Dynamic monitoring of orchard disturbances in mountainous regions of Gannan using long time series data

The Gannan region is a key production area for navel oranges in China, where large-scale development of orchards has significantly contributed to soil erosion. Leveraging the Landsat image dataset on the Google Earth Engine (GEE) cloud computing platform, this study employs the existing Continuous Change Detection and Classification (CCDC) algorithm to analyse surface disturbances resulting from mountainous orchard development. By constructing a Normalised Difference Vegetation Index (NDVI)-time series trajectory, we effectively mapped and quantified these disturbances with high temporal precision. Key findings include: (1) The CCDC algorithm, which integrates texture and topographic features, effectively classifies land cover in the study area. It achieved overall classification accuracies of 95.84% in 2002 and 90.18% in 2023, with corresponding Kappa coefficients of 92.02% and 84.90%. Additionally, CCDC-based change detection of surface disturbances demonstrated an overall temporal accuracy of 85.77%, with an accuracy of 86.11% specifically for detecting disturbances associated with mountainous orchard development, confirming the algorithm’s reliability and applicability in this context. (2) Spatial analysis reveals that orchard expansion in the study area has progressed outward from the central region, primarily driven by the conversion of forest land. The most extensive development occurred in 2003. Additionally, our findings highlight the dual impact of orchard development on soil and water erosion: while initial land disturbance intensifies erosion, subsequent vegetation growth gradually alleviates these effects. These insights offer a new perspective on sustainable orchard management in the southern red soil region and provide valuable guidance for evaluating the environmental compliance of mountainous orchard development. Furthermore, they are highly relevant for authorities in assessing regulatory compliance and monitoring soil and water conservation efforts.