How topographic factors regulate vegetation vigor in reservoir drawdown zones with different levels of hydrological disturbances?

• Quantifies effects of elevation, slope, and aspect on vegetation vigor under varying hydrological disturbance in reservoir drawdown zones. • Topographic factors interact nonlinearly, amplifying impacts on vegetation spatial patterns. • Slope limits recovery in steep, frequently flooded zones; aspect promotes vigor in stable microclimates. Topography plays a fundamental role in shaping vegetation distribution, community structure, and ecosystem functioning. This influence remains significant in hydrologically complex environments, particularly in reservoir drawdown zones (RDZs). However, how topographic factors drive spatial heterogeneity in vegetation across different levels of hydrological disturbance remains insufficiently understood. Clarifying these relationships is essential for interpreting ecological processes and informing vegetation restoration strategies in RDZs. This study selected three mid-channel bars (MCBs) within the Three Gorges Reservoir Region, each located in a distinct hydrological zone—namely, the fluctuating backwater zone, the transition zone between the fluctuating and permanent backwater zones, and the permanent backwater zone—to represent a gradient of hydrological disturbance. Using a combination of the geographic detector and geographically weighted regression models, we quantified the effects of elevation, slope, and aspect on the spatial distribution of vegetation vigor, measured by the Enhanced Vegetation Index (EVI), and analyzed their regional variations. The results showed that: 1) EVI varied significantly among hydrological disturbance zones, with vegetation vigor highest in the permanent backwater zone and lowest in the fluctuating backwater zone. 2) Elevation was the primary factor explaining EVI spatial variation; however, its interactions with slope and aspect produced nonlinear enhancement effects, intensifying the topographic control on vegetation distribution. 3) While elevation dominated overall, slope and aspect exhibited zone-specific regulatory roles: slope notably restricted vegetation recovery in steep areas, and aspect enhanced vegetation vigor in less-disturbed zones by improving local microclimatic conditions. Moreover, the influence of slope and aspect varied across disturbance zones, with aspect playing a stronger role in the permanent backwater zone, and slope exerting greater limiting effects in the fluctuating backwater zone. Although the study was conducted within a single reservoir system, the inclusion of multiple MCBs across distinct hydrological disturbance regimes, coupled with multi-year validation, supports the broader applicability of the findings to other RDZs with similar hydro-topographic conditions. These findings advance our understanding of how topographic factors shape vegetation spatial patterns under varying hydrological regimes and offer valuable insights for ecological restoration in RDZs.