6 A MANUAL OF FORESTRY. 



some cases, only certain species are saleable, while others 

 are without value. Again, some species produce a much 

 higher percentage of timber than others. 



Species with a thin crown are indifferently adapted 

 for wind-breaks, whereas they may be specially suited 

 for nurses over a tender crop. 



The above instances will suffice to show that, the 

 number of species which may be desirable in any given 

 case, is narrowed down by the objects of management. 



2. Adaptability of the Species to the desired Sylviculture^, 



System. 



All species of trees can be treated as high forest, but 

 only a certain number as coppice woods. The conifers 

 of temperate Europe either do not coppice at all, or very 

 indifferently ; even some of the broad-leaved species do 

 not yield satisfactory results.* A selection of species 

 must be made accordingly. 



3. Exposure of Species to damage by External Causes. 



The selection of species to be planted is further nar- 

 rowed by the degree to which they are exposed to 

 injury by external causes, as fire, frost, drought, cold 

 winds, strong gales, insects and fungi. Conifers, for 

 instance, are more exposed to damage by fire than broad- 

 leaved species ; Larch and Silver Fir suffer much from 

 cancer ; Spruce is liable to be thrown by wind ; Beech 

 and Silver Fir are frost-tender, while Scotch Pine and 

 Birch are frost-hardy ; Scotch Pine and Spruce are more 



* Bee page 1 74 of Volume I. 



