Changes in hydrological connectivity of the Ili River corridor and responses of vegetation patterns

River corridors constitute a critical linkage connecting terrestrial and aquatic ecosystems, and hydrological connectivity serves as a key determinant governing the hydrological processes as well as the structure and function of river corridor ecosystems, thereby providing important theoretical guidance for river corridor planning and management. This is particularly relevant for arid-region river corridors, where water scarcity and intensive engineering intervention often coexist and jointly shape ecosystem dynamics. Based on remote sensing data spanning 2013—2023, this study integrated an improved hydrological connectivity index, landscape pattern indices, and spatial analysis together with quantitative statistical methods to systematically examine the spatiotemporal evolution of hydrological connectivity and vegetation patterns along the Ili River corridor at the western end of the Tianshan Mountains, and to explore the relationship between hydrological connectivity and vegetation pattern evolution under the influence of anthropogenic infrastructure, including flood control and management projects and river embankments. The results indicate that from 2013 to 2023, the proportional coverage of grassland in the study area increased by 16.59%, whereas that of woodland decreased by 11.24%, such that the dominant vegetation cover type shifted from woodland to grassland; the aggregation indices of woodland and grassland declined from 78.40 and 71.16 to 71.13 and 65.18, respectively, indicating an intensification of landscape fragmentation. Hydrological connectivity in the study area increased overall during the study period, with the hydrological connectivity index rising by 13.13%; spatially, the proportion of area exhibiting increased connectivity exceeded that exhibiting decreased connectivity by 1.23%. Changes in hydrological connectivity and vegetation pattern exhibited divergent spatial responses: within areas where hydrological connectivity increased, woodland was converted to grassland and the vegetation pattern tended toward fragmentation, whereas within areas where hydrological connectivity decreased, both the direction of woodland-grassland conversion and the trend in vegetation pattern change were reversed. Changes in landscape indices within engineering-affected areas, as identified through a before-after control-impact analysis, revealed a pronounced fragmentation effect, underscoring that anthropogenic infrastructure exerts a measurable and spatially differentiated influence on riparian vegetation structure. These findings collectively reveal that the enhancement of hydrological connectivity within the Ili River corridor has not translated into improved vegetation conditions; rather, it has instead been accompanied by a divergent, direction-dependent relationship with vegetation pattern integrity, departing from the conventional assumption that greater connectivity uniformly benefits riparian ecosystems. This negative correlation appears to be closely associated with the physical scouring and erosive effects exerted by enhanced water flow on vegetation patches, as well as with the lateral disconnection and longitudinal flow concentration induced by flood control embankments. Notably, the magnitude of vegetation pattern change was not symmetric between the two types of areas, suggesting that the ecological consequences of hydrological connectivity alteration are asymmetric rather than proportionally mirrored. Collectively, these results provide a valuable scientific reference for guiding vegetation restoration along the Ili River corridor and for strengthening ecological management and control in engineering-affected areas, and further highlight the necessity of incorporating a moderate-connectivity perspective, rather than pursuing connectivity maximization alone, into future river corridor restoration and water resource management strategies applicable to arid inland river systems more broadly, particularly those subject to intensive flood control and water conservancy engineering.