BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Pinus banksiana | Jack Pine 



GENERAL BOTANICAL CHARACTERISTICS : 
Jack pine is a small to medium-sized, native, coniferous, evergreen tree
with 0.75- to 2.0-inch-long (2-5 cm) needles.  Mature jack pine are
usually 55 to 65 feet (17-20 m) tall and 8 to 10 inches (20-25 cm) in
d.b.h. but can attain a maximum height of 100 feet (30 m) and a diameter
of 25 inches (64 cm) [67].  On extremely harsh, sandy sites, jack pine
is small and bushy [31].  Although the canopy begins showing signs of
decay by age 75, jack pine can live more than 200 years [17].  A
243-year-old jack pine was found in the Boundary Waters Canoe Area in
Minnesota [40].

Jack pine develops a taproot as a seedling and maintains it to maturity.
On deep, well-drained soils, roots of mature trees may penetrate 9 feet
(2.7 m).  The abundant lateral roots are mostly confined to the upper 18
inches (46 cm) of soil [67].

Although the species is predominantly closed-coned, individual trees can
have nonserotinous cones or a combination of serotinous and
nonserotinous cones.  Mature stands with mostly open-coned trees are
common in the southern Great Lakes region and sporadic in the East [29].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
The minimum seed-bearing age of open-grown jack pine is 5 to 10 years.
Some seed is produced every year and serotinous cones accumulate in the
crown.  A mature stand of jack pine may have as many as 2 million seeds
per acre (5 million/ha) stored in unopened cones [35].  Because of
abundant seed production, few mature trees are necessary to regenerate a
stand.  Regeneration after fire in a balsam fir (Abies balsamea) forest
with only 5 relic jack pine per acre (12/ha) averaged 400 jack pine
seedlings per acre (1000/ha) in the first postfire year [74].

The serotinous cones, sealed shut by a resinous bond, require high
temperatures to open.  This heat is usually provided by fire, but hot,
dry weather (air temperatures of at least 80 degrees Fahrenheit [27 deg
C]) also opens some cones [67].  Because temperatures required to open
cones typically occur in the warmest part of the summer, survival of new
germinants may be poor because of drought conditions or lack of time to
become established before winter.

The winged seeds are the smallest of the native North American pines
[35] and are dispersed by gravity and wind.  The effective dispersal
range is about 110 to 130 feet (34-40 m) or two tree heights [53].

Seeds usually germinate rapidly after release when the 10-day mean
maximum air temperature is 65 degrees Fahrenheit (18 deg C) or higher
[35].  Jack pine seeds occasionally exhibit partial dormancy which is
probably broken naturally by heat from fire [4].  Seeds remain viable in
closed cones for years, but viability decreases over time.  Eyre and
LeBarron [35] found that 1- to 6-year-old cones had 78 to 89 percent
seed viability and cones over 5 years old had 62 percent seed viability.
Fifty percent of 20-year-old seeds may be viable [17].

Exposed mineral soil or thin residual humus of about 0.2 inch (0.5 cm)
or less provide the best seedbeds.  The presence of deeper humus has an
adverse effect on establishment; humus deeper than 1.5 inches (3.8 cm)
is a low-quality seedbed [22].  Successful germination and establishment
of jack pine usually occurs only after fire, but mechanical disturbance
may also expose adequate mineral seedbeds [33].  In northeastern
Minnesota, germination averaged 63 percent on mineral soil, 49 percent
on burned duff, 47 percent on scarified duff, and 17 percent on
undisturbed duff.  First-year survival of germinated seedlings was 84
percent on mineral soil, 70 percent on burned duff, 41 percent on
scarified duff, and 41 percent on undisturbed duff [35].

Germination and initial survival sometimes improve with partial shade,
but the positive effect of shade eventually becomes negative because
seedlings soon require higher light levels [10].  Mortality of
2-year-old jack pine seedlings was high under 11 and 20 percent of full
light, but minimal under 43 percent light and higher [69].  Seedling
survival may be low if drought conditions follow germination.  However,
in northeastern Minnesota, 3 consecutive days of 140 degree Fahrenheit
(60 deg C) surface temperatures for 2 hours did not result in
appreciable jack pine mortality [5].

During its first 20 years, jack pine is one of the fastest growing
conifers in its native range [67].  Maximum growth occurrs under 43
percent light and higher [69].

