Western larch (Larix occidentalis): what the agencies record

This page reports what US federal publications say about one tree. It does not identify trees from descriptions or photos and does not say what should be done with any tree. The family overview, tree species in the agency records, explains the sources and holds the comparison table. Another deciduous conifer has its own page, tamarack, and the Wood Handbook compares this wood with Douglas-fir.

At a glance

Item	What the source records
Scientific name	Larix occidentalis Nutt., pine family; a deciduous conifer (Silvics)
Other names, Silvics	Tamarack, western tamarack, and less commonly hackmatack, mountain larch and Montana larch
Native status, USDA PLANTS	Native in Canada and the lower 48 states
Size and age, Silvics	Normally 30 to 55 m (100 to 180 ft) tall at maturity and occasionally over 61 m (200 ft); trees exceeding 230 cm (90 in) in diameter and 900 years of age have been found
Green weight of the wood, NRS-38	48 lb per cubic foot, without bark

Native range and climate

The Silvics of North America handbook (Agriculture Handbook 654, Volume 1, 1990) calls western larch the largest of the larches and the most important timber species of the genus. It grows in the Upper Columbia River Basin of northwestern Montana, northern and west central Idaho, northeastern Washington and southeastern British Columbia, along the east slopes of the Cascade Mountains in Washington and north-central Oregon, and in the Blue and Wallowa Mountains of southeastern Washington and northeastern Oregon.

The handbook describes a relatively moist, cool climate where low temperature limits the upper elevation and deficient moisture the lower. Annual precipitation in larch forests averages 710 mm (28 in) in the north to 810 mm (32 in) in the south, with extremes of 460 mm (18 in) and 1,270 mm (50 in), and one-fifth of it falls from May through August. The frost-free season varies from 60 to 160 days, and frost can occur in any month. On mid-elevation sites snow commonly covers most larch forests from November to late April and accounts for over half the precipitation. Most soils are deep and well drained, mainly Inceptisols and Alfisols, many developed in glacial till or colluvium.

Cones and seed

The species is monoecious, with both kinds of flowers throughout the crown. Silvics says pollen and seed conelets appear several days before the vegetative buds open, usually between April 15 and May 15, with pollination in late May and early June. Cones finish developing in one season, mature by mid- to late August at 2.5 to 4.5 cm (1.0 to 1.8 in) long, and usually begin to open by early September; more than 80 percent of the seeds are usually dispersed by mid-October. The handbook calls larch a good seed producer, with good crops "at about 5-year intervals" in its Montana records. Cone production is infrequent on trees under 25 years old, though trees as young as 8 years occasionally produce cones; abundant crops begin at 40 to 50 years and heavy bearing continues for 300 to 500 years.

Growth, shade and fire

The handbook says larch grows faster in height than any other conifer in the Northern Rockies for the first century, giving this highly shade-intolerant species the height advantage it needs. For the first 50 years larch and lodgepole pine grow at similar rates, and on good sites on the Coram Experimental Forest in Montana they grew at twice the rate of Douglas-fir and three to four times faster than subalpine fir and Engelmann spruce for the first 20 years. Silvics calls larch the most shade-intolerant conifer in the Northern Rockies, tolerating partial shade only as a seedling, and says it grows in even-aged stands. The root system is deep and extensive, with extensive fibrous rooting in the top 50 cm (20 in). It says fire is essential to the maintenance of western larch in natural forest stands, and that mature larches are the most fire-resistant trees in the Northern Rockies because of thick bark, a high and open branching habit and low flammability of the foliage, while seedlings and saplings have very little resistance.

Wood

The Wood Handbook (FPL-GTR-282, 2021) says two-thirds of the lumber is produced in Idaho and Montana and one-third in Oregon and Washington. It describes yellowish brown heartwood, yellowish white sapwood generally not over 2.5 cm (1 in) wide, and stiff, moderately strong, hard, moderately heavy wood with moderately high shrinkage and moderately high shock resistance. The wood is usually straight grained, splits easily and is subject to ring shake, and knots are common but generally small and tight. It names rough dimension wood for building construction, small timbers, planks and boards, railroad crossties, mine timbers, piles, poles and posts, with some high-grade material going into interior woodwork, flooring, sashes and doors, and says the properties are similar to those of Douglas-fir so that the two are sometimes sold mixed. Silvics adds that larch wood contains 4 to 23 percent arabinogalactan, a water-soluble gum with industrial uses.

Wood Handbook figure	Green	At 12% moisture content
Specific gravity (Table 5-3b)	0.48	0.52
Modulus of rupture, lbf per square inch (Table 5-3b)	7,700	13,000
Side hardness, lbf (Table 5-3b)	510	830

The green weight is in the NRS-38 table, the same figure used in the log weight calculator.

Damaging agents the handbook names

Dwarf mistletoe. Silvics calls Arceuthobium laricis the most damaging disease-causing parasite of larch, able to infect seedlings as young as 3 to 7 years old and to continue through the life of the tree. It lists dead tops, lower seed viability, burls, brashness, some mortality and reduced growth, and gives basal area growth reductions of 14 percent for light infection, 41 percent for medium and 69 percent for heavy infection. Seed can be ejected as far as 14 m (45 ft).
Other diseases. Needlecast from Hypodermella laricis, the quinine fungus Fomitopsis officinalis and red ring rot from Phellinus pini. The handbook says nearly all windfallen overmature larches it evaluated had root rots, and ties these rots to wind stability in overmature trees.
Insects. It names the larch casebearer, first detected in the Northern Rockies in 1957, and the western spruce budworm as the two most serious insect pests when it was written, with budworm severing terminal leaders and costing an average of 25 to 30 percent of that year's height growth. The larch sawfly and larch bud moth cause heavy but sporadic damage, and bark beetles are not generally a serious problem, though the Douglas-fir beetle occasionally attacks weakened trees.
Weather and animals. Larch is moderately to highly resistant to windthrow, though isolated old-growth seed trees and those on ridgetops and saddles are susceptible. Being deciduous, its branches seldom accumulate excessive snow or ice. Young larch is extremely sensitive to fluorine and sulfur dioxide fumes. Bears can strip bark from the lower bole of vigorous trees in young stands in spring and often kill them.

For who takes reports of regulated pests, see reporting a pest in the United States, and pests and diseases by country sets out which ones agencies regulate.