TREE RECORDS: GEOGRAPHICAL DISTRIBUTION 71 



central Arizona area. It shows cycles as follows: 13.1, 14.5, 18.5, 

 20.5 (3), and 35 (3, J). The 13.1 and 14.5 are very possibly variants 

 of one about 14 years. The 20.5 again varies from 20.0 to 21.0. 



HIGH LEVEL GROUP (FLH) 



The idea of testing the effect of altitude on the ring-growth was 

 held from an early date. The first actual collection for it was done on 

 June 19, 1920, when Dr. E. J. Brown and the writer went on foot up 

 the canyon above Shultz Pass, where the Weatherford Boulevard has 

 recently been constructed. But the specimens were crudely cut and it 

 was felt that it would be preferable to test tree-growth on the west or 

 southwest slope of the mountain. Accordingly, on July 11, 1920, a 

 trip was made up the southwestern ridge of the mountain from the 

 southern end of Hart Prairie to the cabin used by the experiment 

 station at an elevation of 10,500 feet. Director Pearson and Mr. Haasis 

 of the staff were of the greatest assistance. A very interesting group, 

 numbered Fl 69 to 80, was obtained, including Douglas fir, cork-bark 

 fir, Umber pine, fox-tail pine, and Engelmann spruce. But this seemed 

 to combine too many different species over too great a range of alti- 

 tude; accordingly, the group of yellow pine increment-cores here used 

 was collected with the aid of Mr. Pearson on July 12, 1924, at eleva- 

 tions averaging a little under 9,000 feet, that is, really in two sub- 

 groups, one at the south end of Hart Prairie and the other at a little 

 over 9,000 feet altitude. 



These 10 cores were measured by Mr. D. A. Hawkins, using the 

 long-plot (longitudinal plot) method, and were then tabulated and 

 averaged and the curve, 1770 to 1923, plotted without standardizing. 

 A graphic Hann, shown in figure 4, was made by Mr. F. M. Douglass. 

 In general appearance this smoothed curve has all its variations greatly 

 diminished and is otherwise somewhat discordant compared to the 

 usual Flagstaff tree-records. It introduces a 17-year cycle, which is 

 not common in this region; but its cycles belong to the Arizona class 

 and are as follows: 6.9 (2), 9.1 (oc. £), 13.7 (2, -J), 17.3 (3), 20.5 

 (2, oc. i), 27 (oc. i), and 35 (2, oc. £). 



FLAGSTAFF SHADOW GROUP (SH) 



The old-time winter road to all points north of Flagstaff passed 

 east of the San Francisco Mountains because it was drier, warmer, 

 and had less snow than the west side. The forest regions east and 

 northeast of the peaks are shaded by the mountains from the wet 

 westerly winds, and the special effect observed in this group and 

 others is called the shadow effect. This group of five Swedish incre- 

 ment-cores was collected on July 13, 1924, in a specially selected area 

 nearly on a fine between Sunset Crater and the peaks, and about half a 

 mile west of the main highway. At this place the elevation is very 



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