RESULTS AND ANALYSIS 

 Aerial Production 



Tables 1 through 12 and figures 2 through 5 summarize productivity and litter- 

 accumulation data collected during the 1977-1981 study period. Means are 

 expressed in kilograms per hectare with 90% confidence limits. (For pounds 

 per acre, multiply kilogram per hectare values by 0.892.) When data from both 

 halves of each exclosure were compared for internal homogeneity, only the Ansc 

 community was not homogeneous at the .05 probability level. 



Productivity in 1981 was higher than in 1980, a drought year, and, in most cases, 

 was similar to productivity in 1979. Both 1979 and 1981 are characterized by 

 below-average precipitation during the growing season. However, the dry summer 

 of 1979 followed a wet year and winter of heavy snowfall, whereas the summer of 

 1981 followed a drought year and dry winter. 



Communities exhibiting production similar to 1979 levels are Stco/Bogr-Cafi , 

 Bogr-Cafi/Stco, Stco-Agsm/Bogr, Bogr/Agsm, Agsm/Bogr, Ansc-Agsp, and Agsp/ 

 Bogr-Cafi. The Dist community continued to slowly but steadily increase in 

 productivity, probably as a result of protection from grazing and the presence 

 of subsurface water, although water availability is modified by soil salts. 

 Production in the two warm-season communities, Bogr and Ansc, was only two-* 

 thirds of that measured in 1979. Production in the Arca/Agsm/Bogr community 

 did not regain the level measured in 1979 when unusually high productivity was 

 thought to result from snow accumulation in this coulee site. Productivity 

 of the Dist-Agsm community was higher than in 1979, possibly as a result of 

 grazing in late 1980, but the difference was not significant (p > . 10). 



Frequency and Canopy-Coverage 



Table 13 presents the canopy-coverage data for 1981. Compared to 1980 data, 

 the most significant change is a substantial reduction in canopy-coverage of 

 B outeloua gracilis in six communities (Arca/Agsm/Bogr, Stco/Bogr-Cafi, Bogr- 

 Cafi/Stco, Bogr/Agsm, Agsp/Bogr-Cafi , and Stco-Agsm/Bogr). Canopy-coverage of 

 B. gracilis in these communities in 1981 averages 14.0% compared to 23.6% in 

 1980, a 59% decrease. 



Other changes from 1980 include an increase in coverage of Stipa comata in the 

 Bogr-Cafi/Stco community, an increase of Carex filifolia and decrease of 

 M uhlenbergia cuspidata in the Ansc-Agsp community, an increase of Agropyron 

 ^'^''^^^^ 1" the Bogr-Agsm community, and a decrease of Distich! is stricta in 

 the Dist-Agsm community. (See DNRC 1981 for 1980 dataT) 



