KEYWORDS: Ecosystems, Vegetation, Carbon, Process modeling, Data modeling, Ecology, Geographic information systems, Satellites, Climatology, Near infrared
This study was conducted to develop an appropriate assessment technique to define impact of mountain-desert-oasis ecosystem on net primary productivity (NPP) in northern foothills of Tianshan Mountains. Geographic Information System (GIS) was used to estimate land use/land cover of the mountain, desert and oasis zones. An ecological process model was used to estimate NPP by using data entirely derived from satellite. The results show that landscape heterogeneity was important factor to affect NPP values in mountain-desert-oasis ecosystem. Simulated results indicated a total annual NPP of 1.5081×1014 g C for selected transect in 2002. There was 32.67% of total NPP which came from oasis areas, 28.16% from alpine meadows areas, 9.15% from forests area. Mean NPP values over the selected transect was 150.29 g C m-2 year-1 in 2002. However, NPP values varied greatly with different geography and season.
Heat, precipitation and humidity affect vegetation types and their distribution. However, their degree of effects is highly spatial and temporal dependent. When we study the major factors which affect vegetation cover, we need define a specific region and a time period. In order to study land cover and vegetation change in Xinjiang and to probe its driving force from 1992 to 2000, we analyzed sensitivity of land-cover to climate change using Remote Sensing (RS) and Geographic Information System (GIS) with multi-temporal NOAA/AVHRR NDVI images. Major factors we considered in this study were temperature, precipitation, humidity and their long-term and seasonal impacts on land cover and vegetation change. Results provided different sensitive levels as following: bare lands, partially vegetated lands, agriculture uses and water bodies. Concerning meteorological parameters impact we found in eastern Xinjiang humidity was more important than temperature and precipitation, in southern Xinjiang precipitation had more impact than temperature and humidity, and in both northern Xinjiang and Ili area temperature was more important than precipitation and humidity.
Substantial changes in land use and land cover dynamics have occurred during the last several decades in western China, which include deforestation, desert expansion and intensified land use due primarily to an increasing population, industrialization and agricultural development. These changes have had great impact on ecosystem functions at both local and regional scales. The Gobi Desert area near Zhangye City, Gansu Province, P.R. China has been blamed for the frequent occurrence of dust and sand storms in remote areas such as the Beijing and HuaBei regions. A study was conducted to quantify the land cover dynamics using remotely sensed images from the Landsat MSS, TM and ETM+ sensors for the region near Zhangye city within the Heihe River watershed. The regional landscape ecology for 1977, 1989 and 2002 was quantified using both traditional classification techniques as well as the continuous field method, the latter being a measure of land degradation severity. These remote sensing products were used to quantify the magnitude of the land use and land cover changes over 25 years. The results indicate that agricultural areas increased from 6% to 15% due to increased human activities. At the same time, other land use areas decreased because of conversion into agriculture lands. Land degradation in the region was obvious as evidenced by the increase in lower vegetative areas (0 to 10% fractional vegetation cover) and disappearance of high vegetative areas (90% or more). One of the most noticeable changes is that Zhangye city expanded rapidly during the last 25 years and practically doubled its urban territory.
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