Effects of Postwildfire Mechanical Seeding on Soil Properties in Wyoming Big Sagebrush Communities

Abstract

Reduction of vegetation following wildfire in rangelands of the western United States can result in invasion of exotic annual grasses and elevated soil loss to wind erosion. In response to these threats, various mechanical seeding methods (such as drill seeding and mechanical mixing of broadcast seeds) are commonly employed by restoration practitioners. Despite their common use, little information exists about how additional disturbance from mechanical seeding (following wildfire disturbance) may further contribute to soil loss from wind erosion. Here, we compared the effects of mechanical seeding techniques on soil properties following two wildfires occurring in similar climates with contrasting soil textures (silty loam and gravelly loam soils). Using either a rangeland or minimum-till drill to create furrows or mix broadcasted seeds into soils, we quantified wind erosion risk for unburned sites, burned nonseeded sites, and seeded sites according to soil aggregate stability, horizontal sediment flux, surface microtopography, and soil compaction. Effects of mechanical seeding were small relative to those created by wildfire. For burned areas, differences in site stability were greatest between sites. Following wildfire, the largest decrease in site stability occurred in fine-textured soils, where horizontal sediment transport was increased by nearly five orders of magnitude relative to unburned areas. Despite these initial differences, site stability in fine-textured soils may have improved to a greater degree than stability at the coarse-textured site. Furthermore, we found minimal differences between drill types on site stability but, instead, observed that the largest differences in soil properties were created by furrow versus broadcast seeding. The different outcomes of rehabilitation on site stability found here, paired with the spatial extent to which wildfire affects landscapes, highlights the importance of postfire monitoring of site stability in more locations that vary by soil, plant, landscape, and climatic variables.