Subalpine fir trees (Abies lasiocarpa) are a type of evergreen with many common names. Some call them Rocky Mountain fir or balsam fir, others say mountain balsam fir or alpine fir. While “alpine” technically means that a plant grows above the treeline, the subalpine fir lives in a wide range of elevations, from sea level to mountain tops.
What are the uses for subalpine fir? Homeowners use these firs for landscaping, but that’s not all. Anyone considering the various ways these firs can serve in a backyard should read on. We’ll give all the subalpine fir tree information you need.
I. Appearance and Characteristics
Abies lasiocarpa, the subalpine fir or Rocky Mountain fir, is a western North American fir tree.
Abies lasiocarpa is a medium-sized evergreen conifer with a very narrow conic crown, growing to 20 meters (66 ft) tall, exceptionally 40–50 m (130–160 ft), with a trunk up to 1 m (3 ft 3 in) thick, exceptionally 2.1 m (6 ft 11 in). The bark on young trees is smooth, gray, and with resin blisters, becoming rough and fissured or scaly on old trees. The lowest branches can be observed growing 1 m (3 ft 3 in) above ground level.
The leaves are flat and needle-like, 1.5–3 centimeters (5⁄8–1+1⁄8 in) long, glaucous green above with a broad stripe of stomata, and two blue-white stomatal bands below; the fresh leaf scars are reddish (tan on the inland variety). They are arranged spirally on the shoot, but with the leaf bases twisted to be arranged to the sides of and above the shoot, with few or none below the shoot. The cones are erect, 6–12 cm (2+1⁄4–4+3⁄4 in) long, dark purple with fine yellow-brown pubescence, ripening brown and disintegrating to release the winged seeds in early fall.
There are two or three taxa in subalpine fir, treated very differently by different authors:
- The Coast Range subalpine fir (Abies lasiocarpa) in the narrow sense, is the typical form of the species, occurring in the Pacific Coast Ranges, the Olympic Mountains and the Cascade Range from Southeast Alaska (Panhandle mountains) south to California.
- The Rocky Mountains subalpine fir is very closely related and of disputed status, being variously treated as a distinct species Abies bifolia, as a variety of Coast Range subalpine fir Abies lasiocarpa var. bifolia, or not distinguished from typical A. lasiocarpa at all. It occurs in the Rocky Mountains from Southeast Alaska (eastern Alaska Range) south to Colorado. It differs primarily in the chemical composition of its resin, microscopic features, and in the fresh leaf scars being yellow-brown, not reddish. The Flora of North America treats it as a distinct species, while the United States Department of Agriculture (USDA) includes it within A. lasiocarpa without distinction.
- The corkbark fir Abies lasiocarpa var. arizonica occurs in Arizona and New Mexico. It differs in thicker, corky bark and more strongly glaucous foliage. In resin composition it is closer to A. bifolia than to typical A. lasiocarpa, though the combination “Abies bifolia var. arizonica” has not been formally published. The Flora of North America includes it within A. bifolia without distinction; the USDA treats it as a distinct variety of A. lasiocarpa.
The species is native to the mountains of Yukon, British Columbia and western Alberta in Western Canada; and to Southeast Alaska, Washington, Oregon, Idaho, Western Montana, Wyoming, Utah, Colorado, New Mexico, Arizona, northeastern Nevada, and the Trinity Alps of the Klamath Mountains in northwestern California in the Western United States.
It occurs at high altitudes, commonly found at and immediately below the tree line. It can be found at elevations of 300–900 m (980–2,950 ft) in the north of the range (rarely down to sea level in the far north), to 2,400–3,650 m (7,870–11,980 ft) in the south of the range. West of the Cascade ridge, it can be found at elevations of 1,200–2,000 m (3,900–6,600 ft), while further east (particularly in Western Montana) it can be found from 1,500 to 2,700 m (4,900 to 8,900 ft).
II. How to Grow and Care
Sunlight
Subalpine fir thrives under full sun, where the intensity is paramount to its vigor and development. This plant prospers in environments with robust daily sunlight, which bolsters its growth and overall health. While subalpine fir is tolerant of partial sun, prolonged exposure to lower light levels may impede growth, potentially resulting in a thinner canopy and reduced vitality. Adaptive in nature, subalpine fir adjusts to varying light by altering needle density and orientation to maximize light capture. Ideally, subalpine fir should be planted in outdoor locations that provide maximum exposure to direct sunlight for optimal performance.
Temperature
Native to North and Central America, Europe and Asia, the subalpine fir prefers summer temperatures to be between 18 ℃ and 21 ℃. If temperatures rise and stay above 27 ℃ for too long, the tree will suffer. Conversely, if the temperature drops below -20 ℃ for an extended period in the winter, the tree may struggle to survive. The subalpine fir is best suited to mountain regions where it mostly grows in the wild, meaning that it can be a challenging tree to keep healthy in the Southern Hemisphere, unless it is at a high elevation.
Watering
Originating from mountainous regions, subalpine fir is adapted to environments with periodic moisture availability. It exhibits a preference for consistent moisture but can withstand short dry spells, indicative of its moderate drought tolerance. Watering for subalpine fir should be done once every 1-2 weeks, aligning with its natural intermittent water intake. As an evergreen plant commonly grown outdoors, subalpine fir’s ability to retain foliage year-round contributes to its steady water use throughout various seasons, requiring less frequent adjustments in watering routines compared to deciduous species.
