18 BULLETIN 1233, U. S. DEPARTMENT OF AGRICULTURE. 



inches and 160 trees of an average diameter of 2 inches, making a 

 total basal area of 66 square feet, or 50 per cent more than in the 

 "sheltefwood" plot. 



The equipment and operation of this station has been the same as 

 of Station 14, except that the periodic use of recording instruments 

 fell here on the thud decade of each month. 



F-1G: Timber-line. — Elevation, about 11,500 feet; aspect, N. 10° 

 E.; slope, 40 to 45 per cent. This station represents conditions on 

 the north slope of Pikes Peak, at the upper limits of the Engelmann 

 spruco type, limber pine and bristlecone pine, as well as spruce, being 

 found in the edge of the forest. It is just a few feet outside the 

 timbered zone, which here ends very abruptly. (See PL VI, fig. 1.) 

 Presumably, on account of local wind exposure, the point represents 

 one of the lowest dips in the timborlinc, and was chosen for the obser- 

 vations because of its accessibility. 



Owing to the difficulty of the trip, the station has been visited only 

 at 5-day intervals since its installation in October, 1916. For air 

 temperatures such a program necessitates more than the usual 

 dependence upon the thermograph record, as but one correction of 

 the maximum and one of the minimum is secured for each 5-day 

 period. The system has been to apply these corrections to the trace 

 for each day of the five, witli slight modification, and then to obtain 

 from the trace the maximum and minimum temperature for each 

 day, calculated from midnight to midnight. This, it is thought, 

 would have permitted no serious error over a long period had the 

 recording thermometers been perfectly reliable. Owing to the high 

 wind velocities it was found impossible to obtain a correct record of 

 minimum temperatures in the shelter where the other instruments 

 were located, and as a final resort two other minimum-registering 

 thermometers were placed on more substantial supports. Although 

 these did not fail to register properly, they did not of course rerister 

 the temperatures prevailing in the shelter. The entire temperature 

 record, therefore, presents a combination of values, all of which are 

 not representative of the same point, but doubtless represent the 

 locality well enough. 



The thermometer shelter, anemometer, and evaporimeter were so 

 placed on a tower that an elevation of about 10 feet above the ground 

 was secured for each instrument. The periodic psyehrometer read- 

 ings, which of course do not have great value, were likewise secured 

 at this elevation. The precipitation record during most of the first 

 year was secured by means of an 8-inch gage placed in the shelter of 

 spruce trees 100 feet from the other equipment. It was thought that 

 the trees afforded no more than enough protection from wind to 

 insure a e^ood snow catch. With rain ami little wind, however, it 

 was found, that a 12-inch gage in the open gave much higher values. 

 For this reason the entire precipitation record, except for August 

 and September, 1917, is questionable and lias not been used. No 

 soil moisture determinations have been made at this station. 



The following equipment was used: 



Maximum and minimum thermometers, in standard shelter, October 1, 1916, 

 to February 28, 1918. 



Air thermograph, in shelter, October 1, 1916, fco February 28, 1918. 

 P ochrometer, in shelter, October 1, 1916, to February 28, L918. 

 Anemometer, with register, October 1, 1916, to February 28, 1918. 

 Evaporimeters, inner-cell, Type '2, October 1, 1916, t<> December 31, 1016. 



