"Tundra". ArcGIS StoryMaps. 17 January 2020. Retrieved 5 October 2021. the tundra is a vast and treeless land which covers about 20% of the Earth's surface, circumnavigating the North pole.
Joint Research Centre (European Commission); Johnson, Nancy C.; Scheu, Stefan; Ramirez, Kelly S.; Lemanceau, Philippe; Eggleton, Paul; Jones, Arwyn; Moreira, Fatima M. S.; Barrios, Edmundo (2016). Global soil biodiversity atlas. LU: Publications Office of the European Union. doi:10.2788/2613. ISBN978-92-79-48168-0.
Johnson, Brett M.; Pate, William M.; Hansen, Adam G. (2017). "Energy Density and Dry Matter Content in Fish: New Observations and an Evaluation of Some Empirical Models". Transactions of the American Fisheries Society. 146 (6): 1262–1278. Bibcode:2017TrAFS.146.1262J. doi:10.1080/00028487.2017.1360392.
Joint Research Centre (European Commission); Johnson, Nancy C.; Scheu, Stefan; Ramirez, Kelly S.; Lemanceau, Philippe; Eggleton, Paul; Jones, Arwyn; Moreira, Fatima M. S.; Barrios, Edmundo (2016). Global soil biodiversity atlas. LU: Publications Office of the European Union. doi:10.2788/2613. ISBN978-92-79-48168-0.
Johnson, Brett M.; Pate, William M.; Hansen, Adam G. (2017). "Energy Density and Dry Matter Content in Fish: New Observations and an Evaluation of Some Empirical Models". Transactions of the American Fisheries Society. 146 (6): 1262–1278. Bibcode:2017TrAFS.146.1262J. doi:10.1080/00028487.2017.1360392.