THE CURVE OF THE BIG TREES. 



153 



where moisture accumulates at certain times or where it runs slowly through deep soil; 

 their number, however, is never so great as is the case with other trees, such as pines, 

 firs, and cedars, but this is natural, since a tree whose span of life is so long as that of the 

 sequoia does not need to reproduce itself rapidly. The number of young trees is quite 

 sufficient to prevent the extinction of the species and to insure that 1,000 or more years 

 from now these moist places shall have as many sequoias as they have to-day. (See Plate 

 5, page 139.) 



On dry slopes, however, the case is quite different. In some places we searched and 

 searched, in the hope of finding young trees. There were plenty of mature ones, 500 or 

 1,000 years old or more, but practically no little ones. Now and then a seedhng or a 

 young tree 3 or 4 years old was foimd, and once in a while we came upon large groups of 

 these which had just sprung up. Between this age, however, and an age of many hundred 

 years, it was almost impossible to find a tree. Young trees of other species abounded 

 wherever an old tree had died and given an opportunity, and there were pines, cedars, and 

 firs of every age, from seedlings to those that were dying of senility. Actual count showed 

 that the number of young trees was many times in excess of that of old ones, and that the 



1500 1300 



1000 800 600 400 200 B. C A. P. 200 400 600 800 IQQO 1200 400 1600 1800 2000 



Fig. 38. — Curve of Growth of the Sequoia washingloniana in California. Uncorrected ( 



(See Table E, pp. .308-310.) 



. ) and Corrected ( ). 



number decreased gradually in proportion to the age. With the sequoia, however, no 

 such thing was true. Often the number of young trees was actually much less than that 

 of old ones. If the trees in the future reproduce themselves no faster than they have 

 during the past 500 years or more, the species will ultimately become extinct upon these 

 slopes. Seeds are apparently able to sprout during moist years, and to grow as long as 

 the rainfall continues propitious, but as soon as dry years come the httle trees die. Thus 

 the sequoia in the dry parts of the forest has not been able to reproduce itself, although 

 in the moist parts it holds its own. Apparently the average conditions extending over 

 centuries can not be the same now as in the past. If they were, young sequoias ought to 

 be abundant. The only explanation of the absence of young trees seems to be a change 

 from the past to the present. 



In the face of this stands the curve of figure 38, as it appears after the corrections 

 for age and longevity have been apphed. At the end of our first season's work, when 

 the curve for the trees measured that year was plotted, I confess that I was greatly puzzled. 

 The evidence of the curve seemed too strong to admit of doubt; but at the same time the 

 absence of young trees on the dry slopes where the old ones flourished, together with the 

 abundant evidences of desiccation in other parts of the world, also .seemed too strong to 

 doubt. On returning to the Sierras a second time, however, in 1912, the difficulty soon 

 solved itself. Two things have a share in causing the growth of recent centuries to appear 

 greater than it really is. One of these is the form of the trunk of the sequoia, and the other 

 our choice of places for measurement. The sequoia habitually grows with a round, smooth 



