Thesis (MScAgric)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Soils of semi-arid regions generally have low organic matter contents, primarily attributed to prevailing climatic conditions. Yet, the spekboom thicket, located in the semi-arid region of the Eastern Cape (South Africa) has been distinguished to accumulate large amounts of soil carbon. To further understand this remarkable accumulation, a detailed investigation was carried out to evaluate the distribution, speciation and stability of the soil carbon from directly beneath spekboom (Portulacaria afra) and other “nonspekboom” vegetation within the intact thicket, and from adjacent, degraded (overgrazed), open thicket sites. In the first experimental chapter, the distribution of organic and inorganic C, as well as general soil properties (pH, EC, exchangeable and water soluble cations, hydrophobicity, water stable aggregates) were investigated in the intact (spekboom and nonspekboom) and degraded (open) thicket soils. There were no significant differences in the C content (organic or inorganic) between the spekboom and nonspekboom sites in the intact thicket. Soil organic carbon (SOC) content however was greatly influenced by thicket degradation, whereas, inorganic C remained unaffected. Mean organic C (0-50 cm) ranged from 19-34, 22-62, and 19-58 g C kg-1 for open, spekboom, and nonspekboom sites, respectively. Whereas, mean inorganic C ranged from 2-9 g C kg-1 irrespective of sites, representing 4-22 % of total soil C. However, no significant differences were detected between degraded and intact sites for all (total, organic and inorganic) C stocks, attributed to variation in bulk density. Spekboom soils contained significantly higher concentrations of exchangeable and water soluble Mg, Na, and K, and consequently had higher pH and EC compared to the other sites. Soils tended to be hydrophobic especially at shallower depths in the intact thicket irrespective of vegetation type, whereas soils from the adjacent open sites were not significantly hydrophobic. Macro-aggregates were considerably more stable under intact sites compared to open sites. The second experimental chapter investigated the effects of degradation and vegetation type on the stability and structural chemistry of SOC. This involved partitioning the soil organic matter into particulate and mineral-bound (stable) fractions, and then examining the relationships between the stable organic C fraction and various soil properties as an attempt to elucidate the stabilization mechanism(s). Particulate organic C ranged from 7.0, 9.3, and 14.4 g C kg-1 for open, spekboom, and nonspekboom respectively; representing 22-34 % of total SOC. Stable (mineral-bound) organic C accounted for the largest fraction ca. 60-66 % of total SOC; 28.0 and 26.2 g C kg-1 for spekboom and non-spekboom respectively, versus 17.2 g C kg-1 for open sites. It was concluded that SOC stability was influenced by the inherent residue quality (recalcitrance) rather than soil properties, attributed to the aliphatic (lipids and waxes) and highly aromatic nature of the spekboom litter substrate and particulate OM. These research findings are of fundamental significance in understanding soil organic matter stabilization in semi-arid environments. / AFRIKAANSE OPSOMMING: Gronde van semi–ariede streke het oor die algemeen 'n lae organiese materiaalinhoud, wat hoofsaaklik aan die heersende klimaatstoestande toegeskryf kan word. Tog, het die spekboomruigtes, geleë in die semi-ariede streek van die Oos-Kaap (Suid Afrika), onderskeidelik groot hoeveelhede grondkoolstof geakkumuleer. Om hierdie merkwaardige akkumulasie verder te verstaan, was 'n gedetailleerde ondersoek uitgevoer om die verspreiding, spesiasie en stabiliteit van die grondkoolstof direk onder spekboom (Portulacaria afra) en ander “nie-spekboom” plantegroei binne die intakte ruigte en van die aangrensende gedegradeer (oorbeweide), oop gras areas te evalueer. In die eerste eksperimentele hoofstuk, is die verspreiding van organiese en anorganiese C, sowel as algemene grondeienskappe (pH, uitruilbare en wateroplosbare katione, hidrofobisiteit, water-stabiele aggregate) was in die intakte (spekboom en nie-spekboom) en degradeerde (oop) ruigtes ondersoek. Daar was geen betekenisvolle verskille in die C-inhoud (organies of anorganies) tussen die spekboom en nie-spekboom gronde in die intakte ruigtes gevind nie. Grond organiese koolstof (GOK) inhoud is grootliks deur die ruigte se agteruitgang beïnvloed, maar anorganiese C-voorrade was egter nie beïnvloed nie. Die gemiddelde organiese C-inhoud (0-50 cm) het