METHODS 

 Aerial Producfion 



Twelve permanently fenced exclosures (figure 1) were sampled during the 1981 

 study. (Note: exclosure No. 9, Juho/Ansc-Agsp, shown on figure 1, was not 

 sampled in 1981.) The 1981 productivity sampling procedures were the same 

 as those used in 1977, 1978, 1979, and 1980. The number of samples to be 

 taken per exclosure was calculated to obtain the desired levels of precision 

 using the previous data. Sampling took place from July 17 through August 10, 



After clipping, all exclosures except Ansc, Ansc-Agsp, and Agsp/Bogr-Cafi 

 exclosures were opened for grazing to reduce litter accumulation from previous 

 years. All exclosures were closed to grazing by autumn 1981. 



Frequency and Canopy-Coverage 



Within each exclosure, twenty permanently located 20 cm x 50 cm plots were 

 sampled for frequency and plant canopy-coverage using a modification of the 

 technique described by Daubenmire (1959). Unlike Daubenmire's technique, 

 coverage classes were not used, but plant canopy-coverage for each species 

 was estimated as accurately as possible. The same series of plots were sampled 

 in 1981 as in previous years. These plots have never been clipped. Color 

 transparencies of each plot were taken at the time of sampling. 



Species Density 



Species density, the simplest measure of diversity, was determined for each 

 community based upon canopy-coverage data. In each exclosure, the average 

 number of species per plot (species density) and the number of species per 

 set of twenty plots were calculated. 



Silver Sagebrush Density 



Prior to clipping of the Arca/Aqsm/Bogr exclosure, density of silver sage- 

 brush was measured in 45 0.5m2 plots randomly selected for clipping. 

 Shrubs were assigned to one of three size categories: 



