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, G., Welk, E., San-Miguel-Ayanz, J., 2017. Chorological maps for the main European woody species. Data in Brief 12, 662-666. DOI: https://doi.org/10.1016/j.dib.2017.05.007
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).
Status of Juglans nigra conservation in Europe
Black walnut has high genetic diversity within and between populations. However, genetic diversity in European populations is lower than that of native American populations (Pollegioni et al., 2009). North American populations of the tree show high genetic diversity, which was maintained throughout glacial periods, postglacial recolonization, and fragmentation after European settlement of eastern North America (Victory et al., 2006).
Black walnut shows adaptational differences among North American populations, and research has shown patterns of genetic variation in height growth along climatic gradients and differentiation among populations in fitness traits (Victory et al., 2006; Onofrio, Hawley, and Leites, 2021). The species has a wide distribution and high spatial climatic variability within its range in Europe and America. Therefore, populations show different characteristics and genetic differentiation related to their original local climate (Onofrio, Hawley, and Leites, 2021). For example, populations in warmer climates are taller and have higher growth but are less cold and frost tolerant (Onofrio, Hawley, and Leites, 2021).
However, across its native distribution in North America, black walnut is typically genetically homogeneous. High genetic diversity, low genetic differentiation, genetic homogeneity, and low isolation by distance of black walnut populations in North America have been maintained through the species’ high and extensive gene flow (Victory et al., 2006). Recent fragmentation of populations caused by human activity has had little effect on the genetic diversity of populations, probably because the tree’s long lifespan means too few generations have passed for the effects of recent forest fragmentation to have yet had an effect (Victory et al., 2006). However, rare and local alleles have likely been lost where land in the species’ range has been converted to agriculture (Victory et al., 2006).
Black walnut’s use in silviculture, its reproductive biology, and how it is propagated are important factors in its population genetics (Victory et al., 2006). While selfing is possible, the species is predominately outcrossing, with pollen dispersed by wind and seed dispersed by gravity and animal consumption (Victory et al., 2006). However, the trees fruits can float on water, meaning long-distance seed dispersal is also possible via rivers (Victory et al., 2006). High gene flow via pollen has allowed black walnuts to maintain genetic connectivity between refugial and isolated populations during glacial periods, limiting genetic differentiation (Victory et al., 2006).
The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2024.
Black walnut is genetically like common walnut despite belonging to different sections of genus Juglans (Pollegioni et al., 2009). Hybridization between these two species does occur naturally, creating a hybrid species, Juglans x intermedia. However, hybrids are rare as black and common walnut flower at different times (Pollegioni et al., 2009). Juglans x intermedia shows increased vegetative vigour, distinct disease resistance, good wood quality, and greater winter hardiness than its parental species, making it valuable in forestry in northern Europe (Pollegioni et al., 2009). Cultivars of black walnut are also being crossed to create desirable hybrids (Pollegioni et al., 2009).
The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2024.
Black walnut faces genetic threats primarily from habitat fragmentation, climate change, and pests and disease. Climate change may alter suitable habitats and stress populations, threatening genetic variation. Thousand cankers disease, caused by the fungus, Geosmithia morbida, poses a severe threat, killing infected trees and leading to population declines.
Conservation efforts focus on preserving genetic diversity through habitat protection and restoration and the establishment of seed banks and genetic conservation units. Monitoring and managing pest outbreaks, researching disease-resistant genotypes, and promoting the planting of genetically diverse trees are crucial strategies. In North America, the species’ low differentiation means conservation of a population would capture up to 98% of the neutral genetic variance present (Victory et al., 2006).
The bibliographic review was conducted by James Chaplin of the EUFORGEN Secretariat in August 2024.
Genetic Characterisation of Juglans nigra and its GCUs
Availability of FRM
FOREMATIS
Conifers Network: Report of the fourth meeting
Contacts of experts
NA
Further reading
N/A
References
Onofrio, L., Hawley, G., and Leites, L.P. 2021. Ecological genetics of Juglans nigra: Differences in early growth patterns of natural populations. Ecology and Evolution, 11(12): 7399–7410.
Pollegioni, P., Woeste, K., Major, A., Mugnozza, G.S., and Malvolti, M.E. 2009. Characterization of Juglans nigra (L.), Juglans regia (L.) and Juglans x intermedia (Carr.) by SSR markers: a case study in Italy. Silvae Genetica, 58(1–6): 68–78.
Victory, E.R., Glaubitz, J.C., Rhodes Jr, O.E., and Woeste, K.E. 2006. Genetic homogeneity in Juglans nigra (Juglandaceae) at nuclear microsatellites. American Journal of Botany, 93(1): 118–126.
See details
Designed by Newtvision
