Impact of Huanglongbing on Citrus Orchards: A Spatiotemporal Study in Xunwu County, Jiangxi Province

Due to human activities and changes in land use, the spatiotemporal pattern of citrus has undergone significant changes after the outbreak of Huanglongbing (HLB). We selected time-series Sentinel-2 images to delineate citrus orchard areas following the onset of HLB. This was conducted to extract citrus orchards in Xunwu County between 2017 and 2022. The spatial and temporal patterns and their influencing factors were investigated by spatial analysis. Results show (1) a notable decline in total citrus orchard area by 216.70 km2, primarily witnessed in orchards without insect-proof screens (IPS), shifting towards cropland, bush, and IPS areas. Contrastingly, citrus orchards with IPS exhibited a modest increase from 7.82 km2 to 111.39 km2, predominantly converting from areas lacking IPS, cropland, and bare land. (2) Spatial distribution patterns revealing a "cold in the south and hot in the north" trend. Orchards without IPS are concentrated in central and northern regions, while those with IPS are clustered predominantly in the north, with a recent shift towards the northeast. (3) Landscape analysis indicating a trend of fragmentation of citrus orchards, while a gradual dispersion of orchards without IPS and those with IPS showcased enhanced concentration and aggregation. (4) Orchards with IPS predominantly occupy regions characterized by an elevation ranging between 300 m and 400 m, primarily in the southeast, southwest, and southern directions. These areas exhibit slopes averaging between 10° and 15°, with surface temperatures ranging from 18 °C to 26 °C. Additionally, these orchards tend to be situated in proximity to impervious surfaces and roads.