [49] indicates that creeping juniper is also common on the sandy, rocky borders of swamps and bogs. A creeping juniper community near the Matador Research Station in southern Saskatchewan occupies erodible slopes in dry areas [74].

Aspect/slope: A study of creeping juniper populations throughout Montana revealed that creeping juniper was most frequent on northern aspects with slopes under 40% [79]. In Theodore Roosevelt National Park, the creeping juniper-little bluestem habitat type is restricted to slopes greater than 28% [54]. Butler [20] reported that creeping juniper cover was greatest on moderately steep slopes with shallow and poorly developed soils. Similar habitats were described for little bluestem-creeping juniper habitat types on hilltops and buttes in southwestern North Dakota [59].

Climate: Creeping juniper occurs in areas with continental climates that are typically dry and often experience great annual and diurnal temperature variations. High frost resistance is noted for creeping juniper [69]. Creeping juniper colonies studied in Sherburne County, Minnesota, had very low specific water conductivity, which was among the lowest for evergreen species [12].

In ponderosa pine woodland habitats in northeastern Nebraska, which are likely near the southernmost distribution of creeping juniper, annual precipitation averages 18 inches (460 mm), and summer drought conditions are common. In these habitats, which are between 2,500 and 4,500 feet (760-1,400 m), the frost-free period is 145 to 150 days [108]. Creeping juniper communities near the Matador Research Station experience an arid, cold climate. Temperatures average 5.9 F (-14.5 C) in January and 65.8 F (18.8 C) in July. Annual precipitation averages 12.9 inches (327 mm); 66% is delivered as rain in the summer, and the rest comes as snow [74]. Climatic conditions in a more northern part of creeping juniper's range are described for the miscellaneous upland grassland communities of Alaska's Matanuska Valley. Here annual precipitation averages 15.5 to 18 inches (394-457 mm). This area is driest from February through June. January temperatures average 13 F (-10 C), and August temperatures average 55 F (13 C). Growing season lasts between 73 and 150 days [55].

Elevation: Elevational tolerances are rarely reported for creeping juniper. Miller [79] indicates that creeping juniper is most common below 4,900 feet (1,500 m) in Montana, but creeping juniper stands occurred on sites ranging from 2,150 to 8,200 feet (655-2,500 m). In the middle Rocky Mountains, creeping juniper is common in the foothills/steppe-shrubland vegetation zone that occurs at or below timberline where elevations range from 5,200 to 6,900 feet (1,600-2,100 m) [52].

Soils: Creeping juniper is often described in association with sandy, poorly developed soils. Krajina and others [69] report that creeping juniper prefers high calcium soils and grows in permafrost soils. The creeping juniper/sun sedge habitat type in the Custer National Forest occupies steep north-facing slopes with sandy loam soils. The sand content of soils from 7 stands averaged 57.5% to 72.4%. Organic matter averaged 4.3% to 5.5% [53]. The little bluestem-creeping juniper habitat type in southwestern North Dakota occurs on extremely shallow soils with 26% to 44% exposed rock. Soils are loamy and calcareous with pH levels of 8 to 8.5 [59]. In creeping juniper-dominated stands throughout Montana, soils were poorly developed with thin topsoil and large amounts of rock. Soils had a clay loam texture, were experiencing some surface erosion, and had an average pH of 7.2. The pH range was 4.4 to 8.5. Soil organic matter averaged 4.6% and ranged from 0.8% to 7.4%. Phosphorus concentrations were very low (18 ppm), but potassium concentrations were moderate to high (280 ppm) [79].

SUCCESSIONAL STATUS:
Creeping juniper occurs in both early and late seral communities. In the primary succession of beach and sand dune habitats, creeping juniper is an early colonizer. Likely creeping juniper's persistence in late seral communities is dependent on community composition. Creeping juniper has low shade tolerance [69] and likely decreases as canopy cover increases. However, creeping juniper is typical in grass- or shrub-dominated vegetation described as climax [53,63].

Early or primary succession: Often creeping juniper is indicated as an early or middle species in primary succession of sand dunes, beaches, rock cliffs, and even swamps.

