Preliminary study on the ecological requirements of Humulus japonicus in France
Humulus japonicus (Cannabaceae, EPPO List of Invasive Alien Plants) is an annual vine originating from Eastern Asia which was introduced to Europe and to the USA as an ornamental plant. Within the EPPO region, the species is established in France, Hungary and Italy. The plant displays invasive behaviour in the USA and in Hungary.
To consider the influence of abiotic and biotic factors on the success of establishment of H. japonicus in France, the following parameters were measured: the cover of the species, the propagule pressure, soil moisture, light availability and nutrient levels. This study revealed that high densities of H. japonicus were mainly correlated with high soil moisture and low cover of other plants. The establishment and invasion successes were determined to be correlated to a high propagule pressure (28 seedlings/ha), an early germination and the fact that this climbing vine has long stems which can be prostrate and a plant can cover up to 50 m². H. japonicus acts as an opportunistic species that benefits from habitat disturbance (floods in the site studied in France). In these studies, species diversity was reduced by 50% between non-invaded and invaded quadrats. However, the removal of H. japonicus allowed species richness to be restored.
Sources
Mahaut L, Reygrobellet JP, Fried G (2014) Preliminary study on the ecological requirements and establishment success of the Japanese hop (Humulus japonicus Siebold ; Zucc.) Abstract of the 4th International Symposium on Environmental Weeds and Invasive Plants, Montpellier (FR), 2014-06-19-23.
Mahaut L (2014) Le houblon du Japon (Humulus japonicus, Siebold ; Zucc) une espèce locomotrice ou une simple passagère du train des changements ? Projet de recherche, stage de M2. Université des Sciences et Techniques du Languedoc. Agence Nationale de Sécurité Sanitaire de l’Alimentation, de l’Environnement et du Travail (ANSES), 189 pp.