K Scott, S Setterfield, M Douglas

1
PROGRAM B Project 3.2, Prescribed fire and
biodiversity in northern Australia
Soil temperatures in the Top End
K Scott, S Setterfield, M Douglas Faculty of
Education, Health and Science, Charles Darwin
University, Northern Territory A Andersen CSIRO
Sustainable Ecosystems, Northern Territory
Knowledge of soil temperatures is important
because they determine if seeds germinate

• 1. Diurnal change on surface
• Up to 35C difference between night and day
• Soil under leaf litter and tree canopy stays
  cooler

• 2. Depth and season (at 1.00 pm)
• Hotter on surface than at 1 cm below
• Hotter in late dry season than early dry season

Canopy gap (no litter)
Surface 1 cm depth
Canopy gap (under litter)
Under canopy and litter
Temperature (C)
Temperature (C)
Late dry season (October)
Early dry season (June)
Time of day (16/11/06)

• 3. During a fire
• Peaks rapidly and falls slowly
• Surface gets hotter than 1 cm below
• Fires hotter in late dry season than early dry
  season
• Soil temperature in early dry season fire
  similar to diurnal max

Early dry season (June) Late dry season (October)
Late dry season - surface Late dry season 1 cm
depth
Early dry season surface Early dry season 1
cm depth
Temperature (C)
Temperature (C)
1 cm depth
Surface
Time (min)

• 4. Implications
• Temperatures are never low enough to prohibit
  germination in the growing season (starts
  November)
• Seeds which bury themselves (hygroscopic awns),
  or fall in shady microclimates, are protected
  from high diurnal temperatures
• Seeds dont have a direct advantage of being
  heated by early dry season fire they experience
  similar temperatures at time of germination
• Hotter fires in the late dry season should
  release more hardseeded legumes from dormancy (a
  given temperature extends deeper)