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

Luke J Potgieter,David M Richardson,Mirijam Gaertner,Patrick J O’Farrell

doi:10.1186/s40663-019-0200-4

Abstract

BackgroundNatural 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.MethodsWe 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.ResultsAreas 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.ConclusionsThe 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.

Highlights

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
Analytical framework We developed an approach which combines remote sensing techniques and supplementary spatial data with invasive alien species density data to assess the role of urban vegetation in providing ES and ecosystem disservices (EDS) at a local scale (Fig. 2)
Ecosystem services Areas of high ES provision were characterized by the presence of large trees, which can sequester more carbon, provide more shade for people, and serve as habitat for fauna (Table 2)

Summary

Introduction

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. Trees, provide many benefits that can enhance the well-being of urban residents (Jim and Chen 2008; Nowak et al 2008; Escobedo et al 2010). These include provisioning services such as food, water and timber; regulating services that positively affect climate, floods and water quality; cultural services that provide recreational, aesthetic, and spiritual benefits; and supporting services such as soil formation, photosynthesis, and nutrient cycling. Urban ecosystems generate functions, processes and attributes that can result in perceived or real negative impacts on human well-being (such as aesthetic, economic, environmental, health and social problems), termed ecosystem disservices (EDS) (Roy et al 2012; Shackleton et al 2016; Potgieter et al 2017; Vaz et al 2017)

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