COS 201-5 - Management and environmental factors associated with simulated restoration seeding barriers in sagebrush steppe

Background/Question/Methods

Adverse weather conditions, particularly freezing or drought, are often associated with poor seedling establishment following restoration seeding in drylands like the Great Basin sagebrush steppe (USA). Management decisions such as planting date or seed source could improve restoration outcomes by reducing seedling exposure to weather barriers. We simulated the effects of management and environmental factors on seedling exposure to post-germination barriers for bottlebrush squirreltail (Elymus elymoides), Sandberg bluegrass (Poa secunda), and bluebunch wheatgrass (Pseudoroegneria spicata). We combined germination timing models with daily soil moisture and temperature estimates to calculate yearly germination favorability and post-germination freezing and drought barriers for three planting dates (Oct. 15, Nov. 15, and Mar. 15) and three seed sources or cultivars per species for 5000 sites in each of 40 yrs (water years 1980-2019). We used Bayesian models to test the effects of site environmental variables (elevation, mean annual precipitation, heat load, and clay content) and management choices (seed source and planting date) on germination favorability and barrier occurrence (mean) and variability (coefficient of variation).

Results/Conclusions

Both management decisions and major environmental variables such as precipitation and elevation were strongly linked to mean seedling exposure to barriers, and overall germination favorability, as well as variation in these simulated outcomes. Standardized coefficients suggested that the relative influence of management decision factors, planting date and choice of seed source, were comparable to the most influential environmental variables, precipitation and elevation. In particular, later fall plantings and seed sources with slower germination (lower mean germination favorability) were less likely to encounter freezing and drought barriers. These results suggest that management actions can play a role comparable to site environmental variables in reducing exposure of vulnerable seedlings to adverse weather conditions and subsequent effects on restoration outcomes.