Estimating forest attributes has traditionally been limited to resource intensive field campaigns. To improve existing methods and to better detail mangrove attributes, field campaigns were carried out to quantify mangrove (Avicennia marina) stem and pneumatophore attributes and evaluate allometric variability using a 3D field scanner and sampling approach. Focused on different estuarine typologies, an analysis of mangrove attributes demonstrated lower variance for stem diameter and tree height in Drowned River Valleys (DRVs) and Large Barrier Estuaries (LBEs), but higher variance in Intermittently Open/Closed Estuaries (IOCEs). The proportion of forest width attributed to non-stem elements, such as branches and leaves, was found to be 10 to 40 times higher than the total stem width (at 50-100% of the forest height) for DRVs and LBEs, and 200 to 700 times higher (at 0-50% of the forest height) for Small Barrier Estuaries (SBEs) and IOCEs. In contrast to earlier studies, pneumatophore growth was linked to 56 ± 7% of the tidal range in DRVs, LBEs, and SBEs, and 98 ± 19% of the tidal range in IOCEs. The identified variability in Avicennia marina attributes demonstrated that the simple root-stem-canopy model often used in wave modelling of individual mangroves, does not accurately represent Avicennia marina forests across estuary typologies. New allometric design equations were developed to guide researchers towards calculating tree heights and projected surface areas using stem diameters and densities representative of the estuary typology. These results highlight the importance of estuarine dynamics when developing mangrove models (e.g., for carbon sequestration or coastal protection) and management plans.

Nature-based solutions are increasingly recognized as effective and multifunctional components of climate-resilient flood protection. While tropical mangroves have received substantial attention, temperate riparian forests, particularly willow systems, offer comparable wave attenuation and biodiversity benefits, yet remain understudied. This study assesses the ecological and protective value of three types of willow floodplain forests: a so-called wild-grown willow forest, a pollard willow forest, and a willow plantation. Using field data from the Biesbosch National Park (the Netherlands), we quantified forest structure, ground-dwelling invertebrate diversity, and modelled wave attenuation under storm scenarios. Structural complexity and biodiversity were highest in the wild-grown forest, with significantly greater invertebrate order richness, larger body sizes, and more heterogeneous canopy architecture. The pollard forest showed the highest wave attenuation efficiency due to their dense, low-lying crown structures. The plantation forest showed lower values across both axes. We integrated these findings into a trade-off model evaluating ecological value, flood protection efficiency, and a 50-year simple cost analysis of each forest type as a hybrid solution alongside traditional dikes. While the pollard forest is the most spatially efficient for flood attenuation, the wild-grown system provides greater ecological value at lower lifecycle cost. Our results underscore the importance of tailoring hybrid flood defense strategies to local priorities - balancing biodiversity, spatial constraints, and economic feasibility. The framework developed here can inform ecosystem-based design in delta regions worldwide, supporting integrated climate adaptation that aligns safety with ecological resilience.

Mangroves are increasingly recognised for their ecosystem services, including their capacity to store carbon and adapt to climate pressures by stabilising shorelines and acting as storm barriers. To quantify these services, relevant parameters such as mangrove biomass and drag coefficients have been calculated using allometric equations fitted to field measurements of physical mangrove attributes. However, previous research to quantify mangrove attributes has involved time-consuming hand measurements and long processing times associated with terrestrial laser scanning (TLS). To more efficiently capture and process mangrove attributes, such as the density, diameter, height, and projected area of stems and roots, a novel method for collecting mangrove field data using TLS was developed. Recorded TLS data were compared to field measurements conducted in 12 Avicennia marina forests across 10 estuaries and 4 unique estuary typologies. The results demonstrated the reliable estimation of mangrove attributes using TLS and revealed a link between these attributes and estuarine geomorphology. Mangrove stems were accurately identified in all estuary typologies, with attribute estimations more accurate for forests in Drowned River Valleys (DRVs). A sensitivity analysis revealed that 10–20 trees for DRVs and 35–45 trees for barrier estuaries require point cloud processing to characterise a forest area of 400–1300 m² and to achieve convergent stem diameter and tree height results. The method presented herein offers an efficient way to quantify aboveground stem and root attributes and the surface area of mangrove trees. This data can be used to characterise mangrove forests worldwide and provide fundamental attributes for quantifying ecosystem services.

Mangrove forests reduce wave attack along tropical and sub-tropical coastlines, decreasing the wave loads acting on coastal protection structures. Mangrove belts seaward of embankments can therefore lower their required height and decrease their slope protection thickness. Wave reduction by mangroves depends on tree frontal surface area and stability against storms, but both aspects are often oversimplified or neglected in coastal protection designs. Here we present a framework to evaluate how mangrove belts influence embankment designs, including mangrove growth over time and failure by overturning and trunk breakage. This methodology is applied to Sonneratia apetala mangroves seaward of embankments in Bangladesh, considering forest widths between 10 and 1000 m (cross-shore). For water depths of 5 m, wave reduction by mangrove forests narrower than 1 km mostly affects the slope protection and the bank erodibility, whereas the required embankment height is less influenced by mangroves. Sonneratia apetala trees experience a relative maximum in wave attenuation capacity at 10 years age, due to their large submerged canopy area. Once trees are more than 20 years old, their canopy is emergent, and most wave attenuation is caused by trunk and roots. Canopy emergence exposes mangroves to wind loads, which are much larger than wave loads, and can cause tree failure during cyclones. These results stress the importance of including tree surface area and stability models when predicting coastal protection by mangroves.

