Content uploaded by Leonard Manda
Author content
All content in this area was uploaded by Leonard Manda on Feb 23, 2022
Content may be subject to copyright.
Sustainability2022,14,2355.https://doi.org/10.3390/su14042355www.mdpi.com/journal/sustainability
Article
TheFutureofFood:DomesticationandCommercialization
ofIndigenousFoodCropsinAfricaovertheThird
Decade(2012–2021)
RogerR.B.Leakey
1,
*,Marie‐LouiseTientcheuAvana
2
,NyongPrincelyAwazi
3
,AchilleE.Assogbadjo
4
,
TafadzwanasheMabhaudhi
5,6
,PrasadS.Hendre
7
,AnnDegrande
8
,SithabileHlahla
5
andLeonardManda
4
1
InternationalTreeFoundation,106‐108CowleyRoad,OxfordOX41JE,UK
2
AfricanForestForum,WorldAgroforestryCentre,UnitedNationsAvenue,
NairobiP.O.Box30677‐00100,Kenya;avanatie@yahoo.fr
3
DepartmentofForestryandWildlifeTechnology,CollegeofTechnology,TheUniversityofBamenda,
BambiliP.O.Box39,Cameroon;nyongprincely@gmail.com
4
LaboratoryofAppliedEcology,FacultyofAgronomicSciences,UniversityofAbomey‐Calavi,
Cotonou05BP1752,Benin;assogbadjo@yahoo.fr(A.E.A.);lmanda8@gmail.com(L.M.)
5
CropScience,SchoolofAgricultural,EarthandEnvironmentalSciences,UniversityofKwaZulu‐Natal,
Pietermaritzburg3201,SouthAfrica;mabhaudhi@ukzn.ac.za(T.M.);hlahlas@ukzn.ac.za(S.H.)
6
InternationalWaterManagementInstitute(IWMI‐GH),WestAfricaOffice,
PMBCT112Cantonments,AccraGA015,Ghana
7
WorldAgroforestryCentre,NairobiP.O.Box30677‐00100,Kenya;p.hendre@cgiar.org
8
WorldAgroforestryCentre,YaoundéP.O.Box16317,Cameroon;a.degrande@cgiar.org
*Correspondence:rogeleakey@btinternet.com
Abstract:Thispaperfollowsthetransitionfromethnobotanytoadeeperscientificunderstanding
ofthefoodandmedicinalpropertiesofAfricanagroforestrytreeproductsasinputsintothestartof
domesticationactivities.Itprogressesontotheintegrationoftheseindigenoustreesasnewcrops
withindiversifiedfarmingsystemsformultiplesocial,economicandenvironmentalbenefits.From
itsadventinthe1990s,thedomesticationofindigenousfoodandnon‐foodtreespecieshasbecome
aglobalprogrammewithastrongAfricanfocus.Thisreviewofprogressinthethirddecadeis
restrictedtoprogressinAfrica,wheremulti‐disciplinaryresearchonover59specieshasbeenre‐
portedin759researchpapersin318sciencepublicationsbyscientistsfromover833researchteams
in70countriesaroundtheworld(532inAfrica).Thereviewspans23researchtopicspresentingthe
recentresearchliteraturefortreespeciesofhighpriorityacrossthecontinent,aswellasthatineach
ofthefourmainecologicalregions:thehumidzoneofWestandCentralAfrica;theSahelandNorth
Africa;theEastAfricanhighlandsanddrylands;andthewoodysavannasofSouthernAfrica.The
mainareasofgrowthhavebeenthenutritional/medicinalvalueofnon‐timberforestproducts;the
evaluationofthestateofnaturalresourcesandtheirimportancetolocalpeople;andthecharacter‐
izationofusefultraits.However,thetestingofputativecultivars;theimplementationofparticipa‐
toryprinciples;theprotectionoftraditionalknowledgeandintellectualpropertyrights;andthe
selectionofelitetreesandideotypesremainunder‐researched.Totheprobabledetrimentofthe
upscalingandimpactintropicalagriculture,therehasbeen,attheinternationallevel,amoveaway
fromdecentralized,community‐basedtreedomesticationtowardsalaboratory‐based,centralized
approach.However,therapiduptakeofresearchbyuniversitydepartmentsandnationalagricul‐
turalresearchcentresinAfricaindicatesarecognitionoftheimportanceoftheindigenouscropsfor
boththelivelihoodsofruralcommunitiesandtherevitalizationandenhancedoutputsfromagri‐
cultureinAfrica,especiallyinWestAfrica.Thus,onacontinentalscale,therehasbeenanuptake
ofresearchwithpolicyrelevancefortheintegrationofindigenoustreesinagroecosystemsandtheir
importancefortheattainmentoftheUNSustainableDevelopmentGoals.Toprogressthisinthe
fourthdecade,therewillneedtobeadedicatedCentreinAfricatotestanddevelopcultivarsof
indigenouscrops.Finally,thisreviewunderpinsaholisticapproachtomitigatingclimatechange,
aswellasotherbigglobalissuessuchashunger,povertyandlossofwildlifehabitatbyreapingthe
Citation:Leakey,R.B.R.;Tientcheu
Avana,M.‐L.;Awazi,N.P.;
Assogbadjo,A.E.;Mabhaudhi,T.;
Hendre,P.S.;Degrande,A.;Hlahla,
S.;Manda,L.TheFutureofFood:
DomesticationandCommercializa‐
tionofIndigenousFoodCrops
inAfricaovertheThirdDecade
(2012–2021).Sustainability2022,14,
2355.https://doi.org/10.3390/
su14042355
AcademicEditor:MichaelS.Carolan
Received:11January2022
Accepted:9February2022
Published:18February2022
Publisher’sNote:MDPIstaysneu‐
tralwithregardtojurisdictional
claimsinpublishedmapsandinstitu‐
tionalaffiliations.
Copyright:©2022bytheauthors.Li‐
censeeMDPI,Basel,Switzerland.
Thisarticleisanopenaccessarticle
distributedunderthetermsandcon‐
ditionsoftheCreativeCommonsAt‐
tribution(CCBY)license(https://cre‐
ativecommons.org/licenses/by/4.0/).
Sustainability2022,14,23552of77
benefits,or‘profits’,frominvestmentinthefiveformsofCapital,describedas‘landmaxing’.How‐
ever,policyanddecisionmakersarenotyetrecognizingthepotentialforholisticandtransforma‐
tionaladoptionofthesenewindigenousfoodcropopportunitiesforAfricanagriculture.Is‘political
will’themissingsixthcapitalforsustainabledevelopment?
Keywords:agroforestry;foodsecurity;geneticimprovement;indigenousfruitsandnuttrees;
livelihoods;nutrition;policy;povertyalleviation;ruraldevelopment;treecrops
1.Introduction
Theideaofdomesticatingtraditionallyimportantindigenoustreesasnewcropsin
thetropicsfortheirusefulandmarketablefoodandnon‐foodproductsoriginatedinthe
1980s[1].Thisidea,whichincludesbothcultivationandgeneticimprovement,wastaken
upbytheWorldAgroforestryCentre(ICRAF)in1993,followingaconferenceinEdin‐
burghin1992aimedat‘RebuildingTropicalForestResources’andtheadventofWoody
PlantorReallyGreenRevolution[2].Sincethen,ithasbecomeapan‐tropicalprogramme
expandingacrossthefirsttwodecadesinboththenumberofcandidatespeciesfordo‐
mesticationandtherangeofresearchtopicsinvolvedinitsmultidisciplinaryapproach
[3–10]targeting14ofthe17UNSustainableDevelopmentGoals[11,12]. Non‐timberfor‐
estproductsarecurrentlybelievedtobeusedbyabout44%oftheglobalpopulation[13].
