St Helena gumwood  (Commidendrum robustum)

The St Helena gumwood is classified as Endangered (EN) on the IUCN Red List (1). The subspecies Commidendrum robustum gummiferum is classified as Extinct (EX) and the subspecies Commidendrum robustum robustum is classified as Endangered (EN) (1).

Adopted as the national tree of St Helena in 1977, this highly branched tree has a knarled and crooked trunk and an umbrella-like canopy (1) (2). It produces white flower heads which droop from the ends of branches in the winter and spring months (2). The leaves are seven to ten centimetres long and vary from grey-green to dark green. They are wrinkled, thick and hairy (3).

Endemic to the small island of St Helena in the South Atlantic, 1,960 kilometres from the coast of southwest Africa and 2,900 kilometres east of South America (2).

The St Helena gumwood previously formed subtropical and tropical forest on inland cliffs and mountain peaks (1).

This hermaphroditic plant produces a large amount of seed every year that falls around the parent tree and germinates freely, providing there is no interference by grazing animals or pests (1).

St Helena was settled in 1659 and since then the St Helena gumwood has been exploited for use as timber and firewood. Forests were cleared for use as pastureland and introduced goats grazed heavily on seedlings. Populations were reduced to extremely low numbers by the 1980s, at which point a conservation management plan was started. In 1991, the largest population at Peak Dale was attacked by the jacaranda bug, Orthezia insignis. This sucking insect took sap from the trees and encouraged a black mould that rapidly killed infected trees (2).

Protected by the Endangered Endemic and Indigenous Species Protection Ordinance 7 of 1996, the St Helena gumwood has been the focus of a conservation programme started in the 1980s. An extremely successful biological control programme to combat the jacaranda bug involved the introduction of the ladybird Hyperaspis pantherina from Kenya (2). Following dangerous reductions in populations of the St Helena gumwood, the Millennium Gumwood Forest Project was started and resulted in the planting of 4,300 trees in a previously degraded wasteland in 2000 (2). Other replanting projects are underway, as well as weed clearances (3). Although it is not thought that any pure trees of the subspecies Commidendrum robustum gummiferum exist, the hybrid population at Peak Dale shows some characteristics of this subspecies (4).

For more information on St Helena see:

• St Helena National Trust:
  www.nationaltrust.org.sh/
• Cock, M.J.W. (2003) Risks of Non-Target Impact Versus Stakeholder Benefits in Classical Biological Control of Arthropods: Selected Case Studies from Developing Countries. In: Van Driesche, R.G. (Ed.) Proceedings of the International Symposium on Biological Control of Arthropods, Honolulu, Hawaii, 14-18 January 2002. United States Department of Agriculture, Forest Service, West Virginia, USA. Available at:
  www.bugwood.org/arthropod/day1/cock.pdf