Creeping juniper is important in the early colonization of sand dunes and sandhills in Alberta and Saskatchewan [26,34]. Coupland [26] refers to creeping juniper as a "stabilizing pioneer" on sandy sites. In sand dune areas within Saskatchewan's grassland regions, creeping juniper abundance was greatest on stabilized blowouts characterized by recent erosion but without current erosion. Creeping juniper is the 1st shrub to colonize blowout bottoms and eroding areas; its lateral rooting branches aid in sand stabilization and successional progression [60].

On Great Lakes shores, creeping juniper typically colonizes sandy areas soon after rhizomatous grasses such as European beachgrass (Ammophila arenaria) and/or prairie sandreed have stabilized the sand. Creeping juniper is rare on unvegetated pure sand [28,116]. At Point Beach State Forest in Two Rivers, Wisconsin, creeping juniper establishes on the stable edge of "blowouts" colonized by pioneer grasses. Creeping juniper is important in the next stages of sand stabilization. Its long branches reduce erosion, and its upturned branches allow it to tolerate some deposition. Juniper mats are common on the edge of advancing forest vegetation. A time frame for beach succession was not reported [111].

Creeping juniper is an early colonizer in the succession of Isle Royale National Park's rock shores in Michigan. As water recedes along the banks of Lake Superior, rock shores and cliffs are exposed. These rock surfaces are 1st colonized by lichens and mosses. Increased moss and lichen abundance and density allow sites to conserve more moisture and soil. Rock crevices form due to uneven weathering and collect soil from wind and the breakdown of rock. These crevices provide habitat for pioneer plants including shrubby fivefingers (Sibbaldiopsis tridentata), tufted hairgrass (Deschampsia caespitosa), hairy goldenrod (Solidago hispida), and/or western yarrow (Achillea millefolium). Creeping juniper colonizes and forms vegetation mats after 1 or more of these pioneers establish [24,25].

In the succession of a calcareous fen in the Byron-Bergen Swamp of Genesee County, New York, creeping juniper represents a mid-successional stage. Creeping juniper colonizes small hummocks of hardstem bulrush (Scirpus acutus) and creeps onto marl beds from adjacent northern white-cedar (Thuja occidentalis) communities. Colonization by creeping juniper precedes the advancement of coniferous forests but is not important on hummocks supporting tall shrubs and trees. Creeping juniper stems that were trailing over marl beds but rooted in northern white-cedar thickets averaged 10.8 years old. Oldest stems were 54 years old [98].

Using radio carbon and forest stand dating, Lichter [75] assessed primary succession and forest development in Wilderness State Park in northern lower Michigan. On the youngest dune ridge, American beachgrass (Ammophila breviligulata) dominates. Evergreen shrubs such as common juniper (J. communis) and kinnikinnick occurred on dunes that were 55 to 175 years old, and mixed pine forests developed on 225- to 440-year-old substrates. Creeping juniper cover was 1.1% on 145-year-old dunes and persisted, although coverage decreased, on 345-year-old-dunes. Creeping juniper was missing from substrates over 345 years old that were sampled in the chronosequence [75].

Late or climax succession: Creeping juniper occurs in many grassland habitats that are considered climax vegetation. The creeping juniper/sun sedge habitat type is considered a "topoedaphic climax" type on the Custer National Forest [53]. In the badlands of western North Dakota, creeping juniper is identified in climax communities [63]. For a list of additional climax or stable, late-seral vegetation types where creeping juniper is important, see Habitat Types and Plant Communities.

Shade relationships: As indicated earlier, creeping juniper is not shade tolerant [67,69]. A study of many creeping juniper stands throughout Montana revealed that shrubs produced the shortest twigs on sites with tree overstories [79].

Grazing succession: Creeping juniper coverage may increase with grazing. Creeping juniper was absent or had very low coverage on lightly grazed sites in North Dakota Badlands. Coverage was greater on moderately and heavily grazed sites. Degree of use was subjectively determined by evaluating sites for trails, lounge areas, and distance to water [20].

