PLANT SUCCESSIOH AND RANGE MANAGEMENT. 



11 



Table 1. — Precipitation in the heart of the ivheat-grass formation, 10,000 feet 

 elevation, Manti National Forest, 191Jf-1917, inclusive. 



Year. 



June. 



July. 



Aug. 



Sept. 



1914 



Inches. 



0.35 



2.12 



.18 



4.78 



Inches. 

 0.97 

 1.84 

 1.77 

 3.73 



Inches. 

 1.54 



.30 

 1.81 



.50 



Inches. 



1.23 



1.67 



.39 



.30 



1915 



191 6 



1917 



Average. . . 



1.86 



2.08 



1.04 



.90 



The average precipitation for the month as well as for the season 

 varies widely. The greatest variation since 1914 in rainfall in June 

 was 4.6 inches, the maximum being 

 4.78 inches in 1917, and the mini- 

 mum 0.18 inch in 191G. In July the 

 variation was 2.76 inches, the maxi- 

 mum being 3.73 inches in 1917 and 

 the minimum 0.97 inch in 1914. 

 Nearly 40 per cent of the 0.18 inch 

 of precipitation recorded in June, 

 1916, fell during the first half of the 

 month, while nearly 68 per cent of 

 the 0.97 of an inch recorded in July, 

 1914, fell after July 20. Since only 

 0.35 of an inch of rain was recorded 

 in June, 1914, the soil was far below 

 the average in water content. Ob- 

 servations indicated that the un- 

 questionable slowing down of growth 

 noted after the first week in July, 

 1914, was due to an inadequate 

 water supply. 



Owing to the exceptionally low 

 water requirements for the sur- 

 vival of both the bunched and the 

 turfed species of wheat grass, pro- 

 longed periods of soil desiccation, 

 covering critical periods of one or 

 more seasons, seem to have little effect on well-established plants 

 other than to decrease temporarily the aerial growth and the repro- 

 duction. However, young stands of turfed species usually suffer ap- 

 preciably less injury from soil desiccation than stands of bunch grass 

 of similar age. This is accounted for by the fact that reproduction 

 in the case of the turfed species is largely by extensive rootstocks 

 which have little or no tendency to shoot out until the plant is per- 



<S" — 



/J-"—' 



Fig. 4.- 



Small wheat grass {Agroyy- 

 ron dasystachyum) . 



