The role of bilberry and Alpine lady-fern in soil formation within the Carpathian subalpine spruce forest stands

- Undergrowth vegetation (bilberry and Alpine lady fern) effect on soils was compared.
- Soils under both vegetation were acid and contained mobile forms of Fe and Al.
- B horizons under bilberry contained more C than analogous horizons under fern.
- SOM under fern had a high CH/CF ratio and much lower C/N ratio than under bilberry.
- Alpine lady fern dominance inhibits Fe, Al mobility and spodic horizon formation.

The effect of the understory vegetation in the spruce forests of the upper montane belt on soil properties was investigated. Three types of understory vegetation were included: dominant Alpine lady fern, dominant bilberry or a mix of the two species. All studied soils were derived from sandstone, had acidic soil reactions, were located under similar physiographic conditions and have been populated by coniferous forests with similar to today's understory species for more than thousand years. The effect of Alpine lady fern on soil organic matter accumulation and quality as well as the amount of total Fe and Al and the share of different forms of these elements (linked to humus, amorphous inorganic, silicate and non-silicate crystalline) in the total Fe and Al were compared to the effect of bilberry on the aforementioned soil features. This work aimed to assess if the understory vegetation effect was strong enough to influence pedogenic processes taking place in the soils. The main differences between the studied soil properties were related to organic matter transformation and Fe and Al mobility. They were caused by a different susceptibility of Alpine fern lady and bilberry plant residues to the decomposition. In the soils with bilberry dominance, there were greater amounts of less decomposed organic matter accumulated than in soils with Alpine lady fern dominance in which organic matter was characterised by a high humification degree, large CH/CF ratios and significantly lower C/N ratios. Bilberry in the understory caused the increased Fe and Al mobility. Therefore in soils under bilberry podsolization processes and spodic horizon formation occurred that was indicated by the values of Fe and Al mobility indices. In soils under Alpine lady fern influence, these indices values were lower and the podzolisation processes were not intensive enough to form spodic horizons. In these soils, regardless of the condition favouring podsolization (low pH, spruce forest), the mobility of Fe and Al was slowed. The presence of Alpine lady fern as a dominant understory species resulted in a decrease in solubility of metallo-organic complexes, probably because of the quicker oxidisation of litter then in soils under bilberry. The sites with a mix of Alpine lady fern and bilberry turned out to be in a transitional phase, which with time would probably change to bilberry or fern understory. The ecological role of the studied soils resulting from accumulation of inorganic amorphous Fe, which takes part in anion sorption, thus limiting leaching, was also emphasized.

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