BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Betula alleghaniensis | Yellow Birch 



GENERAL BOTANICAL CHARACTERISTICS : 
Yellow birch is a native, deciduous tree.  It usually ranges from 60 to
75 feet (18-23 m) in height and up to 2 feet (0.6 m) in diameter, and
occasionally grows to 100 feet (30 m) in height and 4 feet (1.2 m) in
diameter [14,44,53].  Open-grown yellow birch crowns are long and wide
spreading; in more dense forest crowns are short and irregularly rounded
[53].  The trunk usually divides into a few spreading branches but
lateral shade produces a straight trunk that extends nearly to the top
of the tree.  In dense stands the trunk is free of branches for over
half the height of the tree [53].  The bark is somewhat lustrous,
separating in thin layers [14] which exfoliate and result in a finely
shaggy appearance [44].  On old trunks, the bark is deeply grooved and
about 0.5-inch (1.2-cm) thick [25].  The root system of yellow birch is
generally shallow but variable.  There is a well-developed extensive
lateral root system; roots spread horizontally or may penetrate more
than 5 feet (1.5 m).  Yellow birch is monoecious [32].  The fruit is a
winged nutlet 0.13- to 0.14-inch (3.2-3.5-mm) long (not including
the wings) [14].

Yellow birch is slow growing [32].  Average longevity is approximately
150 years, but maximum longevity is over 300 years [58].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Yellow birch reproduces primarily by seed; seedlings and young saplings
will sprout but sprouts are weak and short lived.  Older trees do not
sprout [32,74].

Reproductive Age and Seed Crop Production:  Under normal conditions,
yellow birch first reproduces at about 40 years.  Optimum seed
production occurs at about 70 years of age.  However, seeds have been
produced by 7-year-old open-grown saplings, and heavy seed crops have
been produced by 30- to 40-year-old yellow birch in open-grown positions
or in thinned stands.  Yellow birch produces good seed crops at 1- to
4-year intervals, usually with very little seed produced in intervening
years [1,32].  Out of every 10 years, yellow birch averages 1 heavy seed
year, 3.5 medium years, 4.5 light or very light years, and 1 year of
seed failure [82].  The maximum number of successive good crops was 4
years [45].  Yellow birch is a prolific seed producer, and viability is
usually good [32], although seed quality is variable from year to year
[60,82].  Seed longevity up to 8 years has been achieved under
laboratory conditions; under natural conditions viability drops off
rapidly the second year [58,60].  However, Roberts and Dong [99]
reported that a substantial amount of yellow birch regeneration was
derived from 2-year-old seed.

Seed Dispersal:  Yellow birch seed is disseminated by wind, most of the
seed falling after cold weather begins.  The winged nutlets may travel
up to 1,320 feet (400 m) over crusted snow [32].  Effective dispersal is
approximately 2 to 4 times tree height [74].  Korstian [65] estimated
that if yellow birch seeds are released from 50 feet (15 m),
in a 5 mile per hour wind, 50 percent will fall within 700 feet (213 m)
of the release point, and 90 percent within 820 feet (250 m).

Seed Germination:  Yellow birch seeds contain a water-soluble
germination inhibitor.  This inhibitor is inactivated by light.  Under
artificial conditions, seed dormancy is broken by stratification or by
exposure of imbibed seed to cool-white fluorescent light [32].  Yellow
birch seeds germinate and grow best on moist mineral soil enriched with
humus; bare mineral soil and duff alone are unsuitable substrates
[16,64,82,124].  However, in undisturbed stands, germination of yellow
birch seeds usually occurs on mossy logs, decayed wood, in cracks in
boulders and on windthrown tree hummocks [32,67].  Optimum germination
of yellow birch occurs at 59 to 61 degrees Fahrenheit (15-16 deg C)
[27].  A substrate pH of 2.4 completely inhibited germination, and pH
3.0 partly inhibited germination (50.7 percent) [94,96].

