BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Picea mariana | Black Spruce 



GENERAL BOTANICAL CHARACTERISTICS : 
Black spruce is a native, coniferous, slow-growing, small upright tree
or dwarf shrub.  Trees have a straight bole with little taper, and a
narrow, pointed crown made up of short, compact, drooping branches with
upturned ends [35].  Throughout much of its range, trees average 30 to
50 feet (9-15 m) in height and 6 to 10 inches (15-25 cm) in diameter at
maturity [35].  In Alaska, black spruce is occasionally found as a
medium-sized tree up to 60 feet (18 m) tall and 9 inches (23 cm) in
diameter, but it is usually only 15 to 30 feet (4.5-9 m) tall and 3 to 6
inches (7.6-15.2 cm) in diameter [66].  Growth is quite variable
depending upon site conditions.  In swamps in northeastern Minnesota,
black spruce showed progressively slower growth rates from the border
toward the center of swamps.  Eighty-year-old trees at a swamp border
were, on average, 60 feet (18 m) tall, but only 120 feet (37 m) away at
the center of the swamp trees were only 20 feet (6 m) tall [40].

Needles are 0.5-inch-long (1.2 cm), stiff, four-sided, dark bluish green
[35].  The bark is thin, scaly, and grayish brown.  The root system is
shallow and wide spreading.  Black spruce is very susceptible to
windthrow except in the densest stands.  Most roots are found in the
upper 8 inches (20 cm) of the organic soil horizons [65].  Cones occur
in dense clusters in the upper part of the crown.  They are 0.6- to
1.25-inch-long (1.5-3.2 cm), nearly round or egg shaped, dull gray or
blackish, and remain on the tree for several years [66].

In the extreme northern portion of its range, trees may be only 10 to 20
feet (3-6 m) tall and 1 to 2 inches (2.5-5 cm) in diameter when 100 to
200 years old [27].  In these extreme environments, needles and cones
may be only one-half of their normal size [35].  Black spruce may form
krumholz in the far north; here plant height equals the average snow
coverage [20].


RAUNKIAER LIFE FORM : 
   Undisturbed State: Phanerophyte (megaphanerophyte)
   Undisturbed State: Phanerophyte (microphanerophyte)
   Undisturbed State: Phanerophyte (nanophanerophyte)
   Burned or Clipped State: Therophyte


REGENERATION PROCESSES : 
Cone and seed production:  Black spruce has the smallest seeds of North
American spruces, averaging 404,000 per pound (890,000/kg) [55].  Trees
can begin producing seed when as young as 10 years old but generally do
not produce seed in quantity until they are 30 years old or older [65].
Some seed is produced every year, and bumper crops are produced about
every 4 years [65].  Since seed crops seldom fail and the
semi-serotinous cones release seeds over a period of several years,
stands that are 40 years old or older nearly always have a continuous
supply of seeds.  Annual seedfall in mature black spruce stands has been
reported at [29,65]:

     200,000 seeds/acre (494,000/ha) in Minnesota
     990,000-1,692,000 seeds/acre (2.45-4.2 million/ha) in Ontario
     404,000-1,900,000 seeds/acre (1.0-4.9 million/ha) in ne Ontario 
     240,000-528,000 seeds/acre (590,000-1,300,000/ha) near Inuvik, NWT 
     344,000 seeds/acre (850,000/ha) in central Alaska

Dispersal:  Black spruce cones are semi-serotinous.  They remain
partially closed and disperse seed over a period of several years.  In
Minnesota, cones release about 50 percent of their seeds within 1 year
after ripening, and about 85 percent within 5 years [68].  In
northeastern Ontario, cones contained about one-half of their seeds
after 5 years [29]; however, another study in Ontario found that after 3
years, cones retained only about 2 percent of their seeds [65].  Some of
this variation is probably related to weather, as cones tend to open in
warm, dry weather but remain closed in cold, wet weather [29].
Dispersal occurs throughout the year but is greatest in the winter and
spring and lowest in the fall [65].  In northeastern Ontario, 58 percent
of annual seedfall is dispersed in March, April, and May [29].  In
Minnesota, annual seedfall was: 9 percent in August, 19 percent in
September, 38 percent from October through April, 13 percent in May, 14
percent in June, and 7 percent in July [27].  Most seed is dispersed
within about 264 feet (80 m) of a source [36].

