Grassland rehabilitation after alien invasive tree eradication: landscape degradation and sustainability in rural Eastern Cape

Okoye, Perpetua Ifeoma (2016-03)

Thesis (MSc)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: Rehabilitating grassland, a threatened biome, requires a comprehensive management approach that integrates the environmental, economic and social matters in sustaining this system. In the Eastern Cape of South Africa, three Quaternary catchments (QCs) (T35B, T12A & S50E) have been severely invaded by Invasive Alien Plants (IAPs) as well as altered by agrarian intensification and human development. Working for Water (WfW) Alien Plant Clearing Programme have been clearing IAPs in these catchments for the past twelve years. The current research aimed at establishing various degradation gradients occurring in the QCs. This was done by conducting land cover classification and change analysis over time, evaluating soil quality and assessing the success of the WfW program by quantifying the net primary production (NPP) and evapotranspiration (ET) trends on the cleared areas. A novel management scheme for decision makers, driver-pressure-state-impact-response (DPSIR) framework, was therefore suggested for managing these QCs sustainably. The soil analysis showed that phosphorus (P) levels are significantly different (P<0.05) between invaded, cleared and natural sites. High nitrogen (N) and pH were associated with Acacia proliferation in acidic soils. Object based image analysis (GEOBIA) was used for the land use land cover (LULC) classification using Landsat 8 OLI & TIRS imagery. LULC change analyses were carried out on two reference bases [National land cover (NLC) 2000 & Edited NLC (ENLC) 2000]. Land cover change analysis was facilitated by using a framework introducing labels to describe land cover change. Annual MODIS ET (MOD16)/NPP (MOD17) data were used to evaluate the rehabilitation progress in T12A using WfW clearing data. A DPSIR management framework, structuring the sustainable indicators at the QCs in a logical manner, was developed for decision and policy makers for dealing with management issues related to land use, water resources and soil quality management. The present research recommends that additional soil samples need to be collected for validation of soil nutrients status. Medium resolution Landsat imagery used for the LULC mapping provided accuracies of greater than 80%, but could not differentiate between invasive and indigenous trees. Hyperspectral or higher resolution imagery should be explored for mapping and delineating IAPs. Using coarse resolution MODIS products to model ET/NPP did not provide adequate detail of the cleared patches to describe the actual status of WfW clearings and their rehabilitation progress.

AFRIKAANSE OPSOMMING: Rehabilitasie van grasvelde, ‘n bedreigde bioom, vereis 'n omvattende benadering wat die omgewing, ekonomiese en sosiale aangeleenthede in die handhawing van 'n stelsel integreer. In die Oos-Kaap provinsie van Suid Afrika is drie kwaternêre opvanggebiede (QCs) (T35B, T12A S50E) erg deur indringerplante (IAPs) asook verandering deur landbou intensifisering en menslike ontwikkeling ge-affekteer. Die Working for Water (WfW) se uitheemse plant program roei alreeds vir die afgelope twaalf jaar IAPs in hierdie opvanggebiede uit. Hierdie navorsing is daarop gemik om verskeie agteruitgangsgradiënte wat in die QCs voorkom te bepaal deur die evaluering van grondkwaliteit, uitvoer van landbedekking klassifikasie en veranderingsontleding asook. Die WfW rehabilitasie pogings van die afgelope twaalf jaar is deur kwantifisering van die Netto primêre produksie (NPP) en evapotranspirasie (ET) tendense vir die skoongemaakte gebiede beoordeel. ‘n Nuwe bestuurskema, gebaseer op die drywer-druk-stand-impak-reaksie (DPSIR) raamwerk, word ter bevordering van volhoubaarheid in die QCs vir besluitnemers aanbeveel. Die analise van grondvoedingstowwe het getoon dat fosfor (P) beduidend (P<0.05) tussen indringer, skoongemaakte en natuurlike terreine verskil. Hoë stikstof (N) en pH hou verband met Acacia teenwoordigheid in suur gronde. Objekgerigte beeldanalise (GEOBIA) is gebruik vir die grondgebruik grondbedekking (LULC) klassifikasie met behulp van Landsat 8 OLI & TIRS beelde. LULC veranderingsanalise is op twee verwysingsbasisse [National land cover (NLC) 2000 en gewysigde NLC (ENLC) 2000] uitgevoer. Grondbedekkingsveranderingsanalise is deur ‘n raamwerk gefasiliteer wat gebruik maak van etikette om verandering te beskryf. Jaarlikse MODIS ET (MOD16) / NPP (MOD17) data is gebruik om die rehabilitasie vordering met behulp van WfW skoonmaakdata in T12A te evalueer. ‘n DPSIR bestuursraamwerk, wat die strukturering van die volhoubaarheidaanwysers vir die QCs op 'n logiese manier organiseer, is ontwikkel om besluitneming in die hantering van bestuurskwessies met betrekking tot grondgebruik, waterbronne en grondkwaliteitsbestuur te ondersteun. Hierdie navorsing beveel aan dat bykomende grondmonsters versamel moet word om die grondvoedingstofstatus te bevestig. Medium resolusie Landsat beelde wat vir die LULC kartering gebruik is het akkuraathede van meer as 80% verskaf, maar kon nie tussen indringer en inheemse bome onderskei nie. Hiperspektrale of hoër resolusie beelde moet vir kartering van IAPs ondersoek word. Die gebruik van growwe resolusie MODIS produkte om ET / NPP te modelleer het nie voldoende detail vir die skoongemaakte areas verskaf om die werklike status van WfW uitroei en rehabilitasie vordering te beskryf nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98626
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