Abstract. 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 forest (FOR), 2. steppe close to the forest (STE), 3. disturbed forest with regrowth of trees (DWIR), and 4. disturbed forest showing no regrowth 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.

中文翻译：

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蒙古中部森林草原森林扰动后的水文土壤特性控制树木再生

摘要。蒙古中部森林草原是一个敏感的过渡带，通常受到伐木和森林火灾等干扰的影响。此外，加剧的干旱事件加剧了树木的压力，而树木无论如何都处于森林草原的干旱极限。气候变化会增加蒸散量，并减少不连续多年冻土的分布。这项研究的动机来自我们先前的观察，即林分在因火灾或伐木而受到干扰后的恢复方面显示出很大的差异。有时，根本没有树木再生长。由于可用水是该地区森林生长的主要限制因素，因此我们假设水文土壤性质的差异控制着森林的恢复方式。为了验证这一假设，我们分析了森林下的土壤特性，西伯利亚落叶松（Larix sibirica Ledeb）。），位于蒙古中部北部康艾山的森林草原上。我们区分4种植类：1，接近自然的EST（FOR），2 STE PPE靠近森林（STE），3 d isturbed森林无线个[R树egrowth（DWIR），和4 d isturbed森林没有 显示r树木生长（DNOR）。在野外描述了54个土壤剖面，并取样进行土壤化学，物理和水文分析。我们发现在DWIR和DNOR下土壤之间的土壤质地存在显着差异。沙土通常占土壤质地的主要部分，但与DNOR相比，DWIR下的土壤具有更多的淤泥和黏土。土壤pF曲线表明，DWIR下的土壤比DNOR下的土壤具有更高的植物有效田间持水量。此外，与DNOR下的土壤相比，DWIR下的土壤最上层的水力传导率更高。在DWIR和DNOR下土壤的化学性质没有显着差异。我们得出的结论是，干扰后树木再生的差异主要是由土壤水文特性引起的。高植物可用田间生产能力是半干旱条件下森林恢复的关键因素。在最上层土壤层中较高的水力传导性可以进一步支持树木的生长，因为它减少了蒸发损失以及落叶松树苗与草和草药争水的竞争。另一个重要因素是对人类的影响，尤其是在砍伐的森林地带放牧，这常常使幼苗无法生长，从而抑制了森林的恢复。在所有研究的受干扰位置（DWIR，DNOR）都没有永久冻土。因此，我们得出结论，尽管它确实有助于夏季的水利用，但它不是干扰后树长势的主要因素。因为它减少了蒸发损失，并减少了落叶松幼树苗与草和草药争夺水的竞争。另一个重要因素是对人类的影响，尤其是在砍伐的森林地带放牧，这常常使幼苗无法生长，从而抑制了森林的恢复。在所有研究的受干扰位置（DWIR，DNOR）都没有永久冻土。因此，我们得出结论，尽管它确实有助于夏季的水利用，但它不是干扰后树长势的主要因素。因为它减少了蒸发损失，并减少了落叶松幼树苗与草和草药争夺水的竞争。另一个重要因素是对人类的影响，尤其是在砍伐的森林地带放牧，这常常使幼苗无法生长，从而抑制了森林的恢复。在所有研究的受干扰位置（DWIR，DNOR）都没有永久冻土。因此，我们得出结论，尽管它确实有助于夏季的水利用，但它不是干扰后树长势的主要因素。