Agenda, March 25
• Weekly meteorologist
• Tests handed backreviewed
• Fire Ecology lecture
• Lunch/ break
• Fire effects lab at
ACMF
Ecology of Fire- Plants
Sequoiadendron giganteum; fire scar in California’s Yosemite National Park
Outline of Lecture
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Fire ecology in context
Organizational hierarchies
Communities adapted to fire regimes
Plant responses to fire
Woody plant mortality
Fire Ecology in the Context of
Scientific Disciplines
• Ecology: The study of the interrelationships
between organisms, and between organisms and
their environment.
• Disturbance Ecology: The study of relatively
discrete events in time/space that alter organisms,
communities, or ecosystems and/or change
resource availability or the physical environment
(e.g. floods, volcanoes, mining, grazing…)
• Of the above disturbance types, what is fire most
similar to?
• How does fire ecology differ from other types of
disturbance ecology?
What Distinguishes Fire Ecology?
Ice Flow:
•Impacts living organisms
•Impacts physical environment
•Any impact on future
occurrence of ice flows?
VS.
Fire:
•Impacts living organisms
•Impacts physical environment
•Is INFLUENCED and DICTATED
by the biota, by living organisms
•Its impact influences the nature of
subsequent fires feedback loop
What Does Fire Ecology Entail?
The main factors that are addressed in fire ecology:
• Fire dependence or fire-related traits of plants and
animals
• Fire history
• Fire regimes
• Fire effects on soils, water, plant species, animal
species, from individuals to populations,
communities, and ecosystems.
From Individuals to Ecosystems
• As fire influences biota and biota influences fire
behavior and effects on both biotic and abiotic
resources, the ecology of fire can be described for
these feedbacks at multiple organizational levels
• How fire ecology is interpreted depends on the
organizational level of interest
– Ecosystems (fire with plants, fauna, water, soils,
energy and nutrient cycling)
– Communities (fire with plants, fauna and their
interactions)
– Populations (fire with a given plant, fauna species)
– Individuals (fire with individual)
Organizational Hierarchies within
Ecology and Fire Ecology
• Ecosystem: Characterized
by fire disturbance regimes
– Intensity, frequency, extent,
season, severity, synergism
• Community: Fire regimes, &
interspecies/ interpopulation
competition for resources
Oak/palmetto understory, slash pine overstory
– As above, and fire-related
population traits which dictate
one species’ survival over
another’s
– Example: Understory oaks
vs. overstory pines
Organizational Hierarchies, cont.
• Population: Fire regimes, interspecies and intraspecies competition
for resources,
– Age & size distribution, density, and health of population, and
implications for what fire-related traits are in effect
– Example: a group of high-density monotypic Rky. Mt. lodgepole pine are
high-severity fire-adapted population when mature
Age distribution of Douglas-fir
Density of Rky Mt. lodgepole pine stand
Organizational Hierarchies, cont.
• Individual (autecology): Fire regimes, inter/intra
competition, and individual degree of fire adaptation
– Age, size, and stature of individual, and its associated
fire-related traits
– Example: Grass-stage vs. sapling longleaf pine
Why “fire-related trait” and not
“adaptation”?
• “Adaptation” implies that fire was the primary
selective force resulting in a particular trait; often this
is not easily tested or proven
– Example 1: Self-pruning in many Pinus species
increases overall photosynthetic efficiency, also
protects the canopy from crown scorch.
– Example 2: Giant sequoia seeds need bare mineral
soil– is this an adaptation to fire or flooding?
– Example 3: Eucalyptus species are highly volatile– is
this selected for by herbivory or fire?
Why “fire-related trait” and not
“adaptation”, cont.
• All fires are not created equal. One fire may select for a
given species with a given trait, while another does the
opposite.
– Example 1: High-intensity fires with long flame lengths can
scorch and kill adult ponderosa pines, while low-intensity
fires reduce competition and increase nutrient availability
(fire type and intensity)
– Example 2: Soil-stored hard-coated seeds of manzanita
species (Arctostaphylos) break dormancy only if fires are
hot enough and if seeds are still viable (fire frequency, type,
and residence time)
– Example 3: Annual winter burns in SE US pine flatwoods
benefit sprouting species with high carbohydrate reserves,
such as saw palmetto (fire seasonality)
“Fire dependent” communities?
