Homogenizing biodiversity in restoration: the “perennialization” of California prairies

Restoration frequently aims to improve native species biodiversity at a site, but practitioners have limited resources. In diverse ecosystems, the selective use of certain guilds or species can come at the cost of species that are more challenging to incorporate, resulting in the overall homogenization of the ecosystem and a relative loss of biodiversity. We surveyed practitioners who restore California prairies to understand their use of native annual forbs, an important component of the biodiversity in this ecosystem. We found that practitioners preferentially planted native perennial species, mainly grasses. Despite practitioners' recognition of the high conservation value of native annual forbs, they were hesitant to include this guild in their planting palettes because of high costs, low and unpredictable establishment, and lack of seed. We recommend that California annual prairie forbs be seeded in multiple years to enhance establishment, and that monitoring targets be designed to better reflect the high variability in interannual abundance of native annual forbs. These issues are not unique to California prairie, and more broadly, restoration objectives and research across a range of ecosystems should prioritize guilds that are more challenging to establish but are of high conservation concern.