1. On Indices … … to characterise (the state of) plant diversity … using output of Vegie models M. Posch, L Bonten, J Slootweg, GJ Reinds, …

2. Assumption: Model output is probability/suitability/strength of individual plants (not abundances): P j, j = 1,N (0 ≤ P j ≤ 1) ‘Simplest’ indices: Combination of these probabilities i)‘habitat suitability index’ of Ed/Arjen ii)‘plain’ probabilities (see below) The closer the index is to its maximum (=1) the better …

3. We don’t recommend ‘classical’ indices such as Simpson and Shannon, because: - What’s the meaning of the value? - They are maximal at total evenness (want that?)

4. 1-dim example (pH PROPS): Prob averageProb all species

5. pH-[N] examples using PROPS: C25: Orocantabrian Juniperus communis subsp. alpina- and Cotoneaster integerrimus-scrub with Vaccinium uliginosum on siliceous rocks (only) 3 species with PROPS parameters: - Calluna vulgaris - Cotoneaster integerrimus - Vaccinium myrtillus Isolines of individual probabilities:

6. Combined into C25: Prob. all 3 species Prob 2 or 3 species Prob at least 1 species

7. Other (‘more realistic’) example: E10: Frisian-Danish coastal heaths (26 PROPS species)

8. Comparison with HS-index: Probability >= half HS–index Prob all species Conclusions!?

9. Which species? Suggestion: n = number of desired species