212 



MISCELLANEOUS PUBLICATION 1271. U.S. DEPARTMENT OF AGRICULTURE 



Table 6. — Average air temperatures (C.) by months above 

 grazed and wigrazed grassland during the 1970 season 1 



Treatment 



Grazed 

 Ungrazed 



Average temperatures by months 



June 



July 



Aug. 



Sept. 



19.2 



22.0 



21.7 



13.7 



Seasonal 

 average 



Degrees Degrees Degrees Degrees Degrees 



20.7 23.7 22.9 15.2 20.6 



19.1 



1 Average of all temperatures measured at various heights above the 

 ground. 



site. For example, during the week of August 

 9-15, the average range between maximum and 

 minimum values at a depth of 7.5 cm. was 8.2° C. 

 on the grazed site and only 4.8° on the ungrazed 

 site. Similar ranges in extremes at this depth oc- 

 curred on most days throughout the season. 



Wind 



Wind movement was measured by means of 

 small rotating-cup anemometers supported at 15, 

 30, 90. and 130 cm. above the soil surface on the 

 grazed site, and at the same heights on the un- 

 grazed site, except for the uppermost unit which 



was at 145 cm. (canopy height plus 1 meter). 

 Counters which recorded the number of revolu- 

 tions of the anemometer rotors were read daily. 



Wind velocity at a height of 15 cm. averaged 

 2.1 km./hr. on the grazed site and only 0.6 km./ 

 hr. on the ungrazed site (table 11). Wind velocity 

 increased rapidly on both sites as height above 

 the ground increased, reaching an average of 8.7 

 km./hr. (5.4 m.p.h.) at 130 cm. on the grazed 

 site and 8.4 km./hr. (5.2 m.p.h.) at 145 cm. on 

 the ungrazed site. Wind velocity at these points, 

 equidistant above the vegetation canopy, were 

 nearly equal, as expected. 



The development of the vegetation during the 



Table 7. — Profiles of average temperatures (C.) at different 

 heights above the ground surface at 1^:00 a.m., 2:00 p.m.. and 

 10:00 p.m. for the week of July 12-18, 1970 on grazed and 

 ungrazed sites. 



Height 





Grazed 







Ungrazed 





above 

 surface 















4 a.m. 



2 p.m. 



10 p.m. 



4 a.m. 



2 p.m. 



10 p.m. 



Cm. 



Degrees 



Degrees 



Degrees 



Degrees 



Degrees 



Degrees 



145 l 















15.0 



30.0 



19.4 



130 2 



16.1 



30.6 



19.4 















120 



16.7 



30.0 



20.0 



14.4 



27.8 



18.9 



75 



16.7 



31.1 



20.0 



13.9 



28.3 



17.8 



55 



15.6 



30.6 



19.4 



13.9 



28.3 



17.8 



25 



15.6 



31.1 



18.3 



12.8 



29.4 



16.7 



15 



15.0 



32.2 



17.8 



11.1 



32.2 



14.4 



7f, 



13.9 



31.7 



16.7 



11.1 



36.1 



13.9 



2.5 



15.0 



35.6 



17.2 



14.4 



34.4 



16.7 



Average 



15.6 



31.6 



18.6 



13.3 



30.8 



16.9 



1 Height of canopy (45 cm.) + 1 meter. 

 3 Height of canopy (30 cm.) + 1 meter. 



