Global synthesis of the classifications, distributions, benefits and issues of terracing

Abstract

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.

Surface storm flow prediction on hillslopes based on topography and hydrologic connectivity

“…Here, a greater drainage density resulted in accelerated runoff during storm rainfall, while an increased number of terrace levels along the hillslope diminished the surface gradient, thereby delaying response times and attenuating peak flows (Hallema and Moussa, 2014). These results are in line with observations in many other parts of the world (Di Lazzaro et al, 2015;Wei et al, 2016). For example, Kovář et al (2016) found similar effects of agricultural terraces on storm runoff on a similar-sized hillslope in Bohemia (Czech Republic); however, they used the kinematic wave approximation to route storm flow because of lower rainfall intensities and a possibly greater relative contribution from subsurface flow compared to Mediterranean and semi-arid watersheds.…”

Decline in soil moisture due to vegetation restoration on the Loess Plateau of China

“…The Loess Plateau, characterized by the deepest loess deposits in the world, not only has a unique landscape but is also known for its fragile ecosystem, which is especially vulnerable to soil erosion . Although some measures, such as the construction of check dams (Zhao, Mu, Wen, Wang, & Gao, 2013) and terraces (Wei et al, 2016), have resulted in prominent reductions in soil erosion, vegetation restoration has also had an important influence on soil and water conservation (Lu et al, 2012). In addition, vegetation plays a critical role in the global carbon cycle and provides important mechanisms in terrestrial ecosystems that enhance their carbon sequestration capacity and decrease greenhouse gas emissions (Bonan, 2008;Jackson et al, 2008;Pan et al, 2011;Piao et al, 2009).…”

Effects of land preparation and plantings of vegetation on soil moisture in a hilly loess catchment in China

“…Land preparation techniques are the important methods for water conservation and ecosystem restoration along degraded slopes (S. L. Liu et al, ), particularly in the semiarid regions of the Loess Plateau (Chen et al, ; B. J. Fu et al, ). Specifically, land preparation techniques can recreate natural slopes and impede runoff during rainfall events by blocking potential water pathways (Diaz, Weatherhead, Knox, & Camacho, ), which can also result in changes to the soil conditions that may affect hydrological behavior (Wei et al, ). Studies revealed that the runoff coefficients of natural slopes are 2.79 to 11.50 times higher than those of slopes after land preparations (Darvishan, Homayounfar, & Sadeghi, ).…”

“…Before plantations, terrace engineering and land preparation techniques were widely used across hillslopes to reduce soil erosion, improve water conservation, and accelerate vegetation restoration (Mcdonagh, Lu, & Semalulu, ; Wei et al, ). Generally, studies across the globe indicate that 60–96% reductions in runoff and sediment compared with that of natural slopes can be achieved by using diverse land preparation measures (J. G. Liu, Li, Ouyang, Tam, & Chen, ; J. Wang et al, ).…”