Effect of Wildfire on Forest Soils in Maleshevo–Pijanec Region

Abstract

For the last three decades, wildfires have been a significant problem for forests and forestry, causing great economic and environmental damage. They are common in Malesh and Pijanec region, as well as throughout the country. In 2021, a total of 192 wildfires were recorded in North Macedonia. The big wildfire in Maleshevo–Pijanec region occurred in the period 2-11 August 2021, estimated at 6,378 hectares of burned oak and pine forests area. The burnt area is mostly represented by Complex of Mollic and Umbric Leptosol, Regosol and Leptosol with 30.8% of the territory, followed by Complex of Mollic and Umbric Leptosol with 17.4%, Complex of Albic Livisol and Regosol with 11.2% and Chromic Luvisol on Saprolite with 9.4%. In this research, the effects of fire on biological, chemical and physical properties of soils are analysed. The most affected areas after the fire show increased biological activity and an abundance of symbiosis between plants, fungi and bacteria as a result of increased pH and release of nutrients from the ash. The fire significantly affected the soil fauna due to the burning of the root system, so it is severely disturbed up to 2 cm of depth, moderately disturbed up to 8 cm, partially disturbed up to 15 cm and weakly disturbed in the deeper soil layers. Food sources for soil fauna are significantly reduced. Occurrence of certain types of fungi has been recorded in the burned area. The increased biological activity and the increased amount of nutrients have enabled the accelerated multiplication of bacteria. The fire has decreased the capacity for cation exchange (CCE). Sandy soils show lowest CCE after the fire, of 100 meq/100 g of soil in pine stands and 180 meq/100 g of soil in oak stands. Increased soil acidity and increased soil biological activity indicate improved nitrification, especially in burnt acid soils. The fire decreased organic carbon (C) content in soils and caused structural changes in aliphatic compounds, while humic acids remained unchanged. Carbonated plant debris in large quantities are accumulated on the soil surface (to a depth of 2 cm), where it makes up 30-40% of the soil. Burnt soils are black coloured as a result of the coal-fired organic waste and the black ash created by incomplete combustion. Surface accumulated ash (up to 1.5 cm of depth) contains Ca, Mg, K, Si and P. Soil water repellency is present in the burned soils, but it is not strongly expressed and is not a limiting factor for future revitalisation activities. The aggregate composition is significantly changed to a depth of up to 15 cm, mainly through changes in porosity and water retention capacity. It can be concluded that it will take relatively long time for the soils to return to their original condition.