Hydrological soil properties control tree regrowth after forest disturbance in the forest-steppe of central Mongolia

• Main Authors: Schneider, Florian, Klinge, Michael, Brodthuhn, Jannik, Peplau, Tino, Sauer, Daniela
• Format: Text
• Language: English
• Published: 2020
• Subjects: permafrost
• Online Access: https://doi.org/10.5194/soil-2020-52; https://soil.copernicus.org/preprints/soil-2020-52/

The central Mongolian forest-steppe is a sensitive ecotone, commonly affected by disturbances such as logging and forest fires. In addition, intensified drought events aggravate stress on the trees that are anyway at their drier limit in the forest-steppe. Climate change increases evapotranspiration and reduces the distribution of discontinuous permafrost. The motivation for this study came about through our previous observation that forest stands show great differences with respect to their recovery after disturbance by fire or logging. Sometimes, no regrowth of trees takes place at all. As water availability is the main limiting factor of forest growth in this region, we hypothesized that differences in hydrological soil properties control the forest-recovery pattern. To test this hypothesis, we analysed soil properties under forests, predominantly consisting of Siberian larch ( Larix sibirica Ledeb. ), in the forest-steppe of the northern Khangai Mountains in central Mongolia. We distinguished four vegetation categories: 1. near-natural for est (FOR), 2. ste ppe close to the forest (STE), 3. d isturbed forest wi th r egrowth of trees (DWIR), and 4. d isturbed forest showing no r egrowth of trees (DNOR). 54 soil profiles were described in the field and sampled for soil chemical, physical, and hydrological analysis. We found a significant difference in soil texture between soils under DWIR and DNOR. Sand generally dominated the soil texture, but soils under DWIR had more silt and clay compared to soils under DNOR. Soil pF curves showed that soils under DWIR had higher plant-available field capacity than soils under DNOR. In addition, hydraulic conductivity was higher in the uppermost horizons of soils under DWIR compared to soils under DNOR. Chemical properties of the soils under DWIR and DNOR showed no significant differences. We conclude that the differences in post-disturbance tree regrowth are mainly caused by soil hydrological properties. High plant-available field capacity is the key factor for forest recovery under semi-arid conditions. High hydraulic conductivity in the uppermost soil horizons can further support tree regrowth, because it reduces evaporation loss and competition of larch saplings with grasses and herbs for water. Another important factor is human impact, particularly grazing on cleared forest sites, which often keeps seedlings from growing and thus inhibits forest recovery. Permafrost was absent at all studied disturbed sites (DWIR, DNOR). We thus conclude that it is not a major factor for the post-disturbance tree-regrowth pattern, although it does contribute to water availability in summer.