15G THE DEVELOPMENT OE BRITISH EORESTEY 



Spruce, on the other hand, frequently suffers from wind 

 when planted alone, but much depends upon the soil 

 and situation. Light-demanding species invariably re- 

 quire growing in mixture, especially larch and oak, 

 neither of w'hich are able to shade the ground suf- 

 ficiently to suppress surface groAvth after the first forty 

 or fifty years. The former also requires a wind-resist- 

 ing species with it on exposed sites. Light-demanders 

 which may be successfully grown either pure or in 

 mixture are pines, ash, sycamore, poplar, alder, willows, 

 etc. The question of mixing any of these is more 

 a matter of economy than of sylviculture. Districts in 

 which labour supply is deficient, and little or no sale 

 for thinnings exists, are best suited for pure crops, as the 

 latter require less attention when young, and can be 

 more rapidly disposed of in large quantities when mature. 

 Differences of soil and situation must, of course, be 

 studied in all cases, and under average British conditions 

 pure crops, if formed on correct principles, rarely occupy 

 more than two or three acres in one block, although the 

 total area under a given species may predominate very 

 greatly over that occupied by the remainder. 



What may be termed 'main-crop developers' should 

 be important features in all mixtures having light-de- 

 manding, shalloAv-rooting, or wind-sensitive species for 

 the main crop. On damp, fresh soil, or in deep, sheltered 

 valleys they are least required, but on average soils 

 and situations they may make all the difference between 

 the success and failure of the main crop. The main 

 functions of this class of tree are the thickening of 

 the leaf canopy, shading the ground, and providing the 

 main crop with a wind -firm ally at all dangerous 

 points. The most useful of all trees for combining these 

 qualities is beech. It adapts itself to various soils and 

 situations. It can accommodate itself to the shade 



