Endemic greening on The Fynbos: How to achieve the seemingly impossible

4 November 2024

Introduction

Donovan Gillman of Urban Choreography was first approached by a developer in late 2020 to find out if it was possible to grow trees and plants on a tall building in central Cape Town, like the Bosco Verticale in Milan. This paper unpacks Urban Choreography’s vision for how one could successfully and sustainably implement indigenous vertical greening on a building in Cape Town, applied to the upcoming property development, the Fynbos.

At first glance, the Fynbos is a twenty-four-storey urban development with an eye-catching landscape architectural intervention that includes 1200m2 of exterior balcony planters and a roof garden (see Fig 1).

At street level (see Fig 2) the public will be able to access retail establishments and a five-storey inner courtyard space (see Fig 3) where LED lighting is controlled by daylight sensors to match the external lighting conditions. This twenty metre wide internal courtyard features a large central fountain, mature trees and large hanging baskets mimicking the interior of a forest kloof.

The artist’s impressions, however, belie the reality of the project vision: to feature a distinctive aesthetic built around endemic fynbos vegetation.

From the time Urban Choreography was appointed in May 2021 to design the external landscaping of the Fynbos, it was clear that this was not a typical vertical greening project. Drawing from biomimicry and fifty years of horticultural and landscape architectural experience, this project is Donovan Gillman’s swan song, a one-of-a kind, boundary-pushing strategy for sustainable and endemic urban greening. It has been suggested that the building will be the first of its kind in Africa and is a resilient landscape architectural response to the growing environmental challenges facing our cities, resonating with this issue’s theme of regenerative landscapes. In addition to introducing a resilient fynbos planting environment, the building’s landscaping will contribute to reducing the heat island effect, improving stormwater detention, and fostering local bird and insect life.

Urban Choreography’s design vision revolves around key issues relating to the challenge of growing endemic fynbos trees and plants in the city: extreme wind and intense solar exposure resulting in high evaporation and leaf damage; risk of winds uprooting or damaging trees and plants; limited planting space; and water supply risks leading to root damage. The project draws on knowledge of the environment in which fynbos grows, applying natural and technical systems to design a constructed ecological system. This paper carefully unpacks each of these issues and the considerations that have impacted the landscape architectural design strategy.

Table Mountain as a metaphor

Table Mountain is one of the most studied natural environments in southern Africa and its fascinating natural systems and human-related interactions have been the subjects of intensive research and documentation by scientists and the public alike.

Central to the design philosophy of The Fynbos, is the use of Table Mountain as a metaphor to apply principles of biomimicry and bioregional systems design.

This methodology promotes the study of local natural vegetation to determine potential plants from local vegetation types that could be suitable for planting in similar conditions on a particular site. The investigation for plant material suitable for The Fynbos extended to understanding the geology and soil types of Table Mountain as well as surface aspect or slope. The Table Mountain vegetation type is the result of a fire-dominated landscape. Fynbos vegetation requires fires at an interval of ten to fifteen years, rejuvenating the fynbos vegetation species which resprout or reseed after fire. The vegetation on upper slopes of the mountain grows in extremely nutrient-poor soils but never lacks moisture because of the high winter rainfall (2000mm) and an additional 300mm of moisture in summer from the “Table cloth” clouds. Species of trees and plants grow very slowly into dwarfed versions of the same species growing in the valleys. Here, the all-year mountain springs and streams and deeper soil support larger trees, so that despite summer drought and high winds, these trees can live to a great age. Studies by Poulsen (2013), Campbell & Moll (1977) and other botanists have shown that it is not wind that prevent trees and large shrubs from growing on the open lower slopes of the mountain, but a combination of limited moisture in summer and periodic fires that burn young tree seedlings that are unable to resist fire. It is this understanding of the distribution of communities of plants on Table Mountain, their size in these positions and micro-climatic zones, which has formed the basis for the planting strategy on The Fynbos (see Fig 5).

While some Fynbos species can look drab and boring, the large colourful fynbos species are often not long-lived, and some are too large to plant in constrained planters. By selecting hardy species of fynbos shrubs, perennials, groundcovers, and bulbs and augmenting these with their more interesting and compact horticultural varieties, the project aims to create seasonal variation in colour and interest (see Fig 6).

