52 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



years, after the trees have closed up the struggle for existence 

 begins, but in place of the strongest individuals, we see the 

 strongest species brought to the front. In the case we are 

 supposing these will probably be Larch and Ash. In order to 

 keep the other hardwoods alive, therefore, thinning must begin, 

 and in so doing gaps are made, which weaken the leaf canopy 

 and give many of the trees too much side-light. This encourages 

 the growth of strong branches and crooked stems, and disad- 

 vantage the second is repeated. The faster growing species will 

 also meet with too little opposition to keep their stems suffi- 

 ciently clean, and rough timber is encouraged in both ways. 



But suppose it has been decided to ignore the suppressed or 

 slower-growing species and allow the dominant ones to have 

 their own way. What happens then ? Ash and Larch are the 

 principal survivors, and the thickness of the crop of dominant 

 trees, and the quality of the timber, depend a good deal upon 

 the way these two species are distributed. If regularly distributed, 

 and sufficiently close together to keep the stem-cleaning process 

 in motion, fairly clean timber will result, for both being light- 

 demanders and rapid growers (we are assuming that the soil 

 and situation are favourable to both), they will constitute what 

 we have termed a sylvicultural mixture. If, on the other hand, 

 they are evenly distributed, but too far apart to counteract each 

 other's side-growth, wide- spreading crowns will prevail and 

 rough timber result. With regard to these two species, however, 

 the existence of large crowns is not such an evil as it would 

 be with many, but in all cases it means that the proportion 

 of timber to branches is too small, and the crop therefore pos- 

 sesses a lower selling value. 



Probably many of the commoner species of Conifers owe their 

 existence in mixed plantations to the idea that they act as 

 " nurses" to the more desirable kinds, and thus enable the planta- 

 tion to be formed without using so large a number of the latter. 

 Where the raising or purchase of the main-crop species is an 

 expensive matter the plan is worth considering, but so far as 

 the nursing business goes there is little in it. The best nurses 

 or stem-cleaners for any particular species are individuals of that 

 same species, and the reason for this has already been made 

 clear in describing the struggle for existence. It may be, how- 

 ever, that a species may serve as a nurse and also be of more 



