How does the conversion of land cover to urban use affect net primary productivity? A case study in Shenzhen city, China

China has made great economic achievements since the Reform and Opening policy implementation. Shenzhen as the representative city has experienced rapid urbanization and population growth. Urbanization strongly changes the nature of the land surface and has a large influence on the regional ecosystems. In the process of urbanization, fertile cropland and original forest are often destroyed. It is important to regularly monitor the effect of urbanization on the natural environment so as to allow us to control the encroachment to a reasonable extent. Net primary productivity (NPP) is an important productivity indicator of the ecosystem. We obtained land covers from Landsat TM images to quantify urbanization of Shenzhen between 1999 and 2005. We used the Moderate Resolution Imaging Spectroradiometer (MODIS-based) Normalized Difference Vegetation Index (NDVI) data, Landsat-based land cover map, meteorological data and other field data to drive the CASA productivity model and obtain net primary productivity for the study area. Finally, we estimated the effect of urban sprawl on regional NPP. The study on Landsat-based land cover maps indicated that a move towards urban is the most significant landscape change in Shenzhen City and urbanization has irreversibly transformed about 20.21% of Shenzhen's surface during 1999-2005. NPP loss mainly resulted from urbanization during 1999-2005 and totaled to 321.51 Gg of carbon, an average annual reduction of 45.93 Gg of carbon. For every square km of Shenzhen area, NPP was on average reduced by 0.0017 Gg of carbon during 1999-2005. The loss of NPP is equivalent to a reduction in absorption of 520.85 Gg CO2 and release of 385.81 Gg O-2, so urbanization has a large influence on the regional net primary productivity. (C) 2009 Elsevier B.V. All rights reserved.