Energy and material characteristics of different component tissues of eucalyptus urophylla × grandis

Ash content, calorific value and content of selected organic and mineral constituents in leaves, branches, roots, stem-wood and bark of four year old, plantation grown Eucalyptus urophylla × grandis were analyzed. Ash contents of the five component tree tissues ranged from 0.3% to 4.1%, and the order by decreasing ash content was: leaves >; bark >; branches >; roots >;stem-wood. Gross and ash free calorific values of the five component tissues ranged from 17.9 to 20.2 kJ g^-1 and 18.6 to 21.1 kJ g^-1 respectively. Leaves had the highest gross and ash free calorific values and bark the lowest, the order of component tissues by decreasing gross calorific value were: leaves >; roots >; branches >; stem-wood >; bark; and by decreasing ash free calorific value: leaves >; branches >; roots >; stem-wood >; bark. Gross calorific values of the five component tissues showed no significant correlations with crude protein, crude fiber, crude fat, lignin, or α-cellulose content, nor with the content of any of the elements nitrogen, phosphorous or carbon (P<;0.05). In contrast, ash free calorific value did show significant (P<;0.05), moderate to strong positive correlations with crude protein, nitrogen and crude fat content, as well as a significant, strongly negative correlation with crude fiber content. Interestingly though, gross and ash free calorific values were positively and strongly correlated with each other (r=0.93, P<;0.01). It was concluded that relationships between both ash free and gross calorific values and constituents of the component tissues studied are quite complex and clearly influenced by many factors.