Juglans regia L. (syn.: J. sinensis (DC.) Dode) (SE-Eur., temp. Asia) – Commonly planted as an ornamental tree in private and public gardens, as a wayside tree, in orchards,… probably since the middle ages. In the past decades increasingly reported as self-sowing. Unfortunately, the escape of Juglans regia in Belgium is poorly documented.The first subspontaneous records possibly date back to the early 1970’s. By now, Juglans regia has become a very widespread neophyte (although perhaps still absent from the cooler parts of Wallonia) but most records still represent saplings or young, non-flowering trees. However, Juglans regia surely is becoming naturalised locally. Juglans regia is usually found by road verges or canal- and riverbanks, (urban) waste land, disused industrial- and railway yards, gravel-, clay- and sandpits and increasingly also as a pioneer in chalk and limestone grassland. Saplings of Juglans regia often occur in places where no parental trees are present. They are probably dispersed by small mamals.
The recent and massive occurence of Juglans regia in Belgium is possibly induced by global warming. In the British Isles Juglans regia only germinates in the warmer parts of the country (Stace 1997).
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Hetzel I. (2010) Zur spontanen Ausbreitung von Walnuss (Juglans regia) und Esskastanie (Castanea sativa) in Wäldern und Forsten im mittleren Ruhrgebiet. Floristische Rundbriefe 43: 24-43.
Loacker K. (2007) Spread of walnut (Juglans regia L.) in an Alpine valley is correlated with climate warming. Flora 202: 70-78.
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