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The vegetation covering land surface is main component of biosphere which is one of five significant spheres on the
earth. The vegetation plays a very important role on the natural environment conservation and improvement to keep
human being's living environment evergreen while the vegetation supplies many natural resources to human living and
development continuously. Under the background of global warming, vegetation is changing as climate changes. It is not
doubt that human activities have great effects on the vegetation dynamic. In general, there are two aspects of the
interaction between vegetation and climate, the climatic adaptation of vegetation and the vegetation feedback on climate.
On the base of the research on the long term vegetation growth dynamics, it can be found out the vegetation adaptation to
climate change. The dynamic change of vegetation is the direct indicator of the ecological environment changes.
Therefore, study on the dynamic change of vegetation will be very interest and useful. In this paper, the vegetation
change in special region of China will be described in detail.
In addition to the methods of the long term in-situ observation of vegetation, remote sensing technologies can also be
used to study the long time series vegetation dynamic. The widely used NDVI was often employed to monitor the status
of vegetation growth. Actually, NDVI can indicate the vigor and the fractional cover of vegetation effectively. So the
long time series of NDVI datasets are a very valuable data source supporting the study on the long term vegetation
dynamics. Since 1980, a series of NOAA satellites have been launched successfully, which have already supplied more
than 20 years NOAA/AVHRR satellites data.
In this paper, we selected Ningxia Hui autonomic region of China as the case study area and used 20 years pathfinder
AVHRR NDVI data to carry out the case study on the vegetation dynamics in order to further understand the phenomena
of 20 years vegetation dynamics of the whole Ningxia region. Ningxia Hui autonomic region is one of provinces in west
china. Ningxia is a small region with square area of about 66, 4000 km2. Ningxia has special land cover with irrigated
crop land in north and natural grass land in central and south. In addition to NDVI data, we also collected land cover and
land use data and administrative border vector data with the scale of 1:4,000,000 and other data. The results show that
(1)vegetation dynamic of Ningxia presents the characters of one season per year with the length of the growth season
from the first decade May to the middle decade October and the range of NDVI value 0.05-0.25; the season characters
vary with the local area; the max value of NDVI in the central dry area is only 0.2 and the date of reaching the peak of
time series NDVI in the irrigation area is the latest while that in the south mountain area is the earliest; the Helan
mountain area presents the characters of forest and the range of NDVI is narrower than those in the irrigation area and the south mountain area and higher in winter than those in two area above; in recent 18 years, the length of growth
season in whole Ningxia has prolonged one decade, mainly in spring one decade in advance.(2) from 1982 to 1999, the
trend of the whole Ningxia mean NDVI is increasing and presents the stable or better of vegetation growth; compared to
NDVI in 1980's, NDVI in 1990's has increased already and the anomaly of growth season mean NDVI is mainly
negative in 1980's while mainly positive in 1990's; NDVI in the central dry area is the lowest while NDVI in the Helan
mountain is the highest; the values of NDVI in the irrigation area, the Helan mountain area and the south mountain area
are higher than that of the whole Ningxia; the increasing trend of vegetation dynamic in the irrigation area, the south
mountain area and the central dry area is similar with the whole Ningxia while the trend in the Helan mountain area is
increasing from 1982-1988 but decreasing after 1988.
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