2015/05/13

Large vegetation restoration project: Terrace plots created on previously slopping hillsides (Image: Lulu Zhang/UNU-FLORES)

An article recently published by UNU-FLORES scholars Lulu Zhang and Dr. Kai Schwärzel draws attention to the potential consequences of large vegetation restoration projects on water supply in NW China.

Northwest China accounts for 32% of the Chinese territory. In this region, two vital environmental resources are seriously threatened. On the one hand, the soil in Northwest (NW) China suffers from serious erosion and degradation, strongly effecting agricultural output. On the other hand, water scarcity has long been the status-quo due to insufficient precipitation. In addition, rapid population growth and booming economic development have exerted additional pressure on the limited water available in the region, further intensifying the potential for conflict between different water users. Efforts to mitigate one problem are having a negative effect on the other, a project conducted by the Soil and Land Management Unit at UNU-FLORES shows. Addressing these unexpected externalities will require applying a nexus approach to the management of water and soil resources in the region.

(Image: Lulu Zhang/UNU-FLORES)

Soil erosion and land degradation in NW China are the result of low vegetation coverage and long-term intense agricultural activities, particularly in the Loess Plateau region. To improve the environmental quality and health, and increase vegetation coverage, restoration programmes, such as the Natural Forest Protection Programme (NFPP), the Grain for Green Programme (GGP), have been widely adopted in NW China. Two of the main measures used to stabilize soil and enhance land cover are afforestation and the conversion of steep slope land into woodlands. In addition to these vegetational changes, structural and engineering measures are being applied to increase crop yield. Sloping farmland is being levelled to terraces, as a terrace can effectively intercept the surface water and store it in soil for crop growth (shown the the feature image of this article). The construction of sediment-trapping dams is another favoured measure. Considered a “win – win” solution, the dams trap the sediment from upland and thereby reduce the amount of sediment in the river; simultaneously, when a dam is filled, fertile arable land for agriculture is created (see image to the right). A recent study titled “Impact of land-use changes on soil hydraulic properties of Calcaric Regosols on the Loess Plateau, NW China” showed that vegetation restoration has significantly improved the soil hydraulic properties that are responsible for water movement in the soil. The study also shows that, in comparison to generally accepted afforestation, grassland has proven to be more capable of enabling water infiltration and mobility. Tree growth can change the properties of soil in a way that inhibits water from moving through it, while grassland can provide a stable soil macropore system that enhances water mobility.

In addition to reducing soil erosion, vegetation restoration offers numerous other benefits for humankind, including alleviating flash floods, preventing sand and dust storms, and enlarging carbon sequestration capacity. However, implementation of environmental restoration measures to control soil erosion and improve farmland production on-site must also consider the off-site impact on water resources downstream. Water shortage and droughts are the main constraints in NW China. The river discharge in the middle reaches of the Yellow River has continuously declined over the last decades, considered largely a result of land use and climate change (see image below). Enlarging forest coverage (afforestation) will lead to a much higher consumption of water by tree growth; in turn, this will decrease water availability for groundwater recharge and water flow into the river system. As a result, such measures may have considerable adverse effects on the river discharge and the water supply security of a vast part of the region downstream.

(Image: Lulu Zhang/UNU-FLORES)

In light of these developments, forest development policy in water-limited areas has been intensely debated and increasingly questioned in China. Recently, a study titled “Different land management measures and climate change impacts on the runoff – A simple empirical method derived in a mesoscale catchment on the Loess Plateau” demonstrated that expanding an area of forest plantation and terrace without controlling for the effect on water resources can result in a significant decline of river discharge, and further aggravate the water crisis in this region of China. However, this study also provides evidence that, at a local scale, regulation/control of river discharge can be achieved by a direct modification in land management strategies and vegetation cover. A possibility to increase vegetation without significantly decreasing water supply is, for example, to establish more grassland instead of woodlands. Well-managed grassland can, like woodland, effectively prevent soil erosion; however, it consumes much less water.

The environmental restoration programmes implemented in NW China have made great success in reducing soil erosion and improving the degraded environment. However, implementation of these programmes did not take the nexus between the resources water and soil into consideration. Policy-makers should be aware that harmonizing water resource management and land-use management when developing policies for environmental restoration is crucial and urgently needed in NW China. Overprotection of one resource (e.g., soil) may result in a substantial decline in another resource (e.g., water) and may considerably damage regional economic development. To avoid such undesirable outcomes, the soil-water nexus – the inter-dependencies and interactions between soil and water resources management – should be considered in policy development.

Achieving balance and cooperation in the management of a multi-beneficial ecosystem is challenging. To improve the ongoing adaptive land-management policy in NW China, further research that takes a cross-sectoral, trans-boundary perspective to natural resources management at different spatial scales under changing environments is necessary. Without improved knowledge we may miss the chance for enhancing synergies and increase the risks of unnecessary trade-offs.

The studies and conclusions presented in this article are the results of a research project conducted by the Soil and Land-Use Management Unit at United Nations University Institute for Integrated Management of Material Fluxes and of Resources (UNU-FLORES). The project is executed in collaboration with the Chinese Academy of Forestry in Beijing and Technische Universiдt Dresden, and funded by the German Research Foundation (DFG).