Olea capensis

Family

Oleaceae

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Synonyms

Olea guineensis Hutch. & C.A.Sm. Olea hochstetteri Baker Olea lancea Lam. Olea welwitschii (Knobl.) Gilg & Schellenb.

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Vernacular names

East African olive, ironwood olive, Elgon olive, African ironwood, black ironwood (En). Olivier du Cap (Fr). Mushargi, loliondo (Sw).

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Origin and geographic distribution

Olea capensis is widespread from Guinea and Sierra Leone east to Ethiopia and Kenya, and south to South Africa and Swaziland. It also occurs in Comoros and Madagascar, and on Socotra island (Yemen).

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Uses

The heartwood, often traded as ‘ironwood’, is in high demand for flooring, carpentry and panelling, and is widely used for house and bridge construction, counter and table tops, railway sleepers, tool handles and wagon parts. It produces beautiful furniture, turnery and sliced veneer, and is often used by African artists. It is suitable for interior trim, sporting goods, toys, novelties and agricultural implements. In South Africa it has been used traditionally to make assegais. It is also used as firewood and for charcoal production.
The oily fruits are edible and are used in southern Africa in the preparation of beer and lemonade. In East Africa bark decoctions are used as an emetic and anthelmintic, and to treat malaria, venereal diseases and female sterility; bark ash is applied as a dressing to wounds. In Swaziland bark decoctions are taken to treat peptic ulcers, and in South Africa the bark is used for skin lightening. In southern Africa root powder is applied to fractures and joint swellings, and leaf infusions to treat infections of the respiratory tract and pains. The foliage serves as fodder, especially during the dry season. The flowers produce nectar for honey bees. In South Africa Olea capensis has been used as stock for grafting olive cultivars from the Mediterranean region. The tree is considered sacred by the Maasai people and is commonly used in ceremonies.

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Production and international trade

The international trade in Olea capensis wood is very limited. The volumes sold by auction in South Africa in the period 2000–2008 varied from 50 m³ to 300 m³/year. In 2008 the price of first-quality boards of 2.5 cm and 5 cm thick was US$ 1225/m³ and US$ 1335/m³ respectively, and in 2009 the price of 2.5 cm thick and 10 cm thick boards was US$ 2110/m³ and US$ 2160/m³ respectively.

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Properties

The heartwood is pale brown to dark brown, often with irregular grey-black or yellowish streaks. It is distinctly demarcated from the yellowish white to grey, 2.5–5 cm wide sapwood. The grain is straight to slightly interlocked, texture fine and even. The wood surface shows a nice figure and is slightly oily to the touch.
The wood is heavy, with a density of 860–975(–1170) kg/m³ at 12% moisture content, and hard. It air dries very slowly with a marked tendency to surface checking, splitting, warping and distortion. Kiln drying is difficult and should be done at low temperatures. The shrinkage rates are moderate, from green to oven dry 4.0–4.7% radial and 6.7–7.9% tangential. The dried wood is unstable in service unless properly dried. At 12% moisture content, the modulus of rupture is (78–)127–174 N/mm², modulus of elasticity (8600–)16,500–19,500 N/mm², compression parallel to grain (41–)73–84 N/mm², compression perpendicular to grain 19 N/mm², shear (16–)22.5–26 N/mm², cleavage 28–94 N/mm, Janka side hardness 10,050–13,750 N and Janka end hardness 9780–14,200 N.
The wood is easy to saw when green, but difficult to saw and work when dried, and blunts saw teeth and cutting edges rapidly. In working the material should be held firmly. Quarter-sawn surfaces have a tendency to pick up in planing, and a cutting angle of 20° is recommended. The wood finishes with a nice polish without the use of a filler. Pre-boring is necessary in nailing and screwing. The wood does not always glue well with conventional wood glues because of the oily surfaces. It turns fairly well and good-quality veneer has been obtained with slicing. The steam bending properties are satisfactory. The wood is moderately durable to durable. It is sometimes attacked by ambrosia beetles and termites, but is not susceptible to Lyctus beetles. The heartwood is somewhat resistant to impregnation with preservatives, the sapwood is permeable.
Coumarin and secoiridoid glucosides have been isolated from the bark. The lignans (–)-olivil and (+)-cyclo-olivil have also been isolated from the bark.

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Adulterations and substitutes

The wood of wild African olive (Olea europaea L. subsp. cuspidata (Wall. ex G.Don) Cif.) closely resembles that of Olea capensis and is used for similar purposes.

