Juniperus communis

Juniperus communis, the common juniper—also known as ground juniper (although ground juniper is often classified as var. depress)—is a wide-ranging shrub or small tree in the Cupressaceae (cypress family) native to cool temperate areas in the Northern Hemisphere, and may have one of the widest distributions of any woody plant. It is widely found in natural habitats, where its seed cones (“juniper berries”) and foliage are an important food source for numerous species of songbirds, ground-nesting birds, small mammals, and ungulate browsers, and there are dozens of horticultural cultivars for landscape and ornamental use (varying in form from spire-like to prostrate and trailing, and ranging in foliage color from blue to green to golden yellow). It is not used for timber due to its shrubby habit. The species has complex intraspecific variation, and according to one recent treatment, includes 7 major varieties: 3 in North America; 2 in northern Europe; and 1 in Japan. Some varieties, however, have very restricted habitat and distribution—for example, var. charlottensis occurs on Queen Charlotte island in British Columbia, Canada, in nearby Alaskan islands, and on adjacent parts of the British Columbia and Alaskan coasts—and are threatened by habitat degradation. Within North America, the ground juniper (var. depressa) is the most wide-ranging, extending through the northeastern U.S. and across much of Canada into Alaska, as well as extending south into the Rocky Mountains. It tends to grow well in disturbed areas, so its distribution has expanded during the past century. Juniperus communis is a shrub or small tree which has variable growth form, ranging from a low, spreading or upright shrub to a small tree, usually to 5 m (16.25 ft,) tall, but occasionally reaching heights up to 10 m (33 feet). Its leaves are sharp, needle-like but somewhat flattened, and ternate (occurring in threes), with a single white stomatal band on the upper side and a slight keel (ridge) on the underside. The species is dioecious—male and wind-pollinated female flowers grow on separate plants, and only female flowers develop seed cones, which have fused scales and are round and berry-like, up to 1 cm (0.5 in) in diameter. Seed cones ripen to blue or black with a glaucous (waxy) coating, and typically contain 3 to 6 seeds. The seed cones of various Juniperus species make up 2 to 5% of the diet of 66 species of North American mammals, and are also edible by humans—they add the characteristic flavor to gin, and they are featured in teas and herbal supplements. The species is often bird-dispersed, as seed germination rates may be higher following passage through a bird gut. (Adams 2008, Bailey et al. 1976, Martin et al. 1951, Royal Horticultural Society 2012.)

Juniper is a slow-growing tree which may live for up to 200 years. It is dioecious, meaning the male and female flowers are on separate plants. Pollen is dispersed by the wind and the fertilised female flowers eventually produce a hard, green berry. These finally ripen to the well-known blue-black fruit, popular with the birds that are largely responsible for the spread of the tree.

There are at least two subspecies of juniper. The best known, J. communis communis, whose bushes vary between a metre and 10 metres tall, can form tall, conical spires and often appear to have been trimmed into exotic shapes. The evergreen leaves are dark green and the stems are fiercely prickly. The dark purple berries are famous for being used as flavouring for gin. The other subspecies of the plant, J. communis nana, is a matted shrub that grows close to the ground. There might also be a third subspecies, J. communis hemisphaerica, found on sea cliffs in Cornwall and Pembrokeshire. Juniper has been part of human life for centuries. The spiny branches were used as an early form of barbed wire and the berries, as well as flavouring, were used in ancient medicines for horses as well as humans.

More info for the term: tree

Common juniper is possibly the most widely distributed tree in the world [78]. This circumboreal species occurs across North America, Europe, northern Asia and Japan [78,88]. Common juniper is almost completely circumpolar within the exception of a gap in the Bering Sea region [65]. It is widespread in North America beyond the northern limit of trees, occurring from western Alaska and British Columbia to Newfoundland, Greenland, and Iceland [78,88]. Common juniper extends southward through New England to the Carolinas and westward through northeastern Illinois, Indiana, northern Ohio, Minnesota, and Nebraska to the western mountains of Washington, California, Arizona, and New Mexico [47,56,78,88].

