Sixty-One Years of Secondary Succession on Rangelands of the Wyoming High Plains

The slow and uncertain rate of recovery of plant communities after severe disturbance is a major problem on rangelands. Earlier studies sketched the outline of secondary succession on mixed-grass prairie, but were 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 single area. To provide a more complete picture of succession over decades, we began observations in 1977 on 4 areas disturbed from 1 to 51 years previously, and on undisturbed areas of the same 2 soil types with 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-lived grasses. Western wheatgrass [Pascopyrum smithii (Rydb.) A Love] was an exception because it appeared much earlier and in much greater abundance than other long-lived perennial grasses. Blue grama [Bouteloua gracilis (H.B.K.) Lag ex. Steud.) may be another exception; total recovery of this grass may require centuries. Time of appearance in succession seemed to be related to availability of propagules and ease of establishment; persistence of species was related to competitive ability. Abundance of many species fluctuated widely from year to year, but fluctuations did not appear to be related to precipitation. After 61 years, secondary succession had not returned plant communities to the climax state.