LAOC

Larix occidentalis

Western larch

Pinaceae

The Basics

USFS Plant Database

Flora of North America

Western larch is a fast growing, long-lived, deciduous conifer native to alpine and subalpine forests of the northwestern United States and adjacent Canada. Trees over 900 years old have been reported...Western larch occurs in mountain valleys and lower slopes, often in somewhat swampy areas. It needs well-lighted areas for maximum development, so it performs best in open stands. Western larch is usually found at elevations of 460-1,700 m in the northern portions of its range and may be found at elevations over 2,100 m in the southern parts of its distribution.

Western larch is not considered a climax species, but it is a long-lived early successional species...Western larch uses nitrogen more efficiently than evergreen trees, reducing its dependence on soil for nitrogen and increasing its effectiveness as a pioneer in disturbed, infertile habitats. This aggressive pioneer quickly colonizes disturbed areas and grows rapidly, remaining taller than its associates for approximately 100 years...In the absence of disturbance, shade tolerant associates form understories that shade out future generations of western larch seedlings. However, western larch's long lifespan and resistance to damage from fire and pathogens accounts for the presence of relict trees in late-successional stands that can repopulate the stand if fire or other disturbance removes competition and opens the canopy.

The currently accepted scientific name for western larch is Larix occidentalis Nutt. (Pinaceae).

Except when it is young, western larch is rarely found in pure stands. Its most common tree associate is Douglas-fir (Pseudotsuga menziesii), and on low-elevation dry sites it is found with ponderosa pine (Pinus ponderosa). Common associates in warm, moist forests include grand fir (Abies grandis), western hemlock (Tsuga heterophylla), western redcedar (Thuja plicata), and western white pine (P. monticola). In cool, moist, subalpine forest types Engelmann spruce (Picea engelmannii), subalpine fir (A. lasiocarpa), lodgepole pine (Pinus contorta), and mountain hemlock (Tsuga mertensiana) are more common.

Hardwoods that occur with western larch include paper birch (Betula papyrifera), black cottonwood (Populus balsamifera ssp. trichocarpa), and quaking aspen (P. tremuloides).

Major understory associates include common beargrass (Xerophyllum tenax), huckleberry (Vaccinium spp.), thimbleberry (Rubus parviflorus), menziesia (Menziesia ferruginea), ninebark (Physocarpus malvaceus), serviceberry (Amelanchier spp.), Oregon boxwood (Paxistima myrsinites), and bearberry (Arctostaphylos uva-ursi).

Western larch is not considered a climax species, but it is a long-lived early successional species. (Plant Database)

Identification

Bark in mature trees is thick and furrowed into large, flaky plates. Foliage is light green in early season, yellow in late season and needles are held in tufts.

Trees to 50m; trunk to 2m diam., usually (when forest grown) branch-free over most of height; crown short, conic. Bark reddish brown, scaly, with deep furrows between flat, flaky, cinnamon-colored plates. Branches horizontal, occasionally drooping in lower crown of open-grown trees; twigs orange-brown, initially pubescent, becoming glabrous or very sparsely pubescent during first year. Buds dark brown, generally puberulent, scale margins erose. Leaves of short shoots 2--5cm × 0.65--0.80mm, 0.4--0.6mm thick, keeled abaxially, with shallow convex midrib adaxially, pale green; resin canals 20--50 µm from margins, each surrounded by 5--7 epithelial cells. Seed cones 2--3 × 1.3--1.6cm, on curved stalks 2.5--4.5 ´ 3.5--5mm; scales 45--55, margins entire, adaxial surface pubescent; bracts tipped by awn to 3mm, exceeding scales by ca. 4mm. Pollen 71--84µm diam. Seeds reddish brown, body 3mm, wing 6mm. 2 n =24. (Flora of North America)

Threats

Though many insects and diseases can affect western larch, damage is usually more severe in other associated species... Its deciduous habit helps with resistance to pests; if trees are defoliated, they produce a 2nd set of needles later in the season. Repeated defoliation, however, slows growth and may affect competitive ability.

Dwarf mistletoe (Arceuthobium laricis) is the most serious parasite that affects western larch. Diseases include sporadic needle blight (Hypodermella laricis), needlecast (Meria laricis), and root and stem rots.

