IMPORTA^X'E FOR WOOD-PEODUCTION. 



585 



The following table gives the amount of ash in needles and 

 leaves : — 



On comparing the demands of trees with those of agricul- 

 tural crops on the mineral matter in soils, the former is bound 

 to be considerable, for an acre of beech forest requires more 

 mineral matter than an acre of wheat, and spruce forest nearly 

 as much as the latter. It is, however, well-known that a great 

 T^art of these necessary mineral substances, on account of their 

 wide-spread dissemination, affords little cause for anxiety and 

 that only a few substances are really decisive as to the fertility 

 of a soil ; these are sulphates, phosphates, potash salts and lime. 

 In comparing forestry with agriculture, only these substances 

 need be considered ; in their case the demands of forestry for 

 the production of wood are far behind those of agriculture. 



On account of the slight demand made by forestry on the 

 more important mineral nutritive substances, and the fact that a 

 portion of them return to the sapwood and young twigs before 

 leaf- fall, it might be conjectured that forest litter is not indispen- 

 sable for the soil, owing to the small amount of important mineral 

 matter it contains. It should, however, be remembered that, 

 independently of the importance of forest litter in other respects, 

 most forest soils are poor in these very mineral substances, and 

 although the demands made on them by forest trees are small, 

 yet they are continuous ; the necessary consequences of the 

 removal of litter must therefore be similar to those which follow 



* Der chemische Ackersmann, 1862. 

 t Tharandter Jahrbuch, vol. 15, \>. 322. 



