Boomslang – tree snake – is the nickname given to the new Centenary Tree Canopy Walkway. It is an appropriate label for the airy footbridge that winds its way through the treetops of the Arboretum in Cape Town’s Kirstenbosch Botanical Gardens.
A spicy fragrance in the warm, humid air that lingers between the trees lures the visitor who listens in awe to the unfamiliar birdsong. Despite the soaring temperatures, this certainly is quite a retreat! The visitor’s facial features relax noticeably on entering the opulent Arboretum. The woodland of southern African trees and grasses is set in the Botanical Gardens against the northern slopes of the Table Mountain, facing inland and far away from Cape Town’s traffic, noise and smog.
A Cultural Heritage
Kirstenbosch Botanical Garden was created in 1913. The name means Kirsten’s forest and is thought to originate from a family with the name Kirsten who are presumed to have owned the land. At the time the farmland was untended and over-grown. It was British botanist Harold Pearson, driven by his farsightedness and commitment, who recognised the farmland’s potential as a garden. Pearson had taken on a chair in botany at South African College and was looking for suitable terrain for his research. Kirstenbosch was then created as the first garden in the world uniquely for indigenous flora.
Today Kirstenbosch is a Unesco World Heritage Site. Among the highlights of any visit is the Arboretum, the term “highlight” taking on a very literal meaning: for the Garden’s 100th anniversary a walkway – the so called Boomslang – was built that passes between the treetops. It is a very special place: Mulch paths wind their way through over 450 southern African tree species, many from the subtropical regions of eastern South Africa, which grow well on these warm north-facing slopes of the Garden. The Garden’s administration is keen to point out the following species: stink-wood, knobwood, pigeon wood and in particular a magnificent tree aloe: it is 18 metres tall and a feast for the eyes when it blossoms in winter (June). The Arboretum also displays shade-loving herbaceous perennials, shrubs and bulbs that grow in the middle and understorey, or on forest margins.
Building between the Trees
The incline of the Arboretum had inspired those in charge of the South African bio-diversity institute to create a special attraction for visitors: to enable the blossom, leaves, birds, insects and the not all too infrequent “boomslang” (tree snake) to be seen from close up, the new Centenary Tree Canopy Walkway was created on the uphill side of the Arboretum. A precondition for its construction was that it would require little maintenance and would not hinder the tree life. The Walkway was designed to lead away from the incline, to the treetops and back. Architect Mark Thomas was just the man for the job: from the beginning he had in mind a “sinuous, lightweight, non-intrusive steel structure”, winding its way through the trees. This is how it came to be dubbed the Boomslang.
The holes for the column footing were dug out by hand at 12-metre intervals and filled with concrete. The workers were under strict supervision in order to prevent any damage to the roots. Botanist Adam Harrower was involved in the planning from the start and helped to design the route taken by the Walkway. In places he projected an existing path up into the air, thus avoiding a need to fell any trees. At one point, a hole was even incorporated into the Walkway in order to accommodate one of the tree trunks.
Read on in Topos 93 – Fragile Landscapes.
The Boomslang – Kirstenbosch Centenary Tree Canopy Walkway, Cape Town, South Africa
Client: SANBI (South African National Biodiversity Institute)
Architects: Mark Thomas Architects, Cape Town, with Chris Bissett
Engineer: Henry Fagan and Partners, Cape Town
Steel structure: Prokon Services
Botanist: Adam Harrower
Construction: May 2014