146 THE BOOK OF NATURE STUDY 



Trees are often prevented from growing spontaneously where 

 animals are allowed to graze. The Scots pine will nourish on 

 sand-dunes; seedlings will spring up naturally, and will grow 

 into young trees, provided they are protected from animals. 

 When, however, cattle and sheep are allowed to roam at will over 

 the dune the seedlings are destroyed, and the pine has to be 

 planted and enclosed until the young trees have reached a certain 

 height. Foresters are all agreed that animals roedeer, squirrels, 

 above all rabbits do incalculable harm to woodlands and planta- 

 tions. Not only do rabbits destroy young trees, but they eat 

 the bark off the bottom of the young trunks, and thus affect the 

 formation of sound wood, so that even after a lapse of fifty years 

 or more the wood may be found in a state of decay. It is 

 lamented by woodmen that rabbits are getting more " wood keen " 

 than they used to be. Wire netting is now placed 4 feet high, 

 instead of 3, and with an outward slope to prevent the rabbits 

 getting into the wood. Mice, too, do a great deal of harm, especially 

 since hawks, weasels, and stoats have been destroyed. Those 

 animals used to eat the mice, which now exist in large numbers, 

 and devour millions of bushels of acorns. 



METHODS OF OBSERVATION ON WOODS 



In studying woodland vegetation it will be best to begin 

 with the woods nearest to the home or school. In many parts 

 of the country, particularly in the west, farm houses have small 

 belts of woodland around them. This is so usual that there 

 must be some reason for it. Trees not only shelter the pastures 

 and the houses from the force of the wind, but they improve the 

 land in several ways. Their decaying leaves enrich the soil; 

 they prevent too rapid evaporation from its surface, and thus 

 help to retain a certain amount of moisture in it. If such a wood 

 is on a slope it effectually prevents the denudation of the soil, 

 which may be considerable on an exposed hillside owing to the 

 action of water, particularly in heavy rains. Belts of woodland 

 also afford breeding places for birds, which are very useful in de- 

 stroying insects that might otherwise become a pest to the farmer. 



Of late years the municipalities of large towns, in order to 



