Post-fire variability of grey humic soils in thin-leaved grass pine forests of Western Transbaikalia

The article analyzes the post-fire dynamics of morphological, physical, and physicochemical properties of grey humic soils in pine forests growing on slopes in the lower reaches of the Khilok River in Western Transbaikalia. The impact of a low-intensity fire resulted in changes in color, composition, and properties in the upper organic accumulative horizon of the soil in the first year. It has been found that the main physical characteristics reflecting the soil response to fire are the particle size distribution and aggregate state. Immediately after the fire, as well as during the following years, changes in the content of fractions in the particle size distribution and microaggregate composition have been observed, indicating their post-fire dynamics. Structural characteristics of the soil have deteriorated and the degree of aggregation has decreased on young burnt areas. Post-fire changes in the structural properties of the soil in the first post-fire year were confirmed by the fracture of the surface of microaggregates observed during their submicrostructure examination. After 5 years since the fire, an improvement in soil structure and aggregate state has been noted. Chemical analysis has revealed post-fire increases in indicators of actual reaction of the environment, humus, nitrogen, exchangeable bases, CO2 carbonates, mobile forms of phosphorus and potassium in the upper horizons of profiles in the first year, with gradual changes over a 5-year period approaching values found in old-aged burnt areas. It is concluded that the grey humic soils are characterized by variability associated with the transformation of their composition and properties, especially in the first 5-year period after the impact of a low-intensity fire.