In order to provide a more complete picture of succession over decades, Samuel and Hart began observations in 1977 on four areas disturbed from 1 to 51 years previously, and on undisturbed areas of the same two soils types with and without grazing. 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, was an exception because it appeared much earlier and in much greater abundance than other long-lived perennial grasses. Based on these findings, more than 61 years will be needed for plant communities, on drastically disturbed rangeland, to return to pre-disturbance condition. It has been suggested that blue grama, Bouteloua gracilis, reached its present dominance in a climate differing from that of the present; if this is true, the pre-disturbance community may never completely return. The authors note that this is not necessarily undesirable. Rangeland 10-20 years after disturbance may be superior to undisturbed range for cattle grazing. Disturbed range produced more forage in most years and had a much higher percentage of western wheatgrass, which is the most important grass in cattle diets on the Wyoming High Plains. Biological diversity also appears to be higher on disturbed range, which is not dominated by blue grama, as is undisturbed range, but has a much higher percentage of forbs and other grasses.
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