SOIL‐MOISTURE EFFECTS OF CONVERSION OF SAGEBRUSH COVER TO BUNCHGRASS COVER1

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Abstract
Precipitation, soil moisture, runoff, and vegetation were measured on two, 5‐ to 10‐acre, big sagebrush (Artemisia tridentata) watersheds and two, equally small, beardless bluebunch wheatgrass (Agrophron inerme) watersheds that were converted from big sagebrush in 1967. The watersheds are located near Wolcott, Colorado, at an elevation of 7,200 feet, and are mantled with 2 to 3 feet of silty clay soils. Annual precipitation was about 13.5 inches; about 9 inches occurred as rain or snow from April through October and about 4.5 inches accumulated as a snowpack from November through March. Evapotranspiration was about 2 inches greater in 1968 and 1 inch greater in 1969 from the sagebrush watersheds than from the grass watersheds. With a mature stand of grass in 1970 and 1971 the differences in evapotranspiration were within the range of differences measured during the 3‐year calibration period when all four watersheds were sagebrush. Water use was similar in the top 1 foot of soil but slightly more water was used by the grass in the 1‐ to 2‐foot zone and more water being used by the sagebrush below 2 feet. Soil‐water potential data indicated that only the big sagebrush used a small amount of water from the fractured shale at depths below 40 inches. Sagebrush used more water in August and September than the grass.