NET PRIMARY PRODUCTIVITY DYNAMICS AND DRIVING FORCES IN GUANGZHOU CITY, CHINA

Urban expansion and land use/land cover change (LULCC), driven primarily by human activities, have significant influences on the environment; in addition, the two factors, together with climate change, have an impact on urban vegetation. This study explored spatiotemporal dynamics of net primary productivity (NPP) and calculated relative contributions of driving factors from 2001 to 2013 in Guangzhou City, China The effects of climate variables, urban expansion, and subsequent LULCC on interannual NPP variability were analyzed and compared. Results showed that NPP fluctuated and generally declined in Guangzhou over the 13-year study period, especially significant in inner suburbs (southern, eastern, and northern regions (p < 0.05), due to increasingly intensive human activities. LULCC, especially the reduction of cropland due to urban sprawl, resulted in significant NPP losses and positive relative impact index (RII) values, which indicated that LULCC played a negative role in NPP accumulation. More than 67.2% of NPP variability was controlled by LULCC in the whole area under study and mean RII values in all regions were higher than 50%, indicating that the influence of LULCC on NPP variability was greater than that of climate change. Particularly noteworthy is the fact that local climate change had a greater influence on NPP in forested areas (e.g. in the northeastern region), but it should not be ignored that RII kept increasing annually in this region and therefore more efforts paid in conservation were required. In conclusion, urban expansion and LULCC across the whole study area are resulted from human activities, and this, rather than climate change, was the primary driving force for the regional reduction in NPP.