Purpose

Soil moisture is the main factor limiting the growth of vegetation in semiarid areas. A large area of the Loess Plateau has undergone vegetation restoration efforts following an afforestation program initiated in 1999. Understanding how soil moisture responded to afforestation is important for long-term sustainability of ecological restoration measures in this area, especially because the tree planted were non-native species.

Methods

The effects on soil moisture content (SMC) of afforestation (Robinia pseudoacacia and Caragana korshinskii) were measured for different plantation ages (10, 20, 30, and 40 years) on the Loess Plateau. Meanwhile, a comparative with natural restoration grassland for the same age intervals was conducted.

Results

SMC of R. pseudoacacia plots on south-facing slopes and R. pseudoacacia and C. korshinskii plots on north-facing slopes was lowest when vegetation coverage was greatest after 20 and 30 years, respectively; SMC increases over time following natural grassland restoration; soil moisture consumption of all vegetation types was greater in the shallow soil layer (20–200 cm) than in the deep soil layer (200–500 cm) in each recovery period; and based on a three-way ANOVA, the interaction among afforestation year, vegetation type, and soil depth had significant effects on SMC.

Conclusion

In response to societal demand for wood, existing plantations should be thinned, with afforested lands located on north-facing slopes being thinned every 10–30 years (approximately 20 years).

中文翻译：

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黄土高原造林后土壤干燥趋势

目的

土壤水分是限制半干旱地区植被生长的主要因素。在1999年启动的造林计划之后，黄土高原的大部分地区都进行了植被恢复工作。了解土壤水分对造林的响应对于该地区生态恢复措施的长期可持续性至关重要，尤其是因为种植的树木不是本地物种。

方法

在黄土高原不同种植年龄（10、20、30和40年）下，测量了造林（刺槐和锦鸡儿）对土壤水分（SMC）的影响。同时，对同一年龄段的自然恢复草地进行了比较。

结果

在20年和30年后，当植被覆盖率最大时，朝南坡地的假刺槐地块的SMC，朝北坡地的假刺槐和C. korshinskii地块的SMC最低。天然草地恢复后，SMC随时间增加；在每个恢复时期，浅层土壤（20-200 cm）中所有植被类型的土壤水分消耗都大于深层土壤（200-500 cm）；基于三因素ANOVA，造林年限，植被类型和土壤深度之间的相互作用对SMC有显着影响。

结论

为了响应社会对木材的需求，应减少现有的人工林，并每10至30年（约20年）对位于北坡的绿化土地进行稀疏。