Tensofthousandsoftreespeciesaroundthetropicsandsub‐tropicsproduceboth
edibleandmedicalproductswhichhavebeenimportantintheday‐to‐daylivesoflocal
people.Withtheexpansionofagriculturetofeedagrowinghumanpopulation,manyof
thesespecieswereclearedfromthelandtomakewayforasmallnumberofstaplefood
crops,oftenwithlittleregardeitherfortheirtraditionalandculturalsignificanceortheir
diverseandhighlynutritiousfruits,nutsandleaves.Overthefirsttwodecadesoftheir
domestication(1992–2002;2002–2012),researchsoughttodeveloptechniques,skillsand
strategiescapturingthemanypotentialsocialandeconomicbenefitsthatthecultivation
oftheseproductscoulddeliverthroughcommunityagroforestryprojectsandexpanded
marketingandtrade.Inaddition,researchanddevelopmentprojectshavealsobeenini‐
tiatedtoprocessandaddvaluetotheproductsbothlocallyandinternationally.Trees,
especiallyindigenoustrees,playanimportantroleinthecaptureofenvironmental,social
andeconomicbenefits/profitsfromagriculture,describedas‘LandMaxing’[14],byin‐
vestinginthefiveformsofcapital(natural,human,social,physicalandfinancial)andso
convertingtheso‐called‘inevitabletrade‐offs’tosustainablepolicy‘trade‐ons’[15].
Thehighlightsofthefirsttwodecades[16]wereasfollows:
• Greaterunderstandingofethnobotany,traditionalknowledgeofindigenousspecies
andtheirdeliberatecultivationbyfarmers;
• Theapplicationofvegetativepropagationtechniquesincommunity‐basedvillage
nurseriesusingmarcotting/graftingtocapturematuretraitsofindividualtreesand
stemcuttingsforthemultiplicationofelitetreesasputativecultivars;
• Thedevelopmentofappropriatenurserytechniquesforthesexualandasexualprop‐
agationofcandidatespeciesinremotevillages;
• Thedevelopmentofparticipatoryprioritysettingfortheselectionofcandidatespe‐
ciesfordomesticationandintegrationintoagroforestrysystems.Some50localspe‐
cieswereidentifiedforfurtherresearchanddevelopmentaroundthetropicsand
sub‐tropics;
• TheestablishmentofRuralResourceCentrestoprovide:(i)knowledgeandskillsfor
theparticipatorydomesticationoflocalspeciesusingappropriate,low‐technology
techniquesadaptedforuseinremotelocationswithminimalinfrastructureinways
thatallowlocalcommunitymemberstobenefitfromtheirowninitiativesand(ii)the
Sustainability2022,14,23553of77
capacitytodevelopcommunityengagementandinfrastructuretomaximizeenviron‐
mental,socialandeconomicbenefits;
• Thequantificationatthevillagelevelof3‐to10‐foldcontinuoustree‐to‐treeintraspe‐
cificvariationincommunityfarmlandtounderstandtherangeofgeneticvariation
availabletolocalcommunitiesanditsaccordancewithlocalknowledge.Subse‐
quently,thisknowledgewasformulatedtoidentifymarket‐specificideotypes.Pri‐
marily,itwasmorphologicalvariationthatwasinvestigated,butthiswaslaterex‐
pandedintonutritionalandotherbiochemicaltraits;
• Thestartoftheevaluationofgeneticvariationusingmoleculartechnologies;
• Theexaminationofcommunal,socio‐economic,legalandpoliticalissuesaffecting
boththeadoptionandimpactofdomesticatingindigenousfoodandnon‐foodtree
speciesandthemarketingoftheirAgroforestryTreeProducts(AFTPs).
Attheendoftheseconddecade[16],itwasenvisionedthatthedevelopmentsinthe
thirddecadewouldincludethefollowing:
• Improvedcaptureofontogeneticallymaturephenotypesbybetterunderstandingof
thephysiologyofgraftingandmarcotting;
• Analysisofvariationsinnutraceutical,pharmaceuticalandotheringredientsof
AFTPstomeettheneedsofnewmarketopportunitiesandtheidentificationofmar‐
ket‐orientedideotypes;
• Greaterinvestmentinpostharvestprocessingtoexpandlocal,regionalandglobal
tradeopportunities;
• Investigationofreproductivebiologyforincreaseduseofcontrolledbreedingincen‐
tralizedtreedomesticationresearch;
• Upscaledtreedomestication,especiallyinAfrica,focusingonspecieswithimpacton
incomegenerationandnutrition;
• Impactanalysisbasedonwell‐definedcriteriaandindicators;
• Abetterunderstandingoftheroleofdomesticatedagroforestrytreesintheachieve‐
mentofsustainablemultifunctionalfarmingsystemsandwiderlocalandregional
marketing;
• ExpandedopportunitiesforsuccessfulmarketingofAFTPs,includingpublic–private
partnershipsincommercialmarkets;
• Recognitionofintellectualpropertyrightstoprotectpoorfarmersandlocalcommu‐
nitiesfromunscrupulousentrepreneurs;
• Enhancepolicysupportfortheupscalingofintensifiedagroforestrysystems.
ThisreviewexaminesprogressmadeinAfricaoverthethirddecade(2012–2021),as
reportedinthescientificliterature.Thus,itpresentsanupdateonreportsofthework
doneinthefirsttwodecades,ratherthanastate‐of‐the‐artreviewacrossthethreedec‐
ades.
ProgressintheThirdDecade
Weevaluatedthepublishedliterature,bothbyregion/agroecologicalzoneandby
researchtopic/disciplineandfromapan‐Africanpolicyperspective,usingInternetdata‐
basessuchasGoogleScholarandResearchGate,aswellasourpersonalknowledgeand
networks.Asimilarapproachinthefirstandseconddecades[16]examined16research
topicsandover50speciesfromaroundtheworld.Inadditiontoasetofmoregeneral
pan‐Africanresearchpapers,thepresentreviewisfocussedonfourAfricanregions(Hu‐
midWestandCentralAfrica,SahelandNorthAfrica,theHighlandsandDrylandsofEast
AfricaandtheSavannaandMiomboWoodlandsofSouthernAfrica).Thesepaperswere
thenpartitionedintoasetof23researchtopics(Table1).
Sustainability2022,14,23554of77
Table1.Thelistof23researchtopicsusedtocharacterizethescientificliteraturerelatingtothe
domesticationofindigenousAfricanfoodandnon‐foodtreespecies.
NumberResearchTopic
1Thestateofnaturalresourcesandtheirgeneticdiversity,governanceandman‐
agement—understandingtheissues/constraints.
2Ethnobotanyoffoodandmedicinalspeciescandidatesforcultivation—includ‐
ingtheirroleindiets,healthandfoodsecurity.
3Commercialvalueofnon‐timberforestproducts(NTFPs)inlocalmarkets.
