Changes in the radio field (rf) strength at a large time interval are characterized by the term magnitude (H, dB), i.e., the difference between the highest monthly value in winter and the lowest one in summer. In addition to the seasonal swing of rf-tension, there is another feature in the behavior of the electromagnetic field: independent of the season, there has been observed the spread of values of field intensity. In some cases, rf strength values in the winter are close to summer ones. We can explain this scatter of rf-intensity due to the presence of the hysteresis of electro-conductivity, thanks to which rf-tension has a different meaning at the same temperature. Therefore, the terms - seasonal and diurnal variation of the radio field -are to be combined into one term: temperature variation of rf-tension, since they have one reason for formation. It is known that the electromagnetic field strength drops with increasing electrical resistance in the homogeneous medium. In reality, the opposite pattern is observed: an increase in electrical resistance of the underlying surface leads to increased rf-tension. There are several different points of view for explaining this phenomenon: impact of forest vegetation; presence of an additional ionized layer in the atmosphere; appearance of the surface Cennik wave; appearance of the surface Norton wave; presence of longitudinal electromagnetic waves; interference of the surface and underground radio waves; influence of the Sun spots number on the value of rf-tension of LW range for the winter period. The analysis of the published literature and the data obtained by the authors allowed to establish a very interesting and complex interaction of various natural processes, leading eventually to the level of fluctuations of the electromagnetic field of SW-MW-LW ranges. A change of seasons takes place because of the angle of the Earth's rotation axis, which determines the change of positive and negative temperatures in the middle latitudes on the Earth's surface. The presence of negative temperatures makes the living world adapt to the frost. Trees have to be protected from the adverse effects of negative temperatures on the water. It is well known that its volume increases greatly at freezing, which leads to disruption of the integrity of the closed vessel. As a result of the chemical processes occurring in the trunk of the tree, starch is hydrolyzed into soluble sugars, in particular, glycerol. Thus, not only the volume of the water-andglycerol solution reduces, but also the freezing point of water decreases. The emergence of the water-and-glycerol solution increases the electrical resistance of wood to 200 Ohm-m to 10,000 Ohm-m, slowing down osmosis. Trees are moving from the development of the growing season in the resting stage. Changes in the electrical resistance of trees leads to temperature variations of tension of electromagnetic fields of SW-MW-LW ranges.
