734 



AMERICAN FORESTRY 



one must remember also that precipitation in the form 

 of snow goes over to tlie following spring growth and 

 should be included in the rainfall of the succeeding year. 

 Also in regions where there is a pronounced double rainy 

 season, heavy precipitation in winter is necessary in or 

 der to tide over the spring drought, otherwise the tree 

 may put on a false ring (usually easily distinguishable) 

 or even in extreme cases stop growing for the year and 

 show no effect of the summer rains. These features are 

 finely shown in the Prescott trees.* 



In the eighty sections recently examined or collected in 

 North Europe a striking coincidence was found between 

 the growth of these trees and solar phenomena (Figure 

 2.) That some such agreement should exist was not en- 

 tirely unexpected. The 

 question of the relation be- 

 t w e e n sunspots and 

 weather is one upon which 

 doctors and noted ones 

 have disagreed. This in- 

 vestigation was begun to 

 see whether the trees, by 

 representing the weather, 

 would show such connec- 

 tion, if any exists. A very 

 strong and very reasonable 

 connection was found be- 

 tween tree growth and rain- 

 fall in Arizona. But also 

 substantial evidence was 

 found of a relation to sun- 

 spots. To give some idea of 

 it one may say that in the 

 last hundred and sixty years. 

 ten out of the fourteen sun- 

 spot Maxima and Minima, 

 have been followed about 

 four years later by pro- 

 nounced maxima and mini- 

 ma in the tree growth. Also 

 during some two hundred 

 and fifty years of the early 

 growth of these trees they 

 show a strongly marked 

 eleven-year variation. 



But in the very first 

 group of European trees 

 studied, those obtained at Eberswalde, near Berlin, the 

 remarkable fact became at once api)arent that these thir- 

 teen trees from one of those beautiful German forests, 

 show the eleven-year sunspot curve since 1830 more 

 accurately than do the corresponding curves of rainfall 

 or tem|>erature. The eleven-year variation in the trees 

 is shown in the accompanying photograph of one of the 

 Eberswalde sections (l-'igure 3.) It will be seen at once 

 that there is a rhythmic sway in growth, large rings alter- 

 nating with small ones. The arrows jilaced on the pho- 

 tograph are not there to call attention to the larger 



*Sf chapter by the writer in "The Qimatic Factor,' 

 oationi, lU. 



Carnegie Publi- 



growth but to mark the years of maximum sunspots. 

 The other twelve trees of that group dc not show quite 

 so perfect rhythm as this particular part of this section 

 but are like the other parts of this section, showing 

 strongly a majority of the maxima. Taking the group 

 as a whole the agreement is highly conspicuous and the 

 maximum growth comes within six-tentns ol a year of 

 the sunspot maximum. 



In order to test further this coincidence, groups of tree 

 sections were obtained from other parts of Northern 

 Europe, namely. Southern England, outer coast of Nor- 

 way, scattered places along the inner coast of Nor- 

 way, Christiania, Central Sweden, scattered localities 

 in Sweden, Northwest Austria and Southern Bavaria. 



Five of these eight groups 

 are of the Eberswalde type 

 and show the sunspot vari- 

 ation. Of the other three, 

 the trees from the inner 

 coast of Norway as a whole 

 appear to show a reversed 

 cycle, probably because 

 they are deep inland valleys 

 while the southern groups. 

 Northwest Austria and 

 Southern Bavaria, close to 

 the Alps, have combined 

 agreement and disagree- 

 ment so that they cannot as 

 yet be considered to give a 

 definite result. In the six 

 groups, however, repre-' 

 senting the triangle be- 

 tween England, Northern 

 Germany and the lower 

 Skandinavian Peninsula, a 

 variation in growth since 

 1820 showing pronounced 

 agreement with the sunspot 

 curve is unmistakable. 

 Every sunspot maximum 

 and minimum since that 

 date appears in the trees 

 with an average difference 

 in growth of twenty per 

 cent between them. This 

 is shown in the diagram ac- 

 The next most pronounced 

 feature is that five of the eight minima show a small and 

 brief increase in tree growth. This suggestion of a sec- 

 ond maxinumi is of interest because in it we find agree- 

 ment with Hann and Hellmann in their studies of Euro- 

 pean rainfall and sunspots and lend added weight to 

 results which each author obtained but which neither 

 allowed himself to regard as conclusive. In the splendid 

 work of Hellmann u])on the rainfall of the North Ger- 

 man drainage area, it is this inconsiiicuous maximum 

 which he finds the more important of the two. 



In sunnnarizing, two facts and a conclusion stand out 

 prominently. First, it has been shown that trees may. 



TREE SECTION, PINUS SYLVESTRIS, FROM NORTH GERMANY 



Figure 3 The arrows mark the years of greatest sunspots. Note the 

 periodic character of growth. 



companying this article. 



