Mountain Alder - Oregon State University

Mountain Alder
Alnus incana ssp. tenuifolia
(Nutt.) Brietung.
This long-lived, monoecious, early seral, shade
intolerant woody species is the most widely
distributed alder in western North America (3,
6, 9). Alders are nitrogen fixers. They have
a symbiotic relationship with the Frankeria
sp. fungus. It increases ecosystem nitrogen
content (9). A. i. ssp. tenuifolia produces 37-
319 kg/ha (41-349 lbs/ac) annually. Often
this alder is used for rehabilitation in disturbed
riparian zones (2). Closely related subspecies
and varieties have subtle differences from ssp.
tenuifolia, creating taxonomic confusion (6).
In much of Canada, ssp. rugosa overlaps with
mountain alder in habitat and botanical
characteristics. Also referred to as speckled
alder, thin-leaf alder and river alder.
SYN: A. i. ssp. rugosa var. occidentalis, A.
tenuifolia and A. t. var. occidentalis
Plant Characteristics
Prepared by OSU Rangeland Ecology and
Management, May 2005.
VEGETATIVE CHARACTERISTICS
Form and Stature: A deciduous, multi stemmed shrub or small
tree, often 2-5 m (6-15 ft) tall occasionally reaching 42 m (40 ft),
frequently forms thickets. Mountain alder has a smooth, gray green
to grayish brown to reddish brown bark with horizontal slits called
lenticels (6). The twigs are wooly to completely hairless (5),
depending on location.
Leaves: Alternate, egg shaped, coarse, saw-toothed leaves that are
slightly hairy and pale below, 3-10 mm (0.12-0.39 in) long (1, 3, 4,
7). Leaf buds are bright red, slightly hairy and 6.35 mm (0.25 in)
(7) in length.
Inflorescence: Catkins are woody and persistent with both sexes
found on the same plant. Pistillate aments are formed in bud during
the previous growing season. Narrowly winged nutlets are formed
from pistillate catkins (5). Male catkins are 3.8-7.6 cm (1.5-3.0 in)
long and 6.35 mm (0.25 in) thick, drooping in groups of 3 to 4 (1,
7).
Roots: Mountain alder is rhizomatous with associated fibrous roots.
Adventitious roots will form from branches that become submerged
GENERAL HABITAT CONSIDERATIONS
Soil Types and Conditions: Adaptable to a variety of soil types and
pH’s (8). It readily establishes on fluvial or glacial deposits (9).
Mountain alder frequently is found on heavy moist silt loam or sandy
clay soils in association with coarse alluvium. Tolerates poorly
drained soils.
Moisture/temperature requirements: Inhabits low to moderate
elevations but can be found up to 3,048 m (10,000 ft) (8). Found
in Yukon boreal forests, stream valleys and benches often in the
understory of conifer forests, moderate to wide floodplains, abandoned
meanders, islands, point bars, and hill side seeps (6, 7, 8, 9). Downed
alder logs are common in Yukon streams. In the Yukon, it appears
at 247-325 mm (9.72-12.79 in) of annual precipitation (4). Young
stands are often flooded, eventually trapping and building sediments
(9).

Management Considerations
UTILIZATION
Forage and Palatability: Seldom to moderately consumed by
cattle, sheep and goats. Stand accessibility determines amount of
use (6). Cattle probably utilize this species more than sheep and
horses. Often grazed if more palatable species disappear (6, 7).
In the Blue Mountains of Oregon, moderate cattle grazing was
observed (7). This species is often found in grazing induced
communities (9).
Wildlife Use: Varied consumption from light to moderate depends
on location. Young plants, leaves and twigs are eaten by moose,
deer, and elk. Beavers build dams and lodges with sections of
alders. Flowering buds, seeds, leaf buds, and catkins are consumed
by birds. Winter browsing is common. Provides thermal and hiding
cover for big game and birds. (6)
PLANTING
Growth Season and Seedling Establishment: Flowers in March
to April, cones ripen in fall and disperse seeds thereafter. Catkins
expand before the leaves, sometimes in the late winter months.
In the Yukon, it experiences a short growing season (4). Leaves
shed in autumn wile still green (8). European breeds of Alnus
incana are faster growing and taller than their North American
constituents (2).
Propagation: Produces from rhizomes and seeds with low viability.
Thickets are formed from rhizomes or suckers. Bareroots establish
well. Plant potted alders in permanent locations in late spring to
summer. Establishment from direct seeding will germinate best
on exposed mineral soils opposed to organic substrates. In Oregon
and Washington, female cones are often disfigured possibly affecting
viability. Ripe seeds are best established when sown in a cold
frame. Sow directly into the soil in autumn or place the seeds in
cold stratification for 3 months. Sown seeds will grow with a slow
release fertilizer. This species is easy to start on disturbed sites
because of its rapid growth rate. (8)
DISTURBANCE
Response to Competition: Mountain alder can be replaced by
cottonwoods and some Salix species, In Alaska, thick alder stems
inhibit spruce seedlings from establishing by competing for light
and nutrients (8, 9)
Response to Grazing: This species will resprout if subjected to
moderate or occasionally heavy grazing (6). Excessive overgrazing
in mountain alder/ mesic graminoid associations will disrupt species
composition (9). If other more palatable species are grazed,
mountain alder has been known to increase. Improper grazing
causes banks to erode and decreases sediment capture.
Response to Fire: Root crowns resprout and off-site colonization
is also possible following a fire. Fires are generally uncommon
due to location of water. (6)
Response to Drought: Effects of heavy drought will cause stunted
growth and many standing dead stems. Stressed stands will exhibit
more elk browsing on stems and bark. (9)
Mountain Alder
Alnus incana ssp. tenuifolia
(Nutt.) Brietung.
Sources: 1. Davis, Ray J. 1952. Flora of Idaho.
Dubuque, IO: WM.C. Brown Company. 836p.
2. Hendrickson, O.Q., W.H. Fogal and
D. Bugen. 1991. Growth and resistance to
herbivory in nitrogen fixing alders. Can. J. Bot.
69 (9): 1919-1926.
3. Hitchcock, C. Leo and Arthur
Cronquist. 1973. Flora of the Pacific Northwest.
Seattle, WA: University of Washington Press.
730 p. 4. Mossop, Brent and M.J. Bradford.
2004. Importance of large woody debris for
juvenile Chinook salmon habitat in small boreal
forest streams in the upper Yukon river basin,
Canada. Can. J. For. Res. 34:1955-1966.
5. Parish, Roberta, Ray Coupe and
Dennis Lloyd (ed.). 1996. Plants of Southern
Interior British Columbia. Lone Pine Publishing.
464p.
6. Uchytal, Ronald J. 1989. Alnus
incana ssp. tenuifolia. In: Fire Effects
Information System, [Online]. U.S. Department
of Agriculture, Forest Service,
Rocky Mountain Research Station, Fire Sciences
Laboratory (Producer). Available:
http://www.fs.fed.us/database/feis/ [2005, May
16].
7. U.S. Department of Agriculture,
Forest Service. 1937. Range plant handbook.
Washington, DC. 532p.
8. USDA, NRCS. 2004. The PLANTS
Database, Version 3.5 (http://plants.usda.gov).
National Plant Data Center, Baton Rouge, LA
70874-4490 USA.
9. USDI, USGS. Thin-leaf alder. Alnus
tenuifolia. Northern Prairie Wildlife Research
Center. Jamestown, ND. 1p. [Accessed: May
16, 2005]