Acta Hortic. 1215. ISHS 2018. DOI 10.17660/ActaHortic.2018.1215.65 Proc. Int. Symp. on Greener Cities for More Efficient Ecosystem Services in a Climate Changing World Eds.: G. Pennisi et al.

351

The “jardinu” of Pantelleria as a paradigm of resource-efficient horticulture in the built-up environment G.Barbera1,C.Chieco2,T.Georgiadis2,A.Motisi1andF.Rossi2,a1University of Palermo, Department of Agricultural and Forest Sciences, Viale delle Scienze, Edif. 4, I-90128Palermo, Italy; 2Institute of Biometeorology of theNationalResearch Council (CNR-IBIMET), ViaGobetti, 101,I-40129Bologna,Italy.Abstract

The idea of garden is expressed, for the first time in history, by theMesopotamiancivilizationasearlyastheIVmillenniumBCEasdrawingsandpoetrytextsshowingawallfencingonesingletree.Thisisthefirstrepresentationoftheideaofsheltering/protectingatreebyhumanartifactsand,initssimplestform,bringstheidea of the tight relationship between horticulture and urban environment. The“jardinu”ofPantelleria,adrystonewallshaped intoanopen-top towerencirclingasingle citrus tree, fully matches both in its founding idea and its physicalimplementation the elemental idea of theMesopotamian garden. Such traditionalgrowingsystem,developedinPantelleriatocopewithwaterscarcity,isanartifactattheserviceofhouseholds,fullyintegratedintotheurbansettlementsoftheIslandandproviding a valuable source of fresh fruit to families despite the lack of irrigationwater. Currently, asmany as 500 of such structures are still active in Pantelleria,standingasthedistinguishinglandmarksoftheisland.Thesimple,albeitexpensive,principle of enclosing a tree inside a protective wall has many effects on thesurroundingenvironmentandontheeco-physiologicalbehaviorofthetreeitself.Wediscussherethissystem fromthepointofviewofthe interactionsbetweenthetreeand the enclosingwall, focusing on the ability of the “Pantelleria citrus garden” toaffect thewater cycle of the tree and to avoid irrigation at all.Our analysis showsbeyond simple, easily recognizable effects such aswind protection and the relatedreductionsintranspiration,diurnalthermaldynamicsofwall’sstonesactivelyaffectsthe water balance of the system. Implications of this analysis suggest that theknowledge behind the empirical building-rules developed over the years for theconstructionofsuchstructuresareexpressionof thephysicalprinciplesunderlyingtheenvironmentaldynamicsofthe“Pantelleriacitrusgarden”.

Keywords:landscape,terraces,garden,water,ecosystemservicesINTRODUCTIONPantelleria is located inastrategicpositionat thecentreof theMediterraneantraderoutes,andasetofnoticeabletraditionalculturaladaptationshavebeenputinplaceduringcenturiesofhumancolonizationtocopewithitsharshenvironmentandlackofresources.Theextensiveuseofpeculiarpracticescapabletomatchagriculturalneedsturnedtheislandinto a unique dry-stone landscapemade of terraces and dry-stone gardens (jardinu) thatstronglymarkthecharacteroftheisland.THETRADITIONALAGRICULTURALLANDSCAPE80%oftheisland’ssurfaceiscoveredbyterracing/dry-stonewallsandbuildingsthatdevelopacomplexnetworkthroughoutthelandscape(Figure1).Thepresenceofdry-stonesisonethemostdistinctiveaspectoftheisland’sculturalheritage,bothforsimpleterracingandforthedelimitationoflandpatchesandthediffusepresenceofartefactsandbuildings.The climate has a strong Mediterranean connotation, the water deficit being the mostlimitingfactor.Rainfall(400-500mmyear-1)followsthetypicalseasonalpatternofthesemi- aE-mail: f.rossi@ibimet.cnr.it

352

arid Mediterranean with a long dry season during the warmer months. A furtherenhancementof evapotranspiration losses isdue to thehighwind frequency, occurring inmorethan300dayseveryyear(Barberaetal.,2010).

