Browsing by Author "Gaertner, Mirijam"

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    A fine-scale assessment of the ecosystem service-disservice dichotomy in the context of urban ecosystems affected by alien plant invasions
    (2019-10-28) Potgieter, Luke J; Gaertner, Mirijam; O’Farrell, Patrick J; Richardson, David M
    Abstract Background Natural resources within and around urban landscapes are under increasing pressure from ongoing urbanisation, and management efforts aimed at ensuring the sustainable provision of ecosystem services (ES) are an important response. Given the limited resources available for assessing urban ES in many cities, practical approaches for integrating ES in decision-making process are needed. Methods We apply remote sensing techniques (integrating LiDAR data with high-resolution multispectral imagery) and combined these with supplementary spatial data to develop a replicable approach for assessing the role of urban vegetation (including invasive alien plants) in providing ES and ecosystem disservices (EDS). We identify areas denoting potential management trade-offs based on the spatial distribution of ES and EDS using a local-scale case study in the city of Cape Town, South Africa. Situated within a global biodiversity hotspot, Cape Town must contend with widespread invasions of alien plants (especially trees and shrubs) along with complex socio-political challenges. This represents a useful system to examine the challenges in managing ES and EDS in the context of urban plant invasions. Results Areas of high ES provision (for example carbon sequestration, shade and visual amenity) are characterized by the presence of large trees. However, many of these areas also result in numerous EDS due to invasions of alien trees and shrubs – particularly along rivers, in wetlands and along the urban edge where tall alien trees have established and spread into the natural vegetation (for example increased water consumption, increased fire risk and reduced soil quality). This suggests significant trade-offs regarding the management of species and the ES and EDS they provide. Conclusions The approach applied here can be used to provide recommendations and to guide city planners and managers to fine-tune management interventions at local scales to maximise the provision of ES.
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    Conservation begins after breakfast: the relative importance of opportunity cost and identity in shaping private landholder participation in conservation
    (Elsevier, 2013) Conradie, Beatrice; Treurnicht, Martina; Esler, Karen; Gaertner, Mirijam
    The conservation opportunity literature increasingly emphasises opportunity cost as an important determinant of willingness to engage in conservation on private land. We investigated the explanatory power of a group of opportunity cost variables in the decision to participate in a landscape-level conservation initiative on the Agulhas Plain, Cape Floristic Region. Opportunity cost variables outperformed affiliation and demographic variables when used in one model and had almost as much explanatory power as the combined model when used on their own. In the opportunity cost model, conservation was positively related to farm size and education and negatively related to share of income from farming and size of the remnant of natural vegetation on the farm. Of these relationships, that between education and participation was the most elastic: a 1% increase in education led to an almost 2% increase in the likelihood of participating in conservation. A large group of identity variables jointly explained nothing, but a subset of age, gender and Afrikaans language status had some explanatory power when used separately. We suspected this subset of demographic variables to have done nothing but proxy patterns of opportunity cost in the farming community. When re-estimated with the untransformed remnant as a share of farm size rather than an area, similar results were obtained and the negative sign on the remnant was confirmed. We concluded that understanding what opportunity cost conservation imposes on private landholders is not only important, but critical, for predicting which private land will come into and stay in conservation.