4Nutritional/medicinalvalueofwildNTFPs.
5Prioritysettingfordomestication/commercialization—speciespreferences.
6Characterizationofusefultraits:morphologicalandphysical.
7Assessmentsofgeneticvariationanditscharacterization.
8Germplasm,germinationandreproductivebiology.
9Vegetativepropagationofcandidatespecies.
10Selectionofelitetreesandideotypes.
11Productcommercialization—evaluation/marketabilityandprocessing.
12Domesticationconceptandstrategy.
13Testingofputativecultivars.
14Farmercapacitybuilding—roleofRuralResourceCentres,etc.
15Implementationofparticipatoryprinciples.
16Newtechniques,skillsandstrategies(includingsupportforgenderissues).
17Nurserydevelopmentsandimprovedplantingstock.
18Post‐harvestissues.
19ProtectionofTraditionalKnowledgeandIntellectualPropertyRights.
20Tradeandthelaw.
21LocalimpactsofcultivationandmarketingofAgroforestryTreeProducts
(AFTPs).
22Potentialregionalandinternationalimpactsofcultivationanddiversificationof
farmingsystemsandagroecology.
23
Policyrelevancetoupscalingrural/urbandevelopmentandtoglobalsustaina‐
b
ility(hunger,malnutrition,poverty,wildlifehabitat,livelihoodsandsocialeq‐
uity,socialjustice,economicdevelopment,etc.).
2.OverviewoftheLiterature
2.1.Regional
Wereviewedatotalof759articlespublishedbetween2012and2021from4Regions
ofAfrica,recognizingsomeoverlapbetweensocio‐politicalboundariesandbroadecolog‐
icalzones.Outofthesepublications,39%originatedfromHumidWestandCentralAfrica
(HWCA),20%fromSahelianWestandNorthAfrica(SWNA),9%fromHighlandandDry
EastAfrica(HDEA)and15%fromtheSavannahandMiomboWoodlandsofSouthern
Africa(SMWSA).Atotalof17%wereofpan‐African(PA)importance.Intotal,thisis
morethandouble(125%)thetotalnumberofAfricanpaperspublishedoverthefirsttwo
decadescombined(Figure1).
Sustainability2022,14,23555of77
Figure1.Thetotalnumberofresearchpublicationsrelatingtothedomesticationofindigenoustrees
inAfrica,bydecadeandregion.
2.2.ResearchTopics
Whenthe759publicationsweredividedbyresearchtopic,thosefrommosttopics
hadgreatlyincreasedinnumber,withsomenewtopicsalsobeingverywellrepresented,
especially:(i)thenutritional/medicinalvalueofNTFPs(see:[17]);(ii)theevaluationofthe
stateofnaturalresourcesandtheirgeneticdiversity,governanceandmanagement;(iii)
theethnobotanyofcandidatespecies;and(iv)thecharacterizationofusefultraits(Figure
2).However,topicsthatwerenotrepresentedmorefrequentlywere:(i)thetestingofpu‐
tativecultivars,(ii)theimplementationofparticipatoryprinciples,(iii)protectionoftra‐
ditionalknowledgeandintellectualpropertyrightsand(iv)theselectionofelitetreesand
ideotypes(Figure2).Atthepan‐Africanlevel,threetopicswerewellrepresented.These
were(i)thedomesticationconceptandstrategy,(ii)thepotentialimpactofcultivationand
(iii)thepolicyrelevanceandimplicationsforSustainableDevelopmentGoals(Figure2).
Figure2.Thetotalnumberofresearchpublicationsrelatingtothedomesticationofindigenoustrees
inAfricabyresearchtopic(seeTable1)anddecade.
Sustainability2022,14,23556of77
Impressively,inadditiontothisgrowthinthenumberofpublicationsrelatingtotree
domestication,therewasahugeincreaseinboththenumberofresearchteamsinuniver‐
sitiesandresearchinstitutesconductingthiswork(833intotalfrom70countries[532from
34countriesinAfrica;182asresearchpartnersfrom17countriesinEurope;37from11
countriesinAsia;66fromfivecountriesintheAmericas;and16from2countriesinOce‐
ania];seeSupplementaryMaterialsTableS1).Interestingly,thisgrowthwasalsoassoci‐
atedwithmultidisciplinarypartnershipsandagreatlyincreasedrangeandnumberof
sciencejournalspublishingthesepapers(290journalsand28books—seeSupplementary
MaterialsTableS2).
2.3.Species
Intheliteraturefortreedomesticationduringthethirddecade,59Africanspecies
wereidentified(Table2),generallywithdifferentspeciesineachRegion,althoughafew
dryzonespecieswerereportedfromotherregions,notablybaobab(Adansoniadigitata)
beingimportantinthreeregions.Awiderrangeofethnobotanicallyimportantspecies
werealsodiscussed,indicatingthepotentialforfurthergrowthinthefuture.
Sustainability2022,14,23557of77
Table2.Africantreeandotherwoodyspeciesproducingedibleproductsthathavebeenidentifiedasprimecandidatesfordomesticationintheliteratureover
thethirddecade(speciesinboldhavepan‐Africanpriorityintheregion).
HumidLowlandsofWestandCentralAfricaSahelianDrylandsofWestandNorthAfricaHighlandsandDrylandofEastAfrica SavannahandMiomboWoodlandsofSouthernAfrica
A
llanblackiaspp.Vitellariaparadoxa
A
dansoniadigitataSclerocaryabirrea
Prunusafricana
A
dansoniadigitata
A
llanblackiastuhlmannii
A
dansoniadigitata
Irvingiaspp.SclerocaryabirreaZizyphusmauritiana
A
zanzagarckeana
DacryodesedulisTamarindusindicaVitellariaparadoxaUapacakirkiana
GarciniakolaZizyphusmauritianaFicusnatalensisStrychnosspinosa
Colaspp.
A
zanzagarckeanaBalanitesaegyptiacaStrychnoscocculoides
Gnetumspp.
M
oringaoleifera
A
lbiziacoriariaDovyaliscaffra
RicinodendronheudelotiiBorassusaethiopum
M
arkhamialuteaVangueriainfausta
ChrysoplyllumalbidumCarapaproceraTamarindusindicaParinariacuratellifolia
TetrapleuratetrapteraParkiabiglobosaVitexdonianaSizygiumcordatum
CanariumschweinfurthiiVitexdonianaVitexmombassaeVitexspp.
PentacletheramacrophyllaDaliumguineenseSclerocaryabirreaFlacourtiaindica
BaillonellatoxispermaGarciniakolaZizyphusmauritiana
TrichoscyphaaciminataXylopiaaethiopica
A
frostyraxlepidophyllusDetariummicrocarpum
GnidiaglaucaBalanitesaegyptiaca
PausinystaliajohimbeProsopisafricana
Tetracarpidiumconophorum
A
rganiaspinosa
GarcinialucidaIrvingiagabonensis
Gambeyaafricanum
Sustainability2022,14,23558of77
3.AdvancesinDomesticationTechnologiesandTheirApplication
Thefirstandseconddecadesofagroforestrytreedomesticationwerestronglybased
onthedecentralizedconceptofparticipatorydomestication[18]andabottom‐upphilos‐
ophyforveryrapidprogressarisingfromthevegetativepropagationofelitetreesselected
atthevillagelevel.Thefoundationofthiscommunity‐basedapproachwasthedevelop‐
mentofRuralResourceCentresbyICRAF[18]toassistparticipatingcommunitiesacquire
theskills,knowledgeandunderstandingoflong‐known,simplehorticulturaltechniques
suchasgrafting,airlayering(marcotting)andtherootingofcuttings,whichcanbeim‐
plementedbylocalpeopleinremotevillageswithoutaccesstofinancialcapital,andutility
servicessuchaselectricityandpipedwater.Itis,however,importanttorecognizehere
thatthereisaninadequateresourceofpeoplenationally,regionallyandinternationally
withtheappropriateskillsinvegetativepropagationtomeetthescaleoftheneedforthese
techniquesifparticipatorydomesticationistobescaledupacrossAfrica.
