CONSERVATION & ENVIRONMENT NEWS Kirstenbosch Strives to Save Rare and Endangered Silver Tree Kirstenbosch National Botanical Garden in Cape Town, in collaboration with the Botanical Society of South Africa, Table Mountain National Park (TMNP), FABI (Forestry and Agricultural Biotechnology Institute) and the South African National Biodiversity Institute (SANBI), has launched an innovative project to save an endangered tree which only occurs naturally in a tiny area of the Cape Peninsula. The Silver Tree (Leucadendron argenteum), also known as the Silver Leaf Tree, Witteboom, or Silwerboom, is a protected evergreen tree which is part of the Protea family. This enormous silver Protea is naturally confined to a tiny area in and around the city of Cape Town – with its main population growing on the slopes of Table Mountain, notably the Lion’s Head area, above Rhodes Memorial and the mountain slopes above Kirstenbosch National Botanical Garden.
of our garden beds is infested with this devastating organism, which is why many of the Silver Trees in Kirstenbosch are dying.” In a bid to save the Silver Trees, Kirstenbosch, in collaboration with FABI, have launched a phosphite treatment trial. “We are testing the application of a biodegradable fungicide known as phosphite, which can protect plants against Phytophthora die-back. 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,” explains Dr Paap. “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.”
Phosphite is used in South African agriculture and horticulture settings to guard against Phytophthora root and crown Historically, the Silver Tree was widespread rot of several important commercial crops. on Table Mountain, covering much of However, it has never been applied to its slopes in shimmering silver forests. indigenous South African flora. “The team is However, early demand for timber led to much of these forests being felled and now incredibly excited about the first use of this treatment on indigenous South African flora the Silver Tree is a rare and threatened and are optimistic that the trials will confirm species - in danger of becoming extinct the suitability of phosphite application as a in the wild in the next 50 years if we means to protect this iconic tree species,” do not take care of the remaining wild says Dr Trudy Paap from FABI (Forestry And populations. Agricultural Biotechnology Institute). Unfortunately, this rare tree is susceptible “Not only do we hope to find an effective to infection from a fungus called treatment against Phytophthora in order Phytophthora cinnamomi, a soilborne to save the Silver Tree population in pathogen that causes root and collar rot. Kirstenbosch, but we also have the objective Phytophthora feeds on living plant roots of restoring 8000 Silver Trees to sites where and stems, reducing the plants’ ability historically they occurred naturally.” to transport water and nutrients – often leading to the death of the host. Visitors to Kirstenbosch may notice marked trees. This is to assist with the monitoring Dr Trudy Paap, Dr Mesif Gosa from FABI, of the project and people are urged not Mashudu Nndanduleni and Mpendulo to remove these tags. Kirstenbosch are Gabayi, the conservation horticulturists at also calling on the public to stay out of Kirstenbosch National Botanical Garden the plant beds as the microscopic spores explain that this devastating introduced of Phytophthora are easily spread on the pathogen is present in wild Silver Trees bottom of shoes. as well as in the population found in Kirstenbosch National Botanical Garden, Kirstenbosch National Botanical Garden where it is causing the death of many of forms part of a network of exceptional these trees. “Unfortunately, the soil in some National Botanical and Zoological Gardens 178 responsible traveller
