Analysis of land system change and its spatial agglomeration pattern in sandy area of northern Yanchi during past 25 years

Abstract: For discussing the change of land system and spatial agglomeration pattern in sandy area of northern Yanchi during the past 25 years, land use vector data from the interpretation of TM remote sensing images (in the years of 1989, 1995, 2000 and 2007) and ZY-1 O2C satellite image (in the year of 2012) were used as the data sources. The spatial-temporal dynamic change characteristics were comprehensively analyzed by building land use change network model and information entropy model. The former model was used to quantify some elements such as direction, status and trend, which could effectively characterize some significant aspects associated with land change; the latter model was used to describe and express the order degree of the land use system. Furthermore, the spatial agglomeration pattern was expressed by using the GIS density mapping method. Results showed that tremendous changes had taken place in the past 25 years for the land use types in sandy area of northern Yanchi. Cultivated land and unused land showed a drastic reduction, while woodland and grassland expanded significantly, and human activities in the study area were in a positive way to gradually optimize and influence the evolution of landscape pattern Different degrees of mutual transformation appeared between various land use types, among which grassland, woodland, cultivated land and unused land played key roles in the whole network of land use change, and thus determined the characteristics of land use change in the sandy area. The land system change process showed an evolution trend from "balanced" type, "weak balanced" type to "not balanced" type during the past 25 years. Information entropy and equilibrium degree of land use structure was in a fluctuation drop situation, while advantage degree was in a fluctuation upward trend; overall, the land use system of the study area was developing towards a relatively orderly state. From the perspective of spatial analysis, the regions near woodland and cultivated land were hot spots of land use change and the spatial agglomeration features of land use change were different at different periods. Taking the year of 1995 as the demarcation point, the hot zone of land use change was distributed from northeast to southwest direction from 1989 to 1995, however, the hot spot gradually transferred from west to east of the whole region from 1995 to 2012. Through the restoration of vegetation, the ecological environment in the study area had been improved to a large extent, and a land use pattern dominated by grassland and woodland had been formed gradually, effectively reducing the risk of desertification. These conclusions could provide a scientific basis for the research on the mechanism of land use change, sustainable use of land resources, as well as optimization of sandy habitat environment.