Strengths and potential pitfalls of hay-transfer for ecological restoration revealed by RAD-seq analysis in floodplain Arabis species

Achieving high intraspecific genetic diversity is a critical goal in ecological restoration as it increases the adaptive potential and long-term resilience of populations. Thus, we investigated genetic diversity within and between pristine sites in a fossil flood-plain and compared it to sites restored by hay-transfer between 1997 and 2014. RAD-seq genotyping revealed that the stenoecious flood-plain species Arabis nemorensis is co-occurring in pristine and restored sites with its relative Arabis sagittata, which has a documented preference for dry calcareous grasslands but has not been reported in floodplain meadows. We show that hay-transfer maintains genetic diversity for both species. In addition, in A. sagittata, transfer from multiple genetically isolated pristine sites resulted in restored sites with increased diversity and admixed local genotypes. In A. nemorensis, transfer also maintained diversity, but did not create novel admixture dynamics because genetic diversity between pristine sites was less differentiated. Thus, the effects of hay-transfer on genetic diversity also depend on the genetic makeup of each species in the donor communities, especially when material is mixed. Our results demonstrate the efficiency of hay-transfer for habitat restoration and emphasize the importance of pre-restoration characterization of micro-geographic patterns of intraspecific diversity of the community to guarantee that restoration practices reach their goal, i.e. maximize the adaptive potential of the entire restored plant community. Overseeing these patterns may differentially alter the adaptive potential of species present, thereby altering the balance between species in the community. Additionally, our comparison of summary statistics obtained from de novo and reference-based RAD-seq pipelines show that the genomic impact of restoration can be reliably monitored on species lacking prior genomic knowledge.