BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Betula occidentalis | Water Birch 



GENERAL BOTANICAL CHARACTERISTICS : 
Water birch is a highly variable species occurring as a deciduous shrub
or small tree.  On favorable sites it may attain tree stature and grow
to about 33 feet (10 m) tall with several trunks having diameters of
about 14 inches (36 cm) [5,21].  However, it is more often found as a
shrub with several spreading trunks.  As plants mature, dormant buds
hidden beneath the bark at the base of the trunk begin to sprout sending
up small new trunks alongside the original one.  As these grow they also
produce sprouts so that a massive clump of up to a hundred or more stems
of all sizes is produced [30].  This dense thicket of multiple stems may
extend outward for several yards [15,47].  Windthrow is common since
plants are shallowly rooted and grow on sites with high water tables
[30].  The bark is thin, dark reddish-brown or yellowish-brown to brown
to nearly black on young trunks and has pale horizontal lenticels.  It
does not peel as readily the bark of paper birch (Betula papyrifera)
does [21,46].  The leaves are simple, alternate, ovate to elliptic, 0.5
to 2 inches (1-5 cm) long and 0.25 to 1.6 inches (0.7-4 cm) wide, and
usually doubly serrate [5,46].  Mature plants have separate male and
female catkins. One or sometimes two pistillate catkins occur on a
lateral spur and become conelike at maturity.  The fruit is a
broad-winged samara.

In eastern Oregon, eastern Washington, western Idaho, and southern
British Columbia water birch freely hybridizes with paper birch
producing many intermediate forms [20].  This further adds to the high
variability this species exhibits.


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


REGENERATION PROCESSES : 
The dispersal of thousands of small wind-blown seed is water birch's
primary method of reproduction.

Water birch plants are monoecious.  Male flowers occur in narrow catkins
that form in the summer, remain naked until the next spring, and then
elongate and shed their pollen.  The pistillate catkins appear with the
leaves, then become conelike as they mature by late summer or autumn.
Seed, in the form of winged nutlets, are dispersed in the fall by wind
and sometimes by water.  During late fall and winter the catkins
disintegrate on the plant, a process which may be aided by the foraging
activities of small birds such as chickadees or kinglets.  Seeds have
been observed blowing over crusted snow [6,30].

Birch (Betula spp.) seeds are very small and light.  All birch average
from several hundred thousand to a few million seed per pound [6].
Light is apparently needed for good germination.  Seed can germinate
soon after dispersal in the fall or the following spring.  Nursery
managers have found that birch seedlings require shade for 2 to 3 months
during their first summer [6].


SITE CHARACTERISTICS : 
Water birch is typically a riparian plant, occurring almost exclusively
along streams, springs, or other water courses [1,15,21,35].  It is most
often found in colonies adjacent to streams on alluvial terraces or
steep sideslopes [15,18,35,47].  This species is very flood tolerant, in
some areas enduring floods every year [26].  Plants may occasionally be
found on uplands [16,36].

Associated species:  Water birch is commonly found with other riparian
trees and shrubs.  Commonly associated trees include several
cottonwoods, boxelder, bigtooth maple (Acer grandidentatum), aspen,
peachleaf willow (Salix amygdaloides), Douglas-fir, and Rocky Mountain
juniper (Juniperus scopulorum) [25,30,34,35].  Commonly associated
shrubs include red-osier dogwood (Cornus sericea), woods rose (Rosa
woodsii), nootka rose (R. nutkana), chokecherry (Prunus virginiana),
thinleaf alder (Alnus incana ssp. tenuifolia), Saskatoon serviceberry
(Amelanchier alnifolia), sandbar willow (Salix exigua), yellow willow
(S. lutea), inland currant (Ribes setosum), and skunkbush sumac (Rhus
trilobata) [15,18,24,34,47].

Soils:  Water birch occurs on a wide variety of soil textures.  In
Montana, silty or sandy soils overlying a rocky substrate are most
common [15].  In Utah, coarse-textured soils are most common, and most
soils contain at least 35 percent rock fragments [35,47].  Profiles are
usually thin and overlie river cobbles [18].  Water birch has very high
nutritional requirements especially for magnesium and calcium.  Both
elements are normally available for uptake where it grows [26].

Elevation:  Water birch generally occurs at low to middle elevations
[15,18,35,47].  Elevational ranges for the following western states are
presented below [8,13,19,23,33,39,46]:

from 7,000 to 8,000 feet (2,134-2,438 m) in AZ
     2,000 to 9,000 feet (610-2,743 m) in CA
     5,500 to 8,000 feet (1,676-2,438 m) in the White Mtns of CA
     4,920 to 9,000 feet (1,500-2,750 m) eastern slope, southern
                                           Sierra Nevada Mtns of CA,NV
     5,000 to 9,500 feet (1,524-2,896 m) in CO
     3,000 to 8,000 feet (914-2,743 m) in MT
     4,000 to 8,800 feet (1,220-2,685 m) in UT
     5,800 to 8,500 feet (1,768-2,591 m) in WY
              


SUCCESSIONAL STATUS : 
Although water birch communities are normally restricted to streamsides
which receive seasonal flooding, most communities appear to be stable,
with little changes in the vegetation due to flooding [35,47].


SEASONAL DEVELOPMENT : 
Water birch is a deciduous shrub or small tree.  Male catkins begin
blooming in the spring before or as the leaves expand.  After
fertilization the female catkins ripen and develop into conelike
structures which resemble "miniature spruce cones" [24] and
disintegrate on the tree in the fall and winter [6,30].  The leaves turn
yellow before they drop in the fall [36].

Flowering dates for several western states are presented below
[8,33,36]:

  State     Flowering Begins       Flowering Ends

   CA           April                   May
   CO           May                     June        
   ID           Feb                     June
   MT           April                   Sept
   ND           May                     June
   UT           May                     July
   WY           May                     August

Related categories for Species: Betula occidentalis | Water Birch