ESRM 450

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ESRM 450 Wildlife Ecology and Conservation EC
OLOGICAL DISTURBANCE Concepts, Approaches, and
Applications
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Parameters of Disturbance Regimes F
rom White (n.d.)
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(No Transcript)
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Yellowstone Fires of 1988 A shift in biological
and management perspectives
What are the effects of fire size and pattern?
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Fire disturbance is an inherent process in forest
ecosystems An example from PNW
forests

From Agee (1993)
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Low severity fire regimes
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High severity fire regimes
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Landscapes with moderate severity fire regimes
often have complex spatial patterns
Southern Cascade Range,
Oregon
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Wind disturbance
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Wind disturbance in the Pacific
Northwest Cyclonic winds are associated with
tropical storms intensified by the jetstream.
Significant events are recorded every 20
years. 1921 windstorm on the
Olympic Peninsula
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Wind and forest harvest
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Wind and forest harvest
From Kimmins (1999)
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Insects Low vigor trees are at greatest risk

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Tree Mortality
Mountain Pine Beetle
1980 - 2004
Host Type
Pinus spp.
Shaded areas show locations where trees were
killed. Intensity of damage is variable and not
all trees in shaded areas are dead.
www.fs.fed.us/r6/nr/fid/data.shtml
Pacific Northwest Region, Natural Resources,
Forest Health Protection
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Mountain Pine Beetle outbreaks (1959-2002)
Courtesy of Mike Bradley, Canfor Corporation
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Dying Pinus edulis Jemez Mts., October 2002
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Jemez Mts., May 2004
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Interactions among disturbance
agents
Cascade Range, Oregon From
Gara et al. (1985)
Fire, mountain pine beetles, and fungi
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Fire effects on forest landscapes
From Swanson (1981)

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Causes and rates of tree mortality vary with
stand age (Douglas-fir, PNW)
Regen. Full veg. Closed Mature
Old cover canopy
forest forest Stand age (yr) 0 5
5 20 20 100 100 200
gt 200 Mortality rate Very high
High High to mod. Mod. to low
Mod. to low Mortality Phys.
stress, Competition Competition
Pathogens Wind causes
herbivory phys. stress pathogens
wind pathogens
pathogens pathogens wind
competition physiol. disorders
herbivory From Swanson (1981)
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Fire regimes

• What is a fire regime?
• Frequency and severity
• Seasonality, vegetation, controls (climate,
  fuels, ignition sources)
• Fire frequency
• Point fire return interval
• Composite fire interval
• Fire cycle/rotation
• Fire severity (low, mixed, high)

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Fire regime properties
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Low-severity fire in ponderosa pine and other dry
forest ecosystems
Pinus ponderosa
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Pinus contorta
Serotinous cones
Non-serotinous cones
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At treeline, rare patchy fires
Whitebark pine (Rocky Mountains)
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Sagebrush fires can be mixed to high severity
Clint Wright
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Chaparral fires are associated with synoptic
weather (Santa Ana winds) and human ignitions.
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Climatic change and controls on fire
ENSO?
Climate
Temperature increases

• Fire frequency
• Fire severity
• Fire area burned
• Air quality

Topography
Fuels
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Climate-limited or fuel-limited?

• Different fuel types respond differently to
  climate.
• Two mechanisms drying of fuels and production of
  fuels.
• Drying happens seasonally, whereas production
  affects fire on scales from years to decades.

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Managing fire regimes in the context of climatic
change and other stresses
Examples from forests of Western North America
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Mixed conifer (Sierra Nevada, southern
California) Ozone and particulate pollution
Fire exclusion ? high stand densities Extended
warm period ? insects Ponderosa pine, Jeffrey
pine, white fir die Fuels accumulate ? severe
fires Exotic plants increase where fires do
occur.
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Sierra Nevada mixed conifer
Global warming
Fire exclusion
Ozone
Higher temperatures more severe and extended
droughts
Bark beetles and defoliators
High stand densities
Fuel accumulation
Ponderosa and Jeffrey pine mortality
Large severe fires
Changes in species composition (including exotics)
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Lodgepole pine Extended warm period, insects,
pines die, fuels accumulate, sets up for large
fires.
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Interior lodgepole pine
Global warming
Higher temperatures more severe and extended
droughts
Stand-replacing fire regime
Bark beetles and defoliators
Extensive mature cohorts (70-80 yrs)
Lodgepole pine mortality
Large severe fires
Fuel accumulation
Salvage logging
Changes in species composition (including exotics)
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• Multiple disturbances
• Fire and insects are modifying different regions
  (so far).
• Direct effects of global warming melting of
  permafrost.

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Stand-replacing fire
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Stand-replacing beetles
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Stand replacing fire global warming
Black spruce
Ecosystem change
Paper birch
Stand replacing insect kill global warming
White spruce
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Global warming
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Managing fire and fuels is mostly a sociocultural
challenge
Federal fire suppression cost in 2002 1.6
billion (500 per ha burned)
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Target (historical) conditions
Current conditions
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Objective Reduce crown fire hazard Guiding
scientific question How can fuel treatments be
designed to modify fire hazard and potential fire
behavior?
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Thinning
Burning
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• Scientific principles of fuel treatment
• Modifying forest structure
• Raise canopy base height
• Reduce canopy bulk density
• Reduce canopy continuity
• AND reduce surface fuels

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Principle 1 Canopy base height
Dense stand with understory
-------- Canopy base height lt 2 m
-------- Canopy base height gt 6 m
Treated stand after thinning from below
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Principle 2 Canopy bulk density
Dense stand with understory
Canopy BD gt 0.30 kg m-3
Canopy BD lt 0.10 kg m-3
Treated stand after thinning from below
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Principle 3 Canopy continuity
Dense stand with understory
Treated stand after thinning from below
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Surface fuels must be treated following removal
of trees
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Analysis of stand development assists treatment
scheduling
No treatment
2003
2010
2015
2020
Thinning
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Effective fuel treatment programs must consider
large landscapes
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Many constraints to effective fuel treatments
Need lots of tree removal Lack of markets for
small wood EIS, EA and other review Litigation Ris
k of escaped fire Scheduling (20-year cycle)
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Toward science-based fire management and policy

Develop guidelines that quantify the effects of
fuel treatments on fire behavior Integrate
scientific information and human
values (ecological cultural restoration) Develo
p a rational economic approach Educate the
public on living with fire
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Principles of fire-resilient forests
Adapted from Agee (2002)
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How do forest harvest practices compare to
natural disturbance processes?
Standard thinning
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How do forest harvest practices compare to
natural disturbance processes?
Variable density thinning
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How do forest harvest practices compare to
natural disturbance processes?
Clearcut
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How do forest harvest practices compare to
natural disturbance processes?
Multiple clearcuts