Study On The Change Of Net Primary Productivity And Response To Climate In Qilian Mountains In Recent 11 Years

As the best indicator that the growth condition of vegetation factors, regional or global carbon cycle of vegetation, vegetation NPP is monitoring the most effective indicators. This study is based on free data provided a resolution of 1 km, 500 m of MODIS(MOD15A2, MOD09A1) by NASA and combining with climate data form 2003 to 2013. Through the pursuit of pixels, the processing of information, the synthetic method, the slope analysis method, the mean maximum method and the correlation analysis, the different spatial and temporal variations of the annual, the growing season and the seasonal vegetation NPP and their relevances with the climatic factors were studied in Qilian Mountains nearly 11 years. Contribute to understand the land ulitity of study area and the status of the global climate and environment change of the carbon cycle. The results showed that:(1) The variation characteristics of vegetation NPP in Qilian Mountains from 2003 to 2013 years is obvious, and the values of vegetation NPP mainly concentrated in the growing season(from June to September), among summer vegetation NPP has the highest contribution rate, accounts for about 86.39% of the annual total NPP. The average of the vegetation NPP changing from 153.17 to 207.13 gC·m-2·a-1 showed a trend of fluctuations increase slowly from 2003 to 2013; the change trends of vegetation NPP from 2003 to 2013 exited more obvious differences in different seasons, that the biggest change rate of vegetation NPP happened in summer, and the change rates of vegetation NPP decreased in spring, autumn and winter; Mainly due to conditions of temperature, precipitation and snow melt, the vegetation in the whole growing season showed a trend of increase slowly from 2003 to 2013. In Qilian Mountains, the same time of growing heat and monsoon rains is suitable for vegetation growth, and the biggest increase is on June, secondly on July and August, difference in other months.(2) There are big differences of vegetation NPP in Qilian mountains from 2003 to 2013, that the average NPP accumulated maximum value in the eastern region, mostly changing from 200 to 400 gC·m-2·a-1, parts above 500 gC·m-2·a-1, but this accumulated from 100 to 400 gC·m-2·a-1 in central region, from 0 to 100 gC·m-2·a-1 in most of the western region, and the minimum value appeared in desert biomass mountain snow covered area. The vegetation NPP showed a trend of slow increase from 2003 to 2013 in Qilian Mountains, in addition the increase area of 9820 km2, accounting for about 21.04% of the total area of vegetation, the reduce area of 8225 km2, accounting for about 17.63% of the total area of vegetation. In general, the vegetation NPP has increased in Qilian Mountain area in recent 11 years, which indicated the ecological environment is improved. The inter-annual change trend of vegetation NPP existed regional differences in different seasons, among it is the highest in summer of the year, and the increase area of vegetation NPP is also the most.(3) The vegetation types have cultivated vegetation, broad-leaved forest, coniferous forest, scrub vegetation of vegetation of the vegetation NPP above 200 gC·m-2·a-1, and vegetation types have a meadow vegetation, swamp vegetation, grassland vegetation and other vegetation of the vegetation NPP changing from 100 to 200 gC·m-2·a-1, and the vegetation NPP of alpine vegetation and desert vegetation are less than 100 gC·m-2·a-1 The difference of vegetation NPP is related to the vegetation types, and the vegetation NPP of the woody plants is higher than herbaceous plants, and alpine vegetation and desert vegetation mainly suffer indignities restricted that moderate rainfall, which leading to a lower value of NPP.(4) The spring vegetation NPP limited by factor of precipitation is greater than temperature in Qilian Mountains, but the summer precipitation effect on vegetation NPP has weakened than the spring precipitation, by contrast, the influence of temperature to vegetation NPP increased slightly, and temperature mainly decides the growth condition of vegetation in autumn, high temperatures has promoting effect to the growth of vegetation, and temperature and precipitation are very weak in winter, besides snow cover on the vegetation beneficial to keep warm can make vegetation growth. Different vegetation types response to different levels of temperature and precipitation in the Qilian Mountains, which the responses of alpine vegetation, coniferous forest and planting vegetation degree to temperature significantly are greater than precipitation, but the responses of meadow, steppe and desert vegetation to precipitation are greater than temperature significantly, the responses of marsh vegetation and other vegetation types to climate are not obvious.