Description

Evergreen shrub or small to fairly large tree up to 35(–40) m tall; bole branchless for up to 15 m, straight and cylindrical but sometimes irregular or fluted, up to 90(–150) cm in diameter; bark surface of young trees smooth and pale grey, in old trees becoming longitudinally fissured and dark grey, inner bark thick, hard, cream-coloured to orange-brown or greenish, exuding a blackish gum; crown small and dense with steeply ascending branches, or rounded with spreading branches; twigs rounded, glabrous, with scattered white lenticels. Leaves decussately opposite, simple; stipules absent; petiole 0.5–1(–2) cm long; blade elliptical to oblong-elliptical or ovate-elliptical, 3–11(–16) cm × 1.5–5(–6.5) cm, cuneate at base, obtuse to acute or short-acuminate at apex, entire to slightly wavy at margins, leathery, glabrous, glossy green above, pale green below, pinnately veined with 5–7 pairs of inconspicuous lateral veins. Inflorescence a terminal panicle 3–8 cm long, glabrous, many-flowered. Flowers bisexual, regular, 4-merous, fragrant; pedicel short; calyx cup-shaped, c. 1 mm long, with triangular lobes; corolla 2–3 mm long, white, with short tube and elliptical lobes; stamens 2, inserted on corolla tube, c. 2 mm long; ovary superior, flask-shaped, c. 1.5 mm long, 2-celled, style short. Fruit a globose to ellipsoid drupe 0.5–2 cm × 0.5–1 cm, purple-black when ripe; stone with thick and woody wall, usually 1-seeded. Seed with copious endosperm.

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Other botanical information

Olea comprises 33 species, most of them occurring in eastern and southern Africa and in tropical Asia.
Three subspecies of Olea capensis are distinguished: subsp. capensis restricted to South Africa, subsp. enervis (Harv.) I.Verd. restricted to South Africa and Swaziland, and subsp. macrocarpa (C.H.Wright) I.Verd. (synonyms: Olea guineensis Hutch. & Dalziel, Olea hochstetteri Baker) covering the whole area of distribution of the species. They differ in leaf shape and size, and in size of the fruit, subsp. macrocarpa having the largest leaves and fruits. The latter subspecies is often a larger tree than the other two, and consequently more important as a timber tree.
Olea welwitschii (Knobl.) Gilg & Schellenb. has also been considered as a subspecies of Olea capensis, but in most recent taxonomic publications it is regarded again as a distinct species, mainly differing in its usually narrower leaves with longer petioles. Olea welwitschii is widespread from Cameroon east to Ethiopia and Kenya and south to Zambia, Angola and Mozambique, from lowland rainforest to evergreen mountain forest. It is a small to fairly large tree up to 35 m tall, with bole up to 100 cm in diameter, sometimes with large buttresses. Its wood resembles that of Olea capensis and is used for similar purposes, e.g. for construction, flooring, joinery, furniture and sliced veneer. However, its density appears to be slightly lower, 690–820 kg/m³ at 12% moisture content, and the wood is less strong but more stable in service. In Ethiopia the buttresses are cut to make doors. The wood is also used as firewood and for charcoal production. The bark is applied in traditional medicine for similar purposes as that of Olea capensis.
Olea lancea Lam. is also closely related to Olea capensis, but differs in its usually narrower leaves with shorter petioles. It is a shrub or small tree up to 6 m tall and occurs in Madagascar, Réunion and Mauritius. The wood (‘bois de cerf’, ‘bois d’olive blanc’) is used for construction and joinery. Bark decoctions are used to treat infections of the respiratory tract and skin complaints, and leaf infusions as emmenagogue and aphrodisiac.

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Anatomy

Wood-anatomical description (IAWA hardwood codes):
Growth rings: 2: growth ring boundaries indistinct or absent. Vessels: 5: wood diffuse-porous; 7: vessels in diagonal and/or radial pattern; 10: vessels in radial multiples of 4 or more common; 13: simple perforation plates; 22: intervessel pits alternate; 24: intervessel pits minute (≤ 4 μm); 30: vessel-ray pits with distinct borders; similar to intervessel pits in size and shape throughout the ray cell; 41: mean tangential diameter of vessel lumina 50–100 μm; 49: 40–100 vessels per square millimetre; 58: gums and other deposits in heartwood vessels. Tracheids and fibres: 61: fibres with simple to minutely bordered pits; 66: non-septate fibres present; 70: fibres very thick-walled. Axial parenchyma: 78: axial parenchyma scanty paratracheal; 92: four (3–4) cells per parenchyma strand; (93: eight (5–8) cells per parenchyma strand). Rays: 97: ray width 1–3 cells; (98: larger rays commonly 4- to 10-seriate); 106: body ray cells procumbent with one row of upright and/or square marginal cells; 113: disjunctive ray parenchyma cell walls present; 115: 4–12 rays per mm. Mineral inclusions: (150: acicular crystals).
(E. Uetimane, P. Baas & H. Beeckman)

