Effect of gap size and gap shape on chemical soil characteristics in a Hungarian oak-hornbeam forest

Gap-cuttings in the framework of a continuous cover forestry system have an ecological effect on the chemical soil properties. The Pilis Gap Experiment (https://piliskiserlet.ecolres.hu/en) starting in 2019 in the Pilis Mountains in Hungary, investigates the effect of gap size and shape on soil properties in a mature oak-hornbeam forest. This study analyses the soil samples from 2023 regarding the effect of treatments on the pH value, the humus, and soil water content.

A full-factorial design was applied for gap size (small: 150 m² or large: 300 m²) and shape (circular or elongated) including an uncut control. For each treatment, six replicates were used in block design (five treatments, six replicates, altogether 30 plots). From each plot, two 20 cm deep soil samples were taken in the spring of 2023.

The statistical analysis concludes that the effect of the different treatments is not significant on the pH-value, on the humus content of the soil and the soil water content.

The pH value, measured in H₂O, ranges between 4.2 and 5.3 with a mean of 4.60. The values in the circular gaps are higher than the values in the elongated gaps, but the models are not significant. Due to less litter, the soil could be less acidic in circular gaps, where the tree crown is less able to reach the middle of the gap.

The result is similar in the humus content with a mean of 2.8 %. Here, the values in the elongated gaps are higher than the values in the circular gaps, but not significantly. This also can be explained by the amount of litter that reaches the soil. Therefore, with more litter more organic material can be degraded into humus.

Also, the soil water content did not significantly differ from each other. The values are higher in circular gaps than in the elongated gaps and the control. This can be explained by the lower evapotranspiration and interception effect in the circular gaps, where neither the roots nor the crowns of the neighbouring trees can reach the gap centre compared to the elongated ones.

We can conclude that gap-cutting in these dimensions does not modify the soil conditions. In circular gaps, a moderate soil water increment is detectable which can accelerate the regeneration processes.

This article was made in the frame of the project TKP2021-NKTA-43 which has been implemented with the support provided by the Ministry of Innovation and Technology of Hungary (successor: Ministry of Culture and Innovation of Hungary) from the National Research, Development and Innovation Fund, financed under the TKP2021-NKTA funding scheme.