Seedling Establishment and Growth:  Yellow birch seedlings require
overhead light, crown expansion space, and plentiful soil moisture and
nutrients to compete with faster growing associates; conditions found in
gaps are conducive to yellow birch seedling establishment [1,32].  Some
shade improves seedling survival [82].  In one study, heavily shaded
(14-25% of full sun) yellow birch seedlings grew taller and had more
leaf area than those in full sun, but unshaded seedlings accumulated
more biomass [127].  Mortality of yellow birch seedlings is usually very
high [121].  In one study, minimum mortality was estimated as 97 percent
14 months after germination.  Seedling survival is better on disturbed
microsites; seedlings that germinate on litter are unlikely to survive
[26,40].  Seedlings surviving their first year survive to sapling and
larger stages only where there is sufficient light [121].  Surviving
seedlings in hemlock-northern hardwood forests occur on microhabitats
with slightly lower canopy cover than in the surrounding area, primarily
under coniferous rather than mixed canopies [26].  Growth is better on
humus over sandy loams than on decayed logs, mineral soil, or litter
[124].

Vegetative Reproduction:  Greenwood cuttings of yellow birch have been
successfully rooted and overwintered.  Propagation by grafting is also
possible [32].


SITE CHARACTERISTICS : 
Soils:  Yellow birch occurs on moist, well-drained soils of uplands and
mountain ravines [32].  It occurs on various soil types including
glacial tills, outwash sands, lacustrine deposits, shallow loess, and
residual soils derived from sandstone, limestone, igneous, and
metamorphic rock [32].  In the Adirondacks, yellow birch occurs on soils
derived from limestone, gneiss, anorthosite, sandstones, shales, and
conglomerates [67].  The best growth occurs on well-drained fertile
loams and moderately well-drained sandy loams [32].  Even though growth
is poor, yellow birch is often abundant where drainage is restricted.
Yellow birch occurs on muck soils with pH 7.5 to 8.0 [9].  In New York,
yellow birch occurred on wetland soils with soil surface pH ranging from
4.0 to 6.8 [59].  Birches (Betula spp.) are sensitive to soil phosphorus
[90].

Periodic droughts are damaging to yellow birch because of its shallow
roots [55].

Elevation:  In the Adirondacks and the Appalachians, yellow birch
reaches its maximum importance in the transition zone between low
elevation deciduous forest and montane spruce-fir forests.  In the
Adirondacks, it occurs at elevations ranging from 100 feet (30 m) to
3,413 feet (1040 m), but is uncommon above 3,000 feet (914 m)
[10,39,61,67].  The lower slopes to about 2,310 feet (700 m) are
dominated by sugar maple, American beech, and yellow birch.  Between
2,310 feet and 2,970 feet (700-900 m) is a transition zone to spruce and
spruce-fir forests.  In the southern Appalachians the highest importance
value for yellow birch occurs at mid- to high-elevations from 2,800 to
3,000 feet (853-914 m) [19,23].  In western Great Smoky Mountains
National Park, yellow birch tends to be more concentrated in protected
coves at lower elevations, and spreads out of the coves at higher
elevations [19].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Yellow birch is intermediate in shade tolerance.  Leak [71] assigned
yellow birch to the category of persistent successional species.  Yellow
birch is described as opportunistic due to its habit of producing
abundant small seed [40].  Yellow birch seeds comprised a higher than
expected proportion (compared to the abundance of mature trees) of the
seed rain and seedbank of a mixed forest [56].  The presence of yellow
birch in mid- to late-successional stands depends on local disturbance
[28,71]; it cannot reproduce under a closed canopy and requires soil
disturbance and light for seedling survival [32].  Birches respond to
gaps of all sizes, with a peak density found in gaps of about 2,800
square feet (250 sq m) in Pennsylvania.  In the southern Appalachians,
birches exhibited a peak density in 10-year-old gaps [102].  In southern
Appalachian spruce-fir forests, yellow birch seedlings were the most
abundant species in gap plots but not in closed-canopy plots.  They
exhibited the highest growth rate of any species in gaps [122].  The
origin of the gap is apparently important; in upper Michigan, yellow
birch apparently failed to establish readily in gaps formed by stem
breakage because soil was undisturbed [87].  Yellow birch decreased
between 1964 and 1986 in red spruce-Fraser fir (Abies fraseri) stands,
even though there was loss of the Fraser fir to insect attack [18].

