Fire and plants 1

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• Fire and plants (1)
• Individuals Populations
• Plant tolerance to fire
• Fire survival is related to (1) surviving the
  fire itself, and
• (2) tolerating postfire conditions.
• Strategies
• resistance--directly surviving fire example
  giant sequoia, ponderosa pine, perennial grasses.
• resilience--reproducing after fire example
  sprouting oak and aspen, seed reproduction of
  annual cheatgrass.

2
Damage to plant tissues in fire is caused by high
temperature, either directly through combustion
or indirectly through effects on constituent
chemicals and/or metabolic processes. At a
given temperature, the effects depend on (1)
length of heat exposure and (2) hydration of the
cell. Dehydrated (dormant or resting) cells
can endure more heat than hydrated and
metabolically active cells. Not all plant
tissues are equally important. Because of their
modular construction plants can tolerate the loss
of substantial biomass (unlike animals).
Meristematic tissues, such as cambium and buds,
are especially important for survival of the
aboveground plant parts.
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Whelan
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• Reproductive pathways (sexual/asexual
  reproduction)
• Some plants are obligate seeders (e.g., most
  pine species)
• Some reproduce primarily by asexual means (e.g.,
  aspen)
• Some can use both pathways (facultative
  sprouters, e.g., oaks) ? implication the effects
  of fire on seeds is more important to the pine
  community than the oak community in a
  mixed-species forest.
• Are there any "obligate" sprouters?

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• Fire Protection
• Plant response to temperature is affected by
  resistance to heat (e.g., state of hydration) and
  protection from heat. The ability of individual
  cells to survive heat does not vary much among
  species or tissues within a plant the thermal
  death point is 50-55?C. Therefore, protection is
  the key factor that allows some plants to survive
  intense fires.
• Fire protection can be related to three factors
• bark shielding meristematic tissues from heat
• insulation of belowground meristems by soil,
  sacrificing the aboveground parts
• bearing sensitive tissues at heights where heat
  intensity is reduced. Seeds can be protected in
  insulating fruits, burial in the ground, or again
  by canopy height.

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Bark thickness and thermal properties
(species-specific) are the factors determining
the length of heat exposure required to reach
lethal temperature (assume 60?C). Because bark
thickness is closely correlated with dbh, smaller
plants of all species are more susceptible to
heat than larger plants. Note we usually
think of bark in terms of trees, but similar
relationships exist in woody shrubs. Even at
the same bark thickness, thermal insulation
varies with species. In the example cited by
Whelan, pine bark was consistently more
insulating than sweetgum bark. Ambient
temperature affects the relationship the higher
the ambient temperature, the more quickly a
lethal temperature will be reached. Bark
heating is also affected by the relative
flammability of the bark itself (if the bark
catches on fire, insulation is reduced) and by
the ability of bark to reflect energy (smooth,
light-colored bark reflects betterbut dont
carry this too far. The thickness of ponderosa
pine bark is far more important than the
reflective qualities of aspen bark, a very
fire-susceptible species).
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Whelan
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• Relationship to Fire Behavior
• You can see how fire intensity affects bark
  heating intensity in turn is influenced by
  available fuel, which depends on burning season.
• Headfire can have more intensity but for brief
  time backing fire or glowing combustion may have
  greater heating effects.
• Fire scars form where heating is sufficient to
  kill a portion of the cambium usually on the
  uphill side both because fuel tends to accumulate
  there and is closer to the bark, as well as
  heating from eddies as the hot gases circle the
  trees.
• Fire frequency can affect bark heating if
  damaged bark requires time to heal, for example,
  over 7 years for smooth-barked Eucalyptus
  dalrympleana (Gill 1980 cited in Whelan).