Participatorydomesticationprovidesthebasisforthedevelopmentofaself‐help
strategyforcommunityengagement[19,20],leadingtothedevelopmentof‘socially‐mod‐
ifiedcrops’[14,15].Itisfocussedontheintensificationofagroforestryformultipleenvi‐
ronmental,socialandeconomicbenefitsaspartofthethree‐stepapproachtorapidlyre‐
ducinghungerbyclosingtheYieldGapsinstaplefoodcropswhilealsoaddressingmal‐
nutrition,povertyandsocialinjustice[15,21,22].Thishasimportantpolicyimplications
forAfricanpeopleandfortheplanet(seeSection10below).
Inthethirddecade,therehasbeenreducedresearchactivityinParticipatoryDomes‐
ticationledbytheWorldAgroforestryCentre(ICRAF)dueprimarilytoalossofdonor
funds.Thisislessalossofsupportfortheconceptandmoreaneedtomakefundsavail‐
abletoothercauses.Meanwhileanewsourceoffundingbecameavailableforamore
centralizedtop‐downbiotechnologicalprogrammefocussedonalaboratoryapproachto
cropimprovementbygeneticcharacterizationandtreebreeding[23].Itisbasedonthe
acquisitionofknowledgeofthemechanismsofgeneticvariationinmodernsciencelabor‐
atories,againledbytheICRAF[24].Interestingly,inparallelwiththischangeindirection
bytheICRAF,therehasbeenasubstantialincreaseindomestication‐relatedresearchin
Africanuniversitiesandresearchinstitutes(SupplementaryMaterialsTablesS1andS2),
mostofitinsupportoflocallivelihoodsandlanduses.Itmustbehopedthatdecentralized
treedomesticationhasnotsuccumbedtotheprevailingviewthatacademicadvancement
ismoreimportantthanreal‐lifeimpact[25].Indeed.Itisimportanttorecognizethata
participatoryapproachtodomesticationwithbenefitsflowingtolocalcommunitiesises‐
sentialwhenthetraitsbeingselectedarerootedinTraditionalKnowledge[18].
Whilethecentralisedapproachisrelativelyeasytocoordinate,itsresultsdonotal‐
waysfilterdowntosmall‐scalefarmers,whoencounterhightransactioncostswhenre‐
ceivingexternalfarminputs,suchastreeplantingmaterialandinformationontheman‐
agementofcultivars[23].Thus,thecentralisedapproachdoesnotpromotelocaldevelop‐
mentbasedoncommunitydecisionmakingaboutwhichspeciestoprioritiseforcultiva‐
tion;thedevelopmentofefficientfarmmanagementmethodsinasmallholdercontext;or
theresolutionofsocial,economicandpoliticalbarriersfacedbysmallholderfarmers[23].
Thus,perhapstothedetrimentofshort‐termupscalingandimpact,treedomestication
studiesinthethirddecadehavemovedtowardsamuchlonger‐termstrategythanthe
rapidandhighlysuccessfuldecentralizedcommunityapproach.Thisshiftinstrategywill
requireameanstodisseminateimprovedgermplasmtofarmerslackingthefinancialre‐
sourcestopurchasetheplantingmaterial[26].Inadditiontosomeindigenousfruitand
nuttreespecies,thiscentralizeddomesticationprogrammeadditionallyincludesover50
annualorphancrops(cereals,legumes,etc.)asimportantunderstoreyadditionstoagro‐
forestrysystems.Thisisaimedatfurtheringdiversificationoffarmingsystemsanddiets
[27];however,theirsuccessfulintegrationintocomplexagroecosystemsmayrequirese‐
lectionforhigheryieldsinshadyenvironments.
Sustainability2022,14,23559of77
Itisimportanttoemphasiseherethatthesetwodifferentstrategiesarenotmutually
exclusive.Historically,treecropshavebeendomesticatedfromthewildovermillennia
usingdecentralisedhorticulturalapproachesbasedontechniquesofvegetativepropaga‐
tiontocreatecultivarsthatcapturetheuniquecharacteristicsofnaturallyoccurringelite
individuals.Overrecentdecades,centralisedtreebreedingprogrammesbetweenthese
cultivarsandwildrelativeshasledtonewgenerationsofselectedvarieties.
Itisclearfromtheabovesummariesofthesetwostrategiesthattheylieatopposite
endsofadomesticationstrategyspectrum(Figure3)andthattheyhavedifferentmerits
relevanttothedomesticationofindigenoustreesandtoneedsoftropicalfarmersinthe
short‐andlong‐term.Anumberofreviewpapershavebeenwrittenaboutthemeritsof
bothapproachesandtheiruseinrecentyears(Table3),includingtheconceptofasystems
approach[28].So,wewillnotreplicatetheinformationhere.However,toassistdevelop‐
mentagenciesanddonorstounderstandtheirdifferencesandlikelyimpacts,adetailed
cost–benefitanalysiswouldbehelpful.
Figure3.ThespectrumofdomesticationstrategiesformingtheDomesticationSyndrome:Central‐
izedformajorfoodcropsanddecentralizedfornewtreecrops(Reprintedwithapermisionfrom
ref.[26].2019JohnWileyandSonswithunderLicenseNumber5250250091483).
Table3.Sourcesofinformationaboutdifferentdomesticationstrategiesandtheiruse.
DecentralizedParticipatoryApproachCentralizedLaboratoryApproach
Leakey[14,15,18,29]Dawsonetal.[26,30]
Takoutsingetal.[31]Hendreetal.[24]
Degrandeetal.[19,20]McMullinetal.[27]
Essougongetal.[32]Jamnadassetal.[33]
Wouapietal.[34]
Finally,therecentlyrepublishedtreedomesticationstrategyforindigenousfruit
trees[35]presentsoverarchingprinciplesfortheestablishmentofthreeinterlinkedtree
populations:generesourcepopulation,selectionresourcepopulationandproductionre‐
sourcepopulation.Thestrategyincludeswaysinwhichscience‐basedprinciplesforlow‐
technology,appropriatemethodsofvegetativepropagationcanbeusedinremotearea
Sustainability2022,14,235510of77
withoutaccesstoelectricityandpipedwaterandyetmaintainthegeneticdiversityofthe
preferredtraitsoftheelitemothertree[36,37].Thisisthebasisoftheconceptofdecen‐
tralizeddomestication.
4.Pan‐AfricanPrioritySpecies
Inthissection,wereviewtheprogressmadetodomesticatethosespecieswhichfor
ecologicalreasonsarefoundnaturallyacrosstwoormoresocio‐politicalregionsinthe
continentofAfrica.Itisimportanttorecognizeherethatthesespeciesaremuchmorethan
‘FamineFoods’[38,39]andarehighlyappreciatedbylocalpeopleformanydifferentrea‐
sons.
