- Coastal dunes provide many functions and services including coastal protection, recreation, and habitat. Vegetation contributes to dune growth and stability, thereby increasing the coastal protection value of dunes. On the U.S. Pacific Northwest coast, the dominant dune grasses are the introduced non-native American beachgrass (Ammophila breviligulata) and the native American dune grass (Elymus mollis). These grasses grow and stabilize dunes, receiving marine-derived nutrients from macrophyte wrack (i.e., macroalgae) that strands on the beach. This macrophyte wrack enhances available nutrients, but the impact of these nutrients on dune grass growth is unstudied. Thus, we asked, are dune grasses nutrient limited, and if so, to what extent? Plots of dune grasses across the foredune profile were fertilized with varying amounts of nitrogen and phosphorus. A year later, grass morphology and tissue nutrient composition were measured. We found that dune grasses grew more with increased nutrients, and plants at the heel of the dune were more nutrient limited than at the toe and crest. Our results suggest that dune grasses are nutrient limited and grass growth may increase with greater marine-derived nutrients, thus enhancing dune building. By better understanding the extent of nutrient limitation of dune grasses, we can gain insights into the role marine-derived nutrients play in dune building and coastal protection.
- Key Words: beachgrass, Ammophila breviligulata, dune grass, Elymus mollis, nutrient limitation