Outcomes associated with translocation techniques vary between two closely related and critically imperiled plant species

Abstract

Land use and climate change put many rare plant species at risk of extinction. Translocation of rare species within restoration projects may be essential for their future survival, but successful recruitment from translocated individuals can be difficult to achieve. Physaria obcordata and Physaria congesta are endemic to a narrow band of shale outcrops subject to intense energy development in the Piceance Basin (Colorado, U.S.A.). We examined approaches for establishing new populations of these critically imperiled species in suitable but unoccupied habitats within their endemic range by monitoring fall‐sown seeds and fall‐ or spring‐transplanted seedlings for 6 years. Because these species are obligately outcrossing and populations exhibit genetic clustering, we monitored three translocation sites near (<600 m, one cluster) and three far (>600 m, mixed clusters) from the existing conspecific populations. Seeding and spring transplanting were successful for P. congesta but fall transplants did not survive. P. congesta were more than twice as likely to survive in sites near existing populations. Seeding largely failed for P. obcordata but transplanting in either season performed equally well, especially in sites far from the existing populations. Transplants first flowered after 1 year and recruitment occurred after 3 years in both species. Recruitment continued in both species through 2021. Although these species share many life history traits and habitat requirements, we found they differ in important ways relevant to translocation and long‐term population viability. Our work highlights the importance of understanding the unique population ecology of even closely related rare species to improve the likelihood of successful conservation.