136 ENGLISH ESTATE FORESTRY 



plantation should have attained its maximum height-growth, 

 or nearly so. 



The next point to consider is the development of the 

 largest and most prominent trees in the direction of inducing 

 the necessary thickening of the boles. The crowns of the 

 trees at this stage will begin to assume a more or less flat 

 or semi - spherical surface, which will, if encouraged by 

 thinning, increase the leaf area. The larger the latter, the 

 better, other things being equal, will the stem be nourished ; 

 but the actual increase of the clear bole in volume will 

 depend upon its length and crown combined. It is generally 

 found that thinning to produce the desired result must not 

 be delayed too long, otherwise the development of the crown 

 does not take place. The actual number of trees which 

 should stand to the end of the rotation must therefore be 

 fixed in a general way at this period of growth. With most 

 species which are grown on a rotation of about a hiindred 

 years, a hundred and fifty trees to the acre are about as 

 many as are able to develop properly. The selection of 

 this number, therefore, should take place provisionally, and 

 any smaller trees which are likely to interfere with their 

 development be removed or marked for subsequent removal. 

 It is just a question whether thinning at the culmination of 

 height-growth should be carried out in one operation, or 

 extended over a series of years. Much will depend upon 

 the character of the species itself. In the case of oak, it is 

 often found that severe thinning produces an objectionable 

 crop of adventitious or water shoots, which check the growth 

 of the tree and affect its value as timber. The thinning of 

 oak woods, therefore, should always be carried out gradually 

 and carefully, but with larch, beech, ash, and many other 

 species this precaution need not be so carefully observed. 

 Of course too great an opening out of the leaf canopy should 

 be avoided in any case, but it is probably most economical, 

 and more conducive to the rapid growth of the remaining 

 trees, when a fairly heavy thinning is made about the fiftieth 

 or sixtieth year in the life of the wood. 



The effect of such a thinning is, as already said, to 

 stimulate crown development, and this again in its turn 

 increases the breadth of the annual ring throughout the 



