Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Invasive alien plants (IAPs) are known for their detrimental impacts on biodiversity and ecosystem goods and services. A substantial body of research has contributed to our understanding of their impacts on ecology. In comparison the socio-economic aspects of IAPs, are not well understood. Additionally, valuation practises have usually excluded the positive and the non-monetary impacts (benefits and uses) that IAPs hold for local livelihoods. Holistic valuation has been regarded as imperative for decision-making and managerial frameworks. A study was conducted in Elim on the southern Cape coast of the Agulhas Plain, South Africa, which aimed to explore the various impacts of IAPs on the livelihoods of rural land-users. Individual qualitative interviews were conducted face to face with landholders (referred to as farmers) (N = 12) and individuals from the economically marginalized community (referred to as marginalized community) (N = 12). The grounded theory approach to data analysis was used and results of the coding method used were displayed by means of superscripts. Results indicate that farmers were aware of broader uses of IAPs although they themselves did not utilise them as extensively as members of the marginalized communities. Invasive alien and problem plants that held value for both land-users were not perceived as being „invasive‟. Invasive alien plants were believed to have detrimental impacts on biodiversity and ecosystems goods and services which support people‟s livelihoods. Alien clearing programmes such as Working for Water (WfW) and LandCare have done much to alleviate the socio-economic burden of unemployment in this marginalized community. Aside from the social development aims set out by WfW (i.e. employment of low-income communities, poverty alleviation and skills training), knock-on social development benefits (e.g. feelings of pride, responsibility and awareness as well as conflict management skills) were also realised by individuals from the marginalized community that were previously employed by the programme. Farmers regarded alien clearing and management as a process that demands excessive time, energy and financial resources. On single occasions it was found that farmers employed methods other than the conventional clearing and management strategies (e.g. livestock that feed on IAPs and giving refuse IAP biomass from clearing and felling to neighbouring poor communities). No clear consensus was reached about regarding alien clearing and management but more support is desired from government. Working for Water relies on private landholders for alien clearing as it is required by law. This study emphasizes that stronger relationships between government and private landholders as well as more substantial incentives to clear IAPs on private land are prerequisites if required outcomes are to be achieved. Educating society at large about the detrimental impacts of IAPs is fundamental. Additionally, informing landholders on effective alien clearing methods and policies and legislation pertaining to it are key activities for the South African government. Finally, clearing and management programmes need to consider the benefits that local land-users obtain from IAPs when prioritising areas for the management of alien vegetation. / AFRIKAANSE OPSOMMING: Uitheemse indringerplante (UIPe) is bekend vir die nadelige gevolge wat hulle vir biodiversiteit en ekosisteem goedere en dienste inhou. ʼn Aansienlike liggaam van navorsing het bygedra tot ons begrip van die impak daarvan op ekologie. In teendeel, die sosio-ekonomiese aspekte van UIPe word egter nie goed verstaan nie. Daarbenewens, evalueringspraktyke het gewoonlik die positiewe en nie-monetêre impakte (voordele en gebruike) wat UIPe vir plaaslike lewensbestaan hou, uitgesluit. Holistiese evaluering word as noodsaaklik beskou vir besluitneming en bestuursraamwerke. ʼn Studie was uitgevoer in Elim op die Suid-Kaapse kus van die Agulhas-vlakte, Suid-Afrika. Die doel was om die verskillende aspekte van UIP impakte op die lewensbestaan van landelike grondgebruikers aan te spreek. Individuele kwalitatiewe onderhoude is van aangesig tot aangesig gevoer met grondeienaars (na wie verwys word as boere) (N = 12) en individue van die ekonomies gemarginaliseerde gemeenskap (na wie verwys word as gemarginaliseerde gemeenskap) (N = 12). Die gegronde teorie metode tot data analise was gebruik en die resultate van die kodering metode is vertoon deur middel van boskrifte. Resultate dui daarop dat boere bewus was van ʼn wyer reeks van gebruike van UIPe alhoewel hulle dit nie so ekstensief benut het soos die lede van die gemarginaliseerde gemeenskappe nie. Uitheemse en probleem plante wat waarde gehou het vir beide landgebruikers,was nie soseer beskou as „indringers‟ nie. Daar was geglo dat UIPe nadelige impakte het op biodiversiteit en ekosisteme goedere en dienste wat mense se lewensbestaan ondersteun. Programme soos Werk vir Water (WvW) en LandCare wat fokus op die uitroeiing van UIPe, het baie gedoen om die sosio-ekonomiese laste as ʼn gevolg van werkloosheid in hierdie gemarginaliseerde gemeenskap te verlig. Benewens die sosiale ontwikkelings doelwitte uiteengesit deur WvW (o.a. indiensneming van lae-inkomste gemeenskappe, armoedeverligting en vaardigheidsopleiding), is daar ook domino-voordele (bv. gevoelens van trots, verantwoordelikheid en bewustheid sowel as konflik bestuursvaardighede) aangaande sosiale ontwikkeling ervaar deur individue van die gemarginaliseerde gemeenskap wat voorheen in diens van die program was. Boere beskou die uitroeiing en bestuur van UIPe as ʼn proses wat oormatige tyd, energie en finansiële hulpbronne vereis. Op enkele geleenthede was dit gevind dat boere gebruik maak van metodes anders as die konvensionele skoonmaak-en bestuurs strategieë (bv. vee wat voed op UIPe en biomassa wat na afloop van skoonmaak aan die naburige arm gemeenskappe gegee word). Geen duidelike konsensus is bereik met betrekking tot die uitroeiing en bestuur van UIP nie, maar meer ondersteuning van die regering word verlang. Werk vir Water maak staat op private grondeienaars vir die uitroeiing van UIPe. Hierdie studie beklemtoon dat sterker verhoudings tussen die regering en private grondeienaars sowel as meer aansienlike aansporings om UIPe op private grond skoon te maak ʼn voorvereiste is as verwagte uitkomste bereik wil word. Opvoeding van die breër gemeenskap oor die nadelige impakte van UIPe is fundamenteel. Om grondeienaars in te lig oor effektiewe UIP verwyderingsmetodes asook beleide en wetgewing met betrekking daartoe, is belangrikste aktiwiteite vir die Suid-Afrikaanse regering. Ten slotte, skoonmaak- en bestuursprogramme moet oorweging skenk aan die voordele wat plaaslike landgebruikers put uit UIPe wanneer daar geprioritiseer word vir gebiede vir die bestuur van indringerplante.

