| Bailongjiang watershed (shorted as BLJ watershed) is located in the southeastern of Gansu province, as the ecozone among Qinghai-Tibet Plateau, Loess Plateau and the Qinba Mountainous Area, was the important water source and ecological barrier of the upper and middle Yangtze River, and also is significant for the maintenance of ecosystem stability for the Yangtze River Basin. Due to the study area is located in the transitional zone of ecological environment and the increasing population and the development of regional economy, it is facing severe problems, such as, natural disasters, vegetation deterioration, soil erosion, landslide, debris flow and so on. Vegetation net primary productivity (NPP) is an important indicator of the sustainable development of terrestrial ecosystem. The study of NPP in Bailongjiang watershed in Southern Gansu can provide scientific basis not only for the prevention and control of geological disasters but also for the improvement of ecological environment (vegetation management), it will be significant for local ecological sustainable development under global change.Based on MODIS NDVI and meteorological data, spatiotemporal changes of NPP of Bailongjiang watershed during 2000-2013 were simulated via the CAS A model. The relationships between NPP and temperature, precipitation, landslide, debris flow and ecological construction project were analyzed. Preliminary conclusions are listed as bellow:(1) The average annual NPP of Bailongjiang watershed was 500.59 gC·m-2·-1. The mean NPP of evergreen broadleaf forest was the largest one as 924.5 gC·m-2·-1, and the total NPP of deciduous forest was the largest one as 25.17×1011 gC·m-2·-1.(2) The NPP of Bailongjiang watershed in Southern Gansu was obviously changed over the latest 14 years. There was a growing trend with twists and turns. The changes of season total vegetation NPP were summer> spring> autumn> winter, and the total NPP of the four seasons increased gradually.(3) The ratio of the average annual NPP increased and reduced area was 4.92. As to the spatial characteristics of the annual average vegetation NPP, there were some conclusions as below:(a) There is an extremely significant increase of NPP in the area of the two sides of Bailongjiang, especially form Zhouqu County to Wudu District and its northern of the BLJ watershed and the two sides of Minjiang River, (b) The area of slightly increased distributed in the periphery of the moderate increased area, and the moderate increased area distributed in the periphery of the significant increased area, and formed with significant increased area as the core of regional distribution pattern, (c) The unchanged area mainly distributed in Diebu County, Western of Zhouqu County, Northern of Wen County, (d) The slightly reduced area mainly distributed in the southern of Wudu District, (e) The area of the significant reduced and moderate reduced were closely connected and mainly distributed in the suburban area of Wudu District.(4) During 2000-2013, the curve of the average annual NPP and total NPP of different vegetation types kept consistent basically and grown slowly. The vegetation NPP of different counties were also showed a trend of slow growth.(5) The correlation of NPP and precipitation (the average correlation coefficient was 0.33) was higher than that of temperature (the average correlation coefficient is 0.06); precipitation and temperature exerted various influences on different parts of the vegetation NPP.(6) With the increase of the average annual NPP of BLJ watershed, the distribution of landslide point and debris flow relatively reduced. A significant negative correlation with landslide and debris flow was presented. The Pearson correlation coefficient of vegetation NPP and landslides and debris flow were 0.796 and 0.783, respectively.(7) Vegetation NPP were greatly influenced by human activitiesover over the latest 14 years. With the decrease of slop farmland, forest and grass land enhanced, and vegetation coverage increased. While vegetation NPP increased area and formland land changed into grassland area was relatively consistent. Affected by urbanization, vegetation NPP of Wudu decreased. |
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