Distribution of North American varieties is as follows [47,56,78,88,136,63]:

Juniperus communis var. depressa northeastern North America, Idaho, Montana, the Great Plains, and Great Basin; found up to the low arctic in eastern North America

Juniperus communis var. montana high-northern latitudes, circumboreal [45]

Junipers are found across most of the UK and are one of our three native conifers, the other two being Scots pine (Pinus sylvestris) and yew (Taxus baccata). However, it is extremely irregular in its distribution. The subspecies Juniperus communis communis is found in two main populations, one in the Scottish Highlands and the other on the southern English chalk. It is also abundant on parts of the Chilterns, the North Downs and especially Salisbury Plain. Juniperus communis nana is chiefly restricted to north-west Scotland's mountainous regions. Elsewhere, juniper is a widespread tree, found across both temperate and sub-arctic zones.

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Distribution: Alpine and arctic Europe and Asia, N. Africa, N. America.

More info for the terms: shrub, tree, tundra

Common juniper is a native, evergreen shrub or columnar tree [78,136]. Throughout most of North America, common juniper most often grows as a low, decumbent mat-forming shrub reaching up to 4.9 feet (1.5 m) in height and 7.6 to 13.1 feet (2-4 m) across [47,123]. In parts of New England common juniper occasionally grows up to 25 feet (7.6 m) in height, and a treelike growth form is reportedly common in Europe [78]. Height at maturity can range from 2 to 50 feet (0.6-15.3 m) [66]. At polar limits, common juniper grows as a dwarf shrub in forest tundra [65].

The bark of common juniper is thin, shreddy or scaly, often exfoliating into thin strips [56,123]. Twigs tend to be yellowish or green when young but turn brown and harden with age [47,123]. Leaves are simple, stiff and arranged in whorls of 3 [56,123]. Younger leaves tend to be more needlelike whereas mature leaves are scalelike [88].

Male strobili are sessile or stalked, and female strobili are made up of green, ovate or acuminate scales [123]. Berrylike cones are red at first, ripening to a glaucous bluish-black [66].

Morphological characteristics including growth form differ somewhat according to variety. General botanical characteristics by variety are as follows [56,75,123,136]:

Juniperus communis var. depressa - rarely greater than 3 feet (1 m) tall
Juniperus communis var. montana A- low, trailing, mat-forming shrub, stems freely branched, usually less than 3 feet (0.9 m) tall

Individuals can live for more than 170 years [31].

Tree, Shrub, Evergreen, Dioecious, Habit erect, Plants prostrate or spreading, Trees without or rarely having knees, Tree with bark shaggy or peeling, Young shoots in flat sprays, Young shoots 3-dimensional, Buds not resinous, Leaves scale-like, Leaves whorled, Non-needle-like leaf margins entire, Leaf apex acute, Leaf apex obtuse, Leaf apex mucronulate, Leaves < 5 cm long, Leaves < 10 cm long, Leaves not blue-green, Scale leaves without raised glands, Scale leaf glands not ruptured, Scales leaves not or barely overlapping, Scale leaves overlapping, Twigs glabrous, Twigs not viscid, Twigs without peg-like projections or large fascicles after needles fall, Berry-like cones brown, Berry-like cones pink, Bracts of seed cone included, Seeds tan, Seeds brown, Seeds wingless.

Dioecious, shrubby decumbent plant. Branches dense. Leaves in whorls of threes, 8‑12 x 2‑4 mm, subulate, pungent, jointed at base, ± curved to suberect. Male cones axillary, c. 8 mm long; Female cones solitary, 20 mm long, scales 3. Fruit subglobose, bluish‑black, 8‑12 mm broad. Seeds 2‑3, ovoid.

Shrubs or small trees dioecious, to 4 m (if trees, to 10 m), multistemmed, decumbent or rarely upright; crown generally depressed. Bark brown, fibrous, exfoliating in thin strips, that of small branchlets (5--10 mm diam.) smooth, that of larger branchlets exfoliating in strips and plates. Branches spreading or ascending; branchlets erect, terete. Leaves green but sometimes appearing silver when glaucous, spreading, abaxial glands very elongate; adaxial surface with glaucous stomatal band; apex acute to obtuse, mucronate. Seed cones maturing in 2 years, of 2 distinct sizes, with straight peduncles, globose to ovoid, 6--13 mm, bluish black, glaucous, resinous to obscurely woody, with 2--3 seeds. Seeds 4--5 mm. 2 n = 22.

