Terrain gradient response of landscape ecological environment to land use and land cover change in the hilly watershed in South China

There are abundant resources like climate, water, biological and tourism in the middle and upper reaches of the Ganjiang River (MU-GJR), which is an important ecological protection area in hilly areas of South China. The four periods of land use and land cover (LULC) data from 1980 to 2018 and DEM data are the main data support. The LULC change were analyzed with the area proportion, transfers chord diagram and change characteristics map, the response of ecological environment from LULC change was analyzed by using the landscape ecological environment quality (LEEQ) and contribution index. Then the terrain gradient was used to analyze the impact of LULC transfer on ecological environment under different terrain conditions. (1) The LULC characteristics in the study area show that was dominated by forest land and cultivated land (more than 90 %), various types of land transfer significantly from 2010 to 2018, especially the cultivated land, forest land and grassland. The stable type of LULC change was the most widely distributed, followed by the later change type (2010–2018) and mainly distributed in the flat valley, with the largest change range of cultivated land, forest land and grassland. (2) The LEEQ was generally well, but gradually deteriorates. The obvious change of LEEQ was found after 2010. The deterioration type of quality mostly occurs around the city, while the getting better type occurs in the transition area between the city and the mountains. (3) There are more deterioration categories than improvement categories of LULC transfer from 1980 to 2018. The improvement categories were mainly contributed by the transfer to other land to forest land and build-up land to other land. The deterioration categories were mainly contributed by the transfer of forest land to other land. (4) The impact of LULC change on the ecological environment decreases with the increase of elevation, slope and terrain position. There are differences in the impacts of various types of transfer on the ecological environment under the three gradients. In the elevation gradient, the improvement effect were dominant at −105–100 m and 200–500 m, and the deterioration effect were dominant at 100–200 m, 500–1000 m and 1000–2128 m. In the slope gradient, the improvement effect were dominant at 0–2°, 15–25° and 25–69.7°, and the deterioration effect were dominant at 2–6° and 6–15°. In terrain position gradient, improvement effect were dominant at 0–0.32, 0.32–0.51, 0.7–0.9 and 0.9–1.58, and deterioration effect were dominant at 0.51–0.7. Therefore, the specific conditions of different terrain gradients should be considered for land resource development in the middle and upper reaches of Ganjiang River region.