Disturbance

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

Management

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

• “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

• 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

• 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

• Disturbance History, Behavior, Ecology

• The record erasure problem

• The reconstruction problem

• The retrospective problem (natural experiments)

• The replication problem

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

• 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

Fire

• Major disturbance process in many forests

• Important in grasslands also

• Used by humans for millennia

• Being introduced into tropical forest.

Some Controls of Fire

• Fuel Moisture content

• Fuel Continuity

• Ignition and heat spread

• Fire triangle: Fuel, heat, Oxygen

• Fire behavior triangle: Weather, topography, fuel

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

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

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

Fire Size

• 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 km2)

Tillamook Burn(s)1.1933; 311,000 acres (1259 km2)2.1939; 190,000 acres (769 km2)3.1945; 180,000 acres (730 km2)4.1951; 32700 acres (130 km2)

-Biscuit Fire 2002-500,000 acres (2000 km2) -Reflective of Present Fire Management Issues: Wilderness Fight or Leave Exurban Forest-Controversy 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

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

Fire Intensity

• 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

• 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• 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: Fires in study area in 1555, 1849, 1871, 1882, 1891, and 1944Intervals are 1849-1555=294; 1871-1849=22; 1882-1871=11; 1891-1882=9; 1944-1891=53294+22+11+9+54=390390/5=78MFRI=78 yearsMultiple 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 years4532/3500=129% of study area burned in 443 yearsNFR= 443/1.29 = 343.4

Frequency and Severity Relationship

• 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)

• 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

• 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

Flood

• 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)

A. Discharge AmountB. Time LagC. Peak DischargeD. Zone of Flood RiskE. Normal DischargeF. Recession LimbG. Rising Limb

Storm Rainfall event

Hours from start of storm

Landslide/Mass Wasting

• 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)

• 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 Plain

Snow Avalanche

• 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

• 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

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 cone

Composite

Shield

Windthrow• 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)

Pest and Disease

• 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

• 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)

• 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.

Sources

• 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.