128 COMPOSITION OF FOREST CROPS. 



SECTION II. 

 General rules for growing mixed crops. 



We may now lay down the following general rules to be observ- 

 ed in growing mixed crops : 



L The predominant species, whether there be several or only 

 one, ought to be soil-improvers. If the principal species is itself 

 a soil-improver, then the more it predominates, up to the limit 

 at which the crop would become pure, the better in almost every 

 case. But if it is shade-avoiding, then from the time it ceases to 

 form of itself a complete canopy, the auxiliary species ought to 

 predominate to the extent of filling up all the intervals left be- 

 tween the crowns of individuals of the former. Of course the best 

 way in which this predominance could have effect would be if the 

 an auxiliary species constituted a complete understory of growth so 

 as to leave the crowns of the more valuable trees as free as possible 

 to get the full benefit of the sunlight. When the principal spe- 

 cies is a conifer, howmuchsoever shade-enduring it may be, we have 

 a slight modification of the general case owing to the peculiar 

 nature of the leaves of that family of trees, they being, in fact, 

 strongly fibrous and resinous and hence decomposing slowly and 

 forming a bad humus. On this account, in conifer forests it is 

 always desirable to have as complete an understory of broad-leaved 

 auxiliary species as possible, quite irrespective of the proportion of 

 coniferous individuals present. 



II. Shade-enduring species may be intermixed, if they enjoy the 

 same rate of growth in height, or if the sloiver growers can be pro- 

 tected against the more rapid growers either 



(a) By introducing them artificiably a certain numbers of years 

 in advance of the latter ; or 



(b) By their being able to produce an abundant advance 

 growth under the old standing crop, while the more rapid growers 

 can be reproduced naturally in adequate numbers only by means 

 of special regeneration fellings made a sufficiently long time after 

 to give the former the necessary start ; or 



(c) By growing them in sufficiently predominant numbers ; or 



(d) By cutting down or topping or pruning and lopping taller 

 or otherwise invasive individuals of the other species. 



III. A shade-enduring (in other icords, dense-crowned) species 

 may be intermixed with a shade-avoiding (in other icords, spare- 

 crowned) species, when this latter groivs more rapidly or is given a 

 sufficient start ahead of the other. The start must, of course, be 



