Extending Ellenberg's indicator values to a new area: an algorithmic approach

1. Ellenberg's indicator values scale the flora of a region along gradients reflecting light, temperature, continentality, moisture, soil pH, fertilit y and salinity. They can be used to monitor environmental change. 2. Ellenberg values can be extended from central Europe, for which they wer e defined, to nearby parts of Europe. Given a database of quadrat samples, they can be repredicted by a simple algorithm consisting of two-way weighte d averaging, followed by local regression. 3. A database of British samples was assembled from two large surveys. Elle nberg values were repredicted. 4. Except for the indicator of continentality, the correlation of repredict ed and original values was in the range 0.72 (light) to 0.91 (moisture). Th e continentality indicator could not be adequately repredicted by the algor ithm, and is unusable in Britain. 5. Discrepancies between original and repredicted values can be attributed to various causes, including wrong original values, differing ecological re quirements in Britain and central Europe, biased sampling of the British ra nge of habitats, and the occurrence of small plants in shaded or basic micr ohabitats within well illuminated or predominantly acid quadrats. 6. The repredicted values were generally reliable, but a small proportion w as clearly wrong. Wrong values were due to either inadequate sampling of sp ecies' realized niches in Britain or sampling with quadrats that were too l arge and included species that were not close associates.