BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Acer grandidentatum | Bigtooth Maple 



GENERAL BOTANICAL CHARACTERISTICS : 
Bigtooth maple is a deciduous shrub or small tree of variable size.  On
dry sites it is often a shrub, with numerous stems reaching 20 feet (6.1
m) in height.  On moist locations it often occurs as a single- or
multiple-trunked tree growing to 40 or 50 feet (12.2-15.2 m) tall
[5,66].  Mature maple stands in the Wasatch Mountains of southeastern
Idaho and northern Utah are typically 10 to 30 feet (3-9 m) tall with a
relatively closed canopy [55,60].  A 16-year-old bigtooth maple from
Provo Canyon, Utah growing on a north-facing slope at 5,100 feet (1,554
m) in elevation was 43 inches (107 m) tall [13].  Tree-sized bigtooth
maple may attain diameters of 12 inches (30 cm) [30].  Bigtooth maple
and Gambel oak have similar growth rates for their first 15 to 20 years,
but after 20 years, bigtooth maple grows faster in stem and crown
diameter [12].


Bigtooth maple has thin bark [30,67].  The root system is shallow but
wide spreading [63].  The leaves are palmately three- to five-lobed and
mostly 1 to 4 inches (2.5-10 cm) wide [68].  The fruit is a
double-winged samara.  The wings are about 0.75 to 1.25 inches (1.9-3.2
cm) long.


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


REGENERATION PROCESSES : 
Bigtooth maple reproduces sexually and vegetatively.  Reproduction by
seed is important in establishing bigtooth maple in new areas.  Layering
is very common in older plants, however, and is the most effective
method of reproduction in Gambel oak-bigleaf maple communities
[13,15,21].

Seed production and dispersal:  Bigtooth maple flowers are wind
pollinated.  Plants may bear male flowers only or produce both male and
female flowers on the same inflorescence.  Three flowering phenotpyes
exist and include plants which are (1) bisexual each year, (2) bisexual
one year and unisexual with male flowers the other years, or (3)
unisexual with male flowers each year [6].  Trees which change their sex
expression from year to year tend to be unisexual, with only male
flowers in dry years and bisexual in wetter years.  Trees with only male
flowers are also more common on xeric versus mesic sites [6].  Plants
usually flower every 2 or 3 years.  In northern Utah during the 1970's,
bigtooth maple flowered heavily in 1972, 1975, 1977, and 1979, while
only a few plants flowered in other years [6].  The double-winged
samaras are wind dispersed during the fall and early winter.  There are
about 6,350 seeds per pound (13,995/kg) [50].

Seed viability and germination:  Germination generally occurs in April
or May.  Normally only one of the fused double samaras contains a
developed seed [15].  The seeds are susceptible to infestation by
Eucalyptus weevil larvae [4].  Germination tests show that only about 16
to 30 percent of single samaras will germinate and produce normal
seedlings [15,50].  Most maple seed can be stored for 1 to 2 years in
sealed containers without appreciable loss of viability [50].

Seedling establishment:  Bigtooth maple seedling mortality under Gambel
oak-bigtooth maple canopies is very high. In a Utah study, only 184 out
of 39,070 (0.47%) bigtooth maple seedlings per acre, originating from an
exceptional seed crop year, survived five growing seasons [15].  Only
one new seedling appeared during the 5-year period.  Nevertheless,
bigtooth maple produces more seeds than Gambel oak.  The wind-dispersed
samaras exhibit better establishment in new areas than under parent
trees where layering is common [15,21].  Herbaceous vegetation beneath
Gambel oak is often less dense than under bigtooth maple, which allows
for easier establishment of bigtooth maple seedlings [49].

Vegetative reproduction:  Layering is the predominant method of bigtooth
maple reproduction under Gambel oak-bigtooth maple canopies [15,21].  In
a Utah study, bigtooth maple vegetative growth from layering made up
78.5 percent of the total understory canopy coverage of a Gambel
oak-bigtooth maple community [21].  In this study, all reproduction by
maple was vegetative.  No new seedlings were observed.


SITE CHARACTERISTICS : 
Bigtooth maple is chiefly a tree of mountain terrain.  It occupies a
wide range of sites, occurring on many soil types, different aspects,
and in both moist and dry locations [4].  However, it is most often
located in canyons or ravines, on lower slope bases, or on north or east
exposures [2,4,40].  Because it is often associated with canyons or
ravines, bigtooth maple is often locally referred to as "canyon maple."

In the mountain-brush zone of Utah, bigtooth maple is often codominant
with Gambel oak.  Bigtooth maple-Gambel oak brushlands generally occur
between 5,500 and 7,800 feet (1,676-2,377 m) and form a belt between
lower elevation, drier sagebrush or pinyon-juniper types and higher
elevation moister Douglas-fir, aspen, or white fir forests [9,40].
Bigtooth maple tends to occupy the more mesic canyons, while Gambel oak
occupies the slopes [2,25,35,55].  However, in central and northern
Utah, especially in the Wasatch Mountains, bigtooth maple is not as
restricted to mesic sites as in other areas of the mountain-brush zone.
In these northern Utah mountain brushlands, especially north of the
northern distributional limit of Gambel oak near Logan, Utah, bigtooth
maple dominates both ravines and slopes [25,66] and may occur in nearly
solid stands [60,66].  Bigtooth maple occurs abundantly in white fir
forests which adjoin the mountain-brush zone at the same or at higher
elevations in northern Utah and southeastern Idaho [44,55].  In northern
Utah and southeastern Idaho, bigtooth maple is also found in Douglas-fir
and subalpine fir (Abies lasiocarpa) forests [44,62].

