BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Larix laricina | Tamarack 



GENERAL BOTANICAL CHARACTERISTICS : 
Tamarack is a native, deciduous, coniferous, small- to medium-sized
upright tree.  It has a straight bole with a narrow pyramidal crown.
Tamarack is a good self-pruner and by 25 to 30 years of age, trees are
generally clear of branches for one-half to two-thirds of their bole
[26].  Trees generally reach 50 to 75 feet (15-23 m) in height and 14 to
20 inches (46-51 cm) d.b.h. but are occasionally larger.  In Alaska,
trees are often stunted, reaching heights of only 10 feet (3 m) and
diameters of 3 inches (8 cm), but on good sites mature trees are
generally 30 to 60 feet (9-18 m) tall and 4 to 10 inches (10-25 cm)
d.b.h. [26,49].  The maximum age for tamarack is about 180 years,
although older trees have been found [26].

Tamarack has 1-inch-long (2.5 cm) needles that occur in clusters of 10
to 20 on dwarf twigs [22] and turn yellow in the fall before they are
shed.  Erect mature cones are about 0.5 to 0.75 inch (1.3-1.9 cm) long
[26].  Tamarack bark is smooth when young but becomes rough and scaley
on older trees.  The bark is thin, only about 0.25 to 0.5 inch (0.6-1.2
cm) thick on mature trees [28].  The root system is typically shallow
and wide spreading.  Rooting depth rarely exceeds 1.5 feet (46 cm), but
the roots commonly spread over areas greater in radius than the tree
height [7].  On wet and very wet peatlands in Alberta, roots are
generally restricted to the upper 8 inches (20 cm) of soil on hummocky
positions [31].



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


REGENERATION PROCESSES : 
Cone and seed production:  Cone production begins at about 15 years of
age for open-grown trees and 35 to 40 years of age for trees in
well-stocked stands [11].  Large quantities of seed are usually not
produced until trees are at least 40 years old.  Fifty- to 150-year-old
open-grown trees produce the best cone crops, with individual trees
sometimes producing as many as 20,000 cones in a good year [11].  Good
seed crops are produced every 3 to 6 years, with some seed produced in
intervening years.  Tamarack seeds are about 0.12 inch (3 mm) long and
have a wing about 0.25 inch (6 mm) long [26].

Dispersal:  Seeds are dispersed in the fall over a relatively short time
period.  In a Minnesota study, dispersal began about September 1, and by
October 31 about 98 percent of seed had fallen [11].  The remaining seed
fell throughout the winter.  In interior Alaska, 95 percent of tamarack
seeds are shed by November [4].  Tamarack seeds are primarily wind
dispersed, but red squirrels disperse some seed.  Most wind-dispersed
seeds fall within a distance of two tree heights, but a small percentage
travels greater distances [4,11].

Seed destruction and predation:  In Minnesota, small mammals, presumably
mice, voles, and shrews, consume large quantities of tamarack seed off
the ground and can destroy up to one-half of a tamarack seed crop [11].
Also, seeds on the ground are susceptible to infections from bacteria
and fungi.  Consequently, only about 4 or 5 percent of tamarack seed
that reaches the ground germinates [26].  In tamarack stands in New
Brunswick, insects destroyed between 25 and 88 percent of seed produced.
Larvae of the spruce budworm and the cone maggot were responsible for
greatest loss [53].

Viability:  Tamarack seed remains viable for only about 1 year after
dispersal [11].  Typically a large percentage of tamarack seed is
unfilled.  In Minnesota about one-third, and in northern Ontario about
one-half of seed had undeveloped embryo and endosperm [11,15].  At the
northern portion of the species range in the Northwest Territories,
tamarack produced a limited amount of seed, but none was viable [12].

Germination and establishment:  Germinative capacity ranges from about
30 to 60 percent [11].  Neither light nor pH appear to influence
germination appreciably [11,15].  Tamarack seeds require a moist but
unsaturated substrate for germination.  The best seedbed is warm, moist
mineral or organic soil free from competing vegetation [26].
Slow-growing sphagnum mosses also provide a good seedbed, as they have a
tendency to remain moist.  In open swampy habitats, tamarack seedlings
are often found on sphagnum mosses [1,7].  Feather mosses are usually
poor seedbeds because they tend to dry out, but if they remain moist,
they can provide a favorable seedbed [4].  On poorly drained river
terraces in interior Alaska, tamarack seedlings are more abundant on
sphagnum and feather mosses than on sedge tussock tops, troughs between
the tussocks, or litter-covered sites; on well-drained river terraces,
seedlings are primarily restricted to mineral soil [4].  Tamarack
seedlings are intolerant of shade and flooding.  Seedlings may survive a
few years in shade, but most will die unless released.  Partial water
submersion for 1 to 3 weeks kills 1st-year seedlings [11].  In full
sunlight seedlings grow relatively rapidly, reaching heights of 7 to 9
inches (18-23 cm) after one growing season, and 18 to 25 inches (46-51
cm) tall after three [26].  Roots of seedlings growing in nearly full
sunlight may reach depths of 2.5 to 3.5 inches (5-11 cm) after one
growing season, while over the same time period roots of seedlings
growing in shade reach depths of only about 1 inch (2.5 cm) [11].