Postfire succession: Information is lacking (as of 2006) on the recovery of creeping juniper following fire. Likely fire severity and/or degree of prefire disturbance affect creeping juniper survival or recovery. Several studies report partially unburned creeping juniper shrubs following fire [62,79]. However, fire may have eliminated creeping juniper from even-aged ponderosa pine stands in the northern Black Hills of Lawrence County, South Dakota. Even-aged ponderosa pine stands with high stem density (1,300-4,700 stems/ha) and basal area (50-80 m/ha) were burned and cut. There were 6 total treatments: clearcut, thinned, clearcut and burned, thinned and burned, burned, and undisturbed. On all cut sites, trees and slash were removed from the site. Burning took place in May when winds were light, air temperatures were 54 to 70 F (12-21 C), and relative humidities were 30% to 60%. The fire produced flame lengths of 1.6 to 3.9 feet (0.5-1.2 m). Creeping juniper was only observed on study sites before the application of treatments. Sites were visited 1 and 2 years following treatments [121]. For more on this study and other fire studies, see Discussion and Qualification of Plant Response.

Succession after fire in Kluane National Park, Yukon, begins with an herbaceous stage that lasts 1 to 15 years, depending on fire severity and availability of on-site and off-site propagules. A shrub/sapling stage dominated by creeping juniper or russet buffaloberry (Shepherdia canadensis) is typical between 5 and 80 years following fire. The shrub/sapling stage finally succeeds to a white spruce/manzanita (Arctostaphylos spp.) or white spruce/revolute hypnum moss (Hypnum revolutum) community. Length of time that creeping juniper persists as canopy closure increases was not reported [58]. For information on fire regimes in Kluane National Park, see Fire Ecology.

SEASONAL DEVELOPMENT:
Creeping juniper produces staminate and pistillate cones in the spring, and female cones mature in the summer or early fall. In the north-central and Great Plains regions, cones appear in May or June [48,103]. Cones are produced in August or September in the north-central Great Plains and in July in New England [99].

The phenological development of creeping juniper was studied in stands throughout Montana. Twig growth began in early April, turning plants from brown to green. Staminate cones developed as stem growth was initiated. Pollen was released approximately 2 to 3 weeks after shrubs broke dormancy. Plant growth continued into September or early October. Creeping juniper berries appeared 1 to 2 weeks after pollen shed. In mid-November, berries turned from green to purple. The cones took 1 to 2 years to ripen after turning blue or purple [79].

FIRE ECOLOGY

SPECIES: Juniperus horizontalis
FIRE ECOLOGY OR ADAPTATIONS:
Fire adaptations: Creeping juniper recovery following fire depends on the severity of the fire. If fire severity is low and a portion of the creeping juniper canopy survives, partially burned shrubs regenerate. If fire severity is high and the creeping juniper canopy is consumed, recovery is from the germination and establishment of off-site and/or on-site seed sources [79]. Some report that creeping juniper seed germination is stimulated by fire [17]. Postfire regeneration from off-site seed dispersed by wildlife is also likely [41]. However, seedling establishment is considered a rare event [79].

Fire regimes: Creeping juniper persists in a number of habitats that experience frequent or occasional fire, suggesting some fire tolerance. Grasslands that provide habitat for creeping juniper likely burned frequently before fire exclusion practices; however, fire regimes in these habitats are not well documented. Studies in open, forested habitats with creeping juniper are also limited. In the Wallace-Aiken Lake region of southeastern Manitoba, creeping juniper occurred in jack pine (Pinus banksiana) forests that burned "repeatedly." The fire regime was not described [94]. In the Kananaskis Valley watershed of Alberta, creeping juniper occupies limber pine forests that burned in small, recurrent stand-replacing fires at rather long intervals [119].

Ponderosa pine forests: Fire regimes in ponderosa pine forests of Montana and South Dakota have been altered by 20th century fire exclusion practices. Fire frequency in the ponderosa pine/creeping juniper habitat type in central Montana's Little Rocky Mountains was and, in some areas remains, "fairly high." Fire exclusion in some stands has created a dense understory of pole-sized or larger trees that fuel severe fires. In extremely hot xeric areas, however, tree regeneration is slow and the effect of fire exclusion has been minimal [42]. Roberts and Sibbernsen [91] studied the same ponderosa pine/creeping juniper habitat type and suggested that, while even-aged stands suggest fire has been important, evidence of frequent fire is lacking.

