I have two polygon layers, one is about different land owners boundaries and is used for atlas generation, and the other is about forests inside each property. In atlas generation sometimes i want to zoom to the intersection area between the boundary layer (used for atlas iteration) with the forest layer. That is because some times a huge property can have a small part of forest so i want atlas to zoom in to that part of the property.
Create a new layer by clipping the forest layer with the properties layer, and you can use this new layer for the atlas generation. Note that, may be you will have to merge first (bevore clipping) the different polygons of forest.