4.2.2. Influence Factors of Five Main Land Use Types Conversion
Spatial econometric regression analysis demonstrated differences in the influence factors of transformation of the five main land use types in Sangzhi County. The direction and intensity of the 15 explanatory variables differed. The conversion of FL2CL was mainly affected by cultivated land protection policy, the conversion of GL2FL was the result of a positive succession of ecosystem and ecological environmental protection, the conversion of CL2FL was affected by socioeconomic factors and ecological environmental protection policy, the conversion of GL2CL was mainly affected by cultivated land protection policy, and the conversion of CL2URL was mainly affected by social and economic factors. Among the 15 explanatory variables, terrain, territorial, and traffic conditions have significant effects on the conversion of five land use types, and Dis2T has an especially notable effect on the conversion of the other four land use types, except for the conversion of GL2FL. The interpreted variables play a critical negative role in land use conversion in adjacent townships. Among the 15 explanatory variables, territorial and traffic conditions affect the degree of land use conversion in adjacent areas (
Table 6).
The analysis of the influence factors of five main land use types conversion is as follows:
1. Conversion of FL2CL
The conversion of FL2CL was significantly correlated with seven of the 15 explanatory variables. FL2CL was negatively correlated with Slope, Dis2NV, and Dis2TS at the 1% confidence level and with Dis2C and Pfe at the 5% confidence level. FL2CL was positively correlated with Dis2AV at the 1% confidence level and with Dis2T at the 5% confidence level (
Table 6). These findings indicate that the conversion from FL2CL is most significantly affected by slope. Generally, land with a slope greater than 25° is not suitable for cultivated land. The distance from different administrative centers has different effects on the direction and intensity of the conversion of FL2CL. The demand for agricultural land by villages and townships is lower than that of administrative villages and towns. The farther away a location is from the center of villages and townships and the nearer a location is to the center of administrative villages and towns, the more forest land was converted into cultivated land. The demand for agricultural land in county towns is higher than that in ordinary townships and towns. The closer a location is to the county government center, the more forest land is converted into cultivated land. The structure of public financial expenditure affects the conversion of land use. The more public financial expenditure is spent on townships and towns, the less forest land is converted into cultivated land.
The conversion from FL2CL was negatively correlated at the 5% confidence level. Thus, conversion from FL2CL in this township has a significant negative effect on the adjacent townships. W*Slope, W*Dis2TS, and W*Pop were significantly negatively correlated at the 1% confidence level, and W*Dis2T was significantly negatively correlated at the 10% confidence level. Thus, Slope, Dis2TS, Pop, and Dis2T had negative effects on the conversion of FL2CL in adjacent townships. W*Dis2NV, W*Dis2RR, W*Dis2CR, and W*Dis2W were significantly positively correlated at the 1% confidence level, and W*Dis2AV and W*Dis2VR were significantly positively correlated at the 5% confidence level; thus, the explanatory variables, such as Dis2NV, Dis2AV, Dis2VR, Dis2RR, Dis2CR, andDis2W, had positive effects on the conversion of FL2CL in adjacent townships.
2. Conversion of GL2FL
The conversion of GL2FL was significantly correlated with three of the 15 explanatory variables. The conversion of GL2FL was positively correlated with Dis2PR at the 1% confidence level, positively correlated with Dis2NV at the 10% confidence level, and negatively correlated with Dis2C at the 5% confidence level. The provincial highways 228,230, and 305 are distributed in the south of Sangzhi County and exhibit an east–west alignment. Transportation along the provincial highway is convenient, with far less grassland on both sides of the provincial road than cultivated land and forest land. Therefore, the closer a location is to the provincial road, the less grassland is converted into forest land, and vice versa. The closer the proximity to the center of the natural village is and the farther away from the edge of the forest a location is, the less grassland is converted into forest land, and vice versa. The conversion of grassland to forest land is closely related to the market. Generally speaking, the closer to the county town, the more land demand there is for orchards, seedling bases and so on. Thus, the closer the location to the county government center is, the more grassland conversion to forest land occurs. The conversion of GL2FL has the least influencing factors among the five main land use conversion types.
W*GL2FL was negatively correlated at the 1% confidence level, indicating that the area of grassland converted to forest land in this township has a significant negative effect on the adjacent townships. W*Dis2PR was significantly negatively correlated at the 5% confidence level, W*Dis2NV was significantly positively correlated at the 1% confidence level, and W*Dis2C was significantly positively correlated at the 5% confidence level, which indicated that the explanatory variables such as Dis2PR, Dis2NV, and Dis2C had spatial spillover effects on the conversion of GL2FL in adjacent townships.
3. Conversion of CL2FL
The conversion of cultivated land to forest land was significantly correlated with eight of the 15 explanatory variables. Conversion of CL2FL was negatively correlated with Slope, Dis2TS, and Pfe at the 1% confidence level, negatively correlated with Dis2T at the 5% confidence level, negatively correlated with Dis2RR at the 10% confidence level, and positively correlated with Dis2AV, Dis2VR, and Dis2CR at the 1% confidence level. These findings indicate that the higher the slope is, the less the cultivated land is distributed and the less the cultivated land is converted into forest land. Towns with lower public financial expenditure are relatively underdeveloped in terms of social and economic conditions that encourage farmers to leave their hometown for work in cities more often rather than cultivating the land, which may be abandoned and undergo CL2FL conversion. A common practice is using land use conversion to convert cultivated land into forest land and then FL2URL. Therefore, the closer a location is to the township government center, the town government center, or a rural road, the greater the amount of cultivated land is converted to forest land. Because a cultivation radius is necessary, the nearer a location is to the administrative village center and the nearer to the village road, the less cultivated land is converted to forest land, and vice versa. Transportation along the county road is convenient, and the conversion of CL2FL occurs less; thus, the conversion of CL2FL is positively correlated with the distance to the county road.
