SOME SILVICULTURAL ASPECTS AND PROBLEMS OF THE SOIL. 43 



the invasion of a more or less dense ground vegetation. Such 

 growth is not necessarily harmful of itself since it may simply 

 set up a slightly changed edaphic equilibrium, as generally 

 happens in richer soils with good loamy texture ; in fact some 

 species of ground vegetation {e.g. Legumes) may help to 

 improve the soil by the symbiotic fixation of atmospheric 

 nitrogen But where soil conditions are already too far re- 

 moved from the loamy ideal (as in dry sands or in peat), the 

 effect of the opening up of the canopy is to accentuate the 

 unfavourable condition of the soil, while a type of ground flora 

 makes its appearance which further promotes the deterioration, 

 so that the crop is really no index of the possible capacity of the 

 soil under different methods of management. Under such con- 

 ditions, in order to utilise to the full the productive capacity of 

 the soil and to ensure its future fertility, that is in all soils not of 

 the first quality, it is advisable that a light-demanding species 

 should not be grown as a pure crop, a subsidiary species 

 (preferably broad-leaved like beech) with dense canopy should 

 be introduced to provide a soil covering with its heavy deposi- 

 tion of leaf-litter and reduce the invasion of peat-loving, peat- 

 forming species like heather. Even the addition of a few plants 

 per acre produces noticeable results, and it is considered that 

 the production of a heavier final yield of larch itself much more 

 than repays for the small loss of acreage caused by the low 

 value of beech, while the fertility of the soil is retained for the 

 next rotation. It is, of course, immaterial from the edaphic 

 aspect of the question whether the admixture is in the form of 

 practically even-aged trees or of a younger under-planted shade- 

 bearing species. 



Similarly, although immediate economic considerations may 

 be very important with regard to distance of planting and rates 

 of thinning, yet the edaphic aspect is also of importance, in fact 

 is the ultimately important economic consideration. As regards 

 distance of planting, at present the cost must put other con- 

 siderations to a great extent out of count. But the noticeable 

 improvement in soil conditions, and in the growth of crop after 

 canopy is formed, indicates that close planting is advisable, 

 provided early and frequent thinning can be carried out. Again 

 it is inadvisable to attempt anything in the way of heavy 

 thinning, since although temporary rapid growth may be 

 obtained the temporary advantage is lost in a few years through 



