GRAZING INTENSITIES, VEGETATION, AND HEIFER GAINS - 55 YEARS ON SHORTGRASS

Shortgrass rangeland, dominated by blue grama (Bouteloua gracilis [H.B .K.] Lag. ex Steud), was grazed at 3 intensities, equivalent to mean s tocking rates of 16.7, 23.0, and 36.5 heifer-days ha(-1), from 1939 th rough 1994, Few changes in plant communities had been documented by th e early 1970's, In 1992-1994, frequency of occurrence, basal and folia r cover, and biomass at peak standing crop (PSC) were determined on th e remaining pasture at each grazing intensity, and on 3 ungrazed exclo sures, Blue grama and buffalograss (Buchloe; dactyloides [Nutt,] Engel m,) increased, and western wheatgrass (Pascopyrum smithii [Rydb,] A. L ove) and needle-and-thread (Stipa comata Trin, & Rupr.) decreased, as grazing intensity increased. Redthree-awn (Aristida longisieta Steud.) was most plentiful under light grazing. Basal cover and biomass of fo rbs were lower under grazing than in exclosures, but differences in bi omass were not significant. Shrubs and half-shrubs decreased as grazin g intensity increased. Frequency and cover of plains pricklypear (Opun tia polyacantha Haw,) were higher in the exclosures and under light gr azing than under moderate or heavy grazing; biomass was 4 to 6 times a s high in the exclosures as under any grazing intensity. Heifer gains declined linearly with increasing grazing pressure index. Optimum (mos t profitable) stocking rate was about 20% higher than that under the m oderate grazing intensity, under which biomass production was maintain ed and shrub and pricklypear remained at low levels. Returns to land, labor, and management were only slightly higher under the optimum stoc king rate than under the moderate grazing intensity. The moderate graz ing intensity appears to be both profitable and sustainable.