Figure1.VineyardsinthePantelleriaterraceddrystonelandscape.Most features of the agricultural landscape are then shaped in relation to theseparticular environmental traits. A strong limitation to the diffusion of subsistenceagriculturewasfoundbyinhabitantsasrelatedtothemassivepresenceofvolcanicstones.De-stoninghasbeenthemostimportantdriverinstructuringofthehorticulturalsystemofPantelleria since almost all the agricultural land has been reclaimed through it. Such acommonneedtocreatesuitablelivingconditionshasaconsolidatedsocialconvention,giventhemutualworksharingandretributiononthebasisof50%ofde-stonedlandsurface,ascoded in the cunzari e spartiri (arrange and divide) local custom (D’Aietti, 2009). Theconsequentlandfractioningledtothefactthateachfarmerevennowownspatchesoflandin three-four different locations. This latter aspect has several benefits to ensurefood/incomesecurityagainstoccurrenceofadverseevents,anefficientlabourorganizationandmutual sharing,agooddiversityofcropsand local races/genotypes.Altogether, theseaspectshaveconcurredtoanuncommonlyhighbioculturaldiversityandtotheidentityoftheislanditself.Duetothelackoffresh-watersourcesorwells,waterprovisionforhumanand agricultural usage on the island is only throughwater harvesting, and a widespreadsystemoffacilitiesreachedafulldevelopmentasearlyasthePunicages(Mantellini,2015).Rainwater harvesting is shaping every aspect of human activity on the island: there arealmost500 cisterns for storing rainfall storage, andarchitectural elements forhome roofsand gutters especially suited for conveying the rainfall give birth to the typical dammusohouses,easilyrecognizablePantelleriaicons.Dry-stone artefactspresent inPantelleria accomplish anumber of functionsbeyondsoilconfinement/formationanderosionprevention.Animportantrecognizedaspectisthewind-sheltering,protectingcropsbothfromthemechanicaleffectofthewindandloweringtheevaporativedemandoftheatmospherebystronglyreducingwindspeedatcanopylevel.Dry-stonewallsareubiquitouselementsontheisland,bothasapartofaterraceorsimplyas a fencing element of enclosures delimiting the fields. The importance attributed bygrowerstotheaerodynamicroleofthedry-stonewallseasilyemergesfromobservingthat,even in terraces, where their most prominent role is to physically support the soil, theystandabovegroundlevelofferingtheirwind-shelteringeffecttothecropsenclosed.THEJARDINUANDTHEEFFECTOFWALLSONMICROCLIMATEWalls interraces,standing50-100cmabovegroundlevel,createaconfinedspaceofstill air hosting crop canopies, with a fair degree of decoupling from the surroundingatmosphere.Within this confinedair space, cropsare cultivatedaccording to anumberofspecializedculturaladaptationsthatsharethecommonobjectiveofpreventingcanopiestogrowoutside this space to limit evapotranspiration. It is important to remark that canopyconfinementisnottheresultofanatural-shapingeffectofthewindsbut is imposedbyanaccurateandaccuratelyplannedpruningandcanopymanagementtotallycontrolledbythefarmers.Thisiseasilyrecognizablewhenobservinganabandonedoliveterrace,whereolive

 

353

treesgrowintoa fullhigh-bushclearlystandingoutof thedrystonewalls.Thetechniquesadopted largelydependonthespecificphysiologicalcharactersof thespecies,particularlyontheirgrowthhabit.Thecaper,aprostrate lowbushwoodyspecies, fitsnaturallywithinthelimitsdefinedbythedrystonewalls.Inotherspecies,suitabledwarfingpracticesabletostrongly reduce canopy height to less than one meter, approximately the level of theenclosingwalls,areadopted.Thisisthecase,forexample,ofgrapevinesgrowninatypicalprostrate low bush training system (the alberello pantesco), with three-to-four branches,spurpruned,growingclosetothesoilandthedwarfolivetrees,atrainingsystemforoliveuniquetotheIslandofPantelleria(Figure2,right).The giardino pantesco is themost extremely significant example of dry-stonewallsusageforadaptationtowaterdeficitconditions(Barbera,2017).Thecitrusgarden(Figure2, left) is a circular open-top dry-stone tower where a single orange tree is successfullygrownintotalabsenceofirrigation,otherwisemandatoryintheMediterraneanclimate.Incitrus species, in fact, tree vigour control cannot be achieved through strong pruningwithout significant losses in yield and, consequently, citrus trees could not be confinedwithintheregularterracesorfieldenclosureswalls.Tobenefitfromwindprotectioneffectandtolimitairmovementsaroundtreecanopy,thedry-stonewallisraisedtotheleveloftheminimum tree height that can be attained in citrus trees without compromising treeproductivity, i.e., up to four-meter tall. The jardinu (Sicilian vernacular for giardinopantesco)isafacilityattheserviceoffamilies,alwaysclosetoorpartofahouse,toprovidelocally a supply of fresh fruits. The jardinu and its embedded fruitful orange tree can beconsideredaltogetherasanevidenceoftheeffectivenessofdry-stonewallsasinstrumentstoreduceevapotranspirationlossesandimprovewateravailabilitytotreecrops.Beyondwindsheltering,thepeculiaragriculturalsystemsinPantelleriaplayaroleonthe regulation of the water balance through dewfall condensation. While dewfall is notconsidered to play a substantial role in water availability of agricultural systems in theMediterranean, the small size of Pantelleria and the closeness of agricultural fields andterraces to the sea seems to be able to increase the incidence of this component. Forexample,dewfallratesundersimilarconditionswereestimatedintheorderof0.2-0.4mmnight-1 in Lanzarote (Graf et al., 2004) and up to 19%of total annual precipitation in thecoastal drylands of Madagascar (Hanisch et al., 2015). Even if dewfalls have never beenmeasuredinPantelleria,observationssuggestthatthewallscouldcreatelocalconditionsofhighersoilwateravailabilityintheproximityofthewallitself.

