Land-use change can drive substantial environmental shifts, often resulting in altered plant diversity and community composition. Understanding these effects is essential for effective biodiversity conservation and land-management planning. However, few land-use studies integrate remote sensing with field-based surveys to assess long-term impacts on biodiversity at broad spatial scales. This study aimed to compare plant diversity and community composition across different land-use types, then evaluate the landscape-scale impacts of land-use changes over the past 20 years on environments in the Lianhuachi area, a suburban hillside in Taiwan. We conducted the study along the banks of the Houlong River and Huopei River from 2023 to 2025, and established thirty-five 20 m × 20 m plots across six different land-use types. Within each plot, 56 quadrats (1 m × 1 m) were surveyed. Species identity and coverage of all vascular plants were recorded. The results showed that a total of 319 plant species were detected, including 58 exotic and 10 agricultural species. Plant diversity was highest in bamboo and broad-leaved mixed forests, followed by betel nut plantations, while the lowest diversity was found in built-up areas. The coverage of exotic plant species exceeded 70% in all types of agricultural land except bamboo forests. Furthermore, redundancy analysis demonstrated that species composition differed significantly among land-use types, a similar pattern was observed for native herbaceous plants. Using historical aerial photos of 2000-2020, we found that the area of bamboo and broad-leaved mixed forests decreased by 15% during 2000- 2020. Abandoned farmlands and tea plantations increased substantially by 18% and 16%, respectively. Accompanying these land-use changes, landscape-level plant diversity declined by approximately 25%. Bamboo plantations formed through farming practices that create a more favorable environment for native plants, especially woody plants. However, bamboo plantations are different from natural forests in many aspects. The Lianhuachi area has been undergoing a transition in land-use practices associated with reduced plant diversity. If this trend continues, ecosystem services and functions in the region may also decline. The contribution of this study lies in revealing the impacts of human development on the landscape, providing a reference for ecological conservation and land-use planning.