Based on the phenological data for 26 taxa observed in the Altai State Nature Biosphere Reserve and meteorological data from the station Yailu which is working from 1932, it was shown, that the maximum values of the phenological response (deviation of the pollen dispersion start dates) correspond to the maximum change in the thermal regime during 1981–1999; the annual values is 1,8 ± 0,3 day/10 years or 2,3 ± 1,0 day/°C. The calculation of the temperature sensitivity, which means the change of the pollen dispersion start dates on 1 °C, showed that the conifers trees (Pinus sibirica Du Tour and P. sylvestris L.) react by the delay of the start dates to the changes of the average annual temperature; the deciduous trees (Betula pendula Roth and B. pubescens Ehr.) are more likely to reflect the average temperature changes by shift of the pollen start dates. The results obtained for the analyzed 30 years are 1,2 ± 0,5 days/10 years and it agrees quite well with the data for the entire Northern Hemisphere, which is 1,1 ± 0,68 days/10 years. Thus, B. pendula and B. pubescens can be used as a reliable fenoindicators of the North-Eastern Altai geosystem.