CHOICE OF SYSTEM. 109 



high return ; hence it is necessary to select a system under 

 which the factors of the locahty are at least maintained, and 

 if possible improved. 



In the case of exceptionally good localities with a rich fresh 

 soil and a favourable state of moisture and temperature of the 

 air, any system can be adopted which answers to the other 

 requirements of the case. On all localities of only middling 

 quality, and still more so on poor localities, the first considera- 

 tion must be the preservation of the factors of the locality, or 

 else a steady deterioration will set in, which may end in 

 complete sterility. In such cases clear cuttings must be 

 avoided as much as possible,'and every effort made to keep the 

 area permanently stocked with a crop of trees ; in other words, 

 to regenerate under shelter-woods, so as to lead the old crop 

 gradually over into a new crop. Unless this precaution is 

 taken, the degree of moisture in the soil undergoes violent 

 changes, which act most injuriously on production. The 

 systems best adapted in such cases are the shelter-wood selec- 

 tion system, the other shelter- wood systems which produce 

 an uneven aged young wood, the shelter- wood compartment 

 system, and coppice with standards. 



3. Protection against external Daiajers. 



It should be the object of a good management to produce 

 healthy woods, which are capable of resisting successfully the 

 dangers to which they are exposed during life. Though 

 species and method of regeneration are of principal importance 

 in this respect, the system is also of some account. 



Where the object is to counteract the eroding effects of 

 water running down sloping ground, to prevent the occurrence 

 of landslips, avalanches, or devastation through shifting sand, 

 woods of uneven age must be the rule, such as are produced 

 under the shelter-wood selection system, the group system, etc. 



Whether uneven aged woods suffer less from wind, snow 

 and ice than even aged woods is as yet an open question. 



In respect of frost, drought and insects, the clear cutting 



