Pollinators may not limit native seed set at Puget lowland prairie restoration nurseries

Land managers often rely on large-scale production of native seeds in nurseries for replanting into natural environments as part of restoration strategies. Nursery managers question if unmanaged insects can be sufficient to pollinate large increases in native forbs planted into young nurseries in non-native landscapes. This study investigated pollination of deltoid balsamroot (Balsamorhiza deltoidea Nutt.) and sicklekeel lupine (Lupinus albicaulis Douglas) at a native seed nursery compared to dense patches of native plants at a natural Puget lowland prairie to determine if insect visitation affected viable seed production for those two species. In 2011 and 2012, insect visitation rates were recorded for each plant species at more than 62 plots within two study areas. In 2012, seeds were collected from hand-pollinated and naturally-pollinated inflorescences and tested for viability. Overall visitation rates were significantly higher at the nursery than the prairie for both plant species. However, pollen limitation was not evident for either plant species at either site. Natural pollination by insects and supplemental hand-cross-pollination treatments did not yield different quantities of viable seed. Factors other than pollinator visitation, such as soil nutrients and seed handling practices, may be influencing seed viability, but increasing insect visitation will not likely significantly increase seed viability for these two species at this restoration nursery. Planting dense rows of native plant species may be enough to attract a sufficient amount of unmanaged insects to provide adequate pollination for seed production for some species at even young nurseries.