Credit: Jean-Pol GRANDMONT/Wikimedia
Credit: Jean-Pol GRANDMONT/Wikimedia
To learn more about the map elements, please download the "Pan-European strategy for genetic conservation of forest trees"
This distribution map has been developed by the European Commission Joint Research Centre (partly based on the EUFORGEN map) and released under Creative Commons Attribution 4.0 International (CC-BY 4.0)
Caudullo, Giovanni; Welk, Erik; San-Miguel-Ayanz, Jesús (2017). Chorological maps and data for the main European woody species. figshare. Collection. https://doi.org/10.6084/m9.figshare.c.2918528
The following experts have contributed to the development of the EUFORGEN distribution maps:
Fazia Krouchi (Algeria), Hasmik Ghalachyan (Armenia), Thomas Geburek (Austria), Berthold Heinze (Austria), Rudi Litschauer (Austria), Rudolf Litschauer (Austria), Michael Mengl (Austria), Ferdinand Müller (Austria), Franz Starlinger (Austria), Valida Ali-zade (Azerbaijan), Vahid Djalal Hajiyev (Azerbaijan), Karen Cox (Belgium), Bart De Cuyper (Belgium), Olivier Desteucq (Belgium), Patrick Mertens (Belgium), Jos Van Slycken (Belgium), An Vanden Broeck (Belgium), Kristine Vander Mijnsbrugge (Belgium), Dalibor Ballian (Bosnia and Herzegovina), Alexander H. Alexandrov (Bulgaria), Alexander Delkov (Bulgaria), Ivanova Denitsa Pandeva (Bulgaria), Peter Zhelev Stoyanov (Bulgaria), Joso Gracan (Croatia), Marilena Idzojtic (Croatia), Mladen Ivankovic (Croatia), Željka Ivanović (Croatia), Davorin Kajba (Croatia), Hrvoje Marjanovic (Croatia), Sanja Peric (Croatia), Andreas Christou (Cyprus), Xenophon Hadjikyriacou (Cyprus), Václav Buriánek (Czech Republic), Jan Chládek (Czech Republic), Josef Frýdl (Czech Republic), Petr Novotný (Czech Republic), Martin Slovacek (Czech Republic), Zdenek Špišek (Czech Republic), Karel Vancura (Czech Republic), Ulrik Bräuner (Denmark), Bjerne Ditlevsen (Denmark), Jon Kehlet Hansen (Denmark), Jan Svejgaard Jensen (Denmark), Kalev Jðgiste (Estonia), Tiit Maaten (Estonia), Raul Pihu (Estonia), Ülo Tamm (Estonia), Arvo Tullus (Estonia), Aivo Vares (Estonia), Teijo Nikkanen (Finland), Sanna Paanukoski (Finland), Mari Rusanen (Finland), Pekka Vakkari (Finland), Leena Yrjänä (Finland), Daniel Cambon (France), Eric Collin (France), Alexis Ducousso (France), Bruno Fady (France), François Lefèvre (France), Brigitte Musch (France), Sylvie Oddou-Muratorio (France), Luc E. Pâques (France), Julien Saudubray (France), Marc Villar (France), Vlatko Andonovski (FYR Macedonia), Dragi Pop-Stojanov (FYR Macedonia), Merab Machavariani (Georgia), Irina Tvauri (Georgia), Alexander Urushadze (Georgia), Bernd Degen (Germany), Jochen Kleinschmit (Germany), Armin König (Germany), Armin König (Germany), Volker Schneck (Germany), Richard Stephan (Germany), H. H. Kausch-Blecken Von Schmeling (Germany), Georg von Wühlisch (Germany), Iris Wagner (Germany), Heino Wolf (Germany), Paraskevi Alizoti (Greece), Filippos Aravanopoulos (Greece), Andreas Drouzas (Greece), Despina Paitaridou (Greece), Aristotelis C. Papageorgiou (Greece), Kostas Thanos (Greece), Sándor Bordács (Hungary), Csaba Mátyás (Hungary), László Nagy (Hungary), Thröstur Eysteinsson (Iceland), Adalsteinn Sigurgeirsson (Iceland), Halldór Sverrisson (Iceland), John Fennessy (Ireland), Ellen O'Connor (Ireland), Fulvio Ducci (Italy), Silvia Fineschi (Italy), Bartolomeo Schirone (Italy), Marco Cosimo Simeone (Italy), Giovanni Giuseppe Vendramin (Italy), Lorenzo Vietto (Italy), Janis Birgelis (Latvia), Virgilijus Baliuckas (Lithuania), Kestutis Cesnavicius (Lithuania), Darius Danusevicius (Lithuania), Valmantas Kundrotas (Lithuania), Alfas Pliûra (Lithuania), Darius Raudonius (Lithuania), Robert du Fays (Luxembourg), Myriam Heuertz (Luxembourg), Claude Parini (Luxembourg), Fred Trossen (Luxembourg), Frank Wolter (Luxembourg), Joseph Buhagiar (Malta), Eman Calleja (Malta), Ion Palancean (Moldova), Dragos Postolache (Moldova), Gheorghe Postolache (Moldova), Hassan Sbay (Morocco), Tor Myking (Norway), Tore Skrøppa (Norway), Anna Gugala (Poland), Jan Kowalczyk (Poland), Czeslaw Koziol (Poland), Jan Matras (Poland), Zbigniew Sobierajski (Poland), Maria Helena Almeida (Portugal), Filipe Costa e Silva (Portugal), Luís Reis (Portugal), Maria Carolina Varela (Portugal), Ioan Blada (Romania), Alexandru-Lucian Curtu (Romania), Lucian Dinca (Romania), Georgeta Mihai (Romania), Mihai Olaru (Romania), Gheorghe Parnuta (Romania), Natalia Demidova (Russian Federation), Mikhail V. Pridnya (Russian Federation), Andrey Prokazin (Russian Federation), Srdjan Bojovic (Serbia) , Vasilije Isajev (Serbia), Saša Orlovic (Serbia), Rudolf Bruchánik (Slovakia), Roman Longauer (Slovakia), Ladislav Paule (Slovakia), Gregor Bozič (Slovenia), Robert Brus (Slovenia), Katarina Celič (Slovenia), Hojka Kraigher (Slovenia), Andrej Verlič (Slovenia), Marjana Westergren (Slovenia), Ricardo Alía (Spain), Josefa Fernández-López (Spain), Luis Gil Sanchez (Spain), Pablo Gonzalez Goicoechea (Spain), Santiago C. González-Martínez (Spain), Sonia Martin Albertos (Spain), Eduardo Notivol Paino (Spain), María Arantxa Prada (Spain), Alvaro Soto de Viana (Spain), Lennart Ackzell (Sweden), Jonas Bergquist (Sweden), Sanna Black-Samuelsson (Sweden), Jonas Cedergren (Sweden), Gösta Eriksson (Sweden), Markus Bolliger (Switzerland), Felix Gugerli (Switzerland), Rolf Holderegger (Switzerland), Peter Rotach (Switzerland), Marcus Ulber (Switzerland), Sven M.G. de Vries (The Netherlands), Khouja Mohamed Larbi (Tunisia), Murat Alan (Turkey), Gaye Kandemir (Turkey), Gursel Karagöz (Turkey), Zeki Kaya (Turkey), Hasan Özer (Turkey), Hacer Semerci (Turkey), Ferit Toplu (Turkey), Mykola M. Vedmid (Ukraine), Roman T. Volosyanchuk (Ukraine), Stuart A'Hara (United Kingdom), Joan Cottrell (United Kingdom), Colin Edwards (United Kingdom), Michael Frankis (United Kingdom), Jason Hubert (United Kingdom), Karen Russell (United Kingdom), C.J.A. Samuel (United Kingdom).
Turkish hazel shows medium to high levels of genetic variation. Studies report high genetic diversity across its range but lower genetic diversity in populations in Georgia and Türkiye compared with Balkan populations; this is attributed to historical refugial persistence and migration routes, and historical separation (Šeho et al., 2023). Overall genetic diversity is described as moderate among populations, although observed heterozygosity and polymorphism have been reported as high in earlier work, indicating high genetic diversity (Fussi, Kavaliauskas, and Seho, 2010; Šeho et al., 2023). However, genetic research on the species across its range is limited, and patterns of diversity and variation across the species’ full natural distribution are still poorly understood (İslam et al., 2023).
Turkish hazel has clear genetic structuring; studies identify distinct genetic clusters across its natural range, consistent with separate refugia and Holocene migration pathways (Šeho et al., 2023). Three main gene pools are identified: in the Balkans, Türkiye, and Georgia (Šeho et al., 2023). Morphological analyses show similar patterns to genetic distribution, revealing wide genetic divergence among genotypes even within the same locality, which suggests high intra-population diversity (İslam et al., 2023).
Turkish hazel is a monoecious and wind-pollinated tree species with heavy seeds that are dispersed by animals (Šeho et al., 2023). Male and female flowers are separated and mature at different times.
The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2025.