• Fire’s influence is most commonly observed and interpreted
at the community level
• Particular communities can be said to be “fire-adapted” or
“fire dependent”, if the absence of fire significantly changes
community structure, function, and composition, and if the
presence of fire perpetuates the survival and sustenance of
multiple populations therein.
• In many cases, changes in one attribute of a fire regime can
alter community composition, structure, and/or function.
• Communities which are considered fire-dependent are
typically dependant on particular fire regimes.
Communities (forests, shrublands, grasslands) are affected by
fire differently; each community is influenced by a particular fire
regime (fire type, frequency, seasonality, area, severity,
intensity).
Frequent
fire
Longleaf pine forests
Southeastern US
Fire < 5 years
Low intensity, understory,
spring or summer
No fire
Boreal forests
N. Latitudes
Fire > 100 years
High intensity, crown,
Summer, large areas
Tropical rainforest
23o N and S
Fire > 1000 years, small
Mixed severity when it
happens (high moistures)
Florida’s Fire-Dependent Ecosystems
• The Florida Natural Areas Inventory lists 23 terrestrial, 19
wetland communities in Florida: 16 of these are considered
FIRE DEPENDENT– will change significantly if fire regime is
altered
• Most important aspect of fire regime: frequency, which often
determines type, severity, and intensity of fires
• Examples:
– Sandhill
FRI 1-7 yrs
– Dry & Wet Prairie
FRI 1-7 yrs
– Mesic Flatwoods
FRI 3-7 yrs in N. FL, 1-7 in SFL
– Scrubby Flatwoods
FRI 8-25 yrs
– Swamp
FRI 8-100+ yrs
– Scrub
FRI 26-100+ yrs
Florida Ecosystems
• Fire Maintained
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–
–
–
Flatwoods
High pine / Sandhill
Scrub
Sawgrass prairies
Cypress swamps
Other grasslands
Freshwater marshes
Salt marshes
Florida Ecosystems
• Fire Influenced
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–
–
–
–
Upland hardwoods
Swamp forests
Dunes
Subtropical forests
Mangroves
If Fire Regimes are Altered,
Communities Change via 4 Major
Mechanisms
1. Death of older individuals of a given species,
partnered with lack of replacement by offspring,
and subsequent replacement by other species
– Example: Giant sequoia (Sequoiadendron
giganteum) of Sierra Nevada Mts.
Giant Sequoia Fire Ecology
Sequoias are fire, insect, and decay
resistant, but shallow rooting makes
them vulnerable to windthrow
Cones are serotinous & seeds require
bare mineral soil & plenty of sunlight to
germinate & grow
Ponderosa pine under sequoia
• Without fire, sequoia won’t
reproduce: other conifers occupy the
understory and can eventually replace
sequoias (changing community
ecology)
• What aspect(s) of the fire regime has
been impacted by fire suppression in
giant sequoia groves?
Mechanisms of change if
community fire regimes are altered
1. Death of older individuals of a given species,
partnered with lack of replacement by offspring,
and subsequent replacement by other species
– Example: Giant sequoia of Sierra Nevada Mts.
requires mineral soil and has serotinous cones
2. Active replacement by other species that would
normally be killed in fires- they invade slowly but
effectively outcompete existing vegetation
– Example: Pine encroachment into grassy meadows
where fires have been suppressed
Mechanisms
: of change if
community fire regimes are altered
3. The fire environment changes: microclimate,
substrate availability, growing space, site quality
4. Fuel properties change after introduction of new
plants, changing fire behavior
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Moisture content of plant tissue
Chemical composition of plant tissue
Fuel loading
Fuel continuity
Fuel packing ratio
Seasonal availability of fuels
From Communities to Populations
to Individuals
What are the traits of
individual plants that
allow them to survive
and perpetuate their
species in fire’s
presence?