More info for the terms: heath, ultramafic soils

Common juniper can grow on a wide range of sites. It grows on dry, open, rocky, wooded hillsides, sand terraces, maritime escarpments, and on exposed slopes and plateaus throughout its range [18,31,47,50,123]. Common juniper grows along dunes or on dune heath in coastal areas of the Northeast and inland along the Great Lakes [23,101]. It has spread into abandoned fields and pastures in New England [101] and the upper Midwest during the past century. In the southeast it is found on isolated mountains [2].

This species grows on a variety of soil types including acidic and calcareous sands, loams, or marls [9]. It is tolerant of ultramafic soils [85]. In much of Europe common juniper is restricted to well-aerated soils somewhat deficient in both nitrogen and phosphorus. Growth on different soil types is rated as follows [32]:

gravel: fair to poor organics: fair to poor sand: fair to good acidic: fair sandy-loam: good saline: fair to poor loam: good sodic: poor clay loam: fair to poor sodic-saline: poor clay: fair to poor dense clay: poor The following elevational ranges have been reported for common juniper [54,136]:

6,230 to 11,148 feet (1900-3400 m) in CA
4,500 to 9,000 feet (1373-2745 m) in MT
5,295 to 11,065 feet (1615-3375 m) in UT
6,000 to 11,300 feet (1830-3955 m) in WY

Juniperus communis var. depressa grows in crevices in heath mats in Michigan and on nutrient-poor open habitats such as sand dunes or rocky outcrops in the Canadian subarctic [22,63].

More info for the term: codominant

Common juniper is an indicator in a number of forest and
shrubland habitat types and community types. It grows as an
understory dominant with ponderosa pine (Pinus ponderosa),
Douglas-fir (Pseudotsuga menziesii), lodgepole pine
(Pinus contorta), limber pine (P. flexilis),
white fir (Abies concolor), Engelmann spruce (Picea engelmannii),
white spruce (P. glauca), quaking aspen (Populus tremuloides),
blue spruce (Picea pungens), whitebark pine (Pinus albicaulis),
subalpine fir (A. lasiocarpa), or Rocky Mountain bristlecone pine (P. aristata).

Common associates in northern Utah include common snowberry
(Symphoricarpos albus), gooseberry currant
(Ribes montigenum), Oregon-grape (Mahonia repens),
hairy telegraphplant (Heterotheca villosa), timber
milkvetch (Astragalus miser), silvery
lupine (Lupinus argenteus), Thurber fescue
(Festuca thurberi), elk sedge (Carex geyeri), and
bottlebrush squirreltail
(Elymus elymoides) [84,90]. Common juniper is listed as a
codominant indicator species in the following classifications:

Old-growth forests of the Canadian Rocky Mountain national
parks [1]

Forest vegetation on National Forests in the Rocky Mountain and
Intermountain Regions: habitat and community types [4]

Forest vegetation of the Medicine Bow National Forest in southeastern
Wyoming: a habitat type classification [5]

Classification of the forest vegetation on the National Forests of
Arizona and New Mexico [6]

The vegetation of the Grand River/Cedar River, Sioux, and Ashland
Districts of the Custer National Forest: a habitat type
classification [49]

Preliminary forest habitat types of the Uinta Mountains, UT [51]

Forested plant associations of the Olympic National Forest
[52]

Forest vegetation of the Arapaho and Roosevelt National Forests in
central Colorado: a habitat type classification [53]

Forest vegetation of the Bighorn Mountains, Wyoming: a habitat type
classification [57]

Forest vegetation of the Routt National Forest in northwest
Colorado: a habitat type classification [58]

Forest vegetation of the Black Hills National Forest of South Dakota and
Wyoming: a habitat type classification [59]

Forest vegetation of the Gunnison and parts of the Uncompahgre
National Forests: a preliminary habitat type classification
[72]

Forest and woodland habitat types (plant associations) of
northern New Mexico and northern Arizona [74]

Field guide for forested plant associations of the Wenatchee
National Forest [76]

Coniferous forest habitat types of northern Utah [84]

Aspen community types of the Intermountain Region [89]

Aspen community types of Utah [90]

A forest habitat type classification of southern Arizona and its
relationship to forests of the Sierra Madre Occidental of
Mexico [91]

Forest habitat types of Montana [100]

Forest habitat types of central Idaho [122]

