Juniperus occidentalis, or the western juniper tree, is a large shrub or small tree that is native to the western United States. Part of the Cupressaceae family, this tree only grows at the high altitudes in the rocky mountains of the Pacific Northwest.
The juniper family is a proud botanical family. Members of this family account for some of the oldest trees on the planet, the most resilient, some of the largest, and some of the most productive and widespread woody plants.
If you’re feeling curious about other juniper trees, or other trees in general, head on over to 101 Types of Trees where we cover amazing tree species from all around the world. Want to learn more about fruit trees? We’ve got you covered. Want to learn more about old growth? We’ve covered that too!
What do Western Juniper Trees Look Like?
Juniper trees are known for possessing extremely well-developed and wide-spreading root systems. Since this tree species is known to grow in some pretty severe places, it’s a given that it will develop roots that can keep the tree alive in infertile soil, almost no water, and ample sunlight.
The western juniper will develop both lateral roots and a taproot. These massive lateral roots only grow within the top 30 inches of the soil, and they can sometimes extend farther than 3 times the width of the tree canopy. A mature tree will start to develop thin surface roots from these lateral roots to help the tree access nutrients in the topsoil.
Western junipers will also develop a giant taproot. Usually taproots grow super deep into the soil, but that is not the case for the western juniper. Their taproot is actually shorter than the lateral roots are wide. Taproots help create stability, and help the tree access moisture reserves deep in the earth.
Western junipers are pretty small trees, and will grow to be anywhere between 5 and 15 meters in height. Some will call this a small tree, whereas others might refer to it as a large bush.
The largest western juniper on record live in Oregon, and it is only 24 meters tall with a trunk diameter of 5.5 meters! Though small compared to other tree species, that is one girth-y tree!
The western juniper tree has a very full crown with heavy lateral branches. A crown will have either a rounded or a pointed form, but the tree will always look as though the branches are heaving under the weight of their foliage.
Western juniper bark is quite furrowed and shreds away regularly. The bark is a distinct red/brown colour – one of the more identifiable characteristics of the juniper tree – and is rather thin on young trees, and grows to be much thicker on older trees.
This bark thickening helps mature trees protect themselves against fire damage, as wildfires are a very common occurrence in the growing regions of juniper trees.
Western junipers are evergreen conifers, meaning that they possess cones and needles instead of flowers and broadleaves, and that their foliage will persist all year long.
Juvenile leaves (that only occur on very young seedlings) are more needle-like, and are 5-10mm long. Mature western junipers produce leaves in a scale-like form, and they are 1-2mm long.
They are arranged in opposite decussate pairs along a twig and they occur in whorls of tree. The scales are soft to the touch, have a noticeable scent, and are a lovely blue/green color – which is another identifiable characteristic on the juniper species.
How do Western Juniper Trees Reproduce?
The western juniper tree can be either monoecious or dioecious. It usually depends on the growing site and growing conditions. Juniper cones are often referred to as a juniper berry.
Monoecious means that both female cones (seed cones) and male cones (pollen cones) will occur on the same tree. Dioecious means that female cones and male cones will occur on separate trees.
Both a pollen cone and a seed cone will look rather similar. Cones are berry-like in appearance – this is another identifiable characteristic of a juniper tree – and are 2-4mm long. On western junipers, they are a blue/brown color with a white waxy bloom.
Male cones will shed their pollen in the early spring, and the pollen will enter a seed cone. Seed cones contain 3 seeds and take 18 months to mature after their original pollination.
Juniper seeds are dispersed by the animals that eat the juniper cones. These tasty little berry-like cones are grazed upon by many insect, mammal, and bird species, and their digestive tracts actually help with the germination of the juniper seeds.
Western junipers will only start to bear cones around 20 years of age, with their most productive seed crops occur when they are around 50 years old. Mature trees will produce huge seed crops every year, whereas younger trees will only have productive yields every 3-5 years.
What are Some Other Juniper Species?
The Sierra Juniper Tree (Juniperus Grandis)
This tree is also sometimes called the Sierra western juniper tree, though it is technically a small shrub. The Sierra juniper is a tree that is endemic to the western side of North America, and only occurs in small populations in the Sierra Nevada and California.
The Sierra juniper has a stout trunk, red bark that peels off in long sheet-like plates, and grows to be anywhere from 12-26 meters tall.
The Common Juniper Tree (Juniperus Communis)
The common juniper tree has the largest geographical range of any other woody plant. They are exceptionally adaptable and resilient. They grow anywhere on the planet that has temperate and dry growing conditions.
The Rocky Mountain Juniper Tree (Juniperus Scopulorm)
The rocky mountain juniper tree is native to the west coast of North America. They grow specifically in high altitude regions of British Columbia, Alberta, North Dakota, Arizona, New Mexico, and Texas. They grow in dry soils within the top 500 to 2700 meters of altitude. Scopulorum is latin for “of the mountains”, and these trees only grow to be between 5 and 15 meters.
The VirginianJuniper Tree (Juniperus Virginiana)
Virginian juniper trees are also known as the red cedar, eastern redcedar, eastern juniper, or aromatic cedar. They are native to the eastern part of North America, and are the most cold hardy of the juniper trees. They many never grow to be larger than a bush, only obtaining heights of 5 to 20 meters.
The Utah Juniper Tree (Juniperus Osteosperma)
The Utah juniper tree is one of the smallest juniper species, and is more of a shrub than a tree with heights of 3 to 6 meters. They are native the driest regions of the United States, in Utah, Nevada, Arizona, New Mexico, Colorado, Wyoming, Montana, Idaho, and California. They grow at moderate altitudes.
Where do Western Juniper Trees Grow?
Western junipers grow in the Pacific Northwest mountains at high altitudes, usually occurring anywhere between 800 to 3000 meters in elevation. They can be found in Washington, northeastern California, all throughout Nevada, Idaho, and in both eastern Oregon and central Oregon.
A juniper woodland occurs from the Cascade range in Washington towards eastern Idaho, then throughout Nevada and southern California.
Juniper forests can be found growing in dry, rocky sites, where there is less competition for nutrients and water against larger species like the coast Douglas fir and the ponderosa pine.
These trees prefer to grow in canyons, upper slopes, flats, playas, mesas, and foothills. In areas where they receive ample sunlight, they act as more of a herbaceous cover.
What are the Growing Conditions of Western Juniper Trees?
The western juniper prefers dry rocky sites. These soils can be clay soils, rimrock, or rocky soils. The soil is usually very shallow and low in organic matter.
The western juniper tree will only exist in full sun conditions.
Juniper trees are used to not receiving tons of water supply. They occur in regions with extremely low annual precipitation and humidity, and are exposed to high winds. This is why their root systems needs to be so developed, since the soil they grow in could just blow away at any time!
Western juniper trees can exist in temperatures ranging from 36 to 105 degrees Fahrenheit.
What is the Forest Ecology of the Western Juniper Tree?
Western juniper cones are a very important source of food for varies animal and bird species, including mule deer, sage grouse, the American robin, Clark’s nutcracker, and cedar waxwing.
These animals also help disperse juniper seeds by digesting the cones and dispersing the seeds in their droppings.
There has been a noticeable juniper invasion throughout the sagebrush steppe ecosystems of the western United States. Rangeland ecology shows that this has occurred because of fire suppression, overgrazing of livestock, and change in climate. Western junipers are quickly becoming a native invasive species.