4.1.Adansoniadigitata(Baobab)
4.1.1.Ethnobotany,UsesandNaturalResources
Adansoniadigitataisalarge,deciduous,drought‐toleranttreereaching18–25min
heightandwithatrunkupto10mindiameter[40,41].Itistheonlyspeciesofitsgenus
inAfricaandisdistributedacrossthedrylandsstretchingfromSenegaltoSudanandfrom
EthiopiatoNatal.Itprovidesawidevarietyofnon‐timberforestproducts(NTFPs),alt‐
houghtheseareleastusedinsouthernAfrica[40–42].
Inadditiontoitsimportantediblefruits,baobabhasbeendeclaredtobeoneofAf‐
rica’smostimportantleafyvegetables[43],asseenregardingthelivelihoodsoflocalcom‐
munitiesinMali[44].Consequently,ithasbeenidentifiedasahigh‐priorityspeciesfor
domesticationacrossAfrica.Baobabproducts—leaf,fruitpulpandseedkernels—are
widelymarketedandhavebeenapprovedfortradeas‘novelfood’intheEuropeanCom‐
mission.Baobabisadaptabletoadverseclimaticconditions,suggestingitspotentialto
contributetoclimate‐resilientstrategiesinAfrica.Everypartofthetreeisused:roots,
bark,wood,leaves,flowers,capsules,gum,seedsandfruitsforfood,fibreandmedicine.
Itsediblefruitsandleavesarerichinvitamins,makingthemimportantfornutrition.The
barkfibresarealsoimportantproductsformultipleeverydayuses.Acrossthecontinent,
over300usesofthetreehavebeenrecorded.Itsmedicinalproductstreatuptomorethan
20diseases.Theseareusedforsubsistenceand/orsoldbylocalcommunitiestogenerate
income,makingasignificantcontributiontowardspovertyalleviationinruralareas.
InSudan,anethnobotanicalsurveyfound25differentusesforbaobabproducts
[45,46]withpreferencesforsweetleavesandlargefruitswithahighyieldofwhitefruit
pulp,asopposedtoacidicand/orslimypulpandbitterleaves.Rashford[43]hasreviewed
leafpalatability,nutritionalcontentandseasonalconsumptioninSub‐SaharaAfrica,with
widevariationinconsumerspreferences[47].InBurkinaFaso,bothgender‐relatedand
village‐relateddifferencesinuseandmanagementhavebeenrecognized,indicatingthe
needtoseeklocallyappropriatemanagementsystems[45].Theidentifiedtraitswerealso
consideredtobeimportantindicatorsofindividualcandidatetreeswithpotentialfordo‐
mestication.InKenya,baobabisrecognisedasbeingimportantfornutritionaldiversity
inthestaplediet.Fruitpulpisalsoconsumedassnacks,primarilyfreshwithoutanypro‐
cessing[48].However,about60%ofrespondentsstoredfruitsforlaterconsumptionwhen
nutritiousfoodwasscarce.Householdsalsosellbaobabfruitstoaugmenttheirincome
andthustopurchaseotherfoods(45%)andtopayforhealthcare(13%)andeducation
(23%).InSudan,thesaleofbaobabproductscouldbebothnegativelyandpositivelyaf‐
fectedbydifferentinternalandexternalfactors,butthosethatlifthouseholdsoutofpov‐
ertyarebeneficialtoruraldevelopment[49,50].Thisrequiresappropriateinstitutional,
technicalandfinancialsupport.
InKenya,whenamulti‐stakeholderapproachwastakentotheinitiationofacom‐
munity‐baseddevelopmententerpriseforbothbaobabkerneloilandpowderedfruit
pulp,thetargetimpactsweretobenefitcommunitylivelihoodsandtheircapacitytoman‐
ageandutilizetheresource,aswellastoenhanceconsumptionandfoodsecurity[39].
Sustainability2022,14,235511of77
TopromotetheconservationanddomesticationofbaobabacrossAfrica,Gebaueret
al.[51]comprehensivelyrevieweditsecology,diversityandcurrentutilizationandpre‐
sentedideastoencouragefurtherstudiesandinvestmentinthespecies.Theseinclude
studiesofitsphenotypicandgeneticvariation,populationstatus/uses,socioeconomicsof
management/processingandtrade,nutritionalvalue,horticulturalproduction,ecophysi‐
ologyanditsrootsystem.Inaddition,domestication‐relatedstudieshaveconsideredthe
potentialtocultivateyoungbaobabtreesinaleafproductionsystem[43].
4.1.2.GeneticVariationandDomestication
PhenotypicCharacterizationandProvenanceVariation
Anumberofstudiesthisdecadehavesoughttogainadeeperunderstandingofthe
variationinbaobab.Thefirstmadeaproximateanalysisof178fruitsamplesfrom11Sa‐
helianWestAfricasitesinBurkinaFaso,MaliandNiger[52]andevaluatedthevariability
infruitmorphology,aswellassugarandvitaminCcontent.
Likemostsuchstudies,therewasahighlevelofintraspecificvariationbetweenin‐
dividualtrees,buttherewasalsoalinearrelationshipbetweenrainfallandvitaminC
contentacrossthesesites,withvitamincontentbeinghigherinsiteswithlowerprecipita‐
tion.Anegativerelationshipwasfoundbetweenfruitsizeandbothlatitudeandlongi‐
tude,whiletherewasapositivecorrelationbetweensugarcontentandlatitudeandlon‐
gitude.Theauthors,however,concludedthatthelevelsofvitaminCandsugarwithin
sitevariationmeritedamoredetailedstudytoidentifysuperiortrees.Asomewhatsimilar
studyof10provenancesinMali[53]confirmedsomeofthesecorrelations.Thestudyalso
foundthatpulpironcontentwaspositivelycorrelatedwithtopsoilsodicityandbasesat‐
uration,whilepulpvitaminCcontentcorrelatedpositivelywithtopsoilsandfraction,
waterandbasesaturation.Furthermore,significantnegativecorrelationswerefoundbe‐
tweenrainfallandpulpvitaminCcontentandbetweenmeanannualtemperatureand
fruitandpulpweightandpulpfraction,suggestingthatthesetraitsareinfluencedbythe
environment[53].
Inapan‐Africanstudyof17baobabprovenancesfromKenya,Tanzania,Zambia,
Zimbabwe,MalawiandMali,significantvariationwasfoundinthepulpmoisture,pro‐
tein,fibre,ashandelementalcontentamongprovenances[54].However,thereweredif‐
ferencesatthenationallevelinmosttraits,indicatingopportunitiesforselection,bothfor
germplasmconservationandfordomestication.Twofollow‐upstudiesinKenyafound
tree‐to‐treevariationinawiderangeofnutritionalparameters.Inthefirst,treesfrom
coastalpopulationswithlargerfruitsproducedhigherfruityieldsthanthoseinland[55].