Developing a response to extreme wind exposure

Comparing climatic conditions in Milan and Cape Town, Urban Choreography found that although the wind and rainfall are similar, Cape Town experiences longer periods of south-easterly winds in summer. Information gained from case studies of the Bosco Verticale highlighted that it is not only the prevailing wind that needs to be considered, but intense updrafts pose significant challenges: trees on the building could be subjected to a rocking motion which could jerk the trees and root ball out of the planters and onto the ground below. The Bosco Verticale was subject to a wind study by The International Hurricane Centre’s (IHRC) 12-fan Wall of Wind at Florida International University (FIU) which found that the trees’ flexibility enabled recovery from the deformation caused by severe winds (Aly et al 2013). Based on the wind study information and recommendations from the engineers, a double-restraint system was designed for the planting of trees at the Bosco Verticale. This system comprises a cable binding system around the root ball as well as a cable secured to the balcony above and to a flexible tie to the tree trunk.

Using these recommendations, the tree planting design at The Fynbos makes use of a proprietary root ball binding system and a custom stainless-steel cable and flexible tie to the roof of the balcony above. An additional mesh and rockwool blanket will secure the growing medium. To determine optimal placement of trees on The Fynbos, Urban Choreography made use of the project engineer’s wind model of the building. Using this information, it was deduced that certain areas, such as the central areas, have comparatively low wind exposure, but that planting be minimised on the exposed corners of the building.

Designing a resilient water supply system

The unique selling-point of the project hinges on being able to grow and maintain endemic fynbos species in the vertical gardens of the building. Because of constraints around installing trees, tree planting is intended to last for the lifespan of the building while balcony planting is designed to be replanted every eight to ten years.

The project design takes inspiration from the Table Mountain microclimate where thirty species of trees grow at high altitudes on the mountain, down the fertile kloofs and gulleys to the beaches and dunes, all surviving in conditions similar or worse than will be experienced on the building.

Table Mountain is one of the most studied natural environments in South Africa and its geology, hydrology and vegetation have been described in detail. Using these research sources and through fieldwork studies on the mountain, Urban Choreography pieced together a pattern of fynbos growing conditions that relate to changes in altitude, orientation, slope, soil, moisture, and wind conditions. Key findings include understanding that Table Mountain fynbos plant roots almost never dry out due to high levels of precipitation in both summer (from cloud cover) and winter; and the highly mineralised soil substrate that is low in organic matter. The success of the planting on The Fynbos requires a reliable water supply. To ensure that plants on The Fynbos will not suffer periods of drought, a triple-backup water supply is proposed with a a monitoring system that measures twenty-five plant and climatic variables and controls the irrigation.

The triple-backup water supply is primarily based on ground water that is pumped from the basement. This is backed up by secondary water stored on site from storm water runoff and the third water source is water trucked to site from an external source. The irrigation supply relies on three different systems. The primary form of irrigation is via a surface-mounted copper drip irrigation pipe which prevents clogging by roots. The secondary irrigation system is a low-pressure drip line 300 mm below the soil surface. The third irrigation system is a water reservoir in the bottom of the planter that provides water to the growing medium via capillary action and is essential if other water sources are interrupted. The electricity supply also features a triple redundancy system: the primary electricity source is the City of Cape Town, the secondary source is the buildings’ solar panel and battery system, and the third source is a dedicated battery system for  the irrigation.

A systems controller provides micro-irrigation cycles throughout the day rather than one big irrigation at a fixed time as normal irrigation controllers do. To ensure adequate drainage of the planters, especially in the high rainfall Western Cape winter, an air supply pipe is provided to drain excess water from the medium. In a similar way the various other planters have irrigation, air pipes and hold down systems integrated into their fibreglass planters.

One of the risks of working with fynbos plants is that by the time plants begin to show signs of stress, it may be too late to rectify. As a result, a highly specialised monitoring system has been designed to manage plant health proactively and consistently.

