92 Studies in Forestry [CHAP. v. 



from a reference to the tables on pp. 43-45 of the author's 

 British Forest Trees (1893). 



The Chemical Composition of any soil is in so far of im- 

 portance to tree-growth that each of the necessary mineral 

 constituents, always found forming part of the ash to which 

 timber may be reduced by combustion, must be present in it 

 in sufficient quantity in a soluble form. The adaptability of 

 any given soil for the growth of any particular species of 

 woodland crop is determinable by the Law of the Minimum, 

 according to which the minimum amount of any one essential 

 constituent of the necessary food-supply in the soil limits its 

 total productive capacity for a given kind of timber. Thus, 

 for example, Oak and Beech extract very much more potash 

 and phosphoric acid from the soil for the production of their 

 timber than Scots Pine or Spruce ; hence the latter may thrive 

 well on soils where (according to the law of the minimum) the 

 former are of exceedingly indifferent growth owing to the com- 

 parative scarcity of these ingredients. 



As a matter of fact most soils contain the essential con- 

 stituents of tree-food in sufficient quantities to maintain tree- 

 growth of any kind. But as they are not always held in 

 solution, they are not continuously available for imbibation by 

 the root-system ; for it is only when occurring in the form of 

 soluble salts, that the nutrients can be absorbed by the 

 suction-rootlets. It was from this point of view that Gustav 

 Heyer asserted that almost any soil could produce any given 

 kind of timber, provided that it contained the requisite degree 

 of moisture an assertion which, as has previously been shown, 

 is only approximately, but not scientifically correct. 



Sylviculture varies essentially from Agriculture in being less 

 directly dependent on the fertility or inorganic richness of the 

 soil. Though it is quite certain that rich soils, yielding too 

 copious supplies of food-material to be assimilated thoroughly, 

 would produce large quantities of timber, yet it would be of 

 a soft spongy nature, little able to withstand either the attacks 