van 19-34, 22-62 en 19-58 g C kg-1 onderskeidelik vir 'n oop, spekboom, en nie-spekboom areas gewissel. Die anorganiese C-inhoude het vanaf 2-9 g C kg-1 gewissel, ongeag van ligging, wat 4-22 % van die totale grond C uit maak. Daar is egter geen beduidende verskille tussen vervalle en heel terreine vir almal (totaal, organiese en anorganiese) C aandele opgespoor, toegeskryf word aan die variasie in die massadigtheid. Spekboom gronde het beduidende hoër konsentrasies van uitruilbare en wateroplosbare Mg, Na, en K waardes bevat. Dit het ook hoër pH en EC, in vergelyking met die ander areas gehad. Gronde was geneig om hidrofobies te wees, veral op vlakker dieptes in die intakte ruigte, ongeag van die plantegroei, terwyl die gronde van die aangrensende oop areas nie beduidend hidrofobies was nie. Makro grond aggregate was aansienlik meer stabiel onder intakte ruigtes as in die oop areas. Die tweede eksperimentele hoofstuk het die gevolge van die weiding-geïnduseerde degradasie en tipe plantegroei op die stabiliteit en strukturele chemie van GOK ondersoek. Dit het die skeiding van die grond organiese materiaal in die vrye en mineraalgebonde (stabiele) fraksies behels. Daarna is die verhoudings tussen die stabiele organiese C fraksie en verskeie grondeienskappe ondersoek om die stabiliseringmeganisme(s) uit te lig. Die chemiese aard van die blare, plante oorblyfsels, fyn en minerale gebinde organiese C is met behulp van spektroskopie ondersoek. Vrye organiese C voorraad het van 7.0, 9.3, en 14.4 g C kg-1 vir oop, spekboom, en nie-spekboom onderskeidelik gewissel, wat ongeveer 23-34% van die totale GOK verteenwoordig. Stabiele (minerale gebind) organiese C-voorrade is vir die grootste fraksie ca. 60-66% van die totale GOK verantwoordelik. Dit was 28.0 en 26.2 g C kg-1 onderskeidelik vir spekboom en nie-spekboom, teenoor 17.2 g C kg-1 vir 'n oop area. Die mineraalgebonde GOK het geen noemenswaardige korrelasies met die ondersoekte grondeienskappe getoon nie. Dus is tot die gevolgtrekking gekom dat GOK stabilisering eerder deur die plante oorblyfsel se chemiese kwaliteit beïnvloed word. Strukturele chemiese karakterisering (13C CP-MAS KMR) van die spekboom afval en vrye C fraksie het gewys dat weerspannigheid die mees prominente meganisme van koolstof stabilisering van organiese koolstof in die gronde is. Dit word aan die alifatiese (lipiede en wasse) en sterk aromatiese aard van die spekboom substrate toegeskryf. Hierdie ondersoek het tot die fundamentele kennis van grond organiese materiaalstabilisering in 'n semi-ariede omgewings bygedra.

Thesis (MA)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: The succulent thicket plant community of South Africa, particularly Portulacaria afra (in this study referred to as spekboom), occurring in the Thicket Biome, sequestrates an exceptional amount of carbon dioxide (due to its photosynthetic properties), particularly for a warm, semi-arid region and in this capacity is more akin to forest ecosystems. Spekboom has additional favourable characteristics over forested systems regarding carbon trading (CT), namely: economic water use; potential for combating desertification and poverty in arid environments; and ability to withstand stand-replacing fire (spekboom doesn’t burn) which improves its attraction as a commodity in CT and the payments for ecosystem services (PES) industry. Landowners interested in using the capacity of their land for carbon sequestration (CS) are challenged to calculate their plant communities’ sequestration ability and biodiversity potential and therefore to quantify the carbon credits to be sold. The aim of the study was to quantify the CS ability of a selected property unit by vegetation area and to establish the carbon credits value that can be sold in the carbon market. It commenced by highlighting the problem of global warming and its effect on climate change in South Africa. CS is described as a process and a solution to decrease high and rising atmospheric CO2 levels, and its use in the carbon market to attain a monetary value to promote the growing of vegetation or to protect and conserve biodiversity that will enhance carbon stocks. The study site is Bosch Luys Kloof Private Nature Reserve (BLK PNR) in the semi-arid Karoo. Because CS potential is known to follow a rainfall gradient, one expects the semi-arid Karoo to have a low CS potential. However, this area contains spekboom, an extraordinary thicket type that sequestrates carbon at similar rates to forest ecosystems and should therefore reap the benefits of CT. Yet, accurate mapping of this vegetation is critical