142 A MANUAL OF FORESTRY. 



has "been executed. That density must be such as to 

 ensure the most favourable conditions for the further 

 advancement of the young crop ; in other words it must 

 afford sufficient light to the young crop without expos- 

 ing it to injury by frost, drought, or excessive weed 

 growth; at the same time there must be sufficient 

 shelter left to affect the general factors of the locality 

 beneficially. 



It will be easily understood that, apart from the 

 species, the density of the shelter-wood depends on a 

 variety of circumstances, of which the following may be 

 mentioned : 



i. CONDITIONS OF THE LOCALITY. 



The shelter-wood should afford protection against the 

 drying up of the soil, frost, cold winds, growth of weeds, 

 and perhaps also against damage by insects. In localities 

 where the young crop is threatened by one or more of 

 these dangers, the shelter-wood must be kept dark : 

 amongst them may be mentioned poor, loose, stony soils ; 

 southerly and westerly aspects; steep slopes; localities 

 exposed to dry or cold air currents or to great changes 

 of temperature in spring resulting in late frosts ; those 

 inclined to a strong growth of weeds, especially calcareous 

 soils ; where wind-falls are apprehended, or where cock- 

 chafers and other insects are likely to settle. Where 

 the opposite conditions prevail, in other words on gene- 

 rally favourable localities, the shelter-wood may be less 

 dark, with a comparatively light cover overhead. 



ii. CONDITION OF THE SHELTEK-WOOD. 



Old trees have comparatively denser crowns than 

 younger trees. Tall trees give less shade than short 



