How to avoid of of of in the Appendix title

"occurrence probability models" will confuse anybody not in a technical area that uses this term (you can find it by Googling, but it's not the usual terminology in any area I know).

I would suggest

models for probability of occurence;

"models for" and "models of" are more or less interchangeable in many fields of science, and "models for" avoids the repetition of "of".