Modelling the distribution and effectiveness of the protected area network in conserving Himantoglossum calcaratum (Orchidaceae) subspecies in Serbia

Abstract

Himantoglossum calcaratum (Orchidaceae) comprises two subspecies: subsp. calcaratum, a Balkan endemic restricted to the central Balkans, and subsp. rumelicum, which has a broader distribution in southeastern Europe. The distribution patterns of these two taxa and the effectiveness of the current network of protected areas in conserving them have not yet been studied in detail. MaxEnt software was used to assess the current and future potential distribution of both subspecies in Serbia, based on bioclimatic variables, altitude, habitat types, and geological substrates. Six climate change scenarios were used to predict future distributions. Himantoglossum calcaratum subsp. calcaratum is mainly distributed in the western and southwestern parts of Serbia, while H. calcaratum subsp. rumelicum occurs primarily in eastern and southeastern Serbia. The results indicated that the most important factors determining potential distribution were altitude and mean temperature of the driest quarter for subsp. calcaratum, and precipitation of the wettest month, mean diurnal range, and isothermality for subsp. rumelicum. The study highlights that subsp. calcaratum is expected to decline under most climate scenarios, whereas subsp. rumelicum is expected to expand substantially, with an increasing trend in their spatial overlap and hybridisation under future climates. The current national network of protected areas covers only a small fraction of both subspecies. Under future scenarios, the extent of these areas is projected to increase slightly for subsp. calcaratum and decrease slightly for subsp. rumelicum. This underlines the need to establish new protected areas, primarily at low and medium altitudes, and to improve habitat conservation for both subspecies.