Spatial-temporal patterns of net primary production in Anji (China) between 1984 and 2014

Long-term and persistent human disturbances, such as the changes in land use types, have degraded the carbon fixation capacity of forest ecosystems. In Anji, China, the changes in land use types, such as the urbanization and increase of Moso bamboo forest, had changed the distribution of the broadleaf forest, needle leaf forest, and Moso bamboo forest, which in turn affected the net primary production (NPP) at the regional scale. This paper used the Carnegie-Ames-Stanford approach (CASA) model to estimate NPP in Anji during the period 1984-2014. The referenced NPP measured by eddy covariance technique was used to validate the simulated NPP, and the results show that the simulated NPP was consistent with the referenced NPP (R-2 = 0.90, p < 0.01, Root mean square error = 6 g C m(-2) year(-1)). During the period 1984-2014, the annual NPP fluctuated from year to year, but showed a generally increasing trend of 2.99 g C m(-2) year(-1). The total of the mean annual NPP in Anji was 1.16 Tg C year(-1), while the mean annual NPP per unit area was 613 g C m(-2) year(-1). The mean annual NPP per unit area for the Moso bamboo forest, broadleaf forest, needle leaf forest, and agricultural land was 739, 696, 642, and 616 g C m(-2) year(-1). The NPP significantly increased in more than half (57.3%) of the total area. The increase trends in solar radiation (8.1 MJ m(-2) year(-1)) and temperature (0.01 degrees C year(-1)), and the increase of Moso bamboo forest, which increased in 13.3% of the total area, were the major factors associated with the increase in NPP. However, the NPP significantly decreased in 10.7% of the area. This was caused by the urbanization, which increased in 6.5% of the total area. Our findings suggest that managers and policy makers should consider the impact of urbanization on NPP when expanding urban landscape.