Ecological indicator values of British species: an application of Gaussian logistic regression

In a large ecological survey of Britain,13841 quadrats were sampled in 508 1-km squares. The quadrats included 1132 species of vascular plants, of which 643 occurred in 10 or more quadrats. Applying the method of Gaussian logistic regression to data from this survey, ecological optima and tolerances of species were estimated for Ellenberg’s seven ecological indicator variables. Tolerances showed very little relation to the original scales. Most optima were within the range of the original scales but a few species lacked optima for some variables. Optima showed a strong positive relation to original values, but the resulting scale was compressed. We propose a locally-weighted trend line to convert each optimum value to an estimate of the original value. Reprediction using methods based on large-scale quadrat samples offers a very good means of extending Ellenberg’s values to a new geographic area such as Britain.