Soil
The optimum soil for your subalpine fir would be a sand or loam soil that is well-draining, with a pH value of 6-6.5 (so slightly acidic). While the soil should stay moist and not dry out for long periods, try to avoid clay soil – this compacts easily and does not drain well, resulting in your subalpine fir becoming waterlogged.
Fertilizing
For optimal growth, subalpine fir requires fertilization with balanced nutrition fertilizers, such as those with a N-P-K ratio of 10-10-10 or similar. Apply annually, in spring, before new growth begins. Adequate fertilization ensures subalpine fir’s vigorous growth, improved natural conical shape, and enhances resilience. Use about 1/4 pound per inch of trunk diameter, sprinkled around the base, avoiding direct contact with the trunk. During establishment and active growth, subalpine fir might benefit from more frequent feeding. In winter, cease fertilizations to allow subalpine fir to naturally harden off. When applying fertilizer, water thoroughly to help absorption and prevent root burn. Always follow manufacturer guidelines for safe and effective use.
Pruning
The subalpine fir is a very low maintenance tree and requires little pruning. Other than for aesthetic purposes, the primary need for pruning is to remove dead, damaged, or diseased branches. The best time to prune is in late winter or early spring, just as the tree comes out of its dormant state – this can encourage new growth.
When pruning, focus on removing branches that are growing at a strange angle and rubbing against other branches, as this friction can become an entry point for disease. This is best done in a period of dry weather, but if this isn’t going to be possible for a while, it is best to deal with the problem a little sooner, regardless of the weather. Once you have removed problem branches, burn them instead of placing in a compost bin, as this can spread potential diseases.
Propagation
Subalpine fir is often propagated through sowing, with its seeds benefiting from stratification to enhance germination. Practical tips for gardeners include using well-draining soil, maintaining moderate moisture levels, and providing a stable temperature for successful seedling development. Careful handling is important due to its delicate root system during transplanting to a permanent location.
Transplanting
The ideal time to move subalpine fir is between late winter and early spring (S1-S3). This season offers cooler temperatures and regular rainfall, which helps this perennial plant to establish roots well. Choose a site with full to partial sun exposure. When transplanting subalpine fir, use a stake to support its growth.
Pests and Diseases
Pests and diseases can vary significantly by geographic region and local environmental conditions. The list below does not include every potential disease or pest issue. When treating disease or pest problems, it’s best to consult with a local extension service or professional arborist for specific recommendations.
Common Pests
- Balsam Woolly Adelgids (Adelges piceae): These are small, aphid-like insects that feed on the sap of fir trees, causing deformation of new growth, resulting in a “woolly” appearance, and, eventually, tree death.
- Bagworms (Thyridopteryx ephemeraeformis): Caterpillars that construct spindle-shaped bags covered with pieces of twigs and leaves. They defoliate trees, which can lead to reduced growth, branch dieback, and tree death in severe infestations.
- Fir Engraver Beetle (Scolytus ventralis): These beetles bore into the bark of the tree, which can cause the browning of the foliage and the eventual death of the tree.
- Spruce Budworms (Choristoneura spp.): This is the larval stage of a moth that primarily feeds on the buds and needles of spruce and fir trees. Infestations can cause severe defoliation and reduce tree vigor.
- Spruce Spider Mite (Oligonychus ununguis): These mites cause damage by sucking sap from the undersides of needles, leading to a speckled or mottled appearance.
- Western Balsam Bark Beetle (Dryocoetes confusus): Small, reddish-brown beetles that attack stressed fir trees. Damage: Their tunnels cut off nutrients and water flow, potentially leading to branch dieback or tree death.
Common Diseases
- Cankers: These are areas of dead tissue on the bark of a tree, often caused by fungal pathogens. Cankers can girdle branches or trunks, disrupting nutrient flow and causing dieback.
- Heart Rot: A fungal disease that causes decay in the heartwood of the tree.
- Needle Cast: This is a fungal disease that causes needles to turn color (usually brown or yellow) and drop prematurely from the tree. Over time, it can significantly weaken the tree and make it more susceptible to other stressors.
- Needle Rust: This is a fungal disease that causes yellow to orange pustules on needles. Infected needles often drop prematurely, and severe infections can lead to significant defoliation.
- Root Rot: This is a condition typically caused by a variety of soil-borne fungi. It causes the decay and death of root tissue, leading to a decline in the tree’s health and potentially causing tree death.
- Twig Blight: This is a condition usually caused by fungal pathogens, leading to the death of twigs and small branches. Symptoms often include discoloration, wilting, and dieback of twigs and branches.
III. Uses and Benefits
Native Americans used the leaves as deodorant and burned them as incense or medicinal vapor. Powdered bark and other components were used in solutions to treat colds. Resin was used to dress wounds or chewed as gum. The tree boughs were used for bedding. Some Plateau Indian tribes drank or washed in a subalpine fir boil for purification or to make their hair grow.
The light wood is considered poor quality, but sometimes used for wood pulp, general structural purposes and paper manufacture. It is also a popular Christmas tree. It is a popular ornamental tree for parks and large gardens, grown for its strongly glaucous-blue foliage. It can also function as a bonsai. The cultivar Abies lasiocarpa var. arizonica ‘Compacta’ is suitable for smaller gardens, growing as a shrub to 4 m (13 ft) tall by 1.5 m (4 ft 11 in) broad. In the UK It has gained the Royal Horticultural Society’s Award of Garden Merit.
The largest-known specimen, measuring 2.1 m (6 ft 11 in) thick and 39 m (129 ft) tall, had a small door in its trunk and a storage space, which the film crew of the Disney-produced documentary The Olympic Elk (1952) used to store equipment.