Viability:  Germinative capacity of recently ripened seed is high, about
88 percent [55].  Viability decreases with age.  In northeastern
Ontario viability of filled seed averaged 53 percent for 1- to
5-year-old seed, 20 percent for 6- to 10-year-old seed, and 5 percent
for 11- to 15-year-old seed [29].

Germination and seedling establishment:  Black spruce seeds will
germinate and establish on numerous substrates if the seedbed remains
moist but not saturated, and free of competing vegetation [37].
Seedling establishment is best on mineral soils, sphagnum mosses, and
rotten wood [16,65].  Seeds readily germinate on sphagnum mosses,
probably because they are continually moist; however, seedlings are
often overtopped and engulfed by the fast-growing sphagnums [27].
Feather mosses provide a poor seedbed because they have a tendency to
dry out, but black spruce can establish in feather moss during wet
years.

Growth:  Seedlings are shade tolerant, but growth is fastest in full
sunlight [37].  Seedlings rarely grow more than 1 inch (2.5 cm) in their
first growing season.  Three-year-old seedlings are commonly 3 to 5
inches tall [27].  Roots of 1st-year seedlings may penetrate to 2 inches
(5 cm) on upland soils, but when growing in mosses roots rarely reach
depths of 1.5 inches (3.8 cm) after two growing seasons [27].

Vegetative reproduction:  Layering occurs when black spruce's lower
branches become covered with mosses or litter. It is particularly common
in swamps, bogs, and muskegs.  At the northern limit of trees across
Alaska and northern Canada, black spruce reproduces almost entirely
through layering [19].  Seeds may be produced, but few if any are
viable.  


SITE CHARACTERISTICS : 
Black spruce grows on both lowland and upland sites.  At the southern
portion of its range it is found primarily on wet organic soils, but
farther north its abundance on uplands increases.  In the Lake States
and in New England, black spruce is most abundant in peat bogs and
swamps, but is also common on transitional sites between peatlands and
uplands.  In these areas it is rare on uplands, except in isolated areas
of northern Minnesota and the Upper Peninsula of Michigan [36].  In
Alaska, black spruce occupies poorly drained areas, such as cold wet
flats, muskegs, and bogs, but is also common on north-facing slopes
within 5 miles (8 km) of major rivers, and on upland slopes of all
exposures more than 5 miles away from major rivers where white spruce is
absent [25,66].  It often dominates sites in Alaska that are underlain
by permafrost.

Stand characteristics and associated trees:  Because fires occur at
frequent intervals in black spruce forests, most stands are even-aged
[see Plant Adaptations to Fire].  Black spruce commonly grows in pure
stands on organic soils and in mixed stands on mineral soils [65].  On
loamy or clayey moist uplands throughout the boreal region, associates
include white spruce, quaking aspen (Populus tremuloides), balsam fir,
paper birch (Betula papyrifera), and tamarack (Larix laricina) [27].  On
organic sites in the Lake States and New England, black spruce mainly
grows in pure stands, but it is also found in mixed conifer swamps with
tamarack, northern white-cedar (Thuja occidentalis), balsam fir, and
eastern white pine (Pinus strobus) [17,36].  Associated trees on mineral
soil sites in this region include quaking aspen, paper birch, white
spruce, and jack pine (Pinus banksiana) [36].  Jack pine is an
especially common associate on dry, sandy and rocky sites [38].  Other
common associates in the Lake States, especially in transitional areas
between organic soil lowlands and mineral soil uplands, include black
ash (Fraxinus nigra), red maple (Acer rubrum), American elm (Ulmus
americana), balsam poplar (Populus balsamifera), eastern white pine, and
red pine (Pinus resinosa) [36].  In northern New England and
southeastern Canada, black spruce is sometimes associated with red
spruce [38].  In western Canada, it may be found with lodgepole pine
(Pinus contorta), subalpine fir (Abies lasiocarpa), and white spruce
[27].

Understory:  A conspicuous characteristic of black spruce stands is a
nearly continuous ground cover of feather mosses, sphagnum mosses,
and/or reindeer lichens.  Reindeer lichens tend to dominate the ground
cover in northern open black spruce woodlands.  Associated shrubs in
bogs and swamps include Labrador-tea (Ledum groenlandicum), leatherleaf
(Chamaedaphne calyculata), kalmia (Kalmia spp.), downy andromeda
(Andromeda glaucophylia), bog blueberry (Vaccinium uliginosum), mountain
cranberry (V. vitis-idaea), shrub birches (Betula glandulosa, B.
pumila), and creeping snowberry (Gaultheria hispidula).  In the Lake
States, speckled alder and redosier dogwood (Cornus sericea) are the
principal shrubs in some black spruce swamps.  Upland shrubs in the East
include mountain maple (Acer spicatum), beaked hazel (Corylus cornuta),
alders (Alnus spp.), and red raspberry (Rubus idaeus) [27,36,65].