Jack pine does not reproduce vegetatively.


SITE CHARACTERISTICS : 
Jack pine occurs on level to gently rolling sand plains of glacial
outwash, fluvial, or lacustrine origin.  It also occurs on eskers,
sand dunes, rock outcrops, bald rock ridges, and lake shores.  In the
Lake States, it commonly occurs between 1,000 and 1,500 feet (300-460 m)
in elevation with a maximum elevation of about 2,000 feet (610 m).  In
the East, jack pine grows near sea level to about 2,000 feet (610
m), with a population in New Hampshire occurring at around 2,500 feet
(760 m) [34,67].

Jack pine usually grows in dry, acidic sandy soils of the Spodosol or
Entisol Order, but it also grows in loamy soil, thin soil over bedrock,
peat, and soil over permafrost.  Although jack pine does not usually
grow in moderately alkaline soil, it can grow in calcareous soils up to
pH 8.2 if normal mycorrhizal fungi associates are present [67].

Common tree associates of jack pine not mentioned in Distribution and
Occurrence are bur oak (Quercus macrocarpa), northern red oak (Q.
rubra), red maple (Acer rubrum), balsam fir, white spruce (Picea
glauca), tamarack (Larix laricina), balsam poplar (Populus balsamifera),
bigtooth aspen (P. grandidentata), and quaking aspen (P. tremuloides)
[34].

Common shrub associates include prickly rose (Rosa acicularis),
bunchberry (Cornus canadensis), velvetleaf blueberry (Vaccinium
myrtilloides), mountain cranberry (V. vitis-idaea), bearberry (Arctostaphylos
uva-ursi), American green alder (Alnus crispa), Labrador tea (Ledum
groenlandicum), wintergreen (Pyrola spp.), and beaked hazel (Corylus
cornuta) [28,34,46,47,57].

Groundcover commonly consists of reindeer lichen (Cladonia spp.) on
drier sites and feather mosses, especially mountain fern-moss
(Hylocomium splendens) and Schrebers moss (Pleurozium schreberi), on
moister sites [16,34,57].


SUCCESSIONAL STATUS : 
Obligate Initial Community Species

Jack pine invades areas where mineral soil has been exposed by major
disturbance such as fire [17].  It also rapidly invades newly formed
dunes after stabilization by grasses [60].  It is one of the most
shade-intolerant trees in its native range; only aspens, paper birch,
and tamarack are less tolerant [67].

Jack pine begins to show signs of decadence by age 75 [17], decreases in
frequency by 150 years, and may disappear completely after 200 years
[13], although some relic jack pine survive nearly 250 years [40].  In
the absence of fire, jack pine is succeeded by longer lived species such
as red pine (P. resinosa) or white pine, or by more shade-tolerant
species such as balsam fir and black spruce (Picea mariana).  Black
spruce, which often seeds in at the same time as jack pine, grows slower
but lives longer, becoming codominant after 90 years and eventually
succeeding jack pine [16,40,42].  On the driest, harshest sites, jack
pine may persist and form an edaphic climax [67].

Although generally occurring in even-aged stands that regenerated after
fire [34], some jack pine stands are uneven-aged.  Recruitment of jack
pine may occur fairly long after a fire if the stand is only partially
stocked.  In 65 percent of mature stands studied in northern lower
Michigan, the largest individuals differed in age by 10 to 23 years.
Two stands contained 40- to 45-year-old jack pines that had survived a
wildfire 10 years previously, a dominant intermediate class of 22- to
35-year-old pine regenerated after the fire, and numerous smaller
individuals from 4 to 20 years of age [1].  Zoladeski and Maycock [85]
suggest that recruitment of jack pine stops completely 50 years after
stand initiation, and that ultimate success is limited to the earliest
generation of jack pine.

Clearcutting alone or clearcutting followed by burning converts sites
previously dominated by mature jack pine to meadows dominated by Carex
spp. or early successional hardwoods, respectively [67]].


SEASONAL DEVELOPMENT : 
Jack pine staminate and ovulate cone primordia are initiated in late
summer and then go dormant until spring.  Pollen shedding usually occurs
in late spring or early summer but is highly dependent on the weather.
Fertilization occurs 13 months after pollination.  Cones mature in late
summer or early fall, 2 years after initiation [67].

Related categories for Species: Pinus banksiana | Jack Pine