Updated chorology, habitat ecology, conservation assessment and habitat suitability of Centaurea jankae in Romania and Bulgaria

Abstract

Centaurea jankae is a rare species with a restricted distribution in southeastern Romania and northeastern Bulgaria. This study aimed to update the chorology of C. jankae, characterise its habitat ecology and population-level variation, assess its local conservation condition, and model its current potential distribution and habitat suitability. Soil samples and data on topographic and bioclimatic factors were collected to assess environmental conditions. To update the species' chorology, locations reported in the literature were verified in the field. The current potential distribution of the species was modelled in MaxEnt based on 27 presence records and five environmental variables. Of the 14 populations previously reported, six were confirmed: three locations in Romania (Jurilovca–Capul Doloșman, Palazu Mic, and Slava Rusă) and three in Bulgaria (Nevsha, Ravna, and Venchan). Recorded abundance ranged from 1,199 to 4,589 individuals among populations, while flowering individuals represented 9.3–47.1% of the recorded individuals. Ecologically, C. jankae was associated with xerothermal conditions and predominantly sunny aspects and occurred across a broad range of slopes, with higher cover tending to occur on moderately inclined slopes. The species occurred on alkaline soils showing substantial among-population variation in nutrient status. Populations in Romania are linked to drier conditions and more fertile soils, while populations in Bulgaria occur under wetter, more climatically stable conditions. The MaxEnt model yielded a mean test AUC of 0.930 (± 0.056) across cross-validation replicates. Land use/land cover showed the highest percent contribution (42.8%) and permutation importance (39.4%) in the fitted model, while soil type accounted for 24.3% of percent contribution. The potential habitat of C. jankae covered 3,562.68 km² (11.2%) of the study area, of which 1,025.31 km² (3.2%) were identified as highly suitable habitat. Local conservation condition was assessed as unfavourable–inadequate (U1) for four populations and unknown (XX) for two populations. In conclusion, the species' restricted distribution, habitat fragmentation, and anthropogenic pressures highlight its vulnerability and the need to implement appropriate conservation measures to maintain C. jankae populations in the long term.