An analysis of primary productivity reveals a valid positive correlation with climatic indices (mean July temperature, degree days above 0°C, and summer precipitation) when one compares polar deserts, arctic tundra and typical subarctic tundra. This correlation does not apply, however, when one compares typical and southern subarctic tundra. The analysis also suggests that there are viable grounds for distinguishing polar deserts, arctic tundra, and subarctic tundra as independent zones, rather than classing the arctic tundra and subarctic tundra as subzones of the tundra zone.