Evaluating waterbird migratory stopover habitat suitability in the Tumen River Estuary at the junction of China, North Korea and Russia using multi-source remote sensing imagery.

Over the past three decades, numerous waterbird habitats have experienced considerable degradation as a result of the persistent deterioration of wetland ecosystems. Habitat suitability evaluation is a critical tool for restoring and conserving waterbird habitats. However, few studies have specifically examined the effects of temporal land cover changes on the suitability of migratory stopover habitats for waterbirds in transboundary regions. Consequently, this study leverages multi-source remote sensing imagery, applies an object-oriented classification approach for precise land cover extraction, and integrates GIS technology to identify key parameters that directly influence migratory waterbird resting sites. Through the establishment of a habitat suitability evaluation framework, this study aims to reveal the spatial and temporal patterns of habitat suitability in the Tumen River Estuary (TRE) from 1992 to 2021. Results reveal significant recent conversions of forest and grassland areas in the study area of China and North Korea to drylands, while marsh wetlands have been transformed into both drylands and paddy fields. Compared to 1992, the configuration of grasslands, marsh wetlands, and built-up land showed increased complexity in 2021. Notably, North Korea's landscape exhibited the most pronounced and loosely distributed fragmentation trends. The regions with the highest habitat suitability levels within the study area showed a clear declining trend, particularly in the most suitable zones across China and North Korea. This trend corresponds with an expansion of unsuitable areas, largely attributed to increased anthropogenic impacts as the primary driver of habitat suitability decline. The assessment of Moran's I indices highlights a strong spatial autocorrelation in the habitat suitability index across the TRE. The framework model developed in this study is well-suited to assist governmental entities in assessing and protecting habitats vital for endangered waterbird conservation.