Biodegradable facilitation mimics extend the window of opportunity for salt marsh establishment

Coastal wetlands provide critical ecosystem services and function as natural buffers against coastal hazards, yet they are increasingly degraded by human activities and climate change. Restoration is often constrained by strong hydrodynamic forcing and unstable sediment substrates, which narrow the "Window of Opportunity" (WoO) for seedling establishment. Three-dimensional (3D) biodegradable structures serve as Nature-based Solutions (NbS) by mimicking the facilitation functions of vegetation to mitigate these stressors, but their mechanistic role in mediating biophysical feedbacks and extending the WoO remains insufficiently understood. Here, we designed saltmarsh-specific 3D biodegradable structures that mimic key ecological facilitation traits and tailored them to local environmental conditions. Flume experiments quantified hydrodynamic attenuation and sediment stabilization mechanisms, which were subsequently validated in field experiments across natural hydrodynamic gradients. Results showed that aboveground structures attenuated flow velocity and reduced seedling bending, while belowground components enhanced sediment cohesion, elevated erosion thresholds, and stabilized substrates prior to root system development. Establishment success differed between seed sowing and seedling transplantation, with structure effectiveness varying across exposure gradients, demonstrating strong context dependence in WoO expansion. Overall, these findings demonstrate that biodegradable facilitation mimics can effectively extend the WoO for salt marsh establishment under variable hydrodynamic conditions.