Soil Water Withdrawal and Root Characteristics of Big Sagebrush

Abstract

The volume of soil important to an individual big sage- brush (Artemisia tridentata) plant as a soil water reservoir was identi- fied and compared with the root system of the same plant. Experimental sites were located near the bottom, midway and crest of a N-facing slope. The effective winter precipitation at these sites was 511, 368 and 102 mm, respectively, because of relocation of snow by wind. Soils at the three sites belonged to different series despite their proximity and similar parent material. The primary water reservoir for an individual plant extended later- ally 91 cm from the trunk and 91 cm deep. Moisture use zones shifted from surface soil near the plant early in the season, outward and down- ward as the season advanced. Water use decreased sharply in early August after vegetative growth was complete. More than 90% of the root weight for individual big sagebrush plants was located in the volume of soil identified as an important water reservoir. Roots at each study site had a maximum lateral spread of 122-152 cm from the trunk and extended 183-213 cm deep at the two lower sites. Roots were less than 152 cm deep at the upper site, a reflec- tion of the limited water supply and rocky substratum. Maximum lateral root spread was usually in the surface 30.5 cm of soil.