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Wildfire 2009
 

Wildfire 2009

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  • Double or treble the sediment loss from the ‘road’ compared with the burnt area of the catchment.

Wildfire 2009 Wildfire 2009 Presentation Transcript

  • Paper presented at Wildfire 2009 Conference, June 16-17th2009, Lyndhurst, UK
  • Wildfires in Portugal: characteristics, soil degradational impacts and mitigation measures
    Rick Shakesby
    In collaboration with
    A.J.D. Ferreira, C.S.S. Ferreira, C.R. Stoof, E. Urbanek, R.P.D. Walsh
    Photo of Coimbra, 2005: António Ferreira
    “A global initiative to combat desertification”
  • High fire frequency since early 1980s
    Reasons:
    1. Summer dry period
    2. Highly flammable tree plantations
    3. Poor litter and timber waste management
    4. Improved access to forest areas
    Insurance claims, feuds, vandalism
  • Reduction in sediment yield
    caused by increasing cover of stones, vegetation and litter
    Post-wildfire soil erosion
    From: Shakesby & Doerr (2006)
  • Study sites in Portugal
    Águeda Basin
    Vale Torto
  • Water drops
    Águeda Basin, 1988 – 2 years after wildfire
    • Thin stony soils
    • Steep slopes (up to 20-30°)
    • Fast-growing Eucalyptus globulus and Pinus pinaster plantations
    • High rainfall (c.1600 mm)
    • Summer dry period, with pronounced soil water repellency
  • Pasture with mixed woodland
    Pre- 1920s
    Pine
    1920s
    Eucalyptus
    1940s
    Fire
    1986
    Rip-ploughed & planted eucalyptus seedlings
    Pine seedlings
    Eucalyptus
    regrowth
    ‘Mature’ eucalyptus
    Mature pine
    Águeda Basin – land use change
    Post 1986
  • ‘Mature’ Eucalyptus (c. 12 years old)
    Large quantity of highly flammable undergrowth and litter
  • Management responses to fire - Eucalyptus
    Plough and plant Eucalyptus seedlings
    Allow regrowth from stumps
  • Machinery used to rip-plough before planting Eucalyptus seedlings
  • Terraces - preferred preparation for planting Eucalyptus seedlings
  • Stone armouring
    Preferential loss of fine sediment, organic matter and nutrients
    Wildfire – effect on soil erosion
  • Large loss of a range of particle sizes
    Rip-ploughing – effect on soil erosion
    Rip-ploughing disturbs quasi-stable soil, moves soil downslope and dislodges large bedrock slabs
  • Rip-ploughing & Eucalyptus seedling regrowth
    Wildfire & regrowth
    Ploughing
    Fire
    Post-fire soil erosion: schematic
    Soil erosion
    ‘Background’ soil erosion
    Time
  • Post-fire changes, Águeda Basin
    • Increased stone cover in one year from 17 to 42%
    • Preferential loss of organic matter
    • Losses of N, K and P increased by 3-4 orders of magnitude (in eroded sediment)
    • Losses of P for 2 years after fire represent 19-55% of soil nutrient reserves
    • Similarly large losses of orthophosphate and potassium in solutes
  • Research design for testing post-wildfire mitigation measures
    Different treatments applied 9 months after wildfire
    Eucalyptus
    Low
    Burnt control
    Medium
    High
    Unburnt
    Pine needles removed
    Pine
    Bare soil
    Burnt control
    Medium
    High
    Unburnt
  • Post-fire mitigation - pine
    Pine needlefall
    Pine salvage waste
  • Salvage logging waste applied to erosion plots
    Soil loss reduced by 95%
    Eucalyptus: high amount of salvage waste
    Soil loss reduced by 55%
    Eucalyptus: low amount of salvage waste
  • Prescribed fire as a soil conservation tool
    Vale Torto catchment, February 20th 2009
  • Vale Torto – ‘experimental’ fire
    • Catchment = 10 ha
    • Scrub vegetation (fuel load = 23 t/ha)
  • Fire characteristics
    Fire started at the catchment boundary
    Measuring flame temperatures
    • Relatively ‘hot’ for a controlled fire
    • Flame temperatures up to > 800°C, but relatively little soil heating (soil temperatures < 100°C)
    Temperature-sensitive paints
    Paint strips on metal bars
  • Spatial variation in fire severity
    Near the main drainage line
    Higher impact on vegetation and litter
    Near to the watershed
    Lower impact on vegetation and litter
  • Use of sediment fences to monitor soil erosion
  • Fire break/access road on catchment boundary
    Higher soil losses than on burnt land
  • Camelo site – wildfire on July 3rd 2008
    Soil losses up to 2 orders of magnitude higher than at Vale Torto
    • Similar geology, soil, vegetation and relief to Vale Torto
    • Higher fuel load (65 t/ha) compared to Vale Torto
  • Conclusions
    Wildfire causes ‘modest’ soil losses versus some agricultural practices. However…
    Fine sediment, organic matter and nutrients are preferentially removed
    Post-fire ploughing and terracing cause very large downslope soil transfers
    Even an atypically ‘hot’ prescribed fire causes far less soil loss than a wildfire
    Timing of prescribed fire may be critical to limit soil losses
    We still can only guess at the soil renewal rate!
  • Thank you
    ‘Desire’ is an EU-funded project, 2007-12
    “A global initiative to combat desertification”