Research of fire-scarred ponderosa pine trees in the northern Black Hills area of Lawrence County, South Dakota, showed that fire frequency has changed since the late 1800s. Fire frequency was high from the mid-1600s to 1879. Fires burned primarily in the late growing or dormant season. The fire return interval averaged 14 years for the 1450 to 1998 time period and ranged from 1 to 43 years. However, no fires occurred since 1879. Researchers found that ponderosa pine stands in 1998 were even aged, had high density (1,300-4,700 stems/ha), and high basal area (50-80 m/ha). They suggest that this stand structure is much denser than what occurred on the landscape before fire exclusion [121]. For information on creeping juniper to fire at this location, see Postfire succession.

White spruce forests: Creeping juniper is important in the postfire succession of boreal white spruce forests. In the sandhills of south-central Manitoba, white spruce trees are often found in creeping juniper mats, which researchers indicate offer protection from fire. Creeping juniper facilitates the advancement of succession from aspen, primarily quaking aspen (Populus tremuloides), to white spruce [15].

Researchers assessed the fire history of Yukon's Kluane National Park from fire scars, aerial photos, and stand origin dating. The oldest stand originated in 1592, and fire scars recorded after 1940 were lacking. In the Slims River Valley, where creeping juniper occurs and white spruce is the eventual dominant, the average fire return interval was an estimated 231 years. Fire intervals ranged from 80 to 403 years. Fire size averaged 2,430 acres (983 ha) and ranged from 227 to 6,670 acres (92-2,700 ha). For the entire Park, the fire return interval averaged between 113 and 238 years by study area, and the fire return interval for individual sites ranged from 9 to 403 years. For information on succession following fire in this area, see Postfire succession [58].

The following table provides fire return intervals for plant communities and ecosystems where creeping juniper is important. For further information, see the FEIS review of the dominant species listed below.

Community or Ecosystem Dominant Species Fire Return Interval Range (years)
bluestem prairie Andropogon gerardii var. gerardii-Schizachyrium scoparium <10 [70,86]
Nebraska sandhills prairie Andropogon gerardii var. paucipilus-Schizachyrium scoparium <10 [86]
birch Betula spp. 80-230 [106]
plains grasslands Bouteloua spp. <35 [86,123]
blue grama-needle-and-thread grass-western wheatgrass Bouteloua gracilis-Hesperostipa comata-Pascopyrum smithii <35 [86,93,123]
Rocky Mountain juniper Juniperus scopulorum <35 [86]
wheatgrass plains grasslands Pascopyrum smithii <5-47+ [86,87,123]
Great Lakes spruce-fir Picea-Abies spp. 35 to >200
northeastern spruce-fir Picea-Abies spp. 35-200
conifer bog* Picea mariana-Larix laricina 35-200 [35]
pinyon-juniper Pinus-Juniperus spp. <35 [86]
jack pine Pinus banksiana <35 to 200 [22,35]
Pacific ponderosa pine* Pinus ponderosa var. ponderosa 1-47 [5]
interior ponderosa pine* Pinus ponderosa var. scopulorum 2-30 [5,9,73]
aspen-birch Populus tremuloides-Betula papyrifera 35-200 [35,115]
quaking aspen (west of the Great Plains) Populus tremuloides 7-120 [5,50,78]
mountain grasslands Pseudoroegneria spicata 3-40 (x=10) [4,5]
Rocky Mountain Douglas-fir* Pseudotsuga menziesii var. glauca 25-100 [5,6,7]
bur oak Quercus macrocarpa <10 [115]
oak savanna Quercus macrocarpa/Andropogon gerardii-Schizachyrium scoparium 2-14 [86,115]
little bluestem-grama prairie Schizachyrium scoparium-Bouteloua spp. <35 [86]
*fire return interval varies widely; trends in variation are noted in the species review

POSTFIRE REGENERATION STRATEGY [104]:
Prostrate woody plant, stem growing in organic mantle
Secondary colonizer (on-site or off-site seed sources)

