Characteristics of Landscape Pattern Changes in Nandu River Basin and Its Dynamic Response Mechanism to Anthropogenic Disturbance from 1990 to 2020

To explore characteristics of landscape pattern changes in Nandu River basin and its dynamic response mechanism to anthropogenic disturbance, which is important for maintaining ecological protection and land use decision-making in the basin in context of free trade port construction．Based on land use cover data of 1990, 2000, 2010 and 2020, landscape pattern index, moving window method, hemeroby index, geo-information mapping and GIS spatial analysis were used to reveal dynamic changes of landscape pattern characteristics in Nandu River basin, and then relationship between landscape pattern and anthropogenic disturbance was discussed．Results indicated that, in the past 30 years, Nandu River basin showed a staggered landscape pattern dominated by forest land and cropland, with total area of forest land and cropland decreased by 69.95 km² and 43.56 km², respectively, and area of constructed increased by 62.45%．In Nandu River basin, overall landscape fragmentation increased, homogenization of landscape patches intensified and landscape diversity increased, and anthropogenic disturbance was main reason for drastic changes in landscape pattern of central urban agglomeration in Haikou City．Area of slight disturbance occupied the largest proportion of the area, followed by moderate and heavy disturbances; area of slight and strong disturbances increased significantly, area of moderate and heavy disturbances decreases significantly; spatial distribution pattern of anthropogenic disturbance was gradually increasing from southwest（natural landscape）to northeast（human landscape）．Area of "slight → light disturbance" and " heavy → slight disturbance" maps changed most significantly from 2000 to 2010 and from 2010 to 2020, occupying 26.79% and 11.99% of total area of transfer map, respectively．The transfer of low disturbance level to high disturbance level area was obvious．All disturbance areas were significantly correlation with the largest patch index（LPI）from 1990 to 2020．Overall anthropogenic disturbance in the Nandu River basin has increased, especially in Haikou City．Urbanization process is main factor for increase of anthropogenic disturbance, which needs to strengthen ecological environment management and monitoring in the basin．