for accurate carbon stocks assessment. The CS potential of all vegetation communities in the study area had to be established to estimate the carbon stocks in the whole property unit. ArcGIS was used to map the vegetation communities (sub biomes) and eCognition to refine mapping of the Gamka Thicket (containing spekboom) through an object-orientated approach to automated vegetation mapping. For accuracy assessment a heads-up digitized map was created for comparison. The true surface area was calculated for the vegetation classification to ensure accurate area accounting on the mountainous terrain and this calculated area of the mapped vegetation was used to convert area to carbon sequestration potential. By examining the different markets and trading mechanisms for trading in the carbon market, using CS, a marketing strategy for the land units was advised. Results show that due to BLK PNR's history of overstocking, spekboom remains degraded on the study site. This creates an opportunity to restore the vegetation with funding through CT. The sequestration potential of spekboom on BLK PNR was determined through a regional differentiation comparison. The regional differentiation comparison identified that rainfall amount and carbon accumulation are inversely proportional, therefore more arid conditions (<200mm a year, or a dry season longer than seven and a half months) cause spekboom to switch to Crassulacean acid metabolism (CAM) due to water stress, so increasing the rate of carbon accumulation. In wetter environments, where spekboom is not under water stress, it continues in carbon fixation of 3-phosphoglycerate (C3) having a lower carbon accumulation. This is a remarkable finding as CS is known to follow a rainfall gradient: in this instance spekboom is an exception to the norm. Mapped results showed that eCognition classified spekboom poorly, yielding between 64% and 69% correspondence to the accurate manually classified map. As expected three-dimensional area comparative results show that the true surface area on complex terrains was 10% higher than the original (and surveyed) land area of the estate. Results indicate that there are substantial carbon stocks for CT on BLK PNR. This study recommended the most practised form of CT (restoration) for BLK PNR. Over a period of 30 years of restoration on BLK PNR about 46 000 tons of carbon could be sequestrated. At the current price of carbon credits this could accumulate over R3.7 million over the 30-year restoration period. Combining restoration with conservation strategies into one project type has additional favourable characteristics as it takes into account the CS potential of all vegetation communities on the land unit and the ecosystem services it promotes. Conservation of BLK PNR would yield 758 000 tons of carbon. Calculated through emission abandonment, this could be valued at R8-10 million. The economic importance of the vegetation community’s biodiversity on BLK PNR and significant differences between biomes were recorded and implies a total intrinsic value in excess of R830 000 per annum. To date, pilot projects elsewhere have successfully acquired carbon credits for avoided deforestation through the climate, community and biodiversity alliance (CCBA). However, owing to the pilot stage status there is little literature that substantiates the calculation of the monetary value of conservation. This is a fertile area for further research. / AFRIKAANSE OPSOMMING: Die sukkulent-struikplantgemeenskap van Suid-Afrika, in besonder Portulacaria afra (waarna in hierdie studie as Spekboom verwys word), wat in die Struikgewasbioom voorkom, neem ‘n uitsonderlike hoeveelheid koolstofdioksied op (weens die fotosintetiese eienskappe daarvan), veral vir ‘n warm, semi-ariede streek en is in hierdie kapasiteit meer verwant aan woud-ekosisteme. Spekboom het, met betrekking tot koolstofuitruiling (KU) of koolstofhandel, addisionele gunstige eienskappe bo dié van woudsisteme, naamlik lae waterbenutting; potensiaal vir die bestryding van woestynvorming en armoede in ariede omgewings; en die vermoë om brand te weerstaan (Spekboom brand nie), wat sy aantreklikheid as ‘n kommoditeit in KU verhoog, en die betaling vir dienste in die ekosisteem-industrie (BED) verbeter. Grondeienaars wat geïnteresseerd is in die benutting van hul grond vir koolstofopname (KO), word uitgedaag om hul plantgemeenskappe se opnamevermoë en potensiaal vir biodiversiteit te bereken, en gevolglik die hoeveelheid koolstofkrediete wat verkoop kan word, te kwantifiseer. Die doel van die studie was om die KO-vermoë van ‘n geselekteerde