30 



Detailed tables similar to the above can not be made for the 

 other species of eucalypts, but the field notes of the trees given 

 in the Appendix state the age and size of a number of species 

 found growing in various places in the Islands. 



The yield of wood or lumber to be obtained from a grove of 

 a given age will depend, of course, not only on the size of the 

 trees but also on the number of trees per acre. This, in turn, 

 depends on the spacing of the trees in the plantation and the age 

 of the stand. As a rule the older the grove the fewer trees to 

 the acre, since more individuals are crowded out and killed in 

 the struggle for existence. When trees are grown in compara- 

 tively open stands, it sometimes happens that the number of 

 trees at the end of eight or ten years is greater than the number 

 of trees planted, in spite of the trees killed. This is due to the 

 fact that a number of trees blown over send out numerous 

 sprouts, some of which develop into good trees. 



To measure the yield of the various groves examined it was 

 necessary to construct volume tables which show the average 

 volume or contents of trees of various sizes. The volume of a 

 tree of a given species depends on its diameter, height and age. 

 Of two trees having the same diameter and the same height, the 

 older tree has a slightly greater volume, because an older tree 

 is fuller in form and more cylindrical. If very accurate results 

 are desired, all the three factors must be known, but for prac- 

 tical purposes two factors, such as diameter and height, or di- 

 ameter and age, are sufficient. 



Table II shows the average volume in cubic feet of different 

 sized blue gum trees.* 



* The left hand vertical column in this next table, shows the diameter 

 of the tree at breast height; the uppermost horizontal line shows the 

 total height X)f the tree from the ground to the top of the crown. To 

 find the volume of a tree of any given diameter and height, as for ex- 

 ample 10 inches in diameter and 70 feet high, look in the left hand 

 column for the diameter (10), and under the height (70) find the volume 

 of the tree (14.6 cubic feet). 



