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Aspen stands: Fuel or Fuelbreak at a Landscape Scale?

Aspen stands: Fuel or Fuelbreak at a Landscape Scale?. Introduction. Do aspen stands make good strategic (landscape scale) fuelbreaks for community protection and commercial forest protection? Effectiveness varies with burning conditions and fuel loads.

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Aspen stands: Fuel or Fuelbreak at a Landscape Scale?

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  1. Aspen stands:Fuel or Fuelbreak at a Landscape Scale?

  2. Introduction • Do aspen stands make good strategic (landscape scale) fuelbreaks for community protection and commercial forest protection? • Effectiveness varies with burning conditions and fuel loads.

  3. In spite of sophisticated fire management, fire still operates at a landscape scale

  4. 75 year Okanagan fire history map shows: • ½ the area burned at least once • Significant areas re-burned • 90% of lightning fires suppressed at <0.1 ha • Large fires in 1920s, 1930s, 1990s, 2003 • No large fires in Okanagan Mountain Park

  5. Okanagan Mountain Park Fire, 2003 • Severe drought and wind • Entire 10,000 ha park burned in 25,000 ha fire • East half of fire burned before (1920s, 1930s) • No landscape-scale fuelbreaks

  6. South Okanagan fire history • Only 2000 ha of 1.66 M ha burned/year (0.12%) • Not enough fire to maintain fire-dependant ecosystems in crown fire-resistant state • Solutions include community fuelbreaks, prescribed burning, home ignition zone fuel reduction

  7. Limitations/constraints on fuel reduction • Most burned area associated with synoptic-scale weather patterns • Fuelbreaks may fail in extreme burning conditions of drought, low RH, high winds • Prescribed burning is risky, requires skills and experience in short supply, and smoke is a problem

  8. Limitations/constraints on fuel reduction • Prescribed fire effects unlikely to override extreme weather, especially areas subject to wind and drought

  9. Limitations/constraints on fuel reduction • Expensive to reduce fuel loads at landscape scale

  10. Limitations/constraints on fuel reduction • Fuel reduction measures are not one-time events, their impacts are short-term

  11. Weather Conditions & Fuel Moisture Weather Conditions • Three year moisture deficit, Slave Lake area • Dry spring followed light snow pack • Heavy fuels and forest floor drier than normal • Fine fuels dry, warm temp, low RH, windy • Conifer foliar moisture near its annual minimum • Greenup of grass and herbaceous vegetation delayed by drought Chisholm Fire Study

  12. Chisholm Fire Study Fire Weather Observations and Peak Weather Indices For May 28th 2001 • Previous area May record BUI=121 (1991), ISI=41, FWI=60

  13. Chisholm Fire, FBP Fuel Type Map

  14. Weather Conditions & Fuel Moisture Fuel Types • Boreal Spruce (C2) predominates (39%) • Cured standing grass (O-1b) significant (35%) due to reburn in 1998 Mitsue and Chisholm burns • Leafless aspen (D-1) significant (18%), generally has conifer understory • Boreal mixedwood - leafless (M-1) (3%), generally has 25-50% conifer • Mature pine (C-3) significant on benches along Athabasca River, minor overall (3.5%)

  15. Special situations • Grass fuels were 100% cured and standing, due to low snowpack and dry spring • Deciduous stands (0-1) had begun leaf-out, but grass and herbaceous vegetation in stands had not • Extensive 30 year old aspen stands from 1968 Vega Fire along west flank

  16. Chisholm Fire Behavior and Effects in Aspen • All overstory trees killed, all plots • Vigorous aspen suckers, all plots • Herb and shrub response vigorous, all plots • Grass sparse on CFS plots, significant on Vega plots

  17. Chisholm Fire Behavior and Effects in Aspen • Fire intensity 10 times higher on CFS plots, due to fire history, fuel load and rate of spread • Highest intensity established for CFS plot = 228,000 kW/m • Highest intensity established for Vega plot = 27,000 kW/m

  18. Fuel loads and fuel consumption • Much higher fuel loads established on CFS plots due to falldown of natural mortality + 1972 and 1978 fire-killed trees • Downed-woody fuel loads much lower on Vega Fire plots due to salvage logging after Vega Fire

  19. Drought conditions in 1968 and 2001 contributed to high consumption of downed-woody fuel and forest floor

  20. Landscape fuel management interpretations • Higher than predicted aspen fuel consumption if spring burning conditions severe and/or fuel loads high • Under-estimation of potential aspen fire behavior may result in over-estimation of benefits of aspen stands as fuelbreaks

  21. Landscape fuel management interpretations • Large stands of aspen were effective at stopping fire spread under severe spring burning conditions when: • downed-woody fuel loads were light, and • cured grass is not a factor

  22. Landscape fuel management interpretations • Aspen Fuelbreaks should: • Maximize canopy closure to exclude grass, and • Reduce downed-woody fuel loads to a single ground layer

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