A study of growth and economic benefit in the Eucalypus grandis×E. urophylla plantations of the south of Guangxi

On Guangping Forestry Farm in Shangsi County,Guangxi,the growth increment of Eucalypus grandis × E. urophylla clones of six growing year(1- 6 year) were investigated respectively. An economic benefit was evaluated according to the growth increment. The results were as follows: total DBH increment of E. grandis × E. urophylla clones was between 4.0 cm and 15.3 cm,the annual increment and the current annual increment of DBH were 3.4 cm and 2.6 cm; tree height increment was between 5.0 m and 19.2 m,the annual increment and the current annual increment of tree height were 4.3 m and 3.2 m; the total stand volume was between 7.7 m3·hm- 2and 289.7 m3·hm- 2,the annual volume and the current annual volume were33.6 m3·hm- 2and 48.3 m3·hm- 2. Regression analysis showed that there was a linear relationship(R2= 0.9638- 0.9898) between the age and the DBH,tree height,stand volume respectively. And a well logarithmic relationship was also found between the age and the DBH,tree height,stand volume. Therefore it would be possible to estimate the DBH,the tree height and the volume at different ages. In this study,when the stand grew to 6 years old,its output input ratio was 2.3∶ 1.0 and it achieved a profit of 12246 yuan·hm- 2every year.