The main tree species in the Siberian taiga are larch, Scots pine, fir, spruce, Siberian pine and birch. Lightning is more a frequent cause of wildfires in northern Siberia with anthropogenic activity causing wildfires further south, however central and eastern Siberia have been more affected overall by wildfires. They decrease soil quality (organic matter, structure, increased pH, conductivity) also impacting water retention, infiltration and runoff. The scientists wanted to look at the geochemical changes from the forest floor in more detail.

Existing research recorded soil temperature increases up to 700^◦C, with ash remaining on top of the charred soils. The ash contains silicates, oxides, phosphates, carbonates and sulphates but the components change depending on wildfire duration and severity. Ash deposits are lighter than soil so not always localised, with wind and water transporting different volumes across areas. This makes it harder to analyse.

They chose four sites on the banks of Yenisey River in Krasnoyarsk Krai, central Siberia based on wildfires in May 2022. They studied Scots pine with litter floor, larch with Carex and mixed vegetation floor, spruce with Carex and feather moss floor, and birch with Carex and mixed vegetation floor:

They noted that mean annual temperatures varied from 0 to 2.3^◦C between 2006-2022, with daily minimum and maximum varying between −44.4 and 36.9 ^◦C. The highest rain and snowfall were in the mountain taiga surrounding plot 2. Each wildfire was caused by human carelessness. They sampled the ash and forest floor layers including needles, leaves, twigs, cones, herbs and grasses at various stages of decomposition.

The samples were air dried in a lab, ground and sieved. They analysed the pH of the samples, then the organic matter using thermogravimetry. They examined the matter using an electron microscope and spectrometer. They completed statistical analysis using Statistica 10 software.

They found that the Scots pine and larch floors contained higher organic matter and lower mineral residue than the spruce and birch floors. Scots pine was the most acidic with larch, spruce and birch measured as moderately acidic. Ca, K, S, Mg and Al had the highest concentrations across the sites. K was highest for larch, Mg, Al Fe, Na, P, Ba for birch and Ca, S, Mn, Sr for spruce. Birch had the highest concentration of trace and ultra-trace elements but overall, the sites had Zn, B, Cr, Cu, and Ni with low concentrations of Cd, Mo, Co, Li, Sb, Sc, Sn, and Bi.

The highest loss of organic matter was in the birch floor but also a high loss was recorded near Scots pine stems due to the matter combusting at 200-460^◦C. Whilst the ash contains nutrients, it also contains toxic elements that can affect soil regeneration. They also found the highest water runoff and soil erosion up to 2 years after a wildfire. The scientific data is extremely useful for understanding the short term effects and the researchers recommend further longitudinal research to predict and understand the regrowth affected by ash deposits and soil contamination.

Shapchenkova, Olga A., Elena A. Kukavskaya, and Pavel Y. Groisman. 2024. “Fire-Induced Changes in Geochemical Elements of Forest Floor in Southern Siberia” Fire 7, no. 7: 243. https://doi.org/10.3390/fire7070243