Page:Climatic Cycles and Tree-Growth - 1919.djvu/37

From Wikisource
Jump to navigation Jump to search
This page has been validated.
29
COLLECTION OF SECTIONS.

trees, shows so much greater agreement than the others that it has been used alone in drawing final conclusions. Its site was a small, poorly drained level space near the bottom of the valley.

In this group there was no necessity of duplicating the Flagstaff records, and therefore small V-shaped cuttings were made at the edges of the stumps, only triangular pieces of wood giving the outer half century of ring-growth being brought away. These were the samples on which the value of the cross-identification was discovered, as already described. Identical series of rings were observed in nearly every tree of the group.

Climatic Cycles and Tree-Growth Fig 7.jpg

Fig. 7.—Annual rainfall and growth of trees (Group V) at Prescott. Dotted line: rainfall. Solid line: growth.

Out of 67 sections averaging 50 rings each, only 6 gave any identification trouble. In 2 of these, 2 rings were lacking, but when allowance was made for this defect the identification was satisfactory. Another section had 2 extra rings, and another had 2 extra and 3 lacking. The other 2 sections proved especially puzzling and were finally omitted from the means. Of these 6 troublesome sections, the first 5 were very slow growers. Hence it would seem advisable not to use extremely slow-growing trees any more than is necessary. It may be urged that trees do not grow continuously at the slow or fast rate and that we can not tell how much of the change is due to rainfall. On the whole, however, it seems advisable to exclude trees or parts of trees whose identification is extremely difficult. The inner rings if well identified may be extremely useful in carrying back early records, as the slow-growing trees are likely to be among the oldest.

The averages of 4 subgroups and the means of all the Prescott trees will be found plotted in figure 6. The curve of the fifth subgroup is given in figure 7, where it may be compared with the rainfall of Prescott.

SOUTH OF ENGLAND GROUP.

This group of 11 sections was obtained in January 1913 at Fleet, near Aldershot, some 30 miles west-southwest of London. The trees were the common pine, Pinus silvestris, and averaged about a foot in diameter. The growth was very rapid and the wood was full of