An evidence base for improving management effectiveness of alien plants in protected areas : relationships of scale, efficiency and strategy

Cheney, Chad (2019-03)

Thesis (PhDConsEcol)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Invasive alien plants (IAP) pose a direct threat to the biodiversity of South Africa. Extensive invasion has occurred in many of the country’s protected areas, requiring direct management. In many protected areas, including Table Mountain National Park, the selected study area for this investigation, IAP control programmes were established more than 20 years ago and are well resourced. However, limited tangible success, in terms of reduction of overall alien distribution and density has been achieved. It therefore became necessary, both from an economic and conservation perspective, to investigate the likely future trajectory of control programmes and to determine the main drivers of management success. This dissertation aims to provide a scientific rationale for improving management of IAP programmes in four key management areas. Firstly, the current accuracy of distribution and abundance data that is used in management decision making, is determined (Chapter 2). This is an important starting point for understanding management effectiveness as decisions to assign resources and treat areas are based on knowledge of IAP species presence and their associated densities in an area. Secondly, the long-term implications of suboptimal treatment quality is examined through modelling the expected density of IAP invasion after 50 years of treatment at 38 levels of clearing efficacy (Chapter 3). Thirdly, the choice of management clearing strategy is thought to play an important role in determining clearing success. Although a number of clearing strategies have been postulated by management and documented in literature, the potential outcomes of these strategies have not been formally tested. These proposed management strategies are modelled to provide insight into the performance of each strategy, also considering the mediating impact of clearing quality (Chapter 4). Last, there exists a management dichotomy between area-based and species-based planning. The shortcomings of these approaches are identified with an alternative invasion-stage-based planning approach that considers a number of scale dependent range properties offered (Chapter 5). To assess these factors, the presence and absence of all identified alien species were mapped at a fine-scale across the Table Mountain National park, producing a systematic sample of species from a total of 10,057 plots. Results indicated that management data used in decision making largely over estimate IAP distribution and abundance, while under estimating IAP species richness. Fine-scale sampling provided estimates of species richness and abundance that differed in many cases by orders of magnitude from the data that are used by managers. Currently there are adequate resources to deal with the IAP problem, but quality of work is identified as the primary driver failure to reduce alien species densities over the long-term. The modelling of treatment quality revealed that small increases in clearing efficacy above 80% result in increasingly large gains in the areas that can be covered for the same amount of resources. Conversely, any decrease in clearing efficacy below 80% results in rapidly diminishing areas that can be treated annually with the same resources. A key consequence of the current efficacy levels observed in the clearing programme, is that up to 75% of the future resource costs will be required to treat new infestations resulting from re-seeding of the current standing infestations. With increased efficacy, this future cost can be greatly reduced. The quality of clearing also mediates the choice of clearing strategy. As clearing quality increased or decreased above or below 75%, the best performing strategy changed. This highlights treatment quality as a primary driver of long-term clearing success, while the choice of implementation strategy is a secondary factor. One of the key factors identified for management improvement was the frequency for revisiting previously cleared management units for follow-up treatment. It was found that historical revisitation to management units has been greater than two years. As many of the targeted species are able to produce seeds within two years, the invasion of such species has been allowed to perpetuate. The last key finding was that through spatial analysis of population data the same species could be at different stages of invasion at different sites with the park. This result suggests that a single management approach for a species is not warranted. The choice of management approach for a species should consider range properties of occupancy, population density and spatial pattern of the species at different sites and scales. In conclusion, key improvements can be readily integrated into the IAP programme that will lead to substantive improvements in the outcomes of IAP programmes. These include improving the quality data on distribution and abundance IAP and implementing rigorous quality control. Some of the suggested interventions from this work are already being trialled, with marked improvements already visible. Through these improvements, eradication of target species by organised local scale extirpation, is possible.

