What role do urban forests play in building resilience in a treeless biome?

This article is written and shared with permission from Tasmin Faragher - Resilience and Climate Specialist. Tasmin recently delivered a keynote address at the World Urban Forest Forum in Washington, D.C., USA. This article highlights some of the components of the presentation. A link at the end of the article will take you to the full presentation.

Cape Town is South Africa’s oldest and second largest city . It’s located at the bottom of the African continent on a peninsula. It has a 2 446 square kilometer footprint and a Mediterranean climate – hot, dry summers – and wet winters. And wind all through the year. Historic data indicates 475mm rainfall per year, but this has varied radically in recent years. ‘Day zero’ ring any bells? Capetonians do. We learnt the hard way, that historical data cannot be used as the basis for forward planning any longer. But I digress. Back to trees.

Our tree canopy is between 6 and 7% and covers an urban footprint characterised by medium to low density with a population of almost 4.8 million. The economy is driven by financial services and tourism. Its location within an agricultural region makes it an important sector hub. Even though Cape Town and the Western Cape’s economies compares favourably against other South African metros, there are nevertheless also high levels of unemployment and inequality.

Aerial of Cape Town. Photo Credit: City of Cape Town.

Natural Systems – Botanical Ecology

As you can see from the photograph, Cape Town is absolutely a mountain in the sea. This photograph captures the Table Mountain range that extends from Table Bay to Cape Point. On the right is the gently sloping Signal Hill, flanking the mountain’s north face in the middle, with Devil’s Peak to the left.

The Cape Flats is a low-lying sandy area that stretches between the foot of the sandstone Table Mountain and Hottentots Holland mountain ranges. It is visible on the left of the photograph behind Devil’s Peak. Aquifers occur across these geological formations and the groundwater they store is gradually forming part the City’s bulk water supply.

Knowing about the geology is important for understanding what will grow where.

Natural Systems – botanical ecology

The geology, soils, orientation and climate establish many different micro-climates for mountain, lowland and wetland plants. This unique botanical canvas is referred to as the Cape Floral Kingdom, or the fynbos biome. Cape Town is a conservation and biodiversity hotspot, wherein a total of 19 different and distinct vegetation types occur. This botanical uniqueness is protected by World Heritage Status, as are the Table Mountain National Park (located at the very heart of the city); Kirstenbosch Botanical Gardens and Robben Island, where our former president, Mr. Nelson Mandela was imprisoned for 27 years. The city also recently became a Ramsar wetland city.

Fynbos is spectacularly beautiful, but it is not naturally rich in trees, with low and medium shrubs and geophytes dominating. Afro-montane trees are however found in protected ravines, mountain slopes and valleys.

Lastly, low-lying areas are characterised by dune and wetland systems fed by a network of small rivers and streams from the higher mountain slopes.

Left: View of Table Mountain showing Newlands Cricket Ground and Rugby Stadium. Right: Informal settlement towards the north

Apartheid legacy

Cape Town, like other South African cities is deeply affected by the country’s apartheid legacy which is represented by under-investment in infrastructure, including open space. The city’s development started closer to the mountain in more favourable growing microclimates where older, more established areas are now located. Newer, poor areas grew down and out from here onto poorer soils and into harsher micro climates.

It follows that the geology and microclimates have also played a role in the disparity of ‘greenness’ across the city simply because it is a lot harder to grow trees on the Cape Flats, where vulnerable communities typically live.

Tree Canopy

In 2020 the Recreation and Parks Department completed the City’s and South Africa’s first tree mapping project. The mapping used LiDAR to capture 2.75m tall trees and above in addition to:

Area of vegetation (road reserves, parks, private land);
Leafy versus non-leafy areas; and
Percentage of tree canopy.

These elements establish a baseline for monitoring canopy cover changes over time. Follow-up assessments will be undertaken every 5 to 8 years to monitor changes and inform forest management priorities and plans.

This work is to prevent the kind of loss experienced between 2000 and 2020 when the city saw its canopy drop 5.9% from 12%. And direct planting to areas that need it so as to meet the FAO 10% tree canopy goal.

Resilience & Climate Change

You can’t talk about the role of urban forests for climate adaptation and resilient city-making without understanding what resilience is.

The global identification of urban forests for climate adaptation and resilient city-making, puts an onus on understanding their potential role.

Understanding what resilience is, is a start to understanding the role.

Resilience is “the capacity of individuals, communities, institutions, businesses and systems in a city to survive, adapt and thrive no matter what kind of chronic stresses and acute shocks they experience.”

