Scale-Dependent Correspondence of Floristic and Edaphic Gradients across Salt Marsh Creeks
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Biogeographers emphasize the presence of scale-dependence in vegetation-environment relationships. This research addresses the issue of scale-dependence, focusing on spatial correspondence of floristic and edaphic gradients across salt marsh creeks at Skallingen, Denmark. We employed a hierarchical approach, which compared vegetation and soil gradients at both fine and coarse scales. At the fine scale, we used ordination techniques to identify the gradient structure of vegetation and soil data acquired in 1-m 2 plots along transects across creeks. For the coarse-scale comparison, we systematically aggregated the fine-scale information (i.e., gradient structure) into larger blocks, or topographic zones such as point bar, cutbank edge, and marsh interiors. We found poor correlations between vegetation and soil at the fine scale but an improved correspondence at the coarse scale. The poor correspondence was caused by differential spatial extents that the vegetation and soil factors exhibited responding to environmental variations. At the fine scale, modes of plant-plant interactions were the key determinant of species composition and varied significantly across tidal creeks. Soil properties responded less sensitively to topographic and hydrologic changes than vegetation did, however. As the scale of our analysis increased, the fine-scale floristic variation averaged out, and the overall compositional patterns were then governed by broader variations in environmental (edaphic) constraints. Our research accommodates the importance of both biological and environmental components by explicitly emphasizing their simultaneous significance, each perceived at different spatial scales. We conclude that the concept of scale-dependence might serve as an efficient conceptual framework in salt marsh biogeography. 2012 Copyright Taylor and Francis Group, LLC.