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Vegetative insulation is protection of meristems
by other plant parts. Examples bunchgrasses
have meristems protected by thick matted grass
leaves, plus heat goes upward (recall grasses
monocots have meristematic tissue belowground).
Leaf arrangements can protect higher growing
buds of dicots. Longleaf pine (Pinus palustris)
in SE US has protected buds (tissue paper wrapped
around apical bud is unscorched). Also, the buds
are large (greater ability to absorb heat).
Longleaf pine, P. palustris, Nearctica.com
Apache pine, P. engelmannii, Durango, Mex.
The entire plant architecture may be oriented
toward fire protection (suggestion from research
in fynbos, a South African vegetation type with
shrubby plants in a Mediterranean climate,
analogous to chaparral.)
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Xanthorrhoea resinosa (Grass Tree)example of
vegetative insulation Photos students of
Elanora Heights Primary School, Sydney, NSW,
Australia

• Such excellent fire protection around the buds
  that invertebrates burrow into them for
  protection (Whelan)

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Adventitious buds are sources of resprouting from
buds almost anywhere on the plant (adventitious
buds e.g., eucalypts, along stem, and aspen,
adventitious root buds). Resprouting can also
occur from latent axillary buds (normal site of
leaf growth) which were latent before the fire.
These buds are kept latent by plant hormones
(growth inhibitors), but production of inhibitors
is controlled by the apical meristems and is
disrupted when apical meristems are damaged.
La Michilía biosphere reserve, Durango, Mexico
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Roots and underground stems are protected by
soil. Soil is an excellent insulator plus fire
heat goes upward. Many plants can resprout from
suppressed subterranean buds. Especially
effective mechanism for plants with lignotubers,
specialized root-crown structure which both (1)
serve as a source of protected buds and (2) store
starch (energy) for sprouting. Lignotubers are
often found in chaparral species eucalypts.
Fire frequency affects resprouting ability
repeated topkill can eventually deplete resources.
Adenostoma fasciculatum (chamise)
Armstrong, W.P. 2001. Wayne's Word 9 May 2001.
http//waynesword.palomar.edu/wayne.htm.
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North Carolina State University,
http//www.ces.ncsu.edu/depts/hort/consumer/factsh
eets/trees/images/picts/PinusPa2.jpg
Height can protect meristems. Example longleaf
pine has grass stage after germination. The
plant stays small for several years, allocating
photosynthate to roots. Growing bud is protected
by proximity to ground, densely-packed needles
(little oxygen for fire). When height growth
resumes, it is rapid, lifting the bud quickly
above the flames and accompanied by increasing
bark thickness. A SW pine, Apache pine (Pinus
engelmannii) appears to have similar
characteristics. Note that height is only
effective if the vascular tissue of the stem
survives.
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Banksia ericifolia var. ericifolia - Heath
Banksia Australian National Botanical Garden,
http//www.anbg.gov.au/banksia/banksia.html
Flowering can be affected by timing and intensity
of fire. Effects are related to the longevity of
viable seeds in the soil seed bank, degree of
variation between years in seed/mast production.
Example Banksia spp. in Australia have high
variation in annual seed production, short
viability, so fire in high seed year would cause
much greater seed reduction than in low seed
year.
Whelan
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Seeds are generally well-suited for surviving
fire because they are generally dehydrated,
metabolically dormant, and protected by a seed
coat. Example domesticated seeds (pea,
sunflower, wheat) survived 4 h of dry 70-90?C
heat (cited in Whelan). Protection in
Soil Model of seed mortality germination shows
that increasing depth of burial helps seeds
survive fire, but if seeds are buried too deeply,
fewer will germinate. Can use this model to
predict seed germination differences under
different fire intensities in relative terms
e.g., reduced germination under a slash pile vs.
a broadcast burn.
Increasing intensity
Decreasing intensity
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Protection in Canopy Seeds can be protected by
being borne high in the canopy or by being within
insulating fruits. Example seeds of
California conifers began to decline in
germination percentage (viability) after 5 min
heat between 95?C and 110?C, but seeds encased in
whole cones had no viability decline even after 5
min at 250?C (Linhart 1978 cited in Whelan).
Capsules of eucalypts and other protective
fruit structures serve similar purposes.
Eucalyptus angophoroides Australian National
Botanical Garden, http//www.anbg.gov.au/cpbr/cd-k
eys/Euclid/sample/html/ANGOPH.htm
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Seed bank can exist in the canopy as well as the
soil. The ability to retain seeds in canopy
fruits for several years is called bradyspory
(also called serotiny, common term in US but
technically serotiny refers to late-season
seeding, not seeding over multiple years).
Sand Pine (Pinus clausa (Chapm. ex Engelm.) Vasey
ex Sarg. )
North Carolina State University
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Bradyspory/Serotiny Classic example is lodegpole
pine (Pinus contorta) mature seeds are not
released but are retained in sealed cones. Seeds
remain alive (viable) due to intact vascular
connctions. Intense (infrequent200 to 400 yr)
fire melts resin which seals cone, releasing
seeds. They fall into a nutrient-rich (ash)
seedbed where litter is burned off and overstory
trees (competitors) are dead (lodgepole dies
easily in fire), so regeneration is excellent and
new even-aged stand starts.
P. contorta, Nearctica.com
David W. Johnson, USDA Forest Service
Regeneration after Geyser Creek Burn on Windriver
Ranger District Shoshone National Forest,
http//www.forestryimages.org/
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• From FEIS (www.fs.fed.us)
• Individual trees may have serotinous cones,
  nonserotinous cones, or both. The percentage of
  trees in a stand bearing serotinous cones varies
  greatly by region and elevation, and with stand
  age and fire history.
• Young trees produce open cones. The serotinous
  cone trait is not exhibited until trees are 20 to
  30 years old.
• In the Canadian Rockies, typically 80 to 90
  percent of lodgepole pine trees bear serotinous
  cones.
• Northern and central Rocky Mountains percentage
  of trees bearing serotinous cones in a given
  stand ranged from 0 to 85 percent and averaged
  less than 50 percent.
• Type of stand disturbance also influences cone
  serotiny. Stands initiated from high-intensity
  crown fires (a process which selects for the
  closed-cone trait) have a higher percentage of
  serotinous trees than stands which are initiated
  from nonfire related disturbances. Near West
  Yellowstone, Montana, 58 percent of lodgepole
  pine trees in an even-aged, fire-origin stand had
  serotinous cones, while only 38 percent of the
  trees in an adjacent uneven-aged stand had
  serotinous cones.

