Hankel operators on Bergman spaces and similarity to contractions

We consider Foguel-Hankel operators on vector-valued Bergman spaces. Such operators defined on Hardy spaces play a central role in the famous example by Pisier of a polynomially bounded operator which is not similar to a contraction. On Bergman spaces we encounter a completely different behaviour; power boundedness, polynomial boundedness, and similarity to a contraction are all equivalent for this class of operators.