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Disturbance. Why it Matters in (Landscape) Ecology and Resource (Ecosystem) Management. Definition (Pickett and White 1985).

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Why it Matters in (Landscape) Ecology and Resource (Ecosystem) Management

Definition pickett and white 1985
Definition (Pickett and White 1985)

  • “A relatively discrete event in time that disrupts ecosystem, community or population structure and changes resources, substrate availability, or the physical environment.”

Ecological importance of disturbance
Ecological Importance of Disturbance

  • “Resets clock”

  • Mixes ages, composition, structure at multiple spatio-temporal scales

  • Provides diverse habitat and PATHCES – important to biodiversity

  • Ecosystems are dynamic – growth, death, replacement. Disturbance is a major change factor

Synergy in disturbance
Synergy in Disturbance

  • Not often studied; a very complex set of variables

  • Interactions between disturbance types (and chronic situations) recognized as important to landscape dynamics

  • Frequently mentioned when obvious (e.g. drought effects on fire)

Types of disturbance
Types of Disturbance

  • Many different types, operating at many spatio-temporal scales

  • Different types produce divers results (over space and time)

  • Interactions can occur across scales

  • Type of disturbance present in an ecosystem often a function of components, structure of ecosystem as well as physical (climate, topography, etc.) factors.

Studying disturbance
Studying Disturbance

  • Disturbance History, Behavior, Ecology

  • The record erasure problem

  • The reconstruction problem

  • The retrospective problem (natural experiments)

  • The replication problem

Import of disturbance studies
Import of Disturbance Studies

  • Range of Natural Variation (Ecosystem Management)

  • Description of Important Ecosystem Component

  • Conservation Planning

    • Size of reserve

    • Management of disturbance within/without reserve(s)

    • Understanding of disturbance “behavior” within context of management

The disturbance regime
The Disturbance Regime

  • Method to describe disturbances in ecosystems

  • Several variables:

    • Distribution Area/Size

    • Frequency Magnitude (Intensity or Severity)

    • Rotation

    • Return Interval Synergism

    • Most common descriptors used are frequency (MRI or Rotation), severity and size


  • Major disturbance process in many forests

  • Important in grasslands also

  • Used by humans for millennia

  • Being introduced into tropical forest.

Some controls of fire
Some Controls of Fire

  • Fuel Moisture content

  • Fuel Continuity

  • Ignition and heat spread

  • Fire triangle: Fuel, heat, Oxygen

  • Fire behavior triangle: Weather, topography, fuel




Fire size
Fire Sizehttp://video.google.com/videoplay?docid=-3534240493250250879&q=crown+fire&total=610&start=0&num=10&so=0&type=search&plindex=6

  • Mapped by air photo or satellite imagery

  • Normally the area affected by the fire (severity or intensity not considered)

  • Severity a/o intensity may be mapped within the fire polygon (e.g. scorch height, percent crown scorch, mortality)

  • Big Fires: Yacolt 1902 (239,000 acres, 38 people), Tillamook 1933 (311,000 acres), Coast Range 1849 (1million+? Acres), Biscuit 2002 (499,965 acres)

238, 920 acres (967 kmhttp://video.google.com/videoplay?docid=-3534240493250250879&q=crown+fire&total=610&start=0&num=10&so=0&type=search&plindex=62)

  • Tillamook Burn(s)http://video.google.com/videoplay?docid=-3534240493250250879&q=crown+fire&total=610&start=0&num=10&so=0&type=search&plindex=6

  • 1933; 311,000 acres (1259 km2)

  • 1939; 190,000 acres (769 km2)

  • 1945; 180,000 acres (730 km2)

  • 1951; 32700 acres (130 km2)

-Biscuit Fire 2002http://video.google.com/videoplay?docid=-3534240493250250879&q=crown+fire&total=610&start=0&num=10&so=0&type=search&plindex=6

-500,000 acres (2000 km2)

-Reflective of Present Fire

Management Issues:


Fight or Leave

Exurban Forest


Donato 2002 Science Paper:

