GENEBA.L BULES FOB OBOWING MIXED CBOPS. 129 



sufficient to prevent its being ever outstripped and thereby over- 

 topped. 



IV. Shade-avoiding species ought not to be intermixed by them- 

 selves in any permanent manner : For in crops so composed the 

 soil is not only bound to degenerate (violation of Rule 1), but the 

 slower growers must inevitably be suppressed by the rest. 



Exceptions to this Rule : 



(1) On a fertile soil, which a spare or interrupted leaf-canopy 

 cannot hurt, a mixed growth may consist of shade-avoiding species. 

 These must, however, be selected on account of their greatly supe- 

 rior value. 



(2) On very poor soils, such as those on which the Boswellia 

 serrata, &c., thrive, other shade-avoiding species, provided they are 

 sufficiently valuable, such as teak, &c., may be mixed with the for- 

 mer. This mixture is often not only justifiable but also necessary. 

 For instance, in many forests consisting chiefly of Boswellia, the 

 teak has no other nurse to protect it against frosts. 



V. The various species should be thoroughly intermixed, no one 

 species forming in any place a distinct group in the midst of the re- 

 maining growth. If the species in question have dense crowns, such 

 a group would hurt with its heavy shade neighbouring trees of 

 other species, without helping them to any appreciable extent in 

 clearing their boles; while if they possess spare crowns, the soil un- 

 der them must inevitably deteriorate. Besides this, unless the 

 trees in the group and those forming trie surrounding growth 

 possessed the same requirements as to light, the stems standing 

 along the edge of the group would grow unequally, putting on 

 more wood on one side than on the other, and would thus, owing to 

 irregular shrinkage and expansion and consequent liability to warp- 

 ing and even splitting, be ill-adapted for boards and scantlings of 

 the better descriptions. Moreover, since, as has been already shown 

 above (Advantage IX, p. 113-4), a mixture of several species faci- 

 litates the natural regeneration of a forest, the existence of pure 

 groups here and there throughout the forest increases the difficulty 

 of its natural regeneration. 



Exceptions to this Rule : 



(1) When the fertility of the soil varies so that we have well- 

 defined patches of distinctly different degrees of fertility, there is . 

 no alternative but to allow each patch to be stocked with the species,, 

 be it one or several, best suited to it. 



