Management and environmental factors associated with simulated restoration seeding barriers in sagebrush steppe

Authors: Copeland, Stella; BRADFORD, JOHN - Us Geological Survey (USGS); Hardegree, Stuart; SCHLAEPFER, DANIEL - Us Geological Survey (USGS); BADIK, KEVIN - The Nature Conservancy

Submitted to: Restoration Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/2/2022
Publication Date: 5/13/2022
Citation: Copeland, S.M., Bradford, J.B., Hardegree, S.P., Schlaepfer, D.R., Badik, K.J. 2022. Management and environmental factors associated with simulated restoration seeding barriers in sagebrush steppe. Restoration Ecology. Article e13722. https://doi.org/10.1111/rec.13722.
DOI: https://doi.org/10.1111/rec.13722

Interpretive Summary: Adverse weather conditions, like freezing or drought, can lead to high seedling mortality following restoration seeding. In drylands like the Great Basin sagebrush steppe, variability in weather conditions across years is common and likely related to low restoration success in many post-fire seedings, particularly in lower elevation or warmer areas. Management decisions such as planting date or seed source could improve restoration outcomes by reducing seedling exposure to weather barriers. We used lab-based information on germination response to temperature and moisture conditions and modeled soil moisture and temperature to simulate germination and subsequent exposure to weather conditions associated with mortality with three perennial native bunchgrasses commonly seeded for restoration: bottlebrush squirreltail (Elymus elymoides), Sandberg bluegrass (Poa secunda), and bluebunch wheatgrass (Pseudoroegneria spicata). We evaluated differences in outcomes associated with three planting dates (Oct. 15, Nov. 15, and Mar. 15) and three seed sources or cultivars per species as well as the effects of site environmental variables (elevation, mean annual precipitation, heat load, and clay content). Seedling exposure to barriers was strongly linked to management decisions in addition to site mean precipitation and elevation. 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 improve restoration outcomes and decrease their variability by reducing exposure to adverse weather conditions in this region, even in the presence of influential site environmental variables.

Technical Abstract: 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 (U.S.A.). 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 (15 October, 15 November, and 15 March) and three seed sources or cultivars per species for 5,000 sites in each of 40'years (water years 1980–2019). We tested 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). Seedling exposure to barriers was strongly linked to management decisions in addition to site mean precipitation and elevation. 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.