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A QUALITY ASSESSMENT OF THE EXOTIC SOFTWOODS OF EAST AFRICA FOR SAWN TIMBER
D. N. PATERSON
The Commonwealth Forestry Review
Vol. 45, No. 3 (125) (September, 1966), pp. 212-223
Published by: Commonwealth Forestry Association
Stable URL: http://www.jstor.org/stable/42603487
Page Count: 12
You can always find the topics here!Topics: Timber, Softwoods, Indigenous species, Age structure, Plantation forestry, Species, Clearcutting, Forestry, Assessed values, Forestry research
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The amount and quality of sawn timber recovered from important exotic softwood plantation species of different ages was studied by the Utilisation Section of the Kenya Forest Department in 1963. The results obtained are compared with those observed from similar studies with four indigenous tree species taken from natural forest. Additional factors affecting quality are also considered, and all features are related to current sale prices. Recovery from gross overbark log volumes rose from about 30 to 50-60 per cent in 12 years old thinnings, and 35 years old clear fellings of exotic softwoods respectively. The logs were sound and generally circular in section. In contrast, logs from four indigenous species which were overmature and larger in size were generally unsound and irregular in shape, yielding only 26-35 per cent sawn timber from gross overbark log volumes. The proportion of structural quality timber rose from about 20 per cent to 43 per cent at 12 years and 35 years old respectively in the exotic softwoods, while approximately 75 per cent structural quality timber was obtained from the overmature indigenous species. Other factors affecting stand values included basic strength values, ease of extraction and conversion, natural durability and possibility of impregnation, rating as a fine timber, and difficulty of regeneration. Accounting for all factors, it was considered that 12 year old exotic softwood thinnings were only about 15 per cent as valuable as 35 year old clear fellings, and about ten per cent as valuable as the best overmature indigenous species. Although the method of assessing sawn timber by stress (or strength) grades was considered suitable for large sized timber, it was not thought to be ideal for small sized timber, which could often be converted into more profitable products than sawn structural timber.
The Commonwealth Forestry Review © 1966 Commonwealth Forestry Association