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which have passed their prime and show weakness, are dashed to the ground often 
making a great gap in the forest in their fall ; but this is Nature's way the younger 
trees now have a chance, and a stand of young vigorous trees may take the place of 
those which have ceased to be efficient. 
Most of the pruning and cleaning up that New South Wales forests get comes 
about in this way. In the time to come this uncontrolled pruning will be replaced by 
the selective felling of the skilled forester, whose value will depend on that intuitiveness 
which will show him precisely what trees to remove, and in what direction they should 
be dropped to do least harm to the existing forest, and to be of the greatest potential 
benefit to it. 
Twist in Timber. 
This is the resultant of forces represented by the effect of the sun on the one hand 
and the wind on the other. I have published* some evidence and many opinions on 
the subject. 
There are some excellent photographs showing twist in British trees hi The 
Garden for 20th December, 1913, pages 632 and 633. 
The matter is of economic importance, because, in the vast majority of cases, 
untwisted trunks, yielding straight grained timber, are desired by the timber merchant. 
In our New South Wales forests as a rule the greater bulk of the head of a tree 
is to the north, i.e., it faces the sun, which rises in the east and longest influences the 
north. I have known bushmen use this method of ascertaining the north when lost or 
in difficulties. 
(d) Lightning. A good deal of damage arises from this cause in New South 
Wales forests, but because of the vastness of the areas concerned, and of the relatively 
small value of standing timber as a general rule, there ar very few data on the subject. 
Still less are there any data in regard to the relative liability of different kinds of trees 
to be struck by lightning. Here is a field in which observers all over the State can help 
by local observations. 
Schlich deals with the subject in Europe in iv. 556, in a very useful way. 
Lightning is also a source of fires. Silcoxf points out that in the United States 
in 1909, there were reported 294 fires originating from this cause, and he observes that 
such strokes are only dangerous if unaccompanied by rain. 
(e) Drought. Speaking in general terms of all forms of vegetation, trees hold 
out the longest, their roots extending deeply into the soil. A list of trees which resist 
drought would be a catalogue of those found on our Western Plains, and a number of 
these are figured and described in previous parts of the present work. But amongst 
the western trees some only will grow along the banks of creeks or lagoons, or where 
water lasts longest. The problem is a very difficult one to assess the resistance to 
drought of various species, especially as it is complicated with the resistance of selected 
individuals. 
* Port XLI, p. 15 of the present work. t Year book, Dept. of Agriculture, 1910, 410. 
