A scale-optimized assessment of the spatiotemporal evolution of rice-crayfish field fragmentation in the Jianghan Plain, China.

Cultivated land fragmentation is an important structural feature of agricultural landscapes, with implications for agricultural organization, land-use efficiency, and spatial management. Understanding its spatiotemporal dynamics is therefore important for sustainable land management. In China's Jianghan Plain, the rapid expansion of integrated rice-crayfish farming is reshaping regional agricultural landscapes. This study investigates the spatiotemporal dynamics of rice-crayfish field fragmentation (RCFF) in the Jianghan Plain to characterize landscape evolution and support spatial optimization. Using land use data from 2013, 2018, and 2023, we evaluated multiple candidate grain sizes and analysis extents using landscape-metric responses, area information loss, and semi-variogram analysis. The results identified an optimal grain size of 120 m and an analysis extent of 1250 m, with the latter showing the lowest mean nugget-to-sill ratio (0.07) among the tested extents. A comprehensive fragmentation assessment model was then used to quantify the fragmentation level and its spatial and temporal variations. Results showed that RCFF decreased from 0.5730 to 0.4839 during 2013-2023, indicating an overall reduction in fragmentation. Rice-crayfish patches became more aggregated, showed greater spatial connectivity, and became more regular in shape. Significant spatial variation in RCFF was observed, with lower fragmentation levels in the central and southern regions and higher levels in the western and northern regions. This pattern was further supported by an increase in Global Moran's I from 0.469 to 0.613, indicating stronger spatial clustering. The sequential scale-selection procedure and fragmentation assessment framework provide a methodological basis for optimizing agricultural spatial patterns and supporting sustainable land resource management in rice-crayfish farming regions.