We consider discrete qualitative models of ecosystems viewed as collections of interacting living (animals, plants..) and nonliving entities (air, water, soil..), whose conditions of appearance/disappearance are controlled by a set of formal rules (i.e., processes). We present here two methods to statically analyze models. The first one is used to simplify models removing redundant information. The second one is a rule-based method allowing to compare ecosystems. This method relies on a measure of similarity and on an optimization algorithm. In addition, the proposed method allows detecting patterns (i.e., ecological processes or sets of processes) in ecosystems. We have validated the method by applying it against a set of models and patterns provided by research projects of ecologists.