Advanced horticultural monitoring and feedback

The Fynbos landscape design includes a technically advanced greenhouse horticultural intelligence system that will monitor tree and planter evapotranspiration, solar radiation, and other climatic effects to control the nutrition and fertility condition of select trees on all the four façades, podium, roof, and internal planting.

Three tree planters on the north and south side of the building will have an inner pot liner with an additional 300mm depth to accommodate a tree lysimeter which measures the mass of the planter and tree above it to determine evapotranspiration. This information is used in combination with other climatic variables like air temperature and solar radiation intensity, to determine when to irrigate the tree. This information from the tree lysimeters will be fed into an AI-based intelligent control system which will manage the watering and nutrition of the trees and planters in the rest of the building, so they do not become desiccated, wilt, or even die. A research period during construction will allow the design team to refine the AI-based system and to collaborate with the agronomist and their specialists  to fine-tune the system to the conditions (see Fig 7).

To measure the effects of environmental variables on nutrient and pigment quantification, chemometric modelling will be used to optimize plant health and yield. A spectroscope will be used for rapid non-destructive plant stress measurement. This will be referenced to a database of a healthy trees colour spectroscopy from a tree in the nursery. Data collected will be added to the parameters measured by the systems controller and will in turn modify the nutrients that are added to the irrigation water (see Fig 8).

Because of the harsh conditions anticipated for the plants, the horticultural strategy is to avoid fast plant growth and to instead control slow plant growth over time. The effect of this is to control the size of both tree and shrub proportions suited to the various positions on the building. This allows use of the same tree or shrub species to be used in different zones, permitting larger plants on the lower levels and smaller plants higher up. To achieve this, fertilisation will be controlled by a systems controller via a fertiliser injector from which is able to adjust pH and individual fertiliser elements with each micro irrigation cycle.

The vegetation on the building could be a potential fire hazard, so low-flammable plants with less dry material mass were selected. Part of the horticultural maintenance strategy will include regularly removed dead or flammable material. The fire protection system is also designed to manage fires on the exterior of the building.

Developing a custom hydroponic growing medium

The success of the planting strategy on The Fynbos relies on interconnected components that each contribute to the project’s sustainability. Another prong in the horticultural system is developing a bespoke growing medium. Problems experienced in using natural soils as the growing medium (drainage, aeration, waterlogging, nutrient deficiencies, and toxicity) has led to the agricultural greenhouse and horticultural industries turning to soil-less growing media. Urban Choreography has developed a successful system of growing healthy plants, hydroponically (without soil).

A custom hydroponic growing medium has been formulated for The Fynbos to maintain the correct moisture level for root growth while also ensuring adequate drainage to prevent waterlogging.

The growing medium, measured as air-filled porosity, will maintain an air supply to the roots and will provide stability for root anchorage. The growing medium is designed to perform beyond a plants’ lifespan.

Future testing

The planting strategy for The Fynbos uses thirty tree species and twenty shrub species arranged into plant groupings for every five storeys of the building. This strategy, while well-considered and detailed, is still an untested theory. Built into the landscape implementation strategy is a eighteen to twenty-four-month-long research and development period where these specific plant and tree species will be propagated and tested in conditions simulating those of The Fynbos building. Based on the results of this testing phase, plants will be grown from seeds and cuttings and propagated in the custom growing medium and hardened off ready for planting. The intention is that the planting will take eight to ten years to fully establish.

Conclusion

Planting buildings and vegetated urban spaces are essential components of an urban greening strategy, and the benefits of sustainable green urban areas are appreciated now more than ever. There is growing evidence that exposure to nature and living entities is an essential infrastructure feeding human physical, mental, emotional, and spiritual needs.

This paper resonates with this issue's theme of regenerative landscapes in terms of its application of advanced horticultural technology and biophilic design to achieve a resilient urban landscape. The landscape architectural intervention proposed by Urban Choreography draws on natural fynbos ecosystems to artificially create a new type of ecosystem.

At the heart of the project is an ethos of exploring the seemingly impossible: implementing an endemic landscape that is not about the conditions today but designing a landscape that continues to be sustainable in ten, twenty- or fifty-years’ time.