CHAPTER XIV. 

 THE INTERPRETATION OF THE CURVE OF THE SEQUOIA. 



The rate of growth of the vegetation in any given locahty varies from year to year, 

 chiefly because of changes in precipitation and temperature. In northern regions, where 

 there is precipitation at all seasons, temperature is probably the most important factor. 

 Farther south, however, the amount of rain becomes of increasing importance. Professor 

 Douglass has shown, as we have seen, that, in spite of all the accidents to which plants 

 are liable, three or four yellow pines are sufficient to give a record of the rainfall in Arizona 

 with an accuracy of approximately 70 per cent. This is true even where individual years 

 are concerned. If we employ a unit of time longer than a single year, so that the stored-up 

 moisture of the soil and energy of the tree have less effect, and if we base our conclusions on 

 a large number of trees instead of a few, the agreement between rainfall and growth must 

 become much greater than 70 per cent. It would seem, indeed, that with a time-unit 

 of 10 years and with a number of trees amounting to hundreds the agreement ought to 

 be over 90 per cent. This conclusion, however, is based solely on the yellow pine of 

 Arizona. Before it can be applied to other species in other parts of the country, further 

 investigation is necessar3^ In the Sierras, where the sequoias grow, the cHmatic conditions 

 are in many ways similar to those of the high plateaus of Arizona, where the j-ellow pines 

 have their habitat. The total precipitation in the sequoia region, however, is much greater 

 than among the pines, perhaps twice as much. Moreover, there are no summer rains in 

 California, which adds another element of difference. Yet in spite of the differences the 

 two regions are sufficiently alike to cause us to infer that in both places trees of the same 

 species would be similarly influenced by variations of rainfall. The introduction of a 

 new species, however, may completely reverse matters. Hence we are not justified in 

 drawing any conclusions as to the sequoia until we have made a comparison of actual 

 measurements of the growth of the trees year by year with the precipitation at the nearest 

 possible meteorological stations. 



The rainfall of central California — that is, of the portion of the State lying west of the 

 Sierra jNIountains between latitudes .35° and 39° — varies enormously. In the southern part 

 of the Great Valley near Bakersfield and the Kern Lakes it averages only 5 to 10 inches a 

 year, and in no part of the valley does it rise much above 15 inches on an average, though in 

 individual years it rises twice as high. In the Sierras at an altitude of 4,000 feet or more, and 

 in the Coast Range at somewhat lower altitudes, it rises in some places to an average of 

 50 to 60 inches per year. In spite of this difference in amount, however, the proportional 

 variations from year to j'ear in different places are closely similar. This is evident from 

 an inspection of figure 40, which represents the annual rainfall since records began to be 

 kept at selected meteorological stations in various parts of central California. In view of 

 the long, dry season in summer the precipitation is naturally reckoned from July to July 

 rather than from January to January. The first curve represents the rainfall at Fresno. 

 This is placed first because it is the one chiefly employed for comparison with the tree 

 curves. The next curve shows the rainfall at Bakersfield, which lies in the southern part 

 of the Great Valley and is selected partly because it lies well to the south and partly because, 

 with an average rainfall of only about 5 inches, it is the driest place in the whole district. 

 The next two curves represent Portersville and Tulare, which he in the Great Valley, not 

 far from the base of the Sierras, and have been selected because, being about 35 and 50 



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