Environmental modifiers of the relationship between water table depth and Ellenberg’s indicator of soil moisture

Ciara Dwyer,Jonathan Millett,Robin J Pakeman,Laurence Jones

doi:10.1016/j.ecolind.2021.108320

Ciara Dwyer, Jonathan Millett + Show 2 more

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https://doi.org/10.1016/j.ecolind.2021.108320

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Abstract

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.

Highlights

Ellenberg indicator values allocate a score to a plant species based on its environmental preferences (Ellenberg, 1991)
As average water table depth (AWTD) becomes more positive, Ellenberg F (EllF) of plant species in the community increases (Fig. 2, Table 2)
This study demonstrates that the response of the commonly used ecological indicator of soil hydrological status – unweighted mean Ellenberg F – to average water table depth shows some dependency on other biotic and abiotic factors

Summary

Introduction

Ellenberg indicator values allocate a score to a plant species based on its environmental preferences (Ellenberg, 1991). Ellenberg moisture (F) values range from species growing on dry soils (score 1), to wet soils (score 9), to emergent or submerged aquatic species (scores 10–12) They are valuable because they can be combined as a biological indicator that represents the integrated response of the plant community to the hy drological regime that has been experienced (Curreli et al, 2013; Die kmann, 2003; Ertsen et al, 1998; Schaffers and Sýkora, 2000; Wamelink et al, 2002). As such, they are likely more meaningful than metrics derived from direct, short-term, measurements of the physical environment. In addition to the hydrological regime, community mean Ellenberg F values in seasonal wetland habitats may be influenced by a wide range of abiotic and biotic factors, either through their direct impact on soil moisture availability, or impacts on plant responses to soil moisture

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