88 Studies in Forestry [CHAP. iv. 



growth of every kind of forest tree ; for the supply of nutrients 

 available in a soluble form varies with the chemical and the 

 physical composition of the different classes of rocks, the 

 degree to which disintegration and decomposition have ad- 

 vanced, the depth of the soil permeable by the root-systems, the 

 amount of organic matter contained in the soil, and the physical 

 properties with which this is endowed. And the want of any 

 one food-material, or perhaps even an unfavourable condition 

 of one physical factor (more especially one of those relating to 

 moisture or depth), may render a soil unsuitable for the normal 

 development of any given kind of tree. But, undoubtedly, the 

 inferiority of many woodland soils may also be due to poverty 

 in one or other of the essential soluble nutrients, though this 

 is generally combined at the same time with unfavourable 

 physical conditions. The object of scientific sylviculture is, 

 therefore, to plant only such trees as are most likely to attain 

 normal development, and to yield the best monetary returns, 

 without exhausting the soil or allowing its physical properties 

 to become prejudiced or impaired by want of protection from 

 sun and wind. 



From this it follows, theoretically, that the cultivation of 

 coppice-woods, in which the crop is formed entirely of small 

 branches containing relatively larger quantities of mineral sub- 

 stances than are to be found in mature wood, must tend to 

 exhaust the easily available supplies of lime, potash, and phos- 

 phoric acid sooner than crops grown under high-forest. And 

 this theoretical deduction coincides exactly with the results of 

 practical experience; for it is well known that Oak-coppice 

 for tanning- bark, or Osier-holts for withes, should only be 

 made on good land, and that if inferior soil be cleared of Oak- 

 coppice every twelve to sixteen years, it runs great risk of 

 deteriorating. The treatment of timber-crops in high-forest 

 is, as long sylvicultural experience has clearly shown, the most 

 conservative manner of utilizing the soil; whilst copse or 

 coppice under standards stands about midway between the 



