Analysis of Land Use Change in Poyang Lake County

(A) the acquisition of basic data of land use change

Using TM remote sensing images of 1985, 1995, 2000 and 2005, the land use types of 1 1 county around Poyang Lake were interpreted (Figure 6-3 to Figure 6-5 and Figure 6-6). Through the statistical function of attribute data of ArcMap software, important information such as area, perimeter and patch of various land use types are extracted from the map, and on this basis, the land use changes in Poyang Lake area are analyzed. See table 6- 15 for the results of remote sensing interpretation of land type areas.

Table 6- 15 Poyang Lake District 1985-2005 Land Use Statistics Unit: hm2

(b) Analysis of quantitative changes in land use

Analysis on the overall change of land use in Poyang Lake area in 2005.

Comparing the land use types of 1985, 1995, 2000 and 2005 (Table 6- 16), the overall change trend of land use in Poyang Lake area in recent 20 years is: 1998 "Returning farmland to lakes and building towns by immigrants". Residential areas and industrial and mining land increased, with an overall increase in 20 years/kloc-0 16059.43 hm2；; Waters and unused land decrease first and then increase; Grassland is decreasing year by year.

Table 6- 16 Proportion of Land Use Types in Poyang Lake Area in Different Years

Comparing 1985 with the change of land use types in 2005 (Table 6- 17), it is found that in the overall change of land use structure in the lake area, woodland, low coverage grassland and urban land have increased, while paddy field, high coverage grassland and bare land have decreased. Among them, the area of woodland, dry land, paddy field and shrub forest changes greatly, and the proportion of low coverage grassland and construction land changes greatly.

Table 6- 17 Comparison of Land Use Structure between Poyang Lake Area 1985 and 2005

A careful analysis of the changes of secondary types of land use in Poyang Lake area in recent 20 years shows that the overall change rate of cultivated land is 6%, of which paddy field has decreased by 1% and dry land has increased by 7%. Among the woodlands, some woodlands have increased by 13%, while others have decreased in different degrees, especially the shrubbery land has decreased by nearly 17%: the grassland has the largest change range, the high coverage grassland and middle coverage grassland are decreasing, and the low coverage grassland has increased, showing a general trend of reduction and degradation; Construction land, whether it is urban land, rural residential land or other construction land, is increasing in different degrees; Affected by the water level, the waters have been reduced to varying degrees; Among the unused land, bare land and bare gravel land are decreasing, while marshland is increasing, which is mainly affected by "returning farmland to lake" and water level.

2. 1985 ~ 2005 Analysis of land use structure change in Poyang Lake 1 1 county.

Comparing 1985 with the land use structure of counties in Poyang Lake area in 2005 (Table 6- 18), we can see that the cultivated land in Jiujiang County and Jinxian County has changed greatly; The forest land in duchang county and yugan county has changed greatly; Grassland Nanchang County, Jinxian County, duchang county and yugan county have changed greatly; The waters of Nanchang County, yugan county County and Poyang County have changed greatly. Residential areas and industrial and mining land in Xinjian County, De 'an County and Xing Zi County have changed greatly. The unused land in Jiujiang County, Hukou County and De 'an County has changed greatly. The changes are mainly concentrated in cultivated land, forest land, water area, residential area and industrial and mining land, while grassland and unused land change greatly, but the area of change is not much.

Table 6- 18 Comparison of Land Use Structure between Poyang Lake Area 1985 and 2005

sequential

Note: The "+"and "-"in the changing areas respectively indicate the areas increased or decreased compared with 1985 in 2005; "Change ratio" refers to the ratio of the change area of land use types from 1985 to the total area 1985.

(C) Analysis of spatial change of land use

The spatial change of land use is mainly manifested in the transformation between land use types, and the transfer matrix can comprehensively and concretely describe the structural characteristics of regional land use change and the direction of land use type change. The land use conversion matrix can not only provide the total area of various land use types in that year, as well as the area converted into other land feature types and the area converted into its own by other land feature types, but also provide detailed information on the internal conversion of land use in two periods, so as to facilitate the understanding of the loss direction of various land at the beginning of the study and the source and composition of various land use types at the end of the study.

Using GIS software, the spatial analysis extension module Geoprocessing is run in ArcView, and the two topic intersection programs are executed by viewing the Geoprocessing Wizard command in the vegetable meadow. This paper analyzes the spatial superposition of two vector maps of land use in different years, and processes the data of their attribute tables to count the land area transferred (inflow and outflow) in various land use types. In order to facilitate comparative analysis, this paper makes a statistical analysis of land use type transfer in Poyang Lake area in recent 20 years from two aspects.

Analysis on the general characteristics of land use type transfer in Poyang Lake area in 1 year. 20 years

According to the above processing, the land use change transfer matrix from Poyang Lake area 1985 to 2005 is obtained (Table 6- 19).

Table 6-19 Land use change transfer matrix in Poyang Lake area in 2005

Generally speaking, the main flow direction of cultivated land in Poyang Lake area is woodland (1. 5 1%), residential area, industrial and mining land (1. 40%) and waters (0. 67%). The main flow direction of woodland is cultivated land (4. 34%), residential areas and industrial and mining land (0. 58%). The main grassland flow is woodland (27. 4 1%) and cultivated land (10. 63%). The main water flow is cultivated land (3. 28%) and unused land (0. 50%). The main flow direction of residential land and industrial land is cultivated land (1. 4 1%) and waters (0. 44%). The main flow direction of unused land is water (0. 86%).

