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BULLETIN 13, TJ. S. DEPARTMENT OF AGRICULTURE. 



of growth decreases rather abruptly when the tree is still far from 



decadence. Red pine, for example, has a fairly uniform and rapid 



growth until about 100 years old, when a marked falling off occurs, 



the tree growing at a slower rate until its death 100 or 200 years later. 



Jack pine exhibits a similar trait, though its period of rapid growth 



ceases very much earlier than that of red pine. It is this habit of 



sustained growth which gives white pine its great size as compared 



with the two other species. 



The rate of growth varies with the age of the tree, the amount of 



light received, and the fertility of the soil in which it grows. In 



general, growth is more rapid on good soils than on poor, and in 



youth than in old age. The period during which growth is most rapid 



comes earlier when the tree is favorably situated than when it grows 



on poor soil. 



Growth in Height. 



White-pine seedlings grow very slowly, and few of them reach 

 a height of more than a foot during the first 5 years. For the first 

 .3 years annual growth is little more than an inch. Thus 1, 2, and 

 even . 3 year old seedlings are so inconspicuous that they are likely 

 to be overlooked, especially when among grass or weeds. During the 

 following two seasons, when rapid growth commences, the top shoots 

 of the seedlings appear everywhere, giving the impression that they 

 have sprung up in a single year. 



The height growth of seedlings for the first 10 years under average 

 conditions is shown in Table 2. In a nursery or under specially favor- 

 able circumstances the rate of growth may be much faster, while under 

 partial shade it will be slower. 



Table 2. — Height growth of white-pine seedlings. 1 



Age. 



Height. 



Age. 



Height. 



Years. 



Inches. 



Years. 



Inches. 



1 



1.0 



6 



17.0 



2 



1.5 



7 



24.0 



3 



3.5 



8 



32.0 



4 



7.0 



9 



45.0 



5. 



11.0 



10 



64.0 



On good, moist soils height growth is most rapid at about the 

 fifteenth year, when it often exceeds 3 feet annually. On poor, dry 

 soils, however, the maximum may not occur before the fortieth year, 

 and then not equal the growth on good soil. From the time when 

 the growth culminates its rate gradually decreases until toward the 

 end of the second hundred years it amounts to only 2 or 3 inches per 

 year. 



1 From measurements of 1 ,600 young trees. Table from " Natural Replacement of White Pine on Old 

 Fields in New England," by S. N. Spring. 



