A connectivity threshold between grass patches amplifies coastal dune formation

Biogeomorphic systems, key providers of ecosystem services, emerge from self-reinforcing feedbacks between landscape-building biota and geomorphic processes. Typically, these feedbacks are considered to operate at an individual patch scale, yet it remains unclear how interactions between patches shape landscapes at larger scales. Here we show how dune-building grasses form functional clusters of interacting patches that strongly amplify engineering capacity. By analyzing a decade of morphological development in an establishing coastal dune system, we discover that dune height is primarily driven by the initial density of neighboring patches, rather than individual patch size. We identify an S-shaped relationship consistent with a spatial percolation threshold: increasing local patch density triggers an abrupt shift from isolated sand-trapping patches to functionally connected clusters that enhance dune growth. This work reveals an important yet overlooked spatial dimension of ecosystem engineering, one that can be harnessed to inform future restoration designs and enhance ecosystem resilience. Coastal dunes emerge from feedbacks between plants and sand. Here, the authors show that dune-building grasses engineer the landscape beyond the patch scale: physically separated patches can form functionally connected clusters that enhance dune formation.