Temporal and Spatial Factors Influence Native Forb Emergence More Than Sowing Depth

Abstract

Seed-based restoration of native forb species, in the Intermountain region of the western United States, is challenged by a limited understanding of conditions that contribute to establishment success. This study evaluated the differential effects of row cover and a range of sowing depths, which influence soil microclimate, on 20 common native perennial forb species across three sites and 2 yr with and without row cover.Seedlings were counted the spring and fall following the planting year. We hypothesized that larger-seeded species would be more tolerant of deeper seeding depths while small-seeded species would establish better at the shallowest depth increment and that emergence would be better under the row cover. Overall, emergence was low with rates between 0.2% and 1.0% for 16 of the 20 species. Three species emerged between 1% and 2.4% while barestem biscuitroot (Lomatium nudicaule [Pursh] J.M. Coult. & Rose) averaged 6.9%. Environmental factors related to site and seeding year had greater effects on emergence than row cover or seeding depth. Row cover led to generally higher emergence. Deeper seeding depths within the range for rangeland seeding equipment tended to have detrimental effects on emergence, though the effects of seeding depth varied by site, year, and species. Emergence for large-seeded species (2.3%) was significantly greater than small-seeded species (0.5%), but neither were different than medium-seeded species (0.62%).This outcome highlights the challenges restoration practitioners face in the intermountain region. While using the best techniques and most appropriate plant materials improve the chances of successful restoration, largely uncontrollable and often unpredictable factors represented by site and weather variability will continue to be driving factors in semiarid regions.