The Vegetation NPP Dynamic Along The North South Transect Of East China (NSTEC) Based On IBIS Simulation

Climate change is increasingly affecting land surface processes of terrestrial ecosystem, which has become one of research focuses in terrestrial carbon cycle. IBIS (Integrated Biosphere Simulator) model integrates the surface and hydrological processes, terrestrial biogeochemical cycles, and vegetation dynamics into a whole model. It is widely used for contributing to be more in-depth analysis of the global carbon cycle affected by bio-physics, biogeochemistry and vegetation dynamics.By means of IBIS model, the spatial distributions and dynamic change of vegetation NPP along the North South Transect of East China (NSTEC) were explored in order to identify the temporal and spatial patterns of vegetation carbon source and sink, and to ascertain the driving factors underlying the changes of vegetation NPP. The research results will help to improve the understanding of the mechanism of climatic change impact on vegetation NPP variation, and further to project the likely changes in vegetation NPP under various scenarios of climate changes in the future.The main results were as follows:1) Spatial-temporal variation of vegetation NPP along the North South Transect of East ChinaIn general, the annual mean NPP value tends to decline with latitude during the period from 1957 to 2006. Among the various climate zones, the highest annual mean NPP value (761.7 gC/m2/Yr) was in the middle subtropics, and the lowest (193.6 gC/m2/Yr) was in the South Temperate Zone. Among the various vegetation types, the highest (773.2 gC/m2/Yr) was the tropical deciduous forest had, while the lowest(157.3gC/m2/Yr)was in the savanna.Inter-annual vegetation NPP during the past 50 years showed an increasing trend, with the annual NPP value ranging from 1.41Gt C/Yr to 1.72 Gt C/Yr and the average of 1.54 Gt C/Yr, which accounted for 80% of the whole country. The seasonal patterns of NPP were found to increase rapidly in summer and spring, with about 0.0014Gt C/Yr and 0.0012Gt C/Yr increased, accounting for 46.67% and 40% of its annual increment, while NPP increased slowly in autumn and winter, accounting for 13.33%. Monthly vegetation NPP variation was characterized with a single peak curve of normal distribution (the peak of 0.24Gt C/Yr), which occurred in June, followed by in July and May, and the lowersest in December.The annual mean NPP in an area basis along the NSTEC during the past 50 years indicated that 83.56% of the total area increased while 16.44% declined. The absolute increment of NPP occurred in the temperate evergreen conifer forest, dense shrubland and tropical deciduous forest, while the relative increment of NPP occurred in the boreal evergreen forest, temperate evergreen conifer forest and tundra.NPP patterns varied with vegetation types and temperature gradients. The most relative increment rate of the annual mean NPP of tropical evergreen forest and tropical deciduous forest occurred in the area where the annual average temperature (AAT) was 5~10℃. For the temperate evergreen conifer forest and the temperate deciduous forest, AATs were 10~15℃and 0~5℃, respectively. The AAT for the boreal evergreen forest was -10~0℃, while for mixed forest, AAT was 0~5℃. The AATs of the Savanna and grassland were 0~5℃and 15~20℃A, respectively. For dense shrubland and tundra, their AATs were 5~10℃and -10~0℃, respectively.2) Relationship between vegetation NPP changes and climate changes along the NSTEC. Both Annual and seasonal mean temperature showed an increasing trend during the past 50 years, with notable increment in the Norther areas. Precipitation increased in the northern part and central southern regions, while decreased significantly in the the central area of the NSTEC.Based on the spatial distribution of annual mean NPP affected by climate changes, it indicated that the temperature based NPP impact accounted for 28.14% of the total transect area, suggesting the temporal variation of NPP was significantly affected by AAT. Precipitation based NPP impact accounted for 5.54% of the total transect areas, showing that the temporal variation of NPP was significantly affected by annual precipitation. The combined temperature and precipitation based NPP impacts accounted for 2.07% of the total transect area, indicating the temporal variation of NPP were significantly affected by AAT and annual precipitation as well. The complex components accounted for 64.25%, which was affected by other factors in addition to AAT and annual precipitation. Temporal variation of NPP along the NSTEC was mainly controlled by temperature. The temporal variations of NPP in spring and summer were significantly correlated to its seasonal mean temperature. Annual precipitation had less influence on the temporal variation of NPP.3) Projections of NPP pattern change under climate change scenarios in futureAmong the four scenarios of climate changes in future, the maximum vegetation NPP of the NSTEC occurs under the CGCM3_SresA2, with the value of 1.64Gt C, follows by cenario CGCM3_SresB1 with the value of 1.62Gt C, and the lowest occurs under the HadCM3_HC3GG with the value of 1.55 Gt C.For the four scenarios, vegetation NPP of the NSTEC shows an increasing tendency, with the largest increment value of 0.0006Gt C/Yr under the CGCM3_SresA2 and the lowest incement value of 0.0001Gt C/Yr under the HadCM3_HC3GG.