LEVELS OF THE UPPER FOREST BOUNDARY IN NORTHERN ASIA

On the Ural range the elevation of upper timberline changes at grade 7 1 m per degree of latitude in linear regression. Much lengthy cross-se ction - for the semi-arid regions of middle Siberia and adjacent Kazak hstan, and for the regions of eastern Siberia dominated by larch fores ts - 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 ar ctic boundary of taiga in eastern Europe and Siberia lies mostly on av erage latitude 69 degrees 36' E. It correlates with mean July temperat ure 11.2 degrees C, or with duration of the growing season 128 days wi th stable temperature of air exceeding 0 degrees C which amounts to 87 6 degrees. Daily temperatures exceeding 5 degrees and especially 10 de grees C are seemingly less influential there. The value of 11.2 degree s 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 cl ose environmental control regulating the northern and upper boundary o f the northern, mostly coniferous forest on the northern hemisphere.