Salvage Logging reduces

seedling regen and increases

future fire risk

OSU Dean, USFS and

Timber Industry letter

Issues of Academic Freedom


Fire intensity
Fire Intensityhttp://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg

  • Fuel a major factor in intensity (size, shape, arrangement, moisture, continuity)

  • Patchiness of fuel adds to patchiness of fire (intensity)

  • I = 3 (10 FL)2 (in kw/m)

  • Surface, understory, crown fires (<1m, 1 – 3 m, >3m FL)

  • Crown fires release enormous amounts of E and can move very quickly

Fire severity
Fire Severityhttp://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg

  • Difficult to measure

  • Frequently Ordinal (L, M, H)

  • When quantified often a percent of crown burned/dead

  • Reconstruction very difficult, not standardized in fire history studies

Fire frequency
Fire Frequencyhttp://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg

  • MFRI (Mean Fire Return Interval) – the average time between fire events.

    • MFRI = # intervals/total years fire intervals

    • MFRI needs at least 3 fires (2 intervals) to be calculated (although this would be a poor estimate of MFRI)

    • Useful in high frequency regimes (PIPO, etc.)

    • Area or Point calculation?

  • NFR (Natural Fire Rotation) – time needed to burn an area equal to the study area

    • NFR (yrs) = Total time period/% area burned in period

    • (Normally) Multiple fires, can have repeat in certain areas

    • Must define study area (extent)

MFRI:http://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg Fires in study area in 1555, 1849, 1871, 1882, 1891, and 1944

Intervals are 1849-1555=294; 1871-1849=22; 1882-1871=11; 1891-1882=9; 1944-1891=53



MFRI=78 years

Multiple Sites or individual site? Record Erasure? Variation?

NFR: Study Area total is 3500 km2 Study Time Frame from 1555 to 1998.

1555 Fire 949km2;1848 Fire 1876 km2; 1871 Fire 647km2; 1882 Fire 441 km2;

1891 Fire 498 km2; 1944 Fire 121 km2 .

949+1876+647+441+498+121=4532 km2 burned in (1998-1555=) 443 years

4532/3500=129% of study area burned in 443 years

NFR= 443/1.29 = 343.4

Frequency and severity relationship
Frequency and Severity Relationshiphttp://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg

  • Typically, the more frequent, the less severe and vice versa

  • Common assumption for other disturbance processes

  • More frequent fires remove fuels, etc. that cause high severity burns

  • Not completely proven

Responses to influences of fire rowe 1983
Responses to/Influences of Fire (Rowe 1983)http://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg

  • Invaders: pioneers, short-lived. Fireweed

  • Evaders: long-lived propagules stored in soil. Serotinous cones of lodgepole pine. “Help” fire?

  • Avoiders: no fire adaptations; late-successional or “no-fire” environs. Hemlock, Sitka Spruce.

  • Resisters: Survive low- mid (higher?) intensity fires. Many fire adaptations. W. Larch, PSME, PIPO

  • Endurers: Sprout from root-crown. Oaks, Aspen, Madrone.

Human controls of fire
Human Controls of Firehttp://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg

  • Long history of different approaches to fire

  • Change in landscape patterns of patches and related characteristics has changed fire regime

  • Ex-urban development has made fire management far more complex

  • Major debate has always been around three-fold choices:

    • Control all fires aggressively

    • Prescribed burns and other early controls

    • Let burn


  • High intensity flow of water in river/stream systems

  • Affects bed structure and composition, sediment deposition, inputs to streams.

  • Flood Hydrograph reflects intensity

  • Peak curve affected by humans, especially roads in PNW forests (Jones and Grant 1996).

