Page:Climatic Cycles and Tree-Growth - 1919.djvu/53

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41
COLLECTION OF SECTIONS.

which suggest injury, as in 1756 and 1769 and 1770. A very regular recovery from these depressions sustains this idea of their cause. The means of the 2 groups are given on page 116.

A few trees are perhaps available for periods antedating 1740. The centers of 5 are as follows: B 12 in 1682, B 15 in 1641, N 2 in 1497, S 4 in 1510, S 9 in 1660. But the first 3 are from separate localities in Norway and the other 2 are from central Sweden, so it seems hardly profitable to include them here in a group on account of the tendency to reversal between those localities. The section N 2, 400 years old, from high latitude on the Norwegian coast, presents a feature of interest as noted in connection with the Norwegian group, namely, a pronounced fluctuation very nearly 34 years in length. The measures on this tree have been plotted, a mean sinuous line drawn through them, and then this mean line transferred to a different scale, smoothed graphically, and photographed to form figure 38 on page 106. The more formal analysis of this interesting tree-record with the periodograph confirms this periodic fluctuation.

WINDSOR (VERMONT) GROUP.

On return from Europe it seemed desirable to learn how American trees react in similarly moist climates. But it was not easy to secure sections. There are very few large pines near the Eastern cities. One "pitch" pine from 50 miles south of Boston, with more than 100 rings, was secured, but there were no others in that immediate vicinity. Five white-pine sections from near Middleboro, Massachusetts, were obtained, but their rings were too few in number, being only 50 to 60. Finally a satisfactory series of hemlock, Tsuga canadensis, from Windsor, was collected. Six sections came from the northwest slopes of Mount Ascutney at the lower and very steep end of the Brownsville trail. Five of these I cut from the stumps myself and preserved, and one was measured on the stump itself with full cross-identification. The remaining 5 of the 11 were cut from logs in a lumber-yard in Windsor; they came from across the river on a farm about 3 miles from town. Thus 7 or 8 miles separated these two subgroups. But the whole are here retained in one group, for the cross-identification, though difficult, was perfectly satisfactory. In order to be quite sure on this point, the subgroups were left separate until their curves could be compared. The Ascutney subgroup, with one extrapolation, extends back to 1695, and from that date 2 trees were carried back to 1650. A comparison between the 2 and the whole 6 showed harmonious curves in their overlapping parts. This curve shows an average growth of considerably less than 1 mm. in all its earlier years and up to the year 1808, when its yearly growth doubled. This sudden