The invasion of ecosystems by alien species is a growing threat to the delivery of ecosystem services. This study explored the spatial distribution of water hyacinth in the Benoni Lakes and made analysis of its impact on water availability and usability in order to understand the evolution and its propagation rates. The study used satellite imagery for lake level modelling using Remote Sensing and Geographical Information Systems for calculations of area covered by weeds in each lake from 2002 to 2012.The modelling approach illustrates the potential usefulness in projecting invasive plants under climate change and enabled the quantification of long term changes in aquatic weeds. The results showed that aquatic infestations in lakes may be used as powerful predictors of correlations between plant abundance and climate change. The study therefore informs decision makers to identify areas where invasion is likely to occur and increase surveillance for early invaders. / Environmental Sciences / M. Sc. (Environmental Management)

Thesis (DSc)--Stellenbosch University, 2008. / ENGLISH ABSTRACT: No abstract available / AFRIKAANSE OPSOMMING: Geen opsomming beskikbaar

Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Worldwide, invasive alien plants (IAPs) alter aspects of invaded ecosystems including geomorphology, above-ground vegetation, soil seed banks and soil nutrient regimes, thereby affecting the long-term stability of ecosystems. In many cases these invasions call for various management interventions, including restoration. Effects of alien plant invaders on native ecosystems are widely acknowledged, but compared to terrestrial ecosystems, riparian habitats are poorly studied. Riparian habitats are inherently rich in biodiversity, but are particularly prone to invasion by IAPs because of their dynamic nature and because these ecosystems are affected by many anthropogenic activities. This enhances the proliferation of IAPs, especially trees such as Tamarix spp. (e.g. in the southwestern United States), Salix spp. (e.g. in Australia), and Australian Acacia spp. and Eucalyptus camaldulensis (in South Africa). Initiatives such as the Working for Water (WfW) programme in South Africa that are focusing on clearing IAPs, particularly in riparian zones, have reported much success in the short term, but ecosystem recovery remains limited. There is a poor understanding of the nature of the impacts of invasive trees, and of the opportunities that exist for ecosystem restoration. The objective of my thesis was to investigate the effects of the widespread invasions of Eucalyptus camaldulensis in riparian zones. Methodological constraints have been identified as one reason for limited success of restoration projects. Many studies examining the effects of IAPs used a comparative approach of uninvaded (reference) and invaded sites. However, this approach often fails to separate cause from effect. An experimental removal approach has been suggested as an alternative, but it is often inappropriate for large invasive trees owing to time and cost constraints. I used a comparative gradient approach, involving sampling along a continuum from uninvaded sites, and varying E. camaldulensis invasion densities categorised as “lightly”, “moderately” and “heavily” invaded (hereafter the gradient of invasion), each with four replicates (n = 16). This approach enabled me to detect trends that could be reliably attributed to invasion. Furthermore, my study attempted to provide a comprehensive understanding of the effects of IAPs in invaded ecosystems by considering various components of the ecosystem and integrating their feedback relationships to establish the net effects on ecosystem processes. The riparian zone is a unique ecosystem which provides an opportunity for such a multifaceted study examining and integrating the effects of invasive trees on riparian geomorphology, above-ground vegetation, soil seed banks, and soil properties. I studied the effects of E. camaldulensis invasion in riparian zones along the Berg River in the Mediterranean-type climate zone of the Western Cape, South Africa. I asked the questions 1) Are environmental conditions (i.e. the riparian environment created by geomorphological processes) altered by Eucalyptus invasion and if so, are these conditions less suitable for recruitment of indigenous species? 2. Has Eucalyptus invasion altered the composition of indigenous species (potentially limiting post-clearing propagule supply)? 3: How does Eucalyptus invasion change the composition of the riparian soil seed bank; and its potential to re-initiate ecosystem recovery? 4: Do soil properties (physical and chemical) change with Eucalyptus invasion? Data for all four questions were collected in the same sites to enable cross comparisons. For the first question, I employed photogrammetry techniques in a GIS and remote sensing environment to analyse repeated aerial photographs (1938 -2010) to reconstruct the invasion history and riparian geomorphology evolutionary dynamics. For the second and third questions, I compared richness, diversity, evenness and composition of resident above-ground and seed bank vegetation between uninvaded sites and the gradient of invaded sites. For the fourth question, I compared a set of variables describing physico-chemical properties in uninvaded sites to the gradient of invaded sites seasonally. Results of the geomorphology study showed that the riparian zone has been very dynamic over the 70 years, with a 13.5% net decrease in area. There was evidence of channel narrowing, riverbank steepening and river bed incision in areas that were densely invaded. No significant trends were detected in hydrometeorological data. The above-ground vegetation study revealed that species richness, diversity and structural attributes (e.g. height, relative cover and mean basal diameter) of native species decreased consistently along the invasion gradient. Invasion also altered native and alien plant species composition, both of which showed a high preference for lightly invaded sites. The seed bank study revealed that E. camaldulensis invasion had no significant effect on total and native species richness, diversity and evenness, however the effects were bigger on native than alien species. Alien species density was significantly higher than native species density. Invasion also influenced the composition of the native seed bank. However, native seed banks were more diverse than above-ground plant assemblages with some native fynbos species occurring only in the seed bank. In the soil study, I found that soil pH levels were significantly lower in invaded sites than in uninvaded sites in all seasons. Litter cover and thickness increased significantly with invasion intensity. Soil moisture decreased consistently with invasion intensity while temperature increased in winter and spring. Total macro, micro and available nutrients did not vary significantly along the invasion gradient (p > 0.05), but exchangeable cation content was significantly higher in uninvaded than in invaded sites, especially in winter and spring. Narrowing of river channel and steepening of river banks reduces the suitability of the riparian zone to perform certain ecological functions such as soil seed storage and providing space for vegetation to grow. This reduces opportunities for seedling recruitment and consequently reduces species diversity. Conversely, the reduction of species diversity in above-ground vegetation reduces seed input into the soil leading to depauperate soil-stored seed banks. The abundance of seeds of Acacia mearnsii in the soil-stored seed bank poses a threat of secondary invasions post clearing of E. camaldulensis if this is adopted as a management action. The study was successful in addressing the stated objectives. The transition from a native-dominated riparian plant community to a monoculture of E. camaldulensis over c. 50 years has resulted in marked changes to riparian geomorphology and above-ground vegetation, but has yet to radically change the total soil seed bank and soil nutrient concentrations. The findings offer support to the WfW clearing initiatives and show that potential for recovery of native species after removal of the invasive eucalypts still exists. This knowledge not only enhances effectiveness of restoration and long term management of riparian ecosystems, but also advances the field of riparian ecology and restoration. Further experimental work is needed to establish the mechanisms responsible for the changes associated with Eucalyptus invasion. The contribution of agriculture in shaping channel morphology also needs to be investigated. / AFRIKAANSE OPSOMMING: Die langtermyn stabiliteit van ekosisteme wêreldwyd word bedreig deur uitheemse indringer plante (UIPs) wat, onder andere, die geomorfologie, bo-grondse plantegroei, onder-grondse saadbanke en voedingstofstatus van ekosisteme kan verander. In baie gevalle word bestuursoperasies vir indringer plante vereis, en sluit onder andere herstel (restorasie) in. Die invloed van UIPs op inheemse ekosisteme word wyd erken, maar kennis oor oewerbank-habitatte, in vergeleke met ander terrestriële ekosisteme, skiet steeds tekort. Oewerbank-habitatte is inherent ryk aan biodiversiteit maar uiters sensitief vir indringing deur UIPs. Dit is weens die dinamiese aard van hierdie ekosisteme asook vele menslike aktiwiteite in hierdie tipe habitat. Dit dra by tot die vermeerdering van UIPs, veral bome wat byvoorbeeld insluit Tamarix (tamariske) (bv. in die suid-wes van die Verenigde State van Amerika), Salix (wilger) (in bv. Australië) en die Australiese Acacia (wattel) en Eucalyptus spesies (bloekom) in Suid Afrika. Inisiatiewe soos die Werk vir Water (WvW) program in Suid Afrika fokus juis daarop om UIPs vanuit oewerbank areas te verwyder, en alhoewel groot sukses in die kort termyn behaal is, is die herstel van ekosisteme steeds beperk. Daar is dus min inligting beskikbaar oor die impak van indringer bome en gevolglik ook oor geleenthede vir die herstel van hierdie ekosisteme. My tesis ondersoek die impak van die wydverspreide voorkoms van die indringer, Eucalyptus camaldulensis, in oewerbank-omgewings. Beperkte metodes is tans beskikbaar om die impak van indringer plante te ondersoek, en dit is geïdentifiseer as een van die oorsake vir die beperkte sukses van herstelprojekte. Baie studies ondersoek die effekte van UIPs deur natuurlike areas sonder enige indringer plante te vergelyk met areas waar UIPs voorkom. Hierdie tipe benadering kan ongelukkig, in meeste gevalle, nie onderskei tussen die oorsaak en die impak nie. ʼn Alternatiewe voorstel is om UIPs eksperimenteel te verwyder, maar is ongelukkig nie van toepassing op groot bome nie weens die tyd en kostes verbonde hieraan. Ek het gebruik gemaak van ʼn vergelykende-gradiënt benadering wat steekproefnemings langs ʼn geleidelike kontinuum van natuurlike areas sonder enige indringer plante na areas wat effens gematig, en erg ingedring is (hiernaas bekend as die indringer-gradiënt) deur die indringer, E. camaldulensis. Die steekproefnemings van elke kategorie van indringing (geen, effens, gematig en erg) is vier keer herhaal (n = 16). Hierdie benadering het my toegelaat om neigings te identifiseer wat met sekerheid toegeskryf kan word aan die teenwoordigheid van indringers. My studie het ook verder gemik om ʼn omvattende beskrywing van die impak van UIPs in ekosisteme met indringers te verskaf deur verskeie komponente van die ekosisteem, sowel as hul terugvoer-verhoudinge, in ag te neem, en sodoende die totale effek op ekosisteem prosesse te bepaal. ʼn Oewerbank is ʼn unieke ekosisteem wat