Someelitetreeswereselectedwithhighfruitweight,highpulpproportionandinterme‐
diateorsweet‐tastingfruitpulpinthetworegions.Thesecondstudyinsixpopulations
confirmedtheimportanceofintraspecificvariationbetweenindividualtreesatthepopu‐
lationlevel[56],especiallyiniron,zincandvitaminC.Despitethecorrelationsreported
abovebetweenfruittraitsandthelocalenvironment,theseauthorssuggestthatgenetics
playastrongerroleinnutritionalvariationthantheenvironment.Thus,theseresultsfur‐
therillustratetheimportanceoftree‐to‐treevariationinthedomesticationandcultivation
ofthisspecies.
InGhana,itwasconcludedfromstudieson14morphologicaltraitsthatthediversity
ofgeneticvariationmakesitsdomesticationhighlyappropriate[57].Tofurtherdetermine
thepotentialtodomesticatebaobabforitsnutritionalqualities,astudyhasexaminedthe
fattyacidcompositionofseedoilinprovenancesfromacrosstheAfricancontinent[58].
Thisidentifiedsignificantlydifferentmeanprovenancevariation,withthefollowingover‐
allmeans:saturatedfattyacids(17–22%),monounsaturatedfattyacids(32–38%)andpol‐
yunsaturatedfattyacids(22–26%).Palmiticacid,oleicacidandlinoleicacidwerethemost
abundantofeachofthesefattyacids,respectively.Inparallelwiththis,thenutritional
contentofleavesshowedhighvariabilityacrossgenotypesfrom36populations,which
couldbeplacedin4varianceclusters[59].Theseauthorsrecommendedtreebreeding
Sustainability2022,14,235512of77
betweendivergentpopulationstodevelopgenotypeswithhighernutritionalvalues,as
wellasgreatertoleranceofbioticandabioticstress.
Together,theabovestudiesillustratethepotentialtoselecteliteindividualbaobab
treesfordomesticationandexpandedcultivationindrylandAfrica[51]andthatfurther
researchontreegeneticsisneededtocomplementethnobotanicalknowledge[46]toen‐
surethatthecultivatedtreesmeettheneedsofthepeople.
Toaidinthisresearch,germplasmconservationanddomesticationprogrammes,ba‐
obab‘descriptors’,havebeenpublished[60].Theseinclude‘passport’descriptorsdefining
theparametersthatshouldbeobservedwhentheaccessioniscollected;‘management’
descriptorsforaccessionsinthegenebank;‘environmentandsite’descriptors,whichare
site‐specificparametersforcharacterizationandevaluationtrials;and‘site’descriptors
forgermplasmcollecting.Studieshavefoundthatdescriptorstodiscriminatebetween
phenotypeswereequallyexpressedacrossallenvironments.
GeneticVariation
UnlikeotherspeciesinthegenusAdansonia,baobab(A.digitata)istetraploid.How‐
ever,astudyofthevariationinfloralandpollencharactersandchromosomenumberin
specimensfromAfricahasidentifiedanewdiploidspecies,whichhasbeenfoundtoco‐
existwithbaobabbelow800maltitudesinAfricabutisreportedtoextendupto1500m
[61].IthasbeencalledAdansoniakilimasp.nov.andissuperficiallysimilartoA.digitata,
butthespeciescanbedifferentiatedonthebasisoffloralmorphology,pollenandchro‐
mosomenumber.However,byusingacombinationofphylogeneticanalysesandstatis‐
ticalcomparisonsofvarioustraitssuchasflowers,stomataandchromosomecounts,Cron
etal.[62]foundthatA.kilimaisneithercytologicallynormorphologicallydistinct,andthe
authorshavethusreducedtheproposedspeciestosynonymywithA.digitata.
Sixstudieshavesoughttogainabetterunderstandingofthegeneticvariationun‐
derlyingthemorphologicalandnutritionalvariationofbaobab.Thefirstwasaseedling
provenancetrialtoassistabreedingprogrammeforleafproductioninanirrigatedhedge
systeminMali.Itinvolved14provenances—10fromMali,2fromNigerand2from
BurkinaFaso.Highlysignificantdifferencesinleafproductionwerefoundamongprove‐
nancesandfamilieswithinprovenances,withmoderatetolowheritabilityestimatesfor
leafproductivity[63].Strongcorrelationsbetweendiameterandleafproductionindicated
thepotentialtousediameterasapredictorforleafproductionvisàvisitsseasonality.
SomewhatsimilarprovenancetrialswithseedlingswerealsoconductedinMalawi[64–
66].Ingeneral,WestAfricanprovenancesgrewfasterthanthosefromEastAfricabutwith
weakcorrelationsbetweenleafmorphologicaltraitsandclimate,althoughtheleaflet
numberwassignificantlygreaterindrierareas.TheMalawitrialshowedthatthemain‐
landpopulationsweregeneticallydistantfromtheoneontheisolatedLikomaIsland.A
studyinMalawialsosoughttodeterminewhetherthemorphometrictraitsinfruitand
seedcharacteristicswithinandbetweenprovenancescoulddelineatepopulationsfrom
differentzonesintolandraces.Theresultsfoundthatsingleseedweightshowedpro‐
nouncedevidenceofdivergenceofpopulationsintoecotypes[67].
Theotherthreestudiesusedmicrosatellitestoassessgeneticdiversity,thefirstin
sevencoastalandinlandKenyanpopulations[68],thesecondinpopulationsoftheNuba
MountainsofSudan[69]andthethirdinMalawi[67].Allthesegeneticstudiesalsofound
highmorphologicaldiversityinfruitsand/orleaves.Interestingly,therewasevidencethat
somebaobabmorphotypesretainedleavesduringthedryseason[70].Withinthehigh
diversityinthefruitlength,widthandlength/widthratioalongaclimategradientfrom
theBlueNiletoNorthKordofaninSudan,clavateandcrescentshapeswerefoundonly
inNorthKordofan,whilearhomboidshapewasonlyfoundintheBlueNile[71].In
Kenya,thegeneticdiversitywashigh,withlittledifferencebetweencoastalandinland
sites,despitelimitedgeneflowbetweenpopulations.Likewise,therewaslittledifference
ingeneticdiversitybetweensitesinSudan,althoughtwodistinctgenepoolswereob‐
served,withtheoneclosetoamainroadbeingmorediverse,suggestinganinfluenceof
Sustainability2022,14,235513of77
humanintervention[72].InMalawi,moderategeneticdifferentiationwasobserved
amongpopulationsindicatingthepresenceofalargenumberofcommonalleles,resulting
inahomogenisationeffect.Theauthorsattributedthelowgeneticvariationfoundtomar‐
ginalizedpopulations,anthropogenicfactorsandfoundereffects.
Aphysiologicalstudytoexaminegeographicalvariationindroughttoleranceusing
plantsfromMaliandMalawifoundthatbaobabrespondedtowaterstressbyleafshed‐
dingandallocatingmorebiomasstotherootsystem,whileregulatingphotosynthesisand
transpirationbystomatalcontrol[73].Waterstoredinthetaprootwasusedtoprotectold
leavesandfortheformationofnewleavesandroots,withasignificantcorrelationbe‐
tweentaprootwatercontentstomatalclosure.Interestingly,thetwopopulationshaddif‐
ferentdroughtstrategies,suggestingthatselectionfordroughttolerancemaybepossible.
