Nov. i6. 1914 



Revegetation of Range Lands 



99 



the variation in the maximum temperatures in the three zones is fully as 

 great as in the case of the minimum. During the month of July, for ex- 

 ample, the maximum temperature in the Hudsonian zone was 84°; in the 

 Canadian, 90°; and in the Transition, 104° F. The highest temperature 

 in the three zones during the entire growing season was 91°, 97°, and 

 105° F., respectively. 



Precipitation. — The higher temperatures characteristic of the less ele- 

 vated lands are associated in the region of the study with a minimum 

 precipitation. In the valley surrounding the Wallowa Mountains — that 

 is, in the Transition zone — at an elevation of 3,600 feet, the annual pre- 

 cipitation is about 17 inches, the greater part coming in the spring, 

 autumn, and winter. As a result, the vegetation often sufifers for lack of 

 moisture. In the Hudsonian zone, on the other hand, the larger amount 

 of precipitation received is ample, and, with the exception of seedling 

 plants, the vegetation is not affected by drought. 



Figure 2 shows that the Transition and Canadian zones received 51.6 

 and 26 per cent less rainfall, respectively, than the Hudsonian. While 



PLACCOFRCADING 



TRANSITION ZON€ 



CANADIAN ZONE 



HUDSONIAN ZONE 



INCHES or PRECIPITATION 



Fig. 2. — DiaKram showing the total precipitation in the Transition, Canadian, and Hudsonian grazing 

 zones during July, August, and September, 1909, inclusive. 



the actual amount of precipitation during the growing season of 1909 

 was somewhat above normal, the ratio between the amount which fell 

 in the different zones is similar to that of an average year. The greater 

 amount of precipitation at the higher altitudes, together with the com- 

 paratively late date at which growth begins, accounts for the continuous 

 development of the forage. 



Comparative Air Humidity. — Since the Hudsonian zone has a rela- 

 tively lower air temperature, a greater amount of precipitation, and a 

 more humid soil than the lower zones, it would be natural to expect that 

 the relative air humidity would be lower and transpiration less severe than 

 in the lower areas. Figure 3, which gives the daily variations in air 

 humidity derived from evaporation readings, shows this to be the case. 



It was unexpectedly found that in the Hudsonian zone the evaporation 

 was greater than in the Canadian zone immediately below. While the 

 temperature and even the relative air humiditv, a.-^ computed from 

 psychrometer readings, were lower in the Hudsonian zone, the dense 

 timber of the Canadian zone so interrupted the air currents as to materi- 