ʼn geleentheid bied vir ʼn veelsydige studie wat die impakte van indringer bome op oewerbank-geomorfologie, bo-grond plantegroei, grond saadbanke en grondeienskappe, kan bestudeer en integreer. Ek het die impak van die teenwoordigheid van die indringer, E. camaldulensis in oewerbank areas langs die Bergrivier, wat ʼn Meditereense-tipe klimaat het, in die Wes Kaap, Suid Afrika, bestudeer. My studie het die volgende vrae gevra: 1) Is omgewings-omstandighede (bv. die oewerbank-omgewing geskep deur geomorfologiese prosesse) verander deur die teenwoordigheid van die Eucalyptus indringing, en indien wel, is hierdie omstandighede minder geskik vir inheemse spesies?; 2) Het die indringing van Eucalyptus gelei tot ʼn verandering in die samestelling van inheemse spesie gemeenskappe (moontlik beperkte plant voorplantings materiaal nadat die indringer verwyder is)?; 3) Hoe verander die indringing van Eucalyptus die samestelling van saad teenwoordig in die grond (saad bank) van die oewerbank en het dit die potensiaal om ekosisteem-herstel weer aan die gang te sit?; 4) Verander indringer Eucalyptus grond eienskappe (fisies en chemies)? Data vir al vier vrae is by dieselfde plek versamel om vergelykings te kan tref. Vir die eerste vraag het ek fotogrammetrie-tegnieke in ʼn Geografiese Inligting Stelsel (GIS) en afstandwaarnemings-omgewing toegepas om herhaalde lugfotos (1938-2010) te analiseer om die indringings geskiedenis sowel as die oewerbank se geomorfologiese evolusionêre dinamika saam te stel. Vir die tweede en derde vraag, het ek die aantal, diversiteit, gelykheid en samestelling van die bo-grond en saad bank plantegroei tussen natuurlike (geen indringers) en die gradiënt met indringers vergelyk. Vir die vierde en laaste vraag, het ek ʼn stel veranderlikes wat die fisies-chemiese eienskappe van die natuurlike omgewing sonder indringers beskryf, vergelyk met die eienskappe van die indringers gradiënt op ʼn seisoenale basis. Die resultate van die geomorfologiese studie wys dat die oewerbank omgewing baie dinamies was oor die afgelope 70 jaar met ʼn totale afname van 13.5% in rivieroewer-area in die gebied wat bestudeer is. Daar is ook bewyse vir ʼn vernouing van die kanaal, toename in die steilte van die rivierbank sowel as insnyding in die rivierbedding in areas wat ernstige indringing ervaar. Daar was geen beduidende neigings in die hidro-meteorologiese data nie. Die studie van die bo-grondse plantegroei het gewys dat die aantal plantspesies, diversiteit en strukturele kenmerke (bv. hoogte, dekking en gemiddelde basale diameter) van inheemse spesies afneem soos wat die indringings gradiënt toeneem. Indringing verander ook die inheemse sowel as uitheemse plant spesies samestelling. Beide inheemse en uitheemse spesies het areas wat slegs effense indringing wys, verkies. ʼn Studie van die saad bank (aantal sade in die grond) het gewys dat die indringer, E. camaldulensis geen merkwaardige invloed op die aantal, diversiteit en gelykheid van die totale en inheemse spesies teenwoordig gehad het nie. Die aantal uitheemse spesies was merkwaardig meer as die aantal inheemse spesies. Alhoewel indringing ook die samestelling van die inheemse saadbank beïnvloed het, was die inheemse saad bank, waarvan sommige spesies slegs daar voorgekom het, meer divers as die bo-grond plant samestellings. ʼn Studie van die grond het gewys dat die pH vlakke, afgesien van die seisoen, aansienlik laer is in die areas met indringers in vergeleke met areas sonder die indringers. Die hoeveelheid en dikte van plantmateriaal op die grond neem ook toe met ʼn toename in indringers. Die waterinhoud van die grond het afgeneem met ʼn toename in indringers en temperatuur het verhoog in beide winter en lente. Die totale makro- en mikrovoedingstowwe het nie merkwaardig gewissel saam met die indringingsgradiënt nie (p > 0.05), maar die uitruilbare katioon inhoud was aansienlik hoër, veral in die winter en lente-maande, in die areas sonder indringers in vergelyking met die areas met indringers. Vernouing van rivierkanaal en versteiling van rivieroewers verminder die geskiktheid van die oewersone om sekere ekologiese funksies te verrig soos grond-saadstoring en die verskaffing van ruimte vir plante om te groei. Dit verminder geleenthede vir werwing van saailinge en verminder gevolglik spesiediversiteit. Aan die ander kant, die vermindering van die spesiediversiteit in die bogrondse plantegroei verminder saadinsette in die grond en dit lei tot verarming van grondgestoorde saadbanke. Die oorvloed van sade van Acacia mearnsii in die grondgestoorde saadbank hou die bedreiging van sekondêre indringing in na die skoonmaak van E. camaldulensis indien dit wel as 'n bestuursaksie aangeneem word. Hierdie studie het die uiteengesette doelwitte suksesvol aangespreek. Die oorgang van ʼn oewerbank-gemeenskap wat hoofsaaklik uit inheemse plante bestaan na ʼn gemeenskap wat slegs uit E. camaldulensis bestaan, oor ʼn periode van ongeveer 50 jaar, het duidelike veranderinge tot gevolg gehad. Hierdie veranderinge is veral opmerklik in die oewerbank-geomorfologie en bo-grondse plantegroei, maar tot op hede is dit nog nie so opmerklik in die saadbank en grond-voedingstowwe konsentrasies nie. Hierdie bevindinge bied ondersteuning aan die WvW verwyderings-ondernemings en wys dat daar wel moontlike herstel van inheemse spesies kan wees na die verwydering van die indringer Eucalyptus. Hierdie kennis dra nie net by tot verhoogde effektiwiteit van herstelwerk en langtermyn-bestuursplanne nie, maar ook tot die navorsingsveld van oewerbankekologie en-herstel. Verdere eksperimentele navorsing word benodig om die moontlike meganismes wat verantwoordelik is vir die waargeneemde veranderinge, geassosieerd met Eucalyptus indringing, te verduidelik. Die bydrae van landbou tot die vorming van kanaal morfologie moet ook verder bestudeer word.

