61 YEARS OF SECONDARY SUCCESSION ON RANGELANDS OF THE WYOMING HIGH-PLAINS

The slow and uncertain rate of recovery of plant communities after sev ere disturbance is a major problem on rangelands. Earlier studies sket ched the outline of secondary succession on mixed-grass prairie, but w ere based on 1 or 2 years of observation on different areas disturbed at different times in the past, or several years of observation of a s ingle area. To provide a more complete picture of succession over deca des, we began observations in 1977 on 4 areas disturbed from 1 to 51 y ears previously, and on undisturbed areas of the same 2 soil types wit h and without grazing. Observations continued for 11 years. Secondary succession proceeded through the usual stages: annual forbs, perennial forbs and annual grasses, short-lived perennial grasses, and long-liv ed grasses. Western wheatgrass [Pascopyrum smithii (Rydb.) A Love] was an exception because it appeared much earlier and in much greater abu ndance than other long-lived perennial grasses. Blue grama [Bouteloua gracilis (H.B.K.) Lag ex. Steud.] may be another exception; total reco very of this grass may require centuries. Time of appearance in succes sion seemed to be related to availability of propagules and ease of es tablishment; persistence of species was related to competitive ability . Abundance of many species fluctuated widely from year to year, but f luctuations did not appear to be related to precipitation. After 61 ye ars, secondary succession had not returned plant communities to the cl imax state.