Problem with collision (tree) when using ''landscapegrassoutput'' to automate foliage placement

Greetings, I am facing a problem I hope someone will help alleviate. I am populating my landscape using heightmap patterns and associating grayscale with multiple texture in order to automate world creation.
He is a serie of screenshots to better picture what I mean.

So I was able to populate my world with different kind of foliage from grass to trees to rocks to boulder. The problem is that the trees and the boulders does not have collision and I do not see where I can enable them. Since I am not using the foliage tool,the option does not exist. Even when puting the same tree in the foliage tool and enabling ‘‘Block all’’ the tree will only have collision when he has been spawned using the foliage brush.

Can someone help solve my problem? How would I go to set up collision for models generated by the ‘‘landscapegrassoutput’’?