Thesis (MScConEcol)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Soil respiration (Rs) is a major component of CO2 emissions and the global carbon balance. In the context of global change it of interest to understand seasonal patterns of RS in fynbos riparian ecosystems, particularly in invaded-riparian ecotones of these Mediterranean type ecosystems (MTE's) in the Western Cape, South Africa. Riparian ecotones are three dimensional transitional zones that provide multiple ecosystem services and functions and they act as the linkage between terrestrial and aquatic ecosystems where key ecological and geomorphological processes occur. Riparian ecotones are highly prone to disturbance, and because of this reason are also vulnerable to invasion by invasive alien plants (IAPs), notably Acacia species. Invasion by IAPs is considered one of the major threats to global change and biodiversity causing extensive ecological, economical, and social impacts. In south-western Cape, more than two thirds of the riparian environment is invaded to some extent, IAPs replacing the well adapted native species along river systems. In particular, impact of IAPs on soil respiration (Rs) may be relevant, with consequences for ecosystem function and services. Clearing of invaded riparian zones initiated by the Working for Water program has been a successful in eradicating alien plants within riparian areas even though recovery after alien clearing is lagging at many sites, and knowledge on repair of ecosystem function is lacking. Various studies have generated knowledge on carbon cycling and Rs in forests, savanna, grasslands, tundra and Mediterranean shrublands, but little is known about Rs in riparian zones, and even less about soil CO2 efflux in invaded riparian fynbos riparian ecotones. The objective of this study was to contribute to a better understanding and quantifying the effect and impact of IAPs on carbon cycling between and across riparian ecotones with different invasion status: natural, invaded, and cleared. The study areas were located in the south-western Cape and measurements of Rs, soil temperature, soil moisture, root mass, litter mass, and soil properties were carried out in riparian soils of the mountain and transitional stream longitudinal river sections, and uplands fynbos areas of six different perennial river systems. In each site, four to five transects were laid out with one sampling site of each landscape position (wet bank, dry bank, and terrestrial areas) giving a total of 12 to 15 samples per site. Soil respiration measurements were taken over a period of two years, and were done seasonally. Results from this study showed that Rs was different among seasons with highest soil respiration rates in summer. Soil CO2 efflux increased in response to warm and dry conditions during summer, while seasonal soil CO2 efflux declined in autumn and winter in response to wet and cold soil conditions. The large increase in soil CO2 efflux response to warm and dry periods when temperature was 25 to 30 °C over all riparian sites and was highest in invaded sites compared to the natural and cleared sites. A significant difference was found between sites with different statuses with invaded sites leading seasonal Rs rates. Natural and cleared sites did not differ significantly in their CO2 efflux rates, suggesting that clearing of IAPs may put invaded ecosystems on a trajectory of restoration. There were also differences in terms of landscape positions; dry banks zones of the invaded sites had higher rates compared to wet banks and the uplands areas. Our results further suggest that roots are the most important component of overall Rs rates, rather than microbial respiration. When we incubated soils minus roots, little difference was evident, either when viewing the results by invasion status or by landscape position, which suggest that inherent soil differences in terms of microbial respiration were not different. We also use a trenching approach to further investigate this, and though we found Rs to decline significantly, trends later suggest that decomposition of fine and course roots likely obscured the decline in overall Rs due to root respiration. Overall, our results showed that clearing of invaded riparian zones will likely lead to successful restoration of soil functioning in terms of C cycling. Clearing of Acacia-invaded riparian ecotones will likely lead to a decline in root density, and which removes a major component of overall Rs. These results make the investigation of the C balance of invaded riparian ecotones and terrestrial areas critical in order to assess their contribution to regional C cycles. / AFRIKAANSE OPSOMMING: Grondrespirasie (Rs) is 'n belangrike komponent van CO2 uitstroming en die globale koolstofbalans. Binne die konteks van globale verandering is dit van groot belang om die seisoenale patrone van Rs in fynbos oewer ekosisteme, veral in indringer-oewer ekotone, in die Meditereense tipe ekosisteme (MTE's) in die Wes- Kaap, Suid- Afrika te verstaan. Oewerekotone is drie-dimensioneel oorgangssones wat veelvuldige ekosisteem dienste en funksies verskaf. Hulle dien as die verbinding tussen terrestriële en water-ekosisteme waar kern ekologiese en geomorfologiese prosesse plaasvind. Oewerekotone is hoogs vatbaar vir versteuringe, en as gevolg van hierdie rede, is hul ook kwesbaar vir indringing deur indringer plante (IAPs), veral Acacia spesies. Indringing deur IAPs word beskou as een van die groot bedreigings tot en met globale verandering en biodiversiteit, wat ekstensiewe ekologiese, ekonomiese, en sosiale impakte veroorsaak. In die suid- westelike Kaap word meer as twee derdes van die oeweromgewing tot 'n mate binnegedring. IAPs vervang die goed aangepaste inheemse spesies langs riviersisteme. Die impak van IAPs, spesifiek op grondrespirasie mag substansieël wees, met gevolge vir ekosisteem funksies en dienste. Opruiming van hierdie spesifieke oewer sones, geinisieer deur die Working for Water program, was suksesvol in die uitroeing van indringer plante binne oewer areas. Alhoewel herstel na indringer opruiming op baie terreine agter is, is kennis oor die herstel van ekosisteemfunksies gebrekkig. Verskeie studies het kennis ontwikkel oor koolstofsiklisering en Rs in woude, savanna, graslande, tundra en Meditereense struiklande, maar daar is minimale informasie oor oewersones,en nog minder oor grond CO2 uitstroming in indringer oewer fynbos en oewer ekotone. Die doel van