Exploring the savanna and grassland
biomes of Madagascar: an African
perspective
William Bond, Joel Ratsirarson, Tristan CharlesDominique, Lesego Khomo, Muthama Muasya,
Jeannin Ranaivonasy
Dept of Biological Sciences, UCT and
Departement des Eaux et Forets, Univ. Antananarivo
Madagascar
• Mini-continent –world’s 4th largest island
~0.75 million km2
• Currently 400 km of sea between Africa,
Madagascar
• Separated from Africa >100 Ma, and India
from ~89 Ma+
Thickets of southern Madagascar
Global biodiversity hotspot: >60 spp of lemurs, 12000 plant spp, >90% endemic
A very different fauna mostly extinct
Several spp of giant tortoises
2-3 spp of Hippos
One a grazer related to H. amphibius
One (2?) browsers
~ 7 spp of elephant birds
Grasslands are the most extensive
vegetation in both Africa and Madagascar
Humans settled Madagascar <2000 y BP.
Through burning, they converted forest to grasslands and savannas
Most extreme example of fire-induced biome switch on earth?
80% of island = fire-maintained grassland or savanna
The real vegetation map
The formation of the prairies [of
Madagascar] is totally
artificial and the result of fire.
Perrier de la Baˆthie (1921, pp. 9–
13).
• If grasslands <2000 y old then
– Very low grass diversity and species
turnover?
– No endemics?
• No shade-intolerant forbs, trees, shrubs in
grasslands
• No grassland-dependent birds, mammals,
reptiles, insects
Biogeographic clues – C4 grasses
– Very low plant diversity and species turnover?
– No endemics?
C4 grass genera in Madagascar
ENDEMIC
ENDEMIC
Camusiella
Decaryella
Isalus
Lasiorrachis
Neostapfiella
Sclerodactylon
Viguierella
Yvesia
SHARED
WITH
SOUTH
SHARED WITH
SOUTH
AFRICA AFRICA
Acrachne
Alloteropsis
Andropogon
Aristida
Arthraxon
Arundinella
Axonopus
Bothriochloa
Brachiaria
Cenchrus
Chloris
Chrysopogon
Coix
Craspedorhachis
Ctenium
Cymbopogon
Cymbosetaria
Cynodon
Dactyloctenium
Dichanthium
Digitaria
Dinebra
Diplachne
Echinochloa
Eleusine
Elionurus
Enneapogon
Enteropogon
Eragrostis
Eriochloa
Eulalia
Hackelochloa
Harpochloa
Hemarthria
Heteropogon
Hyparrhenia
Hyperthelia
Imperata
Ischaemum
Leptocarydion
Leptochloa
Lepturus
Loudetia
Melinis
Microchloa
Monocymbium
Oxyrhachis
Panicum
Paratheria
Paspalidium
Paspalum
Pennisetum
Perotis
Pogonarthria
Rhytachne
Rottboellia
Schizachyrium
Schoenefeldia
Setaria
Sorghastrum
Sorghum
Sporobolus
Stenotaphrum
Themeda
Trachypogon
Tragus
Tricholaena
Trichopteryx
Tripogon
Tristachya
Urelytrum
Urochloa
Vetiveria
& REST
AFRICA
REST OFOF
AFRICA/ASIA
Crypsis
Dimeria
Euclasta
Garnotia
Halopyrum
Heteropholis
Neyraudia
Redfieldia
Saccharum
Thuarea
Tripsacum
Zoysia
94 genera
8 endemic C4 genera
>200 endemic grass spp
Relative to South Africa
• Madagascar has about 12 000 plant
species, nearly 600 grass spp (5% of the
flora)
• South Africa has 22000 spp, about 910
grass spp (4 % of the flora!!)
• Species:genus ratio 4.3 Madagascar
• Species:genus ratio 5.1 South Africa
• THIS IS NOT A NEW GRASS INVASION
Some key questions for grassland
conservation biology
• How old are grasslands?
• How diverse are grasslands
– Plants
– Animals
• What do grasslands contribute to biodiversity of
forest/grassland mosaics
• What are the major threats to grassland
conservation?
• Can grassland loss be reversed? Can
grasslands be restored?
Are these forest/grassland mosaics a result of deforestation?
