Testing the importance of climate in
controlling the distribution of savannas in
South Africa vs. Argentina
Glenn Moncrieff1, William Bond1,
Sandra Diaz2, Pedro Jaureguiberry2. Lucas Enrico2
1: Botany Department, University of Cape Town,
2: University of Cordoba, Cordoba, Argentina
Holridge’s Life Zones (1947)
(PET)
Climate determines biome distribution so future climates predict future
vegetation?
2000
2050
Climate determines biome distribution so future climates predict future
vegetation?
Climate envelope projections of future biome distribution in South Africa
Midgley et al. 2000. The heat is on. SANBI.
Climate determines biome distribution
• Then different continents, same climate,
same vegetation
• Convergent evolution much studied in
MTEs
• Savannas?
Savanna = ~ continuous grass cover dominated by C4 grasses
compared Africa, Australia, Brazil (‘South America’)
Huge area of
Africa are arid
savannas
NO arid savannas
In Brazil (S. America)
Arid limit coincides
with fire in Brazil
Fires rare in arid
African savannas
South Africa vs Argentina
•
•
•
•
Similar latitudes (sub-tropical)
Similar climates
Soils not as leached as Brazil
Do savanna climates in South Africa support
savannas in Argentina?
– Methods:
• Fit MAXent model to savannas in South Africa using climate
variables
• Use the model to predict savanna distribution in northern
Argentina
• Compare predicted to observed vegetation
Savanna biome in
South Africa
(Mucina Rutherford 2006)
Predicted savanna biome in
South Africa
(Maxent model)
240 S
320 S
Argentina actual veg cover
Eva et al. GCB 2004.
MODIS product
Argentina predicted savanna cover from
Mucina Rutherford 2006 Biome map
Green: montane forest
Red-brown: deciduous forest
Argentina actual veg cover
Eva et al. GCB 2004.
MODIS product
Blue highest P of savanna
Green lower
Yellows, reds, Low
Argentina predicted savanna cover from
Mucina Rutherford 2006 Biome map
South African savanna climates
support dry deciduous ‘forest’
(=‘chaco’) in Argentina
650 mm
850 mm
South African savannas
across an MAP gradient
1000 mm
NO GRASS
Chaco ~550mm
NO GRASS
Chaco ~700mm
NO GRASS
Chaco ~ 850mm
NO GRASS
NO GRASS
NO GRASS
‘Jungas’ ~1000 mm
GRASS!!!!
NO GRASS
Montane foothills >1000 mm
NO GRASS
Montane forest ~1500 mm
Green: montane forest
Red-brown: deciduous forest
Argentina actual veg cover
Eva et al. GCB 2004.
Blue highest P of savanna
Green lower
Yellows, reds, Low
Argentina predicted savanna cover from
Mucina Rutherford 2006 Biome map
Why no savannas in Argentina?
• Bottom-up?
– Not climate
– Soils?
– Elevation?
• Argentina low elevation
• South Africa (and much of Africa) high elevation
South Africa (and much of Africa) has much higher elevation than
NW ‘savanna’ climate region of Argentina
http://www.ngdc.noaa.gov/mgg/topo/globe.html
Why no savannas in Argentina?
• Top-down?
– Fire?
• Chaco is relatively dry (mostly 500 - 1000mm)
• Fires less important in more arid climates
Farmers burn chaco to promote grazing
Many chaco species are intolerant of fire suggesting
little evolutionary history of burning
This is strikign contrast to humid savannas of Brazil with
massive dominance of USOs
Northern Argentina has a high incidence of lightning
So WHY so little grass??
Why no savannas in Argentina?
• Top-down?
– Fire?
• Chaco is relatively dry (mostly < 1000mm)
• Fires less important in more arid climates
• Lightning is at least as common as South
Africa
– Herbivores?
• Argentina suffered massive megafaunal extinction
from ~12000 years ago
• Did the large mammals create savannas?
Giant sloths
Glyptodonts (armadillos)
Tall browsing cameloids
Hippo-like grazers
Domesticated cameloids
The small-bodied survivors
If mammals help create and
maintain arid savannas in Africa
• What happens when the native African
megafauna goes extinct?
• Massive bush encroachment over the
whole of the semi-arid north-western
regions of South Africa
• Are we seeing the extinction after-shock?
An ex-livestock farm in semi-arid S. African savannas
NOT Argentina (see the grass in the understorey)
Marakele National Park
An ex-livestock farm in semi-arid S. African savannas
Global change and the future of
savannas
• ??? Not a simple problem
• Climate is not a a good predictor of
savannas, especially arid savannas
• Fire is far less important in maintaining
arid savannas
• Mammals? What mechanisms?
• Elevation?
Global change and the future of
arid savannas
• ??? Not a simple problem
• Climate is not a a good predictor of
savannas, especially arid savannas
• Fire is far less important in maintaining
arid savannas
• Mammals?
• Elevation?
HELP!!!
With thanks to:
• Kirsten Packer for her excellent 3rd y
project
• Jason Donaldson for his
• And Glenn Moncrieff for his deft hand
at all things numerical – We’ll miss you!
• Funding assistance from:
– Southern Connections for travel to Argentina
– the Andrew Mellon Foundation for their
consistent support