BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Vaccinium myrtillus | Dwarf Bilberry 



GENERAL BOTANICAL CHARACTERISTICS : 
Dwarf bilberry is a slender-branched, somewhat spreading, dwarf
deciduous shrub which reaches 4 to 18 inches (10-18 cm) in height
[57,87,92,97,105].  Plants are typically shorter at higher elevations
[100].  This rhizomatous shrub generally forms open colonies [92].
Roots are fibrous and much branched, with maximum diameters of 0.06 to
0.08 inch (1.5-2.0 mm) [41].  Numerous fine adventitious roots form an
interconnected mat in the top 2 inches (5 cm) of peat [41].

Twigs are green or less commonly yellowish, glabrous or puberulent, and
sharply angled [43,50,92,97].  Stems often become reddish or
orange-tinged when exposed to full sunlight [87].  Branches tend to be
thicker and less numerous than the morphologically similar grouse
whortleberry [43], and dwarf bilberry lacks the unique broomlike
branching typical of grouse whortleberry [87].  Dwarf bilberry also has
larger leaves and flowers and often puberulent stems [98].  Stem
morphology has been examined in detail [69].  The maximum age of aerial
shoots is generally estimated at 15 years [92].  However, in parts of
Sweden, stem ages average 18 years [20].

Small, simple, alternate leaves are ovate to lanceolate or broadly
elliptic with serrate margins [50,92,98].  Leaves are acute to obtuse at
the apex and rounded to broadly cuneate at the base [97,98].  Leaves are
light green and 0.4 to 1.2 inches (1-3 cm) in length [43].  Dwarf
bilberry leaves turn red, yellow, or brown in autumn [95].

The pink, cream, or greenish-white flowers are borne singly in the axils
of new stems [73,92,98].  Flowers are small, waxy, and urceolate to
campanulate [43,50].  Fruit of dwarf bilberry is a spherical berry 0.2
to 0.3 inch (5-8 mm) in diameter [43,65].  Fruit color ranges from dark
red to bluish or purplish black [43].  Dwarf bilberry is single-fruited
[65].  Berries are generally not glaucous, although a glaucous bloom is
occasionally observed [73,92].  Berries contain many nutlets which
average approximately 0.04 inch (1 mm) in length [92,97].


RAUNKIAER LIFE FORM : 
   Phanerophyte
   Geophyte


REGENERATION PROCESSES : 
Dwarf bilberry can reproduce from seed or by vegetative means.

Vegetative regeneration:  Forms of vegetative regeneration appear to be
of primary importance after fire [81] or other disturbance.  However,
colonies increase laterally through rhizome expansion even in the
absence of disturbance.  Annual radial increases average 2.8 inches (7
cm) [(2 to 4 inches) (5-10 cm)] per year [81,92].

Dwarf bilberry possesses an extensive, frequently branched network of
rhizomes averaging 0.12 to 0.24 inch (3-6 mm) in diameter [41].  The
total length of rhizomes occasionally exceeds 3.3 feet (1 m), but the
amount producing sprouts typically measures only 28 to 35 inches (70-90
cm) in length [7].  Rhizome depth ranges from 0.24 to 1.2 inches (6-30
mm) below the soil surface [41,90].  Sprouting ability declines with age
[7].  Although rhizomes of 23 to 28 years of age have been reported
[92], few rhizomes older than 15 years produce aerial shoots with new
growth [7].  The extensive rhizome network allows for rapid regeneration
after disturbance [81].  Where portions of the stem base survive,
regeneration through surviving aboveground axillary buds also occurs
[62].

Seed:  Dwarf bilberry fruit contains an average of 18 to 20 viable seeds
per berry with an average of 18 imperfectly-formed seeds [81,91].  Seeds
weigh an average of 25 mg per 100 seeds [91].  Seed production generally
begins at age three [71] and is subject to considerable annual
variation.  [see Management Considerations - Berry Production].  Bees
are the primary pollinators [79].

