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The combination of land preparation techniques and vegetation could be an effective way to combat soil degradation on vulnerable, steep slopes. Because of the scale of re-vegetation and man-made micro-topographies in regions of hillies and gullies, quantifying the effects of land preparation techniques, precipitation, and vegetation on runoff and soil erosion remains challenging, particularly in semi-arid areas. This study investigated the runoff and erosion characteristics associated with different land preparation techniques (level bench, level ditch, fish-scale pits and adverse-grade tableland) in combination with different tree species (i.e., Caragana microphylla, Pinus tabulaeformis, Armeniaca sibirica, Platycladus orientalis) using network and redundancy analyses (RDA). Network analysis was used to identify the factors (rainfall features, vegetation types, and land preparation techniques) influential in surface runoff and erosion, while RDA was used to focus on the relations between surface runoff, soil erosion, and all of the influencing factors. Our results suggested that land preparation technique could reduce runoff generation on steep slopes, a key process that affects soil loss, although the extent was affected largely by the influence of the combination of the design of the engineering structure and the shape of the vegetation canopy. Our study indicated that Network analysis and RDA are practical methods to quantify the interactions and co-dependencies between rainfall features and other critical factors (vegetation type and ecological engineering) on runoff and soil loss that were difficult to assess previously using classical regression.

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.

Dew plays a vital role in ecosystem processes in arid and semi-arid regions and is expected to be affected by climate warming. Infrared heater warming systems have been widely used to simulate climate warming effects on ecosystem. However, how this warming system affects dew formation has been long ignored and rarely addressed. In a typical alpine grassland ecosystem on the Northeast of the Tibetan Plateau, we measured dew amount and duration by artificial condensing surfaces, leaf wetness sensors and in situ dew formation on plants from 2012 to 2017. We also measured plant traits related to dew conditions. The results showed that (1) warming reduced the dew amount by 41.6%-91.1% depending on the measurement method, and reduced dew duration by 32.1 days compared to the ambient condition. (2) Different plant functional groups differed in dew formation. (3) Under the infrared warming treatment, the dew amount decreased with plant height, while under the ambient conditions, the dew amount showed the opposite trend. We concluded that warming with an infrared heater system greatly reduces dew formation, and if ignored, it may lead to overestimation of the effects of climate warming on ecosystem processes in climate change simulation studies.

Dew, as an important contribution of non-rainfall water (NRW), plays a vital role in ecosystem processes in arid and semi-arid regions and is expected to be affected by climate warming. Infrared heater warming systems have been widely used to simulate climate warming effects on ecosystems. However, how this warming system affects dew formation has been long ignored and rarely addressed. In a typical alpine grassland ecosystem on the northeast of the Tibetan Plateau, we measured dew amount and duration using three independent methods: artificial condensing surfaces, leaf wetness sensors and in situ dew formation on plants from 2012 to 2017. We also measured plant traits related to dew conditions. The results showed that (1) warming reduced the dew amount by 41.6%-91.1% depending on the measurement method, and reduced dew duration by 32.1 days compared to the ambient condition. (2) Different plant functional groups differed in dew formation. (3) Under the infrared warming treatment, the dew amount decreased with plant height, while under the ambient conditions, the dew amount showed the opposite trend. We concluded that warming with an infrared heater system greatly reduces dew formation, and if ignored, it may lead to overestimation of the effects of climate warming on ecosystem processes in climate change simulation studies.

Soil moisture plays a key role in vegetation restoration and ecosystem stability in arid and semiarid regions. The response of soil moisture to rainfall pulses is an important hydrological process, which is strongly influenced by land use during the implementation of vegetation restoration. In this study, vertical soil moisture variations of woodland (Pinus tabulaeformis), native grassland (Stipa bungeana), shrubland (Hippophea rhamnoides), cropland (Triticum aestivum) and artificial grassland (Onobrychis viciaefolia) in five soil profiles were monitored in a typical loess hilly area during the 2010 growing season. The results demonstrated that rainfall pulses directly affected soil moisture variation. A multi-peak pattern of soil moisture appeared during the growing season, notably in the surface soil layer. Meanwhile, the response of each vegetation type to rainfall was inconsistent, and a time-lag effect before reaching the peak value was detected, following each heavy rainfall event. The response duration of soil moisture, however, varied markedly with the size of rainfall events. Furthermore, higher soil water content was detected in grassland and shrubland. Woodland was characterized by relatively lower soil moisture values throughout the investigation period. Our research suggests that vegetation restoration efforts should give priority to grassland and shrubland at the research site. We suggest that more studies should be focused on the characteristics of community structure and spatial vegetation distribution on soil moisture dynamics, particularly within the grass and shrub ecosystems.