FIRE EFFECTS

SPECIES: Juniperus horizontalis

 

  James L. Reveal, University of Maryland

IMMEDIATE FIRE EFFECT ON PLANT:
To date (2006), there are few studies on the effects of fire on creeping juniper. Of these few studies, however, most indicate that some portion of creeping juniper colonies remains unburned following fire. In the Spruce Woods Provincial Park of southwestern Manitoba, creeping juniper mats were not completely burned in prescription fires. A middle patch remained green following the fire, but information on fire season and characteristics was not provided [21]. Bird [15] reports that creeping juniper does not burn readily and serves as a refuge for fire-sensitive white spruce seedlings and saplings in boreal forests. Miller [79] reports that creeping juniper experiences some fire damage, but less than most other juniper species. Likely fire severity, burning conditions, and fire behavior dictate creeping juniper postfire recovery.

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

PLANT RESPONSE TO FIRE:
Creeping juniper's postfire response is determined by the amount of canopy damage. If fire severity is low and a portion of the creeping juniper canopy survives, partially burned shrubs regenerate. If fire severity is high and the creeping juniper canopy is consumed, postfire regeneration is by germination and establishment of off-site and/or on-site seed [79]. Some report that creeping juniper seed germination is stimulated by fire [17], but no field observations are reported. Postfire regeneration from off-site seed dispersed by wildlife is also possible [41].

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Few studies, as of 2006, report on the recovery of creeping juniper following fire, and those that do report that both dead and completely unharmed shrubs are possible on burned sites.

In the subalpine zone in Banff and Jasper National Parks, Alberta, creeping juniper occurs with kinnikinnick, mixed grasses, and sedges on arid south-facing slopes that have burned repeatedly [43].

Creeping juniper was not fully consumed by spring or fall back- and head fires that burned in rough fescue (Festuca altaica)-Idaho fescue-bluebunch wheatgrass habitats in the Sun River Wildlife Management Area west of Great Falls, Montana. Researchers report that the effects of fire on creeping juniper were significant (p≤0.1), and likely fire decreased creeping juniper abundance or production. In many cases creeping juniper did not ignite, but researchers suggested that under more severe fire conditions harm to creeping juniper might have been greater. It was not reported whether or not the effects on creeping juniper were different in the spring and fall fires. Weather conditions at the time of burning were [62]:

  Fall fires Spring fires
Maximum air temperature (C) 10 15.5
Minimum air temperature (C) 7.2 6.1
Maximum relative humidity (%) 50 50
Minimum relative humidity (%) 37 27
Average wind speed (km/h) 8.8 3.2
Fine fuel moisture at ignition (%) 6.3 4.3
Fine fuel moisture at completion (%) 7.4 8.7

The most complete report on fire's variable effects on creeping juniper is a description of 2 prescription fires in central and west-central Montana. The 1st is the Blacktail Hills Fire, which burned a site in central Montana with a sparse Douglas-fir overstory and an understory dominated by shrubby cinquefoil and creeping juniper. At the time of the fire, soil moisture averaged 49.6%, and fine fuel moisture 15%. Twenty-one creeping juniper shrubs were marked and studied before and after the fire. Plants were small; crown area and height averaged 0.08 m and 3.1 inches (7.8 cm), respectively. Just over 50% of the creeping juniper shrubs were killed by fire; 43% were burned but survived; 4% were completely unharmed. When 100% of the crown was consumed, plants died. Only 1 plant with less than 100% burned crown died. Surviving plants tolerated aboveground temperatures of 170 to 513 F (78-267 C); however, several plants that experienced temperatures below 513 F (267 C) died, suggesting that low-intensity fires can harm creeping juniper. Fire-killed plants typically had fire damage into the root system, whereas surviving plants did not [79].

The 2nd prescribed fire report is from the Sun River Fire, which burned a site dominated by creeping juniper, bluebunch wheatgrass, and rough fescue in west-central Montana. At the time of the fire, soil and fine fuel moisture averaged 11% and 32%, respectively. Fire severity was low. Fire spread rate was about 2 feet (0.6 m) per minute, and flame heights were less than 3 feet (1 m). Fire temperature averaged 200 F (91 C). Just 31% of the creeping juniper canopy was consumed; 29% of that canopy was burned but survived; and 40% was unburned. No plants were completely killed. The Sun River site had more extensive creeping juniper mats than the Blacktail Hills site. A lack of fine fuels or greater moisture or humidity levels inside the mat may have prevented fire spread [79].

