Abstract:

This study was aimed primarily at providing information on physical and mechanical properties
of selected eucalypts clones GU7, GU8, GC540, GC550 and GC796; assess the variations of
these properties across growing sites, along tree height and from pith to bark; and compare these
properties with those of their parent materials; i.e. Eucalyptus grandis, Eucalyptus
cammaldulensis, and Eucalyptus urophylla. The physical properties assessed were basic density
(BD) and calorific value (CV) while the mechanical properties included static bending strength
(MOE, MOR, Wmax), maximum compressive strength parallel to the grain (MCS), ultimate
shear strength parallel to the grain (MSS) and cleavage strength (CLR). The test samples were
collected between December 2008 and March 2009 from clonal trials in Kifu and Ikulwe located
in Lake Victoria Crescent and South and Eastern Lake Kyoga Basin Agro ecological zones
(AEZ), respectively. Five well-formed trees were selected for each clone per site, felled and
sectioned into three billets of 1.2m long obtained at breast height (1.3m), 45% and 75% of the
merchantable tree height. The test samples were seasoned to 28 % MC and machined to the final
size of 800 x 20 x 20 mm from which the test pieces were obtained. Test methods were adopted
from British Standard (BS 373:1957) for all properties except for calorific value test where
standard test methods for analysis of wood fuels according to the American Society for Testing
and Materials [ASTM E870-82(2006)] were used. Results showed that clones GC540 and GU7
had higher mean values for basic density, CLR and CV which are the basic properties for
structural timber and fuel wood production. GC540 and GC796 had higher values for MCS,
MOR and CRL compared to other clones tested and parent materials indicating a potential for
use as structural timber and poles with good workability especially with joints. However, MOE
values of all clones tested was lower than that of parent materials. The site x property
relationship was significant for properties BD, MSS, CRL, MOE, MOR and Wmax and this was
most expressed in clones GC540 and GC796. Position along the tree x property relationship was
significant for BD and MCS and was more pronounced in GU7 and GU8 clones. MCS, MSS,
MOE and MOR varied significantly in radial direction while BD and CV did not. It was
concluded that, clonal eucalypts wood at 6-7 years can be used for fuel wood, furniture, posts,
and poles while for construction and other structural uses, advice of registered structural
engineers should be sought. It is recommended that a wider study of wood properties including
microfibril angle, fibre length, kappa number and chemical properties be carried out on all clones
from all agro ecological zones and at higher rotations so as to fully assess the suitability of
clones.