2. Thuja plicata Donn ex D. Don (syn.: T. gigantea Nutt.) (west. N-Am.) – A widely cultivated conifer in private as well as public gardens, parks,… but perhaps less common in cultivation than Chamaecyparis in Belgium. Increasingly escaping in recent times: known since 2004 from an old wall (quay) in the city of Brugge (a tall tree, long persisting). Frequently seen as an ephemeral escape in urban habitats, for instance in cemeteries (abundantly so in Roeselare,…). Saplings easily grow tall but are usually soon destroyed by weed-killer. A future naturalisation in undisturbed conditions in Belgium seems very likely. Doubtlessly widely overlooked. In the past years also increasingly observed in more natural or nature-like conditions (but still close to planted specimens), for instance in marshy woodland in Mollendaalbos (Meerdaalwoud) in Heverlee in 2010.
Thuja plicata is reported as an invasive species in Great Britain (Richardson & Rejmánek 2004) and potential invasive behaviour is expected from Finland as well (Kunttu & Kunttu 2013). Arboreta played an important role in the incipient invasion of this species (Kunttu 2015).
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Selected literature:
Clement E.J. (1982) Adventive news 23. BSBI News 32: 18-20.
Kunttu P. (2015) Jättituija on levinnyt luontoon toistaiseksi vain arboretumeista. Lutukka 31: 117-118. [available online at: http://vieraslajit.fi/sites/alienplantsbelgium.bedefault/files/Lutukka_2...
Kunttu P. & Kunttu S. (2013) Tuleeko jättituijasta haitallinen vieraslaji? Särkisalon Petun tapaus (Will Western Redcedar become an invasive alien species in Finland? Case study from island of Pettu, SW Finland). Lutukka 29(2): 51-54.
Richardson D.M. & Rejmánek M. (2004) Conifers as invasive aliens: a global survey and predictive framework. Diversity and Distributions 10(5-6): 321–331.