The Influence of Ground Fires on the Properties and Erosion of Forest Soils in the Southern Urals (Bashkir State Nature Reserve)

Resumo

The influence of ground fires of different ages on the morphological, hydrophysical, and physicochemical properties and on the humus status of dark gray soils (Luvic Retic Greyzemic Someric Phaeozems (Loamic)), gray soils (Eutric Retisols (Loamic, Cutanic, Humic)), and gray-humus lithozems (Eutric Leptosols) was studied in the Bashkir State Nature Reserve in the Southern Urals Mountains. A decrease in the bulk density, increase in the field, capillary, and total water capacities of the soils, alkalization of the soil solution, and an increase in the contents of organic carbon, nitrogen, and ash elements take place in the upper horizons of the soils affected by fires. The humus state of these soils changes: its composition becomes more humate; the portion of free humic acids decreases, the contents of calcium-bound humic acids and non-hydrolyzable residue increase; and the enrichment of humus with nitrogen takes place. The development of post-pyrogenic erosion on steep (13°–15°) slopes leads to significant differentiation of the properties related to the micro- and mesorelief. In the first year after the fire, the soil layer of 7.1 ± 2.3 cm thick was washed out; in the following three years, the average soil loss amounted to 4.6 ± 1.3 cm per year. Taking into account the soil bulk density, this is equivalent to the annual soil loss of 150–400 and 360–540 t/ha, respectively. The burning of herbaceous vegetation and litter, as well as soil erosion and deposition of eroded material are important factors of current pedogenesis in pyrogenic soils.