According to the inflow situation, the main conversion area is woodland (2. 40%), water area (1. 4 1%) and grassland (0. 82%). Cultivated land (2. 67%) and grassland (3. 8 1%) has been converted into forest land. Woodland (4. 33%), cultivated land (1. 14%) and waters (1. 30%) is mainly converted into grassland. Cultivated land (1. 58%) and grassland (0. 33%) is the main water area. Cultivated land (65,438+09.86%), forest land (4. 62%) and grassland (1.34%) are mainly converted into residential areas and industrial and mining land. Cultivated land (0. 38%) and waters (0. 86%) mainly converted into unused land.

2. Analysis on the characteristics of land use type transformation stage around Poyang Lake area 10.

Before 10 years (1985 ~ 1995), the land use change in Poyang Lake area was relatively small (Table 6- 20). The ratio of outflow to inflow of various land use types is less than 3%, and the largest conversion ratio is the conversion from water to cultivated land (4. 58%). Land use changes are mainly concentrated in cultivated land, urban and rural settlements, industrial and mining land and water areas. The conversion between land use types is not only small, but also relatively simple. If unused land and water are transformed into each other, cultivated land will be transformed into construction land, woodland, cultivated land and grassland.

Table 6-20 Transfer Matrix of Land Use Change in Poyang Lake Area 1985 to 1995

In recent 10 years, that is, 1995 to 2005, the land use in Poyang Lake area changed greatly (Table 6- 2 1). The ratio of outflow to inflow of each land use type is above 5%. Among all the conversions between first-class land types, the conversion ratio is greater than 1%, accounting for 33%. 33% of the total probability. The conversion rate from grassland to woodland is the largest (27. 29%), grassland to cultivated land (10. 90%) and the conversion of cultivated land into construction land (18. 2 1% of new construction land comes from cultivated land). The conversion between land use types is not only large in proportion, but also relatively complicated. Except for unused land, there is a transformation relationship between other types of land. The consequences of this change lead to more dispersed land use.

Table 6-2 1 Poyang Lake District 1995-2005 Land Use Change Transfer Matrix

A comprehensive analysis of the overall changes of land use in Poyang Lake area before 10, after 10 and during the whole study period shows that from 1985 to 1995, the area of mutual transformation between first-class land types totals 64,969.71hm2, accounting for 3.26% of the total area of the study area. From 1995 to 2005, the area transformed between the first-class land types totaled 226804.54hm2, accounting for 1 1.37% of the total area of the study area. In the whole research stage, the area of mutual transformation between first-class land types totaled 246804.98hm2, accounting for 10.87% of the total area of the study area. Statistics show that the land use change in Poyang Lake area in the recent 10 year is more drastic than that in the previous 10 year, which is three times that in the previous 10 year.

Comparing the change direction of primary land types before and after 10, from 1985 to 1995, cultivated land, woodland, residential areas and industrial and mining land are increasing, while grassland, water area and unused land are decreasing; From 1995 to 2005, woodland, water area, residential area, industrial and mining land and unused land are all increasing, while cultivated land and grassland are decreasing. This phenomenon coincides with the implementation of the project of "returning farmland to forests, returning farmland to lakes and building towns by immigrants" in Poyang Lake area since 1998, which is a typical case of human factors and social policies adjusting the direction of land use.

3. Analysis on the characteristics of secondary land use transfer in Poyang Lake area in recent 20 years.

Further analysis of the changes of secondary land use types in Poyang Lake area in recent 20 years shows that the land use types with the largest changes are sparse forest land (outflow ratio is 30.88%, inflow ratio is 23.97%), other forest land (outflow ratio is 60.5 1%, inflow ratio is 59.90%) and low coverage grassland (outflow ratio is 21)

Among the secondary cultivated land types, the main flow directions of paddy fields are dry land (2. 1 1%), sparse woodland (1.22%) and reservoir pit (0.54%). Paddy fields are mainly dry land (1.52%), open woodland (0.69%) and reservoir pit (0.79%). The main flow directions of dry land are paddy field (5.05%), sparse forest land (0.95%), forested land (0.8 1%), urban land (0.79%) and other construction land (0.78%). The conversion to dry land is mainly paddy field (6.62%), sparse forest land (0.69%), reservoir pit and pond (0.79%), sparse forest land (3.70%), forested land (1.36%), high coverage grassland (0.8 1%) and middle coverage grassland.

The land used in urban-rural fringe, industrial and mining areas and residential areas has increased by 16058.79hm2 in the past 20 years, which is 25.42% higher than that of 1985. Urban and rural land, industrial and mining land and residential land mainly flow to dry land, and the types of land flowing in mainly include paddy field, dry land, woodland and sparse woodland. The change proportions are urban land (outflow ratio is 1.54%, inflow ratio is 49.70%) and rural residential land (outflow ratio is 2.42%, inflow ratio is1.99%). Therefore, the construction land in urban-rural fringe, industrial and mining areas and residential areas mainly flows in from other land types, and rarely reverses.

In recent 20 years, the total land use change area of the first-class land type in Poyang Lake area is 246804.98hm2, accounting for 10.87% of the total area of the study area, which does not include the change between the second-class land types of the same land type in the first-class land type. Generally speaking, the degree of land use change in Poyang Lake area is relatively large.