Poisson structures for difference equations

We study the existence of log-canonical Poisson structures that are preserved by difference equations of special form. We also study the inverse problem, given a log-canonical Poisson structure to find a difference equation preserving this structure. We give examples of quadratic Poisson structures that arise for the Kadomtsev-Petviashvili (KP) type maps which follow from a travelling-wave reduction of the corresponding integrable partial difference equation.