A Low Organic Matter Soil Does Not Maintain a Native Grassland Restoration in the Colorado Front Range

摘要

Given that many introduced plant species in rangelands appear to benefit by high plant available nitrogen, low nutrient soils are generally thought to support the restoration of native prairie species in North America (Paske et al. 2000, Sardans et al. 2017). This trend was investigated in 2004 for a restoration performed on a gravel pit adjacent to Boulder, CO, that once composed a relic, mesic grassland dominated by tallgrass species (Cherwin et al. 2009). In 1998, this site was graded, covered with residual topsoil apparently stored for decades, and planted with nine grasses that included dominants from short- to tall-grass prairies. In 2004 this site was surveyed and the relative vegetation cover was estimated at 92% native grass species. While this seemed a highly desirable outcome, about half (48%) of relative cover was represented by a single species, Sporobolus airoides (alkali sacaton). This species is known for its abundance on more arid, saline soils than usually found in the Front Range of Colorado. This restored grassland existed on a soil that contained about half of the organic carbon and total nitrogen of adjacent, native grasslands (Cherwin et al. 2009). The project was an example of a "hedge your bets" approach to grassland restoration (e.g., Choi 2007, Seastedt et al. 2008), and given the high dominance of native grasses produced in this effort, was viewed as quite successful.