Changes in runoff and sediment yield caused by changing sagebrush cover to grass
cover were studied at four small watersheds in western Colorado during a 9-year
period, from 1965 to 1978. Measurements of runoff and sediment yield from the four
watersheds were made for 8 years, at which time two watersheds were plowed and
seeded to beardless bluebunch wheatgrass. The same measurements were then continued for an additional 6 years.
Measurements indicated that conversion to grass caused a reduction in runoff from
summer rainstorms of about 75 percent. Runoff from spring snowmelt increased about
12 percent, and annual runoff from treated watersheds decreased about 20 percent
when compared to control watersheds. Sediment yield from the seeded watersheds was
reduced by about 80 percent; most of this reduction is related to the decrease in runoff
from summer rainstorms.
The size of barren interspaces between plants was reduced on the converted water-
sheds to about 30 percent of those on the untreated watersheds. Linear regression
analysis indicates that a reduction of 38 percent in the amount of bare soil resulting
from planting grass would result in a decrease of 73 percent in sediment concentration.