Creeping juniper did not occur on burned sites in the northern Black Hills of Lawrence County, South Dakota [121]. For information on this study, see Postfire succession.

FIRE MANAGEMENT CONSIDERATIONS:
Information regarding fire effects on creeping juniper is sparse. Research is needed for informed use of fire for the management of creeping juniper.

MANAGEMENT CONSIDERATIONS

SPECIES: Juniperus horizontalis
IMPORTANCE TO LIVESTOCK AND WILDLIFE:
Many wildlife species including big game, small mammals, and birds feed on creeping juniper and utilize creeping juniper habitats [79]. From feces collected from the east slope of the Rocky Mountains in north-central Montana, mule deer diets in January and February were 51.5% to 53.7% juniper and 45% to 51.5% in March and April. Creeping juniper was likely the majority of the juniper consumed, as creeping juniper cover on the winter ranges sampled was 98%. Elk diets were 1.7% juniper in January and February and in March and April were 17.7%. Bighorn sheep diets in January and February were 2.4% juniper and in March and April were 13.5% [66].

Moose: Creeping juniper does not appear to be an important food source for moose. On Isle Royale National Park, creeping juniper was only lightly browsed [83].

Deer: Both white-tailed and mule deer feed on creeping juniper and utilize creeping juniper habitats. Use is typically greatest in the winter or spring. In a review, Kufeld and others [72] found 7 studies that showed heavy winter use, 4 studies that showed heavy spring use, and 2 studies that showed moderate fall use by mule deer. Winter and spring use of creeping juniper is noted in several areas of Montana [36,62,79].

Creeping juniper is an important winter food for mule deer and white-tailed deer in South Dakota's Black Hills [46]. See Palatability/nutritional value for information on the nutrient composition of creeping juniper in this area. In western Canada, Bird [15] reports that white-tailed deer pawed or dug through "considerable" snow depths to reach creeping juniper. On the Sun River Game Range in west-central Montana, wintering mule deer used creeping juniper most; winter use of white-tailed deer and bighorn sheep was rare [95]. In the Snowy Mountains of central Montana, creeping juniper made up 2% of white-tailed deer rumens collected in the spring and just a trace of winter rumens. From 6 mule deer stomachs sampled in the winter, creeping juniper contents were 40% [64]. Findings were similar in north-central Montana's Bear Paw Mountains. Creeping juniper frequency in 6 mule deer rumens collected in the spring was 33%, and frequency was 88% for 8 rumens sampled in winter. Creeping juniper was only found in white-tailed deer rumens taken in the winter, with creeping juniper frequency of 29% in 7 rumens [77].

Researchers thought creeping juniper/little bluestem vegetation in North Dakota's Theodore Roosevelt National Park was utilized as a lounge area by deer. Deer pellet density was typically greatest in this vegetation type. Use of this area was altered by leafy spurge (Euphorbia esula) encroachment; see Other Management Considerations for more information [109].

Pronghorn: Creeping juniper was an important part of winter and spring pronghorn diets in the Matador region of Saskatchewan. Frequency of creeping juniper was 45% in the winter and 25% in the spring based on 21 rumen analyses [30]. Creeping juniper was 0.6% of the total volume of spring and winter pronghorn diets as determined by examining rumen contents from animals collected in Petroleum County, Montana [23].

Small mammals: Small mammal browsing of creeping juniper is likely common. Miller [79] reports that in some areas of Montana, small mammal browsing may be substantial. The number of twigs utilized by small mammals in Montana ranged from 0% to 15%. Berries were gnawed as well. On 1 site, an unidentified marmot species was often observed and may have browsed creeping juniper [79]. Near Treesbank, Manitoba, the contents of 2 prairie vole caches were examined; 1% was creeping juniper berries, and 7% was creeping juniper galls [27].