Domestication
InNiger,farmershavechosenabaobab‐basedagroforestryprogrammethatsuits
theirlivelihoodneedsforitspotentialtoimprovetheirhouseholdfoodsecurityandin‐
come[74].AstudyofseedgerminationtoenhancetheperformanceofseedsofA.digitata
inNigeriafoundthatasoakin98%sulphuricacidforanhourpriortosowingimproved
establishment[75].However,insouthernAfrica,domesticationbeganwiththeselection
ofclonalpropagation,especiallyinZambiaandMalawi[65].Totakeadvantageofthe
highintraspecificphenotypicandgeneticvariationwithinandbetweenpopulations,veg‐
etativepropagationtechniqueshavemanyadvantages.Onestudyreviewingthelitera‐
tureontheuseofvegetativepropagationinbaobabreportedonly30%rootingsuccess
withIBAhormone[76]andrecommendedtheneedforfurtherstudies,especiallyforthe
rootingofcuttingsandmarcotting.Anjarwallaetal.[77]andJenyaetal.[40],however,
reviewed‘topcleft’and‘sideveneer’graftingtechniquesinKenyaandMalawi.Topcleft
graftingshowedslightlymoresurvivalsuccessthansideveneer(71%vs.55%).Using2‐
year‐oldrootstockwasslightlymoresuccessfulthan1‐yearoldones.ThestudyinMalawi
alsofoundthattopcleftgraftshadhighersuccessratesthansideveneergrafts.Theresults
indicatethatbaobabiseasilyamenabletograftingwhendoneattherighttimewiththe
correctsizeofscions—thesameisprobablytruefortherootingofcuttings[37].Bothstud‐
iesrecommendedgraftingforuseindomesticationprogrammes.Nevertheless,whenus‐
inggrafting,attentionmustbepaidtotherisksofgraftincompatibilityandtothecommon
situationthatshootgrowthfromtherootstockcanreplacetheintendedgrowthfromthe
selectedscion.Marcottsandrootedcuttingsontheirownrootsavoidtheserisks[37].
4.1.3.CommercializationofProducts
Asdiscussedearlier,nutritiousbaobabproductsareveryimportantlocallyacross
dryAfricaandhavepotentialmarketsaslifestylefoodproductsinEuropeandintheUSA
[78].Indeed,thankstoprocessingandpackaging,theyhavealreadygainedaccesstoin‐
ternationalmarkets[43]withseveralhundredformulationsinEuropeanmarkets,follow‐
ingapprovalfortradebytheEuropeanCommission.InKenya,womenhavebeenthe
mainactorsinthebaobabvaluechainnetworks,principallytradingunprocessedpulp
knownlocallyas‘mabuyu’,madeoutofbaobab‐pulp‐coveredseeds,sugarandfoodcol‐
our[79].Thiscandyincreasesinvaluefrom<1USD/kgpaidtofruitcollectorsuptoUSD
1.5paidbytheconsumer.Thisisanimportantsourceofextraincomeforruralhouse‐
holds,especiallyinthedryseason,suggestingthatthereisgreatpotentialtoincreasemar‐
ketincomethroughthedomesticationofbaobabtrees.
Toenterinternationalmarkets,foodproductshavetomeetfoodsafetystandards
associatedwithprocessingandproductquality.InMalawi,abaobab‐processingsector
hasemergedtosupplybothfoodandnon‐foodproductstolocalconsumers,basedon
small‐scale,informalenterprises.StudiesbyDarretal.[78]haveshowntheimportanceof
value‐additionthroughapprovedstandardsofprocessingandpackaging.Baobabfruits
mayhaveotherpotentialuses.Forexample,thetransesterificationofbaobaboilhasbeen
carriedouttoassessthepotentialofbaobabkerneloilforuseasbiodiesel[80].Theresults
Sustainability2022,14,235514of77
showthatimportantfuelpropertiesofbiodieselfrombaobaboilmetboththeEuropean
andAmerican(ENandASTM)standards.Baobabisoneoftwospeciesexaminedtoeval‐
uateconcernsaboutecologicalsustainabilityandinequalityarisingfromtheincreased
formalizationoftradeinnaturalproducts[81].Thestudyconcludesthatbetterinformed
andmorerespectfuloflocalknowledgeisneededtoensurerespectforcustomarylaws.
MarketingConcerns
ConcernshavebeenraisedthatdevelopinginternationalmarketsforAfricanindige‐
nousfoodproductscoulddamagelocalsupply,environmentaldegradationandlossof
localdietarydiversity.Theseconcernsforsubsistenceusersofbaobabweregreatestin
WestAfrica,wherethereisahighdependenceontheseproducts,unlikesouthernAfrica,
wherebaobabhasbeenreportedtobe‘underutilized’andwherecommercializationcould
helpreducepoverty[42].Thisconcernwasthesubjectofaconference“Bridgingthegap
betweenincreasingknowledgeanddecreasingresources”intheCzechRepublicin2014,
whichexaminedtheseissues[82].Themeetingconcludedthatresearchshould“address
theimprovementofthelong‐termfoodsecurityandnutritionoflocalcommunitiesinthe
targetregionsby(i)ensuringtheavailabilityofandaccesstobaobabproductswithhigh
nutritionalvalue,(ii)increasingtheuseofbaobabproductsindailydiets,and(iii)raising
incomesfromsellingrawandprocessedbaobabproductsofhighnutritionalvalue”.
Theseobjectivesconcurstronglywiththeinitiativestodomesticateindigenousfoodtrees
asnewcropsforsubsistencefarmers[3,14].Inaddition,Chivandietal.[83]haveidentified
theneedforresearchtofocusonhowtotapintohealthbenefitsofindigenoustreeprod‐
uctsforpeopleandanimalsandtodevelopnewproductssuchasnaturalsweetenersand
pectinsforindustrialuse.Theyalsoemphasisetheenvironmentalandlivelihoodbenefits
arisingfromincreasedcommunity‐basedsustainableutilisationandconservationofthese
treespecies.
Concernshavealsobeenraisedaboutincreasedgrazingpressureonnaturalregen‐
eration.Studieshaveascertainedthatbaobabpopulationsdodeclineunderheavylive‐
stockgrazing,butthattheyaresustainableundermoderategrazingpressures[41],asseed
productionissubstantial[84].However,thepredationoffruitsbybaboonsalsoleadsto
populationdecline,asdoesdroughtduetofailureofthe‘rains’.Theseauthorsdidcon‐
clude,however,thatplantingandprotectionfromlivestockisrequiredtoovercomere‐
cruitmentbottlenecks.
4.2.Sclerocaryabirrea(Marula)
4.2.1.Ethnobotany,UsesandNaturalResources
Therearethreesub‐speciesofSclerocaryabirreainAfrica:subsp.birrea,subsp.caffra
andsubsp.multifoliolata.Theirnaturaldistributionspansdrylandsin29Africancountries,
buttheyprimarilygrowindifferentareasinAfrica.Subsp.birreaisfoundintheSaheland
northernAfrica,andsubsp.caffraisfoundintheMiomboWoodlandsofsouthernAfrica.
InEastAfrica,bothsubspeciesarefound,whileinTanzaniaalonesubsp.multifoliolatais
native,butitcanalsobefoundtogetherwiththeothertwosubspecies.Undergoodcon‐
ditions,thetreecangrowupto15–20m,withameandiameterof80–100cmatmaturity
[85].Generally,S.birreaoccursinareasreceiving200–1600mmrainfallperannumon
sandytoloamysoils.However,inMalawi,S.birreathrivesmainlyinhot,dryareasat
altitudesof500–1000mwithameanannualrainfallof900–1000mmandmeanannual
temperatureof22to23°C.Thespeciesalsothrivesonhydromorphicsoilswithlimited
drainage,whichareseasonallywaterlogged[85].