Mangrove forests are increasingly valued as wave-attenuating buffers in coastal flood defence strategies. However, as mangroves are vulnerable to wave-induced erosion, this raises the question, how can the stability of these protective mangrove forests be promoted? To address this question, we investigate how mangrove dynamics in a microtidal system can be related to different types of foreshores. We used remote sensing to investigate mangrove fringe stability over multiple years in relation to intertidal mudflat width (i.e., emerged at low tide) and the presence stability of cheniers, which are sand bodies on top of muddy foreshores that are characteristic for eroding coastlines. In addition, we investigated local and short-term foreshore effects by measuring wave propagation across two cross-shore transects, one with a mudflat and chenier and one with a deeper tidal flat foreshore. The satellite images (Sentinel-2) revealed that mangrove dynamics over multiple years and seasons were related to chenier presence and stability. Without a chenier, a mudflat width of 110 m (95%CI: 76–183 m) was required to make mangrove expansion more likely than mangrove retreat. When a stable chenier was present offshore for two years or more, a mudflat width of only 16 m (95%CI: 0–43 m) was enough to flip chances in favor of mangrove expansion. However, mangrove expansion remained heavily influenced by seasonal changes, and was highly event driven, succeeding only once in several years. Finally, although mudflat width was a direct driver of mangrove expansion, and could be targeted as such in coastal management, our field measurements demonstrated that cheniers also have an indirect effect on mangrove expansion. These sand banks significantly reduce wave height offshore, thereby likely creating favorable conditions for mudflat accretion landward, and thus mangrove habitat expansion. This makes stabilization - and possibly also the temporary creation - of cheniers an interesting target for mangrove conservation and restoration.

Mangrove vegetation provides natural protection against coastal hazards like flooding and erosion. In spite of their economic and societal value, mangrove forests have experienced a worldwide decline due to human activities. Bamboo structures, formed by poles driven into the soil, are being used to create a sheltered environment for mangrove restoration. The lack of design rules for the structures has led to mixed success rates in their implementation. Improving future designs requires a better understanding of how the bamboo poles affect waves and currents. Currents cause drag forces on the poles, which depend on flow acceleration through the elements (blockage), and the distance from wakes of upstream cylinders (sheltering). We developed a model that predicts the bulk drag coefficient of dense arrays of emergent cylinders in a current, including blockage, sheltering and a balance between turbulence production and dissipation. The model could reproduce measured bulk drag coefficients from the literature within a deviation of 20%. The model also showed that anisotropic structures with small spanwise spacing and large streamwise separation maximize the bulk drag coefficient, and the energy dissipation per pole. The application of the model can guide the design of future mangrove restoration efforts.

Mangrove vegetation constitutes a natural coastal defence against waves and erosion. Despite their protective role, mangrove ecosystems have experienced continuous degradation over the last decades due to human causes. At retreating mangrove coastlines, bamboo structures are built to create new habitat for mangrove colonization. Existing structures have experienced mixed rates of success due to the lack of a scientific basis in their design. Optimizing future structure designs requires investigating the effect of the bamboo poles on waves. We consequently conducted laboratory experiments to measure wave transformation, hydrodynamic forces, and flow velocities inside cylinder arrays, mimicking bamboo poles, with varying cylinder configurations and orientations. The experiments provided relationships for wave transmission, wave reflection, and the drag coefficients for configurations with volumetric porosities between n = 0.64 − 0.9. Configurations with a small lateral spacing (causing higher blockage) and a relatively longer streamwise spacing (causing less sheltering) exhibit larger forces and dissipation per element. Such arrangements enable optimizing wave dissipation at locations where the wave direction has low variability over the year. Placing the poles horizontally instead of vertically increases the forces and wave dissipation per element in relatively deeper water. Based on the experiments, we developed a conceptual analytical model that predicts wave reflection and dissipation through cylinder arrays, including blockage and sheltering. The model can reproduce the influence of cylinder arrangement on wave transformation, and it suggests that accurate predictions of sheltering and wave reflection are important to find optimal designs. Overall, these results provide useful insights on how to model and optimize the design of structures for mangrove restoration.

Mangroves protect coastal areas against hazards like storms or cyclones by attenuating waves and currents, and by trapping floating debris during extreme events. Bangladesh is a very vulnerable country to floods and cyclones, and part of its coastal system is thus being upgraded to a higher safety standard. These upgrades include embankment reinforcement and mangrove afforestation schemes seawards of the embankments. To further strengthen the implementation of combined green–grey infrastructure in future programs, identifying potential mangrove development sites near the polder systems is a necessary first step. We thus developed a tool to systematically identify mangrove sites throughout the coastal area based on open access data. This method identi-fies potential sites for mangrove development based on their distance from existing mangrove patches and suggests the required technique to implement the vegetation depending on the rate of coastline change. Our method showed that approximately 600 km of the coastal stretches placed seawards of embankments are within 10 km of existing mangroves, and could thus be potential sites for mangrove establishment. Out of those 600 km, we identified 140 km of coastline where the land-wards polders are particularly vulnerable to flooding. The sites with highest restoration potential and priority are located in Galachipa, Hatiya, Bhola, Manpura, Khangona, and Boro Moheshkhali. More detailed data collection and local assessments are recommended prior to executing mangrove afforestation schemes. Nevertheless, this method could serve as a useful systematic tool for feasi-bility studies that identify mangrove opportunities in data-scarce areas and help to prioritize data collection at the sites of highest interest.