25 



whether it would pay to fertilize trees grown for commercial 

 purposes. 



When grown in particularly dry localities, or if there should 

 happen to come an extended drought immediately after the trees 

 are planted, it may be necessary to resort to artificial irrigation 

 in order to save the plantation. Where water is available and 

 irrigation is inexpensive, the additional growth of the young 

 trees due to artificial watering will more than make up for the 

 expense involved. As a rule, however, irrigation is probably 

 impracticable for commercial Eucalyptus plantations. 



Because of the rank weed growth in most places in Hawaii 

 it is usually necessary to cultivate one or more times or cut back 

 the grass and weeds in recently established tree plantations. 

 This may be done with a scythe or a hoe, or an ordinary culti- 

 ator may be used where the trees are planted sufficiently far 

 apart. At the end of the first year, after the trees are 5 or 6 

 feet high, they can take care of themselves and as a rule need no 

 other attention, except that they must be protected against fire 

 and cattle, as has already been described. 



Thinning. 



If the trees are planted close enough together, they will make 

 a rapid height growth, each tree endeavoring to overtop the 

 others to a sufficient amount of light. As a result height growth 

 is made at the expense of increase in diameter. In this struggle 

 of the trees to obtain a sufficient amount of light a point is soon 

 reached when certain trees fall too far behind, become over- 

 topped, suppressed, and stunted and become a hindrance to the 

 better and more vigorous trees. It is then a good plan to cull 

 out the suppressed trees in order to give the better individuals 

 a chance to grow in diameter. This process of cutting out the 

 poor trees is known as a thinning. 



The first thinning in a blue gum forest grown for timber or 

 poles may be made, as a rule, when the plantation is seven to 

 nine years old, the vigorous or dominant trees at that time being 

 7 to 12 inches in diameter and 40 to 60 feet high. The rule 

 for thinning stands is to thin lightly and to thin often. If too 

 many trees are taken out at one time and the stand is opened up 

 too much the remaining trees will begin to branch, the danger 

 from windfall is increased, the ground may dry out, and weeds 

 and grass may come in. As a rule the crown cover of the forest 

 should not be broken more than can be filled by the growth of 

 the remaining trees within three or four years. Ten to fifteen 



