Site conditions and recipient plant communities as indicators of the origin of a cryptogenic species. Leucojum vernum L. in North France as a case study
Résumé
Regional lists of protected species commonly include rare plant species that are found in small, isolated populations at the range margin or disjunct. However, such populations often have suspicious origins and may have been historically introduced and now falsely viewed as native. Here I use a simple community ecology approach to assess whether plant community composition and site features can indicate whether local populations of a rare cryptogenic species are more likely of natural or introduced origin. I took the vernal geophyte Leucojum vernum L. in North France as a case study. Using multivariate analyses I show that L. vernum occurs in various plant communities, which correspond to different sets of environmental conditions. More specifically, several community types clearly reflect an introduced origin, with a discrepancy between L. vernum's autecology and site features as well as a number of co-occurring anthropophilous species, including xenophytes. These populations are often associated with more or less ancient human artefacts, such as archaeological sites. In contrast, an equal number of community types likely correspond to natural populations, that are all located at the range margin and connected to the core range via a (former) west-flowing river corridor, pleading for a post-glacial re colonization. I conclude that a cryptogenic species, such as L. vernum in this case study, has a ``socio-ecological signature'' which can indicate whether a given population is more likely native or introduced, and thus informs conservationists on where to prioritize conservation efforts.