and Koeleria cristata . Using Smoliak's (1956) regression equation for yield 

 and 3.65 inches (9.27 cm) of May-June precipitation, one would expect about 

 313 lb. /acre (351 kg/hectare) of forage for the Stco-Agsm/Bogr c.t. This com- 

 pares with a productivity sample value for the Stco-Agsm/Bogr c.t. of 298 lb./ 

 acre (334 kg/hectare). 



Redmann (1975) reviews and contributes some herbage production data for 

 some plant communities which can be compared to the productivity data pre- 

 sented here. 



Grasshoppers 



Grasshopper infestation frequently accompanies drought (Weaver & Albert- 

 son 1956). 



Grasshoppers reached epidemic proportions in some locales in 1977. Un- 

 fortunately, one of these locales was the bottomland along Nelson Creek in the 

 vicinity of most of the exclosures. No study of grasshopper density was made, 

 but biologists working and living in the productivity sampling area estimated 

 grasshopper densities in the lowlands to be 4-10 or more per square meter. 

 Although this was much less than the densities of 50-100 grasshoppers per 

 square foot of Allred (1941), it did significantly lower productivity measure- 

 ments. In hot dry weather when productivity is low, the effect of grass- 

 hoppers can be especially significant. 



Parker (1952) found that seven grasshoppers per square yard consume ten 

 percent of^the forage for one cow. Grasshoppers at densities of .9/square 

 foot (10/m ) to 1. 9/square foot (20/m ) can account for thirty to forty per- 

 cent of the peak standing crop during the three weeks of life in the adult 

 instar (Mitchell and Pfadt 1974). Anderson (1961, 1964), however, found lit- 

 tle correlation between grasshopper density and vegetation loss. Mulkein 

 (1967) discusses several problems with comparing the results of various 

 experiments. 



Grasshopper feeding can be especially detrimental to grasses because 

 grasshoppers eat the plants lower than livestock (Parker & Connin 1964). 

 Countering this trend is the fact that most grasshopper defoliation can oc- 

 cur after the active growth period for cool season grasses (Burleson 1976). 



Grasshopper damage was most severe in the exclosures with an abundance 

 of warm-season short grasses such as Bouteloua gracilis . In the Bogr/Agsm 

 c.t. exclosure B^. gracil is was cropped to the point where it was generally 

 too short to clip. The Stco/Bogr-Caf i c.t. was also hard hit. The Agsm/Bogr 

 and Bogr-Cafi/stco c.t.'s were damaged somewhat less. The Arca/Agsm/Bogr 

 c.t. was not badly infested. The Uist c.t. exclosure had a moderate grass- 

 hopper density, but it was not obvious that much damage was done. The Dist- 

 Agsm ecotone exclosure experienced somewhat more damage, usually to species 

 other than D. stricta . Other types sampled for productivity did not have 

 epidemic populations. 



The combined effects of drought and grasshoppers were striking. One 

 pasture containing several exclosures was not grazed by livestock until 



67 



