Soil properties and plant species can predict population health and potential introduction sites of the endangered orchid Cypripedium calceolus

Abstract

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.