Recruitment predictors of endangered prairie species: A case study of Erigeron decumbens

Background/Question/Methods

Preservation of rare plant species often requires establishment of new populations. Survivorship surveys are the most common method of post-introduction monitoring. However, they provide an incomplete picture of introduction success. This study is an attempt to develop a model for determining introduction success by studying the factors affecting recruitment in introduced populations.  Erigeron decumbens is an endangered forb endemic to the Willamette Valley of western Oregon. Several populations of E. decumbens have been introduced by governmental and private agencies. While there has been some monitoring on the survival of reintroduced plants, no systematic surveys have measured recruitment in the new populations. We monitored recruitment in seven introduced populations, and compared abiotic and biotic characteristics in these and five stable natural populations.

Results/Conclusions

70% of introduced populations produced less than 1 recruit for every 3 survivors. 30% produced at least 1.5 recruits for every 1 survivor. Seed viability had the strongest relationship with recruitment levels demonstrating that seed viability could be a strong limitation for this species (r² = 0.9412). Survivor crown size showed a weak correlation with recruitment levels (r² = 0.2098), suggesting that maternal effects do not affect seed viability. Similarly, previous research has suggested that inbreeding depression limits seed viability in natural populations None of the abiotic factors we studied were significantly correlated with recruitment. This study will provide important guidelines for future reintroductions of Erigeron decumbens, including using multiple source populations to ensure high seed viability.  Our research also demonstrates the utility of recruitment surveys to determine factors important in the success of introduced populations of rare plant species.