The estimation of population size and density of Hungarian crocus, Colchicum hungaricum, on its locus classicus (South Hungary)

Hungarian crocus, Colchicum hungaricum Janka is relict plant species of the Carpathian Basin, where it is known only from its locus classicus, Szársomlyó Hill in southern Hungary. Despite its limited distribution, data on its population have remained scarce. The previous assessments have been conducted with a different methodological approach without detailed explanations; therefore, the results are incomparable. The aim of our study was to reveal the current local distribution range of the species and to estimate its population size and density. Surveys carried out in January 2022 and 2023 revealed that the species occupies a 0.34 km2 area on the southern slope of Szársomlyó Hill. Population size was estimated based on counts of plants in 100 randomly selected 4 m2 plots, with values extrapolated to the total occupied area. To improve estimation accuracy, we applied a representative sampling design covering 0.12% of the species’ local range, combined with generalized linear models assuming quasi-Poisson error distribution and a bootstrap resampling approach. The estimated population size was higher than in previous estimations, exceeded 3.2 million individuals in 2022 and 3.4 million in 2023. Plant density ranged from 0–5 to 120–130 individuals/m2. We suggest that the results gained by this method provides a reliable base for future monitoring of Hungarian crocus, offering valuable insights into its population dynamics and trends.