Legacy check dams and cascading hydrogeomorphic events as drivers of large wood dynamics and storage in a mountain stream

Cascades of hydrogeomorphic disturbances exert a major control on the spatial and temporal dynamics of large wood (LW) in mountain streams. This study examines how sequential disturbances including a debris flow in 2010 following extensive windthrow, a subsequent quiescent period (2010–2024), and an extreme flood in 2024 shaped LW storage in a steep headwater reach (∼2 km) of the Klepáčský Stream (the Hrubý Jeseník Mountains, Czechia) locally stabilized by unmaintained check dams constructed in 1960s. Repeated LW inventories (2016, 2023, 2025) revealed contrasting geomorphic impacts of the 2010 and 2024 events. The 2010 debris flow triggered substantial LW recruitment and deposition that persisted for more than a decade in the upper reach, demonstrating the long-term geomorphic memory of past disturbances. The subsequent quiescent period was characterized by a near-equilibrium between LW recruitment and decay, with localized increases in LW volume likely driven by the natural mortality of mature riparian trees. In contrast, the high magnitude 2024 flood resulted predominantly in LW depletion rather than recruitment, apart from localized input supplied by a small hillslope debris flow. These patterns indicate that the system currently operates within a source-limited stage of the LW cycle, where the legacy of earlier high-magnitude disturbances, combined with the present age structure of riparian forests, constrains contemporary recruitment and dictates the temporal trajectory of LW storage and mobility. Thirteen unmaintained check dams were assessed as secondary LW storage elements. Despite progressive structural degradation, they currently retain ∼29% of the total LW volume, underscoring their disproportionate influence on wood retention. Overall, the findings demonstrate that, under the prevailing disturbance regime, forest stand dynamics and legacy torrent-control structures interact to modulate LW recruitment, storage, and fluxes across decadal timescales. • Cascade of disturbances shaped large wood (LW) storage over two decades. • The 2010 debris flow caused major LW recruitment and long-term deposition. • The 2024 extreme flood led mainly to LW depletion, not new recruitment. • The system is now in a source-limited LW cycle due to past disturbance legacy. • 13 degraded check dams still retain ∼30% of LW, shaping wood dynamics.