Vegetative reproduction:  Layering is a dominant mode of reproduction at
the northern limit of the species' range.  In the southern part of its
range, layering is uncommon but does occur when lower branches become
covered with litter or fast-growing mosses [26].  Curtis [7] reported
that tamarack has the unusual ability to produce root sprouts up to 30
feet (9 m) away from a mother tree.


SITE CHARACTERISTICS : 
Tamarack is most commonly found on cold, wet to moist, poorly drained
sites such as swamps, bogs, and muskegs [22,26,44].  It is also found
along streams, lakes, swamp borders, and occasionally on upland sites.
It becomes more common on drier sites in the northern portion of its
range where it is found on ridges and benches and other upland locations
[26].  In British Columbia, it grows as an upland tree on cool, moist
north slopes as well as on wet organic sites [26].  In interior Alaska,
tamarack is generally restricted to wet and cold sites underlain by
shallow permafrost but occasionally grows in warmer, well-drained
floodplains and upland forests dominated by white spruce (Picea glauca)
[4].

Soils:  Tamarack can tolerate a wide range of soil conditions but most
commonly grows on wet to moist organic soils, such as sphagnum or woody
peat, and is especially common on nutrient-poor, acid peatlands [9,26].
In Minnesota, tamarack occurs on a wide variety of peatland types, from
rich swamps to raised bogs, and is an indicator of weakly minerotrophic
sites (pH 4.3-5.8, Ca 3-10 ppm, Ca + Mg 5-13 ppm) [21].  In
Saskatchewan, tamarack grows on peatland sites with a wide range of
fertility and moisture regimes; it is most common on those with a pH
between 6.0 and 6.9 [23].  Although most commonly occurring on
peatlands, tamarack actually grows best on well-drained loamy soils
along streams, lakes, and seeps, and on mineral soils with a shallow
surface layer of organic matter [26].  However, tamarack is uncommon on
these sites in the southern portion of its range because it is easily
outcompeted by other trees.  It is more common on mineral soil in the
north.

Stand characteristics and associated trees:  Because the species is
intolerant of shade, tamarack stands are usually even-aged [13].  They
occur on wetter sites than black spruce stands.  Across tamarack's range
black spruce is its most common associate.  These two species often form
mixed stands on peatlands.  Throughout much of boreal Canada, other
associates include balsam fir (Abies balsamea), white spruce, paper
birch (Betula papyrifera), and quaking aspen (Populus tremuloides)
[22,26].  In the Lake States and New England, common associates include
northern white-cedar (Thuja occidentalis), balsam fir, eastern white
pine (Pinus strobus), red pine (P. resinosa), quaking aspen, black ash
(Fraxinus nigra), white spruce, and red maple (Acer rubrum) [7,44].  In
Alaska, tamarack is usually found with black spruce and paper birch but
almost never with aspen [26].

Understory:  Tamarack stands tend to cast light shade and have a dense
undergrowth of shrubs.  Tall shrubs associated with tamarack include bog
birch (Betula glandulosa), swamp birch (B. pumila), speckled alder
(Alnus incana ssp. rugosa), willows (Salix spp.), and red-osier dogwood
(Cornus stolonifera).  Low shrub associates include Labrador-tea (Ledum
groenlandicum), bog-rosemary (Andromeda glaucophylla), leatherleaf
(Chamaedaphne calyculata), and blueberries and huckleberries (Vaccinium
spp.).  The ground is usually covered with sphagnum and other mosses
[26].


SUCCESSIONAL STATUS : 
Tamarack is a pioneer or early seral species.  It is often the first
tree to invade open bogs and burned peatlands [26].  In open bogs and
swamps, tamarack is the first tree to pioneer the sphagnum moss mat
floating over water [7].  This invasion toward the center or wettest
portion of a swamp is common [1,18].  It may invade bogs during sedge
mat, sphagnum moss, or ericaceous shrub stages.  Tamarack is extremely
intolerant of shade, however, and eventually, as the peat becomes
consolidated and firm, other conifers replace it.  It is replaced by
black spruce on poorly drained acid peatlands.  In nutrient-rich swamps
it is replaced first by black spruce, and later by northern white-cedar,
balsam fir, and eventually swamp hardwoods [16].


SEASONAL DEVELOPMENT : 
Minnesota:  Buds begin to swell from early to late April.  Needles begin
to emerge from about mid-April to mid-May.  Needles are shed from
mid-September to mid-October.  Flowering occurs from late April to early
May.  Seedfall begins in early September and is nearly complete by late
October [11,16,26].

Wisconsin:  Tamarack begins to leaf out in the early spring before the
ground has thawed.  It takes 4 to 6 weeks for the needles to develop
fully.  The needles turn yellow in late September or early October and
are shed shortly thereafter [7].

Upper Peninsula of Michigan:  Needles begin to emerge in mid-April to
mid-May.  Needles begin to turn yellow in early September and are shed
from mid-September to mid-October.  Flowering occurs in early May, and
cones are ripe by late August [16,26].

Alaska:  Seed dispersal begins in early September and is mostly
completed by late October [4].

New York:  Height growth begins in late May and ends by late August [5].

Related categories for Species: Larix laricina | Tamarack