A Burning Question: Can Long-term Data Inform Fire Management in the Twenty-first Century? - Biodiversity Conservation and Environmental Change - page 61

prevents the establishment of forest trees, and instead promotes the persistence of savanna
or grassland vegetation. Once established, fire prone, grass-dominated ecosystems become
self-sustaining, switching from shade tolerant, fire-sensitive assemblages to fire-tolerant
shade-intolerant vegetation types (Bond 2008, Warman and Moles 2009, Whitlock et al. 2010
Hirota et al. 2011, Staver et al. 2011) (Figure 4.4).

Many grassland/savanna landscapes would
likely persist without human-set fires due to
climatic constraints while others would transition
to woodland/forest. Hence the sensitivity to
anthropogenic activity may vary greatly.

Level of fire activity

(a)

Sensitivity to anthropogenic influence

Biome shift due to anthropogenic influence

Land clearance
intensive grazing

lgnitions

Fire suppression

Ignitions

Climate limited Fuel limited

(b)

Development of grass-
dominated herbaceous layer

Higher CO 2
Higher Rainfall
Loss of Mega-
herbivores

Open tree canopy

Fires carried by
grass layer

SAVANNA/
GRASSLAND

Fire OFF

Increasing flammable
herbaceous layer

Only fire tolerant
savanna trees
(reseeders/
resprouters)
will survive

Shade: No / little
ground cover

Closed Tr ee
Canopy

Fire ON

Fires are
excluded due
to lack of fuel

FOREST

Only shade tolerant
forest trees will survive

Forest Clearance
Lower Rainfall
More Mega-herbivores?

Shade intolerant
savanna trees are
excluded

Figure 4.4 Alternate forest and savanna states, showing the role of fire in driving biome transitions. (a)
Anthropogenic influences along a gradient of climate-limited to fuel-limited fire regimes in low- and
mid-latitudes where a gradient from forest to desert exists. (Solid line represents levels of fire activity
associated with different biomes. Dashed line indicates the degree to which these biomes are sensitive
to biome switching as a result of human impacts on fire regimes (e.g. ignitions, fuel management, fire
suppression, land use) (Whitlock et al. 2010). (b) Feedback loops that maintain savannas and forests as
alternate stable states, showing the role of fire and other factors in driving biomes shifts. In the savanna
state, a feedback between fire and grassy vegetation stops forest trees from recruiting. In forests, a feed-
back between vegetation and shade prevents fire and the recruitment of fire adapted, shade intolerant
species.