Ellenberg indicator values for plant species are widely used metrics in ecology, providing a proxy measure of environmental conditions, without direct measurements. They integrate environmental conditions over time since species will only persist where conditions are favourable. Ellenberg moisture (F) values summarise the hydrological environment experienced by plants. However, the relationship between indicator values and hydrological metrics appears to be influenced by a range of other abiotic and biotic factors, limiting our ability to fully interpret Ellenberg F. Focussing on Ellenberg F, we evaluated how the unweighted mean plant community F value to hydrology, specifically water table depth, is influenced by other environmental factors, ground cover type and alpha diversity in UK seasonal coastal wetlands (dune slacks). As expected, water table depth had the strongest influence on unweighted mean Ellenberg F. We show that unweighted mean Ellenberg F was more sensitive to changes in water table levels for plant communities that were more nutrient limited, when the organic matter layer was thicker and there was less bare ground cover. Unweighted mean Ellenberg F was consistently lower for a given water table depth, when there was lower atmospheric nitrogen deposition, lower loss of ignition (a measure of organic matter content) and more diverse plant communities. These findings help us to better interpret what Ellenberg F indicator values tell us about hydrological conditions, by understanding the factors which alter that relationship.



This research would not have been possible without the site managers, landowners and volunteers. We would like to thank the site managers, Annabel Drysdale, Andrew Craggs, Ben Jones, David Mercer, David Pickett, Marijke Leith, Neil Forbes, Rhodri Dafydd, Rick Southwood, Robert Large, and Tom Cunningham. I would like to thank the landowners Christie Devon Estates, Royal St Georges Golf Course, Princes Golf Course, RSPB, Scottish Natural Heritage, Sefton Council, National Trust, Natural England and Natural Resources Wales. We would like to thank Ivan Pedley, Lisanne van Willegen, Natalie Hunt, Russell Parry, Sally Edmondson and Uta Hamzaoui for vascular and non-vascular identification. We would like to thank Barry Smith, Phil Smith, Stephanie Haworth and Tony Meadow for collecting water table depths. We would like to thank Abigail Sims, Amy Jones, Charlie Patel, Harry Sanders, Lisanne van Willegen, Natalie Hunt, Nicolette Formosa, Richard Mason, Ruth Dunn and Sophia Clarke-Ioannou for fieldwork assistance. We would like to thank those that helped organise the site trips and provided additional information including Graham Earl, Jamie McCartney, James Bledge, John Breeds, Julie Rankin, Paul Ferguson, Paul Larsen, Phil Williams, Pete Gahan, Rebecca Aston, Robert Crawford, Robert Wilby and Sean McLean. We would like to thank Rebecca McKenzie, Richard Harland and Sarah Wappat for technical assistance. This research was possible due to PhD funding to CD from UK Research and Innovation via the Central England NERC Training Alliance (CENTA).