Intensity and Persistence of Soil Water Repellency in Pine Forest Soil in a Temperate Continental Climate under Drought Conditions

Although soil water repellency (SWR) has been reported under different soils, climates, and vegetation types of the world, especially in forest land and following wildfires, the understanding of this variable continues to be rather limited. This study presented the characterization of SWR from wild fire measurements in a Scots pine Peucedano-Pinetum forest in the Kampinos National Park (central Poland), which is characterized by a temperate continental climate. The main objectives were: [i] To evaluate the potential occurrence, intensity, and persistence of soil water repellency in the surface layers of podzolized rusty soils during a dry summer; [ii] to determine whether a wildfire increased SWR, compared to the unburnt condition of soil; and [iii] to identify changes in hydrophobicity 13 months after a fire. The Water Drop Penetration Time (WDPT) test was used to assess persistence and intensity of soil SWR. Hydrophobicity is a natural phenomenon during periods of drought in temperate continental climates. The extreme class of SWR was observed in surface layers of up to 20 cm. A higher hydrophobicity was noted in the older habitats of the Peucedano-Pinetum forest. Maximum WDPT values (10,800 s) were found for an older ecosystem cover, during a dry summer. SWR in fire-affected soils is dependent on the intensity of the fire, as well as displaying spatial and seasonal variability. Thirteen months after a fire, the highest variability in the occurrence of non-wettability, was recorded in the surface layers of areas affected by a weak fire. A positive relationship between soil pH and WDPT values was determined to a 20 cm depth. Prolonged dry periods resulting from global climate change, may enhance the effects of increasing SWR; it therefore seems reasonable for future research on biosphere-climate interactions, to take the presence of hydrophobicity into account.