Page:Climatic Cycles and Tree-Growth - 1919.djvu/44

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34
CLIMATIC CYCLES AND TREE-GROWTH.

All the sections so far in this group came from the west side of Norway near latitude 60°. The remaining two came from farther north and were first examined in the office of Dr. Jelstrup. No. N 1 was a small tree some 6 inches in diameter with its center in 1848. It grew in Mo i Ranen in latitude 66° 15', a 2 days' trip by boat from Trondjem. The rings show a rhythmic character, and a photograph of the thin section presented to me is given in plate 3, b. As in the other similar photographs, the years of sunspot naaxima are marked with arrows. It was cut in 1907 and the outer incomplete ring was taken as of that year. The identification with trees from near Bergen is poor, as would be expected.

No. N 2 was an interesting cross-shaped section from beyond the Arctic Circle, latitude 68° 45'. It had been damaged by forest fires at various times to such an extent that the injured parts of the trunk ceased growing while the rest kept on; hence it was of this extraordinary shape. It was cut in the winter of 1905-6, and the outer ring was taken as of 1905. As a rule the rings were very easy to follow until before the year 1600, and even then by carrying the ring to other arms the identification seemed practically certain. The rings reached a suspiciously small size between the center at 1497 and 1512.

The measuring of this 400-year section was done on December 31, 1912. By noting ring after ring with care, tracing all rings a short distance and following the one case of suspected double across into another arm, there seemed to be no errors, certainly none of doubling and none suspected of disappearance. Letters B, BB, indicating maximmn growth, were placed at the center of groups of large rings as the measuring progressed, without knowledge of any relation between them. That same day, on looking over the measures, a Bruckner period seemed indicated. The maxima were marked as the measuring progressed. See table 3, on page 35.

This series of maxima, 270 years long, from 1561 to 1830, shown in figure 38, permits the application of a 34-year period with an average error of less than 3 years. If that case were alone, I would not include it here, but I believe I shall be able to show it in a number of very old trees in widely separated localities.

From the above description it is evident that we have in this group some very interesting trees, even though they grew far apart. They are probably worth more as individuals than as a group, but until more trees can be added from their various localities the usual method of presenting them here is used. So the group means are tabulated in the appendix, using an extrapolated value of N 1 from its center in 1848 back to 1821. These means will be found plotted in figure 8. They have been corrected for age and reduced to standard size in the