Germination:  Germination averages 35 to 46 percent following various
types of pretreatment.  Germination of seed exposed to low temperatures
(32 degrees F [0 degrees C]) for 3 weeks averaged 41 to 64 percent [81].
Good germination has been reported after seeds were exposed to 14 hours
of light at 82 degrees F (28 degrees C) followed by 10 hours of darkness
at 55 degrees F (13 degrees C) [91].  Fresh seed germinated well under a
similar regime, or when exposed to alternating periods at 71 degrees F
(22 degrees C) and 41 degrees F (5 degrees C) [91].  Heat treatments
were found to produce some germination although the amount was irregular
[62].  The effect of temperature on germination was as follows [62]:

               effect of heat treatment on seed germination
               total germination after 24 weeks - percent -

              50 C            75 C             100 C

control        0               -                 -
30 sec        14               8                20
1 min          0               2                 6
2 min         16               0                 2

                effect of pretreatment on imbibed seeds after
                21 weeks at 0 degrees C - 

 treatment                      percent germination

control                                64
cold only                               6
cold + 50 C for 1 minute               10
cold + 50 C for 2 minutes              14
cold + 50 C for 3 minutes              16
cold + 100 C for 1 minute               8
cold + 100 C for 2 minutes              4
cold + 100 C for 3 minutes              2

Seedbanking:  Evidence for seedbanking in dwarf bilberry appears
contradictory.  Some researchers have observed very few seeds in the
soil despite high coverage at the site and doubt if seed banking is an
important regenerative strategy in this species [89].  Most Vacciniums
are characterized by seed of relatively short viability which is readily
damaged by heat [64].  However, others emphasize the importance of seed
banking in dwarf bilberry [29,35,92].  Soil samples in Wales, for
example, have yielded 28 buried viable seeds per square foot (300 per/sq
m) [92].  In a Swedish forest, seeds were found in the lower humus layer
of 120-year-old stands as well as in the moss-litter layer of 50- and
169-year-old stands, suggesting a "continuous input of seeds" [35].
Seedlings were produced as follows from 25 buried soil cores, each of
which was 4 inches (100 mm) in diameter [35]:

   stand age     cover     frequency      seedlings produced
   (years)        (%)         (%)                (#)

       16          5           80                 22
       29         35          100                 10
       50         58          100                 93
      120         56          100                 49 
      169         60          100                 95

In Sweden, single buried berries occasionally produced clusters of up to
20 seedlings [35].  Longevity of dwarf bilberry seed has not been
documented, although Granstrom [35] reports that many buried seeds may
be "quite old."

Seed dispersal:  Seeds of dwarf bilberry are widely dispersed by many
birds and mammals [35,81].  In laboratory tests, seedlings have
germinated from pellets of various lagomorphs [35].

Seedling establishment:  In many locations, including parts of northern
Europe, seedlings are rarely observed [81,90].  Seedlings of Vacciniums
are also rare in North America [92, (P. Stickney, pers. comm. 1990)].
However, seedling establishment of dwarf bilberry appears variable.
Establishment is reportedly poor on burned sites, on scarified
clearcuts, and in mature closed canopy forests [35].  However, Vander
Kloet [92] reports that on favorable sites in Sweden, seedlings may
number 25 per square foot (270 per square meter).  Initial development
of seedlings is very slow [81].


SITE CHARACTERISTICS : 
Dwarf bilberry grows in open woods, on hillsides, high ridges, hummocky
seepage slopes, and moraines [4,49,92].  In mountains of the Southwest,
it occurs on all slopes and aspects at higher elevations [32].  

Climate:  Upland spruce-fir sites occupied by dwarf bilberry are often
cold and steep [47].  On many sites, snow commonly persists until late
spring [32].

Soils:  Most Vacciniums require acidic soils and can grow on infertile
sites which have relatively small amounts of many essential elements
[53].  Dwarf bilberry requires little potassium and can grow well where
ammonium is the only source of nitrogen [46].  In Scandinavia, dwarf
bilberry appears to be most abundant on sites of intermediate fertility
[20].  It is commonly associated with raw humus in parts of northeastern
Scotland and Scandinavia [107,108].  It commonly grows on shallow, rocky
soils in the southwestern United States [101].  Growth is generally
marginal on poorly aerated soil [53].

