CLIMATE AND TREE GROWTH 119 



approach to true acclimatisation lies in the field of suc- 

 cessive breeding or reproduction from selected types, a 

 process which requires long periods to carry out, and an 

 expenditure of time, care, and study outside the scope of 

 ordinary commercial enterprise, taking the uncertain and 

 problematical results into consideration. The simple 

 method of hardening off tender species, by planting under 

 partial shade and gradually reducing the latter as trees get 

 above the spring or autumn frost line, may possibly be re- 

 garded as a form of acclimatisation. But while this may 

 preserve a species which would otherwise perish during 

 the first few years of its existence, it does not enable the 

 species to develop to its normal size in a climate inferior 

 to that of its native habitat, and from an economic point 

 of view this hardening off is of little value. 



This statement does not, of course, apply to the regenera- 

 tion of such species as ash, beech, or silver fir under 

 shelter wood, as this may be considered the normal 

 method followed under natural conditions, and in primeval 

 woods frost damage is less likely to occur than with crops 

 artificially planted on bare or clear ground. Ground 

 frosts in May of more than 10° or 12° F., although of 

 almost annual occurrence, must be considered abnormal 

 features of the British climate, just as January tempera- 

 tures of 50'^ F. or more are abnormal. Owing to the 

 presence of latent and late developing buds these frosts 

 are seldom if ever fatal, and on good soils and situations 

 trees may completely recover from them in the course of 

 a month or two, and in any case they do not affect the 

 ultimate vegetative development of a species. The fact 

 that silver fir, beech, Spanish chestnut, oak, and other 

 species sensitive to late frosts may be found of great size 

 and height in deep valleys and hollows is a certain proof 

 that late frost alone will not hinder or permanently check 

 the development of a species, although it certainly checks 



