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In many regions of the world, wildfires are becoming more frequent due to the invasion of exotic grasses that are highly flammable and often replace native plants as burned landscapes regrow. To prevent invasive species from dominating post-burn landscapes, land managers are increasingly applying seeds of native plants to suppress invasive plants and encourage ecosystem recovery. However, there is still much to learn about the ability of seeded species to establish and suppress flammable invaders. It is also unclear how previous human-caused landscape changes, such as nitrogen pollution or the removal of shrubs (a common practice in western USA rangelands), affect the success of native seed additions and plant recovery from fire. This study addresses these issues by building on a long-term experiment investigating the legacy effects of past nitrogen pollution and shrub removal in a highly invaded sagebrush steppe ecosystem at Idaho State University’s Barton Ecological Research Area in Pocatello, ID. This experiment burned in a wildfire in August, 2020, providing a unique opportunity to evaluate how a history of nitrogen pollution and shrub removal influences plant recovery from wildfire. We developed three native seed mixes intended to suppress invasive plants, particularly flammable annual grasses, and in April, 2021, we sowed the experimental mixes into research plots within the original experiment.

To measure the initial effects of the experimental seed additions and the legacy effects of previous nitrogen pollution and shrub removal, we collected the data provided here during the summer of 2021, the first growing season following the wildfire. We established 240 monitoring quadrats (1 m²) within the original experiment, dividing the quadrats between areas where shrubs had formerly been (evidenced by stumps) and intershrub areas. At a microhabitat scale, the presence of shrubs alters soil properties and can create legacy effects after shrub death, and we were interested in understanding this following wildfire. In addition, another 112 quadrats were established in auxiliary experiments to evaluate the effects of fire, seeding rate, and the timing of seeding on the plant assemblage. In early July, plant species cover, vegetation height, and aboveground biomass were measured in the quadrats. In late July, we measured soil chemistry in most quadrats. These data will aid land managers in understanding plant assemblages and soil properties following wildfire, and how ecological legacies shape these conditions.