Efforts to restore semi-arid wildlands in the western United States predominantly use seeds and frequently occur in the fall. Fall conditions are often more amenable to seeding, and successfully over-wintered seeds/seedlings are poised to take full advantage of spring moisture. However, winter mortality of fall-germinated seeds has been shown to be a common barrier to seeding success in some regions. Postponing seeding until spring avoids this barrier but presents other risks and drawbacks. One solution proposed to avoid winter mortality, without sacrificing the benefits of fall seeding, is to delay the onset of germination of fall-sown seeds. At six field sites over three consecutive years (18 combinations) in the northern Great Basin of the United States, we compared germination timing and first-year success of seeds treated to delay germination (“treated”) to untreated seeds in drill-seeding experiments. We asked: 1) does the treatment result in delayed germination, and, if so, 2) does a delay reduce winter mortality? Treated seed produced less winter germination than untreated in all 18 site by year combinations. Treated seeds also resulted in higher seedling density in 8 combinations, including 7 of the 8 combinations in which the majority (>50%) of untreated seeds germinated in the winter. We conclude that our treatments consistently delayed germination in the field, but improved seeding success only when winter mortality was a barrier. These findings support continued experimentation with germination-delaying treatments and highlight the need for models that define and predict winter mortality risk.
Audio/Video, Conference Presentation, SER2019
Society for Ecological Restoration