Indicator value is a term that is used in theecology of plants for two different indices. The older usage of the term refers toEllenberg's indicator values from 1974, which are based on a simple ordinal classification of plants according to the position of their realizedecological niche along anenvironmental gradient.[1] Since 1997, the term has also been used to refer to Dufrêne & Legendre's indicator value, which is a quantitative index measuring the statistical alliance of a species to any one of the classes in a classification of sites.[2]
Ellenberg's indicator values[1] were the first model of bioindication proposed and applied to the flora of Central Europe, and they have a long tradition in interpretation and understanding of plant communities and their evolution. The latest edition of Ellenberg's indicator values applies a 9-point scale for each of seven gradients:[3]
R - reaction (soil or water acidity/pH)
N - nitrogen (but really soil fertility or productivity, and not mineral nitrogen)
F -soil humidity or moisture
S - salt (soil salinity)
K - climatic continentality
L - light availability
T - temperature
Indicator values have also been published in 1977 byElias Landolt for Switzerland,[4] by Mark O. Hill and others for Great Britain,[5] France (Baseflor,[citation needed] SOPHY,[6] Ecoplant) and some other floras.[citation needed]
The indicator value of Dufrêne and Legendre from 1997 is an integral part of the indicator value, which quantifies the fidelity and specificity of species in relation to groups of sites in a user-specified classification of sites, and tests for thestatistical significance of the associations bypermutation.[2][7][8]
The indicator value of speciesi for classj is obtained with the equation
Here
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