Yellow birch seedlings do not successfully compete with advance
regeneration of other northern hardwood species, grasses, and forbs
[32].  However, in sugar maple-beech-yellow birch forests, seedlings of
the three dominants were approximately equally abundant [40].  In mature
hemlock-hardwood forests in New York, yellow birch was the third most
common seedling species, distributed randomly as to canopy type [26].
Yellow birch seedlings tend to occur in clumps.  The abundance of yellow
birch seedlings in Quebec was almost always negatively correlated to
that of other tree species even though its seed abundance was positively
related to that of other species [57].  Sugar maple seedlings produce an
allelopathic substance that inhibits the root growth of yellow birch
seedlings [112].

Early Successional Stands:  Yellow birch is a common early to
mid-successional associate in aspen-birch stands [28].  In northern
hardwood ecosystems, yellow birch reaches maximum importance levels
within 15 years of disturbance, and those levels are maintained for at
least 100 years [81].  On Isle Royale, Michigan, a paper birch-dominated
stand that originated after fire early in this century is undergoing
canopy invasion by sugar maple and yellow birch [50].  In New Hampshire,
succession was monitored after experimental deforestation and 3 years of
vegetation suppression.  Yellow birch comprised 0.6 percent of total
biomass in the first year of succession, and increased to 11.8 percent
in the nineteenth year [97].  Second-growth stands usually contain
approximately the same percentage of yellow birch as virgin stands [32].
Yellow birch occurs on fine till with importance peaking at about 80
years.  On sandy soils, the trend is indistinct, probably declining over
time [71].  On old fields in Tennessee, succession included small
amounts of yellow birch in 15-year-old stands.  Yellow birch occurred at
maximum density on 42- and 48-year-old plots, was present in lower
numbers on the 63-year-old plot, and was not present in the old-growth
plots [21].

Mid- to Late-Successional Stands:  Yellow birch is abundant in mid- to
late-successional balsam fir-yellow birch-paper birch-white spruce
(Picea glauca) stands on Isle Royale [50].  It is a major gap-phase
component of sugar maple-beech-yellow birch and hemlock-yellow birch
cover types [32].  The age distribution of yellow birch in a virgin
northern hardwoods forest was somewhat irregular:  There were many
10-year-old saplings, no 40-year-old trees, and many 100-year-old trees
[69].  In Wisconsin, even-aged northern hardwoods contain a high
proportion of yellow birch and uneven-aged stands tend towards pure
sugar maple [80].  In many old-growth stands, yellow birch gradually
decreases in importance as the stand ages.  In Tennessee, in both
hemlock-mixed forest and mixed deciduous forest, yellow birch decreased
between 1935 and 1987 in undisturbed stands [17].

Climax Stands:  Cary [128] described a climax forest in Maine consisting
of red spruce, American beech, maples, and yellow birch.  Hansen and
others [50] described a yellow birch-sugar maple type as the climax
forest on Isle Royale, Michigan.  These forests have not experienced
major disturbances for more than 120 years and include yellow birch of
up to 150 years of age [50].  Yellow birch was present in old-growth
forests in New York.  The average ages of yellow birch trees in two
stands were 200 and 250 years [75].  Forcier [40] explained the presence
of yellow birch in climax stands as a combination of longevity and
micro-succession.  At the single tree level, yellow birch is replaced by
sugar maple which is replaced by beech, which, following a small-scale
disturbance, is replaced by yellow birch [40].


SEASONAL DEVELOPMENT : 
The pistillate catkins of yellow birch form in the fall, and finish
development from late May to early June.  The fruit ripens from late
August to early September [32].  The phenology of yellow birch in
northern Minnesota was reported as follows [4]:

flower appearance          April 2 to May 16
initial bud swell          April 6 to May 1
leaf out                   May 3 to May 25
anthesis                   May 13 to May 29
seed fall (initiation)     August 6
leaf fall                  September 26 to October 4

Related categories for Species: Betula alleghaniensis | Yellow Birch