Innovative treatment to save endangered silver trees

For the first time in Mzansi’s history, a phosphite treatment will be used in a bid to save South Africa’s silver trees from extinction

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In a bid to prevent one of Mzansi’s indigenous flora from going extinct in the next 50 years, an innovative project to save the silver tree has been launched.

The Kirstenbosch National Botanical Garden in Cape Town is hard at work trying to save the rare and threatened species, found naturally, only in a tiny area of the Western Cape.

Conservation horticulturists are administering a phosphite treatment on the protected evergreen tree found in Kirstenbosch. The treatment will be applied to indigenous South African flora for the first time in the country’s history.

According to a media release by the South African National Biodiversity Institute (SANBI), the treatment is only ever used in agriculture and horticulture settings.

This, they explain, is done to guard several important commercial crops against a disease called Phytophthora root and crown rot.

The death of wild Silver Trees

The silver tree, also known as the silver leaf tree, witteboom, or silwerboom, is part of the protea family and is naturally confined to a tiny area in and around the city of Cape Town.

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It grows mainly on the slopes of Table Mountain, the Lion’s Head area, above Rhodes Memorial and the mountain slopes above the Kirstenbosch garden.

Historically, the enormous silver protea was widespread on Table Mountain, covering much of its slopes in shimmering silver forests. However, early demand for timber led to much of these forests being destroyed.  

Now, experts predict future generations might not even get to see this tree within the next five decades.

“Unfortunately, this rare tree is susceptible to infection from a fungus called Phytophthora cinnamomi, a soilborne pathogen that causes root and collar rot. Phytophthora feeds on living plant roots and stems, reducing the plants’ ability to transport water and nutrients – often leading to the death of the host,” SANBI states.

Silver trees
Marked trees at Kirstenbosch that have been injected with phosphite while Silver Tree seedlings have been sprayed. Photo: SANBI

SANBI, the Kirstenbosch National Botanical Garden, the Botanical Society of South Africa, Table Mountain National Park, and the Forestry and Agricultural Biotechnology Institute (FABI), are working together to save the silver tree from extinction.

According FABI’s conservation horticulturist, Dr Trudy Paap, the pathogen is causing the death of wild silver trees at Kirstenbosch.

“Unfortunately, the soil in some of our garden beds is infested with this devastating organism, which is why many of the Silver Trees in Kirstenbosch are dying,” Paap explains.

Treatment, a first for South Africa

Paap and her colleagues are saving the silver trees from extinction by testing the application of a biodegradable fungicide known as phosphite.

She explains, “Phosphite will not eradicate Phytophthora from the soil, but it can protect plants from infection, and can help them recover if they are already infected.”

“We have sprayed some of the silver tree seedlings and injected bigger trees with phosphite. We have also left other plants untreated, as controls, and are monitoring the survival rates of the treated and non-treated trees.”

Silver trees
Kirstenbosch are calling on the public to stay out of the plant beds as the microscopic spores of Phytophthora are easily spread on the bottom of shoes. Photo: SANBI

Paap says their team is incredibly excited about the first use of this treatment on indigenous flora. They are also optimistic that the trials will confirm the suitability of phosphite application to protect this iconic tree species.

“Not only do we hope to find an effective treatment against Phytophthora in order to save the silver tree population in Kirstenbosch, but we also have the objective of restoring 8000 Silver Trees to sites where historically they occurred naturally,” she explains.

Conservation project dubbed essential 

In the meanwhile, visitors to Kirstenbosch may notice marked trees.

This, SANBI states is to assist with the monitoring of the project and people are urged not to remove these tags.

Kirstenbosch are also calling on the public to stay out of the plant beds as the microscopic spores of Phytophthora are easily spread on the bottom of shoes.

The garden forms part of a network of exceptional national botanical and zoological gardens that exist across the country managed by SANBI.

According to Mpendulo Gabayi from SANBI, one of the conservation horticulturists working on saving the Silver Trees explains SANBI’s overall mandate is to explore, reveal, celebrate, and champion biodiversity for the benefit and enjoyment of all South Africans.

“To this end, conservation projects such as this one, which plays an integral part in the protection and survival of indigenous trees, are essential,” Gabayi believes.

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