Forest floor:  Stands in Alaska typically have a thick organic mat.
Live moss-organic matter may be up to 20 inches (50 cm) thick [60].
Forest floor temperatures are typically lower and moisture content
higher in black spruce forests than in white spruce, paper birch,
quaking aspen, or blasam fir forests [59].

Soils and landforms:  Black spruce is tolerant of nutrient-poor soils.
It is commonly found on poorly drained acidic peatlands [17,20].  On
peatlands in Minnesota, black spruce grows best on dark brown to
blackish, moderately decomposed peat that contains much partially
decomposed wood [27].  Poor growth occurs on muskegs with thick
accumulations of poorly decomposed yellowish-brown sphagnum peat.  In
the northeastern United States, black spruce commonly grows on peat
soils that are deeper than 12 inches (30 cm) [6].  On the Laurentian
Shield in Minnesota, black spruce is frequently found on 10 feet (3 m)
of peat, and sometimes on peat 60 feet (18 m) deep [27].  On mineral
soil sites in northern Minnesota and adjacent Ontario, black spruce
occurs on gravelly and bouldery loams and shallow soils over bedrock
[27].  Throughout much of Canada, upland black spruce stands tend to
occur on moist to somewhat wet clay loams and clays on long gentle
slopes and lowlands [27].  In New Brunswick, Nova Scotia, and parts of
Quebec, it occurs on sandy and gravelly outwash plains, river terraces,
eskers, and related landforms [27].  In Alaska, black spruce stands
underlain by permafrost tend to have shallow, mineral soil profiles
[59].  Permafrost tables under black spruce stands in Alaska are often
as shallow as 12 inches (30 cm) [18].

Elevation:  Black spruce is a tree of northern interior lowlands.
Throughout its range it is generally found at elevations between 500 and
2,500 feet (152-762 m) [27].


SUCCESSIONAL STATUS : 
Black spruce is considered a climax species over most of its range.
However, some ecologists question whether black spruce forests truly
attain climax because fires in this forest type usually occur at 50- to
150-year intervals, while "stable" conditions may not be attained for
several hundred years [61].

The frequent fire return interval in black spruce forests perpetuates
numerous seral communities.  Throughout boreal North America, paper
birch and quaking aspen are seral hardwoods that frequently invade burns
in black spruce types [61].  Black spruce typically seeds in promptly
after fire, and with the continued absence of fire, will eventually
dominate the hardwoods.  Throughout much of Alaska, aspen and paper
birch often dominate seral stands until they begin to break up at about
90 years, at which time black spruce attains dominance [25].  Since
fires occur at 100-year or more frequent intervals, seral communities
codominated by aspen and black spruce or paper birch and black spruce
are common and widespread throughout Alaska.

In southeastern Canada and the northeastern United States, balsam fir
and northern white-cedar are more shade tolerant than black spruce and
tend to replace it on "productive" sites [6].  Black spruce is a pioneer
that invades the sedge mat in filled-lake bogs, but it may be preceded
slightly by tamarack.  In time black spruce and tamarack may form a
stable forest cover type in swamps.  However, as the peat soil is
gradually elevated by the accumulation of organic matter, and the
fertility of the site improves, balsam fir and northern white-cedar will
eventually replace black spruce and tamarack [27,40].

Black spruce tends to replace jack pine and lodgepole pine on relatively
dry sites in western Canada [27].


SEASONAL DEVELOPMENT : 
Black spruce flowers in late May or early June in the southern portion
of its range and 1 to 2 weeks later in the northern portion.  Female
conelets develop rapidly and contain mature seeds by about 3 months
after pollination (late August or early September).  The cones release
seeds gradually over a period of years [65].

Beginning and ending of height growth is generally as follows [27]:

         Area       Height growth begins        Height growth ends

     Lake States        June 8-20                  August 1-10
        Maine      late May-early June          mid to late August
       Alberta           June 1                     August 2

Related categories for Species: Picea mariana | Black Spruce