Page:Climatic Cycles and Tree-Growth - 1919.djvu/126

100 England show slight relation to the solar cycle. They show more prominently other variations, which, taken between 1870 and 1900, may have given rise to Lockyer's 3.8-year period (1905, 1906). The full tree record becomes more accordant on a 3.5-year period. In this group there appears to be a slight relation to London rainfall of a direct character, that is, the growth is larger with increased rain. Naturally in such a well-cultivated region there may have been large differences due to treatment of the soil, drainage, and so forth. The other two European groups, one from Pilsen in Bohemia and one from the north slopes of the Alps in southern Bavaria, do not show consistent agreement with the solar variation. Yet the former shows a double sunspot period which is illustrated below.

Coming to the American continent, the Vermont group may also be considered as growing in a wet climate. It shows a very strong single-creasted solar period, but the maxima come 3 years early during the last century. During the preceding century, when the trees were younger, the tree maximum is only 1 year early. The rainfall in this region shows the solar period also, but it is roughly inverted with respect to the tree curve. The Oregon group must be considered as in the wet climate of the temperate zone. It is near the Pacific coast and has abundant rain or snow. The solar cycle is probably in it, but it is not so conspicuous as other short cycles. When these trees are summed up on the 11-year period, they show about 10 per cent total variation with maximum and minimum coinciding with the Vermont group and therefore anticipating the sunspot maximum by 3 years.

The sequoias grow farther south and experience the heavy precipitation of the temperate-zone winter combined with dry-climate summer conditions — that is, the summers are mostly clear, but have occasional sharp local showers, often with lightning. The tree-growth shows a relation to the rainfall in the great valley below and therefore we could expect some similarity to the Arizona pines. This does exist, but the exact 11.4-year cycle shown in the pines is less evident in the sequoias, though unmistakably there. The analysis of the long sequoia record will be shown below. In it several cycles between 7 and 15 years predominate in places. The 11-year period is plainly evident through most of the record and for some centuries is the predominant cycle, but for long periods other slightly differing cycles, such as 10 years, 12.6 years, or 13 years, are more evident. It is as yet impossible to say whether at these times there was a real change in the sunspot period, whether some subordinate period is operating in the sun, or whether only local conditions of some kind are the controlling factor.

The yellow pines of northern Arizona are dry-climate trees. They have a modified winter precipitation of the temperate zone. Spring and autumn have the complete dryness of the "horse latitudes," and the summers have the characteristic subtropical torrential thunder-