• GENERAL BOTANICAL CHARACTERISTICS
• RAUNKIAER LIFE FORM
• REGENERATION PROCESSES
• SITE CHARACTERISTICS
• SUCCESSIONAL STATUS
• SEASONAL DEVELOPMENT

GENERAL BOTANICAL CHARACTERISTICS:

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].

RAUNKIAER LIFE FORM:

Phanerophyte

REGENERATION PROCESSES:

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].

SITE CHARACTERISTICS:

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

SUCCESSIONAL STATUS:

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].

SEASONAL DEVELOPMENT:

Common juniper begins leader elongation in the spring. "Flowering" or cone development dates vary somewhat according to geographic location, but cone development generally occurs from April through June [47,56,66]. Generalized cone development dates by state are as follows [32]:

State          Beginning     End of
               cone          cone
               development   development
Montana        April         May
North Dakota   April         May
Wyoming        April         May

Related categories for SPECIES: Juniperus communis | Common Juniper