Contrasting viability clusters in the fen orchid Liparis loeselii across NE German fens: reproductive output varies with productivity, light and iron concentration

Abstract The decline of many temperate orchid species has intensified efforts to understand the ecological conditions required for conservation. Long-term monitoring of life stages and traits is commonly used to assess population viability. However, comprehensive monitoring is challenging for inconspicuous orchids in spatially discrete subpopulations. Comparing subpopulations within sites from a single census using key viability proxies may therefore provide insight into site-level population viability and identify habitat conditions associated with contrasting subpopulation viability. Across 17 fen sites in NE Germany, 225 individuals from 65 subpopulations of the fen orchid Liparis loeselii were analysed. Analyses tested whether (i) subpopulations formed distinct clusters based on viability proxies, (ii) clusters differed in environmental factors and (iii) clusters were associated with differing plant species composition. Vegetation relevés were conducted, nine environmental factors recorded and viability proxies assessed for each subpopulation. Three clusters with contrasting subpopulation viability were identified. Cluster 1 had a low reproductive output and tall vegetation, Cluster 2 showed high herbivory and low vegetation height, and Cluster 3 high reproductive output and high peat iron concentration. Plant species composition also differed among clusters. At the site level, Cluster 1 dominance was associated with smaller estimated population sizes, whereas sites dominated by Clusters 2 and 3 had larger estimated population sizes. The identified clusters may support initial assessments of site-level population status, although recruitment data are needed to evaluate long-term population viability. Management should promote open, low-stature vegetation mosaics encompassing contrasting hydrochemical conditions, including calcium-rich and iron-rich habitats.