Managing invasive alien plants on private land in the Western Cape : insights from Vergelegen Estate
Jansen van Rensburg, Jacques (2017-03)
ENGLISH ABSTRACT: Invasive alien plants (IAPs) are a major threat to biodiversity and ecosystem services in South Africa and are particularly widespread and damaging in the Cape Floristic Region (CFR). Activities such as agricultural development, the establishment of forestry plantations and urbanization can change environments and provide opportunities for IAPs to spread. Large-scale government-funded management initiatives are underway to reduce the extent of invasions in this region, but they face many challenges. Among these challenges are the huge spatial extent of the invasions and difficulties in coordinating management efforts across large areas of invaded land in private ownership. Scarce funds for large-scale clearing operations need to be optimally used, but little information is available on which to base the planning of such complex undertakings.
This investigation used Vergelegen Wine Estate near Somerset West as a case study to investigate the factors that contributed to alien plant invasion on private land. I studied the effectiveness of one large project that set out to reduce alien plant cover, the challenges that the project faced, and the costs associated with long-term operations to clear IAPs on privately-owned land in the CFR. I documented the current (2016) extent of the problem at Vergelegen and estimated the time and resources that would be required to reduce the remaining invasions to a level where the minimum amount of resources are required to maintain the plants at a low density at low cost ('maintenance level'). Evaluation of this project provides insights into how to better manage IAPs on private land in the CFR.
I found a clear link between human activities, changes in land-use, and the spread and proliferation of IAPs. The area occupied by IAPs increased with increasing land-use change, from 8 % cover in 1938 to 40 % in 2004. The management interventions initiated in 2004 reduced dense stands of IAPs by 70 % over the next 10 years. The challenges associated with managing IAPs on private land included multiple interacting environmental and socio-economic factors. The total cost required to clear Vergelegen to a maintenance level was estimated to be between R55 and 80 million (2015-equavalent Rands; R49 million already spent prior to 2016, plus R6 – 30 million that still will be needed, depending on the scenario). Maintaining the estate was estimated to be R5.9 million per 15-year cycle, amounting to between 7.3 and 10.7 % of the cost to bring the estate to a maintenance level.
Using a wide range of research methods and techniques, I have shown that controlling IAPs at the scale of the operation at Vergelegen is possible, but at a significant cost to landowners. The effectiveness of projects, typically constrained by limited funds, could be increased by adopting an outcomes-based approach to ensure that objectives are achieved. Novel funding pathways need to be investigated by government to support clearing initiatives on private land that form part of larger priority areas to ensure success.
AFRIKAANSE OPSOMMING: Indringerplante is 'n groot bedreiging vir biodiversiteit en ekosisteemdienste in Suid-Afrika en is veral wydverspreid en skadelik in die Kaapse Floristiese Streek. Aktiwiteite soos landbou-ontwikkeling, die vestiging van bosbouplantasies en verstedeliking kan omgewings verander en bied geleentheid vir indringerplante om te versprei. Grootskaalse regering befondsing inisiatiewe is aan die gang om die omvang van invalle te verminder in hierdie streek, maar hulle staar baie uitdagings in die gesig. Een van hierdie uitdagings is die groot ruimtelike omvang van die invalle en probleme in die koördinering van die bestuur pogings oor groot dele van binnegevalle land in private besit. Skaars befondsing vir grootskaalse skoonmaak operasies moet optimaal gebruik word, maar min inligting is beskikbaar waarop die beplanning van so 'n komplekse onderneming baseer kan word.
Hierdie ondersoek gebruik Vergelegen-wynlandgoed naby Somerset-Wes as 'n gevallestudie om die faktore wat bygedra het tot indringerplante op private grond te ondersoek. Ek het die doeltreffendheid van een groot projek, wat uit die staanspoor eerstens die indringerplantbedekking verminder, die uitdagings wat die projek in die gesig gestaar het, en die koste wat verband hou met lang termyn bedrywighede om indringerplantbedekking uit te wis op private grond in die Kaapse Floristiese Streek, bestudeer. Ek het die huidige (2016) omvang van die probleme by Vergelegen gedokumenteer, en die beraamde tyd en hulpbronne wat nodig sou wees om die res van die invalle op 'n lae digtheid teen 'n lae koste in stand te hou (onderhoud vlak). Evaluering van hierdie projek bied insig in hoe om beter bestuur toe te pas van indringerplante op private grond in die Kaapse Floristiese Streek.
Ek het 'n duidelike verband gevind tussen menslike aktiwiteite, veranderinge in grondgebruik, en die verspreiding en groei van indringerplante. Die indringerplante het verhoog met toenemende grondgebruiksverandering, vanaf 8 % dekking in 1938 tot 40 % in 2004. Die bestuur ingrypings vanaf 2004 het digte areas van indringerplante met 70 % oor die laaste 10 jaar verminder. Die uitdagings wat verband hou met die bestuur van indringerplante op private grond sluit in verskeie omgewings- en sosio-ekonomiese faktore. Die totale koste om Vergelegen tot op 'n onderhoud vlak te kry, se kosteberaming was tussen R55 en 80 miljoen (2015 - ekwivalent; R49 miljoen reeds bestee teen 2016, plus R6 - 30 miljoen wat nog benodig sal wees, afhangende van die scenario).
Die onderhoud van indringerplante op die landgoed is na raming R5,9 miljoen per 15-jaar-siklus, teen bedrae van tussen 7.3 en 10.7 % van die koste om die landgoed tot op 'n onderhouds vlak te bring.
Met die gebruik van 'n wye verskeidenheid van navorsingsmetodes en tegnieke, het ek gewys dat die beheer van indringerplante op die skaal moontlik is by Vergelegen, maar teen 'n aansienlike koste vir grondeienaars. Die doeltreffendheid van projekte, tipies beperk deur beperkte fondse, kan verhoog word deur die aanneming van 'n uitkomsgebaseerde benadering en om so te verseker dat doelwitte bereik word. Befondsing opsies moet ondersoek word deur die regering met nodige ondersteuning, om die skoonmaak inisiatiewe en suksesse daarvan op private grond, wat deel van groter prioriteit areas vorm, te verseker.
Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101268
This item appears in the following collections: Masters Degrees (Botany and Zoology)161