Soil moisture in mountain spruce stand

Mountain forests are among the main components of natural environment in Slovakia. They grow mainly in areas with cold climate, on poor soils with unfavorable reaction, often very acidic (pH in H2O < 4.5) and with nutrient deficit. Immissions and acid rain attack forests to a great extent. Global climate changes also represent a new threat. Extremes in air temperatures, excessive amounts of precipitation or on the other hand the lack of water from precipitation, torrential rains or long-lasting drought periods are recorded as a result of a higher amount of heat energy accumulation from the greenhouse effect. Spruce forests are most endangered. Spruce with its root system concentrated in the upper soil layers, where also the highest amount of toxic elements accumulates, suffers more and more from dry and warm periods and it begins to wither due to drought. The occurrence of hydropedological cycles with a low or insufficient supply of available water in the soil is most frequent during summer (July, August). If the soil water potential values approach the value of the wilting point, an expressive decrease in transpiration is observed during the day, whereas its daily course is also suppressed. Gradual soil drying up from the upper layers towards the deepest ones of the physiological profile of soil represents a change in soil moisture stratification, especially after moistening the upper layers of soil with water from atmospheric precipitation. The deeper soil layers need not be re-saturated in such a case. Under drought the whole physiological profile of soil dries up in a relatively short time. Trees are exposed to a strong physiological stress in such conditions and after longlasting drought periods they can get into the state of total exhaustion.