Ecological corridors and ecosystem services: potential for climate change adaptation in Johannesburg, Gauteng

Abstract

Climate change threatens the state of biodiversity and ecosystems worldwide. Furthermore, as urbanisation continues to increase, cities have become even more vulnerable to the impacts of climate change. This makes it imperative for cities to implement climate change adaptation strategies. An Ecosystem Based Adaptation strategy where ecological corridors and the ecosystem services they provide are protected, can potentially increase a city’s adaptive capacity. This study investigated the functionality of ecological corridors and their associated ecosystem services within Johannesburg, South Africa, in order to determine if investing in their protection is a worthwhile climate change adaptation strategy for the city. This study identified two ecological corridors - the Braamfonteinspruit and Modderfontein corridors. A spatial assessment determined that the Braamfonteinspruit corridor consisted primarily of trees, whilst the majority of the Modderfontein corridor consists of planted and natural grasslands. This indicates that both corridors have the vegetation necessary to provide a variety of ecosystem services, including carbon sequestration and temperature regulation. Additionally, both corridors were mostly surrounded by low intensity land uses which helps promote the provision of vital ecosystem services. A vegetation assessment was conducted in both the Braamfonteinspruit and Modderfontein ecological corridors. Vegetation structure, percentage ground cover, composition and species richness was assessed at every study site within each of these corridors. In order to assess species composition, the Braun Blanquet method was used. Both corridors had a low species richness that included mostly herb and exotic species. Both corridors were mostly covered in grassland and no significant difference was found between different ground cover types in each corridor. In order for both corridors to better provide ecosystem services, species richness would need to be increased. Three ecosystem services, namely flood regulation, temperature regulation and carbon sequestration, were investigated within both ecological corridors. The Braamfonteinspruit and Modderfontein ecological corridors had relatively low soil compaction measurements and there was no significant difference between their average soil compaction values. This suggests that both corridors have soil that can easily absorb and retain water, thus aiding with flood regulation. However, there was a significant difference found between soil compaction measurements at the different sites along the Braamfonteinspruit and Modderfontein ecological corridors. There was no significant difference between the cooling effect inside and directly outside both ecological corridors, however this may be because the corridors are cooling down IV surrounding areas. Despite there not being a significant difference between the cooling effect of both corridors, it was found that the Modderfontein corridor, which had more trees than the Braamfonteinspruit ecological corridor, had a slightly higher cooling effect. Clearly both corridors provide the ecosystem service of temperature regulation and due to the fact that surrounding areas are mostly made up of low intensity land-uses, this cool air can flow easily into surrounding areas. Lastly, it was found via two methods that the Modderfontein ecological corridor stores more carbon than the Braamfonteinspruit corridor, which can be attributed to the Modderfontein corridor having more trees which were larger as well as an overall greater green area. Essentially, both corridors can provide carbon sequestration, however larger and an increased number of trees will help increase the provision of this ecosystem service. Based on the results of this study, it can be concluded that both the Braamfonteinspruit and Modderfontein ecological corridors are functional and provide vital ecosystem services that help the City of Johannesburg and its citizens adapt to climate change. It is recommended that both corridors be formally protected and managed in order to increase plant species richness and tree cover. Using ecological corridors and their associated ecosystem services has the potential to be an effective and long-lasting climate change adaptation strategy for Johannesburg