GRAZING AND FORAGE PRODUCTION ON NATIONAL FORESTS 5 



Table 1. — Average temperature (in hours) above and below 40° F., and number 

 of Jwurs freezing, period 1914 to 1922, inclusive 



Month 



January 



February 



March 



April 



May 



June -.- 



July 



August 



September 



October 



November 



December 



Yearly average. _ 

 Monthly average 



Oak-brush type 



Hours 



above 



40° 



59 

 74 



107 

 260 

 4S3 

 671 

 741 

 739 

 635 

 395 

 177 



4, 427 

 369 



Hours | tt™„ Hours 

 bel ° w 'freeSne above 



Aspen-fir type 



685 

 598 

 637 

 460 

 261 



49 

 3 

 5 



85 

 349 

 543 

 658 



4,333 

 361 



533 



467 



462 



248 



79 



17 











22 



175 



382 



522 



19 

 22 



58 

 195 

 409 

 627 

 737 

 727 

 581 

 280 

 101 



20 



2,907 

 242 



S15 



Hours 

 below 



725 

 650 

 686 

 525 

 335 



93 

 7 



17 

 139 

 464 

 619 

 724 



415 



Hours 

 freezing 



670 

 568 

 550 

 321 

 157 



33 

 

 



45 

 243 

 456 



3,725 

 310 



Spruce-fir type 



Hours ' Hours 



above below 



40° 40° 



14 

 8 

 2 



57 

 186 

 548 

 724 

 714 

 513 

 164 



52 



32 



730 

 664 

 742 

 663 

 558 

 172 

 20 

 30 

 207 

 580 

 668 

 712 



3,014 

 251 



5,746 

 479 



Hours 

 freezing 



704 

 546 

 285 



65 

 

 



61 

 357 

 511 

 631 



4,477 

 373 



By reference to Table 1 and Figure 2, it will be seen that freez- 

 ing temperatures did not occur during the period considered in any 



June July Aua. Sept 

 Yc—Mom Growtny Season tl 



Fig. 2. — Average monthly temperature (in hours) above 40° F. and below 32° F. 

 (Period 1914—1922, inclusive.) Temperatures above 40° F. are favorable for plant 

 growth, while freezing temperatures are detrimental. During the main growing 

 season the hours of favorable growing temperatures are at a maximum and the 

 hours of freezing temperatures are at a minimum number 



of the zones during July and August, but that in June and Sep- 

 tember, the other two months of the main growing season, they 

 occurred with considerably frequency in the upper zone and are 

 not absent even from the oak-brush zone. Still more striking is 

 the decrease in the number of hours above 40° 2 in the spruce-fir 



2 Investigations conducted by various workers indicate that at or below 40° F. little or 

 no growth takes place in plants of the character of those which furnish forage in the 

 Wasatch Mountains. 



