Variation in wood density and fibre length among Grevillea robusta (a. cunn ex r.br.) families grown in western Kenya

Abstract

This paper reports on the variation of specific gravity and fibre length among G. robusta families grown at Kodera Forest in Western Kenya. It also states the correlation between these properties and the environmental and growth factors. 2 Grevillea robusta is a high priority farm forestry tree of economic importance in East and Central Africa. It provides a variety of wood products with little interference to the adjacent crops. The wood properties of Grevillea robusta in general and specific gravity and fibre length in particular are not much studied. Reported information on variation of specific gravity and fibre length among G. robusta families is also scanty. Wood samples for the study were taken from a half-sib progeny trial of G. robusta, planted at Kodera in 1991. The 3.5 years old trial had stands representing 36 families from 14 provenances of natural stands of Australian families and 12 Kenyan families. An incomplete block design, with accessions replicated in different plots had been used in the experiment. Linear plots, each of ten trees and an initial spacing of 2 m x 2 m were used. Three trees per family were sampled at random for the determination of the wood properties. Samples for the wood properties were obtained at the intersection of the Magnetic North Direction (MN) and Breast Height points. The specific gravity was determined using the water displacement method (Browning, 1967) while a loupe graticule was used to measure lengths of fibres obtained using Franklins’ method of maceration. The growth factors for each tree sampled were assessed as well. Significant variations in the wood properties among the families were revealed. Families from Australia have higher specific gravity than the Kenyan selections, however the latter have longer fibres than the former. Specific gravity had significant correlation with environmental and growth factors while fibre length had significant association with growth factors only. It is concluded that, at 3.5 years, G. robusta can be selected for specific gravity and fibre length and can be thinned for firewood, aerial biomass and possibly for pulp production for wrapping and packaging purposes. It is recommended the provenances from high altitudes in Queensland be considered for dense wood and the Kenyan selections for long fibre production in future genetic improvement programmes.