PURE AND MIXED WOODS 43 



underplanted later on, thus forming an uneven-aged wood. 

 In the majority of cases beech is the best species to use for 

 this under crop, the action of which may be explained as 

 follows : If a pure wood is planted of some light-demanding 

 species like oak, larch, or ash, after a certain time, depending 

 on the species, the wood begins to open out and forms only 

 a thin canopy which is no longer able to protect the soil. 

 If the wood is then left alone the soil deteriorates, the humus 

 decomposes too rapidly and disappears, and a rank growth of 

 weeds soon covers the soil ; moreover, the trees form large 

 crowns, and if this state of affairs is allowed to continue the 

 timber will not be of first-class quality. 



Oak woods begin to thin out when between thirty and fifty 

 years of age ; and larch between the fifteenth and twenty-fifth 

 years, the actual time being indicated on the ground by the 

 appearance of brambles and other weeds. When this happens 

 a fairly heavy thinning should be made, cutting out all dead 

 and dying trees and very badly shaped ones, so as to allow 

 more light to reach the ground. Then the wood should be 

 underplanted with beech, silver fir, or hornbeam according to 

 circumstances, while Nordmann's fir may also prove suitable 

 for this purpose. Under no circumstances should any light- 

 demanding species be used for the underwood. 



The underwood will grow, slowly it is true, and will in 

 course of time form a thicket under the overwood. From 

 this time on it will throw a heavy fall of leaves to the ground 

 which will form humus, and this will act as a manure to the 

 valuable trees forming the overwood and will cause them to 

 grow rapidly in volume. The soil will be well protected in 

 every way. Individual trees in the underwood, wherever they 

 get enough light, will grow and fill up blanks in the overwood, 

 thus keeping the cover dense and the area fully stocked, and 

 the wood gets the advantages of a mixture. As the trees in 

 the underwood grow upwards they will shade and kill off any 

 small branches formed on the stems of the overwood and will 



