PUBE WOODS OR MIXED WOODS ? 33 



(2.) The fallen leaves, and certain plants which grow in the 

 shade of trees, such as mosses, form a layer of humus, which 

 covers the mineral soil, and produces a suitable proportion of 

 organic matter. 



These two agencies secure to the soil fertility, and above 

 all, a permanent supply of moisture, without which no crop 

 of trees can thoroughly flourish. Whenever the above two 

 conditions are fully secured, the yield-capacity of the soil is 

 maintained, and in many cases improved. Hence, the answer 

 to the question before us runs thus : 



" Only trees which hare a fairly full foliage, and preserve a 

 good leaf-canopy to an advanced age, are fit to be raised in pure 

 woods. Species which do not possess these qualities should be 

 mixed with trees of the former kind." 



Accordingly, foresters arrange the trees grown for economic 

 purposes into two classes. To the first class of trees fit to be 

 grown in pure woods belong the beech, hornbeam, silver fir, 

 spruce, and in a less degree sycamore, Weyrnouth pine, and 

 Douglas fir. To the second class of trees belong larch, birch, 

 poplar, ash, oak, and sweet chestnut. Half-way between the 

 two classes stand Scotch, Austrian, and Corsican pine, inas- 

 much as they benefit the soil up to a certain age, say to forty 

 or fifty years, after which they begin to thin out and join the 

 second class. As a rule, the trees of the first class are shade- 

 bearing, whereas those of the second are light-demanding, in 

 addition to being thin-crowned. It so happens, however, 

 that the second class comprises the most valuable timber trees, 

 more particularly oak, ash, and larch ; hence, mixed woods in 

 which these species form a prominent feature, are indicated in 

 Britain, in preference to pure woods. 



The next question is, how should such mixtures be arranged ? 

 Unfortunately no rational answer has been given to it by many 

 British foresters during the last two generations. Instead of 

 following the good old plan and the ordinary laws of nature, 

 as exhibited by older woodlands, modern foresters conceived 

 the idea of cramming together on the same area about as 