Or are these alternative stable states with ancient origins?
Mosaics caused by deforestation? Or
ancient alternative biome states?
• We explored
– Grassland spp and functional diversity
– Woody plant habitat specialization
– Soil isotopic composition
The deforestation hypothesis
The deforestation hypothesis
Burning (some felling?) destroys forest.
Trees in 20 grassland resist fire by pre-adaptations
The alternative biome state hypothesis
Trees, shrubs in forest interior differ from forest margins which differ from grassland sites
Savanna
Forest margin
Forest interior
We sampled transects in each habitat type counting individuals of woody plant species
and frequency of grassland plants
Methods
• Sampled in transects in the three habitat
types
• Density, size of woody plants as measure
of importance
• Common spp of each habitat scored for
functional traits
– Bud location, bark thickness, architecture,
regeneration mode (sprouting)
• Frequency of grassland plants
Forest interior
Forest margin
Savanna
Uapaca bojeri savanna
What we found for woody plants
• Distinct spp assemblages in forest,
margin, savanna
• Functional trait differences in each of the
three habitats
Ankazobe grasslands NW of Tana
Central highlands
Aristida
rufescens
Loudetia
Themeda
Hyparhenia rufa
Schizachyrium
Aristida sp.
Grasslands dominated by just two species: Aristida rufescens, Loudetia simplex
These are branched grasses able to grow through large piles of dead litter.
These very low diversity grasslands were the norm for central highlands grasslands
Why such low grass diversity?
• Grasses new? Island isolation?
• Long fire suppression killing high lightrequiring grasses (decreasers, increaser
II)?
Themeda triandra declines to negligible cover if
burnt at intervals longer than ~ 3 years in KZN midlands
Anzarabe grasslands unburnt for 10 years!
Uys et al. 2004 Biol Cons
Non-grass component of
grasslands
• Quite diverse with 9-14 species/transect
• Erica spp common with up to 3 spp/transect
• Asteraceous sub-shrubs (Helichrysum) were also
common with up to 5 spp/transect
• These woody spp can penetrate the dense dead litter
layers as they do in old fire-suppressed SA grasslands
• Forbs with USOs were very rare in Central Highlands
grasslands (2-3 spp)
• This is in striking contrast to South African highveld
grasslands where forbs with USOs are abundant and
diverse
•S. African coastal grassland. 305 plant spp of which 201 forb spp
• in 64 x 5m radius plots. Zaloumis, Bond Austral Ecol 2011.
Without burning, these forbs disappear. They are very slow to recolonise an area and
tropical grassland restoration has proven very difficult compared to forests.
Forbs in Madagascar: low diversity, very few with USOs
Why such low forb diversity?
• Grasslands new? Island isolation?
• Long fire suppression killing high lightrequiring forbs?
• In South Africa, fire suppression in high
rainfall grasslands for >8 years eliminates
forbs with USOs but favours woody shrubs
and sub-shrubs
Forb spp composition after 35y burning experiment
BURNT
UNBURNT
Fire treatments (1-5y intervals) had completely different spp
composition from plots unburnt for 10y+. Uys et al. 2004,Biol Cons
Where are Madagascar’s hotspots
of grassland diversity?
• Where are those 600 spp of grass?
• Fire suppression (by law) may have
eliminated grass and forb species
requiring frequent fires
• Are there parts of Madagascar, remote
from government, where grasslands burn
frequently enough to support diversity?
• Or is low diversity an island phenomenon?
• Or an indicator of anthropogenic origins?
Summary
• Madagascar\s C4 grassy biomes neglected until
very recently
• Fascinating analogue to African mainland c4
grassy systems
• Novel questions e.g.
– forest margin spp in RSA?
– Origin and antiquity of our grassland biota
– Coevolution of grasses, browse plants with an entirely
different suite of herbivores
– Megafaunal fruit dispersal: do elephants matter?
Summary
• Where are the grassland diversity hotspots
and how should they be managed?
• How transferable is knowledge from Africa
to an insular biota?
Thanks to
• John Silander, U.Conn for initiating the
Madagascar connection
• The MacArthur Foundation for funding
• The 11 brave Malagasy students for
participating in our grassland ecology field
work
• The University of Antananarivo for hosting
us