A Burning Question: Can Long-term Data Inform Fire Management in the Twenty-first Century? - Biodiversity Conservation and Environmental Change - page 59

Productivity
Aridity

Limited by
biomass

Limited by
fire conditions

Four switches

Vegetation
type

Post-fire
accumulation

Antecedent
rainfall

1. Biomass

Mosic Arid

Fire
season

Recent
weather

2. Availability to burn

Frontal
systems

Diurnal
cycle

Wind,
temperature,
relative humidity

3. Fire spread

Lightning

4. Ignitions

Centuries Decades Years Months Days Hours Instant

(b)

Ignitions

Amount of fire,
fire timing and
intensity, and
spatial pattern
controlled by
people

Fuel
conditions
modified by
long-term
human use

A function of
land manager
practices shaped
by policy
enforcement

Resources
to Burn

Atmospheric
Conditions

Partly determined by burn
timing (land manager
practice)

A function of fire
timing and land use
practices

Figure 4.3 (a) Non-linear relationship between aridity, primary productivity (biomass) and fire fre-
quency, showing highest fire frequencies at intermediate rainfall. In arid environments, fire is limited
by biomass production, while in mesic environments, fire activity is limited by fire conditions (e.g.
moisture content, temperature, and wind-speed). The range of timescales over which climate and wea-
ther variables operate to affect the occurrence of fire, assuming that biomass, availability to burn, fire
spread and ignitions are the 'four-switches' that determine fire regime Murphy (Bond and Keeley 2005,
Bradstock 2010, Murphy et al. 2011). Reproduced with permission from John Wiley & Sons. (b) Humanized
fire triangle, showing how management affects ignitions, resources to burn, and atmospheric condi-