The hazel (Corylus) genus is genetically diverse and has strong potential for rapid genetic gains through breeding (Molnar, 2011). Wild hazel species, including Turkish hazel, are underrepresented in germplasm collections and formal breeding despite offering useful traits for crop improvement (Molnar, 2011) and interspecific hybridization is a common breeding approach. Turkish hazel’s range overlaps with common hazel/cobnut (Corylus avellana), creating the possibility of natural hybrids (Fussi, Kavaliauskas, and Seho, 2010). However, there is clear genetic differentiation between Turkish hazel and common hazel, with no natural hybrids detected, although artificial crosses have been achieved (Fussi, Kavaliauskas, and Seho, 2010). While interspecific hybridization offers valuable breeding opportunities, natural introgression between Turkish and common hazel appears limited, and wild hazel remains an underutilized resource for genetic improvement (Fussi, Kavaliauskas, and Seho, 2010; Molnar, 2011; İslam et al., 2023).
Turkish hazel is increasingly promoted as a valuable “alternative” tree for European planting because of its strong tolerance of harsh sites and low maintenance needs (Šeho et al., 2023). Artificial hybrids with common hazel create opportunities for targeted breeding of Turkish hazel (Šeho et al., 2023). The species’ high resistance to abiotic and biotic stresses, including drought tolerance from a strong root system and frost hardiness, mean existing wild populations are especially important as natural seed reservoirs for conservation and propagation (İslam et al., 2023).
The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2025.
Turkish hazel has been overexploited for its valuable wood, and its original distribution has significantly declined; it now exists in small, isolated populations within its natural range, making the remaining stands critically important for conservation (Šeho et al., 2023). Because of this fragmentation and historical exploitation, populations are vulnerable to local extinction under rapid environmental change, and their genetic resources are at risk if not actively conserved (Šeho et al., 2023).
In situ conservation of remaining populations should be prioritized and gene-conservation units and seed-stands should be established to secure representative genetic material for research, restoration, and assisted migration (Šeho et al., 2023). Ex situ conservation measures such as seed collections, seed orchards, or clonal repositories are also important, and breeding programmes should consider crossing genotypes from genetically distant clusters to maximize adaptive potential and desirable traits (İslam et al., 2023). Further research is needed to map natural distribution and genetic structure of Turkish hazel to support restoration and cultivation activities, allowing the maintenance of native genetic diversity (İslam et al., 2023; Šeho et al., 2023). Human-led planting and controlled hybridization can aid restoration and breeding (İslam et al., 2023; Šeho et al., 2023).
The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2025.
Further reading
Erdogan, V. 1999. Genetic relationships among hazelnut (Corylus) species. PhD dissertation. Corvallis, OR, Oregon State University. https://ir.library.oregonstate.edu/downloads/rb68xf863
Šeho, M., Ayan, S., Huber, G., and Kahveci, G. 2019. A review on Turkish hazel (Corylus colurna L.): A promising tree species for future assisted migration attempts. SEEFOR, 10(1): 53–63. https://doi.org/10.15177/seefor.19-04
Srivastava, K., Zargar, K., and Singh, S. 2010. Genetic divergence among Corylus colurna genotypes based on morphological characters of hazelnut. Biodiversity: Research and Conservation, 17: 13–17. https://sciendo.com/2/v2/download/article/10.2478/v10119-010-0003-5.pdf
References
Fussi, B., Kavaliauskas, D., and Seho, M. 2010. Molecular differentiation of Turkish and Common hazels (Corylus colurna L. and Corylus avellana L.) using multiplexed nuclear microsatellite markers. Annals of Forest Research, 62(2): 173–182. https://doi.org/10.15287/afr.2019.1709
Molnar, T.J. 2011. Corylus. In: C. Kole, ed. Wild crop relatives: Genomic and breeding resources – Forest trees, pp. 15–48. Heidelberg, Germany, Springer-Verlag Berlin. https://doi.org/10.1007/978-3-642-21250-5_2
İslam, A., Ayan, S., Turan, A., Yılmaz, M., Karagol, S., and Çolak, S. 2023. Morphometric diversity for rootstock characteristics of Turkish hazel (Corylus colurna L.) populations in the western Black Sea region of Türkiye. The Black Sea Journal of Sciences, 13(4): 1416–1426. https://doi.org/10.31466/kfbd.1285059
Šeho, M., Kavaliauskas, D., Ayan, S., Čokeša, V., Petkova, K., and Fussi, B. 2023. First insights into genetic structure and diversity of Corylus colurna L. for conservation of its genetic resources and possible assisted migration. Forest Ecology and Management, 549: 121480. https://doi.org/10.1016/j.foreco.2023.121480
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