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Wildlife, Animals, and Plants
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BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Juniperus osteosperma
| Utah Juniper
Utah juniper is a short tree that may live as long as 650 years [83]. Utah junipers grow less than 26.4 feet (8 m) and are often as short as 9.9 to 14.85 feet (3-4.5 m), with a trunk 4 to 7.5 inches (10-30 cm) thick [67,66,75,100]. Sometimes the tree has multiple stems [4].
Under severe site conditions, Utah juniper trees persist in very stunted forms. A 6-inch tree with a 24-inch (60 cm) taproot may be over 50 years old [80]. Utah junipers grow very slowly, usually only about 0.05 inch (0.127 cm) in diameter per year [58,88].
Utah junipers have a taproot that extends deep into the soil (as far as 15 feet (4.5 m)) and lateral roots that may extend as far as 100 feet (30.3 m) from the tree, several inches below the soil surface. Most root biomass is within the first 3 feet (0.9 m) of soil, with fine roots concentrated in the uppermost 18 inches (46 cm) [111] or just below the soil surface [119]. Utah juniper responds to low nutrient levels in the soil by developing extensive networks of fine roots at the base of the tree and at the end of lateral roots. These roots are in part responsible for the competitiveness of juniper versus understory species [72,78]. Junipers compete more efficiently for soil moisture than do herbaceous understory plants; therefore, over time, junipers are more likely to maintain a stable population, while understory plants decrease [8,50,114].
A Utah study concluded that Utah junipers do not use soil moisture from summer precipitation and do not have active roots in shallow soils layers during the summer [40].
Utah juniper is colonized by vesicular-arbuscular mycorrhizae [77].
Phanerophyte
Utah juniper is monoecious and sometimes dioecious [4,67,54,80,123]. It reproduces by seeds in cones and produces abundant seeds in most years [4] or every couple of years [9,62]. Cones have 1 or 2 seeds [66]. The seeds have dormant embryos and impermeable seedcoats, so they need a period of "after-ripening" and usually germinate the second season following maturity [120].
Utah junipers begin to produce seed only when they are about 30 years old [24,58]. Utah juniper seeds are long-lived. In one study, 17% of Utah juniper seeds germinated after 45 years [4,j71]. In general, about 8 to 49% of Utah juniper seeds germinate [58].
Animal transport of seeds is an important factor in the dissemination of juniper seeds [9,24,88], especially by jackrabbits [10,103]. Seeds that have passed through the digestive tract of animals germinate more quickly than those that have not [4].
Utah juniper thrives on very dry sites [66,80,88]. Precipitation patterns in juniper communities vary, but Utah juniper is generally found in areas of 12 to 18 inches (305-457 mm) of precipitation, with extremes of below 10 inches (254 mm)/year [97] to highs of 20 inches (508 mm)[31,88,114]. Utah juniper usually occurs in areas with hot, dry summers and cold, wet winters [9,59,93], although Utah juniper is also commonly found in areas of summer monsoonal precipitation in New Mexico and Arizona [114].
Utah juniper commonly grows on alluvial fans and dry, rocky hillsides [10,67,97,107], with shallow, alkaline soils [27]. Utah juniper is considered a "sodium-sensitive" species [27,107]. In west-central Utah, Utah juniper is found on a range of soil textures, but most often on gravelly loams and gravelly clay loams with a pH range of 7.4 to 8.0 [10]. In the Big Horn Mountains of Wyoming, Utah juniper dominates on limestone soils, whereas ponderosa pine (Pinus ponderosa) in the same elevations dominates on soils derived from granites and sandstones [2].
Decaying organic material below juniper trees may result in a 0.4 to 0.8 inch (1-2 cm) thick water-repellent soil surface [101,102]. Fire apparently destroys this water repellency [101].
Utah juniper occurs at 3,000 to 8,000 feet (909-2424 m) elevation in the Great Basin [80]. In Arizona, Utah juniper occurs at 3,000 to 7,500 feet (909-2273 m) [75], more commonly above 5,000 feet (1515 m) [89]. In California, the plant is common from 4290 to 8580 feet (1300-2600 m) [66] and found as high as 10,000 feet (3030 m) in the Sierra Nevada [9]. In Utah, Utah juniper is found most often from 5,000 to 7,000 feet (1,500-2,100 m) [37]. The upper limits of the pinyon-juniper zone in Utah and northeastern Arizona are from 6,500 feet (1970 m) on north-facing slopes to 8,400 feet (2545 m) on south-facing slopes [6].
Utah juniper is not shade tolerant [88]. It is a climax species in harsh areas where stands are open and regeneration can occur without competition for light.
Across the West, junipers have expanded their historical range in the years since European settlement [4,19,24,29,30,73,116,124], especially into sagebrush-grass communities below areas of traditional pinyon-juniper [10,36,86]. Overgrazing, fire suppression, and climatic change have been identified as potential causes of juniper invasion [19,30,33,37,42,86,95,114]. In the absence of fire or other disturbances, trees eventually dominate the site and crowd out herbaceous and shrub species [4,10,19]. On the Fort Apache Indian Reservation in Arizona, herbaceous cover on a grazed area was twice as high after clearing junipers as on control plots [5].
Juniper litter has an allelopathic effect on some understory species, especially Idaho fescue (Festuca idahoensis), Sandberg bluegrass, and blue grama [24,44,50,70,120]. This effect is particularly evident on heavy, poorly drained clay soils [70]. Broadcasting grass seeds over litter appeared to lower the allelopathic effects [44].
Cheatgrass does not appear to suffer from allelopathic effects [44], and fourwing saltbush (Atriplex canescens) growth increases under juniper canopies [72].
Utah juniper seeds germinate in the spring [13].
Seasonal development of Utah juniper in Arizona is as follows [64]:
| Phenological stage |
Date |
| Bark begins to slip |
March 25 |
| Pollen shedding; seed cones open |
March 25 |
| Approx. start of leader elongation |
April 20 |
| First conspicuous new pollen cones |
August 19 |
| Bark begins to stick |
September 15 |
| Leader elongation ceases |
October 19 |
Related categories for
SPECIES: Juniperus osteosperma
| Utah Juniper
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