Resilience recognises that climate change is one of the most significant shocks and stresses that cities are challenged with. In Cape Town we have identified their potential for heat adaptation, specifically. We must also consider that whilst urban forests have the potential for heat adaptation, which is “resilience through”, resilience “of” is also critical. This refers to the resilience of the trees and forest.

I’ll discuss the shocks a little later in more detail, but before we get there, let’s look at greenhouse gas mitigation and climate change.

Greenhouse Gas Mitigation – CSIR Study (2021)

The potential of trees to mitigate greenhouse gases is well-recognised globally. However, in 2021, the Council for Scientific and Industrial Research (CSIR) researched the potential for trees and plants to mitigate greenhouse gases in Cape Town. It framed the research within the context of changing earth systems and the need to remove carbon dioxide to offset the accelerating pace of global emissions.

The research concluded that the sequestration potential for all vegetation was about ~1% of Cape Town’s emissions, but that this could be increased by improving green spaces, planting trees and restoring habitats, which would potentially get us up to 2%. The reality is that South Africa’s, and Cape Town’s energy is generated by coal fired power stations. This is changing fast, and Cape Town is leading the way, but mitigating greenhouse gases will remain a challenge for some years to come.

Importantly, what does this mean for Cape Town which occurs in a treeless biome? If trees can’t do it? What can? And is it really fair to make it their sole responsibility?

Climate Change Action Plan (2021)

In 2019, a climate change hazard, vulnerability, and risk assessment study was conducted for the City of Cape Town.

Key climate risks based on both the likelihood of a hazard occurring, the magnitude of the hazard, and the likely impact of the hazard on vulnerable people and infrastructure were identified.

Increased heat, heat waves, and very hot days were flagged as significant risks for Cape Town, particularly within urban are affected by heat islands. The number of very hot days, days that are 35 degrees and more will increase to up to 20 days; heatwave days; days that are 32 degrees for more than 3 consecutive days will increase up to 10 days; as will the high fire danger days that will increase up to 20 days. Far future predictions (right column) are even worse.

The heat map on the right illustrates the impacts of the urban heat island effect across the city. Areas most affected are along denser transport corridors where heat is intensified by building materials and building density, in addition to the lack of green. Other vulnerable areas are located on the Cape Flats where heat is particularly acute for those living in poorly built or informal structures. The interior temperatures in these structures can exceed 40 degrees on hot days.

Recommendations are for tree-planting and an urban greening programme. The City is in the process of preparing a Heat Action Plan that includes other interventions such as cooling centres.

Other risks that will affect the greening recommendations are:

Drought and associated water shortages
Flooding and associated impact on people and infrastructure
Coastal erosion and sea-level rise, and associated impacts on coastal infrastructure

To date, climate responsiveness appears to focus on heat and how it affects human health and vulnerable people. I’d like to suggest that additional consideration is needed for other parts of our urban eco-systems, such as trees – and biodiversity loss.

Resilience Strategy (2019) – Open Space Working Group

Cape Town’s resilience strategy is an important part of the policy puzzle because it in many ways sets the stage for the Climate Change strategy. It was developed with support from the Rockerfeller 100 Resilient Cities network and was approved by Council in 2019. The strategy identified pillars, goals and actions, including the establishment of an Open Space Working Group that speaks to a connected, climate adaptive city and envisions Capetonians working together to create place-based responses to shocks and stresses, with a goal to build climate resilience.

The Open Space Working group is the only opportunity for officials to engage around open space, across disciplines and line departments in a way that is generative. Online sessions frame themes which we then explore on site where we can see how policy and management come together, and from there identify what is working well, but also opportunities for improvements.

The webinar sessions looking at Green Infrastructure highlighted issues with managing forests in urban areas, whilst the City and open space sessions highlighted challenges in developing green public spaces, including trees. The image above is of the Klaasenbosch Greenbelt visit where canopy thinning is allowing understory fynbos to establish. The greenbelt connects Table mountain along a waterway and wetlands to the Cape Flats and ultimately the sea.

Successes of the Open Space Working group are numerous, but largely because it is the only opportunity for officials to engage around open space together, across disciplines and line departments in a way that is generative. I feel that many local government officials are reluctant (or too busy) to leave the office and get onto site, which is a danger because our work almost always intersects and the success or shortfalls of policies and strategies are most often only visible through implementation – on site. Hosting online webinars has also worked well because we have been able to share international best practice, which has been incredibly inspirational.

The Open Space Working Group is an action that the Risk and Resilience Department drives, but actions towards climate adaptation and mitigation lie with many other departments, including our colleagues within the department in the Climate Change team.

To access Tasmin’s full presentation, click here.