The concept and data were taken from Berg et al. (2017), who revised and corrected a previous system of indicator values for continentality developed by Ellenberg et al. (1991). Continentality degree is derived from the position of species distribution range on the gradient from oceanic Western Europe (class 1) to continental Middle Asia (class 10). Consequently, continentality amplitude corresponds to the number of phytogeographic continental classes where given species is distributed.
Data source and citation
Berg C., Welk E. & Jäger E. J. (2017). Revising Ellenberg’s indicator values for continentality based on global vascular plant species distribution. Applied Vegetation Science, 20(3), 482–493. https://doi.org/10.1111/avsc.12306
Further references
Ellenberg H., Weber H. E., Düll R., Wirth V., Werner W. & Paulißen D. (1991). Zeigerwerte von Pflanzen in Mitteleuropa. Scripta Geobotanica, 18, 1–248.
Jäger E. J. (1968) Die pflanzengeographische Ozeanitätsgliederung der Holarktis und die Ozeanitätsbindung der Pflanzenareale. – Feddes Repertorium 79: 157–335.