| Solar radiation energy is the main energy for the physical and biological process on the earth surface, and it is the only energy source for plants to produce organic substance. Net Primary Production(NPP) refers to the amount of organic matter that plants accumulate per unit time and area. which is the remaining part of photosynthesis products deducting the organic substance for autotrophic breathing. NPP reflects the production capacity of phytocenosis. Its effect on the environment in desert is particularly significant. NPP is the most important material basis that maintains the vitality of desert ecosystem and perform various ecological functions. At the same time, it is also an indicator to evaluate the coordination between structures and functions of desert ecosystem, which then assesses the interaction between ecosystem and environment.Shapotou National Reserve locates in the northeast of Zhongwei of the Ningxia Hui Autonomous Region, the area neighboring southeast of Tengger desert’s border. In 1994, Shapotou is listed as a national reserve, being the habitation of psammophytic vegetation, sand-control engineering vegetation and other desert ecosystems together with rare endangered wild fauna and flora. It is a specific reserve in our country for the survival and reproduction of wild animals and plants in sand area. This Reserve is the demonstration area of works for preventing desertification. In recent years, our country and local governments of various levels all invest abundant hands and capital to protect ecological environment. This article aims at studying the estimation and analysis of NPP for Shapotou National Reserve, which provides a further insight of the vegetation distribution and the variation features of desert ecosystem in the protection zone,and how human activities,such as tourism, construction, production and daily life, affect vegetation coverage and ecosystem, hence contributing to the promotion of ecological environmental protection work.Based on improved CASA model and simplified calculation method of EET,, combining with LANSAT TM/ETM+/OLI image data and information from local meteorological stations in Shapotpu, this article, by studying some indirect parameters, such as photosynthetically active radiation, temperature stress factors, water stress factors and the maximum efficiency of light utilization, had assessed the NPP of every August in 1990, 1996, 2002, 2007, 2011 and 2014. Spatial-temporal variation analysis was performed for the results, and the environmental factors affecting the variation of NPP in desert ecosystem was also briefly explored. The research results manifest: 1.Water condition is the main factor to cause the inter-annual variation of summer NPP of arid area; 2.Based on the inter-annual variation of NPP, the NPP of Shapotou, under the condition of similar moisture, goes up as a whole, same as the trend of FPAR; 3.Vegetation coverage is the main factor to affect the space distribution of NPP in the reserve; 4.From the point of NPP’s space distribution pattern, the regions of high NPP value mainly concentrate in the principle activity areas for people’s production and living., and human activities is the key trigger leading NPP to change fast and obviously. |
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