eiendomseenheid volgens die oppervlakte onder plantegroei te kwantifiseer en om die waarde van koolstofkrediete wat in die koolstofmark verkoop kan word, vas te stel. Ten aanvang is die probleem van aardverwarming en die uitwerking daarvan op klimaatsverandering in Suid-Afrika uitgelig. KO word beskryf as ‘n proses en oplossing om die hoë en stygende atmosferiese CO2-vlakke te verminder, en die gebruik daarvan in die koolstofmark, om ‘n monetêre waarde te verkry om plantbedekking te bevorder of om biodiversiteit, wat koolstofvoorraad sal vermeerder, te beskerm en te bewaar. Die studieperseel is Bosch Luys Kloof Privaat Natuurreservaat (BLK PNR) in die semi-ariede Karoo. Omrede KO-potensiaal bekend is daarvoor om ‘n reënvalgradiënt te volg, verwag mens dat die semi-ariede Karoo ‘n lae KO-potensiaal sal hê. Hierdie gebied bevat egter Spekboom, ‘n buitengewone struiksoort wat koolstof teen soortgelyke tempo’s as woud-ekosisteme opneem, en behoort daarom voordeel uit KU te trek. Akkurate kartering van hierdie plantegroei is kritiek vir akkurate assessering van koolstofvoorraad. Die KO-potensiaal van alle plantgemeenskappe in die studiegebied is derhalwe vasgestel om die koolstofvoorrade in die totale eiendomseenheid te skat. ArcGIS is gebruik om die plantgemeenskappe (sub-biome) te karteer en eCognition is gebruik om die kartering van die Gamkaruigte (wat Spekboom bevat) deur ‘n objek-georiënteerde benadering tot geoutomatiseerde plantegroeikartering te verfyn. Vir akkuraatheidsassessering is ‘n vergelykbare plantegroeikaart per hand versyfer. Die werklike oppervlakte van die gebied is vir die plantegroeiklassifikasie bereken om akkurate oppervlakberekening van die bergagtige terrein te verseker, en hierdie berekende oppervlakte van die gekarteerde plantegroei is gebruik om oppervlakte na koolstofopname-potensiaal te herlei. Advies oor ‘n bemarkingstrategie vir die grondeenhede is gegee, deur die verskillende markte en uitruilings- of handelsmeganismes vir handel in die koolstofmark te ondersoek. Resultate toon dat weens die BLK PNR se geskiedenis van oorbeweiding, Spekboom op die studieperseel gedegradeer het. Dit skep ‘n geleentheid om die plantegroei met befondsing deur KU te herstel. Die opname-potensiaal van Spekboom op BLK PNR is deur ‘n streeksdifferensiasie-vergelyking bepaal. Die streeksdifferensiasie-vergelyking toon dat hoeveelheid reënval en koolstofakkumulasie omgekeerd eweredig of proporsioneel is, en gevolglik veroorsaak meer ariede omstandighede (<200 mm/jaar, of ‘n droë seisoen van langer as sewe en ‘n half maande) dat Spekboom weens waterstres na Crassulacea-suurmetabolisme (CSM) oorskakel, en sodoende die tempo van koolstofakkumulasie verhoog. In natter omgewings, waar Spekboom nie aan waterstres onderwerp word nie, gaan dit voort met koolstofbinding van 3-fosfogliseraat (C3) en het ‘n laer koolstofakkumulasie. Dit is ‘n merkwaardige bevinding aangesien KO daarvoor bekend is dat dit ‘n reënvalgradiënt volg: in hierdie geval is Spekboom ‘n uitsondering op die reël. eCognition het Spekboom swak onderskei, en slegs ‘n ooreenstemming van tussen 64% en 69% met die akkurate hand-geklassifiseerde gehad. Soos verwag, toon vergelykende resultate van driedimensionele oppervlakte dat die werklike oppervlakte byna 10% hoër is as die oorspronklike (en gemete) grondoppervlak van die eiendom. Resultate dui aan dat daar aansienlike koolstofvoorrade vir KU op BLK PNR is. Hierdie studie beveel die mees gebruikte praktyke van KU (herstelproses) vir BLK PNR aan. Oor ‘n hersteltydperk van 30 jaar op BLK PNR kan ongeveer 46 000 ton koolstof opgeneem word. Teen die huidige prys van koolstofkrediete kan dit meer as R3.7 miljoen oor die hersteltydperk van 30 jaar akkumuleer. Die kombinasie van herstelprosesse en bewaringstrategieë in een tipe projek, hou addisionele voordeel in, omdat dit die KO-potensiaal van alle plantgemeenskappe op die grondeenheid en die ekosisteem-dienste in berekening bring. Bewaring van BLK PNR sal 757 913 ton koolstof lewer. As dit in terme van die staking van uitlatings bereken word, kan dit teen R8-10 miljoen gewaardeer word. Die ekonomiese belangrikheid van die ekosisteem en plantgemeenskap-biodiversiteit op BLK PNR impliseer ‘n totale intrinsieke waarde van meer as R800 000 per jaar. Loodsprojekte elders was suksesvol in die verkryging van koolstofkrediete vir die vermyding van ontbossing deur die klimaat-, gemeenskap- en biodiversiteitsalliansie (KGBA). Vanweë die loodsprojekstatus, is daar egter min literatuur beskikbaar wat die berekening van die monetêre waarde van bewaring staaf. Dit laat ruimte vir verdere navorsing.