Figure2. Thejardinu(giardinopantesco)drystonetowerwithasinglecitrustreegrowinginside(left).Anolivetreegrowinghorizontallywithintheairspacedelimitedbydrystone walls (right). Four-meter long branches are supported by stones topreventrooting.Our microclimate observations of the giardino pantesco (Barbera et al., 2012;Georgiadisetal.,2014)(Figure3)showthatthedrystonewallsubstantiallyinfluencesthe

354

internal patterns of atmospheric parameters and enters into the diurnal dynamics of thegeneral energybalanceof the system in a less-than-intuitivewaydue to thehigh thermalinertia of the stones (Figure 3). Such active rolemay greatly enhance dewfall occurrencebothonstonesandonfoliagesurfaces.AsevidencedinFigure4,a24-htemperaturecycleisobserved:duringthedaytheinternalstonesarecoolerthantheexterior,sothatairhumidityis in conditions to condensate, while at night they are warmer than the exterior. Theconsequent dissipation of the heat cumulated during the night reduced temperatureexcursionatnight,anditispositivelyaffectingcitrusadaptation.

Figure3. Wind,temperatureandhumiditysensorspositionedintheinternalandexternaloftheFAIjardinu.

 

355

Figure4.IRthermalimagesofthejardinuwall.CONCLUSIONSAn intelligent development of knowledgeable agricultural techniques still connoteshumanimpactinPantelleria.Thelocalagriculturalsystemshavebeendevelopedwithtimetocopewiththeneedtoensureafoodsupplyforlocaluseand,then,forexternalmarket,ina difficult environment, scarce in resources and exposed to strongwinds. Landscapewasshaped through drystone (locally obtained through an efficient de-stoning) terracing, andtheprocesshasbeenaccompaniedwithconcomitantadaptationsofculturalsystemstothespecific features of the terracing system in a highly specialized and intimate way. Theempirismofthetechniquesisonlyapparent,sincetheyarebasedonadeepunderstandingofsophisticatedatmosphericandphysiologicalprocesses.Inaresource-limitedenvironmentsuch as theMediterranean (Laureano, 2005),with a long dry summer season, the use ofwalls toprotectcropshasa longhistory:growingrainfedcropsundera longwater-deficitperiod would be a challenge to self-provisioning and survival of human activities andsettlementsthathavetorelyonthelocalresources.ThejardinurepresentsanexampleofextremeadaptationthatcanbefoundelsewhereintheMediterranean,specificallyinarelicformofsemi-abandonedremainsintheIslandofFolegandros (Greece), but also in the Lanzarote grapevines growing in holes through thelapillitoreachthesoillayer,orintheDalmatianIslandsdrystonecirclesinKornatiNationalPark(Croatia).Theseexamples,altogethersuggestadeephistoricallinkageintraditionalagriculturalknowledgethathasprovedtobeabletopermeatethroughculturesacrossthehistoryoftheMediterranean.This flowof knowledgehas allowed thepersistenceof physical structuressuch as the drystone walls composing the physical landscape. And, in addition, theknowledge materially associated to their building and maintenance, and the agriculturaltechniques and crops growing inside these structures in a remarkably high bio-culturaldiversity,arestillalive.UNESCO(2014)hasidentifiedthecommunityoftheislandas“…thetruecustodiansofthetraditionalknowledgeregardingthetechniqueofcultivatingthe“headtrainedbushvines” (vite ad alberello)…, andPantelleria terraces and gardenshave tobeconsideredaswholecorpusoftraditionalknowledgerecognized”.Initscomplex,then,thespeciallandscapecharacterizingtheislandintegratesbuilt-upenvironmentintoa fully functional,resource-efficient,agriculturalsystem(BarberaandLaMantia,1998).Thespecial landscapefeaturesinPantelleria, includinganumberof jardinu(many of them restored and brought back to the island heritage), concentrate traditionalknowledge,hostahighbio-culturaldiversity,andoffersawiderangeofecosystemservices,includingare-invigoratedtourism.TodayPantelleria,anditspeculiarhorticulture,islivingonthetracksofsuchamulti-culturaltradition,butthereistheurgetocopewiththerecentchangesthatoccurredintheglobaleconomicscenario,findingnewwaysofkeepingthetraditionalagriculturallandscapeof the Island still active and profitable despite the high costs for human labour and

