ENVIRONMENT 107 



and 0.43 mm. The apparent strong effect of slope in different parts 

 of the North Transect appears again here and emphasizes the value 

 of further work directly on that point. The growth on the North 

 Transect is 142 per cent greater and at the brook 179 per cent greater 

 than on the South Transect, and the same inference prevails as with 

 the yellow pines. 



Limber pine — Limber pine (Pinus flexilis) occurs in the three 

 transect groups and the basin group at 9,500 feet. Three trees in the 

 basin have a mean ring-size of 0.69 mm. The others of two trees each 

 have 0.93, 1.02 (variable), and 1.00 mm. (variable). Thus, we can 

 not make conclusions from the data on this tree, except that the 

 reduced growth in the basin, 9,500 feet elevation, is very likely a 

 result of temperature. 



Engelmann spruce — Two specimens of this tree in the timberline 

 group, 11,500 feet, give a growth of 0.95 mm., and four specimens at 

 the brook give 1.16 mm. This difference is quite as likely to be tem- 

 perature as moisture. 



Fox-tail pine — Three trees of this species, Pinus aristata, were 

 included in the timberline group, with an average growth of 0.63 mm. 



Age correction — No age correction has been used in these figures, 

 but as the selection of trees uniformly favored the larger and older ones, 

 it is not likely that such correction would materially alter the results. 



Summary — The area tested on Pike's Peak lies on the east slopes, 

 chiefly below the basin. The pines and Douglas firs here show evidence 

 that water is the prominent controlling factor, the pines having some- 

 what larger growth than the firs. The limber pines tested had an 

 average growth between the other two, but were variable and, except 

 that they give the same tree records as the others, there was no decisive 

 material regarding their sensitiveness to moisture-supply. A single 

 group of fox-tail pine gives a similar curve. Engelmann spruce had a 

 larger growth at the brook, 8,700 feet, than at timberline, 11,500 feet, 

 and its ring record is far different from the other species tested. Near- 

 ness to running water greatly increases growth in all the species, and 

 apparently in the yellow pines and firs does not interfere with their 

 success as climatic recorders. 



SAN FRANCISCO PEAKS AREA 



These beautiful peaks, 12,760 feet high, 10 miles north of Flagstaff, 

 have the rounded mass of an ancient volcanic cone, with the huge 

 outlying spread of Elden Mountain (9,000 feet) stretching off to the 

 southeast. They are surrounded by pine forest for miles in every 

 direction and give favorable opportunity for certain tests. 



Altitude effect — Two groups, all yellow pines, may be compared 

 to get an idea of this effect, namely, Fort Valley, at an elevation 



