Diverse seed mix with green manure and alternating grass/forb rows promotes diversity of Conservation Reserve Program plantings in central and eastern Montana, <scp>United States</scp>

Abstract Introduction The establishment of the Conservation Reserve Program (CRP) plantings in semiarid regions is challenging due to variable weather that can result in extreme temperature fluctuations and prolonged drought conditions. Methods We evaluated four management methods to improve plant diversity and density in eastern and central Montana, United States, using three sites and a staggered start design. We used two measurement methods to quantify the abundance of individual plant species, stem densities, and estimated plant densities based on frequency grids. Results Both measurement methods showed similar patterns. Only the management treatment that included additional sown species resulted in higher plant diversity. When planting year and restoration age interactively influenced diversity metrics, the drier conditions during early spring following planting (2018 planting year) always had lower diversity initially but displayed stronger increases in diversity with time since planting. Grass density generally increased with restoration age, while forb density decreased. Despite the decrease in forb density with increasing restoration age, floral resource abundances did not change significantly. Conclusions Similar patterns observed for both measurement methods suggest that sowing more plant species results in more established plant species. If similar trends continue over time, years with dry conditions during early spring may be more amenable to establishing CRP plantings. Moreover, a frequency grid can reliably be used to estimate plant density in the northern Great Plains.