The effects of invading young sagebrush (Artemisia rothrockii) on the water status of an herbaceous meadow in the Eastern Sierra Nevada

Anthony Darrouzet-Nardi
University of California, Berkeley

Rothrock sagebrush (Artemisia rothrockii) invades montane meadows on the Kern Plateau in the Eastern Sierra Nevada. Sagebrush is typically associated with drier terraces or drier soil patches within more mesic terraces. It is not clear whether it contributes to soil drying after it invades. We hypothesized that young sagebrush shrubs contribute to soil drying by their transpiration, thus accelerating the conversion of herb-dominated sites to sagebrush patches. To test this, we manually removed young sagebrush shrubs from 3.5 x 3.5 m plots in an area with 4-8 year old sagebrush plants. Time domain reflectometry measurements of soil moisture in the removal and control plots showed no difference between treatments at any soil depth down to 60 cm over the entire growing season. We also measured transpiration rates of sagebrush and meadow herbs. These corroborated the soil moisture data by showing that young sagebrush shrubs are not transpiring enough water to dry out meadow soils. Meadow soil moisture levels are highly variable seasonally and across sites in this study. We conclude that the effect that young sagebrush have on soil moisture is small compared to this variability. Large-scale hydrological changes such as a falling water table and smaller-scale fluctuations in underground water sources are likely more significant factors than sagebrush transpiration in determining water availability.