BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Acer macrophyllum | Bigleaf Maple 



GENERAL BOTANICAL CHARACTERISTICS : 
Bigleaf maple is a long-lived deciduous tree exhibiting a high degree of
variation in size and form.  Trees in open habitats generally have
short, stout boles that support massive spreading limbs which form a
broad, rounded crown [3,20,37].  Trees shaded under an overstory of
taller conifers generally have straight boles and narrow crowns [37].
Mature trees commonly attain heights of 50 to 70 feet (15-21 m) with 1.5
feet (0.5 m) diameter trunks and live to 150 to 300 years or more
[20,21,37].  In logged areas, plants commonly grow as multistemmed
individuals because numerous stems arise from the stump following
cutting.  The root system is shallow but wide spreading.

The bark of bigleaf maple retains moisture well, especially in coastal
environments where plants are often covered with mosses, liverworts, and
ferns [21,37].  The leaves are the largest of all maples (Acer spp.).
They are generally 6 to 12 inches (15-30 cm) across and nearly as long,
shiny dark green above but paler below, and palmately divided into five
broad, coarsely toothed lobes [37,53].  The greenish-yellow perfect or
staminate flowers are arranged in a raceme at the end of twigs.  The
fruit is a fused, double-winged samara.


RAUNKIAER LIFE FORM : 
   Undisturbed State:  Phanerophyte (mesophanerophyte)
   Burned or Clipped State:  Chamaephyte
   Burned or Clipped State:  Hemicryptophyte


REGENERATION PROCESSES : 
Bigleaf maple can reproduce both sexually and vegetatively but relies
primarily on sexual means of reproduction on undisturbed sites.  Its
reproductive strategy involves dispersing numerous seeds which germinate
on the forest floor, creating a bank of persistent seedlings.  Seedlings
remain in a stunted form until stand-opening disturbances create
conditions more favorable for rapid growth [24,30].  

Seed production and dispersal:  Bigleaf maple begins to produce flowers
at about 10 years of age [46].  Trees growing in open habitats begin to
produce seed at an earlier age and produce larger quantities than trees
growing in shade [20].  Flowers are insect pollinated.  The heavy,
double-winged samaras are dispersed by the wind in late fall and early
winter [30].  Small mammals and birds may also disperse some seed.

Seed viability and germination:  Bigleaf maple seed remains viable for
only a few months.  Seeds normally germinate during the winter following
dispersal; those which do not germinate soon begin to decay [24].  Even
indoors, seed cannot be stored at room temperature or at cold
temperatures for even short periods of time [46].  Germination occurs on
both mineral and organic seedbeds.  Predation of seed by rodents can
significantly reduce germination.  In Douglas-fir forests in Oregon, 30
to 40 percent of seed protected from rodents emerged, but less than 2
percent of unprotected seed emerged [23].

Seedling development:  Moisture stress, light intensity, and predation
seem to be the primary causes of seedling mortality [24,30].
One-year-old seedlings in Oregon averaged 2.3 to 3 inches (6-8 cm) in
height [24].  Seedling growth under Douglas-fir overstories is slow; it
may take 10 years for seedlings to reach 10 inches (25 cm) in height
[23].  Young seedlings are susceptible to rodent, slug, and other
invertebrate predation.  Rodents clip the roots belowground or pull
entire seedlings into their burrows [24].  Bigleaf maple seedlings are
highly palatable to black-tailed deer, and intensive browsing frequently
retards seedling growth.  An Oregon study found that 90 percent of 15-
to 20-year-old seedlings had been browsed and suppressed to about 3 feet
(1 m) in height [24].

Studies in Oregon show that both recent germinants and older seedlings
are found in the understory of Douglas-fir forests.  However, seedlings
are not particularly shade tolerant and are significantly more abundant,
taller, and older in small forest openings than on adjacent sites under
a dense overstory [52].  Beneath undisturbed young conifer overstories
or under dense understory vegetation, seedlings rarely survive long, due
to low light levels.  In several different-aged Douglas-fir stands in
Oregon, few seedlings older than 15 years of age were found [24].
Seedlings that were older than 15 years were mostly found in stands that
had sustained windthrow 20 years earlier.  Seedlings readily germinated
in clearcuts, but an influx of herbaceous vegetation in subsequent years
dramatically diminished the light intensity reaching seedlings and
caused large die-offs.

Vegetative regeneration:  Bigleaf maple sprouts vigorously from the root
crown after it is top-killed or cut.  Haeussler and Coates [30] reported
that suppressed trees are extremely persistent and can die back and
resprout repeatedly under overmature conifer stands.


