BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Alnus viridis ssp. crispa | American Green Alder 



GENERAL BOTANICAL CHARACTERISTICS : 
American green alder is a deciduous, ascending shrub usually reaching up
to 10 feet (3 m) in height [18,30,48,58].  Occasionally, it may reach
heights of 20 to 30 feet (6-9 m) [10,21].  Growth rates vary with site
and location, but usually decrease at higher elevations [24,30].
American green alder often forms dense thickets [10,58,59].  The bark is
yellowish-brown and twigs have sessile, pointed axillary buds [10,24].
Leaves are ovate or elliptic and glabrous above, but pubsecent below.
The margins are serrated with very fine teeth [4,18,30,48,58].

The roots of American green alder are shallow and have nodules
containing nitrogen-fixing microorganisms [8,10,21].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Sexual reproduction:  American green alder is monoecious [10,14,24].
The female catkins turn woody and conelike at maturity.  The seeds are
winged nutlets [48,58] that are dispersed by wind and water [21,37,45].
One study estimated American green alder seed to be 40 percent viable
[61].

Germination from seed on disturbed habitats is the primary form of
reproduction for American green alder [24,25].  The seeds invade and
colonize bare mineral soil [24,37,60] in areas such as avalanche tracks,
talus slopes, fresh alluvium, and soils left by retreating glaciers
[24,58].  In interior Alaska, the frequency of occurrence of alder
species is three times greater on bare mineral soil than on organic
surfaces [60].

Vegetative reproduction:  American green alder sprouts from the root
crown if damaged or cut.  Sprouting often occurs after mechanical site
preparation [24] and natural disturbances such as avalanches [41] and
fire [33,35,45,46].


SITE CHARACTERISTICS : 
American green alder occurs at elevations from sea level to 6,600 feet
(2,000 m) [21] on steep to level terrain.  It occupies habitats ranging
from open tundra to open conifer forests [18,20,57] but cannot withstand
a dense overstory [24].  It can occur singly or in thickets along
streams, lakeshores, coasts, bogs, or muskeg margins, and as an
understory component in conifer forests [21,24].  American green alder
is usually associated with some source of moisture, but is adapted to
somewhat drier conditions than other alders [21].  The wetter sites are
more favorable for high nitrogen-fixing activity [27].  Its shallow
roots make it well adapted to the generally cold, harsh climate
characteristic of sites which it inhabits, where the soil may be only
shallowly thawed [8,24].

Soil textures range from sandy to gravelly or rocky; green alder often
occurs on morainal soil left by retreating glaciers [21,24,58].  Soils
supporting American green alder in deglaciated areas are generally
acidic (pH 5.0-6.5) [24,53].


SUCCESSIONAL STATUS : 
Facultative Seral Species

American green alder is semi-shade tolerant [24,44] and is considered a
pioneer or seral species [21,25,26].  It invades and inhabits terraces
above the floodplain which are subject to occasional flooding [8,56],
and is a pioneer on alkaline glacial outwash [59].  After fire, American
green alder sprouts from the root crown and establishes by seed from
plants in adjacent unburned areas [33,35,45].  The bare mineral soils
created by these disturbances are prime sites for American green alder.
These shrubs provide shade that reduce soil temperatures, allowing
spruce and other genera to establish [1,9]. 


SEASONAL DEVELOPMENT : 
The pistillate catkins of American green alder emerge before or with the
leaves in spring; staminate catkins are produced during the previous
growing season [10,21,24,48].  Flowering takes place from May to June,
with fruits maturing in July [24,58,61].  Cones ripen from mid-September
to mid-November, depending on latitude and elevation, and seed dispersal
takes place immediately thereafter [48,58,60].  The leaves do not turn
color, but remain green until they are dropped in the fall.

Related categories for Species: Alnus viridis ssp. crispa | American Green Alder