For thousands of years, humans have created different types of terraces in different sloping conditions, meant to mitigate flood risks, reduce soil erosion and conserve water. These anthropogenic landscapes can be found in tropical and subtropical rainforests, deserts, and arid and semiarid mountains across the globe. Despite the long history, the roles of and the mechanisms by which terracing improves ecosystem services (ESs) remain poorly understood. Using literature synthesis and quantitative analysis, the worldwide types, distributions, major benefits and issues of terracing are presented in this review. A key terracing indicator, defined as the ratio of different ESs under terraced and non-terraced slopes (δ), was used to quantify the role of terracing in providing ESs. Our results indicated that ESs provided by terracing was generally positive because the mean values of δ were mostly greater than one. The most prominent role of terracing was found in erosion control (11.46 ± 2.34), followed by runoff reduction (2.60 ± 1.79), biomass accumulation (1.94 ± 0.59), soil water recharge (1.20 ± 0.23), and nutrient enhancement (1.20 ± 0.48). Terracing, to a lesser extent, could also enhance the survival rates of plant seedlings, promote ecosystem restoration, and increase crop yields. While slopes experiencing severe human disturbance (e.g., overgrazing and deforestation) can generally become more stable after terracing, negative effects of terracing may occur in poorly-designed or poorly-managed terraces. Among the reasons are the lack of environmental legislation, changes in traditional concepts and lifestyles of local people, as well as price decreases for agricultural products. All of these can accelerate terrace abandonment and degradation. In light of these findings, possible solutions regarding socio-economic changes and techniques to improve already degraded terraces are discussed.

A B S T R A C TTerracing has long been considered a strategy for soil and water conservation in many mountainous regions of the world. However, the effectiveness of terracing is limited by many factors, such as climate, soil properties, topography, land use, culture, demography and socioeconomic status. The aim of this critical review is to evaluate the roles of terracing on water erosion control in China. A meta-analysis of 601 runoff and 636 sediment observations involving a diversity of terrace structures was conducted. These 1237 observations involved level terraces, slope-separated terraces, slope terraces, zig terraces, fanya juu terraces and half-moon terraces, wide geographical locations within China, a diversity of land uses from forests to bare land, and a slopes ranging from 3°to 35°. The results confirmed that terracing significantly and positively affected water erosion control. In terms of different terrace structures, bench terraces were superior with respect to runoff and sediment reductions. Land use also played a crucial role in the efficiency of erosion control; terraces associated with tree crops and forests conserved the greatest amount of soil and water. In addition, a significant positive correlation between slope gradient (3°-15°and 16°-35°) and the effect of terracing on water erosion control was observed with the greatest decreases in water erosion occurred at slopes of 26°-35°and 11°-15°. This study revealed the effectiveness and variations of terracing with respect to water erosion control at the national scale and can serve as a scientific basis for land managers and decision makers. However with increasing urbanization, terrace abandonment increases as does the loss of place-based knowledge regarding terrace construction and maintenance.

Noncanonical nucleic acid structures, such as G-quadruplex (G4) and i-Motif (iM), have attracted increasing research interests because of their unique structural and binding properties, as well as their important biological activities. To date, thousands of small molecules that bind to varying G4/iM structures have been designed, synthesized and tested for diverse chemical and biological uses. Because of the huge potential and increasing research interests on G4-targeting ligands, we launched the first G4 ligand database G4LDB in 2013. Here, we report a new version, termed G4LDB 2.2 (http://www.g4ldb.com), with upgrades in both content and function. Currently, G4LDB2.2 contains >3200 G4/iM ligands, ∼28 500 activity entries and 79 G4–ligand docking models. In addition to G4 ligand library, we have also added a brand new iM ligand library to G4LDB 2.2, providing a comprehensive view of quadruplex nucleic acids. To further enhance user experience, we have also redesigned the user interface and optimized the database structure and retrieval mechanism. With these improvements, we anticipate that G4LDB 2.2 will serve as a comprehensive resource and useful research toolkit for researchers across wide scientific communities and accelerate discovering and validating better binders and drug candidates.