Patch fragmentation accelerates alpine meadow degradation through altering soil water migration

The bidirectional coupling of hydrological and ecological processes is pivotal for maintaining ecosystem stability. Fragmented patch patterns are widespread in degraded alpine meadows worldwide, redistributing soil hydrothermal resources and potentially exacerbating ecosystem degradation. However, direct observational evidence regarding how alpine meadow fragmentation affects soil water migration remains limited, and little is known about the coupling mechanisms behind the “patch pattern–water migration–grassland degradation”. In this study, we first investigated key soil water migration processes based on centimeter-level inversion models derived from unmanned aerial vehicle (UAV) imagery and in situ measurements on the Qinghai-Tibetan Plateau (QTP). We then analyzed the effects and underlying mechanisms of fragmentation on soil water migration and discussed restoration implications for degraded alpine meadows. The results showed that: 1) patch fragmentation intensifies the vertical heterogeneity of soil water infiltration by altering soil bulk density and saturated hydraulic conductivity, and regulating precipitation percolation; 2) isolated vegetation patches (IV) with well-developed roots and favorable soil structure generate a soil water potential gradient with adjacent bare soil patches (BP), driving lateral soil water flow and sustaining high soil water storage; 3) the microtopography formed by IV and surrounding depressed BP enhances air circulation and near-surface water vapor exchange, thereby accelerating evapotranspiration. We conclude that patch fragmentation exacerbates soil water loss in alpine meadows, and priority should be given to vegetation rehabilitation on the BP surrounding IV.