. Carnegie Institution of Washington publication. 66 CLIMATIC CYCLES AND 1900 1905 FIG. 14.—Early test of correlation between tree-growth and rainfall by years; Flagstaff. was made. In this the lower curve represents the average annual growth of 25 trees and the upper curve is the precipitation 12 miles distant. The latter is taken from November 1 to November 1 in order to carry the snowfall into the following season of growth. This study suggested the investigation of the time of year to begin annual means of rainfall, which has already been presented in Chapter II. Figure 4 giv
. Carnegie Institution of Washington publication. 66 CLIMATIC CYCLES AND 1900 1905 FIG. 14.—Early test of correlation between tree-growth and rainfall by years; Flagstaff. was made. In this the lower curve represents the average annual growth of 25 trees and the upper curve is the precipitation 12 miles distant. The latter is taken from November 1 to November 1 in order to carry the snowfall into the following season of growth. This study suggested the investigation of the time of year to begin annual means of rainfall, which has already been presented in Chapter II. Figure 4 gives a comparison between Flagstaff rain and the two Flag- staff groups, and also shows how the best time of beginning the year was deter- mined. It proved to be November 1 at Flagstaff and September 1 at Prescott, where the nature of the ground gives more chance of conserving moisture. The great difference between individual trees in response to rain is also shown in figure 5. It is evident that quick-growing trees serve as better indicators. THE PRESCOTT CORRELATION. Five subgroups, numbering in all 67 trees, were obtained from different points in the vicinity of Prescott. These all cross-identified among themselves with entire success, both as individuals and as groups. The group curves are shown in figures 6 and 7, but in com- parison with the Prescott rainfall they differed greatly, the group nearest the city showing much the best accordance. Accordingly this group is plotted by itself in figures 7 and 15 with the rainfall curve. On the whole there is much agreement, as may be seen by comparing the crests and troughs of one with those of the other. The most con- spicuous discrepancy is in 1886, where the rainfall decreases and the growth of the trees increases. In 1873 the growth seems to have responded to the decrease in rainfall, but to a greatly diminished degree. The tree maximum of 1875, one year behind the extreme maximum of 1874 in the rainfall, is entirely reasonab
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