hierdie studie is om 'n bydrae te lewer koolstofsiklisering beter te verstaan, en die impak van IAPs op koolstofsiklisering te kwantifiseer tussen en oor oewerekotone met verkillende indringer statusse: natuurlik, binnegedring en skoongemaak. Die studie areas was geleë in die suid- westelike Kaap, en maatstawe van Rs, grond temperature, grondvogtigheid, wortelmassa, plantafvalmassa, en grondeienskappe is uitgevoer in oewergrond van die berg en transisionele stroom longitudinale rivier seksies, asook terrestriële fynbos areas van ses verskillende standhoudende riviersisteme. In elke area is vier tot vyf transekte uitgelê met een monsternemingsarea van elke landskapsposisie (nat bank, droë bank en terrestriële areas) met 'n totaal van 12 tot 15 monsters per area. Grondrespirasie maatstawe is geneem oor 'n periode van twee jaar, en is seisoenaal uitgevoer. Resultate van die studie het getoon dat Rs verkil het tussen seisoene, met die hoogste grondrespirasietempo in die somer. Grond CO2 uitstroming het toegeneem in reaksie op warm en droë kondisies gedurende somer, terwyl seisoenale grond CO2 uitstroming afgeneem het in herfs en winter in reaksie op nat en koue grond kondisies. Die grootste toename in grond CO2 uitstroming was in reaksie op warm en droë periodes wanneer temperature gewissel het tussen 25 tot 30˚C oor alle oewersones, en was die hoogste in binnegedringde sones, vergeleke met die natuurlike en skoongemaakte terreine. 'n Beduidende verskil is gevind tussen terreine met verskillende statusse in CO2 uitstromingskoerse‚ 'n aanduiding dat opruiming van IAPs binnegedringde ekosisteme op 'n trajek van restorasie plaas. Daar was ook verskille in terme van landskapsposisies; droë bank sones van die binnegedringde terreine het hoër tempos gehad, vergeleke met die nat bank en die hoogland areas. Ons resultate dui verder aan dat wortels, eerder as mikrobiologiese respirasie, die mees belangrike komponente van Rs koerse uitmaak. Toe ons grond minus wortels inkubeer, is min verskille opgemerk, as gekyk word na die resultate deur indringer status of landskapsposisie, wat toon dit dat inherente grondveskille in terme van mikrobiologiese respirasie nie verskillend is nie. Ons het verder ook 'n sloot-benadering gebruik om verdere ondersoek hierop in te stel, en alhoewel ons bevind dat Rs aansienlik afgeneem het, dui neigings later aan dat afbraak van fyn en growwe wortels die afname in gehele Rs as gevolg van wortel respirasie waarskynlik verdoesel. Ons resultate dui daarop dat opruiming van binngedringde oewers klaarblyklik sal lei tot suksesvolle restorasie van grondfunksionering in terme van C siklisering. Opruiming van Acacia- binnegedringde oewer ekotone sal vermoedelik lei tot 'n afname in worteldigtheid, en wat 'n belangrike komponent van die gehele Rs kan verwyder. Hierdie resultate maak die ondersoek van die C balans van binngedringde oewer ekotone en terrestriële areas krities, om sodoende hulle bydrae tot streeksgewyse C siklusse te asseseer.

>Magister Scientiae - MSc / The occurrence and spread of Invasive Alien Plants (IAPs) is a threat to global water resources and natural ecosystems due to high water use rates. With the current climate change projections and their ability to survive extreme environmental conditions, these species pose a huge threat to grazing resources, water availability and ecosystems in general. Routine monitoring and understanding their distribution and potential vulnerable areas is fundamental as it provides the requisite baseline information to guide clearing efforts and other related management and rehabilitation initiatives.

Dealing with invasive alien species (IAS), have become a more common problem for themunicipalities of Sweden over the past years. IAS is one of the largest threats to biologicaldiversity and the spread of invasive alien plants is caused by transportation, travel, climatechanges but also infrastructure projects. Thus, the risk of spreading them must be dealt withearly in the progress of handling soil masses. This study examines if recommended routines(with the aim of reducing the risk of spreading invasive plants) are incorporated inmunicipalities and how well they function. It further examines if routines for invasive plantsare related to the size of the municipality, due to differences in economy and resources. Aform was sent to all 290 municipalities in Sweden and 132 answered. The results show thatmany of the recommended routines are not well incorporated across municipalities. Routineswith demands of knowledge about IAS to coworkers or entrepreneurs is less functioning thanroutines of intern information, such as where invasive plants are established on propertiesthat’s own by municipalities. Results show that available resources and economy due to sizeof the municipalities do not influence the level of incorporation of routines. It’s warranted formunicipalities to establish functioning routines within the organization to prevent increasingspread of invasive alien plants in an early stage. The issue should be addressed in decisionsmade by politicians to confirm the level of priority since the benefits of prevention is higherthan benefits of elimination and eradication.

Thesis (MScConEcol)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Acacia saligna, or Port Jackson, is an Australian Acacia which has spread throughout the Western and Eastern Cape provinces of South Africa where it has become invasive and a prominent feature of the vegetation. In areas where A. saligna establishes it replaces natural vegetation, alters ecosystem processes and interferes with agricultural practices. Consequently large management efforts have been made to eradicate this invasive alien tree. However, its large and persistent soil stored seed bank, even in the presence of management and biological control agents, poses a serious obstacle to its successful removal. Furthermore the reproductive output and the size of the seed bank of A. saligna over its whole distribution as well as the variation of seed production and the seed bank with environmental conditions in time and space is poorly known. Understanding the seed bank dynamics of A. saligna in time and space is essential for reducing invasive success and achieving management objectives. This study has filled this knowledge gap through studying the seed production and seed bank of A. saligna over its invaded range in South Africa, including how environmental factors influence these factors in time