Red alder (Alnus rubra): 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.

At a glance

Item	What the source records
Scientific name	Alnus rubra Bong., birch family (Silvics)
Other names, Silvics	Oregon alder, western alder and Pacific coast alder
Native status, USDA PLANTS	Native in Alaska, Canada and the lower 48 states
Size and age, Silvics	On favorable sites 30 to 40 m (100 to 130 ft) tall and 55 to 75 cm (22 to 30 in) in diameter; a record tree measured 198 cm (78 in) in diameter; usually matures at 60 to 70 years, with a maximum age the handbook words as usually "about 100 years"
Green weight of the wood, NRS-38	46 lb per cubic foot, without bark

Native range and sites

The Silvics of North America handbook (Agriculture Handbook 654, Volume 2, 1990) calls red alder the most common hardwood in the Pacific Northwest. Its range runs from southern California (latitude 34 degrees north) to southeastern Alaska (60 degrees north). The tree is generally found within 200 km (125 mi) of the ocean and below 750 m (2,400 ft), and it seldom grows east of the Cascade Range in Oregon and Washington or the Sierra Nevada in California, although the handbook notes several isolated populations in northern Idaho. It describes climates from humid to superhumid, with annual precipitation from 400 to 5,600 mm (16 to 220 in), and says either rainfall above 630 mm (25 in) a year or access to ground water is needed for good development.

Silvics says red alder grows on soils from well-drained gravels and sands to poorly drained clays and organic soils, with the best stands on deep, well-drained loams of alluvial origin. It tolerates poor drainage and some flooding in the growing season, so it prevails along stream bottoms and in swamps, but it is not common on droughty soils. The handbook names Douglas-fir, western hemlock, western redcedar, grand fir, Sitka spruce, black cottonwood and bigleaf maple among the common tree associates, and lists a forest cover type (Society of American Foresters Type 221) named for the species.

Catkins, seed and early growth

The handbook says red alder reaches sexual maturity at 3 to 4 years for individual trees and 6 to 8 years for most dominant trees in a stand. It is generally monoecious. Male catkins hang in clumps and lengthen in late winter from 2 or 3 cm to 7 or 8 cm (3 in); female catkins are upright and 5 to 8 mm (0.2 to 0.3 in) long. Moderate seed crops come almost every year and bumper crops every 3 to 5 years. The seeds are small winged nuts in woody, conelike strobili 11 to 32 mm (0.4 to 1.3 in) long, number 800 to 3,000 per gram, and are carried a long way by wind, with most shed in late fall and winter. Silvics says seedlings establish well on moist mineral soil in full sunlight, can take partial shade for a few years, and then need full sun. It records seedlings growing 1 m (3.3 ft) or more in the first year on favorable sites and says seedlings aged 2 to 5 years can reach more than 3 m (9.8 ft) of height growth a year.

The handbook says young red alder sprouts vigorously from the stump and can be repeatedly coppiced on short cycles, with rootstock mortality rising with each harvest, and that older trees rarely sprout.

Growth, shade and roots

Silvics says red alder grows fast when young: on good sites trees may be 9 m (30 ft) at age 5, 16 m (52 ft) at age 10 and 24 m (79 ft) at age 20. On an average site Douglas-fir and red alder reach the same height at what the handbook calls "about age 45", and after that the conifer is taller. The handbook classes red alder as intolerant of shade, needing more light than any of its tree associates except black cottonwood, and reports natural stands thinning from 124,000 stems per hectare (50,000 per acre) at age 5 to 1,665 per hectare (675 per acre) at age 20. It also says the species prunes itself extremely well, so boles are typically clear and slightly tapered.

The root system is extensive and fibrous. The handbook says red alder roots carry nodules formed with an actinomycete of the genus Frankia, which fix nitrogen from the air, and calls red alder the only commercial tree species west of the Rocky Mountains able to do so. Nodules appear soon after germination and can reach 80 or 90 mm (3.1 or 3.5 in) across on large trees. It reports annual fixation of up to 320 kg per hectare (290 lb per acre) in pure stands, and says the species raises soil organic matter and nitrogen and lowers soil pH.

Wood

The Wood Handbook (FPL-GTR-282, 2021) says the wood runs from almost white to pale pinkish brown with no visible line between heartwood and sapwood. It calls red alder moderately light, intermediate in most strength properties, low in shock resistance and relatively low in shrinkage, and names furniture as the main use, with sash and door panel stock and other millwork. It also calls the tree the principal hardwood for commercial manufacture of wood products in Oregon and Washington. Silvics adds cabinets, pallets, plywood, flakeboard, paper and fuelwood.

Wood Handbook figure	Green	At 12% moisture content
Specific gravity (Table 5-3b)	0.37	0.41
Modulus of rupture, lbf per square inch (Table 5-3b)	6,500	9,800
Side hardness, lbf (Table 5-3b)	440	590

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

Damaging agents the handbook names

Silvics calls red alder fairly free of most insect and disease problems, especially when young and uninjured.

Rots and cankers. A white heart rot, Phellinus igniarius, is named as probably the major cause of cull in older trees. Three canker diseases, Didymosphaeria oregonensis, Hymenochaete agglutinans and Nectria galligena, cause some damage in young stands, with slight overall impact. The handbook says wood stain and decay move quickly in cut trees and that once residual trees are injured, decay organisms can invade rapidly.
Defoliators and borers. The forest tent caterpillar, western tent caterpillar, alder woolly sawfly, striped alder sawfly, alder flea beetle and a leaf beetle have caused substantial damage, though the handbook says reports of mortality are rare. A flatheaded borer, Agrilus burkei, can kill twigs and branches, and the alder bark beetle breeds mainly in slash and young stressed trees but can attack healthy ones when its numbers are high. Ambrosia beetles attack logs and slash on the ground.
Weather and fire. Ice storms and unseasonable frost have caused mortality and top damage. Fire is rarely a damaging agent because alder stands carry little flammable debris, and the handbook says alder has been planted as a firebreak. Windthrow is not common, which it attributes to intermingled roots and branches and the absence of leaves in winter storms.
Animals. Black-tailed deer browse young trees occasionally, mountain beaver sometimes girdle small stems and branches, and meadow mice girdle young stems in years of high populations.

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.