Monitoring the Spatial Dynamics of Mikania micrantha During the Flowering Season Using Multi-epoch UAV Imagery: A Case Study North of Liyu Lake, Hualien, Taiwan

Abstract. Mikania micrantha is one of the most aggressive invasive alien plant species in low-elevation landscapes of Taiwan. This study used fixed-wing UAV imagery to monitor its flowering-season distribution in a primary monitoring area north of Liyu Lake, Hualien County, eastern Taiwan. Rather than treating the dataset as a continuous annual time series, the analysis was based on three flowering-season observation epochs acquired on 14 January 2021, 7 December 2021, and 4 January 2024. UAV imagery was collected using an eBee X platform and processed in Pix4Dmapper Pro to generate high-resolution RGB orthomosaics with an average ground sampling distance of 3.08 cm/pixel. M. micrantha patches were delineated through manual image interpretation, and kernel density estimation (KDE) was applied to evaluate changes in spatial concentration and hotspot distribution. The interpreted infestation area decreased from 2,094.74 m² in the first epoch to 1,361.94 m² in the second, then increased to 1,799.09 m² in the third. KDE results showed a similar pattern, with persistent core infestation zones and renewed expansion in surrounding areas, including a new hotspot in the southeastern part of the monitoring area. These findings demonstrate the practical value of UAV-based monitoring for adaptive invasive plant management.