SITE CHARACTERISTICS : 
Bigleaf maple has bimodal distribution along a moisture gradient.  It is
more abundant on sites occupying the moister and drier habitats than on
intermediate sites [16].  Although it is most common on moist sites,
stands also occur on xeric, sparsely vegetated talus slopes [6,20].
Dyrness and others [16] hypothesize that stands at these moisture
extremes tend to have open overstories and that bigleaf maple is only
able to survive under these somewhat open conditions.  Bigleaf maple's
shade tolerance is reported as low to moderate [39].  Research has shown
that bigleaf maple seedlings are able to establish themselves under
coniferous stands but will not survive more than a few years unless they
receive sufficient light [24].

Bigleaf maple most often grows where soils are moist [20].  It attains
its best development and sometimes forms pure stands on deep alluvial
soils near streams [20].  It is extremely flood tolerant [39] and often
persists in floodplain habitats.

On low elevation upland sites in Oregon and Washington, it occurs as
scattered trees in moist locations within relatively open canopied
Douglas-fir, western hemlock, western redcedar, grand fir, redwood, or
mixed-evergreen forests [16,21,33,54].  In fact, it is one of the only
hardwood trees encountered commonly throughout low elevation Pacific
Northwest coniferous forests.

Because of higher rainfall and humidity and a short dry season, bigleaf
maple occurs over a broader range of sites in the western Cascades of
Oregon than in other parts of its range [60].  Here it is typically
mixed with conifers and may comprise up to 20 percent of stand basal
area [24,60].

At the southern portion of its range, in southern and central
California, bigleaf maple is usually riparian.  In the Sierra Nevada,
North Coast Ranges and Klamath Mountains of California, it is more
generally distributed and grows scattered on uplands within redwood,
Douglas-fir, and mixed-evergreen forests [28,54].

Soils:  Bigleaf maple is found on a variety of soils from deep and loamy
to shallow and rocky [30].

Common associates:  Common associates in the northern part of its range
are red alder, Douglas-fir, western redcedar, grand fir, western
hemlock, black cottonwood, Oregon white oak, vine maple (Acer
circinatum), Pacific yew (Taxus brevifolia), and Oregon ash.  Common
associates in the southern part of its range include California-laurel
(Umbellularia californica), redwood, willows, Pacific madrone, white
alder, coast live oak, and California sycamore (Platanus racemosa) [20].

Elevation:  Upper elevational limits are as follows [20]:

    up to 1,000 feet (305 m) in coastal British Columbia
          1,500 feet (457 m) on the Olympic Peninsula, Washington 
          3,400 feet (1,036 m) in the central Coast Range, California
          5,500 feet (1,676 m) on west slope of the Sierra Nevada Mtns
          7,000 feet (2,134 m) in the southern Coast Range, California


SUCCESSIONAL STATUS : 
The successional role of bigleaf maple in Pacific Northwest coniferous
forests is not clear.  It appears to be a seral species.  In the western
Cascades of Oregon, Hawk [32] found bigleaf maple to be more common in
early seral stages of Douglas-fir forests and attributed this to bigleaf
maple's inability to survive the dense shading which occurs in older
stands.  However, Bailey [5] observed that along the southern Oregon
coast, bigleaf maple was found under both dense and open canopy forests,
and in young, mature, and old growth forests.  Observations of bigleaf
maple occurrence over a wide range of forest conditions may possibly be
attributed to the fact that seedlings of bigleaf maple often establish
under overstories of conifers or other hardwoods.  However, they are not
particularly shade tolerant.  Seedling growth rates are very slow, and
seedlings can survive for only about 15 years, unless a disturbance
opens the overstory and allows better light penetration [24,29].  An
Oregon coast study found that bigleaf maple seedlings were most abundant
in 40- to 80-year-old Douglas-fir stands [23].

Along low elevation streams and rivers, bigleaf maple often occurs in
hardwood forests which are maintained by flooding.  In the northern
Cascades, bigleaf maple, black cottonwood, and Douglas-fir are common
riparian dominants in areas disturbed by flooding during the past 50 to
80 years [2].  On the Olympic Peninsula of Washington, succession along
the Hoh River is dependent on the ages of four terrace levels formed
from the erosional activity of the river.  Bigleaf maple was found
primarily on the first (youngest) terrace, forming a 400-year-old Sitka
spruce-bigleaf maple-black cottonwood community which eventually gives
way to Sitka spruce-western hemlock forests [19].

In the interior valleys of Oregon, bigleaf maple and Douglas-fir are
considered late seral or climax and often follow Oregon white oak stands
[21,29].  


SEASONAL DEVELOPMENT : 
Flowering and leaf emergence occur simultaneously in late March or April
[30,51].  Fruit ripening generally occurs between September and October,
and seed is dispersed from October through January [46].  Leaf fall in
western Oregon is mostly completed by the third week in October [13,51].
An Oregon study found that about 90 percent of leaves fell within a few
weeks after the first frost [13].
 

Related categories for Species: Acer macrophyllum | Bigleaf Maple