Coniferous forest habitat types of central and southern Utah [138]

Aspen community types on the Bridger-Teton National Forest in
western Wyoming [139]

Classification and gradient analysis of forest vegetation of
Cape Enrage, Bic Park, Quebec [140]

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This species is known to occur in association with the following Rangeland Cover Types (as classified by the Society for Range Management, SRM):

More info for the term: shrub

109 Ponderosa pine shrubland

110 Ponderosa pine-grassland

216 Montane meadows

314 Big sagebrush-bluebunch wheatgrass

315 Big sagebrush-Idaho fescue

401 Basin big sagebrush

410 Alpine rangeland

411 Aspen woodland

902 Alpine herb

904 Black spruce-lichen

907 Dryas

912 Low scrub shrub birch-ericaceous

916 Sedge-shrub tundra

920 White spruce-paper birch

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This species is known to occur in association with the following plant community types (as classified by Küchler 1964):

K001 Spruce-cedar-hemlock forest

K002 Cedar-hemlock-Douglas-fir forest

K005 Mixed conifer forest

K008 Lodgepole pine-subalpine forest

K011 Western ponderosa forest

K012 Douglas-fir forest

K013 Cedar-hemlock-pine forest

K015 Western spruce-fir forest

K016 Eastern ponderosa forest

K017 Black Hills pine forest

K018 Pine-Douglas-fir forest

K019 Arizona pine forest

K020 Spruce-fir-Douglas-fir forest

K021 Southwestern spruce-fir forest

K022 Great Basin pine forest

K023 Juniper-pinyon woodland

K037 Mountain-mahogany-oak scrub

K038 Great Basin sagebrush

K040 Saltbush-greasewood

K052 Alpine meadows and barren

K055 Sagebrush steppe

K056 Wheatgrass-needlegrass shrubsteppe

K063 Foothills prairie

K064 Grama-needlegrass-wheatgrass

K065 Grama-buffalograss

K066 Wheatgrass-needlegrass

K067 Wheatgrass-bluestem-needlegrass

K081 Oak savanna

K093 Great Lakes spruce-fir forest

K095 Great Lakes pine forest

K096 Northeastern spruce-fir forest

K097 Southeastern spruce-fir forest

K098 Northern floodplain forest

K110 Northeastern oak-pine forest

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This species is known to occur in the following ecosystem types (as named by the U.S. Forest Service in their Forest and Range Ecosystem [FRES] Type classification):

FRES11 Spruce-fir

FRES15 Oak-hickory

FRES17 Elm-ash-cottonwood

FRES19 Aspen-birch

FRES20 Douglas-fir

FRES21 Ponderosa pine

FRES23 Fir-spruce

FRES26 Lodgepole pine

FRES28 Western hardwoods

FRES29 Sagebrush

FRES30 Desert shrub

FRES34 Chaparral-mountain shrub

FRES35 Pinyon-juniper

FRES36 Mountain grasslands

FRES37 Mountain meadows

FRES38 Plains grasslands

FRES44 Alpine

Differing from the type variety in the decumbent habit and recurved larger leaves. Forms dense patches near the tree limit and up to 4200 m. Fruit medicinal.

Systems

• Terrestrial

Juniper is found on well-drained rocks and soils and tolerates extremes of climate and pH. In Scotland, it occurs on cold, wet acid sites and grows amongst heather and whinberries. In the south of England it is found on hot, dry chalky hillsides. The largest southern population of juniper in England is inside the Ministry of Defence's Establishment at Porton Down in Wiltshire. Here there are estimated to be over 14,000 bushes. It is thought that many of these date from the introduction of myxomatosis and the reduction of the rabbit population, which led to reduced grazing of the seedlings.