Growth and development

Olea capensis is characterized as a shade tolerant species. Initial growth of seedlings may be up to 1.1 m/year, but after about 4 years the tree grows slowly. In Tanzania, 31-year-old trees were 12–15 m tall with a bole diameter of 12.5–14.5 cm.
In southern Africa trees flower periodically, at intervals of 2–4(–7) years. Fruits ripen 0.5–1 year later. They are eaten by birds such as hornbills and doves, which may disperse the stones. Stones that have past the digestive system of birds germinate after 4–6 months. Studies of faecal samples of chimpanzees in Rwanda showed that these often contained Olea capensis stones. Monkeys, wild pigs, fruit bats and squirrels have also been recorded to feed on the fruits. Investigation of the roots revealed the presence of vesicular mycorrhizae.

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Ecology

Olea capensis is characteristic of humid mountain forest. In West Africa it is restricted to mountains above 600 m altitude, in Central Africa it occurs at 1000–2800 m altitude, and in East Africa it is mainly found at 1500–2700(–3200) m altitude. In South Africa Olea capensis is locally a dominant canopy tree, especially in forests along the coast. In East Africa Olea capensis can dominate the climax vegetation in lower and mid-altitude montane forest, together with Olea europaea L. subsp. cuspidata (Wall. ex G.Don) Cif. and Podocarpus latifolius (Thunb.) R.Br. ex Mirb. In Ethiopia it is often found together with Juniperus procera Hochst. ex Endl. and Afrocarpus falcatus (Thunb.) C.N.Page.
In general, Olea capensis prefers regions with an annual rainfall of 800–1500 mm and a mean annual temperature of 14–18°C. Young trees prefer well-drained, deep, loamy and fertile soils. Once established, they are quite drought resistant and they also grow in poor soils.

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Propagation and planting

Natural regeneration in mountain forest in south-eastern Ethiopia was reported to be poor, but in Tanzania it was reported to be abundant. In South Africa seedlings are often abundant in the forest, but many die off as a result of diseases such as damping-off.
For sowing, the use of fresh stones is recommended. One kg contains 1500–3300 stones. The germination rate is about 35% and germination takes 2–9 months, but sometimes up to 2 years. Whole fruits or stones can be collected from the ground. Stones can be stored for up to 3 months, but they should be cleaned from pulp by rubbing in running water and subsequently dried for about 5 days. At a low temperature of 3°C they can be stored for longer periods. Before sowing the dry stones should be soaked in water for 2 days. Wildlings are sometimes also collected for planting. Planting should be done during the wettest part of the year. Seedlings of about 180 cm tall with lower leaves stripped off are often used for planting into the field.

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Management

In Tanzania Olea capensis is grown in plantations in clusters of up to 10 trees at close spacing (1 m × 1 m) with nurse trees such as Grevillea robusta A.Cunn. An interval of 7–8 m is maintained between the clusters. Olea capensis does not interfere much with crops and has been recommended for agroforestry systems. The young tree can be managed by lopping, pollarding and coppicing. In South Africa trees showed regeneration by coppices in 40% of cut stems.

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Diseases and pests

Olea capensis is often browsed by goats as well as wild animals such as elephants and antelopes, but it recovers well.

Harvesting

In plantations the boles can be harvested for timber about 75 years after planting. In forests in southern South Africa, where Olea capensis is a dominant canopy tree, trees are harvested under a 10-year felling cycle and selected according to externally visible criteria of maturity.

Yield

In Tanzania well-established stands of Olea capensis had a standing volume of about 20 m³/ha 25–30 years after planting.

Handling after harvest

It is recommended to remove logs soon from the forest after felling because the sapwood is prone to fungal and insect attacks. Freshly harvested logs sink in water and cannot be transported by river.

