b) the alvar climate, the coldest mountain climate since the biotemperature is between 0 °C and 1.5 °C (biotemperature can never be below 0 °C). It corresponds more or less to the coldest tundra climates and to the ice cap climates (EF) as well.

Holdrige reasoned that plants net primary productivity ceases with plants becoming dormant at temperatures below 0 C and above 30 C. Therefore, he defined biotemperature as the mean of all temperatures but with all temperatures below