Temporal Simulation And Spatial Study Of NPP And NEP Of Forest Ecosystem In Qinling Mountains Area Based On C-FIX Model

Qinling Mountains stand in the middle of China's inland and on the two sides of them are different climate types of the north and the south. The forest ecosystem of Qinling Mountain plays an leading role in carbon cycling in a large scale of area as carbon sink, which is of great essen in the condition of great climatic change and severe greenhouse effect. Base on the remote sensing data, meteorological data and other data from year 1998-2009 of Qinling Mountains forest ecosystem in Shaanxi Province, and with the C-FIX model, this paper simulated and estimated the NPP and carbon sink of vegatation of this area. According to the simulating results, this paper analyzed the NPP variation in both time and spacial zones of the ecosystem, evaluated the carbon sink capacity and impacts. Conclusions we draw are as follows.(1)NPP special distribution and variation of Qinling Mountains forest ecosystemThe mean value during the 12 years is 74.34 gC·m-2·a-1, the average annual amount is 54.65 TgC·a-1. Contrast with the beginning time of the study(1988), the average NPP shows an increment of 9.22 gC·m2·a-1 at the ending year(2009) and which of annual amount is 0.65 TgC·a-1. In 12 years, the NPP value is in a downward trend in the region mainly in the southern and northern boundary of Qinling Mountains, the southern Ankang area, Langao county and the western part of Hanzhoung city. Except for the few areas, the NPP values basically in an upward trend, to Western Lueyang County, Ningqiang County and the northern part of the study area boundary at the obvious. The growth of 10-15 gC·m-2·a-1 in the whole study area is the largest, which is 30.41%, and the area of growth is less than 10 gC·m-2·a-1 is the smallest, only 0.08%.(2) NPP time series variation of Qinling mountains forest ecosystemThe mean value of NPP during the 12 years ranges from 709.27-852.22 gC·m-2·a-1. Listing seasons by contributions to NPP value in a descending order is as follow: summer(30.23 TgC·a-1,55.33%)> spring(13.65 TgC·a-1,24.98%)> autumn(9.43 TgC·a-1, 17.27%)> winter(1.32 TgC·a-1,2.42%). Monthly mean value ranges from 5.10 to 150.90 gC·m-2·month-1, and reaches a peak in July(150.90 gC·m-2·a-1,19.49%) and a fall in the valley in January(5.10 gC·m-2·month-1,0.66%)(3) NPP distribution features of different vegetational forms in Qinling mountains forest ecosystemNPP per unit area in the study area is maximized in evergreen and deciduous broad-leaved mixed forest(804.45 gC·m-2·a-1), followed by evergreen broad-leaf forest(802.57 gC·m-2·a-1), then bushwood(797.65 gC·m-2·a-1); to the opposite, the minimum number shows in deciduous coniferous forest(588.40 gC·m-2·a-1), then meadow(711.56 gC·m-2·a-1), plowland(747.37 gC·m-2·a-1); which stay in middle level are broadleaved deciduous forest(788.56 gC·m-2·a-1), thick growth of grass(762.99 gC·m-2·a-1) and evergreen needleleaved forest(759.21 gC·m-2·a-1).(4) Responding of NPP towards climatic change in Qinling mountains forest ecosystemNPP value showed significant correlation to temperatures of the same month and the second month. Temperature of the same month impacted NPP to the most, meanwhile NPP generated a influence on temperature in a time lag. Temperature is a crucial factor of NPP changing and NPP value goes up with temperature.Also, NPP value showed significant correlation to precipitation of the same month and the second month while the precipitation of the third mounth shows little correlation on NPP value. Precipitation impacted NPP in the same way as temperature but not as severe as temperature.(5) NEP of Qinling mountains forest ecosystem and variation of carbon sink/carbon sourcesAt a average level of 1998?2009,99.99% of area in Qinling Mountains forest ecosystem acted as carbon sinks and only 0.01% as carbon sources, the capacity of carbon sink is 54.32 TgC·a-1. Mean NEP value of each season are spring(140.56 gC·m-2·a-1), summer(334.65 gC·m-1·a-1), autumn(80.66 gC·m-2·a-1), winter(-2.03 gC·m-2·a-1). The study area acted an carbon sink in spring, summer, autumn and the capacity of them is summer>spring>autumn; only in winter, the study area acted as carbon source. The average change rate during the continuous 12 years is 9.11%, it implies the carbon sink capacity of Qinling forest ecosystem is growing and is identical with expectation of this paper.