Researchers documented the vegetation present in black-tailed prairie dog towns in central Billings County, North Dakota. Creeping juniper was present in 2 of the 4 towns evaluated. Creeping juniper was present in the older towns that were not expanding due to topographical restrictions. Whether or not creeping juniper absence was a result of black-tailed prairie dog disturbances associated with expanding towns was not discussed. Use of creeping juniper was not reported [105].

Birds: Numerous bird species were common in the deciduous forest underbrush dominated by creeping juniper in southwestern Manitoba. Bird species included mourning doves, rose-breasted grosbeaks, hermit thrushes, western wood-pewees, black-billed cuckoos, blue jays, catbirds, brown thrashers, chipping sparrows, clay-colored sparrows, and yellow warblers [14]. In the mixed-grass prairie of Manitoba, creeping juniper was significantly (P<0.05) correlated with Baird's sparrow. Baird's sparrow was not detected on transects dominated by Eurasian grasses, where creeping juniper cover was lower than on native prairies. For more information, see Other Management Considerations [122].

Creeping juniper was an important winter food for sharp-tailed grouse observed northeast of Glendive, Montana. Fifteen percent of the winter feeding observations was on creeping juniper [107].

Insects: In North Dakota thatching ants occurred on a mound partially colonized by creeping juniper. Because there were few ants, it was suggested that creeping juniper was crowding out the ant colony, which was thought to prefer nesting in open conditions [118]. In Illinois Beach State Park, however, researchers found that creeping juniper was associated with thatching ant mounds. Some creeping juniper stems even emerged from the mounds. Researchers suggested several reasons for the association: ants may choose to build nests near certain species, ants may have dispersed creeping juniper seed at their mounds' edges after consuming the cones, or soil near the mounds may have been altered by ant waste products in a way that favors creeping juniper. Evidence was strongest for the 3rd idea. Researchers noted that ants gnawed off stems encroaching their mounds, and vegetation associated with mounds must tolerate clipping [10].

Palatability/nutritional value: Dittberner and Olson [31] rate the palatability of creeping juniper as poor for domestic livestock and elk, fair for white-tailed deer, and good for mule deer, pronghorn, nongame birds, and small mammals in Montana, Wyoming, and North Dakota. Morris and others [82] rate the winter forage value of creeping juniper as good to excellent for mule deer in Montana.

From collections made from many sites throughout Montana, creeping juniper leaves and twigs averaged crude protein values of 5.5% in spring, 6.3% in summer, and 5.7% in fall and winter. These crude protein values were low when compared to other deer browse. Selection of creeping juniper may be related to deer distributions, lack of other more desirable forage, and/or availability of creeping juniper [79].

Seasonal fluctuations in nutritional composition of creeping juniper shrubs in South Dakota's Black Hills are provided below. Those portions of the plant typically consumed by deer were used in the analysis [46].

  Carotene Moisture Ash Crude fat Crude protein Crude fiber N-free extract Ca P Fe Mn

mg/g

% ppm
January 10.1 50.5 2.7 6.3 3.3 12.6 24.5 0.83 0.078 168.4 19.9
May 22 47.2 2.6 5.9 3.4 12.2 28.7 1 0.081 213.9 47.9
June 25 49.9 2.5 4.9 3.6 11.4 27.7 0.79 0.087 169.9 21.9
October 37.2 55.1 2.2 6.5 3.8 10.3 22.2 0.72 0.085 93.3 23.3

Cover value: The low-growing stature of creeping juniper makes it useful cover only for small wildlife species or insects. Dittberner and Olson [31] rate creeping juniper as fair to poor cover for game birds, nongame birds, and small mammals.

VALUE FOR REHABILITATION OF DISTURBED SITES:
While the number of studies reporting successful use of creeping juniper in restoration or revegetation projects is low, creeping juniper has a number of desirable characteristics for revegetation and tolerates a wide range of conditions. Stephens [103] reports that creeping juniper is the "finest plant" for preventing soil erosion. Watson and others [117] indicate that creeping juniper is drought and cold tolerant, grows in basic or acid soils, withstands browsing, and is long lived. Creeping juniper is desirable for watersheds with erodible, harsh, and exposed sites [81].

