COMPARISON OF THE SPECIFIC GRAVITY VARIATION OF Swietenia macrophylla, Khaya senega/ens;s AND Pau/ownia fortunei

Abstract

Since the existing natural forests have become increasingly subjected to conservationpressure, forest plantations have been recognized as an alternative to meet the future~demand for sawn timber. A major drawback for the efficient utilization and promotion ofnew species such as Khaya senegalensis and Paulownia fortunei as well as muchfamiliar Swietwnia macrophy/la is the lack of information regarding their woodproperties grown under local conditions. The present work was designed to determinespecific gravity of each species, investigate the variation of specific gravity within thespecies and to determine the effect of growth rate on specific gravity.

Specific gravity variations were studied in 79 year old Swietwnia macrophylla, 49 yearold Khaya senegalensis and 16 year old and Paulownia fortunei trees. Three trees wereselected from each species and pith to bark variation was investigated in sample disksremoved at breast height, 50%' and 80% heights of the bole length. Radial variationswere studied at percentage distances from the pith.

The mean numerical specific gravity values obtained for Swietwnia macrophylla. Khayasenega/ensis and and Paulownia fortunei were 0.511,0.617 and 0.317 respectively andthese values suggest that the values are comparable to those earlier published data forother countries. The results of this study indicate that general pattern of radial variationof specific gravity in both Swietwnia macrophylla and Khaya senegalensis was to remainuniform from pith to bark. This pattern was evident at all the height levels. In Paulowniafortune, the radial trend was to show a gradual increase from pith to bark at all the heightlevels. The axial trend of Swietwn!a macrophyl/a was higher specific gravity at the base,drops to a minimum at mid height and increase again to a maximum at merchantabletop. Khaya senegalensis showed a gradual increase from base to top. The axial variationwas not significant in both these species. and Paulownia fortunei showed a significantreduction of specific gravity from base to top.

To investigate the effect of growth rate on specific gravity, sample disks were extracted atbreast height and ring width and whole ring specific gravity were measured based on thegrowth rings identified from pith to bark. Results indicated that no substantial anddefinite relationship appears to exist between whole ring specific gravity and ring widthrepresenting the growth rate in Swietwnia macrophyl/a. Khaya senegalensis (diffuseporous)and and Paulownia fortunei (ring-porous).