Environmental Controls on Multiscale Spatial Patterns of Salt Marsh Vegetation

Abstract

In coastal environments, biogeographic patterns are generally influenced by surface elevation and horizontal distance from sea water. However, it is still unclear whether these major topographic factors are significant controls of vegetation patterns across spatial scales at which different physical processes operate. This study investigated such a topography-vegetation relationship in a Danish salt marsh, focusing upon two scales: a macro-scale (ca. 500 m) across the marsh platform, encompassing seaward and landward areas, and a meso-scale (ca. 25 m) across tidal creeks. While long-term sea-level variation and grazing influenced the macro-scale pattern, short-term fluvial-geomorphic processes drove the meso-scale pattern. Despite these different underlying processes, similar floristic gradient structures between the two scales were identified by nonmetric multidimensional scaling. The gradient represented an ecological sequence from early to late succession, and strongly correlated with surface elevation. However, the gradient did not show any significant relationship with distance from shoreline or tidal channels. Our results suggest that, in salt marshes, elevation plays a still more important ecological role than the horizontal position relative to sea water at both macro- and meso-scales. The presence of one such fundamental component makes the system relatively simple, and will facilitate future scaling attempts.