I2O Studies in Forestry [CHAP. vi. 



ductive capacity of the soil, but also conserve this in a higher 

 degree than could otherwise be the case ; whilst, at the same 

 time, they are able to utilize to the utmost possible extent the 

 chemical power of the light requisite for the due performance 

 of the assimilative functions by the foliage. This closer canopy 

 and greater density of crop generally become of all the more 

 importance as the crops advance in age, and begin to approach 

 maturity ; hence in this prolonged maintenance of canopy lies 

 the principal value of many kinds of mixed crops. 



2. The Soil is maintained in better Condition and Productive 

 Capacity than is the case under many kinds of Pure Crops. Pure 

 woods of thinly-foliaged and light-demanding genera of trees, 

 like Oak, Ash, Maple, Larch, and Pine, when once they have 

 completed their chief growth in height and have begun to 

 exhibit their natural specific tendencies with regard to increase 

 of growing-space, are unable to conserve for themselves the 

 general quality and productive capacity of the soil in conse- 

 quence of the interruption of canopy, the decrease in the 

 number of stems forming the crop, and the subsequent bad 

 effects to the surface-soil wrought by insolation and exhausting 

 winds. Hence the expenses of underplanting are usually un- 

 avoidable. But as, during the earlier periods of development, 

 these light-demanding genera are at the same time of more 

 rapid growth than the shade-bearing kinds, Beech, Spruces, 

 Silver Firs, and Hornbeam, in mixed crops they can, with now 

 and again a little assistance in the way of tending wherever 

 necessary, usually assert themselves as the predominating poles 

 and trees, thereby acquiring just the position naturally best 

 suited for their present growth and good future development. At 

 the same time the shade-bearing genera, forming the dominant 

 and more or less dominated classes of the crop, mechanically 

 protect the soil against the exhausting and deteriorating in- 

 fluences of sun and wind ; whilst, by their richer fall of leaves, 

 they contribute valuable material for the formation of humus 

 or mould, that natural manure of woodlands, which exerts very 