356

investments required. The added value of the heritage represented by the traditionalagriculturallandscapeanditsecosystemandculturalservicesmaygreatlycontributeinthisrespect.ACKNOWLEDGEMENTSAuthorswill always gratefully rememberDr. Giovanni Rallo and thank Donnafugatawinery for the donation of the Giardino Pantesco to the FAI (Italian Environment Fund):withoutsuchinvaluabledonation,nothingofthiswouldbepossibleandtheinsightsaboutaprecioushorticulturaltraditionalknowledgecouldgetlost.ManythanksalsoduetoFAIthatmadethegardenavailableforourstudies.LiteraturecitedBarbera,G.(2017).Theelementarygarden.ArchitetturadelPaesaggio34,18–20.Barbera,G.,andLaMantia,T.(1998).Sistemaagricoloepaesaggionell’IsoladiPantelleria.ItalusHortus23,28.Barbera, G., Cullotta, S., Rossi-Doria, I., and Rhul, J. (2010). I paesaggi a terrazze in Sicilia: metodologie perl’analisi,latutelaelavalorizzazione.StudieRicerche-ARPASicilia7,306–391.Barbera,G.,Georgiadis,T.,Motisi,A.,andRossi,F.(2012).Culturaladaptationoftraditionalcropsandauniquedrystonelandscape:theIslandofPantelleria.Paperpresentedat:theInternationalMeetingonAgrobiodiversityacrossLandscapesinaChangingWorld.Domestication,AdaptationandInnovation(Montpellier,France).D’Aietti,A.(2009).IlLibrodell’IsoladiPantelleria(Trapani,Italia:IlPettirosso),pp.480.Georgiadis,T.,Barbera,G.,Carotenuto,F.,Lenzi,J.,Motisi,A.,andRossi,F.(2014).Howatraditionalagriculturalprotectionstructureactsinconditioningtheinternalmicroclimate:astatisticalanalyticalapproachtoGiardinoPantesco(PantelleriaIsland-Italy).Ital.J.Agrometeorol.18(1),41–58.Graf,A.,Kuttler,W.,andWerner,J.(2004).DewfallmeasurementsonLanzarote,CanaryIslands.MeteorologischeZeitschrift13(5),405–412https://doi.org/10.1127/0941-2948/2004/0013-0405.Hanisch,S.,Lohrey,C.,andBuerkert,A.(2015).Dewfallanditsecologicalsignificanceinsemi-aridcoastalsouth-westernMadagascar.J.AridEnviron.121,24–31https://doi.org/10.1016/j.jaridenv.2015.05.007.Laureano, P. (2005). The Water Atlas: Traditional Knowledge to Combat Desertification (UNESCO-sponsoredprogrammesandpublications).Mantellini, S. (2015). The implications of water storage for human settlement in Mediterranean waterlessislands: theexampleofPantelleria.Environ.Archaeol.: J.Hum.Palaeoecol.20 (4),406–424https://doi.org/10.1179/1749631415Y.0000000005.UNESCO.(2014).IntangibleCulturalHeritagenominationfileno.00720forinscriptionontherepresentativelistof the intangible cultural heritage of humanity in 2014. http://www.unesco.org/culture/ich/doc/download.php?versionID=30503.