Linking Biodiversity, Vegetation Structure, and Safety of Flood Protection Dikes under Compound Climate Stressors

Along the rivers March and Thaya in eastern Austria, 80 km of flood protection dikes have been constructed and rehabilitated since 2006. These structures are predominantly setback flood defenses that only interact directly with river discharge during flood events. Embedded within a Natura 2000 floodplain landscape, the dikes represent linear infrastructure elements that fulfil a dual function: they provide technical flood protection while simultaneously forming important ecosystems at the interface between riparian forests, agricultural land and settlement boundaries. Vegetation cover on flood protection dikes plays a key role in slope stabilization and erosion control, particularly under extreme hydrometeorological conditions. Beyond their protective function, dikes act as linear green corridors that enhance landscape connectivity and provide habitats for insects and small fauna. Biodiversity on these structures is therefore a crucial factor influencing ecosystem resilience, while degraded vegetation cover increases vulnerability to erosion, drought stress, and mechanical failure during extreme events and climate change poses increasing challenges for flood protection dikes. Prolonged drought periods weaken vegetation cover and reduce root cohesion, whereas more frequent intense precipitation and flood events impose additional stress through surface runoff, saturation, and erosion. Understanding how vegetation management affects ecosystem functioning under these compound stressors is therefore essential for assessing future vulnerability and resilience of flood defense infrastructure. Within the framework of the CLIMD research project, this study investigates how different management strategies, including mowing regimes, removal or retention of cut biomass, grazing by cattle and horses, and partial abandonment of maintenance, affect vegetation structure, biodiversity, biomass production, and soil water and nutrient dynamics across 20 dike sites along the March-Thaya system. The study sites span a broad gradient of environmental settings, ranging from floodplain forests to intensively managed agricultural landscapes. Data collection includes biomass assessments, biodiversity surveys, soil analyses, and high-resolution measurements of soil moisture and temperature in different depths. By integrating field observations, management scenarios, and climate projections into a biomass-based modeling framework, the study aims to quantify safety factors of dike sections and identify how biodiversity-driven vegetation complexity can enhance resilience while reducing vulnerability to extreme weather events.