102 PLANTING 



trees introduced into a mixture, the more difficult does the 

 task of correctly mixing them become. 



(iii) Mixtures by Patches or Groups. However, a 

 mixture by patches is as a rule the best method of forming 

 an even-aged mixture. It is the easiest and safest method 

 of forming a mixture, and any change in the character of 

 the soil can be utilised to the fullest advantage. 



The patches may be of any size J, J, J, or I acre, or even 

 more. By such a method, any ill-effects produced by lack of 

 pruning, or by difference in height growth, is confined only to 

 the trees forming the outside rings of the patches. Therefore, 

 the larger the patch, the less harm results from any indiscre- 

 tion in this respect. Though if the patches be too large, 

 they are, to all intents and purposes, small pure woods, and 

 the disadvantages of pure wood have to be considered. 



It should be remembered that mixtures are found in 

 natural virgin forest more often than pure crops. But 

 Nature's method of mixing trees is to a great extent by 

 patches, though the patches are often small. 



In the case of a mature forest, it will sometimes appear 

 that the mixing has been by single trees. But this is not so 

 in a general way. For an old tree dies and leaves a vacant 

 space, which usually becomes very thickly seeded, and, 

 although there may be many species seeded on this area, it 

 will usually happen that in a year or so one species will have 

 suppressed all others, and a pure patch grows up. And 

 again, at other times, another patch may be seeded with 

 another species, owing to differences in seed years and other 

 causes. And so it happens that the fine, tall, clean trees so 

 often to be found in virgin forest, have usually been drawn 

 up and pruned by trees of their own species. 



And apart from this fact, it is very much easier for 

 mixtures to be grown successfully when thick natural seed- 

 ing has taken place, producing perhaps 100,000 plants to the 

 acre, than when artificial planting at 3 or 4 feet apart has 

 taken place ; for in the former case side branches hardly 

 have a chance of developing. 



Again, it is an important .matter that, when planting 



