80 CLIMATIC CYCLES AND TREE-GROWTH 



Road descends sharply, following the bed of Ruxton Creek. The 

 laboratory is situated on a small southern tributary, Jack Creek, 

 just above their confluence. Dr. Clements has made extended ecologi- 

 cal studies on a certain area, the Transect, which extends a half mile 

 up the high, wooded slopes to the north and perhaps a third of a mile 

 up the shorter and more barren slopes to the south. The north branch 

 of this transect has very steep slopes in the lower part near this creek 

 and the Cog Road, and gentler slopes above. So the collections there 

 were divided into upper and lower groups. The upper group, PP 

 11 to 20, has an average altitude of over 9,000 feet and includes 5 yellow 

 pines, 3 Douglas firs, and 2 limber pines. These 10 cores were meas- 

 ured by Mr. Austin, using the long-plot method. They were stand- 

 ardized, and the curve, 1655 to 1919, was smoothed as usual, and the 

 part since 1750 is shown in figure 5. It resembles the neighboring 

 groups very closely indeed. Its cycles are 6.8 (2), 8.6 (2), 9.3, 13, 

 17.2, 22.6 (2), and 34.5 (2, oc. £). 



LOWER NORTH TRANSECT GROUP (LNT) 



The lower group, PP 21 to 27, in the North Transect, was 250 feet 

 below the upper, estimated in vertical height, which makes it about 

 8,800 feet above sea-level. Mr. Austin measured these cores also by 

 the long-plot method, and the curve, 1644 to 1919, smoothed after 

 standardizing, is shown (after 1750) in figure 5. The result shows a 

 rather even curve, more complacent than the trees farther from the 

 brook. It compares closely with the other group curves. Its cycles 

 are 11.1 (2), 16.0, 20.4 (2), 21.3 (oc. -£), and 40, which approximate 

 but are not exact in their conformity to the Rocky Mountain cycles. 



SOUTH TRANSECT GROUP (ST) 



South of the Alpine Laboratory the slopes rise abruptly up to 

 some very barren sand areas on Baseball Ridge. A collection of 10 

 increment-borings was made here with the help of Dr. Gorm Loftfield 

 at an average level perhaps of 8,900 feet. Two of these are yellow 

 pine, 6 are Douglas fir, and 2 are limber pine {Pinus flexilis) . They 

 cross-identified well and were measured by Mr. Austin and stand- 

 ardized. The curve 1570 to 1919 was smoothed as usual and the result 

 (since 1750) is given in figure 5. It shows vigorous variations which 

 make it probably the best representative curve of this Pike's Peak 

 area. Its cycles also are entirely typical of the Rocky Mountain 

 zone; 9.8 (2), 17.2 (2), 19.7 (3, oc. \), 25.2 (2), 31.1, and 34 (oc. $). 



BROOK GROUP OF DOUGLAS FIR (BDF) 

 Ten trees were tested along Ruxton Creek near the Alpine Lab- 

 oratory, with the purpose of forming a brook group and of learning 

 whether the Engelmann spruce reacts to abundant ground-water in the 



