BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Acer negundo | Boxelder 



GENERAL BOTANICAL CHARACTERISTICS : 
Boxelder is a native deciduous small to large tree with an irregular
form.  The trunk often divides near the ground into a few long,
spreading, rather crooked limbs, which branch irregularly to support a
broad, uneven crown.  When growing among other trees, boxelder forms a
high, open crown, with the undivided portion of the trunk much longer
and usually straighter than that of an open-grown tree [27].  This
variable-sized tree may reach 70 feet (21 m) in height and 3 feet (0.92
m) in diameter but is more often medium sized, from 40 to 50 feet (12-15
m) high and from 1 to 2 feet (0.3-0.6 m) in diameter [27].  Boxelder may
also appear as a large shrub [50], and in upland soil on the Great
Plains this tree is usually only about 25 feet (8 m) high with low,
crooked branches [45].

Boxelder has a fast growth rate [33,41] and a short life span [46]; it
typically lives for 75 years, with 100 years maximum longevity [33].
Growth is rapid when young; long, smooth, green annual shoots extend 2
feet (0.6 m) or more in a year.  At maturity growth slows and brittle
trunks and limbs shatter; old trunks frequently put out clusters of
sprouts and sometimes develop large burls [31].

A drought-tolerant tree once established, boxelder's roots are shallow
and spreading, except on deep soils [41,46].  The bark is light grey and
smooth but becomes furrowed into narrow, firm ridges and darkens with
age.  Twigs are stout, light green to purplish or brownish with a
polished look or are often covered with a whitish bloom that is easily
rubbed off.  The blunt buds are 0.125 to 0.25 inch (2-5 mm) long with
one or two pairs of scales and are coated with fine white hairs [27].

Boxelder is the only maple with divided leaves.  The three to seven
leaflets are from 6 to 15 inches (15-38 cm) long, light green above and
greyish green below, usually without hairs.  The leaflets are shallowly
lobed or coarsely toothed [27].  This completely dioecious tree has pale
green male and female flowers with a strongly pronounced reduction of
flower parts, and contains no rudimentary parts of the opposite sex.
Male flowers are on slender stalks in loose clusters, and female flowers
are arranged along a separate stem [27,54].

The fruit is composed of two fused, winged samaras which eventually
separate upon shedding.  The angle separating the two wings is less than
60 degrees [27].  The samaras, about 1.5 inches (4 cm) long, hang in
long chains on slender stalks, mature in autumn, and remain on the tree
well into the winter [31].  Each contains a single seed without an
endosperm [39].  Seeds are 2 to 3 times as long as they are wide and are
markedly wrinkled.

Many ecotypes of this species occur.  Varieties are distinguished by the
morphological characteristics of glaucousness, pubescence, or color of
the branches and/or samaras.


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Boxelder reproduces both sexually and asexually [41].  Large seed crops
are produced each year [39].  Seeds persist through the winter; they are
dispersed by wind or by birds and squirrels [31,51].  Wind will carry
these winged seeds up to 100 yards across a snow surface [31].

Boxelder establishes by seed under a wide range of conditions:
immediately after disturbance on moist disturbed soil [40], along
riverbanks [51], and in areas with heavy cover and medium to heavy
competition [28].  In southern Illinois, Hosner and Minckler [28]
reported reproduction of boxelder on areas with light, medium, and heavy
duff:

                      light duff        med duff       heavy duff
                     (over 0.5 in)   (0.5 to 2 in)    (over 2 in)

No. of 1- and              
2-yr-old seedlings        121              90              35

Vegetative reproduction is also common on damaged plants of this
species.  New shoots will appear on exposed or injured roots [50].
After the extreme drought condition of the 1930's in the Great Plains,
during which nearly all boxelder trees in shelterbelts 30 years or older
died back to the ground, many trees recovered by producing root sprouts,
forming a dense hedge or undergrowth [1]. In shelterbelts of the
northern Great Plains, boxelder has a dense growing habit resulting from
the plant suckering at the root collar [13].  Seven years after timber
harvest in a South Carolina bottomland, sprouts from boxelder stumps
greater than 20 inches (51 cm) in diameter were reported to be dying or
losing vigor [38].  Although this species will produce abundant sprouts
after disturbance, the primary method of reproduction is through seed,
due to the quantity produced each year and the facility of its
distribution.


SITE CHARACTERISTICS : 
Boxelder generally grows on moist sites along lakes and streams, on
floodplains, and in low-lying wet places where its shallow root system
can find abundant moisture [31].  Hardy to extremes of climate [41],
boxelder is drought tolerant once well established and can also
withstand short periods of flooding [46].

Soils:  This species is able to tolerate a wide variety of soils but
shows a strong preference for well-drained, aquic soils [35].  Although
boxelder will grow on soils from gravel to clay, it grows best on deep,
sandy loam, loam, or clay loam soils with a medium to rocky texture and
a pH of 6.5 to 7.5 [9].

Associates:  Throughout its range, boxelder is most often associated
with various species of cottonwood (Populus spp.) and willow (Salix
spp.).  On the northern Great Plains, boxelder will generally outlive
cottonwood and willow to become an associate in American elm (Ulmus
americana), hackberry (Celtis occidentalis), mulberry (Morus spp.), and
green ash communities [2].  In the central Great Plains and in the
eastern United States, boxelder occurs with elms (Ulmus spp.), sugar
maple (Acer rubrum), basswood (Tilia spp.), and ashes (Fraxinus spp.),
which eventually replace boxelder in the overstory along with other more
durable and shade-tolerant species [31,51].  At higher elevations on the
Utah plateaus, boxelder occurs in the riparian zone with water birch
(Betula occidentalis), narrowleaf cottonwood (Populus angustifolia),
willows, and blue spruce (Picea pungens) [31].  In New Mexico and
Arizona, scattered along streambeds in riparian forests at higher
elevations, boxelder is a typical canopy dominant with Arizona alder
(Alnus oblongifolia) and coyote willow (Salix exigua) [35].

Elevation: The elevational ranges for boxelder in several states 
are as follows [9,29,31,35,36,46]:

     AZ        from  4,450 to 8,000 feet (1,356-2,438 m)
     CO              4,500 to 7,870 feet (1,372-2,400 m)
     MT              2,240 to 4,500 feet (680-1,372 m)
     NE              2,600 to 4,500 feet (792-1,372 m)
     NM              6,350 to 6,775 feet (1,935-2,065 m)
     ND              2,310 to 3,840 feet (704-1,170 m)
     SD              3,000 to 3,500 feet (914-1,067 m)
     UT              4,000 to 10,000 feet (1,219-3,048 m)             
     WY              3,500 to 7,700 feet (1,067-2,347 m)
     Mexico          4,600 to 5,947 feet (1,400-1,800 m)


SUCCESSIONAL STATUS : 
Boxelder occurs in a variety of forest types ranging from early to late
seral, making its successional position difficult to determine.  It is
moderately shade tolerant but does not reproduce in its own shade.  It
usually establishes under pioneering species such as cottonwood and
willow, particularly in the northern Great Plains [2], and is then
followed by more shade-tolerant, climax species [40].  In Arizona and
New Mexico, boxelder is a dominant or codominant overstory species in
several high-elevation riparian communties [48].


SEASONAL DEVELOPMENT : 
Boxelder flowers from March through May with or before the appearance of
the leaves.  The fruit, a winged samara, ripens from September through
October and is dispersed from September through March [39,50,53].
Boxelder's leaves turn a dull yellow color in the autumn and drop
throughout the fall and winter [40].

Related categories for Species: Acer negundo | Boxelder