144. 



trees; the secondary stand is formed of trees which began to lose in the 

 race, were dropping behind in ^ro^tli and general progress, and were 

 to be culled oat. 



h. The number of trees per acre in the stand necessarily 

 decreases as the stand grows older. The rate varies with species and witl 

 site. The following tnble gives the number of trees per acre of spruce 

 on the first four sites, and of pine, beech and oak, on site I, at dif- 

 ferent ages, assuming that 5^00 trees per acre were planted of each 

 species: 



the elimination on Site I. An average of 2500 trees 

 dropped out in 20 years. More elimination had taken place on 3ite I 

 at 20 years than on Site IV at 40-60 yenrs and above. Conservative 

 thinnin t . effect. 



Poor nites have less growth, even with more room. These ate all 



i figures. 



It will be noticed that the pines dropped out rapidly, because 

 of their intolerance. Site I pine land is nevertheless poor land. 



Die oak site is good land and there is less decimation. 



The besch follows the spruce; it is fully as tolerant, but has 

 a larger crown and demands more room, otc. 



A 100 year oak is only half grown. It requires a 2-century rota- 

 tion, so the above figures for oak are not quite in the same class as Hi 

 the othfl. .;',. Oak at 20 years still has enormous numbers of trees per 

 acre, and the big drop comes at 20-40 years. 



i. A similar decrease in numbers takes place in wild-woods, 

 tho here it is more erratic, slower or faster in different ca.^es. If it 

 is too slow for the good of the stand, the stand is stagnated, usually 

 on poor sites. But lodgepole on a good site may do the sa^d thing. Jack 

 pine, .Norway pine, and spruce also show this effect. 



J_. The forester is interested in the amount of growing space 

 necessary fot the tree at different periods of its life on properly 

 stocked land. One acre contains about 4900 square yards (70 x 70); call 

 it 5000 aq.yda. Then 



>flPQ no. of sq. yds. growing space per tree. 



no. of trees per A 



In the wild-woods the trees are placed more irregularly than in 

 a cared-for stand, and they grow more irregularly. The freeing and rid- 

 dance of suppressed trees takes plAce by fits and $erks. Groups of 

 trees are separated out. They lack balance or adjustment; there is a 

 greater number of trees ftn a young stand, and they clean more thoroly 

 than in the old stand, where there is a smaller number. 