and space. The seed rain of A. saligna was assessed at 10 sites across its distribution in South Africa. The seed rain of A. saligna at the sites was determined through the use of seed rain traps. Twenty five traps were placed out at every site during November 2010 (pre-dehiscence) which was collected again during April 2011 (postdehiscence). The seed bank of A. saligna was estimated through sampling at 25 sites across its distribution range in South Africa. The seed bank was sampled during April 2010 (postdehiscence), November 2010 (pre-dehiscence) and April 2011 (post-dehiscence) through taking 50 litter and soil samples at every site which gave a total sampling size of 3 750 for both the seed in the soil and litter over its distribution in South Africa. In addition the average tree diameter, tree density, average number of Uromycladium tepperianum induced galls per tree, the summer aridity index, De Martonne aridity index, winter concentration of precipitation, temperature of coldest month and the soil texture for every site was determined. The damage done by the seed feeding weevil, Melanterius compactus, was also estimated for the seed rain study sites. Water availability during the hot summer months was assessed as the most important factor governing seed production and seed bank size. Riparian and non-riparian water regimes were shown to be important in understanding the seed bank dynamics of A. saligna over its distribution range in the Cape Floristic Region. In non-riparian A. saligna populations the seed production and consequently the size of the seed bank and its rate of accumulation is limited by both water and temperature and in riparian A. saligna populations, only by temperature. Therefore, two environmental gradients influence the seed bank dynamics of Port Jackson in South Africa. In non-riparian A. saligna populations the number of seed produced and the accumulation of seed in the seed bank generally increases along the west coast of South Africa from Clanwilliam towards Cape Town and along the south coast from Cape Town towards Port Elizabeth. Seed banks are larger closer to the coast, when A. saligna populations of similar age are compared. In riparian A. saligna populations, the number of seed produced generally increases from Port Elizabeth towards Cape Town and from Cape Town towards Clanwilliam, again, with larger seed banks being accumulated closer to the coast, when populations of similar age are compared. This study provides managers with a useful tool for prioritising management efforts. / AFRIKAANSE OPSOMMING: Acacia saligna of Port Jackson is ‘n indringerplant in Suid-Afrika wat afkomstig is uit Suid-Wes Australië. Acacia saligna is ‘n onmisbare kenmerk van die plantegroei in die Wes en Oos-Kaap. Waar Port Jackson vestig, verplaas dit natuurlike plantegroei, verander dit ekosisteem prossesse en verhinder dit landbou praktyke. Gevolglik is groot bestuurspogings aangewend om hierdie indringer plant uit te roei. In die teenwoordigheid van bestuursprogramme en biologiese beheer bly A. saligna lewensvatbaar as ‘n gevolg van die plant se groot blywende grond saadreserwes. Verder is die saad produksie en saadbank grootte van A. saligna oor sy verspreiding bereike asook hoe dit met omgewingstoestande in tyd en ruimte interreageer en varieer grootendeels onbekend. ‘n Goeie en omvattende begrip van die saadbankdinamika is belangrik om die indringings vermoë van die plant te verlaag en om bestuursdoelwitte te bereik. Hierdie studie vul die bestaande gaping in die kennis aangaande die saadbank dinamika van A. saligna aan deur die saadproduksie en die saadreserves van die indringerplant oor sy verspreiding in Suid-Afrika te bestudeer, insluitend hoe omgewingstoestande die saadbankdinamika beïnvloed in tyd en ruimte. Die saadreën vir 10 A. saligna populasies was bepaal deur die gebruik van saadlokvalle. Vyf-entwintig lokvalle was uitgeplaas in elke bestudeerde Port Jackson perseel gedurende November 2010 (voor-saadval) wat weer gaan haal is gedurende April 2011 (na-saadval). Die saadbank van A. saligna was bepaal in 25 populasies van die boom gedurende April 2010 (na-saadval), November 2010 (voor-saadval) en April 2011 (na-saadval) deur die neem van 50 blaar- en grondmonsters by elke perseel wat ‘n totaal van 3 750 blaar- en grondmonster gee oor die hele verspreiding van A. saligna in Suid-Afrika. Verder is die gemiddelde boomdeursnee, boomdigtheid, gemiddelde Uromycladium tepperianum geinduseerde galle per boom, die somers droogtheids indeks, De Martonnes droogtheids indeks, die winter konsentrasie van presipitasie, die temperatuur van die koudste maand en die grond tekstuur van elke Port Jackson stand bepaal. Die skade wat die saad voedende kewer, Melanterius compactus, aanrig aan die sade van A. saligna is ook vir die persele waar die saadreën eksperiment uitgevoer is, bepaal. Die beskikbaarheid van water vir A. saligna in die droë somermaande is bepaal as die belangrikste faktor wat die grootte van die saadproduksie en saadbank beïnvloed. Oewer en nie-oewer water omgewings is bevind as noodsaaklik om die saadbank dinamika van A. saligna oor die indringerplant se verspreidingareas in die Kaap Floristiese Streek te verstaan. In nie-oewer A. saligna populasies word saadproduksie en gevolglik die grootte en tempo van akkumulasie van die saadbank deur beide water en temperatuur omstandighede beperk, terwyl in oewer A. saligna populasies word die indringerplant slegs deur temperatuur omstandighede beperk. Gevolglik blyk dit dat twee water beskikbaarheids gradiënte bestaan waarop die plant reageer wat dan uitgedruk word in die plant se saad produksie en gevolglik ook die plant se saadbank. In nie-oewer Port Jackson populasies neem die saadproduksie en die tempo waarteen die saadbank akkumuleer algemeen toe langs die weskus van Clanwilliam na Kaapstad en van Kaapstad na Port Elizabeth, met grootter saadproduksie en saadbank akkumulasie nader aan die kusgebiede, wanneer A. saligna populasies van dieselfde ouderdom vergelyk word. In oewer Port Jackson populasies neem die saadproduksie en die tempo waarteen die saadbank akkumuleer algemeen toe van Port Elizabeth na Kaapstad en van Kaapstad na Clanwilliam, met grootter saadproduksie en saadbank akkumulasie nader aan die kusgebiede, wanneer A. saligna populasies van dieselfde ouderdom vergelyk word. Hierdie studie verskaf bestuursplanne met ‘n nuttige raamwerk waarvolgens uitroeiing en beheer programme vir A. saligna beplan kan word.

