SYLVICULTURE 31 



combination of deep-rooting with shallow-rooting trees is very 

 desirable ; for lessening the risk from forest fires a mixture of 

 deciduous with coniferous trees is serviceable ; insect and 

 fungus attacks may to a certain extent be combated in a 

 similar manner by interspersing species which are particularly 

 prone to these dangers (Scots Pine, Spruce, Larch) with the 

 less frequently injured broad-leaved trees. Such action is, 

 however, no complete protection, and mixtures that in some 

 ways appear to be excellent must often be renounced on 

 account of more weighty considerations. 



Species selected for even-aged mixture must realise the 

 following conditions : (i) they must be suitable to the situa- 

 tion ; (2) they must not be too dissimilar in their rate of 

 growth ; and (3) they should possess different forms of root 

 system. Only rarely can all these requirements be satisfied, 

 and so it happens that instead of the best form of mixture 

 that of even age, with a distribution of the species by single 

 trees other means have often to be adopted in bringing the 

 different kinds together. 



The arrangement may be made by grouping the species 

 suitably, or if by single trees, having them of dissimilar age. 

 In mixing by area in woods of even age, single rows and 

 narrow strips are not to be recommended. With unequal 

 rate of development the more slowly growing species become 

 suppressed, and interference through the removal of the 

 aggressive members an operation often delayed too long 

 generally results in making a deficient crop of badly formed 

 stems. The group system of mixture is that best adapted to 

 utilising the varying quality of the ground ; but in its adop- 

 tion it must be kept in mind that the larger the clumps, 

 the less likely are the other advantages of a mixture to be 

 realised. 



Formation of Woods by Sowing and Planting 



The establishment of woods may be by the spontaneous 

 action of nature, when the term natural regeneration is used ; 



