474 REAHING OF THE ESTABLISHED CROP. 



figures for the average area occupied by each stem of the more 

 important species at different ages : — 



At 20 years ... ... 1 square metre 



„ 40 „ ... ... 4 „ „ 



„ ou „ ... ... y „ „ 



„ 80 „ ... ... 11'7 „ „ 



,,100 „ ... ... 15-4 „ 



Arranging the above figures in a differentt manner, they show- 

 that if there are 1,000 trees at the age of 20 years, at the age of 

 40 years there will be only 250, at 60 years 111, at 80 years 85,. 

 and at 100 years only 65. These figures show clearly how much 

 severer a thinning should be between the ages of 20 and 40 years- 

 than between 80 and 100 years, the severity being in inverse 

 proportion to the age of the crop. Also see Appendix A. 



(b) Species. Trees require more room in proportion to their 

 shade-avoiding nature, and hence a crop of a shade-avoiding species 

 must be thinned more severely than a crop of the same densifty cont- 

 posed of species more tolerant of shade. Schuberg's experiments 

 in the Black Forest, in crops containing individuals from 40 to 80 

 years old, gave the average number per acre of stems of four seve- 

 ral species as follows, the species being arranged in the order of 

 their ability to endure shade : — 



Spruce ... 860 



Beech ... 690 



Silver fir ... 610 



Scots' pine ... 530 



In other words, if the space occupied by the pine be represented 

 by 100, the figures for silver fir, beech and spruce would be res- 

 pectively 87, 69 and 63. 



(c) The soil. — Owing to greater rapidity of growth and fuller 

 development of both crown and roots, good soil will have on it 

 fewer individuals than the same area of inferior soil, the difference 

 however diminishing rapidly with age. This is tantamount to say- 

 ing that the struggle for room both in the ground and in the leaf- 

 canopy during the stage of longitudinal growth is severer and 

 begins earlier, but is sooner over, in favourable than in unfavour- 

 able soil. In the case of some species the total extension of crown 

 attained varies to such an enormous extent according to the soil 

 in which the trees may be growing, that individuals in good soil 

 may possess a spread from three to four times as great again as 

 those in poor soil ; whereas in the case of species that affect poor 

 soils the difference will all but disappear after an early age (only 



