PROTECTION 165 
danger becomes. Pure forests of shallow-rooted spe- 
cies, such as the spruce, are often leveled to the 
ground by the acre in this way in Europe. The best 
way to prevent the wind’s destructive influence is to 
plant deep-rooted species, to preserve protective belts, 
and to cut with great caution. On mountain sides 
where the soil is thin, it is often very difficult to 
prevent serious windfalls. The danger increases as 
the forest grows older and the limbs grow larger. 
Insects and fungi enter the wounds which have been 
produced by the breaking of limbs, and rot soon 
follows. 
Heavy rain often causes considerable damage. In 
tropical countries the leaves of delicate species are 
stripped from the branches by heavy downpours of 
water. Too much rain causes erosion, and helps the 
wind uproot trees by increasing their weight and 
softening the soil. 
Hail is extremely injurious in some countries, es- 
pecially in southern Europe. 
In northern climates great injury is caused by 
snow press. Just as some trees by the flat lateral 
position and pliability of their branches seem espe- 
cially adapted to windy countries, so do many trees 
with their conical form and pliant limbage seem 
well fitted to shed the great mass of snow and ice 
which forms in northern climates. In many instances 
