黄土高原不同植被恢复方式对土壤水分坡面变化的影响

在黄土高原大规模退耕还林(草)背景下,土地利用变化对土壤水分及其时空结构会产生极大影响。以坡面为研究对象,根据两种植被恢复类型(撂荒草地和人工刺槐林地)土壤水分坡面变化趋势的差异,探究不同植被恢复方式对土壤水分坡面空间结构影响。结果表明:所调查的两个区域(延安羊圈沟和长武烧盅湾)皆表现为人工刺槐林地坡平均土壤含水量显著低于撂荒草地坡;且人工刺槐林地坡的土壤水分的坡面差异性皆比撂荒草地坡低。虽然两种恢复类型的土壤水分沿坡底到坡顶皆呈现降低的趋势,但是该降低趋势在两种恢复类型间存在一定差异:撂荒草地坡土壤水分沿坡面的变化趋势随深度增加有加强的趋势,且总体上,长武烧盅湾撂荒草地坡土壤水分沿坡面变化趋势比延安羊圈沟更明显;相比之下,人工刺槐林地坡土壤水分沿坡面的变化趋势随深度增加有变弱的趋势,且该趋势明显比撂荒草地坡弱;两个地区刺槐林地坡土壤水分沿坡面变化趋势不存在明显差异。综上所述,虽然不同降雨背景下土壤水分会表现出一定差异,但土壤水分的坡面变化趋势及不同恢复方式对其影响是相似的,即人工刺槐林地坡对土壤水分的过度消耗不仅会导致土壤水分亏缺,而且削弱了土壤水分的坡面变化趋势;而撂荒草地对土壤水分及其空间结构的维持有相对积极的意义。通过分析不同植被恢复方式对土壤水分坡面变化趋势的影响,能够更深入的了解不同植被恢复方式的土壤水文效应,同时可为以坡面为单元的退耕还林中植被科学配置提供一定的参考。

Effects of different vegetation restoration types on the slope difference of soil water content in the Loess Plateau, China

Along with large-scale "Grain for Green" in the Loess Plateau of China, the land-use change significantly affected the soil water content (SWC) and its spatial-temporal pattern. In this study, we investigated the hill slopes, and the effects of different vegetation restoration types (abandoned farmlands and black locust forestlands) on the spatial pattern or heterogeneity of the SWC were explored based on the differences in the slope trends of SWC between two vegetation restoration types. The results indicated that the average SWC of black locust forestland slopes was significantly lower than that of the abandoned farmland slopes in both zones. Furthermore, slope differences in the SWC in the black locust forestlands were lower than those in the abandoned farmland slopes. Along the hill slopes, although the SWC both showed decreasing trends from the bottom to top in the two vegetation restoration types, both types also exhibited certain differences in their trends. The decreasing trend of SWC in the abandoned farmland increased with increasing soil depth. Furthermore, the decreasing trend of the abandoned farmland SWC was more obvious in Shaozhongwan of Chang Wu county than it was in Yangjuangou catchment of Yan an. In contrast, the decreasing trend of the black locust forestland decreased with increasing soil depth. Moreover, the decreasing trend in the black locust forestland from the bottom to top was lower than that of the abandoned farmland. In addition, the variation trend of the SWC along slopes in the black locust forestlands showed no obvious differences between the two zones. In summary, although the different rainfall background would lead to differences in SWC, its variation trend along with the hill slopes including the effects attributed to different vegetation restoration types were similar between the two zones. Moreover, the excessive consumption of soil water by the black locust forestland not only led to soil water deficits but also diminished the variation trend of SWC along the slopes. In contrast, the abandoned farmlands maintained relatively positive SWC and spatial patterns. By analyzing the effects of different vegetation restoration types on the variation trends of SWC along the slopes, the soil hydrological effect of different vegetation restoration methods could be enriched. Moreover, our findings could provide a useful reference for the scientific allocation of vegetation during the "Grain for Green" process based on the slopes.