Fig. 2.

The location of 73 Environment Canada weather stations where soil temperature at a 5cm depth was recorded between 1984 and 2006. Green circles indicate weather stations where the minimal soil temperature was above –6.4 ° C, yellow circles indicate weather stations with minimal temperatures between –6.4 and –14.1 °C, and red circles indicate weather stations with minimal temperature below –14.1 °C (Environment Canada 2014; http://weather.gc.ca/). Weather stations with 5 years or less of recorded data are marked with a ‘*’. See online Supplemental Table S.1 for additional information, including the number of years recorded.