A fine-scale assessment of the ecosystem service-disservice dichotomy in the context of urban ecosystems affected by alien plant invasions

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 shrubsparticularly 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.

The importance of assessing positive and beneficial impacts of alien species

“…Guerin et al (2018), for example, suggested that meta-analyses quantifying the impact of alien species might not be fully objective, as these studies are often characterised by selection bias toward highly deleterious taxa (but see also Kuebbing and Nuñez 2018, who argued that potential publication biases do not necessarily invalidate findings). Another potential consequence is the risk of implementing controversial management policies: management decisions based only on deleterious impacts ignore the fact that there might be conflicts of interest among stakeholders (Zengeya et al 2017;Potgieter et al 2019a;Kumschick et al 2020a).…”

Urban Ecosystem Disservices in the Global South

“…Psychological impacts consist of all UED that cause negative feelings or emotions, such as discomfort, anxiety or fear due to, for example, animal excrement or plant litter causing disgust (Lyytimäki et al 2008;Agbenyega et al 2009;Limburg et al 2010) or feelings of insecurity and fear of bodily harm when in urban green spaces (Tzoulas et al 2007;Hofmann et al 2012;Delshammar et al 2015;Shackleton et al 2015). For many urban residents, areas with uncontrolled or overgrown vegetation instil feelings of anxiety and fear, since these spaces can provide cover for dangerous or unattractive wildlife, such as snakes, spiders and insects, and facilitate crime or criminal activity by providing cover for criminals (Lyytimäki 2014;Shackleton et al 2015;Lyytimäki 2017;Escobedo et al 2018;Potgieter et al 2019a). The expansion of urban areas into natural ones and the promotion of recreational outdoor activities can create an overlap of habitats which has led to increased human-wildlife conflicts (Bombieri et al 2019).…”

“…In both Global North and South countries, studies have found that people experienced a fear of crime or being victims of crime in urban green spaces (Jansson et al 2013;Sreetheran and Van Den Bosch 2014;Shackleton et al 2015;Sreetheran and Van Den Bosch 2015;Lyytimäki 2017;Mouratidis 2019) and often these negative emotions lead to residents limiting their use of such spaces. Potgieter et al (2019a) found that criminal activity was unevenly distributed across the urban landscape of Cape Town and was either facilitated or limited by topographical features, such as hills, dunes or waterbodies, and physical features of the landscape, such as vegetation structure or type. Fear of crime is more prevalent among woman than men (Sreetheran and Van Den Bosch 2014).…”

“…Similarly, Potgieter et al (2019a) developed a replicable approach to assess the role of urban vegetation in providing UES and UED at a local scale. They applied remote sensing techniques (integrating LiDAR data with high-resolution multispectral imagery) and supplementary spatial data to identify areas of high UES and UED provision, in Cape Town, South Africa (Potgieter et al 2019a).…”

Plant invasion as an emerging challenge for the conservation of heritage sites: the spread of ornamental trees on ancient monuments in Rome, Italy

“…The important role of tall alien trees as the invasive species that exert the most negative impacts in urban contexts has been repeatedly highlighted (McLean et al 2017;Potgieter et al 2019a). Indeed large size, and specifically plant height, is one of the major predictors of the capacity of non-native plants to spread and become invasive (Pyšek et al 2012) as well as one of the main reasons for why non-native trees are among the most widespread and harmful invasive species worldwide (Bucharova and van Kleunen 2009;Richardson and Rejmánek 2011;Pyšek et al 2014;Rejmánek 2014).…”