In Great Britain and/or Ireland:
Plant / epiphyte
resupinate fruitbody of Amylostereum laevigatum grows on dead, fallen branch of Juniperus communis

Foodplant / saprobe
fruitbody of Basidiodendron rimosum is saprobic on dead, decayed wood of Juniperus communis
Other: minor host/prey

Foodplant / saprobe
sessile to subsessile apothecium of Calycellina juniperina is saprobic on leaf of Juniperus communis

Foodplant / sap sucker
Chlorochroa juniperina sucks sap of Juniperus communis

Foodplant / saprobe
epiphyllous, erumpent, solitary or a few together, short-stalked apothecium of Chloroscypha sabinae is saprobic on dead leaf of Juniperus communis
Remarks: season: 9-3

Foodplant / pathogen
erumpent apothecium of Colpoma juniperi infects and damages live twig of Juniperus communis
Remarks: season: 5-7

Foodplant / sap sucker
nymph of Cyphostethus tristriatus sucks sap of ripe berry of Juniperus communis
Other: major host/prey

Foodplant / parasite
epiphyllous, immersed apothecium of Didymascella tetraspora parasitises live leaf of Juniperus communis

Foodplant / gall
emergent telium of Gymnosporangium clavariiforme causes gall of witches broom branch of Juniperus communis
Remarks: season: 4-5
Other: sole host/prey
minor host/prey

Foodplant / parasite
telium of Gymnosporangium cornutum parasitises live leaf of Juniperus communis
Remarks: season: 4-6
Other: unusual host/prey

Foodplant / saprobe
epiphyllous acervulus of Seimatosporium coelomycetous anamorph of Gymnosporangium juniperi is saprobic on dead leaf of Juniperus communis

Foodplant / saprobe
fruitbody of Hyphodontia arguta is saprobic on dead, decayed wood of Juniperus communis
Other: minor host/prey

Foodplant / saprobe
fruitbody of Hypochnella violacea is saprobic on dead, decayed wood of Juniperus communis
Other: unusual host/prey

Foodplant / saprobe
superficial pseudothecium of Kriegeriella minuta is saprobic on dead, fallen leaf of Juniperus communis
Remarks: season: 8-3

Foodplant / saprobe
superficial or erumpent through cracks in bark ascocarp of Lophium elegans is saprobic on dead wood of Juniperus communis

Foodplant / saprobe
hysteroid apothecium of Lophodermium juniperinum is saprobic on dead leaf of Juniperus communis
Remarks: season: 8-10

Foodplant / saprobe
spongy, pulvinate colony of Capnophialophora anamorph of Metacapnodium juniperi is saprobic on twig of Juniperus communis

Foodplant / open feeder
larva of Monoctenus juniperi grazes on needle of Juniperus communis
Other: sole host/prey

Foodplant / gall
larva of Oligotrophus juniperinus causes gall of uppermost leaves of Juniperus communis

Foodplant / saprobe
resupinate fruitbody of Peniophora cinerea is saprobic on dead wood of Juniperus communis
Other: unusual host/prey

Plant / resting place / on
apothecium of Rutstroemia juniperi may be found on recently dead twig (small) of Juniperus communis
Remarks: season: 5-9

Foodplant / saprobe
subcuticular mycelium of Seynesiella juniperi is saprobic on dead leaf of Juniperus communis

Foodplant / saprobe
superficial synnema of Sphaeridium anamorph of Sphaeridium candidum sensu Fuckel is saprobic on dead cone of Juniperus communis
Remarks: season: 1-12

Foodplant / saprobe
sporodochium of Stigmina dematiaceous anamorph of Stigmina glomerulosa is saprobic on leaf of Juniperus communis

Plant / resting place / on
female of Thrips juniperinus may be found on live Juniperus communis
Remarks: season: 1-12

Foodplant / saprobe
fruitbody of Trechispora kavinioides is saprobic on dead, fallen, decayed twig of Juniperus communis

Plant / associate
basidiocarp of Tremella karstenii is associated with branch of Juniperus communis

Foodplant / feeds on
Trisetacus juniperinus feeds on Juniperus communis

Foodplant / feeds on
Trisetacus quadrisetus feeds on Juniperus communis

Foodplant / saprobe
punctiform sporodochium of Troposporella dematiaceous anamorph of Troposporella monospora is saprobic on dead leaf of Juniperus communis

Foodplant / saprobe
Tubulicrinis accedens is saprobic on dead, decayed wood of Juniperus communis

Foodplant / saprobe
Tubulicrinis subulatus is saprobic on dead, decayed wood of Juniperus communis
Other: minor host/prey

More info for the term: severity

Common juniper does not sprout after disturbance. Surviving individuals serve as sources of seed for adjacent areas. Postfire regeneration is more frequent in proximity to existing populations of common junipers [31]. Regrowth can generally take place after fire if some of the basal branches remain alive [82], which only occurs in fires of low severity or where spread is patchy.