TounderstandthepopulationstabilityofmarulaintheBushbuckRidgeareaof
SouthAfrica,treedensityandsize–classdistributionprofileswereevaluatedinareaswith
differentlanduses.Treedensitywashighestinhomegardensduetodiscardedseedsfrom
householdbeermakingandlowestincropfields[86].Femaletreedensitieswererela‐
tivelyconstantacrossallland‐usetypes,suggestingthatthecombinationofculturaland
Sustainability2022,14,235515of77
economicvaluescanconservespecies,althoughharvestingthemforfuelwoodinrange‐
landsmayposeathreat.Theauthorsconsiderthatsuchfindingsmayberelevanttoother
social‐ecologicalsituationswherenaturalresourcesareimportantforsustainingliveli‐
hoods.
AmaturetreeofS.birreacanproduceasmanyas91,000fruits.Thesecanbeeaten
freshorfermentedtomakebeer[85],whiletheediblekernelsarerichinahighlynutri‐
tiousoil.TheleavesandthebarkofS.birreaalsohavemedicinaluses,andthewoodcan
becarvedintoutilitarianitemssuchasspoonsandplatesordecorativeanimalfigures
[85].Inaddition,thespeciesisabrowseforlivestockandprovidesshadeforcerealcrops.
WithinmanyAfricancommunities,thefruitsandkernelsinparticular,havegreat
culturalandceremonialvalue[85].Nevertheless,thenaturalresourceisunderconsider‐
ablepressureduetotheextensiveclearingofwoodlandsforsettlementandagriculture,
whichthreatentheecosystemservicesandgeneticdiversityofthespecies[85].Despite
this,asurveyinsouthernAfricafoundthatlocalcommunitieshadpositiveattitudesto‐
wardstheconservationofmarulatreesandwerealsokeentoparticipateintheirdomes‐
tication[87].Itwasalsoclearthatthereisaneedformoreinformationaboutlocalman‐
agementstrategies[88],includingitsvulnerabilitytowildlifepressuresfromfruitand
seedpredation,especiallyfromelephants[89].AnethnobotanicalsurveyinNamibia
foundthat87%ofthepopulationhadindigenousknowledgepasseddownfromtheir
parents,withamajorityindicatingthatthespecieswasinadeclinenotbeingaddressed
byanymanagement[90].
InZimbabwe,astudycomparedthedistributionandstemdensitiesofmarulainnat‐
uralvegetationandonfarmsandfoundthattherewerenearlytwiceasmanytreesin
farms(7vs.4stems/ha),withfemaletreesoutnumberingmales(55vs.34%)[91].Theau‐
thorconcludedthatthisistheresultoffarmerprotectionoffruitproducingfemaletrees
andadvocatedtheneedforfurtherworktodomesticatethisspecies.Anotherstudyex‐
aminedtheharvestingandutilizationofthespeciesbysmallholdercommunities[92,93]
andfoundthat49%ofhouseholdsconsumedripefruitsraw,while76%alsomadeatra‐
ditionalfermentedwine/beerand54%consumedthekernels.Theutilizationofthese
productsisamajorsourceofincomeforlocalpeoplemeetingtheeconomicneedsofpoor
communitiesinruralareaswhilealsocontributingtofoodandnutritionalsecurity[85].
Indeed,thelargerfruitedS.birreasubspeciescaffraismorecommonlycultivatedashome‐
steadtreesinsouthernAfricathanissubspeciesbirreaintheSahel,duetoitstendencyto
havelargerfruits.
4.2.2.GeneticVariationandDomestication
MarulawasoneoftheprioritytreespeciesidentifiedfordomesticationbytheICRAF
andlocalfarmersinthe1990s.When21provenances(20ofS.birreassp.caffraand1ofS.
birreassp.birrea)fromMalawi,Zambia,Zimbabwe,Namibia,Botswana,Tanzania,
MozambiqueandMaliwereplantedinMangochi,Malawi,thereweresignificantdiffer‐
ences—uptothreefold—betweenthepopulationsformostvegetativegrowthtraits[94].
StudiesinNamibiaandSouthAfricafoundsomeevidencethatfarmershaveinitiated
domesticationbyselectingdesirabletreesinthelands[95].TheMarracuenepopulation
fromMozambiquewasrankedtopforheight,diameteratbreastheight,crownwidthand
crowndepth.After7years,only8populationshadfruits,ofwhichtheMarracuenepop‐
ulationhadthegreatestfruityieldwithconsiderabletree‐to‐treevariationinfruitproduc‐
tionrangingfrom1to1228fruitspertree[94].Afollow‐upstudythenfoundsignificant
variationamongtheprovenancesinthenumberoffruits,fruitweight,pulpweight,seed
weight,fruitlengthanddiameter[85],withnocorrelationbetweenthenumberoffruits
andotherfruittraits.Theauthorsrecommendedthatstudiesshouldinvestigatefruittaste
andotherqualitytraits.Aweakrelationshipbetweenfruitingandvegetativegrowthsug‐
geststhatgrowthshouldnotbeusedasapredictoroffruiting[96].Likewise,onlymod‐
eratecorrelationshavebeenreportedbetweenfruityieldandcrowngrowth.Thus,more
workisneededtounderstandanypossiblerelationshipsbetweenvegetativegrowthand
Sustainability2022,14,235516of77
fruiting.Relevantheremaybetherecentlyreportedprovenancedifferencesintheirsus‐
ceptibilitytoleafpredationbyinsectpestsinMalawi[97].
Geneticvariation,especiallytree‐to‐tree,inmanyparametershasimportantimplica‐
tionsfordomesticationofthisspecies[36,95,98].Inafollow‐upprovenancestudyfive
yearslater[99],phenologicaltraitsdifferedbetweenprovenances,althoughwithsome
overlap.LikemanyindigenousfruitandnutspeciesinAfrica,marulaisadioeciousspe‐
cieswithmaleandfemaletrees.Theearliestfloweringwasintheeasternprovenances
(MozambiqueandSwaziland)andlaterinothers.Theearlyfloweringgenotypesfruited
andmaturedbetweenAugustandJanuary,whilethelaterprovenancesfruitedfromSep‐
tembertoMay,withmaletreesfloweringslightlyearlierthanfemales,butsometrees
classifiedasfemaleinoneyearwerefoundtohavesomemaleflowersinthenextseason.
Fruityieldsalsodifferedbetweenyears(2016/2017versus2017/2018),indicatingprobable
environmentalinfluencesonphenology.Theseresultssuggestaneedformoredetailed
phenologicalstudies.ThisisespeciallythecaseintheSahel,wherethefloweringseason
inSenegal(FebruarytoMarch)isonlyafewmonthsafterthatinthesouthernhemisphere,
withfruitingfromApriltoJuly[100].However,atthemostsoutherlysite(Amaly),there
wasasmallamountoffloweringfromOctobertoNovember.Nevertheless,markeddif‐
ferenceswereobservedbetweenandwithinsitesfortheleafingandfloweringphasesand
asignificantdifferencewithinand