Fig. 2.

Frequency of daily mean temperatures at treeline for 370 treeline sites across the globe obtained by combining temperatures from the Woldclim climate data base and treeline positions assessed with Google Earth (a unconstrained season, i.e., all days of the year; b restricted to days with a daily mean >0.9 °C, c as b, but disregarding days too dry for tree growth (solving the local water balance equation with a bucket model). Note, data in b and c are spanning such a wide range, because they include daily mean temperatures for all individual days that exceed 0.9 °C from all climatic zones (J. Paulsen and C. Körner, unpublished)