Effects of Seeding Rate and Sowing Season on the Establishment Success of Wyoming Big Sagebrush (Artemisia tridentata subsp. wyomingensis)

Sagebrush seedings in Wyoming big sagebrush ( Artemisia tridentata Nutt.) ecosystems often experience high failure rates. We tested the hypotheses that 1) sowing season impacts spring seedling emergence, 2) increasing seeding rate will result in higher seedling emergence, 3) pressing seed into the soil surface improves seeding outcomes, and 4) year is an important factor in sagebrush seedling emergence. Over four study years, we used a randomized complete block split-plot design to compare eleven seeding rates sown on seven dates throughout fall and winter at two locations in central Utah. We also seeded paired plots during the fall sowing seasons with a roller-packer wheel treatment to improve seed-soil contact. Each spring, seedling density was recorded. Data was analyzed using generalized linear mixed models (GLMMs) and Pearson correlation. Year strongly impacted seedling density ( P < 0.0001), with emergence limited or nonexistent in two study years. In years where emergence occurred, seeding rate was related to seedling density with a positive linear relationship ( r = 0.32; P < 0.0001) indicating a similar percentage of seed emerged regardless of seeding rate. Mid-fall and fall sowings resulted in 7 to 8-fold higher seedling density than a traditional mid-winter sowing. The application of a roller-packer treatment did not affect seedling emergence when compared across multiple years ( P = 0.5493) or multiple sowing seasons within a single year ( P = 0.9920). Finally, a correlation analysis indicated a negative relationship between snow depth at the time of sowing and seedling density the following spring ( r = −0.18; P < 0.0001). Overall, these findings show that sagebrush seeding efforts can be improved by altering the sowing season from winter to fall and increasing seeding rates, but annual environmental conditions serve as a primary bottleneck in sagebrush establishment.