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On the Ural range the elevation of upper timberline changes at grade 71 m per degree of latitude in linear regression. Much lengthy cross-section - for the semi-arid regions of middle Siberia and adjacent Kazakhstan, and for the regions of eastern Siberia dominated by larch forests - exhibit parabolic regression of timberline levels upon geographic latitude. The longitudinal gradient of timberlines presumably depends on radiation balance related with the amount of precipitation. The arctic boundary of taiga in eastern Europe and Siberia lies mostly on average latitude 69 degrees 36’ E. It correlates with mean July temperature 11.2 degrees C, or with duration of the growing season 128 days with stable temperature of air exceeding 0 degrees C which amounts to 876 degrees. Daily temperatures exceeding 5 degrees and especially 10 degrees C are seemingly less influential there. The value of 11.2 degrees C deviates by about 1 degrees C from the value of ’above 10 degrees C’ for three summer month reported by Langlet 1935, which shows the close environmental control regulating the northern and upper boundary of the northern, mostly coniferous forest on the northern hemisphere.