The effects of terracing and vegetation on soil moisture retention in a dry hilly catchment in China

In water-restricted erosive mountains environments, large-scale vegetation plantation and diverse terracing measures have been widely used as the most powerful ecological-restoration tools to control water erosion and improve local degraded ecosystems, further enhancing the complexity of terracing, vegetation, and soil water relationships. In this study, 70 sampling sites across different hillslopes were selected and used for biweekly soil water measurement in a typical loess hilly catchment of China. The most typical terracing measures (broad bench terraces-BBT, narrow bench terraces-NBT, level ditch terraces-LDT, counter-slope terraces-CST, and half-moon terraces-HMT) and introduced vegetation types (wild peach, apricot, arborvitae, poplar, and Chinese pine) were included in the study. Based on multi-site measurements, the effects of terracing and vegetation on the profile of soil moisture dynamics at a depth of 2 m were analyzed. Results show that terracing generally has a very positive role in soil water enhancement. Compared with slope risers, terracing can increase soil moisture by 0.87% (±0.82%) to 37.71% (±9.01%), which benefits ecological restoration. However, the effects of various terracing measures on soil water differed. BBT measures were the most powerful in soil water recharge, with an incremental ratio of 21.88%, which is 4.94, 5.95 and 4.21 times that of CST (5.19%), LDT (4.43%) and NBT (3.68%), respectively. The existence of different plant communities can increase the uncertainties and complexities of soil water status. Introduced trees and shrubs generally induce a greater reduction in soil water than do natural plants in similar environmental conditions. The few remaining original hillslopes covered by natural grasses can better preserve soil water, because of large differences in water use strategies between planted and natural species. Such findings are expected to provide important references for the proper selection of terracing and artificial vegetation toward enhancing the efficiency of water conservation and ecological restoration in dry and degraded regions.