Alder

Three types of Alder have ranges that include the Matanuska Valley. These are:

• American Green Alder (Alnus crispa)
• Sitka Alder (Alnus sinuata)
• Thinleaf Alder (Alnus tenuifolia)

If you want to tell these apart, measure the length of the stalks connecting the cones to the tree:

• Cones with stalks longer than 12 millimeters and mostly longer than the cones. Buds on young twigs have short or no stalks and are about 12 millimeters long with overlapping scales. --> Sitka Alder (Alnus sinuata)
• Cones have short stalks that are less than 12 millimeters long and the cones themselves are less than 12 millimeters long. --> thinleaf alder (Alnus tenuifolia)
• Cones are 10-15 millimeters long, brown to dark brown, and have a slender stalk 6-12 millimeters long. Buds are long and pointed, about 6-10 millimeters long. --> American green alder (Alnus crispa)

[Source: Leslie A. Viereck and Elbert L. Little, Jr., Alaska Trees and Shrubs, U.S. Department of Agriculture, Agriculture Handbook No. 410, 1972].

Otherwise, the different types of alder in the Matanuska Valley have some features in common:

 Twigs are dark when young, gray when older.

Bark is smooth and gray with horizontal lines (lenticels)

Winter buds may have short stalks or no stalks. They have a soft, rounded, dark pink appearance with overlapping scales.

Flowers: Female and male flowers grow on the same tree. The female flowers are a similar elongated shape but much smaller than the male flowers. Male flowers form narrow catkins, 7.5 to 12.5 cm long. In early spring look closely at the alder flowers for tiny grains of yellow pollen.

Fruits: Clusters of 3 to 9 slender-stalked old, dead hard blackish or dark brown cone-like fruits. Close up of the cones

Seeds: elliptic with two broad wings.

Roots: Alder roots often have nodules that "fix" nitrogen into the soil. That is, they draw nitrogen out of the air and put it into the soil where, often it is available as a nutrient to other plants.

Seasons: Alder blooms during May and June. Its seeds provide food for song birds during fall and winter.,

Ecology: Common on graveled slopes and flood plains, forming thickets from sea level to above tree line. Alder is a pioneer tree that invades areas soon after disturbances such as landslides, logging, glacial retreat, and road construction. Alder also acts as a nurse tree for spruce, providing protection from wind and sun while the spruce is young and fragile.

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This page last updated June 4, 2006