Effects of grazing after wildfire on soil health in eastern Montana

Abstract

Rangelands are resilient to grazing and fire. However, the resilience of rangelands may be degraded by livestock grazing too soon after wildfire. Due to the growing interest in soil health and its link to sustainable grazing, following a large wildfire (109,346 ha, Lodgepole complex in 2017) we tested the effect of grazing (grazed verses no grazing) on three indicators of soil health in ponderosa pine savvanas of the northern Great Plains. We measured indicators of soil hydrologic function (i.e., soil hydraulic conductivity), properties related to nutrient cycling (i.e., soil organic matter, plant available nutrients, pH), and soil structure (i.e., aggregate stability) in 2019 and 2020. Grazing occurred two out of three years following the fire. Most indicators of soil health were not appreciably affected by grazing post-fire. However, we detected a marginally significant negative effect of grazing on soil organic matter. Specifically, soil organic matter was 7% greater in ungrazed than grazed areas. No other grazing treatment effects were detected. Several soil health metrics varied between sampling years. Our results suggest that grazing(two out of the three years) following fire is unlikely to negatively affect many indicators of soil health of ponderosa pine savannas in the northern Great Plains. The increased organic matter observed by resting did not have an appreciable impact on the other soil health metrics. These findings suggest that soil health indicators are relatively resilient to grazing after wildfire and have implications for grazing policy post-fire.