The effects of abiotic factors (rate of PAR, air temperature and relative humidity, vapor pressure deficit) on the daily dynamics of the water potential in foliated (needled) shoots of Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth) trees during the growing season were studied in a fresh bilberry pine forest in the European part of the middle taiga (southern Karelia). Based on the analysis of model data, it was established that the contributions of the leading environmental factors to the formation of the water potential in coniferous and deciduous plants are comparable, and no interspecific differences were found. The similarity of the environmental factors dominance is shown for the two species, namely PAR rate effect dominance in July, relative air humidity in August, air temperature in September. In June, however, significant differences between the species were revealed in the governing influence of environmental factors on the water exchange in Scots pine (relative air humidity) and silver birch (PAR rate). These differences are supposed to be due to the biological traits of the formation of shoots and leaves (needles) in the coniferous and deciduous plants during the period of intensive growth. At the same time, we observed a somewhat inert response of the water potential in the foliated shoots of woody plants to abrupt changes in abiotic factors during the day, which is due to the mechanism of endogenous regulation of the water exchange. The similarity of the leading abiotic factors and their contributions to the formation of the water potential for coniferous and deciduous woody plants through the growing season suggests that taxonomically different species growing in the same climatic region have similar adaptation mechanisms.