Ouellet, C. E.; Sherk, L. C. (1967). "Woody Ornamental Plant Zonation: Ii. Suitability Indices of Localities". Canadian Journal of Plant Science. 47 (4): 339–349. doi:10.4141/cjps67-064. ISSN0008-4220. pdfArchived 2020-08-01 at the Wayback Machine
Ouellet, C. E.; Sherk, L. C. (1967). "Woody Ornamental Plant Zonation: Ii. Suitability Indices of Localities". Canadian Journal of Plant Science. 47 (4): 339–349. doi:10.4141/cjps67-064. ISSN0008-4220. pdfArchived 2020-08-01 at the Wayback Machine
"Hardiness zones of Portugal"(PDF). Repositório Institucional da Universidade de Lisboa. pp. 60–62. Archived(PDF) from the original on 2021-02-02. Retrieved 2020-09-19.
Ouellet, C. E.; Sherk, L. C. (1967). "Woody Ornamental Plant Zonation: Ii. Suitability Indices of Localities". Canadian Journal of Plant Science. 47 (4): 339–349. doi:10.4141/cjps67-064. ISSN0008-4220. pdfArchived 2020-08-01 at the Wayback Machine
"Hardiness zones of Portugal"(PDF). Repositório Institucional da Universidade de Lisboa. pp. 60–62. Archived(PDF) from the original on 2021-02-02. Retrieved 2020-09-19.
"Home". hardiness.inforest.gr. Archived from the original on 2021-06-02. Retrieved 2021-05-30.
Ouellet, C. E.; Sherk, L. C. (1967). "Woody Ornamental Plant Zonation: Ii. Suitability Indices of Localities". Canadian Journal of Plant Science. 47 (4): 339–349. doi:10.4141/cjps67-064. ISSN0008-4220. pdfArchived 2020-08-01 at the Wayback Machine