Dynamic Change Of Cropland Percentage Coverage In Taizhou Region Of Jiangsu Province

With the growth of world population and development of science and technology, the changes of land use and cover caused by human beings have exerted great impacts on global ecosystem. They have changed the composition and pattern of ecosystems on local, regional and global scales. More studies on land use dynamics and driving mechanisms need to be carried out in order to reveal the rules of land use change on landscape scale, which are the theoretical foundation of scientific management and effective protection of natural resources.Cropland is one of the most important types of land use and also one of the most important types of landscape elements. Currently, many studies showed that cropland area in China is declining rapidly. As China has the highest population in the world, the decline in cropland area will bring far-reaching impacts on land resource security. Therefore, it is significant to gather the information of cropland resources and understand the change process of cropland in regional development.Taizhou located in the Yantze River Delta, which has dense settlements and developed agriculture in eastern China. The Yantze River Delta was one of the regions that have the highest urbanization level and growth rate of development. As one of the central cities in the Yantze River Delta, the dynamic of cropland in Taizhou is typical and representative in this region.To understand the change process of cropland and its rule, we examined the variation of cropland percentage coverage (CPC) in Taizhou region from 1995 to 2006 with a neighborhood analysis, using the Landsat TM images of 1995,2000 and 2006. The major findings included the following six points.(1) From 1995 to 2006, the reduction of the total cropland area was continuously accelerated. The results of landscape indices'calculation showed that the cropland in study area became more fragmented and heterogeneous and showed less connectivity.(2) The average relative amplitudes of most CPC zones in 2000-2006 were much greater than those in 1996-2000. And the average relative amplitude of CPC descended with increasing CPC from 0 to 80%, reached a minimum at 80%, then rised with increasing CPC in 80%-100%.(3) Except for 0-5% CPC zone, all the average absolute amplitudes of CPC zones during 2000-2006 were significantly greater than those during 1995-2000. The average absolute amplitude rose with increasing CPC in 0-55%, and then decreased a bit in 55%-80%. After 80%, it increased rapidly again.(4) The curves of pixel frequencies-CPC showed similar mono-peaked patterns in the 3 years, but the peak values and their corresponding CPC decreased from 1995 to 2006. The frequencies of landscape pixels increased in low and moderate CPC zones, reduced in high CPC zones, suggesting that the large cropland patches had been vanishing.(5) The results of cropland area changes showed that the 40%-80% CPC zones accounted for about 90% of the area changes of the cropland in the two periods, and the CPC of mode zones in 2000-2006 were smaller than those in 1996-2000. As the quantity was so small, the CPC zones beyond 40%-80% contributed little to the total cropland changes.(6) The area proportion of the 60%-80% CPC zones declined significantly, while that of the 40%-60% CPC zones increased rapidly. The reduction rate of CPC was prone to be increased in the areas with relatively dense settlements and roads.Overall, the total cropland area declined at continuously increased rate from 1995 to 2006 in study area. Meanwhile, landscape fragmentation and spatial heterogeneity increased year by year. The results suggested that both stability and area change rate of the cropland were closely related to local CPC, and the 40%-80% CPC zones, which contributed most to the total cropland change, needed main protection. As cropland is an important type of landscape element, its development contains a complex evolution of structure and function. Therefore, further researches are necessary on the mechanisms underlying the interaction among different landscape elements at different locations or on different scales.