  • R.O.S.E.s important in PNW floods (Pineapple Express)

  • Discharge Amounthttp://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg

  • Time Lag

  • Peak Discharge

  • Zone of Flood Risk

  • Normal Discharge

  • Recession Limb

  • Rising Limb

Hours from start of storm

Storm Rainfall event

Landslide mass wasting
Landslide/Mass Wastinghttp://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg

  • Important input to streams

  • Synergy with rainfall, soil moisture content

  • Slope angle important (angle of repose)

  • Intensity a measure of volume of scar (inputs)

  • Colluvial deposits eventually make up stream bed (round alluvial) material

  • CWD also delivered

  • Roads affecting rate, amount of inputs

Jokulhlaups yokel lowps
Jokulhlaups http://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg(Yokel-lowps)

  • Glacial outburst flood

  • Dam from glacier lobe fails, releasing lake behind dam catastrophically.

  • Quick or slow melting; lifting or bursting of glacier

  • Can cause mudflows across sandurs

  • Jokulhlaups of Columbia Basin were huge; came from Missoula Lake (about 40 events?) during Wisconsin era of Glaciation (ended about 10,000 years ago). Largest estimated at 2130 km3 of water

  • Important formation process for much of the landscape of Columbia Basin

  • Had effects in Willamette Valley also

Sandar Plainhttp://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg

Snow avalanche
Snow Avalanchehttp://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg

  • Mass of snow flowing downslope

  • Enormous energies due to speed, mass

  • Controlled by many factors related to snowpack, especially stable slabs on unstable layers (not-bonded)

  • Triggered when stress applied to snowpack

  • Can focus in gulleys or cover large areas

  • Related patterns of vegetation, other ecological factors (e.g. grizzlies)

Lahars debris flows
Lahars/Debris Flowshttp://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg

  • Hot or cold mixture of water, rock, mud that flows down a slope of a mountain, generally due to volcano activity

  • Triggers: landslides (rain, earthquake, eruptions), glacial melting/serac failure, eruption.

  • Almost always on volcanoes


  • Magma chamber underneath active volcano moves upwards, released violently. Explosive eruption of lava due to build-up of gases. Viscosity of magma another important factor: Thick  explosive (build-up). Thin  less explosive.

  • Lava, pyroclastic materials, ash, gases

  • Intensity can compare with hydrogen bombs

  • Cinder cone (boom), Shield, Composite,

Cinder conehttp://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg




  • Trees uprooted during excessive wind events

  • Soil moisture content, topography, soil depth important considerations

  • Synergistic with fire, disease (supplies dead material, weakened trees susceptible to other disturbance)

  • Generally smaller areas than fires, other events

  • Provides small gaps for succession

  • Root-mound topography

  • Can be Isotropic (trees fall in one direction)

Austrian Forestry Department. 150 m/hr winds)http://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg

Pest and disease
Pest and Diseasehttp://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg

  • Many different diseases affect ecosystems

  • Often synergistic with other disturbance (weakened/stressed/dead organisms)

  • Insects, fungi, bacteria, viruses

  • Spread (dispersal) related to distribution of “subjects” and related behaviors, ability to move.

Invasive species
Invasive Species http://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg

  • Introduced species that frequently have enormous impacts on natives

  • Lack predators, other controls

  • Out-compete or prey on existing species

  • Can change nutrient cycles, food web, other important ecological systems

  • Especially destructive on islands or similarly isolated ecosystems.

  • Can also alter disturbance regimes (e.g. cheatgrass)

Managing disturbance or disturbing management
Managing disturbance (or disturbing management)http://upload.wikimedia.org/wikipedia/en/e/eb/NASA_Biscuit_fire.jpg

  • On-going experiment

  • Frequent failures (Los Alamos fire)

  • Overall attempt to re-introduce disturbance into ecosystems and try to restore RONV

  • TNC, other conservation groups, feds lead in this area.


  • Jones, J.A. and Grant, G.E. 1996. Long-term stormflow responses to clearcutting and roads in small and large basins, western Cascades, Oregon. Water Resources Research. 32: 959-974.

  • Pickett, S. T. A., and P. S. White. 1985. The ecology of natural disturbance and patch dynamics. Academic Press, Orlando, Florida, USA.

  • Rowe, J.S. 1983. Concepts of fire effects on plant individuals and species. In Wein, R.W. and D.A. Maclean (eds.), The role of fire in northern circumpolar ecosystems: pp. 135-54. New York: Wiley and Sons.