THE CUEVE OF THE BIG TREES. 



151 



been considered. The diagrams shown in figures .35, 36, and 37, together with tables 

 A, B, and G, on pages 301 and 323, demonstrate how these factors have been obtained and 

 applied in the case of the sequoia. Little need be said of them except to call attention to 

 one or two peculiarities. It will be seen that in figure 35, showing the average rate of growth 

 by centuries, the curve is very regular from 600 to 1800, but that after that, when the trees 

 begin to be old, it rises. This may imply that, whereas trees which are to live to great age 

 grow slowly during their youth, when they get to old age they grow rapidly. Possibly this 

 is because when the trees reach the ordinary age-Umit of the species most of the individuals 

 which had been growing with them die, and only the few old specimens are left. It is the 

 habit of the sequoia to grow in groups, oftentimes half a dozen trees of the same age forming 

 a circle. Frequently a tract of many acres is covered with trees of practically the same 

 age. While a large number of them are alive, they naturally hinder one another's growth, 

 but when most of them attain an age of 1,700 or 1,800 years — their three score and ten — the 

 majority die. Then the few that are left have all the sun and soil and rainfall, and may 

 be expected to grow more rapidly than ever before, or, at least, more rapidly in proportion 

 to their age. It is possible, however, that a part of the apparent increased growth of old 

 trees may be due to another cause, which will be discussed when we come to take up the 

 correction for flare and for buttresses. 



25 



20 



^ 15 

 I 

 I 10 



O 



100 200 300 400 500 



1000 



2000 



2500 



3000 



1500 



Age of troes in years 



Fig. 36. — Sequoia washingloniana : Corrective Factor for Age, plotted by Centuries. 



(See Table A, p. 301.) 



The other of the two main corrective factors, that for longevity, can not be obtained 

 without a large number of trees. The 450 sequoias available serve to make it fairly accu- 

 rate, but not wholly so, for in the corrected curve shown in figure 38 the early parts have been 

 depressed too much. The growth of the various groups of sequoias for different periods of 

 then- Uves is shown in figure 37, and it is evident that the older trees in their youth, and to a 

 less extent in their maturity, grow decidedly less rapidly than do those which do not Uve 

 so long. From the five curves given in the upper part of figure 37 it would perhaps be 

 possible to deduce corrective factors apphcable to each group and to each decade of the hfe 

 of each group. This would involve so much risk of error, however, that I have not done it. 

 Instead I have obtained the average growth of each group during the first 1,000 years of 

 its hfe (provided, of course, it lived so long) and have plotted this in the broken hne at the 

 bottom of figure 37. Through this has been drawn a smooth soUd hne which I have used 

 as the basis for the corrective factor for longevity as given in Table B, page 301. No 

 correction is apphed to the nine youngest groups, and a single factor is used for all of the six 

 oldest groups. To this is probably due the fact that the early parts of the curve of figure 38 

 fall unduly low. As has been already indicated, the purpose of the main corrections, except- 

 ing that for absence of rings, is to reduce the curve of tree growth as nearly as possible to a 