Common juniper also reestablishes after fire through off-site seed dispersed by birds or mammals. Poor seed dispersal from existing stands along with low germination rates can explain why some favorable sites are not readily occupied by common juniper [31].

It is possible that seed protected by overlying soil can survive at least some fires. After low-severity fires, some seed may germinate. However, Mallik and Gimingham [82] observed that high temperatures did not increase germination in common juniper seed and little seed germinated after fire.

More info for the term: heath

In a Scottish study, common juniper was killed by 1,472 oF (800 oC) heat treatment when heath was burned. Plants made only "feeble regrowth" when burned at 1,112 oF (600 oC). However, following treatment at 752 oF (400 oC), new shoots were produced [82].

More info for the terms: fire regime, fire severity, severity

Common juniper is generally killed or seriously damaged by fire [24,25]. Patchy fires may allow individual plants to survive in protected areas such as on rocky cliffs. More rarely, portions of a lightly-burned plant may survive. The amount of damage this species incurs increases with increasing fire severity [120].

In the boreal forest of Quebec, at least 37% of common junipers survived fire. Although the dominant fire regime here is crown fires or "important surface fires covering large areas," common juniper often survives on sites made up of exposed bedrock or where protected by lakes and island complexes. Survival can occur if fire affects only part of an area or where fires are of low intensity. In some cases, fires of low intensity "can allow sections of the plant to survive and reproduce vegetatively" [31].

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More info for the terms: climax, competition, lichens, succession

Common juniper is intolerant of shade and is usually found in open environments [31]. Common juniper is often regarded as a colonizing plant but reaches maximum abundance on harsh, stressed environments in which competition is lacking [31,107]. Common juniper occurs as an important understory species in a number of climax communities within the southern Rocky Mountains including some Douglas-fir, subalpine fir, limber pine, Engelmann spruce, and blue spruce stands [6,91,122]. Common juniper becomes prominent in many high-elevation spruce-fir forests in Colorado as much as 100 years or more after fire or other disturbance [21]. In the boreal forest of eastern Canada, however, common juniper begins to decline after approximately 70 years after disturbance. On harsh open sites, it can persist for much longer which creates patchy habitats [31].

Common juniper is described as a seral species in common juniper/bearberry (Arctostaphylos uva-ursi) communities of the southwestern Yukon where it is ultimately replaced by spruce (Picea spp.) and buffaloberry (Shepherdia canadensis) [34]. In Arizona and Colorado, common juniper is prominent in seral stands with Oregon-grape [36] and in the northern Rocky Mountains, it occurs in late seral stands in Douglas-fir/ninebark (Physocarpos malvaceus) and Douglas-fir/Rocky Mountain maple (Acer glabrum) habitat types [121]. It is prominent in old-field or "early settlement" communities of New England, but it "disappears" from areas maintained in timber [39,40]. In pitch pine (Pinus rigida) communities of New England, common juniper replaces initial colonizers such as lichens, blueberries (Vaccinium spp.), and grasses, and is in turn, replaced later in succession by pitch pine [87]. In black spruce communities of northern Saskatchewan, common juniper is most prevalent in secondary successional stages occurring from 11 to 30 years after disturbance [113]. In Michigan, common juniper is a colonizer on dune blowouts [96].

More info for the terms: adventitious, cover, dioecious, monoecious, shrubs

Common juniper is typically dioecious but occasionally monoecious [128]. Seed usually matures during the second growing season [56,123,126,136], although there have been some reports of cones maturing within only one season [128].

Common juniper produces large cone crops at irregular intervals [66]. Cones are ovoid to ellipsoid [123] and contain 1 to 3 seeds [56,128]. Germination rates for common juniper seed are relatively poor and defective seed may also be relatively common. Pack [97] reported that up to 60% of common juniper seeds examined were defective. In northwestern Quebec, the majority of seeds produced by "older" plants (94.8%) were non-viable. A majority of seeds produced by "younger" plants (80%) were viable. Approximately 40 to 60% of "older" plants were sterile [31]. Under harsh conditions, female plants may decrease reproductive efforts and less viable seed is produced [83].

