Objective The Loess Plateau is characterized by an arid climate, and soil water resources serve as a critical limiting factor for regional vegetation construction. The distribution characteristics and nfluencing factors of soil water under different afforestation modes remain unclear, requiring systematic comparative research. This study aims to investigate the differences in soil moisture dynamics between pure and mixed forests on the Loess Plateau and to identify their key influencing factors, thereby providing a theoretical basis for optimizing afforestation models and promoting the sustainable use of soil water resources.
Method A total of 1 453 sampling plots were compiled from 187 publications, including peer-reviewed journal articles and academic dissertations published between 1981 and 2024, focusing on soil moisture changes in pure and mixed forests on the Loess Plateau. The effects of major factors on soil moisture content were analyzed using the upper boundary line method and the Geodetector method.
Result (1) Soil moisture exhibited clear vertical differentiation between pure and mixed forests. In the 0-100 cm soil layer, pure forests had significantly higher soil moisture than mixed forests. No significant differences were observed in the 100-200 cm layer, whereas mixed forests showed significantly higher soil moisture in the 200-500 cm layer. (2) Soil moisture was influenced by multiple factors. In both afforestation models, soil moisture first increased and then decreased with increasing mean annual temperature and altitude. With increasing mean annual precipitation, soil moisture in pure forests increased initially and then stabilized, whereas it continuously increased in mixed forests. With increasing stand age, soil moisture in pure forests decreased initially and then remained stable, whereas in mixed forests it exhibited a decreasing-increasing trend. (3) Mean annual precipitation contributed the most to soil moisture variation in both pure and mixed forests (pure forests: 23.3%; mixed forests: 39.4%). The explanatory power of interactions between any two factors was greater than that of individual factors, with the interaction between mean annual precipitation and altitude showing the strongest effect (pure forests: 51.6%; mixed forests: 59.0%).
Conclusion Soil moisture differs significantly between pure and mixed forests on the Loess Plateau. Pure forests exhibit higher water-holding capacity in the 0-100 cm soil layer, whereas mixed forests show stronger water retention in deeper layers (200-500 cm), with no evident differences in the 100-200 cm layer. Mean annual precipitation is the dominant controlling factor, and its interaction with altitude provides the highest explanatory power. These findings suggest that both precipitation and topographic conditions should be jointly considered in afforestation planning to optimize forest structure and enhance the sustainable use of soil water resources.
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