CLIMATIC CYCLES. 



335 



is related directly to the sun-spot cycle, and its shifting is the cause of changes 

 in temperature and rainfall. This affords a ready explanation of divergent 

 effects in different regions, and promises to furnish a basis for completely 

 harmonizing the various climatic changes with the sun-spot period. Hun- 

 tington's general conclusion as to the basic correlation of climate with sun-spots 

 has already been quoted (p. 326). In essence, it is illustrated by the fact 

 that in northern Germany relatively continental conditions of climate, i. e., 

 abundant storms and rain in smnmer, and early heating of the ground in spring, 

 prevail when sun-spots are numerous, and relatively oceanic conditions when 

 they are few. During periods when the sun-spots are few, the storm-belts 

 tend to disappear and the storms are concentrated in the main continental area. 

 It is clear that rainfall is greater in the storm-belts, which are marked at the 



Jl.Oyrs. ;i. 



,-'Mm. 

 - H2 



'\j^\./\y\nj\rK/\A/'^.'n^'''''^>y\f^''^^'^^^^^^^^ 



1400 



Fig.1 



^-./' 



\ /\ f\ i"* /~\ •'■v '"^v '"\ /** r^ /"^ '\ r\ '^ '"> /"^ 1'% '"• /\ /**t '"x 



Fig.2 



1800 

 Arizona Tree Qrowfb and Cycles 



1900 



Ebertwalde Trees:—. 

 Sunspot Ntfmbefs: 100- 



A.^^ 



^J^ 



Fig.3 



Fig. 30. — Correlation of tree-growth with 11-year and 21-year cycles. 

 After Douglass. 



times of many sun-spots, and less in the intermediate areas of deficient stormi- 

 ness. It is generally less during sun-spot minima, when the storm-belts tend 

 to disappear. Huntington (I. c, 522) has likewise shown that terrestrial 

 temperatures are reduced by cyclonic storms, but this effect is probably felt 

 more in equatorial regions than in the storm-belt. As a consequence, while 

 it seems fairly certain that the sun-spot cycle affects terrestrial climates 

 through its control of cyclonic storms, the actual changes of temperature and 

 rainfaU in particular must be found in the shifting of the storm-belt and the 

 behavior of storms in each region. 



The correlation of the growth of trees with the 11-year cycle has been firmly 

 estabhshed by the work of Douglass and Huntington. Similar though less 

 certain correlations have been indicated for crop plants (Huntington 1914 : 

 239), and there can be little question that they will be found to hold for native 

 vegetation. The annual charting of a permanent and denuded quadrat in a 

 plant community throughout a sun-spot cycle ought to reveal decisive effects 



