Species Density 



Table 14 shows species density for 1981. In general, species density increased 

 substantially from 1980 levels. (See DNRC 1981.) The extent of increase, however, 

 is variable. The Ansc community shows the greatest change in species density. 

 Average species per 0.1m2 plot jumped from three to five during the 1978-1980 

 period and to 6.2 in 1981, while the number of species per 20 plots jumped 

 from 20 and 22 during the 1978-1980 period to 29 in 1981, 



These changes in the Ansc community seem to be a result of the 1980 drought, 

 from which it has not recovered. The increase in species density may be a 

 result of Andropogon scoparius mortality and a consequent increase in sites 

 available for colonization by other species. Canopy-coverage of A. scoparius 

 decreased from 55.5% in 1978 and 60.2% in 1979 to 41.4% in 1980 and 38.6% in 

 1981. Production levels of A. scoparius in the Ansc community decreased from 

 an average 85% of total production during the 1978 and 1979 period to 52% of 

 total production during the 1980 and 1981 period. This community was the only 

 one not internally homogeneous in 1981. (It also was determined to be non- 

 homogeneous in 1977 and 1979.) Agropyron spicatum . not an aggressive species 

 in the study area, is now present throughout the Ansc community in small 

 quantities. 



Silver Sagebrush Density 



Total silver sagebrush density as determined by 45 0.5m2 samples is 7.78 

 individuals per square meter with a frequency of 87%. Small individuals 

 exhibited a density of 5.87/m2 and a frequency of 80%. Medium-size indi- 

 viduals exhibited a density of 1.55/m2 and a frequency of 40%. Large 

 individuals had a density of 0.35/m2 and a frequency of 13%. 



Climate and Readily Available Soil Moisture 



Precipitation data for the recording period are presented in table 15. Readily 

 available soil moisture is shown in table 16. Accurate temperature data were 

 not collected until August due to difficulties with equipment operation. These 

 data are therefore not presented, although thermographs are on file at DNRC. 



May-June precipitation was 3.2 inches. Only 1.1 inches of this total came 

 from rains depositing 0.5 inches of precipitation or more in a 24-hour period. 

 By July, readily available soil moisture was 7% or less in the rooting zones 

 of all communities with the exception of the 3-inch depth of the Arca/Agsm/Bogr 

 community. The upper soil level of some communities showed some improvement in 

 August, but was once again near exhaustion by September. Readily available soil 

 moisture in the Stco-Agsm/Bogr community was nearly nonexistent throughout the 

 sample period except at the 30-inch depth. 



14 



