Comparing National and High-Resolution Mangrove Mapping: A Case Study from Northern Australia

Mangroves are vital coastal ecosystems that provide shoreline protection, support biodiversity, and contribute to carbon sequestration. Monitoring their spatial dynamics requires reliable mapping techniques that account for both long-term changes and fine-scale variability. This study compares mangrove extent maps derived from national-scale Digital Earth Australia (Simpfendorfer et al.) Mangrove dataset (30 m resolution) for 1991 and 2022 with high-resolution mapping generated from georeferenced aerial photography (1m, 1991) and PlanetScope satellite imagery (3 m, 2022). The aim was to assess the differences in spatial extent sensitivity when quantifying mangrove extent changes over three decades in the coastal plains of the Mary River catchment, northern Australia, utilising the DEA dataset and High-resolution imagery. DEA Mangrove datasets were processed using thresholding (> 20% canopy cover) and converted to polylines, and the seaward extent was extracted. High-resolution maps were developed through manual digitisation and index-based classification. Comparative analysis has been conducted using the Wilcoxon and the Shapiro-Wilk tests. This analysis revealed that the DEA over and underestimated mangrove extent, particularly along narrow fringing zones and fragmented patches. High-resolution imagery captured localised erosion, regeneration, and extent contraction that were not visible in coarse-resolution data. The results highlight that the complementary value of combining DEA time-series products with regional-scale datasets or in situ observations can enhance mangrove monitoring. This integrated approach is particularly useful for mangrove conservation and management efforts in remote and challenging environments like northern Australia.