Genetic resources and breeding

In many regions Olea capensis is becoming rare due to over-exploitation. This is the case in many mountain regions in Ethiopia, Kenya and Tanzania. Locally in South Africa, already by 1890 over-exploitation of forests where Olea capensis dominated had made conservation measures essential. However, in forests in southern South Africa, it is still the most common canopy tree. Olea capensis is legally protected in South Africa and harvesting is regulated. Some provenance testing has been done in Tanzania with the aim of selecting the best trees regarding growth performance for larger-scale planting.

Prospects

The heavy weight and hardness of the wood of Olea capensis are serious drawbacks for many applications. However, the nicely figured wood is attractive for furniture and sliced veneer. Plantations could produce wood with good export prospects, but the rotation cycles needed are quite long. Olea capensis is an interesting species for planting in degraded forests throughout its natural distribution area. Studies to determine the genetic variation are needed, as well selection of provenances with superior bole characteristics for timber production and investigations on optimal silvicultural systems. In countries with high deforestation rates, immediate action is needed for in-situ conservation of remaining stands.

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Major references

• Bekele-Tesemma, A., 2007. Useful trees and shrubs for Ethiopia: identification, propagation and management for 17 agroclimatic zones. Technical Manual No 6. RELMA in ICRAF Project, Nairobi, Kenya. 552 pp.
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• Coates Palgrave, K., 1983. Trees of southern Africa. 2nd Edition. Struik Publishers, Cape Town, South Africa. 959 pp.
• Friis, I., 1992. Forests and forest trees of northeast tropical Africa: their natural habitats and distribution patterns in Ethiopia, Djibouti and Somalia. Kew Bulletin, Additional Series 15, H.M.S.O., London, United Kingdom. 396 pp.
• Green, P.S., 2002. A revision of Olea L. (Oleaceae). Kew Bulletin 57: 91–140.
• Hines, D.A. & Eckman, K., 1993. Indigenous multipurpose trees of Tanzania: Uses and economic benefits for people. [Internet] Cultural Survival Canada, Ottawa, Canada. http://www.fao.org/ documents/show_cdr.asp?url_file=/docrep/X5327e/x5327e1c.htm. Accessed March 2010.
• Maundu, P. & Tengnäs, B. (Editors), 2005. Useful trees and shrubs for Kenya. World Agroforestry Centre - East and Central Africa Regional Programme (ICRAF-ECA), Technical Handbook 35, Nairobi, Kenya. 484 pp.
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Other references

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• Bamuamba, K., Gammon, D.W., Meyers, P., Dijoux-Franca, M.G. & Scott, G., 2008. Anti mycobacterial activity of five plant species used as traditional medicines in the Western Cape Province (South Africa). Journal of Ethnopharmacology 117(2): 385–390.
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Afriref references

Sources of illustration

• Bekele-Tesemma, A., 2007. Useful trees and shrubs for Ethiopia: identification, propagation and management for 17 agroclimatic zones. Technical Manual No 6. RELMA in ICRAF Project, Nairobi, Kenya. 552 pp.
• Hawthorne, W. & Jongkind, C., 2006. Woody plants of western African forests: a guide to the forest trees, shrubs and lianes from Senegal to Ghana. Kew Publishing, Royal Botanic Gardens, Kew, United Kingdom. 1023 pp.
• von Breitenbach, F., 1974. Suid-Kaapse bosse en bome. Die Staatsdrukker, Pretoria, South Africa. 328 pp.

Author(s)

•	R. Aerts Division Forest, Nature and Landscape, Katholieke Universiteit Leuven, Celestijnenlaan 200E, Box 2411, BE-3001, Leuven, Belgium

Editors

•	R.H.M.J. Lemmens PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
•	D. Louppe CIRAD, Département Environnements et Sociétés, Cirad es-dir, Campus international de Baillarguet, TA C-DIR / B (Bât. C, Bur. 113), 34398 Montpellier Cedex 5, France
•	A.A. Oteng-Amoako Forestry Research Institute of Ghana (FORIG), University P.O. Box 63, KNUST, Kumasi, Ghana

Associate editors

•	E.A. Obeng Forestry Research Institute of Ghana (FORIG), University P.O. Box 63, KNUST, Kumasi, Ghana

Photo editor

•	G.H. Schmelzer PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands

Correct citation of this article

Aerts, R., 2011. Olea capensis L. [Internet] Record from PROTA4U. Lemmens, R.H.M.J., Louppe, D. & Oteng-Amoako, A.A. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>. Accessed .

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