Coastal areas face increasing threats from erosion, driven by stronger storms, rising sea levels, and human activity. To protect our shores, natural solutions like healthy salt marshes are critical, as their plants and roots act as natural barriers, stabilising soil and reducing erosion.
In our research, we explored whether greater plant diversity in salt marshes contributes to stronger protection against soil erosion. Previous studies suggest that a diverse array of plants might enhance soil stability, but the exact relationship has remained unclear.
We carried out a detailed study in two distinct regions of the UK with contrasting soil types: Essex, where the soil is rich in clay and naturally more resistant to erosion, and Morecambe Bay, known for sandy soils that erode easily. We carefully extracted soil cores from these salt marshes and subjected them to controlled erosion tests in a laboratory setting, simulating wave and water impacts.
We found that salt marshes with higher plant species diversity experienced significantly lower soil erosion rates. Particularly interesting was the discovery that plant diversity mattered even more in areas with sandy soils, where the risk of erosion is higher. As the number of plant species increased from just two to nine per square meter, the variation in erosion rates dropped dramatically, indicating that diversity makes salt marshes more consistently stable.
Plant diversity seemed to enhance soil stability primarily by increasing root biomass – the mass of roots underground. More diverse plant communities tend to have a variety of root structures, depths, and growth strategies, helping soil resist erosion more effectively. For example, we found that marshes dominated by a single grass species eroded much faster than those with a mix of grasses, rushes, and flowering plants, each with distinct root systems.
Our findings emphasise the importance of plant diversity in ecosystems like coastal marshes. While soil type remains crucial for stability, biodiversity significantly boosts resilience, especially in erosion-prone environments. Protecting and restoring plant diversity isn’t just beneficial for the environment – it’s an essential tool in safeguarding coastal communities against climate-related erosion and flooding.
The insights from our study provide critical support for coastal management strategies, demonstrating the value of biodiversity conservation as a practical and cost-effective approach to coastal protection.