Thesis (MScConsEcol (Conservation Ecology and Entomology))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Riparian ecosystems of the Mediterranean south-western Cape region are projected to experience significant decreases in streamflow due to climate change and increased demands for water associated with human demographic trends and increasing living standards. Aggravating this problem are woody invasive alien plants, such as Acacia mearnsii, whose impacts, including those on catchment water yields, have justified extensive eradication programmes such as Working for Water (WfW). WfW has been highly successful in managing invasive alien species in some areas, while at the same time enhancing the quality of life of poor South Africans. Unfortunately, the managers of these eradication initiatives often experience a lack of information on the species- and site-specific ecological properties that may aid in prioritising sites more prone to invasion, essentially inhibiting accurate management output. Knowledge, such as that associated with the possible future distribution of invasive species in a changing environment, may help to optimise eradication initiatives. I therefore determined whether woody plants portray different physiological (vulnerability to cavitation) and wood anatomical traits (wood density, vessel resistance to implosion, vessel lumen and wall diameters) across three prominent riparian zones in the south-western Cape that each differ in streamflow quantity – to gain a mechanistic understanding of how woody species, especially invasive species, adapt their hydraulic strategy across this proxy for water availability. Using factorial ANOVA’s, to distinguish any differences in plant physiological and wood anatomical responses to water availability within and between species, showed Acacia mearnsii having consistently higher drought-tolerance (lower P50 values and denser wood) compared to native species under reduced water availability. These results supported the significant variation in drought-tolerance strategies that exist within and between taxonomically different species across different environments. Water availability thus has a strong selective effect on functional traits of species; however, minimum water potentials were more useful in describing in situ hydrological conditions than streamflow. Additionally, a non-causal relationship between wood anatomical traits and drought-induced cavitation was observed. Therefore, using only wood anatomical measurements to assess drought-tolerance of species might not be accurate across all species. This mechanistic approach to assess the invasive potential of species under projected drier conditions has great practical value. It can be used to improve species selection for restoration initiatives, and is of great value for future use in prioritizing eradication programmes. / AFRIKAANSE OPSOMMING: Rivieroewer ekosisteme in die Mediterreense Suidwes-Kaap streek kan groot afnames in stroomvloei verwag, wat meestal toegeskryf kan word aan klimaatsverandering en die verhoogde aanvraag na water geassosieerd met stygende populasiegrootte. Uitheemse indringerplante soos Acacia mearnsii vererger hierdie probleem. Laasgenoemde spesies plaas groot druk op opvanggebiede se water opbrengs, en vorm grootliks die rede waarom uitroeiing programme soos Werk vir Water (WfW) gestig is. WfW het al groot suksesse behaal in die bestuur van uitheemse indringerplante, en terselfdertyd die lewenskwaliteit van arm Suid-Afrikaners verhoog. Ongelukkig sukkel hierdie indringer uitroeiing inisiatiewe telkens met ongenoegsame bewyse wat kan help om leiding te verskaf by die prioritisering van areas meer geneig tot indringing. Die gevolg is dat onvoldoende bestuurs besluite gemaak kan word. Gevolglik sal kennis geassosieerd met die moontlike toekomstige verspreiding van hierdie indringerplant in ʼn veranderlike omgewing help om uitroeiing programme meer akkuraat te stel en gevolglik waardevol wees t.o.v. prioritisering van kwesbare areas. Die doel van hierdie studie was om die kwesbaarheid van sleutel inheemse houtagtige rivier spesies en veral die dreigende indringerplant Acacia mearnsii, te bestudeer in terme van verlaagde stroomvloei soos voorspel vir die Wes-Kaap fynbos ekosisteem. Deur te bepaal of houtagtige plante verskillende fisiologiese (kwesbaarheid teen xileem blokkasie) en anatomiese (hout digtheid, vat weerstandbiedendheid teen inmekaarkolking, vat holte en wand deursnee) hidrologiese eienskappe tentoonstel gemeet tussen drie prominente rivieroewer sones in die suidwes Kaap wat variëer in stroomvloei kwantiteit, verskaf ʼn meganistiese begrip van hoe spesies, veral die indringerplante, hul hidrologiese strategieë ten opsigte van droogtes kan aanpas. Faktoriële ANOVAS’s tussen spesies en liggings het getoon dat beide plant fisiologiese en hout anatomiese data beduidend variëer tussen taksonomies verskillende spesies. Veral Acacia mearnsii het deurgaans laer P50 waardes asook hoër houtdigtheid getoon, ‘n teken van hierdie spesies se verhoogde droogte toleransie in vergelyking met die inheemse spesies. Wat beduidend is is dat spesies-spesifieke lewensstrategieë ten opsigte van droogte toleransie in hierdie rivieroewer sones voorkom. Resultate het bevestig dat water beskikbaarheid ʼn groot rol speel in die seleksie van funksionele karaktereienskappe in plante, maar, dat minimum water potensiaal meer akkuraat was om in situ hidrologiese toestande te beskryf as wat stroomvloei kon. Die verhouding tussen plant fisiologiese en hout anatomiese karaktereienskappe was indirek as gevolg van spesies-spesifieke lewensstrategieë. Gevolglik sal die allenige gebruik van hout anatomiese eienskappe om droogte toleransie in plante te assesseer onakkuraat wees omdat daar ʼn swak verhouding tussen hout anatomie en droogte-geïnduseerde xileem blokkasie bestaan. ʼn Meganistiese benadering om die indringing potensiaal van spesies onder voorspelde droër kondisies te assesseer, asook om spesies seleksie vir restourasie doeleindes op te skerp, is prakties uitvoerbaar, en van groot waarde vir toekomstige gebruik in uitroeiing en restourasie inisiatiewe.

The invasion of ecosystems by alien species is a growing threat to the delivery of ecosystem services. This study explored the spatial distribution of water hyacinth in the Benoni Lakes and made analysis of its impact on water availability and usability in order to understand the evolution and its propagation rates. The study used satellite imagery for lake level modelling using Remote Sensing and Geographical Information Systems for calculations of area covered by weeds in each lake from 2002 to 2012.The modelling approach illustrates the potential usefulness in projecting invasive plants under climate change and enabled the quantification of long term changes in aquatic weeds. The results showed that aquatic infestations in lakes may be used as powerful predictors of correlations between plant abundance and climate change. The study therefore informs decision makers to identify areas where invasion is likely to occur and increase surveillance for early invaders. / Environmental Sciences / M. Sc. (Environmental Management)