Disturbance

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

2. 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.”

3. 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

4. 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)

5. 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.

6. Studying Disturbance • Disturbance History, Behavior, Ecology • The record erasure problem • The reconstruction problem • The retrospective problem (natural experiments) • The replication problem

7. 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

8. 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

9. Fire • Major disturbance process in many forests • Important in grasslands also • Used by humans for millennia • Being introduced into tropical forest.

10. Some Controls of Fire • Fuel Moisture content • Fuel Continuity • Ignition and heat spread • Fire triangle: Fuel, heat, Oxygen • Fire behavior triangle: Weather, topography, fuel

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12. 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)

13. 238, 920 acres (967 km2)

14. Tillamook Burn(s) • 1933; 311,000 acres (1259 km2) • 1939; 190,000 acres (769 km2) • 1945; 180,000 acres (730 km2) • 1951; 32700 acres (130 km2)

15. -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

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

17. 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

18. 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

19. 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)

20. MFRI: 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=53 294+22+11+9+54=390 390/5=78 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

21. 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

22. 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.

23. 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

24. 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)

28. Discharge Amount • Time Lag • Peak Discharge • Zone of Flood Risk • Normal Discharge • Recession Limb • Rising Limb Hours from start of storm Storm Rainfall event

29. 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

31. 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

33. Sandar Plain

34. 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)

36. 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

38. 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,

40. Cinder cone Composite Shield

43. 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)

45. Austrian Forestry Department. 150 m/hr winds)

47. 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.

48. 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)

49. 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.

50. 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.