Evolution of ecosystem services in the Chinese Loess Plateau under climatic and land use changes

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 Carnegie-Ames-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. NPP was steady between 1990 and 2000, and then increased greatly after 2000. Ecosystem services are interlinked closely and complexly. Correlation analyses indicated a positive relationship between the difference in sediment export and water yield (r(2)=0.776**) from 1975 to 2008, with negative correlations between the difference of NPP and water yield (r(2)=-0.422**)/sediment export (r(2)=-0.240*) from 1990 to 2008. This, to some extent, implies that there are tradeoffs between the services of water yield and sediment control/NPP, and there is synergy between sediment control and NPP. Climatic and land use changes are the major drivers on ecosystem services fluctuation. Correlation analyses showed that the decrease of precipitation significantly hindered water yield (r(2)=0.980**) and sediment export (r(2)=0.791**). The increase of temperature exerted a slight negative influence on water yield (r(2)=-0350**). A spatial concordance existing between the 'cropland to grass/woodland' area and the high sediment control (r(2)=0313**)/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. (C) 2013 Elsevier B.V. All rights reserved.