Study On Spatial - Temporal Evolution Of Vegetation Coverage And Its Driving Factors In Shaanxi Province

The growth of vegetation follows certain rules. Vegetation coverage can improve reflect climate changes and developments in eco-environmental. Shaanxi Province is located in the Northwest Territories. It has many latitudes and geomorphic units, its precipitation and temperature between the territory of North and South has geographical difference. It also has complex and diverse vegetation types. Thus, the study on vegetation cover change in Shaanxi Province and its driving factors has important practical significance to the Protection of natural forest in southern Shaanxi, the Construction of standardization of agricultural vegetation in Guanzhong, the Vegetation construction in loess plateau of Northern Shaanxi and ecological restoration.In this paper, the SPOTNDVI data of 2000-2010, digital elevation model weather, socio-economic development, land cover and related statistical data are used to study nearly 11 years of space-time evolution of the vegetation cover characteristics of Shaanxi Province by the RS and GIS technology. The main driving factors were discussed in detail analysis. Here are the following conclusions:(1) The NDVI distribution of Shaanxi Province has strong spatial differences. NDVI mean has a gradually decreases from south to north. The descending order of seasonal changes of NDVI mean is summer-autumn-spring-winter. Changes during the year showed a single peak, with higher 6-9 months, most lush vegetation growth in August, and the lowest in February.(2) The rate of vegetation NDVI Shaanxi Province is 0.084/10a increments from 2000 to 2010. There were two leaps in 2000-2002 and 2008-2010, the growth rates were 7.81% and 6.35%. Changing of the seasons is the highest in summer and autumn, followed by the spring and the lowest in winter. The interannual variability of vegetation NDVI growth in different zones showed this trend:Northern Shaanxi> Guanzhong> Southern Shaanxi. In addition to the urban construction land, inter-annual and seasonal NDVI for the remaining land cover types were on an increasing trend.(3) The vegetation of Shaanxi Province has staged change characteristics:where from 2000 to 2005, the NDVI increasing, decreasing ratio was 73.86%and 26.14%, an increase of more than 2005 to 2010. The linear trend of the interannual vegetation NDVI has evident spatial variation:reduced area was less than 7%and mainly distributed in the downtown area of Xi’an City, Weinan City. The proportion of the obviously improved regional was close to 10%, concentrated in the Yan’an city in Central and Eastern, North-West and North-East of Guanzhong region. From a seasonal perspective, the improved vegetation concentrated in summer and autumn and lowest in winter. The interannual fluctuation characteristics of NDVI are clear:"less volatile southern and northern fluctuations, both high and low volatility" features. High range centrally located in North Shaanxi and Guanzhong region, area reached 7281.96km2, accounting for 3.54% of the total, is striped mainly along the Eastern North Shaanxi and also included Heyang County, Chengcheng of Northeast of Guanzhong and so on. The low volatility area scattered in southern Shaanxi, the proportion is less than 0.6%.(4) Every elevation range of Shaanxi Province showed an increasing trend, 700-1100m and 1100m-1500m NDVI are the highest growth area, growth rate are 23.88% and 23.48%, and the most dramatic changes in NDVI. Vegetation activity in high altitude is least obvious. During the study period, the NDVI vegetation increases with the increase of increase, range of 7-15 ° and 15-25 ° share the maximum NDVI area, the proportion of area is 27.06% and 27.78%. The NDVI within 25-35 ° slope land, within the maximum slope of the linear trend of NDVI values, improving trend is most obvious,35° above the regional vegetation is relatively stable. Population and GDP notably impacts on vegetation NDVI. The NDVI showed degradation when the population> 5,000 people/km2 and GDP> 5000 Yuan.(5) Climate warming and drying trend of Shaanxi Province from 2000 to 2010 is clear. Decline in precipitation is at the rate of 13.49/10a, over the same period, temperature is rising at the rate of 0.809/10a. There are positive and negative correlations between Vegetation NDVI and climatic factors. The linear relationship is not significant. Impact of climatic factors is reflected that it can control the growth law of vegetation. NDVI vegetation response to precipitation and temperature was not at the same period, and the rainfall lagging is more evident. In addition, the main vegetation changes are attributed to human activity. The effects of ecological reconstruction project are evident, such as afforestation, returning farmland to forest, the development of fruit and forest in the plain and so on.