TENDING OP WOODS DURING EARLY YOUTH. 193 



simultaneously or beforehand a special shelter-wood, or 

 nurses. The trees selected for this purpose must be frost- 

 luirdy and possess a thin, or moderately dense crown. The 

 best nurses in temperate Europe are Birch, Scotch Pine, 

 and Larch. Where danger from late frost is excessive, 

 Larch, owing to its early sprouting, is less well adapted 

 as a nurse, but it does very well in all other localities. 

 In moist localities Alder and Wallows have been similarly 

 used. 



The nurses may be distributed evenly over the area, 

 or be placed in alternate lines. They are re- 

 moved when the tender species can do without them. 

 Frequently some of the nurses are retained so as to form 

 a mixed wood. 



c. Cold Winds. 



The effects of raw cold winds are often more disas- 

 trous than frost produced locally by radiation. Where 

 they are to be feared, lateral as well as vertical shelter is 

 required. This may be given either by adjoining woods 

 of sufficient height and density, or, in their absence, by 

 artificial shelter-belts, or wind-breaks. These must be 

 dense, and they should be established some time before 

 the area to be protected is placed under cultivation or 

 regeneration. The species of which wind-breaks consist 

 should, if possible, be evergreen, and with dense crowns 

 coming close to the ground, such as Spruce. 



An alternative measure consists in mixing a hardy 

 species, such as Scotch Pine, with a tender crop. Or 

 the wood is treated under the selection system, when 

 trees of all ages are intermixed on the same area. In 

 that case, the middle-aged and younger trees provide 



VOL. II. O 



