Fine‐scale hydrological niche segregation in coastal dune slacks

Questions: Hydrological niche segregation is widespread and has been found across a range of different habitats. Different plant species can occupy distinct hydrological niches, and as a result fine-scale variability in hydrology can structure plant communities. However, these patterns may not be as clear in habitats where differences in hydrology are more short-lived, such as coastal dune slacks. We explored the extent that the hydrological regime structures dune slack plant communities. Location: Ainsdale Coastal Sand Dune National Nature Reserve, UK. Methods: Six hundred quadrats were surveyed, 100 in each of six coastal dune slacks. Water table levels are recorded monthly in each slack. Metrics summarising hydrological regime were calculated and adjusted for each quadrat based on elevation. We tested the relationship between water table depth, plant communities and topography across and within dune slacks. Results: Half (three) of the slacks showed a significant influence of hydrology on plant community composition. The three that did not were the ones that varied least topographically and contained less diverse plant communities. We also provide indirect evidence of niche segregation by modelling species-specific responses between mean water table depth and probability of species presence. Conclusions: We demonstrate that hydrology is a dominant driver of plant community composition across dune slacks. However, plant communities are not always structured by hydrology, demonstrating the complexity of vegetation patterns. Topographic variation appears to impact plant community patterns, as do successional processes, highlighting the need to create diverse habitats for slack restoration and management.