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RESEARCH PRODUCT

Short-term spatio-temporal spring grassland fire effects on soil colour, organic matter and water repellency in Lithuania

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Abstract. The aim of this work was to study the short-term effects (first 9 months after the fire) of a low-severity spring boreal grassland fire on soil colour, soils organic matter (SOM) and soil water repellency (SWR) in Lithuania. Three days after the fire we designed a plot of 400 m2 in a control (unburned) and unburned area with the same geomorphological characteristics. Soil water repellency analysis were assessed through the 2 mm mesh (composite sample) and in the subsamples of all of the 250 samples divided into different soil aggregate fractions of 2–1, 1–0.5, 0.5–0.25 and < 0.25 mm, using the Water Drop Penetration Time (WDPT) method. The results showed that fire darkened the soil significantly during the entire study period due to the incorporation of ash/charcoal into the soil profile. Soil organic matter was significantly higher in the first two months after the fire in the burned plot, in comparison to the unburned plot. Soil water repellency (SWR) of the composite sample was higher in the burned plot during the first two months after the fire. However, considering the different aggregate fractions studied, the SWR was significantly higher until 5 months after the fire in the coarser fractions (2–1 mm, 1–0.5 mm) and 7 months after in the finer (0.5–0.25 mm and < 0.25 mm), suggesting that the leachability of organic compounds is different with respect to soil aggregate size fractions. This finding has implications for the spatio-temporal variability of fire effects on SWR. SOM was significantly negative correlated with SWR (composite sample) only in the two months after the fire. These results demonstrated that in the first two months the hydrophobic compounds produced by fire were one of the factors responsible for the increase in SWR. Subsequently repellent compounds were leached, at different rates, according to particle size. The impacts of this low severity grassland fire were limited in time, and are not considered a~threat to this ecosystem.