Return to Native Trees of the Southern Rocky Mountains

Capt. Lewis Branded a tree with his name Date &c. I marked my name the Day & year on an alder tree, the party all cut the first letters of their names on different trees. William Clark, November 23, 1805.

Alder is a common large shrub or small tree, widespread on the banks of streams in the foothills and in the montane, and on southwestern mesas, to 10,000 feet elevation. TypicallyAlder has many stems starting together at ground level. Alder may reach 40 feet high, though usually it is about 10 to 20 feet high; the trunk diameter grows to 7 inches. Alder often grows near Water birch, which it somewhat resembles. Alder has distinctive woody "cones" that resemble miniature pine cones, about 1/2 inch long. The "cones" are really the female catkins or fruit. Alder blooms in late March and early April.

Deer, elk and moose make moderate use of the twigs and leaves for food, as do muskrats, beavers, and cottontails. Beavers also eat the bark, and use the stems for dam-building. Seeds and buds are a winter food source for many birds. The wood was once preferred by outdoorsmen for firewood. The largest known Mountain alder grows in Bandelier National Monument, New Mexico; it is 59 feet high with a trunk about a foot in diameter.

The scientific name is Alnus incana var. tenuifolia. It is very similar to the alder of northern Europe, Alnus incana . Tenuifolia means slender-leaved and this tree is sometimes called the Thinleaf alder.

Leaves: 1 to 4 inches long; doubly toothed; to 2.5 inches wide and wrinkled. Leaves alternate but so close together as to appear opposite, and often in clumps of 2 or 3 at end of twigs. Six to nine parallel veins are noticeable. Leaf size is usually about twice Water birch leaf size.

Stems twigs soft reddish brown; pith triangular in cross-section. Thicker than birch twigs. Buds reddish on a short stalk, with two scales.

Fruit 3/4 inch long woody "pine-cones"; dark brown when mature. Some stay on all year. Flowers from April to August. These little cones are a sure sign of Alder.

Bark Smooth and thin; usually pale gray. Whitish or gray horizontal ridges or marks on branches (lenticels or breathing pores) do not differ much in color from the bark color, unlike the case in the Water birch. The lenticels may form warty bumps on the bark. The bark may have a silvery or grayish cast over brown, or can be pale brown or even dark brown, but not so dark as Water birch bark.

Arizona Alder

Arizona alder is found in comparatively cool and moist locations in Ponderosa pine or oak woodlands from 4500 to 6000 feet elevation in New Mexico. Its most northerly location is Mount Taylor northeast of Grants. Similar in appearance, setting, and ecological role to the Mountain Alder, Arizona alder can grow larger than Mountain alder, over 30 feet tall, and sometimes reaches 60 feet or more. Its leaves have V-shaped bases, unlike the flat or round base of the Mountain alder leaf, and 9 to 13 side veins, whereas Mountain alder leaves have 6 to 9 side veins. The bark is checkered in small plates and may be brown or reddish while Mountain alder bark is usually gray. The scientific name Alnus arizonica.