|A young silvertree at Kirstenbosch Botanical Gardens, Cape Town|
|Map of the extant population of silvertrees in the Cape Peninsula|
Leucadendron argenteum (silver tree, silver leaf tree, Afrikaans: Witteboom, or Afrikaans: Silwerboom) is an endangered plant species in the family Proteaceae, which is endemic to a small area of the Cape Peninsula, South Africa. Most grow in and around the city of Cape Town, but outlying (perhaps introduced) populations exist near Somerset West (Silwerboomkloof), Paarl and Stellenbosch. It is a protected tree in South Africa.
The silvertree is a striking evergreen tree, growing 5–7 m tall (sometimes up to 16 m). It is erect and well-proportioned with a thick, straight trunk and grey bark. The soft, silky leaves are shiny silver, lanceolate, 8–15 cm long and 2 cm broad, with their distinct silvery sheen produced by dense velvety hairs. The wind-pollinated flowers are produced in dense globose inflorescences 4–5 cm diameter, and give off a pleasant scent. Like all Leucadendrons, this tree is dioecious, with separate male and female plants. The fruit is a heavy woody cone, containing numerous seeds; each seed is a small nut with a silky-haired helicopter-like parachute, enabling it to disperse by wind. After germination it pushes up two green, bare and leathery cotyledons.
This enormous silver Protea is naturally confined to a tiny area in and around the city of Cape Town. Its main population grows on the slopes of Table Mountain, notably the Lion's Head area, above Rhodes Memorial and the mountain slopes above Kirstenbosch National Botanical Garden.
In addition there are three tiny outlying populations nearby, in Stellenbosch, Somerset West and Paarl (It has not yet been established for certain whether these are natural outliers, or were planted here in early Cape history). The Somerset West population is located within a natural heritage site called Silvertree Gorge, in the Spanish Farm suburb.
Historically, the silvertree was more 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 felled and now the silvertree is a rare and endangered species.
Status and conservation
Table Mountain is perhaps the only place where these trees grow naturally, as the populations near Stellenbosch and Paarl (though conceivably natural) may have been introduced from Table Mountain.
In the face of urban development, inappropriate fire management, and invasive alien trees such as pines and gums, silvertrees have been driven from about 74% of their natural range. Mortality of these short-lived trees is negligible after a burn, but then increases to about 5% per annum. During a longer term absence of burns however, sudden die-offs may occur, even in a matter of hours. This is believed to be the combined result of (warm) berg winds and diseased roots which are weakened by Phytophthora root rot which inhibits their water absorption.
An estimated 40 to 50 percent of the extant native population burned in the fire of 26 to 27 January 2006. As recruitment of seedlings only occurs naturally after fire, this was a necessary stage in the life-cycle of this Fynbos species, and the population has recovered totally.
A major deterrent to propagation of the silver leaf tree is its short life span, as most don't live more than 20 years. This doesn't affect their conservation however, as fires rejuvenate populations on average every 15–20 years by killing the surviving adults and triggering the release of the canopy seed bank (in the cones), and germination of the soil seed bank. Seeds remain viable for at least 80 years. Juveniles take 5–7 years to flower and set seed, whereafter the populations are ready to burn again.
|Wikimedia Commons has media related to Leucadendron argenteum.|
A large silvertree near Rhodes Memorial
A silvertree forest on the lower slopes of Devil's Peak
Partial removal of the invasive pine plantations allowed silvertree forests to gradually return.
- List of Southern African indigenous trees
- Peninsula Granite Fynbos
- Rhodes Memorial
- Newlands Forest
- Hilton-Taylor, C.; et al. (1998). "Leucadendron argenteum". IUCN Red List of Threatened Species. 1998: e.T30350A9539214. doi:10.2305/IUCN.UK.1998.RLTS.T30350A9539214.en.
- The Plant List: A Working List of All Plant Species, retrieved 27 December 2016
- "Protected Trees" (PDF). Department of Water Affairs and Forestry, Republic of South Africa. Archived from the original (PDF) on 5 July 2010. Retrieved 13 June 2013.
- "IDM Cape Peninsula - Ld arge". www.proteaatlas.org.za. Retrieved 2017-08-02.
- "Threatened Species Programme | SANBI Red List of South African Plants". redlist.sanbi.org. Retrieved 2017-08-02.
- "Archived copy". Archived from the original on 2007-09-30. Retrieved 2006-01-27.CS1 maint: archived copy as title (link)