View article

Many endangered plant species remain absent in rewetted, previously drained fens. We performed a 3-year introduction experiment with endangered fen species (10 Carex-and 6 bryophyte species) in 4 hydrologically restored fens to investigate which factors hamper establishment and survival. Carices were introduced both as adults and seedlings, mosses as gametophyte mats. Introductions were done on (initially) bare soil to exclude excessive competition for light during the first year: this allowed us to discriminate between the species’ fundamental and realized niches. Overall first year survival of the introduced plants was high in all fens (mean survival= 96%), indicating that abiotic conditions were within the species’ fundamental niches. However, survival analysis revealed that a decrease in relative light intensity (RLI) at the soil surface during consecutive years (indicating an increase in biotic competition for light) explained high mortality rates in most species. As a result, overall final survival was lowest in the two most productive (low light) fens (mean survival= 38%), while most transplants had persisted in the two less productive (high light) fens (mean survival= 79%). In accordance, taller and faster-growing species had a higher overall survivability as they were able to outgrow light limitation, suggesting asymmetric competition, and they thus occupied a broader realized niche than smaller and slower-growing species. Light limitation also drove the loss of 5 out of 6 bryophyte species. Overall, adult Carex plants performed better than seedlings and bryophytes. We conclude that both dispersal limitation and asymmetric competition for light …