SILVICULTURE. 185 



positive measures must be resorted to for collecting 

 and destroying the broods of insects before they 

 have time to do damage. Considerable amounts 

 of money are spent in this direction in European 

 forest management, amounting in ordinary times 

 to from one-half to one cent per acre, but, from 

 time to time, the pests break out in such numbers 

 that no remedies will avail.^ Some loss must 

 be sustained, which is, however, of less moment 

 if the crop had already developed to suitable size 

 and can be harvested when the trees have been 

 killed. 



Wind-storms are a danger to older timber, es- 

 pecially of shallow-rooted species, like the spruce, 

 and on soft soils and exposed slopes or mountain 

 tops. Here care must be taken in keeping the 

 stand well thinned, so that the trees may get accus- 

 tomed to the swaying of the winds in more open 

 stand. In this way they are induced individually 

 to form a better root system and become wind-firm, 

 while in the dense stand their strength was only in 

 the union with neighbors. 



Under conditions where damage from windfall 

 is to be expected, it becomes necessary to arrange 

 the felling areas so that no stand of old tijnber be 

 suddenly exposed to the prevailing winds by the 



' In Bavaria, in one year (1891), ;Jsoo,ooo, or 20 cents per 

 acre of property and ;^l.8o per acre infested, were spent in combat- 

 ing one insect, the nun, without much effect. The premature har- 

 vesting of 60,000,000 cubic feet was the result of the damage. 



