Transcript Document

Seminars
1. “Plant Talk” – Thurs April 1 12:00 PM in FA 214.
Giles Thelen: “Insect herbivory stimulates
allelopathic exudation by an invasive plant and
the suppression of natives.”
2. EECB Colloquium OSN 102 at 4:00 PM
Thursday April 1. Lonnie Aarsen, Queens
University. “Ecology – less than a science or
more than a science?”
Abstracts and assignments
1. Abstracts – Extention? Due April 4.
2. Grad Student lectures – April 13 lab period.
What order? Anyone need handouts made?
3. “class conference” April 27.
4. Term papers due April 28.
Outline
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Importance of fire in range and forest
Fire regimes
Types of fire and their effects
Species responses to fire
Effects on environment and soil
Fire as a management tool
Fire in sagebrush steppe ecosystems
Reading
1. Textbook Chapter 13
2. Chapter 12, Fire, and selected pages from
chapter 16, Disturbance. Barnes et al. 1998.
Forest Ecology 4th edition. J. Wiley and Sons,
New York. (on reserve)
3. Chapter 22, Prescribed fire in rangeland
management. From heady and Child 1994.
Rangeland Ecology and Management.
Westview press, Boulder. (on reserve).
Extent of fire effects
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Widespread, occurs in most ecosystems at
some time.
Some systems adapted to frequent fire: longleaf
pine, ponderosa pine, chaparral
Table 16.1 textbook: type, frequency, and
intensity of fire in diverse ecosystems
Handout page 1 – vegetation regions and
generalized fire freqencies for North America
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Range from >1000 years in northern hardwood to <5
years in tallgrass prairie.
Fire Regime
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Definition: the kinds and immediate effects of fire
characteristic for an area.
Includes: type, frequency, size, intensity, severity
and timing.
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Ground Fire: burns soil organic matter/litter.
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Slow moving, not intense, but very destructive
Usually occurs in areas with thick organic layer – forest,
peat bogs etc.
Surface Fire: burns along soil surface
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Fast, intermediate intensity
Burns understory vegetation, removes above-ground
biomass of herbaceous species but usually does not kill
roots or perennating buds
Hot surface fires can generate ground or crown fires
HEADFIRES – burn with wind. More intense
BACKFIRES – burn against wind. Less intense.
Crown fire: burns canopy of adult trees
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Can be quite intense and destructive
Fire Behavior
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Fire behavior includes: buildup, rate of spread, type
of spread, rate of combustion
Text figure 16.1: determinants of fire behavior
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Ignition pattern
Fuel properties (physical properties, arrangement,
quantity, moisture)
Weather (temperature, humidity, wind)
Topography (configuration, slope)
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For prescribed burns, important to understand
determinants and effects of fire behavior!
Role of fire
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Acts as a disturbance – clears space
Alters chemical and physical properties of soil
Releases some nutrients in ash (eg, P)
Volatilizes C and N
“Resets” cycling (burns accumulated biomass)
Affects species composition and diversity
Alters wildlife habitat
Affects presence and abundance of insects and
pathogens
Fire as disturbance
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Fire is one of the dominant disturbances in most
forest ecosystems worldwide
In grassland, can increase production
substantially IF during a wet year (response
dependent on which resource limiting)
Removes biomass, provides substrate for
establishment, increases light penetration,
releases nutrients
Thins even-aged stands
Maintains diversity (intermediate disturbance
hypothesis; “resets succession”)
Effects on abiotic conditions
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Burning of organic matter and heating of soil.
Can change soil chemistry
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Increases pH
Decrease soil N and C but potential increase in fixation
and mineralization rates
Increase soluble minerals (but susceptible to leaching)
Can create an “unwettable layer” below soil surface
(especially if species burned has oily exudates). This can
cause “fire-flood” situation – e.g. chaparral burns;
landslides afterward.
Microclimate effects: altered infiltration (may be
reduced), greater irradiation & temperature
fluctuations
Pathogen outbreaks and sanitation
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Dense, even aged stands following fire can be
susceptible to disease or insect outbreaks
Diseased or infested stands create fuel
conditions conducive to intense fire
Intense fire destroys pathogens allowing
establishment of vigorous even aged stand
And so on…
Ground fire can also control pathogens – e.g.
longleaf pine
Species responses to fire
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Avoiding damage: characteristics include
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Thick bark (e.g. pines, oaks)
Buried buds or lignotuber (grasses, aspen, Eucalyptus)
“grass stage” – longleaf pine.
Deep rooting and rapid growth
Self-pruning (prevents “fire ladder”)
Fire resistant foliage
Rapid decomposition (no fuel buildup)
Recovering from damage:
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Resprouting (rhizomes, root crown, lignotuber,
epicormic shoots)
Deep rooting (allows rapid regrowth)
Species responses to fire
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Recolonising after fire:
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Early flowering and seed production (esp. with short fire
interval)
Asexual reproduction
Wind-borne seeds
Serotony
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Promoting fire: pyrogenic species
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Flammable foliage and bark
Volatile compounds
Short stature
Retention of foliage near ground, retention of dead
branches
Species persistence
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Propagating by seed:
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Invaders – copious short lived, wind dispersed seed.
Pioneer species (‘fireweed’)
Evaders – store seed in canopy or soil. Seeds evade
high temps, then germinate rapidly after fire. Serotinous
pines.
Avoiders – shade tolerant, arrive later in succession.
Lack fire adaptation. Sugar maple.
Surviving fire:
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Resisters – adult stages survive low intensity fire.
Sequoia. Many members are also evaders.
Endurers – resprout from perennial buds after fire.
Include trees, shrubs, grasses.
Fire for management
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“prescribed burning” is an ancient practice
Humans worldwide have used fire for numerous
purposes:
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Clear space for safety
Create “green pick” for game
Encourage medicinal plants
Drive game
In western North America, fire frequency
decreased around 1870’s
Almost ceased with fire suppression 1900.
Fire suppression
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Why was this policy implemented?
Fire suppression
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Why was this policy implemented?
Based on observations of northern hardwood
forests (rarely burn)
Misunderstanding of role of fire in west
Fear of fire, destruction of property etc.
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Result?
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Fire management and prescribed
burning
Prescribed burning: concentrates on setting of fire
in a manner that will achieve desired purposes.
In rangeland and forest: used to alter vegetation
composition, increase forage quality and quantity,
manage for wildlife, reduce wildfire risk, prevent
catastrophic fires,control exotic species, maintain
“wilderness character”, maintain particular
communities (longleaf pine, tallgrass prairie)
Fire management and prescribed
burning
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How should fire be managed and used?
Is there a role for fire suppression – where, how,
why?
Fire in sagebrush steppe
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Should fire be suppressed here? Is there a role
for prescribed burning?
Historic fire regime – 20-150 year fire return
interval. Sage fire sensitive, recruits by seed.
Perennial grasses, rabbit brush, more tolerant.
Current frequency (with cheatgrass) can be
under 10 years.
Fire creates vegetation type conversion after
invasion of annual grasses (D’Antonio and
Vitousek).
Breaking the cycle?
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Is there a way to re-establish “natural” fire regime
How could this be accomplished?
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Tomorrow: vegetation sampling in 30-year-old
burn.