To withstand the surge of species loss worldwide, (re)introduction of endangered plant species has become an increasingly common technique in conservation biology. Successful (re)introduction plans, however, require identifying sites that provide the optimal ecological conditions for the target species to thrive. In this study, we propose a two‐step approach to identify appropriate (re)introduction sites. The first step involves modeling the niche and distribution of the species with bioclimatic and topographical predictors, both at continental and at national scales. The second step consists of refining these bioclimatic predictions by analyzing stationary ecological parameters, such as soil conditions, and relating them to population‐level fitness values. We demonstrate this methodology using Swiss populations of the lady's slipper orchid (Cypripedium calceolus L., Orchidaceae), for which conservation plans have existed for years but have generally been unfruitful. Our workflow identified sites for future (re)introductions based on the species requirements for mid‐to‐sunny light conditions and specific soil physico‐chemical properties, such as basic to neutral pH and low soil organic matter content. Our findings show that by combining wide‐scale bioclimatic modeling with fine scale field measurements it is possible to carefully identify the ecological requirements of a target species for successful (re)introductions.

Background and Aims To counteract the ongoing worldwide biodiversity loss, conservation actions are required to re-establish populations of threatened species. Two key factors predominantly involved in finding the most suitable habitats for endangered plant species are the surrounding plant community composition and the physicochemical parameters of the soil rooting zone. However, such factors are likely to be context- and species-dependent, so it remains unclear to what extent they influence the performance of target species. Methods We studied large and small Swiss populations of the endangered orchid Cypripedium calceolus. We measured functional traits related to C. calceolus plant and population performance (clonal patch area, plant height, number, of leaf, stems, flowers and fruits), realized vegetation surveys, soil profile analyses, and tested for relationships between plant traits and the surrounding vegetation structure or soil physicochemical parameters. Results Large populations contained bigger patches with more stems and leaves, and produced more flower per individual than small populations. Neither vegetation alliances nor soil classes per se could predict C. calceolus functional traits and population size. However, functional traits explaining population performance and size were related to specific soil parameters (soil organic matter content, pH and phosphorus), in addition to a combination of presence-absence of plant indicator species, relating to ecotones between forests and clearings. Conclusion We show that even for species that can grow across a wide range of vegetation groups both indicator species and specific soil parameters can be used to assess the most favourable sites to implement (re)-introduction actions.

Background and Aims – To counteract the ongoing worldwide biodiversity loss, conservation actions are required to re-establish and regenerate populations of threatened species. Two key factors predominantly involved in finding the most suitable habitats for endangered plant species are the surrounding plant community composition and the physicochemical parameters of the soil rooting zone. However, such factors are likely to be context- and species-dependent, so it remains unclear to what extent they influence the performance of the target species. Methods – Here, we studied 34 Swiss populations of the highly endangered orchid Cypripedium calceolus. We measured functional traits related to plant and population performance, realized vegetation surveys, and soil profiles analyses, and tested for relationships between plant traits and the surrounding vegetation structure or soil physicochemical parameters. Results – We found that neither vegetation alliances nor soil classes per se could predict C. calceolus functional traits and population size. However, we found that C. calceolus functional traits explaining population performance and size were related to specific soil parameters, namely soil organic matter content, pH and phosphorus, in addition to a combination of presence-absence of six plant indicator species, relating to ecotones between forests and forest gaps. Conclusion – We show that, even for species that can grow across a wide range of vegetation groups, such as the Lady’s Slippers orchids, both indicator species and specific soil parameters can be used to assess the optimal sites to implement (re)-introduction actions.