W*CL2FL was negatively correlated with CL2FL at the 1% confidence level; thus, the area of cultivated land converted to forest land in this township has a significant negative effect on the adjacent townships. Ten explanatory variables had spatial spillover effects on the conversion of CL2FL in adjacent townships. CL2FL was negatively correlated with W*Slope, W*Dis2TS, and W*Pfe at the 1% confidence level, with W*Dis2T at the 5% confidence level, and with W*Dis2PR at the 10% confidence level. CL2FL was positively correlated with W*Dis2VR, W*Dis2CR, and W*Dis2W at the 1% confidence level, with W*Dis2AV at the 5% confidence level, and with W*Elevation at the 10% confidence level. Dis2PR, Dis2W, and Elevation had no significant effect on the conversion of CL2FL but had a spatial spillover effect on the conversion of adjacent townships. Dis2NV and Dis2RR did not have a spatial spillover effect on adjacent townships.
4. Conversion of GL2CL
The conversion of grassland to cultivated land was significantly correlated with eleven of the 15 explanatory variables and was negatively correlated with Slope and Dis2RR at the 1% confidence level, with Dis2W, Dis2VR, Dis2PR, Pop, Urb, and Pfe at the 5% confidence level, and with Elevation and Dis2CR at the 10% confidence level. The conversion of GL2CL was positively correlated with Dis2T at the 1% confidence level. Generally, land with a slope greater than 25° is not suitable for cultivated land. The higher the slope is, the higher the elevation is and the less the conversion of grassland to cultivated land occurs. The shorter the distance to waters is and the more convenient transportation is, the lower the cost of cultivated land development, revitalization, and reclamation are, and more grassland is cultivated in land conversion. In Sangzhi County, the towns have fewer grassland resources, and the farther away a location is from the town government center, the more grassland is cultivated in land conversion. The conversion of grassland to cultivated land is closely related to the development, revitalization, and reclamation of cultivated land, which mainly occur in some low hilly areas with more grassland resources, such as townships and towns with lower population density, a lower urbanization rate, a less developed economy, and lower public financial expenditure. The conversion of grassland to cultivated land is mainly distributed in the west, east, and northeast of Sangzhi County. The main townships in the top five areas are Hekou, Yanwukou, Zhuyeping, Baishi, and Renchaoxi.
W*GL2CL is negatively correlated with GL2CL at the 1% confidence level, indicating that the area of grassland converted to cultivated land in this township has a significant negative effect on the adjacent townships. Nine explanatory variables have spatial spillover effects on the conversion of grassland to cultivated land in adjacent townships. GL2CL was negatively correlated with W*Slope and W*Pop at the 1% confidence level, with W*Dis2NV and W*Dis2TS at the 5% confidence level, and with W*Elevation and W*Urb at the 10% confidence level. GL2CL was positively correlated with W*Dis2CR and W*Dis2PR at the 1% confidence level and with W*Dis2RR at the 5% confidence level. Dis2NV and Dis2TS have no significant effect on the conversion of grassland to cultivated land but have a spatial spillover effect on the conversion of grassland to cultivated land in adjacent townships. Dis2VR, Dis2W, and Pfe have no spatial spillover effect on adjacent townships.
5. Conversion of CL2URL
This change was negatively correlated with nine of the 15 influence factors and was negatively correlated with Dis2C at the 1% confidence level, with Elevation and Dis2W at the 5% confidence level, and with Dis2RR at the 10% confidence level. The conversion of CL2URL was positively correlated with Dis2AV and Pop at the 1% confidence level, with Dis2TS and Dis2T at the 5% confidence level, and with Dis2PR at the 10% confidence level. The closer a location is to the county government center, the greater the demand for construction land is and the more cultivated land is converted into construction land. Urban and rural construction land is concentrated in low-elevation areas. The higher the elevation is, the less cultivated land is converted to urban and rural construction land. The closer the location is to waters, the greater the convenience of using water for production and living and the more the cultivated land is converted to urban and rural construction land. The shorter the distance from rural roads is, the more convenient transportation is and the more the cultivated land is converted to urban and rural construction land. The conversion of CL2URL was mainly distributed in the county town and surrounding towns. Therefore, the farther away a location is from the administrative village center, the township government center, and the town government center, the more the cultivated land is converted into urban and rural construction land. An increase in population increases the demand for urban and rural construction land, which leads to the continuous transformation of cultivated land with better physical and geographical conditions into construction land. Population has a significant effect on the transformation of cultivated land into urban and rural construction land. Due to the basic farmland dominating both sides of the provincial highway, land use conversion is strictly controlled; the closer a location is to a provincial highway, the less the cultivated land is converted into urban and rural construction land.
W*CL2URL is negatively correlated with CL2URL at the 5% confidence level, indicating that the conversion of cultivated land into urban and rural construction land area has a significant negative effect on adjacent townships. Four explanatory variables have spatial spillover effects on the conversion of cultivated land from adjacent townships to urban and rural construction land. W*Dis2C, W*Dis2T, and W*Urb were significantly positively correlated with CL2URL at the 1% confidence level, and W*Dis2RR was negatively correlated with CL2URL at the 10% confidence level. Urb has no significant effect on the conversion of CL2URL but has a spatial spillover effect on the conversion of adjacent townships. Elevation, Dis2W, Dis2AV, Dis2T, Dis2PR, and Pop have no spatial spillover effect on adjacent townships.