South of central Utah, bigtooth maple occurs primarily in mountain
canyons.  Throughout Arizona and New Mexico, it appears restricted to
mesic locations, and has been classified as an obligate riparian species
in New Mexico [18].  It is mostly restricted to white fir or Douglas-fir
habitat types at comparatively low elevations (about 7,000 feet [2,134
m]), where it is often the understory dominant, typically reaching 60 to
90 percent cover [1,46].  Such sites are cool, shady and moist, and
generally along the lower portions of slopes, steep-sided canyons, or
gentle drainages [23,46].


Soils: In northern and central Utah, solid maple stands are often found
on soils high in calcium [66].  Soil pH values from Utah stands range
from about 6.0 to 8.0 [4,63].  Plants are often found on medium to rocky
soil textures but may be found on many other types [63].

Common associates:  Trees and shrubs associated with bigtooth maple in
the mountain-brush zone include white fir, Gambel oak, aspen,
serviceberry (Amelanchier alnifolia), ninebark (Physocarpus malvaceous),
snowberry (Symphoricarpos oreophilus), Wood's rose (Rosa woodsii),
Oregon grape (Berberis repens), myrtle pachystima (Pachystima
myrsinites), curlleaf mountain-mahogany (Cercocarpus ledifolius),
juniper (Juniperus spp.), big sagebrush (Artemisia tridentata), and
chokecherry (Prunus virginiana) [9,21,60].  Herbaceous plants often
associated with bigtooth maple in this zone include bedstraw (Galium
spp.), sedges (Carex spp.), Utah peavine (Lathyrus pauciflorus),
American vetch (Vicia americana), feather Solomon-plume (Smilacina
racemosa), cheatgrass (Bromus tectorum), biscuitroot (Lomatium
dissectum), Kentucky bluegrass (Poa pratensis), and many wheatgrasses
(Agropyron spp.) [2,9,21].

Elevational ranges for several western states are as follows
[20,30,53,68,69]:

from  4,500 to 8,000 feet (1,372-2,438 m) in Arizona
      7,000 to 8,000 feet (2,134-2,438 m) in Colorado
      4,000 to 6,500 feet (1,219-1,981 m) in Texas
      4,200 to 7,300 feet (1,280-2,810 m) in Utah
      5,800 to 7,300 feet (1,767-2,225 m) in Wyoming


SUCCESSIONAL STATUS : 
Due to widespread disturbances such as logging, intensive livestock
grazing, mining, and fire suppression, the successional role of bigtooth
maple is unclear in the mountain-brush zone of Utah.  The extent of
oak-maple brushlands before settlement is unknown.  Bigtooth maple or
Gambel oak appears to be the dominant or codominant climax or long-term
seral species.  On most sites from Brigham City, Utah southward, Gambel
oak appears to be the climax dominant.  In the Wasatch Range from
north-central Utah to southeastern Idaho and on some sites in central
Utah, bigtooth maple becomes more prominent and appears to be dominant
at climax [9].

Bigtooth maple is currently invading many Gambel oak stands.  On many
sites, maples and oaks are segregated by topography, with bigtooth maple
occupying canyons, ravines, and slope bases, and Gambel oak occupying
the slopes [2,25,35,55].  Slope bases and ravines serve as sites from
which bigtooth maple can invade Gambel oak stands [26,57].  In the past
30 years, bigtooth maple has invaded many central and northern Utah oak
stands from such sites and has spread throughout the oaks to dominate
both ravines and slopes between drainages [21,26,49].  Some cooler sites
in this zone are capable of supporting white fir.  On such sites,
bigtooth maple may be replacing Gambel oak, but further succession could
lead to dominance by white fir [21,26].

Early ecological descriptions of the Gambel oak zone in Utah make no
mention of oak-maple communities and generally describe bigtooth maple
as occurring along water courses or streambanks [26].  The recent
invasion of bigtooth maple into oak stands shows that it has a much
broader ecological amplitude than previously thought.  Physiological
research shows that bigtooth maple can grow with oaks on the drier open
slopes because it is relatively tolerant of low water potentials [19].
If bigtooth maple is physiologically able to grow with Gambel oak under
the more xeric conditions of the open slopes, why has it only recently
invaded?  Harper and others [26] hypothesize that prior to fire
suppression, fire frequency would have been much greater on the drier
open slopes than in the ravines, and thus kept the vigorously sprouting
Gambel oak dominant.  With fire suppression, bigtooth maple has been
able to invade oak stands.  However, there have been no comparative
observations regarding fire frequency along drainages versus open
slopes, nor have there been any studies documenting the sprouting
response of bigtooth maple on these contrasting sites [26].  Research is
needed in this area.  Rogers [57] believes that increases in Gambel oak
and bigtooth maple over the past century are largely due to a
combination of fire suppression, cessation of livestock grazing, and
climatic changes.

Above the mountain-brush zone in Utah and Idaho, bigtooth maple occurs
as a seral understory tree or shrub in Douglas-fir, white fir, and
subalpine fir habitat types [44,62].

In Arizona and New Mexico, bigtooth maple occurs as a shade-tolerant,
climax understory shrub in white fir and Douglas-fir habitat types
adjacent to drainages [17,23].


SEASONAL DEVELOPMENT : 
Bigtooth maple is deciduous.  The flowers and leaves generally expand at
the same time in late April or May, about 2 weeks before Gambel oak
[21].  Seeds in central Utah mature between late July and mid-August,
with seedfall beginning in mid-August [21].  The leaves turn various
shades of red and orange before being shed in September or October [35].

Flowering times for some western states are as follows [20,21,30,67]:

Location      Begining of Flowering    End of Flowering

  AZ                April                   ----              
  TX                April                   May
  UT                April                   May
  WY                May                     July

Related categories for Species: Acer grandidentatum | Bigtooth Maple