Seed movements and seedling fates in disturbed sagebrush steppe ecosystems: Implications for restoration

Understanding species establishment patterns and community structure following disturbance, and developing effective restoration methods requires knowledge of both the movements and fates of seeds. I used a restoration experiment in a severely disturbed sagebrush steppe ecosystem near Kemmerer, Wyoming to examine the effects of soil surface characteristics and seed morphology on seed entrapment and retention, and the effects of soil surface characteristics on soil water potential and seedling emergence and survival. Seeds of native species with awns, mucilaginous seedcoats, wings, hairy pappi, or no appendages were sown over soil surface treatments consisting of silty loam sail, sand, gravel, surface mulch, shrub mimics, and large and small holes. Seeds that lacked appendages and that had small surface areas did not exhibit significant horizontal movement or redistribution. Seeds with appendages that resulted in exposure of a large surface area to the wind did exhibit significant redistribution, despite apparent adaptations for seed burial or retention. When the entire seed population was considered, the effectiveness of the treatments for trapping and retaining seeds was large holes > small holes greater than or equal to gravel greater than or equal to shrub mimics > soil greater than or equal to sand. Surface mulch neither gained nor lost seeds. The most effective treatments for seedling emergence had among the least negative soil water potentials and included large holes, surface mulch, and sand. Gravel provided an inadequate growing medium, and both shrub mimics and small holes accumulated fine-textured soils resulting in highly negative water potentials and low seedling emergence. Once a seedling emerged, the probability of survival was reasonably high (56.3% over 2 yr) regardless of treatment. This study indicates that soil surfaces that trap and retain high densities of seeds with large surface areas may have little or no effect on seeds with small surface areas, and may or may not result in high seedling emergence and survival. Restoring diverse native ecosystems requires creating soil surface features that can trap and retain seeds with varying morphologies as well as provide favorable conditions for seedling establishment.