Elevation:  Dwarf bilberry typically grows at middle to high elevations.
Elevational range by geographic location is as follows
[26,49,100,85,92,98]:

      from 7,000 to 12,000 feet (2,134-3,660 m ) in the Southwest
           8,000 to 11,000 feet (2,438-3,355 m) in AZ
           7,500 to 13,000 feet (2,286-3,965 m) in CO
           4,300 to 8,000 feet (1,311-2,438 m) in MT
           9,500 to 11,000 feet (2,896-3,965 m) in UT
           8,500 to 8,500 feet (2,591-2,591 m) in WY
           656 to 3,800 feet (200-1,150 m) in Britain
           > 5,250 feet (1,600 m) in the Cascades and Rocky Mtns.        
           3,000 to 5,000 feet (914-1,524 m) east of the Cascades


SUCCESSIONAL STATUS : 
Dwarf bilberry occurs as a climax dominant in many high elevation
spruce-fir forests of western North America [5,25,84].  In high
elevation Engelmann spruce-subalpine fir and lodgepole pine forests of
Colorado, it assumes prominence after the first postfire century,
following the decline of rose (Rosa spp.), grouse whortleberry, and
kinnikinnick.  During later stages, it commonly assumes dominance with
cliffbush (Jamesia americana) and common juniper (Juniperus communis).
Occurrence of dwarf bilberry by stand age has been documented as follows
in Colorado [16]:

                         spruce - fir
                         stand age (years)

                   1   2   8    8   18   74   200    280   290   300   400
density (avg. # 
    stems/plot)   -    -  66.6  45.0 -  171.0 151.5  79.2  96.3 132.8  136.8
frequency (%)     -    -  80    40      100   100    60    70   100     80

                          lodgepole pine
                          stand age (years)

                  8     18   18    85  108   115  190  248   251  257
density (avg. #
     stems/plot) 68.4  66.6  10.8 43.2 100.5  -   66.6 21.6  38.8 97.8
frequency (%)    40    80    20   80   100    -   80   21.6  60   100

In southern Finland, dwarf bilberry becomes abundant during secondary
succession after species such as fireweed (Epilobium angustifolium) have
flourished and declined [96].

In some locations, this shrub may become important in early seral
communities.  In parts of Britain, dwarf bilberry and lingonberry
commonly codominate heather communities soon after fire but then decline
in later successional stages [81].  Natural dieback of 12-year-old
bilberry stands has been reported [7].


SEASONAL DEVELOPMENT : 
Phenological development of dwarf bilberry varies with climate,
latitude, and longitude [95].  New leafy shoots generally develop in
March or April [81].  In a Finnish study, annual vegetative growth began
as buds began to swell on May 13 [95].  By June 1, leaf buds had
completely opened and vegetative growth continued until early to
mid-June.  Leaves were colored or shed by October 19 [95].  The active
growth period lasted approximately 5 months.  Development tends to be
delayed at higher elevations [81].

Seed set and berry formation begins two to four weeks after pollination
[81].  Berry ripening is completed about 50 days after flowering [95].
Phenological development was documented as follows in a Finnish study
[95]:

                               average # of days (since Jan. 1)

  beginning of veg. dev.                   136.3
  leaf buds begin to open                  147.6
  leaf buds completely open                152.3
  start of budding                         150.6
  opening of flowers                       153.4
  cessation of growth                      176.3
  beginning of green berry phase           170.8
  berries ripening                         202.1
  autumn color begins                      222.6
  autumn color ends                        292.2

Generalized seasonal development by geographic location is as follows
[49,73,95,97]:

     location         flowering         fruiting
 
     n ID             May-August           --
     AZ               June-July            --
     Southwest        May                 July
     s Finland        mid-May              --
     n Finland        early June           --

Related categories for Species: Vaccinium myrtillus | Dwarf Bilberry