Immediate effects of burning sagebrush vegetation on soil nutrient dynamics and fertile islands in a cold desert ecosystem

Abstract

Wildfire is a major disturbance in western U.S rangelands that causes changes to soil nutrients. In cold desert shrublands, microsites form under shrubs where soil biochemical cycles are more active. We aimed to determine the immediate effects of prescribed burning on soil nutrients under big sagebrush (Artemisia tridentata) canopies and the interspaces between shrubs. We hypothesized that burning A. tridentata vegetation would lead to an immediate increase in total C (TC) and N (TN), bicarbonate phosphorus (HCO₃^–-P), nitrate (NO₃^–), and ammonium (NH₄⁺) under shrub canopies. The study was conducted in October and November 2018. The treatments included Control-Interspace (CT-ISP), Control-Undershrub (CT-USB), Burned-Interspace (BRN-ISP) and Burned-Undershrub (BRN-USB). Soil samples were collected at 0-5 cm depth before, nine and twenty-three days after burning. In burned treatments, NH₄⁺ was significantly higher under the canopies than the interspaces between shrubs nine and twenty-three days after burning. In the unburned treatments, there was no difference in soil pH, NH₄⁺, NO₃^–, TC, and TN between and within the shrub canopies. NO₃^– showed no significant changes after burning. HCO₃^–-P was greater under canopies in the unburned treatments and increased mainly in the canopies nine and twenty-three days after burning. In the burned treatments, TN and TC were greater in the canopies than interspaces nine and twenty-three days after burning. Soil pH increased in the canopies and interspaces nine and twenty-three days after burning. Soil nutrients were greater under shrub canopies compared to the interspaces, therefore highlighting the impact of fire in sustaining island of fertility in sagebrush ecosystem.