FIRE ECOLOGY
SPECIES: Pinus banksiana | Jack Pine 



FIRE ECOLOGY OR ADAPTATIONS : 
Of all boreal forest conifers, jack pine is best adapted to fire [66].
With medium thick bark [15], mature individuals have only a moderate
tolerance of fire, but populations survive because of delayed seed
release from serotinous cones, early reproductive maturity, fast growth
rates in full sun, and preference for mineral soil seedbeds [54,66].

In a model that integrates plant population dynamics and disturbance,
jack pine is used to illustrate a species that maximizes the probability
of being reproductively mature at the time of the next recruitment
opportunity.  Fire provides the regeneration opportunity which usually
results in mortality of the mature forest [27].

Cone serotiny:  The resin of serotinous cones melts when heated, usually
at temperatures in excess of 140 degrees Fahrenheit (60 deg C).  In one
study, cones opened in 80 seconds at 200 degrees Fahrenheit (93 deg C)
and within 20 seconds at temperatures above 400 degrees Fahrenheit (204
deg C).  Seed viability is not markedly affected by heating, unless the
cone ignites, which results in complete loss of seed viability.  For
cones at 8 percent moisture content, the interval between cone opening
and cone ignition lies between about 200 and 1,300 degrees Fahrenheit
(93-705 deg C), depending on the time of exposure.  Cones exposed to
temperatures of 800 degrees (427 deg C) or less did not ignite during a
5-minute test.  Cones ignited in 60 seconds when exposed to temperatures
of 900 degrees (482 deg C) Fahrenheit and in 2 seconds when exposed to
temperatures of 1,300 degrees Fahrenheit (705 deg C).  Heating cones at
900 degrees Fahrenheit (482 deg C) for 30 seconds had no adverse effect
on germination.  Jack pine seeds unprotected by cones remain viable when
exposed to high temperatures until the wings ash and the seed coats
crack [9].  Crown torching does not ignite cones because the high
temperatures are unlikely to last more than 3 minutes [9].

Regeneration:  Seeds are dispersed from cones after fire and germinate
on burned duff or mineral soil exposed by fire.  Regeneration failures
are associated with low-severity surface fires that result in little
crown involvement [76] or in little duff removal [11].    

Fire regime:  Estimates of fire intervals in jack pine forests are
generally less than 50 years [40].  Based on jack pine fire scars, the
shortest and longest times between major fires in jack pine forests of
northern Ontario were 5 and 30 years, respectively [50].  The mean fire
return interval for jack pine forests in the Athabasca Plains in
northern Saskatchewan and northeastern Alberta is 38 years [16].  Large
upland ridges and ridge complexes, far from natural fire breaks, burn
most frequently.  Jack pine forests that burn more frequently than every
5 to 10 years become pine barrens [31].  Major stand-replacing fires in
the Boundary Waters Canoe Area occurred in years with summer droughts
[40].

The accumulation of litter and debris on the forest floor over time
increase the likelihood of moderate- or high-severity fire [40].  A
lichen mat, a highly flammable and continuous fuel source at ground
level, develops within 40 years and is important in supporting fires in
jack pine forests [16]. 

Mature and immature jack pine forests have very different stand and fuel
characteristics and, therefore, exhibit different fire behavior.  The
mature jack pine fuel type in Ontario is characterized by 635 jack pine
per acre (1,569/ha) averaging 58 feet (17.7 m) in height, and 5.8 inches
(14.7 cm) in d.b.h. with an understory of black spruce [76].  The base
of live crown in mature jack pine forests is typically 33 feet (10 m)
above the ground surface [42].

After observing 12 experimental fires under different weather
conditions, Stocks [75] grouped fire behavior in the mature jack pine
fuel type into three categories:  (1) surface fires with slow to
moderate rates of spread, low to medium flame heights (0.3 to 3.3 feet
[0.1-1.0 m]), and a fire intensity less than 140 btu/s/ft (<500 kW/m);
(2) vigorous surface fires with various degrees of torching or
intermittent crowning, flame heights about 6.6 feet (2 m), and fire
intensities of 140 to 870 btu/s/ft (500-3,000 kW/m); and (3) extremely
vigorous surface behavior with high rates of spread (33 feet per minute
[10 m/min]) that result in active crown fires with intensities over 1160
btu/s/ft (4,000 kW/m).  Because of the gap between the crown base and
the surface fuels, sustained crown fires in this fuel type are rare,
even with windspeeds above 16 miles per hour (25 km/h) at 33 feet (10 m)
above the ground surface [76].

The immature jack pine fuel type is characterized by 3,489 live jack
pine stems per acre (8,614/ha) averaging 26.9 feet (8.2 m) in height and
2.1 inches (5.3 cm) in d.b.h. with an understory of 3,953 dead,
suppressed jack pine stems per acre (9,760/ha) ranging from 7 to 20 feet
(2-6 m) in height [76].  The extremely dense nature of the stand and the
vertical fuel continuity make it difficult for fires to spread at even
moderate rate without crown fuels becoming involved [74].  Active crown
fires occur at intensities of 1,450 btu/s/ft (5,000 kW/m) [76].  This
fuel type crowns at a lower rate of spread than any other boreal forest
fuel type [42].  Of 12 experimental fires in immature jack pine stands,
the only two fires that did not crown had very low spread rates of 2.3
and 6.9 feet per minute (0.7 and 2.1 m/min), representing minimum
conditions for continuous fire spread in this fuel type.  The rate of
spread for the other 10 fires that crowned ranged from 26 to 162 feet
per minute (7.9-49.4 m/min) [74].  Short-term spread rates and
intensities as high as 223 feet per minute (68 m/min) and 17,350
btu/s/ft (60,000 kW/m) have been documented [76].

Temperatures during 18 surface fires in an open jack pine barren in
northern Ontario were recorded.  The ground vegetation consisted of
sweet-fern (Comptonia peregrina), blueberries (Vaccinium spp.), and
abundant lichen and moss.  Temperatures recorded at 2 to 4 inches (5-10
cm) above the ground ranged from 248 to 1013 degrees Fahrenheit (120-545
deg C).  Fires with temperatures greater than 662 degrees Fahrenheit
(350 deg C) occurred in dense vegetation with more than 0.7 ounce per
square foot (235 g/sq m) fuel dry weight.  High wind speeds appeared to
have a cooling effect on the fire temperatures [73].


POSTFIRE REGENERATION STRATEGY : 
   Tree without adventitious-bud root crown
   Crown residual colonizer (on-site, initial community)
   Initial-offsite colonizer (off-site, initial community)

Related categories for Species: Pinus banksiana | Jack Pine