BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Betula glandulosa | Bog Birch 



GENERAL BOTANICAL CHARACTERISTICS : 
Throughout much of its range, bog birch is a deciduous, low and
spreading to erect shrub, with one to several main stems from 3 to 6.5
feet (1-2 m) tall [4,19,60,63].  The smooth, thin bark is reddish brown,
becoming dark gray, and does not peel readily [60].  The twigs have
yellowish, crystalline resin glands [60,63].  The 0.4- to 1-inch-long
(1-2.5 cm) leaves are nearly orbicular [4].

In the arctic, towards the northern limit of its distribution, bog birch
is a prostrate shrub, often less than 8 inches (20 cm) tall [62].
Vegetative reproduction is prevalent in these northern plants and clones
often form large continuous mats [22].

Characteristics used to distinguish bog birch (Betula glandulosa) from
swamp birch (Betula pumila var. glandulifera) include [6]:

                   B. glandulosa              B. pumila var. glandulifera

samara wings    narrow: (less than 1/2        broad: (greater than 1/2 as
                as broad as the body)         broad as the body)

leaves          broadly ovate to orbicular,   obovate, greater than 10
                less than 10 teeth per side   teeth per side

size            generally less than 6.5 feet  up to 13.1 feet (4 m)
                (2 m)
chromosomes     2n = 28                       B. pumila 2n = 56


RAUNKIAER LIFE FORM : 
   Phanerophyte
   Chamaephyte


REGENERATION PROCESSES : 
Throughout much of Alaska, Canada, and the contiguous United States, bog
birch reproduction is primarily sexual.  Plants produce abundant, small
seeds which are dispersed by wind.  At the northern distributional limit
of bog birch, plants rarely produce viable seed and regenerate by
vegetative layering [22,62].

Seed production and dispersal:  Bog 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 [5].  Most individuals produce numerous
catkins which generally contain 30 to 50 winged samara fruits [62].
Each samara contains a single seed.  The small seeds average between 3
and 5 million per pound [5].  Samaras are dispersed principally in the
fall by wind.  During late fall and winter the catkins disintegrate on
the shrub, a process which may be aided by the foraging activities of
small birds such as chickadees and kinglets [5].  This releases any
remaining seed to fall on the snow.  Seed has been observed blowing over
crusted snow [5].  Any remaining seeds are dispersed in the spring [62].

Germination:  Seed that are dispersed in the fall and those that
overwinter on the plant are viable [49].  Germination occurs fairly
rapidly under normal temperatures after winter stratification [34].  How
long bog birch seed remains viable is not known; however, seed of most
Alaska shrubs lose their viability if they do not germinate during the
first or second growing season [34].

Northern Plants:  In the arctic, recruitment of new individuals from
seed is almost nonexistent.  These northern plants regenerate by
vegetative layering; little or no sexual reproduction occurs.  Here
clones develop by lateral extension of branches beneath the surface moss
layer, rooting at nodes, with only short vertical branches extending
above the surface vegetation [62].  It is hypothesized that the
successful establishment of seed may be restricted by the short growing
season of the northern environment [62].


SITE CHARACTERISTICS : 
Bog birch is typically a wetland species occurring in fens, swamps, bogs
(both sphagnum and nonsphagnum), muskegs, moist-to-wet tundra, wet
meadows, moist-to-wet basins, and along low gradient streams and lakes
[4,18,29,37,43,44,60].  This birch has a very high frost tolerance and is
distributed over large areas of permafrost [30].  Permafrost prevents
water percolation, which often results in the development of extensive
muskegs and bogs.  Bog birch has a moderate to high shade tolerance [30]
and is found in the understory of many black and white spruce taiga
communities of Alaska and Canada [14,55,60].  It is apparently more
common within black spruce types than white spruce.  Black spruce
typically occupies poorly drained sites, such as those underlain by
permafrost, which contain a thick mat, often made up of sphagnum mosses
(Sphagnum spp.), sedges (Carex spp.), and grasses.  Bog birch may be
interspersed on moist cottongrass-dominated tundra sites or occur on
hummocks in wet tundra sites [60].  On some alpine sites it occasionally
occurs in relatively dry rocky habitats [4,27].

Soils:  Surface layers often have large accumulations of organic matter.
In fens and swamps these are normally peats derived from nonsphagnum
mosses and sedges; in bogs peats are normally derived from sphagnum
mosses.  Floodplain soils may have surface textures of silt, fine sandy
loam, or organic loam [29].
 
Soil-water relationships:  Krajina and others [30] reported that the
nutritional requirements of bog birch are low and stated that "It
prefers soils in which accumulation of acid mor humus forms causes
eluviation of nutrients, especially calcium and magnesium, from the
uppermost soil horizons."  This is consistent with other researchers
[37,49] who observed bog birch to be uncommon or lacking in swamps and
fens with minerotrophic (rich in minerals and nutrients), poorly drained
soils but common in ombrotrophic (low nutrient), acidic bogs.  However,
Pojar and others [44] found bog birch occurring only in minerotrophic
swamps which derived their water as runoff from adjacent mineral uplands
high in dissolved ions, but absent from ombrotrophic, acidic,
sphagnum-derived peat bogs.

Swamp birch (Betula pumila var. glandulifera) has been reported in
minerotrophic fens [10,49], weakly minerotrophic swamps [21], and
ombrotrophic bogs [8,10].

Swamps, fens, wet meadows, swales, and low gradient streams often flood
seasonally.  These areas often hold standing water in the spring, and
water tables often remain near the soil surface throughout the summer
[18,29,43,44].

Elevation:  Elevational ranges for western states are presented below
[11,19,38,43,63]:

from 6,500 to 7,500 feet (1,981-2,286 m) in CA
     7,700 to 11,400 feet (1,734-3,475 m) in CO
     4,000 to 8,000 feet (1,219-2,438 m) in MT
     6,000 to 11,000 feet (1,829-3,354 m) in UT
     6,400 to 10,500 feet (1,951-3,201 m) in WY


SUCCESSIONAL STATUS : 
Bog birch is typically found on sites where the water table is kept high
from runoff of nearby uplands.  Bog birch maintains itself in these
moist habitats and appears to be a topoedaphic climax species [35,44].


SEASONAL DEVELOPMENT : 
Bog birch is a deciduous shrub.  The 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."  The majority of seed are dispersed in the
fall.  

Flowering dates for several western states are presented below
[11,41,51]:

State      Flowering Begins    Flowering   Flowering Ends

 AK                            May-June            
 CO             April                        August
 ID             April                        June
 MT             June                         Sept
 ND                            Mid-June  (B. pumila var. glandulifera)       
 SD                            Mid-June  (B. pumila var. glandulifera)
 UT             July                         July
 WY             June                         Aug

Fruit ripening dates for the following states are presented below
[51,60]:

State       Fruits reach maturity

 AK             July-August     
 ND             August-Sept (B. pumila var. glandulifera)
 SD             August-Sept (B. pumila var. glandulifera)

Related categories for Species: Betula glandulosa | Bog Birch