Download Fire and Vegetation

Fire Effects on Vegetation
September 16, 2010
Tallgrass Prairie: TTYP
• First, think to yourself. Write down any
causes, effects, and mechanisms that
explain this landscape.
• Then, discuss with a partner and be
prepared to share with the class.
Fire in Tallgrass Prairie
• Primary role in maintenance and
development
• Alteration in physical environment,
particularly the litter layer
• Changes in resource availability, rapid
regrowth
• Plant level mechanisms
• Human management and the importance
of timing
Fire’s Effects on Vegetation
• Fire alters the physical environment through removal of
live and dead plants from the community
• Selectively eliminates part of the plant community
• Other plant species are unchanged or have adaptions for
regrowth
• Temporarily reduces resource competition
– Increase in moisture, nutrients, and light
• Any plant can be killed by a fire of
sufficient severity!!!
Understanding the Plant Response
• Plant adaptations based on strategies of
resource allocation
Plant mechanisms for
establishing after fire
• Survival – due to “fire adaptive traits”
– Tolerance - persistence of same individual
– Vegetative regeneration
• Post-fire regeneration (of new plants)
– Seed survival (protection)
– Seed dispersal
– Adaptation to post-fire conditions
Many pine species have
high tolerance of fire (“resistance”)
(Jack, Ponderosa, Longleaf pine)
• Thick bark
• Self pruning
• Deep root system
Species with 1.0 to 1.3cm bark
thickness are resistant to fire.
• Intense-fast moving fire
– Plant protected
• Intense-slow moving fire
– Greater susceptibility to
damage or mortality
• Mature > young
Thick bark of
Ponderosa Pine
Fire tolerance of seedlings
Longleaf pine - “grass stage”
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Prolonged grass stage
Store large amounts of carbohydrates in roots
Thick, moist foliage cover protects terminal bud
Plant height grow fast after fire - terminal bud lift up before
the next fire
Vegetative Regeneration
(sprouting)
• Part of an individual plant survives and fire
stimulates resprouting
• Allocation of resources in different ways
• Both aboveground and belowground
possible
Root collar sprouts
– Dormant buds insulated from fire by bark and
store energy required for sprouting
Lignotubers
– Swellings at the
base/root collar of shoots
of shrub species
– Fire stimulates sprouting
Eucalyptus shrubs in Australia
Root suckering from
adventitious buds
– Adventitious buds: Develop from places other than the
shoot apical meristem (stems, roots, leaves)
– Root suckers are stimulated by fire in some species
Basal Meristems
• Grasses have meristems at leaf base (protected
from heat and damage)
• High root-to-shoot ratio
• Some grasses (e.g., Pandanus) also receives
protection from leaf sheaths
Above-ground Resprouting
• Some plants re-sprout from dormant epicormic buds
beneath the bark (often deep) – stimulated by fire
• The ability to survive and re-sprout depends on:
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Tree height
Scorch and char heights
Tree species
Tree age
Fire severity
• Examples:
– Oaks
– Eucalyptus
Mechanisms of Post-Fire
Regeneration
• Seed Survival (protection from fire)
– Stored in the soil (“soil seed bank”)
– Enclosure within fruits in the canopy
• Seed dispersal
• Adaptation to post-fire conditions
Seed Protection: enclosure within
fruits
• Serotiny - Cone scales are held closed by
resinous material and it melts out by the
heat of fire and cause to release seeds
– Jack pine, Lodge pole pine
Seed Protection:
soil seed bank survives fire
Tradeoff between survival of seeds from fire and
germination of seeds in different depths (Whelan 1995)
Ground orchids start to
bloom after rains following
a fire (buried seed)
Scarification of seed coat
• Heat from fire scarifies (breaks open) the
hard seed coat and stimulates rapid
germination
Lupine
Seed dispersal
• Dessication: Many seeds
retained in fruits and heat
of the fire dessicate the
fruit and causes to release
seeds. (Eg: Sun Flower
Seeds)
• Small seeds dispersed far
distances by wind.
• Dispersal by birds,
mammals
Dormant cells in seeds in dehydrated
state tolerate high temperatures
• Sun flower seeds – Tolerates 70-90°C for
4 hours
• Jack pine seeds– Tolerates 370°C for 15
Seconds
Adaptation to post-fire conditions
• How might post-fire conditions favor plant
establishment and growth?
• Some seeds germinate best on scarified
(bare) soils
– Lodgepole pine
• Some plants only grow well under
conditions of high resource availability and
low competition
– some early successional colonizing species
Community Response
• Mortality and response of plants to fire
varies among plant species and plants of
different age/developmental stage
• Fire can shift plant community structure
and composition
– Influences successional processes
• Example: Tallgrass prairie
– Spring burn has differential influence on cool
and warm season grasses
Studying Fire
Effects
• Burned vs.
Unburned
• Pre vs. post-burn
• What assumptions
are being made?
Studying Fire Effects
Assumptions:
• Burned vs. Unburned
– the only difference between the two areas is
the treatment i.e. soils, successional stage,
disturbance history
– treatment is uniform, no within burn variation
• Pre-burn vs postburn,
– treatment is uniform
Scottish heathland example
TTYP
FIRE
FIRE
Fire Regimes and Vegetation
• Fire frequency
• Season of fire
• Severity
• Duration
• Extent of burning
• Fire frequency
Plant species may be eliminated from a site if
fire occurs too often. (Determines the species
composition)
Short fire free intervals (<20 years)
Intermediate fire free intervals (20-75 years)
Long fire free intervals (>100 years)
Short fire free intervals (<20 years)
Low-severity surface fires will occur
Fire tolerant herbaceous species will dominate.
Species composition will not change.
Intermediate fire free intervals (20-75 years)
Fuel buildups and continuous in distribution.
High-severity fire results.
Greater changes in plant composition.
Long fire free intervals (>100 years)
High-severity fire results
Postfire & prefire vegetation are markedly different
Season of fire
Affects plant survival and flowering.
Eg: Spring fire on rangelands in the Western United
States damage to annual grasses and favors to
dormant perennials.
Fire Severity
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Low severity fire
damage to fire sensitive species.
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Moderate or high severity fire:
stimulate germination, renew plant
community, change in species composition.
Duration of fire
• Long duration of fire increase the mortality of plants.
• Causes to produce high temperatures in below
ground.
Large extent of fire
•Limit seed dispersal from neighboring systems.
•Prone to eliminate more species.
•Results more dry and warm conditions.