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High seed mobility can be an alternative to seed
survival. Example fireweed (Epilobium) has
short viability in the soil seed bank but rapidly
colonizes burned areas by dispersing into them.
This may or may not be a specific adaptation to
fire, because high seed production and dispersal
mechanisms are common to many weedy, pioneering
species (e.g., dandelions).
Washington State University, http//www.wsu.edu80
80/wsherb/images/Onagraceae/epilobium.html
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• Multiple adaptations
• Redwood has fire-resistant bark root crown
  stem sprouts
• Chaparral species produce seed at early age,
  fire-resistant seeds with long viability,
  fire-related germination cues sprouting from
  lignotubers.
• Traits of 35 Mexican pine taxa (number of taxa
  in parentheses) serotinous cones (11), good
  regeneration on burned localities (25),
  resprouting capacity (8), grass stage (4), fast
  initial growth (4), thick bark (27), bud
  protected by heat resistant scales (1),
  self-pruning capacity (18), and recovery from
  crown scorch (3). Twelve taxa have four (Pinus
  caribaea var. hondurensis, Pinus greggii, Pinus
  jeffreyi, Pinus devoniana, Pinus muricata var.
  muricata, Pinus patula and Pinus teocote), or
  five (Pinus hartwegii, Pinus leiophylla, Pinus
  montezumae, Pinus oocarpa, and Pinus pringlei)
  types of fire-related traits.

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Mortality due to fire is important for planning
salvage and reforestation activities. Mortality
can be surprisingly difficult to estimate,
because trees may die from apparently light
fires, may survive intense fires, may resprout.
Ryan Reinhardt (1988 CJFR 181291-1297)
developed models for predicting fire mortality
for many western conifers mortality was related
to bark thickness and crown volume killed. Both
pooled (all species) and species-specific models
were developed. These models are used in FOFEM.
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Estimating tree mortality after wildfire
Fulé, P.Z., A. García-Arévalo, and W.W.
Covington. 2000. Effects of an intense wildfire
in a Mexican oak-pine forest. Forest Science
46(1)52-61.
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Mortality can be difficult to judge immediately
post-fire. At La Michilía, we were over 90
correct about which trees died, but seriously
underestimated the survivors. There is a
further complication some of the oaks were
topkilled but resprouted in the canopyare these
trees survivors? new sprouts? Need to follow
measurements for years. Ponderosa pine
mortality from Chimney Spring interval burning
area took over a decade to appear. Finally,
mortality may be due to a variety of factors,
where the fire is only one component.
Oaks sprouting, La Michilía biosphere reserve,
Durango, Mexico