Abstract

Seedling survival of fall-sown seeds over the winter and subsequent emergence in spring is a major demographic bottleneck limiting recruitment in dryland restoration. Deeper sowing can place seeds in a more favorable soil environment with more stable moisture and moderated temperatures, but emergence from these depths is often constrained by the greater distance seedlings must grow to reach the surface and by mechanical resistance in the upper soil layer. In the first chapter of this thesis, we evaluated the use of a slow-release gibberellic acid (GA₃) polymer seed coating to aid in seedling emergence from deeper sowing depths. We compared the emergence of untreated and GA₃-coated seed of Penstemon palmeri and P. pachyphyllus seeded at shallow and deep sowing depths in field trials near Santaquin, Utah, USA, in 2023 and 2024. Overall, emergence was lowest in shallow uncoated treatments and highest when deeper sowing was combined with GA₃ coating. The combined treatment increased emergence by as much as 111-fold relative to shallow uncoated seed and reduced the cost per 100 established plants by more than 90% in some cases. These results indicate that slow-release GA₃ seed coatings can expand the practical sowing depth range for small-seeded forbs and improve restoration efficiency in dryland systems. The second chapter of this thesis addresses the same seedling emergence barrier using a different approach by modifying seedbed conditions to reduce the physical resistance seedlings encounter during emergence. Here we evaluated whether placing a composite of compost, biochar, and bark mulch directly within the seed row could improve seedling emergence, particularly when paired with deeper sowing. In the greenhouse, two perennial grasses were sown across multiple depths with and without mulch. Without mulch, emergence declined sharply with depth; with mulch, emergence was maintained or even improved. In the field, nine grasses and forbs were sown at shallow (15 mm) and deep (45 mm) depths, with and without an in-furrow mulch treatment, in a sagebrush-steppe site near Santaquin, Utah, USA. Across species, emergence was generally lowest when seeds were sown at a shallow depth without mulch and often highest when seeds were sown at a deep depth with mulch. Relative to the shallow, no-mulch treatment, the combination of deep sowing and mulch increased plant density several-fold in strongly responsive species. At the same time, more moderate gains (2- to 3-fold) were observed in other species (typically large-seeded grasses), with much of that response attributable to deeper sowing alone. These results indicate that restoration success can be improved by combining deeper sowing with technologies that reduce biological and physical barriers to emergence. Together, the findings of this thesis show that seed coatings and microsite amendments can help overcome the seedling emergence bottleneck and provide practical tools for improving native plant restoration in sagebrush-steppe ecosystems.

Degree

MS

College and Department

Life Sciences; Plant and Wildlife Sciences

Rights

https://lib.byu.edu/about/copyright/

Date Submitted

2026-04-16

Document Type

Thesis

Keywords

dryland restoration, sagebrush-steppe, seedling emergence, sowing depth, seed enhancement, gibberellic acid (GA₃), in-furrow mulch, microsite amendments

Language

english

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