BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Sorbus americana | American Mountain-Ash 



GENERAL BOTANICAL CHARACTERISTICS : 
American mountain-ash is a native, smooth-barked, deciduous shrub or
small tree 10 to 30 feet (3-9 m) tall, with an average d.b.h. of 4 to 10
inches (10-25 cm).  It has a short trunk; slender, spreading branches;
and a narrow, open round-topped crown.  In closed canopies it tends to
have a longer trunk, with the lower portions branch-free [10,12,21].  It
tends to be slow growing and short-lived.  The roots are fibrous [39].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Sexual reproduction:  There are approximately 388,000 seeds per pound
(352,000/kg) [48].  The seeds are largely dispersed by birds.  In
studies to determine the amount of time the seeds are retained in the
gut of various birds, the maximum time between ingestion and defecation
was 30 minutes, indicating that the distance of dispersal is probably
not great but could be on the order of a few hundred feet to a few miles
[48].  The seeds require 60 or more days of cold stratification at 33 to
41 degrees Fahrenheit (0.6-5 deg C) [20].  American mountain-ash
reproduces well over a wide range of forest stand and site conditions on
Isle Royale, Michigan.  The greatest amount of reproduction occurred in
birch (Betula spp.)-fir-spruce cover types [19].

Seedling numbers from 400 to 2,920 per acre (1,000-7,300/ha) were
reported on Isle Royale and adjacent islands in Minnesota.  The number
of saplings ranged from 40 to 1,064 per acre (100-2,660/ha), while the
number of adults ranged from 2 to 3 per acre (4-6/ha) (browsed sites)
and from 18 to 149 per acre (45 to 373/ha) (unbrowsed sites) [46].
                         
Asexual reproduction:  American mountain-ash will sprout from the stump
when top-killed [7,8,9].


SITE CHARACTERISTICS : 
American mountain-ash prefers moist habitats from the borders of swamps
to rocky hillsides.  It is commmon in openings or in woods, scattered on
uplands along edges of woods, roadsides, and under semiopen stands
[10,28].  It will grow well in a stunted form on relatively dry soils
[21].

Most American mountain-ash in the White Mountains of New England occurs
from 2,310 to 4,290 feet (700-1,300 m), decreasing in abundance at the
higher elevations [30,42].  Soils in this area are youthful, shallow,
and infertile; the climate is cool, windy, and humid [42].  In the
Adirondack Mountains of New York, American mountain-ash rarely occurs
below 3,135 feet (950 m) and is generally found on well-drained to
imperfectly drained Spodsols or Inceptisols [10,28,31].  In the boreal
forests of Ontario, density of American mountain-ash was highest on
sites with scattered mature or semimature coniferous and deciduous
species and lowest on conifer sites with relatively closed canopies or
on sites that had been logged and then planted [34].


SUCCESSIONAL STATUS : 
Facultative Seral Species

American mountain-ash is shade intolerant [28].  American mountain-ash
is listed as a subordinate species in advanced old-field succession
community types [45].  In a study of secondary succession in
high-elevation spruce-fir forests, American mountain-ash had an average
of 152 stems per acre (382/ha) and an average d.b.h. of 1.5 inches (3.9
cm) (smaller than average), with a moderate amount of reproduction (1
seedling per 25 sq m plot).  This density is higher than usually found
in mature canopies, which is on the order of 4 to 20 stems per acre (10
to 50/ha) in red spruce (Picea rubens)-balsam fir (Abies balsamea)
[1,29].  It therefore appears to be more abundant in early seral
communities, but it is present at low densities in old-growth stages of
spruce-fir communities [13,44,45].

Seven years after logging, browse species (including American
mountain-ash) were 3 to 8 times more abundant on logged sites than on
undisturbed control plots [35].  In Tennessee, American mountain-ash
increased in biomass as the canopy cover of Fraser fir (Abies fraseri)
decreased with fir mortality [5].

Cooper [9] noted that American mountain-ash was part of an early seral
community in rock crevices on the shores of Isle Royale, Michigan,
establishing with or shortly after shrubs.  In 17 years, the stunted
shrubs of American mountain-ash in these rocky clefts had grown to a
height of 6 feet (1.8 m) [9].

The number of American mountain-ash twigs almost doubled over 3 years
following clearcutting.  Most of the twigs were on stems that survived
the logging [22].


SEASONAL DEVELOPMENT : 
American mountain-ash flowers from May to July; fruit ripens in August.
The berries remain on the tree and are available to birds all winter
[10,12].

Related categories for Species: Sorbus americana | American Mountain-Ash