Germination and seedling establishment of common juniper is "difficult" [31,60]. Ideal germination conditions are moist, compact soil with sufficient oxygen diffusion [31]. Germination has been reported to range from 7 to 75%, depending on the specific treatment and seed source [66].

Juniper seeds have a semipermeable and thick seedcoat with a dormant embryo [97]. Common juniper seed requires a period of warm temperatures followed by a period of cold temperatures lasting approximately 7 months [31]. Generally the germination rate of seeds that are not afterripened is only around 1% [97]. High temperatures, alternating temperatures, freezing and thawing, removal of the seedcoat, or the application of hydrogen peroxide, dilute acids, carbon dioxide, or light had little influence on the germination of juniper seeds.

Steele and Geier-Hayes [121] report that common juniper seed is dispersed by animals and not stored in the soil. However, Major and Pyott [80] report that common juniper seed persists in cropped soils in California. Seeds of common juniper are dispersed by gravity, water, birds, or mammals. Digestive processes apparently do not harm most juniper seeds and may actually enhance germination [8,37]. Birds are the most important dispersal agents of common juniper [31]. More than 60 to 85% of common junipers present in the sand dune region surrounding Lake Michigan are believed to have originated from bird-disseminated seed. Birds also contribute to the spread of common juniper into old fields of New England [101]. Rosen [109] reports that domestic sheep may also serve as a dispersal agent since junipers are often associated with sheep driveways. Strong winter winds can push seeds across frozen snow cover [109].

Increases observed in seedling numbers during certain periods are the result of favorable conditions for establishment. Establishment is more likely in open spaces between older shrubs and may be favored by grazing [109].

Common juniper does not sprout after foliage is removed. However, adventitious root development can occur when branches come in contact with the ground become buried. In the subarctic, plants are often buried at least partially, and production of adventitious roots may aid in water and nutrient intake. A higher proportion of common juniper cuttings from northern populations rooted as compared with southern cuttings. Cuttings from female shrubs may exhibit better rooting potential than cuttings from male plants [63].

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More info for the term: phanerophyte

Phanerophyte

More info for the terms: shrub, tree

Shrub, tree

Year Assessed

• Needs updating

Assessor/s

Reviewer/s

Justification

Protected in the UK under Schedule 8 of the Wildlife and Countryside Act as amended.

Canada

Rounded National Status Rank: N5 - Secure

United States

Rounded National Status Rank: N5 - Secure

Rounded Global Status Rank: G5 - Secure

Reasons: Throughout western United States and Canada, usually on rocky or sandy wooded hillsides.

Juniper is believed to have declined by up to 60% of its pre-1960 population, although with adult bushes being long-lived, it is possible for moribund populations with no regeneration to affect the true status of the species. The biggest threat to the plant is over-grazing, which prevents the regeneration of young bushes. However, too little grazing also affects the spread of juniper by allowing larger trees to shade out the adult bushes. In the uplands, juniper is also threatened by moorland burning for game shooting, which prevents the plants regenerating or leads to a fragmented cover. However, the threat to the species is greater in England than it is in Scotland.

More info for the terms: cover, density

Common juniper generally appears to increase in response to grazing
[19,102]. Butler [19] observed highest relative common juniper
cover in stands heavily grazed by cattle in green ash (Fraxinus pennsylvanica) draws
of the North Dakota badlands as follows:

Density Relative Foliar Relative (stems/m2) density cover (%) cover lightly grazed* 0.01 0.02 0.59 0 moderately grazed 0.01 0.23 2.15 3 heavily grazed 0.07 0.11 2.40 5
*sites were classified by the number of trails, extensiveness of
lounging areas and distance from water into moderate and heavily
grazed.

Juniper is listed under the UK Biodiversity Action Plans and included in English Nature's Species Recovery Programme. It is also part of Plantlife's 'Back from the Brink' project. Many juniper populations are within Sites of Special Scientific Interest (SSSIs), and there are grants available to landowners to encourage proper management of the plant. The Forestry Commission Woodland Grant Scheme is also being used to maintain populations where these occur within a woodland context. Juniper is a component of several important habitats, particularly upland scrub woodland, and the loss of this species within this habitat removes a vital element of its biodiversity. It is also planned to carry out a series of regional surveys to assess the age range and reproductive potential of native juniper populations. This information will enable new populations to be established in areas where trees have been lost in order to restore the associated habitats.