Western larch is considered the most fire-resistant tree in its range. Fire is an important part of western larch's ecology; without fire or other stand replacing disturbance, western larch will not regenerate successfully and will eventually be replaced by more shade-tolerant species. Western larch's extremely thick basal bark protects its cambium from overheating. Low resin content and light lichen growth also decrease flammability. Western larch's characteristic high, open crown; open stand habit; and self-pruning lower branches minimize ladder fuels and risk of crown fire. Its deep roots are protected from surface and ground fires... Needles of western larch are less flammable than other species' due to their small size. Because they are never more than 5 months old, they maintain a higher water content than other conifers' needles that are replaced every 2 or 3 years. (Plant Database)

Uses

Native Americans used western larch for treatment of cuts and bruises, tuberculosis, colds and coughs, sore throats, arthritis, skin sores, cancer, and for blood purification. They also made syrup from the sap, ate the cambium, and chewed solidified pitch as gum. Arabinogalactan, the gum from the tree, is used for lithography and in food, pharmaceutical, paint, ink and other industries. The most desirable sources of this gum are waste butt logs. Oleoresin from western larch is used to produce turpentine and other products. (Plant Database)

Reproduction

Breeding system - Western larch is monoecious with both staminate and ovulate cones distributed throughout the crown... Male western larch cones are 1 cm long. Ovulate cones are papery, 2.5-3.5 cm and 1.3-1.6 cm wide with long subtending bracts.

Pollination - Western larch pollen is distributed by wind and is less abundant than that of other conifers.

Seed dispersal - Most of western larch's small, light, long-winged seeds are distributed within 100 m of the parent. However, depending on wind conditions, they may be dispersed up to 250 m or more...Western larch seeds are viable only until the year following fertilization.

Seedling Establishment and Growth - On average 1 western larch seedling will establish for every 53 seeds produced and dispersed. Seedlings grow rapidly and vigorously, averaging 5 cm of growth during the 1st season and 30 cm per year over the next 4 years. Western larch seedlings grow faster than all major associates except lodgepole pine, and the species grows faster than any other Rocky Mountain conifer until 100 years of age.

Asexual regeneration - Western larch does not reproduce by sprouts, but propagation by cuttings has been successful. (Plant Database)

Species Distribution

Western larch occurs from southeastern British Columbia and extreme western Alberta southward into eastern Washington, western Montana, northern Oregon, and northern and west-central Idaho. It has been established in a planting in Salt Lake County, Utah, and one source reports that its range extends into Colorado. (Plant Database)

Citation

USDA Plant Database http://plants.usda.gov/characteristics.html USDA, NRCS. 2016. The PLANTS Database (http://plants.usda.gov, 4 February 2016). National Plant Data Team, Greensboro, NC 27401-4901 USA.

Flora of North America http://www.efloras.org/flora_page.aspx?flora_id=1 Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. 19+ vols. New York and Oxford.

Silvics of North America Burns, R.M., and B.H. Honkala. 1990. Silvics of North America (Volume 1: Conifers, Volume 2: Hardwoods). USDA Forest Service Agricultural Handbook 654.

Intermountain Herbarium http://intermountainbiota.org/portal/collections/harvestparams.php Consortium of Intermountain Herbaria. 2016. http//:intermountainbiota.org/portal/index.php. Accessed on February 04.

Burke Museum Plant Image Collection The plant image collection at the Burke Museum, University of Washington.

Jepson Manual http://ucjeps.berkeley.edu/eflora/ The Jepson Manual: Vascular Plants of California. B.G. Baldwin, D.H. Goldman, D.J. Keil, R. Patterson, T.J. Rosatti, and D.H. Wilken [editors]. 2012. 2nd edition, thoroughly revised and expanded. University of California Press, Berkeley, CA., hardcover; 1600 pages. ISBN-13: 978-0520253124.

USGS Plant Species Range Maps http://esp.cr.usgs.gov/data/little/ Critchfield, W.B., and Little, E.L., Jr., 1966, Geographic distribution of the pines of the world: U.S. Department of Agriculture Miscellaneous Publication 991, p. 1-97. Little, E.L., Jr., 1971-1978, Atlas of United States trees, volume 1,3,13,17, conifers and important hardwoods: U.S. Department of Agriculture Miscellaneous Publications.