AFRIKAANSE OPSOMMING: Indringer uitheemse plante (IUP) hou 'n direkte bedreiging vir die biodiversiteit van Suid-Afrika in. Uitgebreide indringing het plaasgevind in baie van die land se beskermde gebiede, wat direkte bestuur vereis. In baie beskermde gebiede, insluitend Tafelberg Nasionale Park, die geselekteerde studiegebied vir hierdie ondersoek, is IUP beheerprogramme meer as twintig jaar gelede gestig en is dit goed befonds. Beperkte tasbare sukses, in terme van die vermindering van algehele indringer verspreiding en digtheid, is egter behaal. Dit was dus nodig om, vanuit 'n ekonomiese en bewaringsperspektief, die moontlike toekomstige trajek van beheerprogramme te ondersoek en die belangrikste dryfvere van bestuursukses te bepaal. Hierdie proefskrif poog om 'n wetenskaplike beweegrede te verskaf vir die verbetering van die bestuur van IUP programme in vier sleutel bestuursgebiede. Eerstens word die huidige akkuraatheid van verspreidings- en oorvloeddata wat in bestuursbesluitneming gebruik word, bepaal (Hoofstuk 2). Dit is 'n belangrike vertrekpunt om bestuur doeltreffendheid te verstaan, aangesien besluite om hulpbronne toe te ken en werksareas aan te wys, gebaseer is op kennis van die teenwoordigheid van IUP spesies en hul gepaardgaande digtheid in 'n gebied. Tweedens word die langtermyn implikasies van suboptimale behandelingskwaliteit ondersoek deur die verwagte digtheid van IUP indringing na 50 jaar se behandeling op 38 vlakke van doeltreffendheid skoon te maak (Hoofstuk 3). Derdens word daar gedink dat die keuse van skoonmaakstrategie deur bestuur ‘n belangrike rol speel in die bepaling van die sukses van skoonmaak. Alhoewel 'n aantal skoonmaakstrategieë deur die bestuur voorgestel en in die literatuur gedokumenteer is, is die potensiële uitkomste van hierdie strategieë nie formeel getoets nie. Hierdie voorgestelde bestuurstrategieë word gemodelleer om insig te verskaf in die prestasie van elke strategie, met inagneming van die bemiddelende impak van skoonmaak kwaliteit (Hoofstuk 4). Laastens bestaan daar 'n bestuursdigotomie tussen areagebaseerde en spesiegebaseerde beplanning. Die tekortkominge van hierdie benaderings word geïdentifiseer met 'n alternatiewe indringer-stadium-gebaseerde beplanningsbenadering wat 'n aantal skaalafhanklike omvangseienskappe oorweeg (Hoofstuk 5). Om hierdie faktore te evalueer, is die teenwoordigheid en afwesigheid van alle geïdentifiseerde uitheemse spesies op 'n fynskaal regoor Tafelberg Nasionale Park gekarteer, wat ‘n sistematiese steekproef van spesies uit ‘n total van 10,057 plotte gelewer het. Resultate het aangedui dat bestuursdata wat in besluitneming gebruik word, IUP verspreiding en oorvloedighed oorskat, terwyl dit die rykdom van IUP spesies onderskat. Fynskaalse steekproefneming het skattings van spesiesrykheid en oorvloed gegee wat in baie gevalle van grootteorde verskil van die data wat deur bestuurders gebruik word. Tans is daar voldoende hulpbronne om die IUP probleem te hanteer, maar die kwaliteit van werk word geïdentifiseer as die primêre rede hoekom daar gefaal word om die uitheemse spesies digthede oor die langtermyn te verminder. Die modellering van behandelingskwaliteit het aan die lig gebring dat klein toenames in die doeltreffendheid van skoonmaak bo 80% tot toenemende groot winste lei in die gebiede wat vir dieselfde hoeveelheid hulpbronne gedek kan word. Omgekeerd, lei enige afname in effektiwiteit onder 80% in vinnig afnemende areas wat jaarliks met dieselfde hulpbronne behandel kan word. 'n Belangrike gevolg van die huidige doeltreffendheidsvlakke waargeneem in die skoonmaakprogram, is dat tot 75% van die toekomstige hulpbron koste nodig sal wees om nuwe infestasies te hanteer as gevolg van saadskiet van die huidige staande infestasies. Met verhoogde doeltreffendheid, kan hierdie toekomstige koste aansienlik verminder word. Die kwaliteit van skoonmaak bepaal ook die keuse van die skoonmaakstrategie. Aangesien die skoonmaakkwaliteit gestyg of verlaag het bo of onder 75%, het die beste presterende strategie verander. Dit beklemtoon die kwaliteit van behandeling as 'n primêre dryfveer vir die sukses van skoonmaak oor die langtermyn, terwyl die keuse van implementeringstrategie 'n sekondêre faktor is. Een van die sleutelfaktore wat vir bestuursverbetering geïdentifiseer is, was die frekwensie vir herbesoeke van voorheen skoongemaakte bestuurseenhede vir opvolgbehandeling. Daar is bevind dat historiese herbesoek aan bestuurseenhede langer as twee jaar was. Aangesien baie van die geteikende spesies binne twee jaar saad kan produseer, is die indringing van sulke spesies toegelaat om voort te duur. Die laaste sleutelbevinding was dat, deur middel van ruimtelike analise van bevolkingsdata, dieselfde spesie op verskillende stadiums van indringing op verskillende plekke binne-in die park kan wees. Hierdie resultaat dui daarop dat 'n enkele bestuursbenadering vir 'n spesie nie geregverdig is nie. Die keuse van bestuursbenadering vir 'n spesie moet die eienskappe van besetting, bevolkingsdigtheid en ruimtelike patroon van die spesies op verskillende terreine en skale oorweeg. Ten slotte, kan sleutelverbeterings maklik geïntegreer word in die IUP program wat tot wesenlike verbeterings in die uitkomste van die IUP programme sal lei. Dit sluit in die verbetering van die kwaliteit data oor verspreiding en oorvloed van IUP en die uitvoering van streng gehaltebeheer. Sekere van die voorgestelde ingrypings van hierdie werk word alreeds beproef, met beduidende verbeterings wat reeds sigbaar is. Deur hierdie verbeteringe, is die uitroeiing van teikenspesies deur georganiseerde plaaslike skaaluitsterving moontlik.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105691
This item appears in the following collections: