Due to the lengthy historic land use by humans and the climate change characterized by warming and drying, the Loess Plateau has been plagued by ecosystem degradation for a long time. A series of ecological conservation projects launched since the 1970s altered the land use pattern greatly, and exerted a profound influence on the ecosystem services. Based on the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) and CarnegieAmes-Stanford Approach (CASA) models, we assessed the historical fluctuation of sediment control, water yield, and net primary production (NPP) in the Loess Plateau. The results showed that sediment retention was greatly consolidated indicated by the sharp decrease of sediment export. Water yield decreased at first and increased later. Both sediment export and water yield showed an increasing 'spatial homogenization' tendency during the period. the 'cropland to grass/woodland' area and the high sediment control (r 2 =0.313 ⁎⁎ )/NPP (r 2 =0.488 ⁎⁎ ) area indicated that the land use change from cropland to woodland/grassland significantly consolidated sediment control and NPP production. The observed spatio-temporal variation of ecosystem services and their correlations provide an operable criterion for land use management policies.

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Many studies have been conducted on ecosystem services and double counting is a frequent problem that causes uncertainty and poor reliability of estimating the value of ecosystem services. By referring to previous studies of ecosystem service valuation, our research has identified the basic causes of double counting. These include ambiguous definitions and inconsistent classifications of ecosystem services, poor understanding of ecosystem complexity, inadequate recognition of exclusiveness and complementarities of individual ecosystem services, spatio-temporal scale dependence of ecosystem services, and overlap and lack of cross-referencing between ecosystem service valuation methods. Measures for reducing double counting in ecosystem service valuation are proposed as follow: (1) identifying the spatiotemporal scales of ecosystem services; (2) valuing the final benefits obtained from ecosystem services; (3) establishing consistent classification systems for ecosystem services; and (4) selecting valuation methods appropriate for the study context.