BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Alnus viridis ssp. sinuata | Sitka Alder 



GENERAL BOTANICAL CHARACTERISTICS : 
Sitka alder is a deciduous shrub or, rarely, a small tree.  Plants are
typically multistemmed and bushy, up to 10 or 15 feet (3 or 4.6 m) tall,
often forming dense thickets [3,39].  Occasionally, plants may grow to
30 or 40 feet (9 or 12 m) at lower elevations [3,27].  Height growth
generally decreases with increasing elevation [22].  The resilient
branches are seldom damaged by snow creep or avalanches, allowing dense
thickets to form on steep slopes subject to these disturbances [17].  On
these sites the 3 to 6 inch (7.6-15.2 cm) diameter stems often point
downhill and then bow strongly upwards [17,20,38].  The bark is thin,
smooth, and reddish brown or gray [25,39].  The leaves are alternate,
ovate, 0.8 to 2.5 inches (3-10 cm) long, shiny green, with doubly
serrate margins [39].  Sitka alder has a shallow root system [27].

Male and female flowers occur on the same plant in catkins.  The
separate male and female catkins are in small clusters on the same twig
[20].  Clusters of three to six pistillate catkins are approximately 0.5
inch (1.25 cm) long, each with a long, 1 to 1.5 inch (2.5-3.75 cm) stalk
[25,27].


RAUNKIAER LIFE FORM : 
   Undisturbed State:  Phanerophyte (microphanerophyte)
   Undisturbed State:  Phanerophyte (nanophanerophyte)
   Burned or Clipped State:  Hemicryptophyte


REGENERATION PROCESSES : 
Sexual reproduction:  Male and female flowers of Sitka alder occur in
catkins on the same plant.  The small (about 0.5 inch [1.25 cm] long)
female catkins are wind pollinated, and turn semiwoody and conelike at
maturity.  The fruit is a small, single-seeded nutlet with wide lateral
wings.

Seeds are dispersed during the fall [20].  Sitka alder's seeds are
lightweight and have broad wings about as wide as the body of the nut,
which allows them to travel long distances by wind and water [44].

Germination from seed on disturbed habitats is the primary form of
reproduction of Sitka alder [20].  The wind-dispersed seeds colonize
bare soil created by disturbances such as fire, avalanches, soil slump,
and retreating glaciers.  Seeds require a moist mineral soil for
germination, which normally takes place in the spring.  Studies in
western Washington found that it takes 3 to 4 years for Sitka alder
seedlings to reach 3 feet (1 m) in height, and 10 years to reach 13 feet
(4 m) [22].  Seedlings take 4 to 7 years to start producing seed
[28,34].

Vegetative Reproduction:  Sitka alder plants can sprout from the root
collar or stump when damaged.  Although alder wood is resilient and
somewhat limber, avalanches can damage plants, which afterwards often
sprout [38].  Sprouting also often occurs from root crowns following
fire [47].

Propagation:  Stem cuttings of Sitka alder seldom, if ever, produce
roots [26].


SITE CHARACTERISTICS : 
Sitka alder is generally found at middle to high elevations in the
mountains of northwestern North America.  It is moderately shade
tolerant [20,31], which allows it to survive under stands of lodgepole
pine (Pinus contorta), Engleman spruce (Picea engelmannii), subalpine
fir, grand fir (Abies grandis), western hemlock, mountain hemlock (Tsuga
mertensiana), Douglas-fir, and Pacific silver fir [1,7,40,46]; however,
it cannot tolerate a dense overstory.  Scattered thickets of Sitka alder
are normally located on cool moist sites, on north-facing slopes, or
other shady aspects [3,37,40,46].  It is a vigorous invader of talus
slopes, avalanche chutes, seepage areas, and high elevation mountain
swales, which often have an abundance of surface moisture [29,43].
These sites are often subject to deep winter snow accumulations and
recurrent avalanches.  Although typically mentioned as a seral shrub of
cool, moist, shady upland sites, it also occurs along cool mountain
streams in Oregon and Washington [23,29].

Soils:  Sitka alder is found on a wide variety of parent materials and
soil textures [20].  Surface soil textures vary from silts to coarse
sands, and are consistently more acidic than those in adjacent conifer
communities [7,40].  Soils under Sitka alder are normally higher in
available nitrogen than soils in adjacent communities, since this
species can fix between 18 to 55 pounds per acre (20-62 kg/ha) of
nitrogen annually [20].  Its ability to fix nitrogen allows it to invade
sterile mineral soil recently exposed by glaciers or avalanches [20].

Associated species:  Sitka alder is commonly found with shrubs such as
Rocky Mountain maple (Acer glabrum), vine maple (A. circinatum),
elderberies (Sambucus spp.), willows (Salix spp.), prickly currant
(Ribes lacustre), mountain ash (Sorbus spp.), rusty leaf menziesia
(Menziesia ferruginea).  Commonly associated herbs and forbs (usually
shade tolerant) include heartleaf miners lettuce (Montia cordifolia),
Siberian miners lettuce (M. sibirica), arrowleaf groundsel (Senecio
triangularis), wild ginger (Asarum caudatum), lady fern (Athyrium
felix-femina), queencup beadlily (Clintonia unifloria), broadleaf arnica
(Arnica latifolia), sidebells shinleaf (Pyrola secunda), pioneer violet
(Viola glabella), nettles (Urtica dioica), northern bluebells (Mertensia
paniculata), and bracken fern (Pteridium aquilinum) [2,6,7,9,40].

Elevation:  Sitka alder is mostly distributed above 3,000 feet (914 m)
[3].  Sitka alder does not grow below 1,640 feet (500 m) in Washington
[22].  Elevational ranges for the following western states are presented
below [6,12]:

from 3,500 to 8,000 feet (1,067-2,438 m) in MT
     5,700 to 7,000 feet (1,737-2,134 m) in Eagle Cap Wilderness, OR


SUCCESSIONAL STATUS : 
Sitka alder is generally considered a pioneer or early seral species,
capable of colonizing disturbed or sterile soils and often appears on
avalanche chutes, talus slopes, fresh alluvium, and at the head of
retreating glaciers [20,34,38].  On steep terrain in heavy snowpack
areas, recurrent avalanches are partially responsible for the creation
and maintenance of Sitka alder communities [17].  The soils exposed by
avalanches provide an ideal seedbed for Sitka alder seeds.  Once
established, its resilient wood, bowed growth form, and ability to
resprout if stems are broken allow Sitka alder to withstand repeated
avalanche destruction, which would normally kill other plants.  Other
Sitka alder communities appear to be stable and long-lived and are
apparently midseral or even climax.  When conifers are removed by
disturbances such as wildfire, avalanche, or massive soil slumping,
Sitka alder quickly invades disturbed sites having high water tables or
seasonally high moisture such as from snow melt [7].  Dense stands of
Sitka alder that develop can sometimes retard the establishment of
conifers on the site, and these stands appear to be stable [2,46].


SEASONAL DEVELOPMENT : 
The staminate catkins of Sitka alder are produced during the preceeding
growing season, and are exposed during the winter.  The pistillate
catkins emerge with the leaves in the spring [18].  Flowering occurs in
the spring, cones ripen in mid-September to mid-November depending on
latitude and elevation, and seed is dispersed immediately thereafter
[20].  Leaves remain green until they are dropped in the fall.

Related categories for Species: Alnus viridis ssp. sinuata | Sitka Alder