258 Studies in Forestry [CHAP. xn. 



a beneficial layer of humus. By means of the carbonic acid 

 and the ammonia evolved during the process of humification, 

 a stimulus is given to the formation of larger supplies of 

 nutrient salts within the soil. These are not required for the 

 annual production of foliage or timber ; but as the density 

 of canopy overhead, and the mossy covering which often clothes 

 the soil under conifers, both combine in preventing the nutrients 

 being wasted by a rank growth of weeds, or being washed out 

 of the soil by the unbroken descent of heavy rainfall, it practi- 

 cally follows that the sum total of soluble nutrients is, at 

 the end of a coniferous crop that has been prudently managed, 

 considerably larger than it was at the time the planting with 

 Pines, Spruces, or Silver Firs was undertaken. 



Many tracts throughout Germany, that half a century ago 

 bore fine woods of Oak and others of the nobler species of 

 broad-leaved trees, are to-day covered with Spruce and Scots 

 or Austrian Pine in consequence of imprudence in the manage- 

 ment of the former deciduous crops, and of the want of know- 

 ledge (since dearly purchased) that where a good leaf-canopy 

 is not maintained, an undergrowth is requisite for the safe- 

 guarding of the productive capacity of the soil, or for its 

 improvement if signs of incipient deterioration have already 

 made themselves apparent. And in England the same may 

 be said of many portions of the old Oak woods in the State 

 properties, the New Forest and the Forest of Dean, parts of 

 which have had to be transformed into coniferous woods in 

 consequence of neglect of the conservation of the produc- 

 tivity of the soil. In the low demands that it makes on mineral 

 nutrients, in the power of accommodation it exhibits with regard 

 to soil-moisture, and in its capacity for improving poor soil or 

 recruiting those that are temporarily deteriorated from exposure 

 to inimical influences, there is no tree of the forest that can 

 be more safely relied on to yield yeoman service than the 

 common Pine. On poor sandy land it can form a crop where 

 other trees fail to thrive ; and even on inferior classes of soil it 