Plant Traits Impacting Response
to Fire
• Flower & seed production stimulated
• Seed germination stimulated (seed or soil
conditions)
• Rapid growth & development (longleaf pine)
• Thick bark (pines, mature hardwoods)
• Adventitious buds (gallberry, pond pine)
• Root/basal meristem sprouting (oaks, grasses)
• Serotinous cones (sand pine)
Individual Plant Responses (firerelated traits) to Fire
• Classification of fire responses (Rowe, 1983)
1. Invaders (well-dispersed weedy species with shortlived seeds
2. Evaders (species with long-lived seeds stored in the
soil or in the canopy
3. Avoiders (shade-tolerant species with slow
recolonization rates- usually killed by fire)
4. Resisters (adults can withstand fires, otherwise
intolerant of fire)
5. Endurers (sprouters)
Invaders
Cogongrass (Imperata cylindrica)
•Cogongrass invades southeastern pine forests that typically have
grass understories.
• Cogongrass is much taller (up to 4 ft) than native grasses, increasing
fuel loading and promoting fire
• Resulting fires are more intense than those occurring in typical pine
stands  mortality of even (fire resistant) longleaf pine = alteration of
the natural fire regime
Invader: Melalueca quinquenervia
• A fire promoter
• Melalueca invades wetland areas of
S. Florida
• Has very flammable vegetation due
to volatiles
• Fires in Melalueca stands are
intense, often developing crown fires.
Avoiders
• White fir (Abies concolor)
•Shade-tolerant
•Colonizes under canopy
of fire-tolerant species in
mixed-conifer or pine
forests, primarily
•Low crowns encourage
torching during fires, young
trees act as ladder fuels
into adult crowns
•Relatively thin-barked and
resinous
•Shallow roots susceptible
to soil heating
White fir sapling
Avoider: Chinese tallow tree
(Sapium sebiferum)
•
A fire suppressor
• Invades grasslands and shrublands in the eastern U.S.
• Produces leaf litter that is high in moisture content that decreases
flammability of surface fuels
• Shades out grasses and shrubs
Resisters
• Ponderosa pine (Pinus ponderosa), longleaf and
slash pine
– Thick, corky insulative bark
– Self-pruning at maturity
– Occurs in open
stands
– High foliar moisture
– Susceptible to fire
when young
– Fire regime is low
intensity, frequent
surface fire
Endurers = Sprouters
• Saw palmetto (Serenoa repens)
– Flammable foliage
– Rhizomes store carbohydrates for immediate post-fire
sprouting response
– Outcompetes obligate seeders
– Can also reproduce via seeds
Evaders
• Manzanita (Arctostaphylos glauca): Chaparral fire regime is
high-severity, high-intensity, low frequency (50-100+ yrs.),
crown fire type
– Obligate post-fire seeder, hard seed coat cracked
– Increased seed production at older ages
– High intensity fire kills endurers (sprouting competition)
Adult manzanita
Young manzanita “stand”
Post-fire manzanita mortality and
regeneration
Manzanita seedlings
When mortality DOES occur, how
and why does it happen?
Foliage mortality
Temperature F
150
146
142
138
134
4
2
0
130
– high when dormant and
moisture low
– low in early summer
– varies by species
12
10
8
6
126
• Resistance to heat
Time (min)
• Mortality is time &
temperature dependent
• Can be delayed
Fire-Caused Plant Mortality
• Fuel characteristics affect lethal
heating
– Heat disperses in open stands
– High fuel loads increase heat
release
– High fuel moisture content
decreases heat
– Litter and duff accumulations
increase heating at base of stem
(esp. around old trees)
• Burn prescriptions also affect heat
loads
– Frequent fires reduce fuel loads
– Ignition pattern
– Season of burn
Woody Plant Mortality- foliage
• Crown scorch (dead foliage)
– increases as air temperature
increases
• Crown mortality affected by:
– stand & shrub density
– fuel concentrations at the base of
trees
– bud dormancy & heat resistance
– foliar moisture content
– presence of flammable
compounds
• Crown consumption = crown
mortality (nearly always)
Woody Plant Mortality- cambium
• Stem & cambium mortality affected
by:
– bark thickness, moisture & heat
resistance
– stem diameter & degree of heat
girdling
– heat received during all stages of
combustion
• Damage to tree stems managed by:
– controlling fire intensity & flame length
– reducing duff & litter consumption
• Shrub stems usually killed
Woody Plant Mortality- roots
• Root mortality affected by:
– depth of lateral and feeding roots
– moisture content of duff/litter and surface soils
– duration of fire heating
• Damage to roots managed by:
– knowing where roots are located
– regulating duff & litter consumption by burning at
specified moisture contents