The impacts of climate variation and land use/cover change on net primary productivity in the Tumen River Basin

In the context of climate variation and land use/cover change (LUCC), terrestrial ecosystem has substantially changed over the past few decades, which can be reflected by the variations in net primary productivity (NPP). The Tumen River Basin (TTRB), the center of Northeast Asia, was selected as the study site. On the basis of long-term series of normalized difference vegetation index (NDVI) data sets accompanied with a developed product of meteorological data, the optimized Carnegie Ames Stanford Approach (CASA) model and other common statistical methods as well as the approach of transition matrix were utilized to reveal the spatio-temporal changes of NPP and the effects of climate variation and LUCC on NPP from 1982 to 2012 in TTRB. The results indicated that throughout the past 31 years NPP exhibited a general upward trend on both spatial and temporal levels whereas the spatial downward trend accounting for 38% of the area and obvious fluctuations in the temporal trend plot of NPP variability collectively connoted the partial degradation of ecosystem in TTRB. The correlation analysis between NPP and climatic factors at spatial and temporal scales revealed that temperature affected local NPP greater than precipitation. The quantitative evaluation for the impact of LUCC on NPP underscored that national ecological policies were largely effective in the restoration of ecosystem. The more prominent role of climate variation on NPP than LUCC indicated that the new ecological strategy should pay more attention to the relations between NPP and climatic variables. Simultaneously, assistant measures should be added to form a holistic management scheme for the ecosystem in TTRB.