FOREST TYPES IN CENTRAL ROCKY MOUNTAINS. 43 



Other temperatures in the Pikes Peal: Region. — The remaining tem- 

 perature records for the Pikes Peak region (Table 9) are t hose obtained 

 at the special stations in the vicinity of the control station, all hut. 

 one at practically the same elevation, and designed to show the dif- 

 ference between types on slopes of different exposure. It is shown 

 that a difference of exposure may create as great a difference in local 

 air temperature as a difference of 1,000 or 2,000 feet in elevation; 

 hence, so far as air temperatures determine, almost any species may 

 find the proper conditions for initiation at a middle elevation. 



In Table 9 the same plan has been followed as in Table 8, the records 

 being for a variety of periods and none covering the whole period 

 during which the control station has been operated. Several of the 

 records do not have sufficient individual value to warrant the com- 

 putation of means for every month. In these records one month in 

 each quarter has been considered, and the annual means have been 

 derived from these four months, a comparison being made, of course, 

 with the same months at the control station. 



It is seen from Table 9 that the growing season excesses of the 

 outlying stations are somewhat greater than the excesses for the 

 whole year, where both have been computed, except at Station F-2A, 

 which, like the control station, represents conditions 20 feet above 

 the ground. These facts may account for the low summer tempera- 

 tures of the control station, as compared with other stations in the 

 Pikes Peak series. 



When the most typical pine and spruce stations shown in Table 

 9 are compared with corresponding types at different elevations, as 

 shown in Table 8, namely, F-2 with M-l, and F-3 with L-l, it is 

 found that the air temperatures of corresponding forest types vary 

 in the same direction, but that the local variations are not so great 

 as those in which a difference in elevation is involved. The pine 

 type locally may be 4.4° warmer than the control station, if the ground 

 conditions for the whole year arc considered, but at a lower elevation 

 the pine type is 4.8° warmer. Here the agreement is close. 



One of the local spruce types is decidedly cooler than the control 

 station for the summer period in which record has been secured, but 

 the other is cooler only during the winter. In the first spruce type 

 there is a very marked depression of the minima, undoubtedly due 

 to cold air drainage; but in the second type the summer maxima are 

 so high as to lead to the belief that the poorly sheltered thermometers 

 received some direct insolation, the possibility of which was not sus- 

 pected during the observations. It is to be noted that insolation, 

 re:i clung the ground through breaks in a heavy canopy, produces 

 very sharp effects on account of the stagnation of the air. Because 

 of the factors possibly affecting the record for F-3, more significance 

 should be attached to the soil temperatures, which more clearly show 

 the general coolness of this site. 



It is noted that the western yellow pine ridge (F-12), like the con- 

 trol station, is freely exposed to wind and is practically no warmer 

 than the control station. It will also be remembered that this site is 

 reproducing to Douglas fir and limber pine, as well as to yellow pine, 

 and that the yellow pine is in a very unhealthy condition. This 

 condition is equally well brought out by the soil temperatures. In 

 the summer, at least, lower air temperatures occur at F-4, where 

 the maxima are not high on account of the easterly exposure, and 



