Dynamical degrees of (pseudo)-automorphisms fixing cubic hypersurfaces

We give a way to construct group of pseudo-automorphisms of rational varieties of any dimension that fix pointwise the image of a cubic hypersurface of p^n. These group are free products of involutions, and most of their elements have dynamical degree < 1. Moreover, the Picard group of the varieties obtained is not big, if the dimension is at least 3. We also answer a question of E. Bedford on the existence of birational maps of the plane that cannot be lifted to automorphisms of dynamical degree < 1, even if we compose them with an automorphism of the plane.