| Abstract: | There is little quantitative information on the water-regime requirements of individual plant species in Britain. In Continental Europe, the requirements of over 2000 species were described by Ellenberg using indicator values (ranking) and by Londo in terms of the influence of the water-table (phreatophyte). These systems were used to characterize the vegetation of English grazing marsh ditches and wet grassland.On ditch banks, the species near the water were obligate phreatophytes with high Ellenberg F indicator values, whereas those at the bank top were mainly aphreatophytes. Ordination of ditch species showed a correlation between the F value of the species and ditch-water depth. In grassland, F values were correlated with the mean depth of the water-table and its degree of fluctuation, suggesting that species differ in their sensitivity to seasonal variation in water-table depth. Plant communities and individual quadrats may also be characterized by the mF of the species present. Where vegetation is subject to a changed water-table, the impact of this change may be quantified using the mF value.The F indicator values of Ellenberg appear valid for a range of British species and situations. Experimental studies are required to validate F values and investigate any interactions with other environmental factors, including those others ranked in the Ellenberg system: light, temperature, continentality, soil reaction, nitrogen and salinity. |
