陕北黄土区不同林地土壤干燥化效应

退耕还林还草工程虽然取得显著成效,但是加剧了区域土壤水分亏缺与土壤干燥化程度,同时制约着植被构建。选取陕西省吴起县金佛坪流域山杏、油松、刺槐、小叶杨和沙棘5种植被类型,对照荒草地。采用人工土钻法取样,分析不同植被类型0—10 m的土壤湿度特征和土壤干燥化效应。结果表明:各植被类型浅层和深层土壤水分均存在显著差异;与荒草地相比,各类林地均出现土壤水分过度消耗,其中刺槐林过耗量最大,山杏林最小;各林地均出现土壤干层,其中刺槐林、小叶杨林和山杏林土壤干层都已达到10 m以下,植被是深层土壤水分的主要影响因素。5类林地的土壤干燥化指数平均值39.26%,都远高于荒草地-9.57%。土壤干燥化强度为小叶杨(80.19%)刺槐(78.03%)沙棘(55.38%)山杏(37.94%)油松(32.34%),这是树种、林木大小和密度、林分生物量、树龄等生长指标综合作用的结果。在今后植被恢复中,应注意根据当地土壤水分条件,合理选择节水树种和合理设计林分结构,尽量避免或减轻土壤干化,维持较高的植被稳定性。

Soil desiccation effects under different vegetation types in the Loess Region of Northern Shaanxi

Although projects undertaken to return farmlands to forests and grasslands has achieved remarkable results, it has aggravated the soil water deficit, soil desiccation intensity, and has also restricted the vegetation restoration. Five different vegetation types (Armeniaca sibirica, Pinus tabuliformis, Robinia pseudoacacia, Populus simonii, Hippophae rhamnoides) and a grassland were selected to analyze the soil moisture and soil desiccation in 0-10 m soil profile. The results showed that the moisture differed significantly in the shallow soil, as well as deep soil between the vegetation types. Compared with the grassland, soil moisture was excessively consumed in all vegetation types, the Robinia pseudoacacia forest consuming the most, and the Armeniaca sibirica forest consuming the least. Soil desiccation appeared in all vegetations types, and the desiccated soil layer of Robinia pseudoacacia forest, Populus simonii forest, and Armeniaca sibirica forest had reached below 10 m, implying that the vegetation is the primary factor influencing the deep soil moisture. The average soil desiccation index of the five vegetation types was 39.26%, which is much higher than that of the grassland (-9.57%). The order of soil desiccation intensity was as follows:Populus simonii (80.19%) > Robinia pseudoacacia (78.03%) > Hippophae rhamnoides (55.38%) > Armeniaca sibirica(37.94%) > Pinus tabuliformis (32.34%). This result can be attributed to the comprehensive effect of tree species, tree size and density, stand biomass, tree age, etc. In the future, for restoration of vegetation, we should pay attention to the rational selection of water-saving tree species combined with a design for stand structure according to the local soil water conditions, so as to avoid or reduce soil desiccation and maintain high vegetation stability.