Plants at risk of extinction: the
case of some Madagascar
wild yam species (Dioscorea spp.)
By Vololoniaina H. JEANNODA
Madagascar Plant Specialist Group
Department of Plant Biology and Ecology
University of Antananarivo
Rosewood illegal exploitation
Baobab: Adansonia perrieri EN
Y
A
M
S
Sartidia perrieri collected last in 1910
By Perrier de la Bathie, probably EX
Facts about yams in Madagascar
• Madagascar is home to more than 40 species of wild endemic yams
(about 10% of yam global diversity). Cropwild relatives.
• Almost all wild yams are utilized.Tubers are consumed even those
that are known to be toxic. They are mostly used during lean period
as supplement to or replacement of rice.
• Some species tubers are watery (more than 90% of water) and are
used in dry regions to cook food
• Some species are medicinal
• 12 out of 35 assessed taxa are threatened: CR, EN, VU (Kennerley
and Wilkin, 2014)
Madagascar yams’tubers are all edible
Toxic, but edible
D. bemarivensis
watery
D. soso
D. antaly
Scientific names
Conservation status (Kennerley &Wilkin, 2014)
Dioscorea acuminata
EN B2ab(i,ii,iii,iv,v); C2a(i); D
Dioscorea alatipes
VU B1ab(iii,iv,v)+2ab(ii,iii,iv)
Dioscorea bako
EN B1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v); C1
Dioscorea buckleyana
EN B1ab(v)+2ab(v)
Dioscorea decaryana
CR B1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v); D
Dioscorea madecassa
EN B1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v)
Dioscorea namorokensis
EN B1ab(iii,v)+2ab(iii,v)
Dioscorea orangeana
EN B1ab(iii,v)+2ab(iii,v)
Dioscorea proteiformis
VU B1ab(iii,iv,v)+2ab(iii,iv,v)
Dioscorea pteropoda
VU B1ab(iii,iv,v)+2ab(iii,iv,v)
Dioscorea sambiranensis ssp. Bardotiae
EN B1ab(i,ii,iii,iv,v)+2ab(i,ii,iii,iv,v)
Dioscorea sambiranensis ssp. Sambiranensis
VU B1ab(v)+2ab(v)
Ecology and biology of yams
• Species distributed in all regions of the country
• Habitats: mostly in all types of forest (« oviala » :
ovi=yam of the ala=forest)
• Liana, dioecious (male and female flowers separated),
can regenerate from seeds or tubers.
• Aerial parts are annual. They die when the also yearly
formed tuber(s) come(s) to maturity
• Dormancy during dry season, tuber sprouting and
seeds germinating at the beginning of the wet season,
with the first rains
Vine
Some traits of yams
Fruits and seeds
Female flowers
Male flowers
Yams in Madagascar are threatened because of:
Degradation of habitat due to:
• Logging
• Bush fires
• Mining
• Agriculture (slash and burn)
• Limited range of distribution
• Reduced or fragmented habitat
Slash and burn
Mining
Threats on
yams
Fragmented habitat and bushfires
Mining
Yams in Madagascar are also threatened due to
causes that are more specific to them
• Targeted exploitation of yam species for consumption and/or for
local market
• Over exploitation although digging tuber is difficult
• Unsustainable exploitation (holes not filled and head of tuber is not
put back in the soil)
• Seedlings are fragile and can be eaten by animals
• Often tubers are extracted during lean period, when the fruits and
the seeds are not formed yet and before tubers come to complete
maturity, thus regeneration impossible
• Population small or declining (but more to be investigated)
• Climatic change beginning to be perceived and impacting on
regeneration: rain comes later and wet season is shorter.
Head of tuber
Head of tuber
Local market
Digging yam
THREATS
ON
YAMS
Local market
Some examples of threatened yams
in all parts of Madagascar that can go
extinct without any conservation
action
Dioscorea bako
Western part of the country
In dry deciduous forest (Central
Menabe): Endangered
The most appreciated yam in the
region
Threats:
Limited range of distribution
Unsustainable overexploitation of the
tubers even inside protected area
Population presumably very small and
declining. People now have to walk on
very long distance (5km) before finding
one individual
Forest severely degraded by slash and
burn
Climate change is starting to be
perceived : delayed rain
Habit
Fruits and seeds
Slash and burn
Dry untouched forest
Cooked tubers
Flowers
Dioscorea decaryana
Central part of the island, on high
plateaux (Ambatofinandrahana)
Remnants of low scrubby forests on
small marble outcrops
Critically endangered
Known only of one restricted locality
with 40 mature individuals (Wilkin,
2013)
Threatened by bush fire, marble
mining, possible drought
Tubers are not really exploited but
herdsmen can dig the tubers when
keeping their zebus and grill them.
Very fragile habitat and small
population can lead to extinction of
the species
Habit
Habitat
Dioscorea orangeana
Northern tip of the Island
(Antsiranana)
Dry sclerophyllous forest on
limestones or sand
Endangered
Threats:
Very limited range and probably
decreasing population
Over exploitation in an unsustainable
way for self consumption and trade on
local market even if now localzed in a
new protected area
Tubers
Local market
Flowers
Habitat
Littoral forest
Dioscorea madecassa
Eastern part of the island
Lowland inland and littoral rainforests
(only three localities: Vatovavy,
Ifanadiana and Manombo)
Endangered
Threats: Very degraded and
fragmented habitats due to:
Uncontrolled slash and burn
agriculture
Logging and wood harvesting
Small population in each locality
Exploitation for self consumption
(rarely according to communities
because hard to find)
Local communities report of the
existence of patch of forests that have
disappeared and where they used to
collect D. madecassa.
tubers
habit
Dioscorea alatipes
Southern part of the island, arid zone
with 400 -450mm of rain and 9-11
months of dry season
Forest on sand or limestones in Toliara
region (Mahafaly plateaux)
Vulnerable
Threats:
Very fragile habitat
Unsustainably over-exploition by local
communities for self-consumption and
local market
Expanding agriculture (slash and burn)
Expanding settlements (semi-nomad
populations regularly undergoing
famine)
Climate change: decreasing and
delayed rains
Status can be revised to those reasons
harvesting
Habit
To summarize, all the main threats
that lead to a risk of extinction can
apply to the treatened species of
yams, but!
First Yam conservation actions in Madagascar
• Cultivation of cultivated yam species (ancestors’ crop) forgotten to
the benefit of wild yams and other tuber crops ( program led by the
Faculty of Science in collaboration with Swiss Cooperation NGO)
• Many NGO’s involved in spreading yam cultivation among
communities all over the country.
• National strategy for the promotion and development of yam
cultivation has been set up in Madagascar (national yam days)
• Our hope then: exploitation of wild yams would regress
• BUT, UNFORTUNATELY no market for the yam produced by local
communities and the taste of wild yams is far more appreciated
• So the exploitation of wild yams is still going on
• Thus making the risk of extinction still real for wild endemic yams
First actions in yam conservation in Madagascar
Training local communities
National and local authorities
Setting up yam nurseries
Yam national day
Cultivation of domestic yam
Yam cooking contest
However, new actions have being set up lately
and bring more hope
• Associating wild yams and cultivated ones in the
fields (Kew Madagascar Conservation Center) in
northern and central Madagascar with the full
involvement of local communities
• In situ cultivation of wild yams in the same
regions
• Idem in southern Madagascar with the Sulama
(Sustainable Land Use in Madagascar)
Mixed cultivation of yams
Preparing herbarium sample
by local community
Training local
communities
Preparing setts for cultivation
Raising awareness on wild yam
Ex situ cultivation
of wild yams
Wild species cultivated
Thank you for your attention