Several guidelines may increase the successfulness of creeping juniper plantings. Doran [32] reports that creeping juniper cuttings root easily without treatments, and that cuttings taken in fall or winter may root better than those taken in summer. Others indicate that 2-year-old stock may establish and survive better than younger stock and recommend transplanting dormant shrubs in the spring when moisture is likely available. Establishment of creeping juniper is slow. Shrubs appear sensitive to mine spoils and typically do better if there is top soil on mine sites [81].

Rocks may provide shelter for creeping juniper and thus increase its survival on reclamation sites, but an understanding of weather patterns and plant tolerances is necessary. In the revegetation of the East Decker Coal Mine in southeastern Montana, creeping juniper was planted near rocks such that plants were exposed to northwestern or southeastern aspects. Following the 1st winter, mortality of creeping juniper was lower for plants with southeastern than northwestern exposures. Winter dehydration may have killed shrubs on northwestern exposures. Following the summer, however, some shrubs on southeastern exposures died. Researchers suggested that there is likely a trade-off between protection and exposure to harsh conditions [13].

OTHER USES:
Past uses: A review reports that creeping juniper was used by the Cheyenne Tribes of eastern Montana. Juniper leaves were burned when women were in labor to encourage delivery. Incense from juniper burning was used to alleviate fears of thunder and to purify participant and items used in the Sun Dance. A tea of creeping juniper was used to treat coughs and sore throats. For heavy coughs, fleshy creeping juniper cones were chewed and the juice swallowed [57].

Current uses: Numerous creeping juniper cultivars are used in home and city landscapes. Creeping juniper cultivars are attractive ground covers and tolerate harsh conditions [16,68,112]. 'Prince of Wales juniper' is heat and drought tolerant and considered useful in water-efficient landscapes in Utah [51]. 'Quonset' juniper, which is likely the hybrid Juniperus fassettii, survived temperatures of -40 F (-40 C) and 100 F (40 C) on low snow and heavy snow sites [37].

OTHER MANAGEMENT CONSIDERATIONS:
Relationships with associated native vegetation: In mixed-grass prairies of the Spruce Woods Provincial Park in southwestern Manitoba, 98.9% of white spruce seedlings occurred in association with creeping juniper. The researcher noted that creeping juniper likely provides a favorable microclimate for seedlings and may decrease the chance of white spruce mortality when prairie fires burn. Following prescription fires, creeping juniper mats were not completely burned, and white spruce seedlings in the unburned patches survived [21].

Relationships with associated nonnative vegetation: Several studies report decreases in creeping juniper abundance or animal use of creeping juniper habitats when sites are invaded by nonnative species. In mixed-grass prairies of Manitoba, creeping juniper cover was significantly (P<0.05) lower on prairies with a greater abundance of nonnative Eurasian species than on prairies dominated by native species. Native prairies dominated by blue grama (Bouteloua gracilis), obtuse sedge (Carex obtusata), porcupine grass (Hesperostipa spartea), and little bluestem had an average creeping juniper cover of 9.0%. Nonnative prairies dominated by smooth brome (Bromus inermis), Kentucky bluegrass (Poa pratensis), and/or leafy spurge had an average creeping juniper cover of 1.8%. Creeping juniper was significantly (P<0.05) correlated with Baird's sparrow in this area; Baird's sparrow was not detected on transects where nonnative Eurasian species dominated [122].

Creeping juniper-dominated stands in North Dakota's Theodore Roosevelt National Park suffered significant (p≤0.05) species richness loss when invaded by leafy spurge. Species richness in leafy spurge-free stands was 31.8/stand and 13.0 in infested stands. Differences in the abundance of creeping juniper on infested and uninfested stands were not reported [19]. Deer pellet density, which is typically highest in creeping juniper-little bluestem vegetation in the park, was reduced when vegetation was infested with leafy spurge. Researchers considered this vegetation type a lounge area for deer and thought that decreased use of type may be because of leafy spurge toxins [109].

Pests: Creeping juniper is a potential host for rust and blight infections; for more information, see [89].

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