METHOD OF THINNINGS. 39 



carefully preserved; it prevents the layer of dried 

 leaves from being blown away, keeps the soil moist, 

 enriching it at the same time with its organic detritus, 

 and so far from injuring as some have maintained 

 the future trees of the forest by drawing nutritive 

 elements from the soil at their expense, it ensures 

 for them a vigour of growth which they would not 

 otherwise have attained. 



Between the level of this shrubby growth and that 

 of trees with spare and contracted crowns which 

 are cut away to set free the more promising trees, 

 there are overtopped individuals of all heights. It is 

 always advisable to preserve such trees, if they can 

 survive till the next thinning operations come round . 

 Besides the fact that they can in no way injure the 

 taller trees, their preservation enables the forester 

 to step in with a bold hand in setting free the crowns 

 of species that rejoice in plenty of space and light. 



In order that thinnings may have their full effect 

 they must be repeated whenever the stock becomes 

 too dense to admit of the normal development of the 

 crown ; in a word, we must follow step by step the 

 progress of development. Now experience tells us 

 that during the phase of upward growth they must 

 be made more frequently than during the phase of 

 diametral increase ; but that for each period the 

 requirements of growth are satisfied by their repeti- 

 tion at equal intervals of time. Generally speaking, 

 we may say tha,t up to seventy years thinnings should 

 be made every ten years ; after this age every fifteen 

 or twenty years, according to species. 



It only remains for us to find out at what age we 



