Only the southernmost selleck inhibitor part of this region is covered by mixed forest with the same soil type. Analysis of data from separate stations showed that there are two areas in the study region where the temporal soil moisture changes are quite different. Soil moisture changes in the upper 20 cm are caused by the interaction of two opposite processes: seepage and evaporation (Rode 1965). Precipitation water quickly infiltrates into the soil and as soon as seepage stops, the process of evaporation starts. This explains why only ‘rapid’ moisture fluctuations occur within the upper soil layers, blocking the formation

of evident directional tendencies. Below the top 20 cm layer, moisture seeps only slowly into the underlying layers. Moisture

movement from the deeper layers back up to the soil surface is also a relatively slow process (Rode 1965). This explains why systematic see more common features of temporal soil moisture changes can be documented only for the 0–50 cm and deeper layers. Soil moisture changes during spring (April–May) in the 0–50 and 0–100 cm layers are shown in Figure 3. At the beginning of the growing season the soil water content is sufficiently high as snowmelt leads to saturation of the soil. Within the 0–50 cm layer an increase in soil moisture is observed over most of the northern part of the taiga zone, whereas in the south of this zone, this parameter decreases. Furthermore, in the south of the zone soil moisture increased slightly before the mid-1980s and then decreased rather sharply from the end of the 1980s. Similar tendencies were also noted in the 0–100 cm layer. This soil moisture decrease since the 1980s appears to have

been caused by CYTH4 a reduction in snow depth and snow cover duration in the Russian sector of the Baltic Sea Drainage Basin (see Bulygina et al. 2009). Reductions in soil water storage in spring are closely related to winter changes in the NAO index, which strongly affects the climate of the Baltic Sea region (BACC 2008). Since the 1990s, there has been an intensification of the zonal circulation type (with prevailing westerly winds), leading to a greater frequency of milder winters (Hagen & Feistel 2005, 2008). In such conditions there are more days with winter thaw (Groisman et al. 2010), when thawed soils absorb moisture, and surface water downloads into the groundwater. As a result, there is a decrease in spring soil water storage. In summer (June–August) soil moisture values are smaller than in spring owing to the consumption of the thaw water accumulated in the soil in winter and early spring. The main tendencies of soil moisture changes remain the same as in spring (Figure 4) and become more apparent in both the 0–50 cm and 0–100 cm layers. Before the mid-1980s, the soil moisture increase became especially obvious in the north of the zone, and the rates of this increase and subsequent soil moisture decrease were also higher (by an absolute value) than in spring.