Severe depletion of soil moisture following land-use changes for ecological restoration: Evidence from northern China

Abstract

Soil moisture is fundamental to ecosystem sustainability in arid and semi-arid regions, and characterizing temporal variations in soil moisture levels in response to changes in land use is important in assessing whether vegetation that has been restored as part of ecological restoration can be sustained. Such an assessment is presented here based on 78 recent publications focused on China’s initiatives at ecological restoration including the ‘Grain for Green’ programme and the ‘Three Norths Shelter Forest System’ project. The study analysed 1740 observations at 83 sites in eight provinces in northern China to determine temporal and spatial variations in soil moisture and the causes of those variations. Changes in land use for restoration of ecosystems led to severe depletion in soil moisture levels – as low as 9%, determined gravimetrically – in the 0–100cm layer of soil. The extent of depletion was influenced significantly by the choice of species for restoration (trees, shrubs, or grasses) and land use before the restoration. Deliberate restoration of vegetation may have the largest negative impact on soil moisture at sites that receive less than 600mm of annual precipitation and may be practical only when it exceeds 600mm. Afforestation decreased the levels of soil moisture significantly, whereas natural restoration had no significant effect on soil moisture. Therefore, natural restoration is the better option for maintaining the stability of water resources in arid and semi-arid regions. Afforestation would be a poor choice for places in which annual precipitation is close to or less than potential evapotranspiration but a better choice if annual precipitation is adequate. In planning revegetation initiatives, planners must understand that different environments support different vegetation types, and therefore require different solutions.