Page:Climatic Cycles and Tree-Growth - 1919.djvu/134

From Wikisource
Jump to: navigation, search
This page has been validated.
108
CLIMATIC CYCLES AND TREE-GROWTH.

several maxima at about 8.5-year intervals. Pattern E gives the Vermont analysis. The solar cycle shows well for the last 150 years, but is preceded by a 9.2-year cycle for about 50 years, and then by the solar cycle again. This tree curve is shown in figure 27, page 78.

The Arizona pines are given in pattern F. The double-crested solar cycle shows in the larger part of it, but is best developed in the upper and lower thirds. By sighting along these vertical rows, a dark line in the upper third, indicating the more pronounced minimum, comes in straight line with the lesser dark minimum line in the lower third, indicating a transfer of emphasis from one-half of the 11-year cycle to the other half in passing the seventeenth century. This was noted above in connection with the analysis of the same record by a series of curves in figure 33, page 103. Further study of this pattern, however, gives information as to how and when that change took place.

Changes in the 11-year tree-cycle of Arizona — A careful examination of an early differential pattern of the Flagstaff tree record gave the following probable history of the 11-year variation in Arizona:

Table 7.—Changes in the 11-year tree-cycle of Arizona.
Years. Period. Remarks.
1395-1550 11.3 Double crests throughout, except 1476 and 1487, where the second crest fails.
1550-1595 14.3 Heavy double crest.
1595-1661 11.0=0.5 Heavy single crests with trace of double diminishing to small variable singles.
1661-1667 16.0(?) Possibly 1 long interval.
1677-1770 12.5 Double crests mostly; going to 10.8 from 1702 to 1722.
1770-1793 9.0 Sharp single crest continuing second crest of preceding double.
1793-1817   Doubtful.
1817-1910 11.6 Rather broad, heavy crests, sometimes double; 1864 has too little and 1875 too much crest.

The interval from 1830 to the present time divides also extremely well on a 21.0-year period, and fairly well in one of 7.3 years.

In obtaining this result no comparison was made with the sunspot record. So the following is of interest:

Table 8.—Changes in tree and sunspot cycles compared.
Trees. Sunspots.
Years. Period. Years. Period.
1595-1661 11.0=0.5 years 1615.5 to 1660.0 11.1 (?) years.
1661-1677 16(?) 1660.0 to 1675.0 15.0
1677-1770 12.5 mostly and 10.8 1675.0 to 1769.7 10.5
1770-1793  9.0 1769.7 to 1788.1  9.2
1793-1817 Doubtful. 1788.1 to 1816.4 14.15
1817-1910 11.6, 21.0, or 7.3 1816.4 to 1905 11.08