Iroko

Introduction

Formerly known as Milicia excelsa Benth. and Hook f., and Milicia regia A. Chev.

Environmental

Listed in the IUCN Red List of Threatened Species as LR – Lower Risk (near threatened): close to being classed as Vulnerable. Also meets CITES Appendix II criteria. [Information courtesy of Timbmet Ltd]

Distribution

C. excelsa has a wide distribution in tropical Africa, from Sierra Leone in the west, to Tanzania in the east. C. regia is confined to West Africa, where it occurs from Senegal to Ghana. There does not appear to be any significant difference between the timber of the two species.

The tree

C. excelsa attains very large sizes, reaching 45m or more in height and up to 2.7m in diameter. The stem is usually cylindrical and mostly without buttresses. It occurs in the rain, and mixed deciduous forests.

The timber

When freshly cut, or when unexposed to light, the heartwood is a distinct yellow colour, but on exposure to light it quickly becomes golden-brown. The sapwood is narrow, being about 50mm to 75mm wide, and clearly defined. The grain is usually interlocked and the texture is rather coarse but even, and the wood weighs on average 660 kg/m³ when dried. Large, hard deposits of calcium carbonate called 'stone' deposits, are sometimes present in cavities, probably as a result of injury to the tree. They are often enclosed by the wood and not visible until the time of sawing, though the wood around them may be darker in colour, thus giving an indication of their presence.

Drying

The timber dries well and fairly rapidly, with only a slight tendency to distortion and splitting.

Strength

Iroko has excellent strength properties, comparing well with teak, though weaker in bending and in compression along the grain.

Working qualities

Medium to difficult - Iroko works fairly well with most tools, though with some dulling effect on their cutting edges, especially when calcareous deposits are prevalent. On quarter-sawn stock, there is a tendency for grain to pick up due to interlocked grain, and a reduction of cutting angle to 15° is usually necessary to obtain a smooth surface. An excellent finish can be obtained if the grain is filled. It takes nails and screws well, and can be glued satisfactorily.