Page:Climatic Cycles and Tree-Growth - 1919.djvu/38

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CLIMATIC CYCLES AND TREE-GROWTH.

moisture. The trees had formed a border to a little plot of cultivated land with a southwesterly exposure. The average age was 54 years. The rings were all extremely plain, averaging 2 to 4 mm. in size, and cross-identification was everywhere perfect. Of the 50 or 60 rings, about 10 had marked characteristics and were easily recognized in nearly every section. It was noted that a few sections had numerous rings more sharply defined on the summer side of the dense red portion than on the usual winter edge. One of the 11 sections is shown in plate 3, A.

The appendix contains a table of mean tree-growths of the 11 British sections; the years 1859 to 1863 inclusive show means of 6 trees only, as some did not extend back that far; of these, 2 had their centers about 1858, 2 in 1857, and 2 in 1855. The owner of the land informed me that the trees had all been planted at the same time, and therefore this apparent discrepancy may be due to sections cut at different heights above the ground. These means are plotted in figure 8.

For ready comparison it seemed desirable to standardize this British curve as well as each of the other European curves. Each curve is therefore corrected for changing rate of growth with age and also very slightly smoothed to get rid of the confusing effect of the 2-year "seesaw " described later. In the present group, after careful consideration, the standardizing line follows the tree-growth through a uniform curve in the earlier years and becomes straight in the later years. Percentage departures from this mean standard line give the standardized curve. These percentage departures smoothed by Hann's formula will be found plotted in figure 23, together with similar curves from the other European groups.

OUTER COAST OF NORWAY GROUP.

On the advice of Dr. H. H. Jelstrup of Christiania, I visited the Forest School of Sopteland, a small place located about 18 miles south of Bergen, near latitude 60°. The elevation is but little above sea-level, and irregular intervening hills give slight protection from the North Sea storms. This group of 10 Pinus silvestris sections was collected on January 3, 1913, from logs in the yard of the Forest School. The logs had been cut within a week or two in Os, 12 miles to the south, on an exposed part of the coast and probably close to sea-level. Os is on the north shore of one of the larger inlets entering on the north side of Hardanger Fjord.

The average diameter was 6 to 8 inches and the average date of the center was about 1840, but one extended back to about 1800 and another to 1700. The average size of rings was about 1.25 mm. The group cross-identified extremely well and on a preliminary inspection seemed to show somewhat rhythmic variations in growth. In these