Outbreeding, seedling establishment, and maladaptation in natural and reintroduced populations of rare and common Silene douglasii (Caryophyllaceae).

Reintroductions are increasingly used to enhance declining populations, yet comparative data for critical germination and establishment phases are seldom available for both rare and common herbaceous perennials. After introducing a total of >1800 seeds, we compared experimentally manipulated and natural populations of widespread Silene douglasii var. douglasii relative to rare S. douglasii var. oraria, known in only three coastal headlands. Despite equivalent ex situ germination, oraria field plots produced significantly fewer juveniles than douglasii plots indicating that seedling survival limits plant establishment. We also evaluated transplant vs. seed reintroductions as restoration tools, the effect of inbreeding on fitness, and the potential importance of buried seed pools. Germination declined rapidly for seeds over 1-2 years old, and only 2.2% of newly collected seeds of oraria survived as seedlings. Transplant survival over 5 years was greatest for outbred progeny; furthermore, 75% of the new seedlings emerged near outbred progeny from the original reintroduction. Despite similar ovule numbers and pollinator visitation, transplants exhibited 49-179% maladaptation in the formerly grazed site, with significantly lower fruit and seed set than adults in more diverse natural populations. This study experimentally identifies several key factors affecting plant reintroductions, facilitating effective development of large-scale reintroduction strategies for native perennials.